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Environmental Monitoring and Assessment (2005) 101: 175–202 c© Springer 2005

THE EFFECTS OF URBAN AREAS ON BENTHICMACROINVERTEBRATES IN TWO COLORADO PLAINS RIVERS

NEAL J. VOELZ1,∗, ROBERT E. ZUELLIG2, SEN-HER SHIEH3 and J. V. WARD4,†1Department of Biological Sciences/MS 262, St. Cloud State University, St. Cloud, Minnesota,U.S.A.; 2Department of Fishery and Wildlife Biology, Colorado State University, Fort Collins,

Colorado, U.S.A.; 3Department of Ecology, Providence University, 200 Chung-Chi Road, Shalu,Taichung County, Taiwan; 4Department of Limnology, EAWAG/ETH, Uberlandstrasse 133,

Dubendorf, Switzerland(∗author for correspondence, e-mail: [email protected])

(Received 19 August 2003; accepted 28 January 2004)

Abstract. Water demands in arid and semi-arid areas, coupled with increased human populations andconcomitant changes in land use, can greatly alter aquatic ecosystems. A good example of this type ofsystem occurs along the eastern slope of the Colorado Rocky Mountains, U.S.A. Long-term macroin-vertebrate metric data from the Big Thompson and Cache la Poudre Rivers, Colorado, were collectedat one site above, and three sites in and downstream from urban areas. These data were compared bothwith regional reference and single reference sites in the respective rivers. Using the surrogate variablesof potential urban impact (population and housing units), and the environmental gradient representedprimarily by chemical factors, it was determined that there was an effect of urban land use that wasreflected in the macroinvertebrate assemblages in both rivers. The most robust results were usuallyseen when regional reference data were used. However, even using only the upstream reference sitein either river indicated some negative impacts from the urban areas. The long-term data, particularlyin the Cache la Poudre River, showed that water quality has not been getting worse and there is someevidence of a slight improvement in downstream reaches, even with increased urban development.

Keywords: long-term data, macroinvertebrate metrics, urbanization, water quality

1. Introduction

Water is one of our most precious resources and as the human population growsthe demands on our water supply increase. In addition to the increasing demand onwater, humans impact ecosystems directly through land use change and indirectlyby generating non-point source pollution that is introduced into streams and riversvia urban runoff. Thus the need to monitor these systems over long time periodsin order to distinguish natural variability from anthropogenic stress is necessaryfor management (Resh and Rosenberg, 1989; Risser, 1991). Long-term data areimportant not only for detecting environmental trends but also for putting the presentin perspective (Magnuson, 1990).

There is a pressing need to evaluate water quality for both anthropogenic use andaquatic life (Patrick, 1992; Davis and Simon, 1995; Karr and Chu, 1999). Although

†Present Address: 2298 Todd Street, Eugene, Oregon, U.S.A.

176 N. J. VOELZ ET AL.

current water quality monitoring approaches (e.g., short-term monitoring of manystreams in an ecoregion; Clements et al., 2000; Kay et al., 2001) are effective waysto evaluate water quality, long-term studies are crucial for separating the differencesbetween natural and anthropogenic changes in water quality (Elliott, 1990; Naimanet al., 1995). Long-term studies provide the necessary historical (i.e., background)information to help separate sources of observed variation. In addition, the temporalscale of a study may greatly influence how the results are construed (Cooper et al.,1998). The need to monitor long-term temporal changes in aquatic assemblages withrespect to pollution has been known for some time (e.g., Richardson, 1928), but onlyrelatively recently have more long-term ecological studies on aquatic ecosystems,particularly streams, been conducted (e.g., McElravy et al., 1989; Patrick, 1992;DeShon, 1995; Armitage and Gunn, 1996; Wright and Symes, 1999).

Water demands in arid and semi-arid areas coupled with increased human pop-ulations and concomitant changes in land use, are particularly important areas forstudy. A good example of this type of system occurs along the eastern slope of theColorado Rocky Mountains, U.S.A. Human population levels have been increasingat a high rate in this area (2000 U.S. Census Bureau data) with potentially negativeeffects on water quality due to typical stressors associated with urbanization. Inaddition, historical expansion of agriculture in Colorado (and elsewhere along thefront range) have not only put strains on local water supplies but have lead to presentday regional changes in ecosystem dynamics, such as the transport of pollutantsfrom the plains to the mountains because of changes in atmospheric circulationpatterns (Rapport et al., 1998).

Runoff from urban areas can be extensive, contain numerous chemicals andcause increased temperatures and sediment loads in receiving water bodies(Novotny and Olem, 1994; Paul and Meyer, 2001). Relative to agricultural lands,urban areas can have similar land applications of some chemicals (e.g., phosphorusand herbicides; Creason and Runge, 1992) and the runoff from urban areas cancontain a much greater variety of pollutants (Novotny and Olem, 1994). Untreatedstormwater runoff from urban areas can contain levels of some parameters (e.g., totalsolids) that exceed those found in untreated wastewater (Pitt and Field, 1977). Thesepollutants entering streams as a result of urbanization can be harmful to stream or-ganisms (e.g., Schlosser, 1982; Kemp and Spotila, 1997; Paul and Meyer, 2001).

Aquatic macroinvertebrates have been widely used as indicators of water qualitybecause they have several attributes not possessed by other water quality indicators(Goodnight, 1973; Hawkes, 1979; Rosenberg and Resh, 1993). Balanced monitor-ing programs incorporate a variety of biological, physical and chemical variables(Rosenberg and Resh, 1993; Barbour et al., 1999) over long time periods. Long-termmonitoring programs that include a wide variety of water quality indicators havebeen employed on several drainages along the front range of Colorado providingan opportunity to study stream response to urbanization.

The goals of the present study were to: 1) examine several common macroin-vertebrate metrics to determine if urban impacts occur in the Big Thompson and

URBANIZATION EFFECTS ON LOTIC INVERTEBRATES 177

Cache la Poudre Rivers. 2) Determine if having only one reference site – traditionalupstream/downstream study – was adequate for detecting impacts as compared withusing multiple regional reference sites. 3) Establish if long-term data, collected inspring and autumn, provide any additional insight into the water quality assessment;and 4) assess whether any impacts found were related to the environmental gradient(primarily physical/chemical).

2. Study Site Descriptions and Selection of Reference Sites

The two streams used for determining potential impacts from urban areas were theBig Thompson and Cache la Poudre Rivers (Table I; Figure 1). The Big Thomp-son River originates at about 3350 m a.s.l. on the eastern slope of the ContinentalDivide in Rocky Mountain National Park, Colorado, U.S.A. At 2283 m a.s.l. theBig Thompson runs through the small mountain town of Estes Park (2703 people,1980 U.S. Census; 5413 people, 2000 U.S. Census), which discharges secondary-level treated wastewater to the river. In addition, Olympus Dam is situated at thedownstream end of Estes Park, which provides main channel water storage. Down-stream of Estes Park and Olympus Dam, the river enters the Big Thompson Canyon(Roosevelt National Forest), an incised, high-gradient reach extending to thebase of the foothills (1615 m a.s.l.). At the mouth of the canyon the riverleaves the national forest and becomes a plains stream traversing an urbanthen agricultural landscape. About 10 km downstream from the canyon mouth,the Big Thompson River flows through the southern section of the City ofLoveland.

The City of Loveland has grown from a population of 30215 to 50608 during1980–2000. Housing units have increased during the same period from 12198 to20299 (U.S. Census Bureau data). Four sampling sites were selected along a 17 kmreach of the Big Thompson River downstream of the plains/mountain interface tomonitor the long-term changes of benthic macroinvertebrate communities.

Site 1 (reference; 1505 m a.s.l.; Figure 1) is located above all known impactsfrom the City of Loveland; however, water diversion may affect this site. In addition,some sediment and possibly other pollutants may occasionally enter the river froma reservoir ditch located a few km upstream from site 1 (R. Buirgy, Big ThompsonWatershed Forum, personal communication). Riparian vegetation consists of a fewsmall willows (Salix spp.), grasses and sedges. Site 2 (6.9 km below site 1) isapproximately 800 m upstream from the Loveland wastewater treatment plant dis-charge (secondary treatment). Russian olive (Eleagnus angustifolia), grasses anda few large cottonwoods (Populus sp.) comprise the riparian vegetation. Site 3 isca. 1.4 km below the wastewater treatment plant discharge (Figure 1). The riparianvegetation consists of large cottonwoods and other deciduous trees with a groundcover of grasses. Large mats of filamentous algae were commonly observed dur-ing the study. Site 4 (ca. 1475 m a.s.l.) is below all potential impacts from the

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Figure 1. Location of the Big Thompson and Cache la Poudre Rivers in the state of Colorado andlocation of the study sites. WWTP refers to wastewater treatment plant.

City of Loveland and is located 7.8 km downstream from site 3. Agricultural ac-tivity is prevalent in this area but there are no irrigation return ditches upstream.However, there are 10 diversions (outflows) from the lower foothills to site 4. Afew cottonwoods line the banks, but grass cover is sparse due to cattle grazing.The river bottom at all sites is predominantly cobble, gravel and sand, with somesilt at site 4. Sites 2–4 are also potentially impacted by untreated city stormwaterdrainage.


