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ALGAL COMMUNITY COMPOSITION (JUNE-SEPTEMBER 2008) AND SUCCESSIONAL TRENDS (2004-2008)

LONG LAKE, SHAWANO COUNTY, WISCONSIN

All work and report by Robert Bell, Ph.D.

Professor of BiologyUniversity of Wisconsin-Stevens Point

Stevens Point, WI 54481

TABLE OF CONTENTS

Acknowledgements 3

Summary 4

I. Introduction 5

II. Materials and Methods 6

III. Results 7

IV. Discussion14

V. Appendix 21

TABLE OF TABLES

Table 1. Algal Phyla from Long Lake, Shawano County, WI, 2008, by date. 8

Table 2. Most Common Algal Genera and Phyla, and Their Relative Population Density in Cells Counted from Long Lake, Shawano County, WI, 2008 by date. 11

Table 3. Algal Community Composition by Phylum from Long Lake, Shawano County, WI, 2008 by date. 15

TABLE OF FIGURES

Figure 1. Long Lake, Shawano County, Wisconsin. 7

Figure 2. Algal Community Composition from Long Lake, Shawano County, WI, 2008 by Phylum. 8

Figure 3. Algal Community Composition in Long Lake, Shawano County, WI, 2008 by Phylum. 9

Figure 4. Three Dominant Algal Phyla in Long Lake, Shawano County, WI, 2008. 9

Figure 5. Most Common Cyanobacterial Taxa in Long Lake, Shawano County, WI, 2008; Coelosphaerium (left) and Microcystis (right). 10

Figure 6. Most Common Green Algal Taxa in Long Lake, Shawano County, WI, 2008; Scenedesmus (left) and Ankistrodesmus (right). 12

Figure 7. Most Common Ochrophyte Algal Taxa in Long Lake, Shawano County, WI, 2008; Melosira (left) and Asterionella (right). 13

Figure 8. Most Common Cryptophyte and Euglenophyte Algal Taxa in Long Lake, Shawano County, WI, 2008; Cryptomonas (left) and Phacus (right). 14

Figure 9. Growth Trajectories (by Linear Regression) of Cyanobacteria in Long Lake, Shawano County, WI, from 2004-2008. 17

ACKNOWLEDGEMENTS

I thank the Long Lake Property Owners Association for their support of this project. I particularly want to thank Bob Holzbach for his many efforts on behalf of this work. He has tirelessly provided lake access, boat transportation, personal observations, and historical accounts of Long Lake. Without his assistance my work would have been much

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more difficult and less rewarding. I also thank Joe Richards, UWSP undergraduate research student for his assistance with the 2008 sample analysis.

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SUMMARY

2008. The 2008 algal community in Long Lake was a “text-book” example of a residential, moderately-eutrophic (nutrient-enriched) temperate-zone body of water. Samples were collected five times, between 13 June and 8 October, and there were forty-six genera of algae, from six phyla present in analyzed material. It was a typical season in that the three dominant algal groups waxed and waned in ways seen in dozens of other lake studies and often given as an example in high-school and college ecology textbooks.

The green algae (Chlorophyta) dominated early, peaking in mid-summer and declined into the fall. The diatoms (Ochrophyta) were early dominants with the greens but declined in mid-summer before becoming the dominant group in the fall. The blue-green algae (Cyanobacteria) started slowly building over the season to be co-dominant with the diatoms in the fall. The other three phyla contributed 7-31% of the total community with greater contributions early and late in the season.

Twelve algal genera were present in all five samples, ten genera were particularly abundant, and five genera were dominant – Cryptomonas (Cryptophyta), Scenedesmus (Chlorophyta), Asterionella and Melosira (Ochrophyta), and Coelosphaerium (Cyanobacteria). Some subset of these five genera dominated each sample and the five most common genera in each sample accounted for half or more of all cells counted.

2004-2008. Based on the body of algal community samples collected and analyzed from Long Lake since 2004 the water quality is getting a bit better. Most importantly, there are fewer blue-green algae (as measured by total genera, cell counts, dominant genera) now than at the start of collecting. This is good for the food web since nothing eats the blue-greens, some of them form aesthetically-displeasing mats that float and die, and some can produce toxins. Along with the reduction in blue-greens there has been an expansion of the other algal groups. The diatom lineage has a stable and strong presence; this is good for the food web since many organisms (zooplankton, snails, small fish) use them as a preferred food item. The green algae and the other phyla contribute significant diversity and nutritious prey items that also support the food web in the lake.

While not enumerated or identified, rough estimates of zooplankton (the microscopic animals that eat algae) have been conducted along with the algal work over the years. There has been a general trend upward in diversity and biomass over time that also suggests an improvement in water quality. Lakes are complex entities but the simple view of aquatic ecology (see cover illustrations) starts with health (diversity and biomass) at the bottom of the food web and this trickles “up”. The better the algal diversity and nutritional value, the better the zooplankton, the better the fish, the happier the people.