The more detailed site descriptions for the Cache la Poudre River that have beenpresented elsewhere (Boyd et al., 1986; Camargo et al., 1992; Shieh et al., 1999,2002; Voelz et al., 2000) are only briefly described here. The Cache la Poudre Riveroriginates near the Continental Divide in Rocky Mountain National Park (3290 ma.s.l.), Colorado, U.S.A.

There are three cities located along the plains segment of the Cache la PoudreRiver that may have some impact on the macroinvertebrate assemblages. The Cityof Laporte (500 people, 1980 federal census; 2691, 2000 census) is located about5 km upstream from the beginning of the study area and depends on Fort Collinsfor water and wastewater treatment. The City of Fort Collins is the main urban areawithin the study reach. It grew slowly in population from 1910 to 1970 (8210–43377 people), but has since grown at an exceedingly fast pace. Between 1980and 2000, the population of Fort Collins increased from 65092 to 118652 andhousing units have increased from 24665 to 47755. There are no known domesticwastewater discharges above Fort Collins. Downstream from Fort Collins is theCity of Timnath (<1000 people) that uses water and wastewater facilities providedby Fort Collins.

Four sites were also chosen downstream of the plains/mountain interface onthe Cache la Poudre River along a ca. 18 km stretch (Figure 1). Site 1 (1515 ma.s.l.) is located approximately 15 km downstream from the mouth of the PoudreCanyon and no known point source of pollution occurs above this site. However,elevated lead levels (i.e., exceeding the aquatic life standard; US EPA, 1986) haveoccasionally been measured at this site, perhaps from either gasoline-contaminatedgroundwater or water releases to the river from a reservoir with high lead con-centrations (Mueller, 1990). In fact, lead values exceeded the standard only twiceduring the study period (May 1990 and 1991). Site 2 is situated about 1.6 kmdownstream from the point where treated wastewater from Fort Collins enters theCache la Poudre River and 7.2 km downstream from site 1 (Figure 1). The setting isurban with most potential impacts coming from untreated stormwater drainage andtreated domestic wastewater. Site 3 is ca. 1 km downstream from a second wastew-ater treatment plant and 6.5 km below site 2. However, the effluent is not normallydischarged to the Cache la Poudre River. Site 4 (1472 m a.s.l.) is located 3 kmdownstream from a third wastewater plant and is 4 km downstream of site 3. Thereis some agricultural land use between sites 3 and 4, consisting predominantly ofrow crop agriculture and rangeland. There are no irrigation return ditches betweensites 1 and 4, although there are four stream diversion channels between these sites(and an additional 4 diversions upstream of site 1 to the lower foothills). However,one small tributary, which mostly drains agricultural land, enters the river betweensites 3 and 4. The substrate at all sites is primarily composed of cobble, gravel andsand.

Determining adequate reference conditions for relatively large, plains riversthat originate in mountainous areas is difficult, because many of these rivers areimpacted in numerous ways, have been altered by humans since the early 1800s


(Wohl, 2001) and no ecological data are available prior to the beginning of irrigatedagriculture that began in the 1860s. For this reason, we included reference streamsfrom Wyoming and New Mexico (i.e., beyond the ecoregion). There is some evi-dence supporting this approach as geographical boundaries and ecoregions may notnecessarily provide strict guidelines for determining reference condition (Corkum,1989; Karr, 1999; Heino et al., 2002).

The following criteria were used to initially identify potential reference streams.1) Streams drain on the eastern side of the continental divide and sampling sitesare located in the plains section (and thus are middle order streams). 2) Headwatersare in the mountains, at an elevation of approximately 3000 m a.s.l. or greater. 3)No (or no major) point source of pollution occurs upstream from the reference siteand non-point impacts were determined to be relatively minimal; and 4) mountaininvertebrate taxa (e.g., Arctopsyche grandis (Banks), Megarcys signata (Hagen))are rare (i.e., <1% by abundance) or absent at the site as these taxa are typi-cally found at higher elevations (especially M. signata). We believe this approachto determine reference condition is appropriate because plains streams that orig-inate in the mountains will still contain some mountain segment properties (e.g.,reduced temperature range, some faunal components), especially in the transitionzone where the stream exits the mountains and enters the plains. For this reason, weomitted reference sites that were located immediately below the plains/mountaininterface.

Ten streams (including the upper most sites on the Cache la Poudre andBig Thompson Rivers) were identified to provide the reference condition(Table I). Additional evidence for using this set of streams was obtained by ex-amining the similarity among taxa lists. Most streams had >60% taxa in com-mon. Some streams had >70% taxa in common (e.g., Big Thompson, Cache laPoudre and the Wyoming streams; Gallinas, Cache la Poudre and Sapello). Low-est similarity in taxa lists occurred between most streams and the Pecos River(35–55%).

Chemistry data for most reference streams were collected only during macroin-vertebrate sampling periods (i.e., spring and/or autumn). All dissolved oxygenreadings were >6.0 mg/L. NO3–N readings ranged from <0.05 to 0.57 mg/L,though most readings were <0.2 mg/L and most PO4–P levels were <0.1 mg/L(many <0.05 mg/L). The pH ranged from 7.0 to 8.5 and temperature values were1–22 ◦C. Conductivity varied from 69 to 1420 µS/cm, except for the Pecos River,which had values of approximately 420–2000 µS/cm. However most conductiv-ity readings in the reference streams were between about 125 and 500 µS/cm.Samples were collected in riffle areas for all reference streams and the bot-tom substrate was predominantly cobble, gravel and sand at most sites. Basedon visual descriptions, it appeared that the Pecos River and Tecolote Creek hadhigher amounts of sand than other reference streams (Jacobi, 1983; Smolka,1987).


3. Materials and Methods

3.1. MACROINVERTEBRATE SAMPLING

More detailed sampling procedures for the reference streams are found in the refer-ences listed in Table I. Spring samples for the Big Thompson River were collectedfrom 1982 to 1989 (except 1983 when high water precluded sampling) and 1992 to1993. Autumn samples were obtained from 1982 to 1989 and 1996 to 2000. Springsamples in the Cache la Poudre River were collected from 1981 to 1996 (except1983 when high water precluded sampling) and autumn samples were collectedfrom 1981 to 2000. No samples were gathered in 1996 at site 4.

In the Cache la Poudre and Big Thompson Rivers, a standard Surber sampler(0.09 m2) with 500 µm mesh net was used to collect three samples of benthicmacroinvertebrates from riffles at each site during spring and autumn. Sampleswere then poured through a 600 µm sieve in the field. Each sample was taken froma different substrate within each riffle, if possible. In May 1992 a new samplingprogram was initiated in the Big Thompson River (Plafkin et al., 1989). Two sampleswere collected from each site with a kicknet sampler (500 µm mesh net). A metalframe was used to enclose 1.0 m2 of stream bottom. Benthic samples were preservedwith 70% ethanol.

In the laboratory, macroinvertebrates were separated from organic material usinga low-power scanning magnifier (2.5×) and stored in 70% ethanol. Most sampleswere completely sorted whereas samples containing large numbers (visually deter-mined) of organisms (usually Chironomidae) were subsampled. Subsamples (1/4or 1/8 of a sample) were randomly chosen using a gridded tray. The organismsfrom the three Surber samples of each sampling site were combined at this point,making a composite sample. Macroinvertebrates were identified to genus (accord-ing to Pennak, 1978), except for the members of the Oligochaeta and Nematoda,which were not identified further. Usually >500 individuals were identified fromeach composite sample.

Although careful and consistent records and identifications were made for thebenthic macroinvertebrate surveys, new identification techniques, refinement oftaxonomic identification (e.g., Merritt and Cummins, 1996) and continued mon-itoring of the Big Thompson and Cache la Poudre Rivers led us to make somechanges in the original identifications. In all cases, cross reference with Pennak’s(1978) key was made to keep taxonomic designations consistent for data analyses.Macroinvertebrate data for the reference streams were standardized to conform tothe level of taxonomic resolution used in the Cache la Poudre and Big ThompsonRiver studies.

Several studies have examined the most efficient metrics to analyze biomonitor-ing data (e.g., Barbour et al., 1992; Hynes, 1994; Kerans and Karr, 1994; Norris,1995, several papers in Davis and Simon, 1995; Fore et al., 1996; Barbour et al.,


TABLE II

Metrics used to analyze the macroinvertebrate data and their predicted response to urbanization

Predicted macroinvertebrate response to urban

Metric effluents

Total number of taxa Decrease

Number of EPT taxa Decrease

Number of clinger taxa Decrease

Percent scrapers Decrease

Percent dominant taxon Increase

Percent EPT Decrease

Percent Diptera Increase

Percent Oligochaeta Increase

Hilsenhoff’s biotic index (HBI) Increase

Community tolerance quotient (CTQa) Increase

1999). Although some disagreement exists as to the best metrics or statistical meth-ods for biological assessment (see Wright, 1995; Fore et al., 1996; Downes et al.,2002), based on the recommendations of previous studies (e.g., Barbour et al.,1999; Royer et al., 2001) and our knowledge of the systems, we used 10 indicesto analyze the Big Thompson and Cache la Poudre River macroinvertebrate data(Table II). Values for Hilsenhoff’s biotic index (HBI), a measure of organic pollu-tion (Hilsenhoff, 1987), were taken from Barbour et al. (1999). We only used theactual community tolerance quotient (CTQa) of the biotic condition index (BCI;Winget and Mangum, 1979) since some habitat and chemical variables (e.g., sul-fate values) were not available for most reference streams. The BCI incorporatesmacroinvertebrate tolerance to alkalinity, sulfate and sedimentation.

Some of the metrics used in our study are standard (e.g., total number of taxa,percent dominant taxon), whereas we felt that others would best indicate any ur-ban impacts. For example, because urban discharges may contain higher nutrientlevels this could affect the algal assemblages. In turn this could have at least twodifferent effects, one being a change in food resources (e.g., from edible to ined-ible algae) and the other an alteration of the habitat (e.g., increased filamentousalgae). Thus the percentage of scraper taxa and the number of clinger taxa could beaffected.

To examine whether the macroinvertebrate assemblages in the Big Thompsonor Cache la Poudre Rivers may be affected by urban influences, we analyzed the10 macroinvertebrate metrics using box and whisker plots (visual examination;see Gerritsen, 1995), and Kruskal–Wallis analysis of variance (P ≤ 0.05; mostKruskal–Wallis results P < 0.01) with Student–Newman–Keuls (SNK) multiplecomparisons tests (α = 0.05 for SNK tests) using SPSS version 11.0 for Windows.


We examined the reference dataset including and excluding Big Thompson andCache la Poudre site 1 versus sites 2–4, and only the Big Thompson or Cache laPoudre site 1 versus their respective sites 2–4 (traditional upstream/downstreamstudy). We focused our attention on the major significant patterns associated withthe reference site data versus sites 2–4, as only a few comparisons also indicatedsignificant differences between 2 or 3 of the other sites (e.g., site 2 different from3 and 4).

To determine if long-term data could provide additional insight into the changesin water quality, Wilcoxon signed ranks tests were used to compare the first 5(1982–1986; Big Thompson) or 6 (1981–1986; Cache la Poudre) years of au-tumn metric data with the last 5 (1996–2000) or 6 years (1995–2000) within eachsite. Long-term trends of the 10 metrics were also examined for the complete au-tumn Cache la Poudre River data (1981–2000), the longest available dataset, usingspearman rank correlations. All analyses were made using SPSS version 11.0 forWindows.

3.2. WATER CHEMISTRY

Conductivity, dissolved oxygen, pH, NH4–N, NO3–N, PO4–P and/or total P weremeasured in the Big Thompson and Cache la Poudre Rivers. Water chemistry pa-rameters were measured approximately monthly in the Big Thompson River from1980 to 1995 at sites 1 and 3, 1979 to 1999 at site 2, and 1987 to 1995 about 3 km up-stream from site 4. In addition, a dataset for March–November 2001 was examinedfor comparative purposes (R. Buirgy, Big Thompson Watershed Forum, unpub-lished data). Chemical data and analyses for the Cache la Poudre River were takenfrom three sources (Richard et al., 1993; Voelz et al., 2000; and USGS, unpublisheddata). Richard et al. (1993) analyzed numerous physical/chemical parameters forsites 1 and 4 from 1980 to 1992. Voelz et al. (2000) provide an analysis of 10water chemistry parameters in the Cache la Poudre River for sites 1 and 4 (1980–1995), site 2 (1981–1993) and site 3 (1982–1991). In addition, datasets from theUSGS containing values for conductivity, dissolved oxygen, pH, NH4–N, NO2–N +NO3–N, total P and SO4 were analyzed for sites 1 (1975–1999) and 4 (1979–1999).Standard methods (APHA, 1981, 1985) were followed for measuring most waterchemistry parameters. Unfortunately water chemistry sampling protocol and qual-ity control were not as rigorously followed as they were for macroinvertebrates.Several laboratories were used for analyses and records were not kept of waterchemistry meters used to measure some variables. Seasonal Kendall tests wereused to analyze long-term trends in chemical parameters within sites (Hirsch et al.,1982; Gilbert, 1987). These tests were done using mass per volume data (e.g., mg/L)as trend analysis indicated no significant trend in stream flow over the study period.Analyses were performed using WQSTAT Plus (Intelligent Decision Technologies,Longmont, CO, U.S.A.).


4. Results

4.1. TAXONOMIC COMPOSITION OF THE STUDY RIVERS

Over 175 taxa (primarily genera) were collected in the Big Thompson and Cache laPoudre Rivers during the study period. The majority of macroinvertebrates collectedwere insects. The most common taxa collected were Tricorythodes minutus (Traver)and Baetis spp. (mayflies), Cheumatopsyche spp. and Hydropsyche spp. (caddis-flies), Oligochaeta (segmented worms), Simulium spp. (black flies), and Cricotopusspp., Glyptotendipes spp., Orthocladius spp. and Stictochironomus spp. (midges).The midges were consistently among the predominant benthic macroinvertebratescollected during the study.

4.2. EFFECTS OF URBANIZATION ON MACROINVERTEBRATE METRICS

Average metric values for the reference streams were indicative of higher qualitywhen Big Thompson and Cache la Poudre River site 1 were excluded, but there waslittle difference in metric values between spring and autumn when those sites wereeither included or excluded (Table III). Visual examination of box and whiskerplots indicated that most metrics usually showed differences between the referencecondition and Big Thompson and Cache la Poudre River sites 2–4, but no differencesamong sites 2–4 (Figure 2).

TABLE III

Average metric values (and ranges) for the reference streams, including/excluding Big Thompson andCache la Poudre Rivers site 1

Metric Spring Autumn

Total number of taxa 24.9 (12–44)/30.2 (22–44) 26.6 (17–40)/31.5 (23–40)

Number of EPT taxa 10.5 (3–18)/12.8 (7–18) 11.0 (4–20)/14.0 (9–20)

Number of clinger taxa 14.1 (6–23)/15.9 (10–20) 14.6 (6–24)/17.6 (12–24)

Percent scrapers 12.7 (1.1–32.9)/24.6(10.2–32.9)

10.3 (0.7–35.0)/19.9 (3.0–35.1)

Percent dominant taxon 31.1 (16.3–70.5)/27.2(18.6–50.0)

30.9 (11.0–67.8)/24.5(11.0–38.3)

Percent EPT 53.8 (18.6–82.8)/65.9(51.1–82.8)

60.1 (20.3–93.7)/67.8(48.5–80.4)

Percent Diptera 32.2 (4.5–74.1)/19.6 (4.5–36.0) 23.7 (2.5–51.1)/10.6 (2.5–28.1)

Percent Oligochaeta 4.9 (0–37.3)/2.3 (0–9.1) 5.7 (0–34.9)/2.5 (0–17.8)

Hilsenhoff’s biotic index (HBI) 4.8 (2.7–6.6)/4.2 (3.3–4.7) 4.7 (3.2–6.3)/4.5 (4.0–5.3)

Community tolerance quotient(CTQa)

77.9 (48.0–102.0)/75.5(69.0–88.2)

78.9 (66.0–98.6)/76.2(70.3–81.8)


Figure 2. An example of a common pattern, using Hilsenhoff’s biotic index (HBI), where the referencesites (in this case all reference stream data) were significantly different from sites 2–4, but sites 2–4 were statistically similar. Both graphs are for spring. Big Thompson River top, Cache la PoudreRiver bottom. The box represents the 25th and 75th percentile, vertical lines extend to 10th and90th percentile, horizontal line and small, black square in the box represent the median and mean,respectively.

For both the spring and autumn Cache la Poudre data, 8–9 of the metrics weresignificantly different (Kruskal–Wallis test, P ≤ 0.006) between the reference con-dition and all downstream sites (2–4) when reference data included or excludedBig Thompson and Cache la Poudre site 1. In general, a similar pattern was


observed in the Big Thompson River with 6–8 metrics showing significant differ-ences (Kruskal–Wallis test, P ≤ 0.020) between the reference and all downstreamsites. The exception was autumn in the Big Thompson for the full reference set whenonly 4 metrics showed significant differences (Kruskal–Wallis test, P ≤ 0.010). Allsignificant differences in metrics indicated worse conditions downstream.

We also examined the relationships among the various reference datasets andeach individual site (Tables IV–VI). In general a similar pattern emerges, with thefull reference dataset generally indicating more significant differences with indi-vidual sites. In fact, a stronger change is noted especially in the Cache la PoudreRiver when differences are examined between the reference condition and individ-ual sites. This happened because the above interpretations looked at relationshipsbetween reference conditions versus all potentially impacted sites (2–4) taken to-gether. For example, there were higher numbers of significant differences betweenthe reference condition and an individual site in several cases (e.g., Cache la Poudresite 2) because some metrics only showed a difference between the reference andthat one site ((Tables IV–VI). Other patterns also emerged from this view of thedata. Data for the Big Thompson (Table VI A) indicate some longitudinal change,with site 2 (some urban land use influence and above the wastewater treatmentplant) often having fewer significant differences with the reference datasets thandownstream sites. The Cache la Poudre results (Table VI B) indicate that already atsite 2, which is near the middle of the urban area and below the discharge from thefirst wastewater plant, there are many differences with little (one fewer significantdifference) or no change downstream of site 2. Again, all significant differences inmetrics indicated worse conditions downstream.