In summary, Long Lake has a moderately diverse algal community whose overall diversity has increased from 2004 to 2008, along with a decrease in blue-green algal diversity and biomass. These can be seen as hopeful trends to support continued work to reduce watershed nutrient input and improve lakeside nutrient and landscape management.

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I. INTRODUCTION

Algae need carbon dioxide, water, sunlight, and a variety of inorganic nutrients, all in adequate amounts. The term algae is very general, this group of organisms encompasses both prokaryotic (like bacteria) and eukaryotic (like us) cell types. The algae range from single-celled to many meters long, some swim with flagella while others float or alter their buoyancy via physiological alterations. These organisms can be filamentous, colonial, tubular, sheet-like, and about every shape in between. They can be blue-green, green, yellow, black, brown, gold, pink, red, or orange.

There are 9 or more major groups or phyla of algae. Each group has a unique set of photosynthetic pigments and each group responds differently to changing environmental conditions. Individual taxa (like a genus) are grouped in a phylum based on shared characteristics such as pigments, cell type, and reproduction. Within that phylum groups are further subdivided based on more specialized shared and distinct characteristics relative to the other members of that division. These subgroups are called classes, orders, families, and genera. In this study I identified algae to genus and phylum. Algae within the same phylum (since they’re related to each other) typically respond in a similar manner to seasonal and nutrient changes. Seasonal changes in the composition of the algal communities in Long Lake were traced via changes in the relative abundance of algae at the genus and phylum level.

Algae are considered primary producers (see cover illustrations) in most aquatic food webs (along with macrophyte vegetation). They are responsible for capturing solar energy via their photosynthetic pigments and using that trapped energy to convert inorganic carbon dioxide into organic sugars. These sugars store some of the captured solar energy in their chemical bonds. The algae use the sugars to make other new organic matter (proteins, carbohydrates, nucleic acids, lipids) as they grow and divide. Consumers and decomposers also use these sugars for energy and recycle much of the other organic matter as well. Algae are critically important components of the aquatic food web as many zooplankters (microscopic animals) as well as many larger consumers (snails, planktivorous fishes) have a diet based largely on algae.

Net growth rates of algae are determined by the difference between growth (production of new algae via asexual and sexual reproduction) and death (consumption, parasitism, natural death). Algae differ in their digestibility (shape, size, production of sticky mucilage) and nutrient value (proteins, lipids, carbohydrates) to consumers and consequently some taxa are preferentially removed from the community by predation while others are largely ignored by consumers and continue to expand their biomass during the growing season. The algae present at any point in time are frequently based more on what hasn’t been eaten than what is growing the fastest. It’s often these “not eaten” algal taxa, especially the Cyanobacteria (or blue-green algae) that become persistence bloom formers in ever earlier and longer cycles.

The microbial decomposition loop (detritivorous) is fed largely by the algae. It is in the sediments that bacterial consumption of the dead algae can reduce oxygen content to anoxic levels setting the stage for fish kills. The seasonal pattern typical of lakes like Long

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Lake is one of spring and summer algal growth (fed by nutrients either input or resuspended from the sediments); summer and fall decomposition in the sediments (converting organic matter to inorganic nutrients again); and resuspension of nutrients into the water column during spring and fall overturn. If there is a flux of nutrients in the fall it’s possible that more algae will overwinter beneath the ice. This can lead to increasing larger standing crops of undesirable algal taxa (see section above).

Different groups and taxa also respond differentially to seasonal fluxes in temperature, oxygen, and nutrients. The types of algae present, their relative abundance, and the dynamics of the algal community over time can provide insights into trophic status and might suggest possible remediation strategies or might provide evidence that watershed-level controls of nutrient inputs is having some effect. Most aquatic algal communities are limited by phosphorus and the timing and point of origin around phosphorus availability usually determines when and what algae will bloom.

II. MATERIALS AND METHODS

Long Lake algae samples were collected five times during the 2008 growing season (06/13, 07/17, 08/14, 09/10, and 10/08). Collections were made with Mr. Bob Holzbach. Surface water samples were collected at the western end of the lake (Figure 1, site 1), off the small point on the southeastern-edge weed bed (site 2), and at eastern end near the inlet/outlet (site 3). Bottom (benthic) and attached (periphyton) samples were collected along the shore, dock, and shallows in front of W7917 Shady Lane (site 4 - Holzbach residence). Collections were made with a plankton net, dip bottles, and hand-grabs. The samples were transferred to 120-mL high-density polypropylene white bottles and stored cold until processing. All samples were collected, processed, and analyzed by R. Bell.

Algal samples were fractionated into fresh and iodine-preserved aliquots. Initial evaluations revealed general homogeneity between samples and consequently all samples were pooled for analysis. Fresh samples were surveyed immediately to provide the most accurate genus list. Preserved samples were stored, cold, until counting.