The relationships among sites were different when only site 1 in either riverwas used alone as the reference. For both rivers, there were usually fewer signifi-cant differences between site 1 and sites 2–4 as compared with the larger referencedatasets (Table VI). This was especially true for Big Thompson site 2 results, whichhad the fewest significant metric differences when only Big Thompson site 1 wasused as a reference. There was more change observed in the Cache la Poudre us-ing only site 1 as a reference and in all cases most metrics indicated significantdifferences between site 1 and sites 2–4. As for the larger reference dataset analy-ses, all significant differences in metrics indicated worse conditions downstream.Percentage dominant taxon, Ephemeroptera, Plecoptera and Trichoptera (EPT) andOligochaeta often showed no significant differences among sites.

4.3. LONG-TERM DATA

Another of our goals was to determine if long-term data could provide additionalinsight into the changes in water quality. There were no significant differencesamong metrics calculated from data collected during the first and last 5 years atsite 1 on the Big Thompson River (Wilcoxon signed ranks tests, Z = −0.1 to−1.8, P = 0.07–0.89). Percent EPT and Diptera at Big Thompson site 2, percent


TABLE IV

Average metric values (and ranges) for the Big Thompson River sites (A, spring; B, autumn). Sta-tistically significant differences are shown among the various reference datasets and sites 2–4, andamong sites 2–4 (Kruskal–Wallis P ≤ 0.05, followed by Student–Newman–Keuls α = 0.05)

Metric Site 1 Site 2 Site 3 Site 4

(A) Spring

Totalnumber oftaxa

21.0 (18–28) 19.0 (10–27)b,c 14.4 (7–19)a 15.5 (11–20)a

Number ofEPT taxa

9.0 (7–12) 6.3 (3–11)a 4.0 (0–8)a 4.6 (2–7)a

Number ofclinger taxa

12.0 (8–16) 9.3 (6–16)b,c 6.3 (0–9)a 6.6 (4–9)a

Percentscrapers

8.0 (1.4–14.2) 2.7 (0–11.2)a 0.8 (0–4.2)a 0.3 (0–1.0)a

Percentdominanttaxon

36.6 (19.0–70.5) 46.5 (22.9–74.1)b,c 44.3 (25.9–58.7)b,c 52.3 (29.4–86.2)b,c

Percent EPT 47.5 (25.2–77.6) 28.0 (4.4–77.1)d 15.2 (0–40.9)a 11.7 (1.1–19.3)a

PercentDiptera

35.0 (5.4–74.1) 34.7 (17.0–67.3) 70.4 (23.7–94.3)a,e 51.2 (11.4–79.4)b,c

PercentOligochaeta

7.1 (0–36.3) 16.0 (0–61.4)b,c 13.8 (0–52.5)b,c 35.8 (0.3–86.2)a

Hilsenhoff’sbiotic index(HBI)

5.2 (4.5–6.3) 5.9 (4.5–7.4)b,c 6.1 (4.9–6.9)b,c 6.6 (5.7–7.7)a

Communitytolerancequotient(CTQa)

79.0 (67.9–91.8) 93.6 (82.4–108.0)a 96.5 (81.2–108.0)a 94.8 (82.1–108.0)a

(B) Autumn

Totalnumber oftaxa

22.3 (18–27) 17.3 (10–23)a 17.2 (10–23)a 16.2 (6–25)a

Number ofEPT taxa

8.7 (6–11) 6.3 (4–12)a 6.3 (3–10)a 4.8 (3–9)a

Number ofclinger taxa

11.8 (9–16) 9.6 (6–14)a 9.1 (5–12)a 7.1 (4–13)a,e,f

Percentscrapers

8.3 (0.7–21.8) 5.4 (0–18.1)b,c 7.7 (0.3–44.3)c 6.2 (1.0–43.6)c

Percentdominanttaxon

36.2 (13.0–67.8) 48.1 (19.0–90.4) 40.1 (13.0–88.5) 35.4 (19.7–89.1)

(Continued on next page)


TABLE IV

(Continued)


Percent EPT 59.3 (20.3–86.2) 67.5 (14.5–95.0)b,c 51.2 (21.6–95.7)c 48.8 (23.8–91.0)c

PercentDiptera

23.7 (3.8–38.8) 19.9 (1.8–49.8) 38.8 (3.4–74.1)a,e 34.4 (6.4–59.7)b,c,e

PercentOligochaeta

7.9 (0–34.8) 5.3 (0–37.4) 6.8 (0.4–16.9) 14.3 (0.7–37.3)b,c,e,f

Hilsenhoff’sbiotic index(HBI)

5.0 (4.1–6.3) 4.7 (3.1–7.2) 5.1 (2.1–6.1) 5.7 (4.0–6.6)a,e

Communitytolerancequotient(CTQa)

80.9 (69.9–93.0) 92.8 (65.6–105.0)a 94.0 (71.6–105.4)a 97.5 (78.1–105.2)a

aSignificantly different from all reference datasets.bSignificantly different from combined reference site data.cSignificantly different from the reference site data with Big Thompson and Cache la Poudre sites 1excluded.dSignificantly different from site 1 (reference).eSignificantly different from site 2.fSignificantly different from site 3.

dominant taxon, HBI and CTQa at site 3 and CTQa at site 4 were significantlydifferent between years (Z = −2.0 to −2.2, P = 0.03–0.04). Overall each siteshowed little change in the Cache la Poudre River. Only total and clinger taxaat site 1 and percent scrapers at site 2 were significantly different between years(Z = −2.2, P = 0.03 for all analyses). At site 3, EPT and clinger taxa, and CTQa

and at site 4 percent EPT and HBI were different between years (Z = −2.0 to−2.2, P = 0.03–0.04). All significant differences between times in the Cache laPoudre River indicated changes in metrics that could be interpreted as improvingconditions. The opposite was found in the Big Thompson River as significantmetric changes in all but percent dominant taxon at site 3 suggested degradingconditions.

Long-term trends of the 10 metrics were examined for the complete autumnCache la Poudre River data (1981–2000) using spearman rank correlations. Totaland clinger taxa showed significantly positive increases for all sites (rs = 0.47–0.70,P = 0.001–0.04). Significant trends were also observed for EPT taxa at sites 2 and4 (rs = 0.61 and 0.71, respectively, P < 0.01), percent EPT at site 4 (rs = 0.58,P = 0.01) and percent Diptera at sites 1 and 4 (rs = 0.55 and −0.57, respectively,P = 0.01). With few exceptions, these results, and those that were not significant,indicated trends that suggest improving stream condition.


TABLE V

Average metric values (and ranges) for the Cache la Poudre River sites (A, spring; B, autumn).Statistically significant differences are shown among the various reference datasets and sites 2–4, andamong sites 2–4 (Kruskal–Wallis P ≤ 0.05, followed by Student–Newman–Keuls α = 0.05)


(A) Spring

Total number of taxa 23.9 (12–36) 18.5 (14–26)a 18.9 (14–26)a 17.1 (13–22)a

Number of EPT taxa 9.9 (3–15) 5.3 (2–9)a 4.9 (3–9)a 4.4 (3–7)a

Number of clingertaxa

14.1 (6–23) 8.6 (5–15)a 7.9 (4–14)a 7.5 (6–11)a

Percent scrapers 8.0 (1.1–26.6) 0.8 (0–2.8)a 1.0 (0–4.7)a 0.9 (0–3.5)a

Percent dominanttaxon

30.6 (16.3–50.0) 48.9 (16.4–88.8)a 39.6 (20.0–83.2)b,c 42.9 (21.4–59.6)b,c

Percent EPT 49.9 (18.6–79.0) 10.7 (0.4–22.2)a 16.1 (4.9–27.2)a 12.1 (1.7–50.6)a

Percent Diptera 38.4 (16.6–67.1) 50.9 (7.3–83.7)b,c 61.5 (11.5–88.5)a 73.0 (32.4–92.6)a,d

Percent Oligochaeta 5.3 (0–37.3) 32.3 (0.3–88.8)a 18.3 (0–83.2)d 12.4 (0.5–57.7)d

Hilsenhoff’s bioticindex (HBI)

4.9 (2.7–6.6) 6.9 (6.0–7.9)a 6.5 (5.4–7.6)a 6.6 (5.9–7.3)a

Community tolerancequotient (CTQa)

78.5 (48.0–102.0) 98.7 (64.9–108.0)a 99.4 (84.9–108.0)a 100.3 (75.3–108.0)a

(B) Autumn

Total number of taxa 26.9 (17–35) 21.8 (7–33)a 22.4 (12–30)a 19.5 (8–27)a

Number of EPT taxa 10.9 (4–16) 7.1 (2–12)a 6.3 (2–11)a 5.8 (3–8)a

Number of clingertaxa

14.9 (6–21) 10.9 (2–16)a 9.9 (5–16)a 8.3 (5–12)a,d

Percent scrapers 6.8 (1.1–25.1) 2.3 (0.2–12.9)a 3.7 (0–12.2)a 2.0 (0–8.2)a

Percent dominanttaxon

30.6 (15.5–57.6) 36.3 (15.0–75.4) 36.8 (20.2–53.6) 39.5 (18.6–64.0)

Percent EPT 56.8 (20.6–93.7) 42.7 (8.4–91.2)b,c 49.2 (3.0–76.1)b,c 47.5 (12.3–86.2)b,c

Percent Diptera 30.1 (4.4–51.1) 35.5 (6.1–70.0)c 32.7 (7.5–66.5)c 34.9 (9.7–84.0)c

Percent Oligochaeta 5.9 (0–34.9) 13.2 (0.3–75.4)b,c 12.0 (0–50.4)b,c 11.9 (0–45.3)b,c

Hilsenhoff’s bioticindex (HBI)

4.7 (3.2–6.0) 5.8 (4.3–6.9)a 5.9 (4.6–7.7)a 5.9 (4.3–7.1)a

Community tolerancequotient (CTQa)

78.8 (66.0–98.6) 92.3 (66.4–108.0)a 99.1 (86.6—108.0)b,c,d 99.3 (86.6–108.0)b,c,d

aSignificantly different from all reference datasets.bSignificantly different from combined reference site data.cSignificantly different from the reference site data with Big Thompson and Cache la Poudre sites 1excluded.dSignificantly different from site 2.