For analysis, 1ml aliquots of preserved material were placed into a Sedgewick-Rafter counting cell and allowed to settle for 1hr. Random fields were counted at 400X under an Olympus ZH20 Inverted Microscope with long working distance lenses. Colonial and filamentous organisms were counted as a single unit if intact. Counts were conducted until the sample total reached 300 per date. Generic identification was from standard freshwater reference texts including (but not limited to) “Freshwater Algae of the United States (G.M. Smith), Freshwater Algae of the Western Great Lakes Area (G. Prescott) and “Freshwater Algae of North America (R. Sheath, et al.).

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Figure 1. Long Lake, Shawano County, Wisconsin. Collecting sites (1-4) as referenced in text.

III. RESULTS

2008. The algal community in Long Lake during 2008 was fairly typical of similar regional lakes. Densities of six algal phyla, represented by forty-six genera, fluctuated during the sampling period (Table 1). Thirty-nine of the 46 taxa (85% of total genera) identified from Long Lake were from three phyla (10-Cyanobacteria, 18-Chlorophyta, and 11-Ochrophyta) (Appendix 1). These are the dominant groups in most temperate zone lakes, especially those with moderate eutrophication.

TABLE 1. Algal Phyla from Long Lake, Shawano County, WI, 2008, by date.DATE

PHYLUM 06/13 07/17 08/14 09/10 10/08Cyanobacteria 9 23 17 39 32Chlorophyta 31 42 55 25 19Ochrophyta 29 20 17 29 38Dinophyta 3 0 1 1 2Euglenophyta 12 7 3 2 6Cryptophyta 16 8 7 4 3

100 100 100 100 100

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The green algae (Chlorophyta) dominated the early samples in 2008. This group was the most common phyla in June, July, and August samples, exceeding the combined total of the next two most common groups in July and August. They remained abundant (19-25%) into the fall samples but were not the dominant taxon in those samples (Figure 2). Greens respond quickly to spring nutrient fluxes and grow faster at the cooler temperatures seen before August.

06/13 07/17 08/14 09/10 10/080%

10%20%30%40%50%60%70%80%90%

100%

CryptophytaEuglenophyta

DinophytaOchrophyta

ChlorophytaCyanobacteria

DATE (2008)

% A

lgal

com

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ylum

Figure 2. Algal Community Composition from Long Lake, Shawano County, WI, 2008 by Phylum.

The diatoms were co-dominant with the greens early, also using the spring nutrient flux before summer silica limitations likely caused slow growth in July and August (Figure 2). The fall turnover and nutrient resuspension led to resumed growth and resulted in their dominance in the last two sample periods (September and October).

The blue-greens, opposite of the greens, grow slower during the cooler spring and early summer periods and accelerated their growth rate as the temperatures rise. From early season values of 9% the blue-greens rose to nearly 40% of all cells counted in September and were co-dominant with the diatoms at the end of the season (Figure 2).

The other phyla (Euglenophyta, Cryptophyta, Dinophyta) made their greatest contributions to the algal community during the early and late sample periods (Figure 2, Figure 3). Thirty-one percent of the first sample (June) was cells from these three phyla. They are all fairly tasty and easy to digest so their consumption by zooplankton during the growing season was high. This consumption results in a lower number of cells present in the samples counted. The low values imply insignificance but it’s important to remember that these organisms are growing fast, are being heavily eaten, and as such are important components of the ecosystem. Their fairly high starting levels hints that the under-ice conditions in the winter were well-oxygenated (a good thing). This is because these three phyla of algae contain organisms that can be both photosynthetic (when there’s sun) and can eat other things (bacteria, algae) when it’s dim and can’t support photosynthesis. For them to survive under the ice in strong numbers requires reasonable levels of oxygen.

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06/13 07/17 08/14 09/10 10/08

0

10

20

30

40

50

60

EuglenophytaDinophytaCryptophytaOchrophytaChlorophyta

DATE (2008)

% A

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Figure 3. Algal Community Composition in Long Lake, Shawano County, WI, 2008 by Phylum.

The three dominant phyla accounted for most of the cells counted across all sample periods (Figure 4). In all samples except the first one (June); the greens, diatoms, and cyanobacteria comprised from 83% to 93% of all cells counted. The strong representation of the other three phyla in the spring sample (31%, as described in the previous paragraph) reduced cell counts for the three dominant phyla to a season low of 69%.

06/13 07/17 08/14 09/10 10/08

0102030405060

Cyanobacteria

Ochrophyta

Chlorophyta

DATE (2008)

% A

lgal

com

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Figure 4. Three Dominant Algal Phyla in Long Lake, Shawano County, WI, 2008.

In the next four sections are expanded, more detailed results from each of the three dominant phyla (Cyanobacteria, Chlorophyta, and Ochrophyta) and a summary of the detailed results from the other three phyla (Euglenophyta, Cryptophyta, and Dinophyta).

Cyanobacteria. The blue-green algae or cyanobacteria in Long Lake 2008 comprised less than 10% of the algal community sampled in June. They increased to nearly 40% of cells counted in September before ending the season as a 32% component of the total algal community in October. The cyanobacteria displayed an increasing trend over the sampling periods (Figure 4). There were 10 cyanobacterial genera identified over the five sample periods (Appendix 2) but only four were present in all samples (Anabaena, Coelosphaerium, Microcystis, Oscillatoria), and only two genera (Coelosphaerium, Microcystis) were dominant taxa in any sample period. These two taxa combined contributed from 4% (June) to 24% (September, October) of all cells counted in 2008.

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Coelosphaerium forms small, fairly dense colonies of dozens of cells enclosed in a layer of gelatinous mucilage that is hard to get into the mouth of a consumer and is even harder to digest (Figure 5). It was the most common organism present in this phylum. Coupled with high growth rates the tendency of this organism to stay together in chunks even when split by a predator or mechanical action leads to its rapid population expansion as temperatures increase. This organism was the most abundant genus counted in the September samples (16.3% of all cells counted), it was the second most common genus in the October samples (12.3%), and was third most common in the July (8.3%) and August (9.7%) samples (Table 2).

Figure 5. Most Common Cyanobacterial Taxa in Long Lake, Shawano County, WI, 2008; Coelosphaerium (left) and Microcystis (right).

Also colonial, the genus Microcystis forms larger, more expansive colonies of more distributed cells (Figure 5). The amorphous colonial mucilage is less dense and makes for more frequent fragmentation. This organism is an occasional gut item found in larger zooplankton, snails, and amphibians. Several species of this genus can produce toxins. In those documented cases of Microcystis toxicity the population densities have been much higher than those seen in this study but it should continue to be monitored. This genus was twice in the top 5 (4th

– September, 3rd – October).

TABLE 2. Most Common Algal Genera and Phyla, and Their Relative Population Density in Cells Counted from Long Lake, Shawano County, WI, 2008 by date.

GENUS PHYLUM %06/13 Cryptomonas Cryptophyta 12

Scenedesmus Chlorophyta 11Asterionella Ochrophyta 9.3Melosira Ochrophyta 9Phacus Euglenophyta 7.7% of total 49

07/17 Scenedesmus Chlorophyta 18.7Ankistrodesmus Chlorophyta 10.3Coelosphaerium Cyanobacteria 8.3Cryptomonas Cryptophyta 6.7Melosira Ochrophyta 6.3

11

% of total 50.3

08/14 Scenedesmus Chlorophyta 17.7Ankistrodesmus Chlorophyta 13.3Coelosphaerium Cyanobacteria 9.7Cryptomonas Cryptophyta 7Oocystis Chlorophyta 6.7% of total 54.4

09/10 Coelosphaerium Cyanobacteria 16.3Asterionella Ochrophyta 13.7Scenedesmus Chlorophyta 9.3Microcystis Cyanobacteria 7Melosira Ochrophyta 6.7% of total 53

10/18 Asterionella Ochrophyta 18.3Coelosphaerium Cyanobacteria 12.3Microcystis Cyanobacteria 9.7Melosira Ochrophyta 9.7Fragilaria Ochrophyta 5.7% of total 55.7

The only other cyanobacterial taxa present in all five samples were the filamentous genera – Anabaena and Oscillatoria. These organisms were never the dominant taxa in the cell counts but have the potential to become nuisance organisms because the can form benthic mats on the sediment surface and then rise off the sediment due to the accumulation of photosynthetically-produced oxygen bubbles under the mat. When they float to the surface they slowly photo-oxidize and die resulting in visually unpleasant glops of dead, brown, floating algae. As these macroscopic aggregations sink into the sediments they are decomposed by bacteria over the winter. This has two unfortunate side effects. One is the recycling of large amounts of inorganic nutrients from the recycled algal bodies and the other is the reduction of oxygen in the under-ice water column due to the increased metabolism of the bacteria decomposing the dead algae.

Chlorophyta. The greens ranged from a high of 55% of all cells counted (August) to a low of 19% in October. This phylum was the dominant group in June, July, and August; and a sub-dominant in September and October (Table 1, Figure 4). The greens were the most diverse group in the study with 18 genera present over the season but most were rare or sporadic. Only three genera – Scenedesmus, Ankistrodesmus, and Oocystis – were present in all five sample periods (Appendix 1). All three taxa were in the top 5 most common genera in at least one period (Table 2) and together they occupied 7 of 25 possible top 5 genera slots over the 2008 sampling period. The Chlorophyta was the second most represented phylum in the list of 5 most common genera by sample date.

The green alga Scenedesmus was the most common organism counted across the entire study period and across all phyla. This small, colonial green alga (Figure 6) was one of the top 5 most common genera in four of the five samples. A very common, cosmopolitan genus, it was the most frequently counted organism in the July and August samples, accounting for nearly 20% of all cells counted in those two periods. It was the second most common genus in June and third most common in September (Table 2). The organism has a high growth rate but is also very heavily consumed because its adult cells are relatively small and its mode of asexual reproduction forms small daughter colonies that are even easier to ingest.

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Figure 6. Most Common Green Algal Taxa in Long Lake, Shawano County, WI, 2008; | Scenedesmus (left) and Ankistrodesmus (right).