4.4. DIFFERENCES IN SAMPLING PROTOCOLS

One difficulty that exists with our comparative study is the differences in samplingmethods among the reference stream studies. Most reference stream samples were


TABLE VI

Summary of the number of metrics that showed significant differences among the various referencedatasets and sites 2, 3 or 4 during spring and autumn for the Big Thompson (A) and Cache la Poudre(B) Rivers. Data are from Tables IV and V

Number of significant

metrics

Season and reference data Site 2 Site 3 Site 4

(A) Big Thompson River

Spring – all reference sites 8 10 10

Spring – excluding Big Thompson and Cache la Poudre site 1 8 10 10

Spring – only Big Thompson site 1 4 7 8

Autumn – all reference sites 6 5 7

Autumn – excluding Big Thompson site 1 and Cache la Poudre site 1 6 7 9

Autumn – only Big Thompson site 1 4 5 7

(B) Cache la Poudre River

Spring – all reference sites 10 9 9

Spring – excluding Big Thompson and Cache la Poudre site 1 10 9 9

Spring – only Cache la Poudre site 1 9 8 8

Autumn – all reference sites 8 8 8

Autumn – excluding Big Thompson and Cache la Poudre site 1 9 9 9

Autumn – only Cache la Poudre site 1 6 6 6

collected with either a Surber or a circular sampler. Jacobi (1978) compared aSurber and a circular sampler and determined that although there were significantdifferences in density, there were no differences between the samplers with regardto total number of taxa collected. Based on his data (Jacobi, 1978) we were able tocalculate some of the metrics used in our study. We determined that there were alsono significant differences for number of EPT taxa, and percentage EPT, dominanttaxon and Diptera (Wilcoxon paired sample signed ranks, Z = −0.05 to −1.7, P =0.08–0.96).

In addition to differences in samplers, there are also differences in mesh sizesamong the studies (500–750 µm, Table I). Some evidence suggests that usingmetrics, instead of absolute numbers, may reduce this concern. First, given the aboveanalysis of Surber versus circular samplers, significant differences were found indensities between samplers, but no differences when the data were converted tometrics. This suggests that the relative proportions, for example, of various taxamay be similar. This has also been found for the Cache la Poudre River, Boulderand Saint Vrain Creeks along the front range, where collections were made atmountain, plains/mountain interface, and plains sites with 250 and 500 µm meshSurber samplers and compared for differences in commonly used metrics (Cox and


Zuellig, unpublished data). Second, samples from St. Vrain Creek, CO (Ward, 1986and unpublished) were collected at the same time with two Surbers with differentmesh sizes (240 and 720 µm). Differences in metric values between the two meshsizes were relatively small in most cases, especially given the large difference inmesh sizes.

4.5. WATER CHEMISTRY

In general, most of the water chemistry parameters for the Big Thompson Riverexhibited increased levels downstream from site 1, with large increases at site 3(NH4–N and NO3–N) or site 4 (PO4–P). However, the concentration of NO3–Ndropped between sites 1 and 2 (0.70 to 0.39 mg/L). Average conductivity, NH4–N, NO3–N and PO4–P levels increased approximately 2 (615–1134 µS/cm), 6(0.06–0.34 mg/L), 4 (0.70–2.91 mg/L) and 28 (0.02–0.97 mg/L) times, respectively,between sites 1 and 4. The median pH (ca. 8.1) and average dissolved oxygen (DO)concentration (9.3–10.3 mg/L) remained relatively similar across sites. No waterquality standard violations were detected at any site in the Big Thompson River(US EPA, 1986).

Monthly (March–November) Big Thompson River data for 2001 (only for sites2–4) exhibited similar trends to those described above, with a few exceptions.Conductivity values were still higher at sites 2–4 than earlier values for site 1, butthe differences among sites were less. NH4–N concentrations at sites 2–4 weremuch lower in 2001, but the increasing levels downstream were still evident. PO4–P values at site 3 were approximately 5 times higher in 2001 than the averagepreviously recorded and there was little difference in concentration between sites3 and 4.

Significant long-term trends of chemical factors within sites on the Big Thomp-son River (seasonal Kendall analyses; P ≤ 0.05) indicated positive trends for con-ductivity at sites 2 and 3, pH at sites 1 and 2, and NO3–N at site 3. Negative trendswere found for DO at sites 2–4 (no readings below 5.0 mg/L), NH4–N at sites 1–3,and NO3–N at sites 1 and 2.

The overall longitudinal chemical gradient in the Cache la Poudre River wassimilar to that observed in the Big Thompson, with large increases occurring atsites 2 and 4. Depending on the dataset examined, average conductivity, NH4–N,NO3–N and PO4–P or total P increased about 3–5-, 3–18-, 6–7- and 6–17-foldbetween sites 1 and 4. The longest datasets available for sites 1 (1975–1999) and 4(1979–1999) showed that conductivity increased about 3 times (359–1233 µS/cm)between these sites, while NH4–N, NO2–N + NO3–N and total P all increased about6–7 times (0.04–0.24, 0.5–2.9, 0.03–0.15 mg/L, respectively). SO4 concentrationsincreased approximately 9-fold between sites 1 and 4 (59.1–551.9 mg/L). Voelzet al. (2000) also found increasing BOD5 and turbidity downstream from site 1,with a doubling of values between sites 1 and 4.


The median pH (7.8–8.2) and average dissolved oxygen concentration (8.5–10.1mg/L) remained relatively similar across Cache la Poudre River sites, though a dropin DO did occur between sites 1 and 2; however, most DO values at site 2 were >8.0mg/L. Violations of DO standards (i.e., <5 mg/L; US EPA, 1986) occurred for site2 during February 1984, September 1988 and 1989, and October 1992. Violationswere also observed at site 3 during August 1985, and at site 4 in July 1989 and1992, and during August and September 1992. The DO standard was not violatedafter 1992 at any site.

Statistically significant (seasonal Kendall analysis; P ≤ 0.05) long-term trendsof chemical variables within sites on the Cache la Poudre River presented in Voelzet al. (2000) showed that conductivity increased during that study at all sites. NO3–Nconcentrations also increased at site 2. Significant decreases were noted for PO4–Pat sites 1 and 4, and for BOD5 and NH4–N at site 4. Significant Kendall analyseswere found in the longest chemical record for sites 1 and 4, with conductivity, NH4–N and SO4 exhibiting negative trends at site 1, and NH4–N and total P showingnegative trends at site 4. In addition, DO exhibited a positive trend at site 4.

5. Discussion

The need to understand more about the ecology of larger, plains rivers in aridand semi-arid areas is vital given not only their importance as ecological unitsbut also as resources for an increasing human population. One confounding factorin separating natural from anthropogenic-induced changes in rivers is the naturallongitudinal change associated with lotic systems (Vannote et al., 1980; Downeset al., 2002). Overall some environmental conditions (e.g., temperature, predom-inant substrate) were similar at our study sites and there was relatively little ele-vational gradient. In addition, the study reach was short, with sites 1 and 4 onlyseparated by a distance of ca. 17–18 km. Thus comparisons among sites, withregard to long-term changes, are plausible because confounding factors such asrapid change in elevation, with its concomitant change in numerous environmentalparameters, does not occur in these rivers at the scale of this study.

Rapport (1989) defined three ways that may help us separate, what he termed,healthy from sick ecosystems (see Norris and Thoms, 1999). These three ways are:1) the absence of distress defined by measured characteristics or indicators; 2) theability of an ecosystem to handle stress (its resilience), and 3) the identificationof risk factors such as industrial or sewage effluents. This paper addresses the useof indicators (macroinvertebrate metrics) and the identification of risk factors (in-creasing urban land use, physical–chemical parameters). Resilience was addressedfor the Cache la Poudre River by Voelz et al. (2000) using multivariate statisticsand Kendall’s coefficient of concordance. Their study found that major changes inmacroinvertebrate assemblage structure within sites corresponded with the highestrecorded discharge in 75 years (1983) and were temporary, with taxon richness


recovering to pre-1983 levels within a few months at most sites. However, theirstudy did not specifically assess the impacts of urban areas on water quality butsuggested that even impacted biotic assemblages may have some resilience to dis-turbance.

The analyses of the macroinvertebrate metrics indicate that urban impacts occurin both the Big Thompson and Cache la Poudre Rivers. It was expected that themacroinvertebrate responses in the Big Thompson River would be less than inthe Cache la Poudre given, for example, that the City of Loveland is smaller andhas fewer housing units. However, in general this was not the case. Although thepopulation growth of the City of Loveland has been lower than Fort Collins, itis possible that because the stream is smaller (e.g., lower average discharge) anyincrease of runoff may have a greater effect. Also, much of the growth in FortCollins is occurring in stormwater basins that no longer drain to the Cache laPoudre River because they were historically incorporated into extensive irrigationcanal networks.

Our data support significant effects of the urban areas on macroinvertebrates witheither spring or autumn data for the Cache la Poudre River. The lowest numberof differences in the Cache la Poudre River macroinvertebrate metrics occurredduring spring using only site 1 as a reference, but there were still 6 metrics showingsignificant differences between the reference and downstream sites. In the BigThompson River the fewest metrics showing significant differences at downstreamsites occurred using the full reference dataset (autumn) or only site 1 (spring andautumn). This may indicate that Big Thompson site 1 was a poor reference site andalso overly affected the total reference dataset. Thus, had the Big Thompson Riveronly been monitored during one season or only with site 1 as reference, the datawould suggest a different view of this river.

Our results show that having only one reference site still provides some insightinto the effects of urban areas on macroinvertebrates (Table VI). This is especiallyevident in the Cache la Poudre River, as most metrics indicated significantly worseconditions at sites 2–4. A similar pattern was seen in the Big Thompson River, excepta stronger longitudinal component was observed. This is interesting because riversthat originate in the mountains in the western U.S. have had extensive modificationduring the past ca. 200 years. Not only have urban areas increased in the plains,but also beaver trapping, logging and water diversion, among other impacts, inthe mountain portions of these streams have likely influenced the plains sectionsof these rivers (Wohl, 2001). Thus, although the reference sites may be partiallydegraded due to impacts from land use in the mountain sections and diversions at theplains/mountain interface, they still provided some evidence that urban influencescan further affect macroinvertebrate assemblages.

There are several problems, however, with having only a single reference site onthe same stream. For example, the reference site may initially be degraded and notgive an accurate picture of water quality or the site can become degraded with time.In addition, natural longitudinal variation can confound interpretation of potential


impacts, though this was probably not an issue in our study given the relatively shortdistance between sites and little change in elevation. Finally there may be a problemwith intercorrelation among sites which may violate assumptions of independence(see Downes et al., 2002).

The results of the long-term analyses indicate that at least the Cache la PoudreRiver is either experiencing little change or conditions are getting slightly better.The long-term chemistry and macroinvertebrate assemblage patterns in the BigThompson suggest an increasing impact, though it should be noted that some changeoccurred in the way macroinvertebrates were collected.

Long-term monitoring can also be used to determine if having only one or afew years of data give a different impression of water quality than if data are col-lected regularly over long time periods. Many recent macroinvertebrate monitoringprograms have taken the approach of collecting data in numerous streams for oneor a few years over broad geographic areas to determine the quality of these wa-ter bodies (e.g., Clements et al., 2000; Kay et al., 2001). In order to address thisquestion we looked at our metric data for all individual years and for 2–3 years ofthe best possible data combined (averages), and compared them with the averagesfor the reference conditions. While in any given year at sites 2–4 in either river afew metrics were near the averages for the reference sites, in all cases values forthe majority of metrics were much lower than reference averages. Thus, althoughlong-term data provided information on changing conditions (better or worse) inthese rivers, we would not have received a false impression of the water quality inthese rivers had we only sampled once or a few times and compared our results toreference conditions.

Agricultural land use occurred along both rivers between sites 3 and 4, howeverour results indicated that the urban influences had already impacted the macroin-vertebrate assemblages especially for the Cache la Poudre River. Interestingly, astudy on secondary production of macroinvertebrates in the Cache la Poudre Riverconducted at sites near the sites in the present study showed that lowest productivityoccurred upstream from the urban area (reference site), highest productivity at asite near where the river exits the urban area and intermediate levels of secondaryproduction at the farthest downstream site (Shieh et al., 2002). Had this variablebeen used alone to determine the impacts of urban land use (and some agriculture)it might have suggested a benefit of urban areas. However, Shieh et al. (2002) alsolooked at food web dynamics and found that the higher secondary production atdownstream sites was primarily due to a few taxa, especially the non-tanypodinaeChironomidae. This corresponds with the general view observed in this study.

The overall message from our analysis of the macroinvertebrate metrics is thatdifferences exist between the reference condition and the sites in and below therespective urban areas. In all cases these differences indicate worse conditions atthe downstream sites. However, analysis of longer-term data suggests no worseningtrends or somewhat better conditions within sites at least in the Cache la PoudreRiver, even with increased urban development (also see Shieh et al., 1999).


The difference in mesh sizes and sampling protocols among the referencestreams used in our study suggests caution in interpreting some of our results.However, comparisons of different samplers and mesh sizes suggest that althoughdensities can be different, relative proportions of macroinvertebrate taxa are similar.In addition, many of the reference sites have likely been degraded due to increasingdevelopment along the eastern slope (front range) of the Rocky Mountains, espe-cially since some data were collected ∼20 years ago. Thus it may be impossible toaccurately determine the reference condition for larger, front range streams fromcurrent sample collection.

Using the surrogate variables of potential urban impact (population and housingunits), and the environmental gradient represented primarily by chemical factors,it is evident that there is an effect of urban land use that is reflected in the macroin-vertebrate assemblages in both the Big Thompson and Cache la Poudre Rivers. Theresults from the environmental analyses suggest some reasons for the observed im-pacts on the macroinvertebrate assemblages. Although few or no violations of waterquality standards were observed in either river, increased concentrations of manychemical variables, especially nutrients, with distance downstream from the urbanareas may more indirectly affect the organisms. Although it is beyond the scope ofthis paper to examine the numerous individual components from urban runoff, weattempted to choose macroinvertebrate indices that allow us to examine a few ofthese constituents and relate them to what was known about the physical/chemicalgradient. In addition, it should be kept in mind that there likely are multiple effectsof some pollutants. For example, sediments that enter rivers from unstable streambanks or construction can directly affect the biota through abrasion, and indirectlyby smothering habitat, and carry bound contaminants downstream. Sediment is themain pollutant in U.S. rivers (US EPA, 1998) and a major component of urbanrunoff (Novotny and Olem, 1994). Although sedimentation was not measured inthis study (although some turbidity data were analyzed), an examination of changesin metrics may provide insight into the potential effects of sediment pollution fromurban areas.

The effects of suspended sediments on aquatic macroinvertebrates are relativelyunknown, as most work has dealt with sediment deposition (Ward, 1992; Waters,1995; but see Culp et al., 1986). Lower levels of sedimentation have little effecton benthic macroinvertebrates (e.g., Rabeni and Minshall, 1977), but in general areduction in diversity occurs in response to increased levels of deposited sediments(e.g., Gammon, 1970; Brusven and Prather, 1974; Ogbeibu and Victor, 1989; Zuelliget al., 2002). Richards et al. (1997) found that clinger and scraper taxa declinedwith increased sedimentation. In a study that experimentally manipulated benthicfine sediment levels, Angradi (1999) observed reductions in EPT taxa richness andan increase in the proportion of Ephemeroptera that were Baetidae when sedimentlevels were increased. Gammon (1970) found large reductions in densities and someloss of taxa due to suspended sediments, whereas Gray and Ward (1982) observeddifferential responses to sediment input, but little loss of taxa.


The results of sediment pollution studies indicate that although some levels ofsuspended and deposited sediment may not reduce the number of taxa, it is likelythat proportional changes may occur and will be reflected in percentage compositionindices (e.g., EPT and Diptera) and in an index like the CTQa, as was found in thisstudy. Unfortunately in some cases, the composition measures proved to have highvariability. In addition we can make predictions that if sediment was a problem,certain taxa may be lost whereas others may not be affected or even may benefitfrom the impact. A good example of this is the mayfly Tricorythodes minutus,one of the most abundant taxa found throughout the study. Tricorythodes minutusis relatively common in plains sections of Colorado streams (Ward, 1986) and isapparently well adapted for streams that can have large sediment loads, becausetheir first pair of respiratory gills are enlarged and provide a protective covering fortheir other gills (Gammon, 1970; Gray and Ward, 1982). This presumably shieldsthe gills from fouling by sediments. So it is possible that this protective coveringallows this species to be abundant at all sites, especially those downstream fromthe urban areas.