The very small, unicellular green alga – Ankistrodesmus – is a very common organism around the world and its size makes it a heavily eaten organism (Figure 6). It has been shown to have high intrinsic growth rates with moderate temperatures and levels of nutrient enrichment. This genus was twice in the top 5 most common genera (Table 2). It was the second most common genus (second to Scenedesmus) in the periods of maximum green algal density – July and August. The other genus found in all samples was the small, oval, rapidly-dividing, and cosmopolitan genus – Oocystis, and like Scenedesmus and Ankistrodesmus, it is a very heavily consumed ala and was the 5th most common genus in August, its only time in the top 5 most common genus list (Table 2).

The only other green algae present in at least four sample periods were the small, unicellular genus Golenkinia and the larger unicellular genus Staurastrum. These algae were consistently present but not in significant amounts (2-5% of all cells counted). Golenkinia is a common food item; Staurastrum has a relatively slow growth rate.

Ochrophyta. This phylum was represented by 11 genera over the 2008 sampling period. This phylum is very large and diverse but all genera identified in 2008 were from the large subgroup of ochrophytes called the diatoms. These unusual organisms produce silica-based coverings and most are small unicellular organisms are chains of cells that can easily fragment. They are capable of high growth rates but are subject to growth limitation during the summer and early fall seasons due to silica removal from the water column. The fall turnover of the water column resuspends silica and often stimulates a fall growth burst of diatoms. There were three genera of diatoms (Asterionella, Melosira, and Fragilaria) that were present in all five sample periods and they occupied 8 of 25 possible top 5 most common genera slots making the ochrophytes the most commonly encountered phylum during the 2008 season. Two other genera (Navicula and Synedra) were identified in four of the five sample periods.

The chain-forming genus of centric (radially symmetrical) diatom Melosira (Figure 7) was one of only three algal genera that landed on four of the five sample period most common genus lists (the others were the green Scenedesmus and the blue-green Coelosphaerium). Unlike the other two genera, it was never the most abundant in any period and was generally near the bottom of the 5 most common genus lists. It was 4th most common in June and October, 5th most common in July and September (Table 2).

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Figure 7. Most Common Ochrophyte Algal Taxa in Long Lake, Shawano County, WI, 2008; Melosira (left) and Asterionella (right).

The cells of Asterionella form very distinctive star-shaped colonies that easily fragmented (Figure 7). This genus was present in all five samples and in the top 5 most common genera three times. It was the 3rd most common genus in June, dropped out of the top 5 list in July and August before rising to the 2nd most common genus in September and it was the most commonly counted genus in October when it represented more than 18% of all cells counted (Table 2).

Other phyla. The other three phyla contain mostly unicellular organisms that are small, easy to digest, nutritious and therefore heavily eaten. This likely keeps them off the most common genus lists because predation rates exceed or match growth rates. The small, motile, unicellular Cryptomonas (Phylum Cryptophyta, Figure 8) has very high growth rates but is one of the most preferred food items in the water column. It was present in all five samples and appeared on the 5 most common genus list three times, all early in the season. It was the most common genus counted in June before dropping to 4th most common in July and August and then dropping completely off the list in September and October (Table 2). The small, motile, unicellular genus Phacus (Phylum Euglenophyta, Figure 8) was the only other organism present in all five sample periods, it was in the top 5 genus list once, coming in as the 5th most commonly counted genus in the June sample (Table 2). There were no Dinophyta taxa found in more than three sample periods and none were ever in the top 5 most common genera (appendix 1).

Figure 8. Most Common Cryptophyte and Euglenophyte Algal Taxa in Long Lake, Shawano County, WI, 2008; Cryptomonas (left) and Phacus (right).

IV. DISCUSSION

General. Assuming the widely-accepted rubric that better water quality brings with it less blue-green algae and more of all the other groups then all indications are that water quality in Long Lake is improving. The general trend over the five years of sampling is one of decreasing cyanobacteria density and diversity with a concomitant increase in diversity and biomass of other, more desirable, less aesthetically-displeasing algae to feed the food web in the lake (Table 3). The changes are not dramatic and may not yet be clearly visible to the naked eyes of

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the lake inhabitants but the trend is there. This encouraging trend should be used to support continued or expanded attempts to reduce watershed and lake-side nutrient input.

TABLE 3. Algal Community Composition by Phylum from Long Lake, Shawano County, WI, 2004-2008, by date.

2004 PHYLUM 06/25 08/06 09/09 10/06 11/03Cyanobacteria 19 30 22 51 55Chlorophyta 39 40 43 19 20Ochrophyta 18 22 30 27 21Dinophyta 11 3 1 0 1Euglenophyta 9 4 4 3 1Cryptophyta 4 1 0 0 2




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Cyanobacteria. There were 10 cyanobacterial taxa counted in 2008 (Appendix 1) but only a few were common or dominant. In past years there were usually more taxa (13 in 2004, 12 in 2005, 11 in 2006, 9 in 2007) but most taxa were rarely seen and infrequently occurring taxa could be missed by the enumeration procedure. Cyanobacterial taxa were in the top 5 genera counted six out of 25 possible times in 2008 (Table 2) compared to nine times in the top five during the 2004 season, eight times in the top five during the 2005 season, seven times in the top five during the 2005 season, and six times in the top five during the 2008 season.