Increased levels of plant nutrients are also common in urban runoff and cancause changes in the periphyton assemblage structure, even at low concentrations(Peterson et al., 1985; Hart and Robinson, 1990). This change in periphyton mayresult in effects on macroinvertebrates in at least two ways (also see Dodds andWelch, 2000). First, shifts in algal resources can negatively affect the food base forsome organisms such as scrapers. Second, some benthic invertebrates are influencedby changes in algal assemblages because a change in habitat structure occurs (seeDudley et al., 1986). As for sediment, shifts in algal resources and/or structuremay differentially affect individual taxa. For example, Hydropsyche spp. and Baetisspp., both of which are predominant taxa in the Big Thompson and Cache la PoudreRivers, have been found to respond positively to either macroalgal habitat structure(Hydropsyche spp.) or both structure and associated food resources (Baetis spp.;Dudley et al., 1986). The increased level of plant nutrients (NH4–N, NO3–N andPO4–P) found in this study, as the rivers flowed through and exited the urban areas,has been observed in other research (e.g., Osborne and Wiley, 1988; Tate and Heiny,1995).

In conclusion, data on macroinvertebrates and water chemistry showed thatboth rivers are negatively impacted by urban land use. Negative effects of agri-cultural practices were only seen in the Big Thompson River, but this relation-ship was neither strong nor consistent. The most robust results were usuallyseen when regional reference data were used. However, even using only the up-stream reference site in either the Big Thompson or Cache la Poudre Rivers in-dicated some negative impacts from the urban areas. Once these streams enterurban areas, they do not recover to reference condition as they move downstream.Although urban impacts were detected, the use of long-term data, particularlyin the Cache la Poudre River, showed that water quality conditions have not


been getting worse and there is some evidence of improvement in downstreamreaches.

Acknowledgements

Discussions with R. Bramblett, R. Buirgy, T. Eddy, K. Fausch and L. Smolkaprovided several useful ideas for improving this paper and sources of data. Dr.Boris Kondratieff, Colorado State University, kindly provided taxonomic assis-tance. Thanks to M. Shrode for constructing Figure 1. We are grateful to both theBig Thompson Watershed Forum, and the Water Quality Division of the WyomingDepartment of Environmental Quality (Watershed Program) for providing unpub-lished data.

References

Angradi, T. R.: 1999, ‘Fine sediment and macroinvertebrate assemblages in Appalachian streams: Afield experiment with biomonitoring applications’, J. N. Amer. Benthol. Soc. 18, 49–66.

A.P.H.A.: 1981, Standard Methods for the Examination of Water and Wastewater, 15th ed., AmericanPublic Health Association, Washington, DC.

A.P.H.A.: 1985, Standard Methods for the Examination of Water and Wastewater, 16th ed., AmericanPublic Health Association, Washington, DC.

Armitage, P. D. and Gunn, R. J. M.: 1996, ‘Differential response of benthos to natural and anthro-pogenic disturbances in 3 lowland streams’, Int. Rev. Ges. Hydrobiol. 81, 161–181.

Barbour, M. T., Gerritsen, J., Snyder, B. D. and Stribling, J. B.: 1999, Rapid Bioassessment Protocolsfor Use in Streams and Wadeable Rivers: Periphyton, Benthic Macroinvertebrates and Fish, 2nded., EPA 841-B-99-002, U.S. Environmental Protection Agency, Office of Water, Washington,DC.

Barbour, M. T., Plafkin, J. L., Bradley, B. P., Graves, C. G. and Wisseman, R. W.: 1992, ‘Evaluation ofEPA’s rapid bioassessment benthic metrics: Metric redundancy and variability among referencestream sites’, Env. Tox. Chem. 11, 437–449.

Boyd, W. L., Martin, K. L., Warbington, R. C. and Fausch, K. D.: 1986, Cache la Poudre River Survey1985, Colorado State University, Fort Collins.

Brusven, M. A. and Prather, K. V.: 1974, ‘Influence of stream sediments on distribution of macroben-thos’, J. Ent. Soc. Brit. Colum. 71, 25–32.

Camargo, J. A., Ward, J. V. and Martin, K. L.: 1992, ‘The relative sensitivity of competing hydropsy-chid species to fluoride toxicity in the Cache la Poudre River (Colorado)’, Arch. Env. Cont. Toxicol.22, 107–113.

Clements, W. H., Carlisle, D. M., Lazorchak, J. M. and Johnson, P. C.: 2000, ‘Heavy metals structurebenthic communities in Colorado mountain streams’, Eco. Appl. 10, 626–638.

Cooper, S. D., Diehl, S., Kratz, K. and Sarnelle, O.: 1998, ‘Implications of scale for patterns andprocesses in stream ecology’, Aust. J. Ecol. 23, 27–40.

Corkum, L.: 1989, ‘Patterns of benthic invertebrate assemblages in rivers of northwestern NorthAmerica’, Freshw. Biol. 21, 191–205.

Creason, J. and Runge, C.: 1992, Use of Lawn Chemicals in the Twin Cities. Report #7, MinnesotaWater Resources Research Center, University of Minnesota, St. Paul.


Culp, J. M., Wrona, F. J. and Davies, R. W.: 1986, ‘Response of stream benthos and drift to finesediment deposition versus transport’, Can. J. Zool. 64, 1345–1351.

Davis, W. S. and Simon, T. P. (eds.): 1995, Biological Assessment and Criteria: Tools for WaterResource Planning and Decision Making, Lewis Publishers, Boca Raton, Florida.

DeShon, J. E.: 1995, ‘Development and Application of the Invertebrate Community Index (ICI) ’, in:W. S. Davis and T. P. Simon (eds.), Biological assessment and criteria: Tools for water resourceplanning and decision making, Lewis Publishers, Boca Raton, Florida, pp. 217–243.

Dodds, W. K. and Welch, E. B.: 2000, ‘Establishing nutrient criteria in streams’, J. N. Amer. Benthol.Soc. 19, 186–196.

Downes, B. J., Barmuta, L. A., Fairweather, P. G., Faith, D. P., Keough, M. J., Lake, P. S., Mapstone,B. D. and Quinn, G. P.: 2002, Monitoring Ecological Impacts. Concepts and Practice in FlowingWaters, Cambridge University Press, Cambridge, UK.

Dudley, T. L., Cooper, S. D. and Hemphill, N.: 1986, ‘Effects of macroalgae on a stream invertebratecommunity’, J. N. Amer. Benthol. Soc. 5, 93–106.

Elliott, J. M.: 1990, ‘The need for long-term investigations in ecology and the contribution of theFreshwater Biological Association’, Freshw. Biol. 23, 1–5.

Fore, L. S., Karr, J. R. and Wisseman, R. W.: 1996, ‘Assessing invertebrate responses to humanactivities: Evaluating alternative approaches’, J. N. Amer. Benthol. Soc. 15, 212–231.

Gammon, J. R.: 1970, The Effect of Inorganic Sediment on Stream Biota, Water Poll. Control Res.Ser. No. 18050 DWC, U.S. Environmental Protection Agency, Washington, DC.

Garn, H. S. and Jacobi, G. Z.: 1996, Water Quality and Benthic Macroinvertebrate Bioassessment ofGallinas Creek, San Miguel County, New Mexico, 1987–1990, U.S. Geological Survey, WaterResources Investigations. Report 96-4011, Albuquerque.

Gerritsen, J.: 1995, ‘Additive biological indices for resource management’, J. N. Amer. Benthol. Soc.14, 451–457.

Gilbert, R. O.: 1987, Statistical Methods for Environmental Pollution Monitoring, Van NostrandReinhold, New York.

Goodnight, C. J.: 1973, ‘The use of aquatic macroinvertebrates as indicators of stream pollution’,Transact. Am. Microscop. Soc. 92, 1–13.

Gray, L. J. and Ward, J. V.: 1982, ‘Effects of sediment releases from a reservoir on stream macroin-vertebrates’, Hydrobiologia 96, 177–184.

Hart, D. D. and Robinson, C. T.: 1990, ‘Resource limitation in a stream community: Phosphorusenrichment effects on periphyton and grazers’, Ecology 71, 1494–1502.

Hawkes, H. A.: 1979, ‘Invertebrates as Indicators of River Water Quality ’, in: A. James and L. Evison(eds.), Biological Indicators of Water Quality, Wiley Press, Chichester, UK, pp. 2-1–2-45.

Heino, J., Muotka, T., Paavola, R., Hamalainen, H. and Koskenniemi, E.: 2002, ‘Correspondencebetween regional delineations and spatial patterns in macroinvertebrate assemblages of borealheadwater streams’, J. N. Amer. Benthol. Soc. 21, 397–413.

Hilsenhoff, W. L.: 1987, ‘An improved biotic index of organic stream pollution’, Great Lakes Entomol.20, 31–39.

Hirsch, R. M., Slack, J. R. and Smith, R. A.: 1982, ‘Techniques of trend analysis for monthly waterquality data’, Water Resources Res. 18, 107–121.

Hynes, H. B. N.: 1994, ‘Historical Perspective and Future Direction of Biological Monitoring ofAquatic Systems ’, in: S. L. Loeb and A. Spacie (eds.), Biological Monitoring of Aquatic Systems,Lewis Publishers, Boca Raton, Florida, pp. 11–22.

Jacobi, G. Z.: 1978, ‘An inexpensive circular sampler for collecting benthic macroinvertebrates instreams’, Arch. Hydrobiol. 83, 126–131.

Jacobi, G. Z.: 1983, Biological Monitoring at Ambient Surveillance Stations, 1980–1981, ReportEID/WPC – 83/2, New Mexico Health and Environment Department, Santa Fe.