The linear regression lines of cyanobacterial growth trajectories over the five years of this study bear this out (Figure 9). The line tracking the 2004 season was the steepest, meaning the blue-greens were expanding their densities at a fast rate and easily dominating the community be the end of the season. The slope of the lines, and their final value on the Y axis (% community composition) for cyanobacterial growth in the years 2005-2008 are shallower (indicating reduced growth) and terminate lower (indicating a small overall component of the community).

130 150 170 190 210 230 250 270 290 3100

10

20

30

40

50

60

Day of Calendar Year

% C

omm

unity

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Figure 9. Growth Trajectories (by Linear Regression) of Cyanobacteria in Long Lake, Shawano County, WI, from 2004-2008.

The genera Coelosphaerium and Microcystis were present in every sample, these taxa are cosmopolitan and their abundance is generally associated with inorganically-enriched (especially phosphorus) waters. In previous years Coelosphaerium (a spherical colony) was a dominant in four of five sample periods during 2004, five of five sample periods (2005 and 2006), and two of five sample periods in 2007. In many of those cases it was present in much higher densities than it was in 2008. It was the most common taxon at the end of the season in 2004 (29% of all cells counted) and 2005 (27% of all cells counted) and second most common taxon in 2006 (12% of all cells counted). In 2007 this genus was present in all five samples but did not rise to dominance until late July and

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through August. In the last sample of 2007 (09/24) Coelosphaerium was only the seventh most abundant taxon (4% of all cells counted). In 2008 it was the most abundant genus in September and 2nd most common in October but at much lower densities (16% and 12%, respectively). The multi-year data trend for this organism is down; a reduction in the dominance of this organism is a good thing.

The colonial Microcystis was a dominant taxon in one of the 2004 samples, two of the 2005 samples, and one of the 2006 samples. In 2007 it was present in all five samples and was in the top five dominant taxa in four of the five sample periods. This nuisance organism was the second most common taxon at the end of the 2007 sample season (14% of all cells counted). For 2008 it was less common and less dense; it appeared only twice on the list of 5 most common genera and represented less than 10% of all cells counted at the end of the season. This is also a good thing.

The other common cyanobacterial taxa from 2004-2007 were filamentous genera (Lyngbya, Phormidium, Gloeotrichia, Anabaena, Spirulina) but none other than Anabaena and Spirulina ever rose to dominant positions in past years and none of them did so in 2008. These variations of subdominant taxa are not uncommon and are indicative of the dynamic and variable conditions that exist in a lake from one year to the next. In 2007 the simple filaments of Phormidium were present in four of five sample periods but never in the top five most common taxa. The larger heterocystous filaments of Anabaena were also present in four of five samples. None of the other cyanobacterial taxa were present in more than three sample periods. Oscillatoria, an organism similar to Phormidium showed a similar pattern in 2008.

Unlike 2004-2006, and like 2007, the Cyanobacteria were not the dominant taxa at the end of the 2008 sampling period. Usually cyanobacteria exhibit a waxing trend throughout the growing season and in most moderately-eutrophic lakes like Long Lake they form an overwhelming majority of cells counted in the late season samples. This trend is typically caused by the combination of not being eaten, a fall surge in nutrients, and an extended temperature tolerance that allows them to survive deeper into the fall/winter than most of the eukaryotic algae.

Of note however, in the final 2007 sample (September) of blue-green algae made up only 20% of the total (Table 3). In 2008, while not the dominant phylum in the final sample (October, Ochrophyta was dominant with 38% of cells counted) there were significant numbers of cyanobacteria (32%). This variability among years is typical and indicative of the complexity of aquatic ecosystems and the limits of the current sampling system. The blue-greens are very durable and tolerant of severe environmental conditions. They can persist in the sediments for years before fluxing again in response to drought, temperature, wind conditions, rain/flooding events – all of which we cannot control.

Some Cyanobacteria, including Microcystis are capable of “blooming” and in the bloom state may produce toxins that can harm aquatic life, pets, and potentially humans. At this time in Long Lake it is not near bloom proportions and does not appear to be a toxin-producing threat but should be monitored in the future. Overall, the relative abundance of the cyanobacteria in the algal community at season’s end has generally declined over the five years of this study (55% in 2004, 49% in 2005, 39% in 2006, 20% in 2007) but did tick up a bit this year (32%). In the long-term this might be a statistical blip but it could also be interpreted as a sign that the water quality of Long Lake is improving.

Chlorophyta. Green algae (Chlorophyta) were represented by 18 genera in 2008 cell counts (Appendix 1); previous years saw similar numbers of taxa (15 in 2004, 16 in 2005, 13 in 2006, 16 in 2007). The most common taxa over the years were Oocystis, Selenastrum, Scenedesmus, and Staurastrum. In 2004 green algae taxa were in the top five taxa five times while they were in the top five taxa eight times in 2005 and five times in 2006. In 2007, the green algae were in the top five dominant taxa a total of eight times (of a possible 25) compared to seven times in 2008 (Table 3). As with the Cyanobacteria, there were many green algal taxa that were of only minor importance or abundance and many were only seen in one or two of the five sampling periods (Appendix 1). These organisms may have simply not been abundant or they may have been preferentially-selected food

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items for the zooplankton and planktivorous fishes. This level of analysis cannot distinguish between these two possibilities.

A diverse group of green algae are present in Long Lake and this group is a generally a good group to have in the algal community. They are usually edible and nutritious, and the larger ones provide valuable surface area for diatom colonization. Green algae do not produce toxins, and are not associated with water taste or odor problems. A few genera, including some present in Long Lake, can, like discussed earlier in the Cyanobacteria section, form benthic mats that can float, die, and become a nuisance. These taxa, such as Oedogonium, Cladophora, and Spirogyra, are not significant components of the Long Lake food web at this time but they are present and all three of them have been shown in other systems to become problem organisms. Part of the problem with the mat-floating-mat cycle is that dense mats can reduce or eliminate rooted aquatic plants. This competition and reduction of macrophyte vegetation is not good for the lake.

Ochrophyta. Diatoms are the most common and successful group of organisms within the phylum Ochrophyta. These unique organisms collect silica from the water and polymerize it into intricate glass cases called frustules that they use in place of a more traditional, organically-derived cell covering. These organisms are common food items and are easily ingested and digested. There were 11 genera of diatoms identified in the 2008 Long Lake samples compared to 9 genera counted in 2007, 11 genera counted in 2006, 13 genera counted in 2005 and 15 genera identified in 2004. The most common taxa were Asterionella, Fragilaria, and Melosira (= Aulacoseira) – together they were in the top five most abundant taxa eight times (Table 3).

A typical pattern for diatoms in temperate lakes is to start with low abundance in the early season before rising in abundance into the summer. Often there is a marked reduction in abundance in late summer due to silica depletion (required for cell walls). Fall turnover (resuspending silica) often leads to a late season diatom spike. This was not the case in Long Lake in 2004 or 2005. In both years diatoms started at around 20% of the community and held steady with small declines heading into the September or October samples. Diatoms represented 21-31% of the final sample in both years. In 2006 the diatoms started strong and ended strong with only a small decline in July. The diatom community, dominated by three taxa, was very steady across the entire sampling season of 2006. Percent algal community composition by diatoms dipped below 35% only once (July) and ended the season at 35%. The 2007 season saw the strongest diatom representation in the five years of study. This group never made up less than 35% of cells counted and was consistently in the 35-40% of cells counted range in all 2007 samples. For 2008 the diatoms displayed a minor drop in abundance relative to the greens and blue-greens. They were not the dominant phylum until the final sample (October) and their contributions to the overall community ranged from 17 – 38% over the season.

There is no immediate or obvious explanation for this trend of increasing diatom abundance but given the typically beneficial aspects of diatoms in ecosystem function it is nothing to be concerned about. The more diatom genera present in the algal community the healthier the ecosystem. On the downside of diatoms, a few genera have been known to produce toxins and there are “nuisance” diatom species that can bloom under eutrophic conditions. These blooms can cause fishy taste and odor problems as well as visually-displeasing brown films and clouds. None of those taxa are present in Long Lake as yet.

Other phyla. As in the previous four years, the other three phyla (Dinophyta-dinoflagellates, Euglenophyta-euglenoids, and Cryptophyta-cryptophytes) were of varying but mostly minor significance. Diversity is considered a good thing and the presence of these groups, especially the cryptophytes is a positive indication of a fairly healthy and balanced aquatic system.

The dinoflagellates have never been a major component of the Long Lake system but there are several genera that are present. Only the genus Peridinium has been in the 5 most common genera, and that has only occurred three times over the five years of the study. The dinoflagellates usually account for only a percent or two of total cells counted. During infrequent, rapid growth phases they may rise to 4-7% of all cells counted but

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rarely more than something in that range. The highest dinoflagellate cell count in the five years of the study was 13% (mostly Peridinium) in September 2005 (Table 3)

The euglenophyte genera Trachelomonas, Euglena, and Phacus have all been sporadically abundance over the five year sampling period. These taxa do best when there is organic enrichment in the water, their minor role in Long Lake is typical and good. This phylum has been in the top 5 genera seven times over the five years (Euglena -1, Phacus – 4, Trachelomonas – 2). Euglenophytes are small, motile, and unicellular; this makes them a good food item. Their non-rigid cell covering is easily disrupted and the cells, like their relatives the green algae, are fairly nutritious. Much of the carotene we consume in vitamins and health supplements are commercially produced by continuous-culture techniques using greens and euglenophytes.