Karr, J. R.: 1999, ‘Defining and measuring river health’, Freshw. Biol. 41, 221–234.


Karr, J. R. and Chu, E. W.: 1999, Restoring Life in Running Waters. Better Biological Monitoring,Island Press, Washington, DC.

Kay, W. R., Halse, S. A., Scanlon, M. D. and Smith, M. J.: 2001, ‘Distribution and environmental tol-erances of aquatic macroinvertebrate families in the agricultural zone of southwestern Australia’,J. N. Amer. Benthol. Soc. 20, 182–199.

Kemp, S. J. and Spotila, J. R.: 1997, ‘Effects of urbanization on brown trout Salmo trutta, otherfishes and macroinvertebrates in Valley Creek, Valley Forge, Pennsylvania’, Amer. Midl. Nat.138, 55–68.

Kerans, B. L. and Karr, J. R.: 1994, ‘A benthic index of biotic integrity (B-IBI) for rivers of theTennessee Valley’, Eco. Appl. 4, 768–785.

Magnuson, J. J.: 1990, ‘Long-term ecological research and the invisible present’, Bioscience 40,495–501.

McElravy, E. P., Lamberti, G. A. and Resh, V. H.: 1989, ‘Year-to-year variation in the aquatic macroin-vertebrate fauna of a northern California stream’, J. N. Amer. Benthol. Soc. 8, 51–63.

Merritt, R. W. and Cummins, K. W.: 1996, An Introduction to the Aquatic Insects of North America,Kendall/Hunt Publishing, Dubuque, Iowa.

Mueller, D. K.: 1990, Analysis of Water-Quality Data and Sampling Programs at Selected Sites inNorth-Central Colorado, U.S. Geological Survey, Water Resources Investigations Report 90-4005,Denver, Colorado.

Naiman, R. J., Magnuson, J. J., McKnight, D. M. and Stanford, J. A.: 1995, The Freshwater Imperative.A Research Agenda, Island Press, Washington, DC.

Norris, R. H.: 1995, ‘Biological monitoring: The dilemma of data analysis’, J. N. Amer. Benthol. Soc.14, 440–450.

Norris, R. H. and Thoms, M. C.: 1999, ‘What is river health? ’ Freshw. Biol. 41, 197–209.Novotny, V. and Olem, H.: 1994, Water Quality. Prevention, Identification and Management of Diffuse

Pollution, Van Nostrand Reinhold, New York.Ogbeibu, A. E. and Victor, R.: 1989, ‘The effects of road and bridge construction on the bank-

root macrobenthic invertebrates of a southern Nigerian stream’, Environ. Pollut. 56, 85–100.

Osborne, L. L. and Wiley, M. J.: 1988, ‘Empirical relationships between land use/cover patterns andstream water quality in an agricultural catchment’, J. Environ. Manage. 26, 9–27.

Patrick, R.: 1992, Surface Water Quality: Have the Laws been Successful? Princeton University Press,New Jersey.

Paul, M. J. and Meyer, J. L.: 2001, ‘Streams in the urban landscape’, Ann. Rev. Ecol. Syst. 32, 333–365.Pennak, R. W.: 1978, Freshwater Invertebrates of the United States, 2nd ed., Wiley-Interscience, New

York.Peterson, B. J., Hobbie, J. E., Hershey, A. E., Lock, M. A., Ford, T. E., Vestal, J. R., McKinley, V. L.,

Hullar, M. A. J., Miller, M. C., Ventullo, R. M. and Volk, G. S.: 1985, ‘Transformation of a tundrariver from heterotrophy to autotrophy by addition of phosphorus’, Science 229, 1383–1386.

Pitt, R. and Field, R.: 1977, ‘Water quality effects from urban runoff’, J. Amer. Wat. Assoc. 69,432–436.

Plafkin, J. L., Barbour, M. T., Porter, K. D., Gross, S. K. and Hughes, R. M.: 1989, Rapid BioassessmentProtocols for Use in Streams and Rivers. Benthic Macroinvertebrates and Fish, EPA/440/4-89/001, U.S. Environmental Protection Agency, Office of Water, Washington, DC.

Rabeni, C. F. and Minshall, G. W.: 1977, ‘Factors affecting microdistribution of stream benthicinsects’, Oikos 29, 33–43.

Rapport, D. J.: 1989, ‘What constitutes ecosystem health? ’ Persp. Biol. Med. 33, 120–132.Rapport, D. J., Gaudet, C., Karr, J. R., Baron, J. S., Bohlen, C., Jackson, W., Jones, B., Naiman, R.

J., Norton, B. and Pollock, M. M.: 1998, ‘Evaluating landscape health: Integrating societal goalsand biophysical processes’, J. Environ. Manage. 53, 1–15.


Resh, V. H. and Rosenberg, D. M.: 1989, ‘Spatial-temporal variability and the study of aquatic insects’,Can. Ent. 121, 941–963.

Richard, M., Klonicki, T. and Thompson, K.: 1993, Analysis of Water Quality Data for the Cachela Poudre River for 1970–1992, Technical report prepared for Kodak Colorado Division, FortCollins.

Richards, C., Haro, R. J., Johnson, L. B. and Host, G. E.: 1997, ‘Catchment and reach-scale propertiesas indicators of macroinvertebrate species traits’, Freshw. Biol. 37, 219–230.

Richardson, R. E.: 1928, ‘The bottom fauna of the middle Illinois River, 1913–1925: Its distribution,abundance, valuation and index value in the study of stream pollution’, Bull. Illinois Natur. Hist.Survey 17, 387–475.

Risser, P. G.: 1991, Long-Term Ecological Research: An International Perspective, Wiley, New York.Rosenberg, D. M. and Resh, V. H. (eds.), 1993, Freshwater Biomonitoring and Benthic Macroinver-

tebrates, Chapman and Hall, New York.Royer, T. V., Robinson, C. T. and Minshall, G. W.: 2001, ‘Development of macroinvertebrate-based

index for bioassessment of Idaho rivers’, Environ. Manage. 27, 627–636.Schlosser, I. J.: 1982, ‘Trophic structure, reproductive success, and growth rate of fishes in a natural

and modified headwater stream’, Can. J. Fish. Aquat. Sci. 39, 968–978.Shieh, S.-H., Kondratieff, B. C., Ward, J. V. and Rice, D. A.: 1999, ‘The relationship of macroinver-

tebrate assemblages to water chemistry in a polluted Colorado plains stream’, Arch. Hydrobiol.145, 405–432.

Shieh, S.-H., Ward, J. V. and Kondratieff, B. C.: 2002, ‘Energy flow through macroinvertebrates in apolluted plains stream’, J. N. Amer. Benthol. Soc. 21, 660–675.

Smolka, L. R.: 1987, Intensive Water Quality Survey of Tecolote Creek in San Miguel County, NewMexico, New Mexico Environmental Improvement Division, Report EID/SWQ-87/6, Santa Fe.

Tate, C. M. and Heiny, J. S.: 1995, ‘The ordination of benthic invertebrate communities in the SouthPlatte River basin in relation to environmental factors’, Freshw. Biol. 33, 439–454.

US EPA: 1986, Quality Criteria for Water, United States Environmental Protection Agency, EPA440/5-86-001, Washington, DC.

US EPA: 1998, National Water Quality Inventory: 1996 Report to Congress, United States Environ-mental Protection Agency, EPA 841-R-97-008, Washington, DC.

Vannote, R. L., Minshall, G. W., Cummins, K. W., Sedell, J. R. and Cushing, C. E.: 1980, ‘The rivercontinuum concept’, Can. J. Fish. Aquat. Sci. 37, 130–137.

Voelz, N. J., Shieh, S.-H. and Ward, J. V.: 2000, ‘Long-term monitoring of benthic macroinvertebratecommunity structure: A perspective from a Colorado river’, Aquat. Ecol. 34, 261–278.

Ward, J. V.: 1986, ‘Altitudinal zonation in a Rocky Mountain stream’, Arch. Hydrobiol Suppl. 74,133–199.

Ward, J. V.: 1992, Aquatic Insect Ecology. 1. Biology and Habitat, Wiley, New York.Waters, T. F.: 1995, Sediment in Streams, Sources, biological effects and control, AFS Monograph 7,

American Fisheries Society, Bethesda, Maryland.Winget, R. N. and Mangum, F. A.: 1979, Biotic Condition Index: Integrated Biological, Physical,

and Chemical Parameters for Management, U.S. Department of Agriculture, Forest Service,Intermountain Region, Ogden, Utah.

Wohl, E. E.: 2001, Virtual Rivers, Yale University Press, New Haven, Connecticut.Wright, J. F.: 1995, ‘Development and use of a system for predicting macroinvertebrates in flowing

waters’, Aust. J. Ecol. 20, 181–197.Wright, J. F. and Symes, K. L.: 1999, ‘A nine-year study of the macroinvertebrate fauna of a chalk

stream’, Hydrol. Process. 13, 371–385.Zuellig, R. E., Kondratieff, B. C. and Rhodes, H. A.: 2002, ‘Benthos recovery after an episodic

sediment release into a Colorado Rocky Mountain river’, W. N. Amer. Nat. 62, 59–72.

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