The small, motile, unicellular cryptophyte Cryptomonas is the only member of this phylum that is a significant component of Long Lake cell counts. This genus has been in the top 5 most common genera 6 times over the study period, three of those came in 2008. Like the euglenophytes, these cells have a non-rigid covering that is easy to disrupt and the cells are very nutritious.

Conclusions. The algal community data from Long Lake over the five years, 2004-2008, show a fairly typical season succession pattern and give no indication of any major problems with the lake. The data indicate a moderately enriched (eutrophic) lake. During the five years of study the basic community structure has not changed significantly at either the phylum or genus levels but some positive trends can be drawn. A review of the season-ending algal community compositions shows a reduction in the numbers of cyanobacteria and an increase in the numbers of diatoms. These in turn may influence the following spring community compositions where there have been fewer cyanobacteria and more diatoms counted each year. These are good things but given the complex set of variables that influence lake chemistry and its biotic community they could change or they may be natural variation. Five years is a very brief snapshot of the life of a lake.

I suspect the inorganic enrichment that has pushed the algal community in Long Lake towards cyanobacteria is a combination of multiple sources both long-term and short-term. Long-term inputs could include upstream agricultural/watershed inputs, local geological conditions (leaching of naturally occurring nutrients from the basal material), and local anthropomorphic inputs (fertilizing of lawns, septic systems, surface runoff). Short-term influences include temperature, rainfall, and wind. The small size, rapid growth rates, and differential consumptions rates make the algae quick to respond to each year’s combination of variables. Each year’s unique combination of characteristics sets the conditions for a different subset of genera to dominate but overall patterns remain fairly stable.

Once a body of nutrients is introduced to a lake system it is very difficult to manage or eliminate them. These nutrients undergo a season change in location and form. The spring overturn of the lake resuspends available inorganic nutrients from the sediments. The algae assimilate these nutrients and consequently they are incorporated into organic molecules (DNA, protein) or are stored (“luxury storage”) in excess of their current need. As algae are eaten their organic and inorganic matter is echoed through the food web and becomes organic material within the various levels of consumers. Consumer waste, consumer death, and algal death all contribute abundant inorganic and organic matter to the sediments throughout the year but particularly in the fall/winter when most algae and aquatic plants die back. In the fall and winter the decomposing bacteria in the sediments metabolize these mostly organic forms of nitrogen and phosphorus back to inorganic forms that are once again available in the following spring during lake overturn.

In closing, Long Lake is a typical temperate zone lake with significant shoreline residential development and an agricultural watershed. The lake shows signs of moderate nutrient enrichment but the five years algal community trends are positive with a reduction in the abundance of cyanobacteria and in increase in abundance and diversity of other algal groups. If current efforts to reduce nutrient inputs are not continued or expanded then the problem of algal blooms and the potential of fish-killing oxygen depletion will continue to increase. The problems took a long time to develop and the solutions will be equally slow to take effect. Various nutrient

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abatement strategies are possible. They vary widely in effectiveness and cost. They include, in no particular order, but are not limited to:

Upstream diversion of water into the marshes to reduce sediment and nutrient load prior to water entering Long Lake.

Planting of vegetation buffer strips along the shoreline and the reduction/elimination of excessive fertilizer use in the residential landscapes around Long Lake.

Alum treatment of the sediments to seal off the resuspension of nutrients for several years.

Removal of sediments.

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Appendix 1. Algal Genera from Long Lake, Shawano County, WI, 2008 by date.

DATE 06/13 07/17 08/14 09/10 10/08 SamplesTimes in

PHYLUM GENUS # % # % # % # % # % Presenttop 5 taxa

Cyanobacteria Anabaena 9 3.0 6 2.0 1 0.3 10 3.3 8 2.7 5

Aphanizomenon 0.0 0.0 0.0 7 2.3 4 1.3 2Coelosphaerium 8 2.7 25 8.3 29 9.7 49 16.3 37 12.3 5 4Cylindrospermum 0.0 0.0 0.0 2 0.7 5 1.7 2Gloeotrichia 5 1.7 8 2.7 0.0 0.0 0.0 2Merismopedia 1 0.3 3 1.0 0.0 0.0 0.0 2Microcystis 2 0.7 11 3.7 14 4.7 21 7.0 29 9.7 5 2Nodularia 0.0 0.0 0.0 9 3.0 0.0 1Oscillatoria 3 1.0 7 2.3 3 1.0 13 4.3 8 2.7 5Phormidium 0.0 9 3.0 4 1.3 5 1.7 6 2.0 4

10 TOTAL 9 23 17 39 32

Dinophyta Peridinium 10 3.3 0.0 0.0 0.0 2 0.7 2Amphidinium 0.0 0.0 3 1.0 2 0.7 3 1.0 3

2 TOTAL 3 0 1 1 2

Chlorophyta Ankistrodesmus 18 6.0 31 10.3 40 13.3 11 3.7 7 2.3 5 2Botryococcus 0.0 0.0 1 0.3 3 1.0 0.0 2Chlamydomonas 3 1.0 0.0 0.0 0.0 1 0.3 2Cladophora 0.0 0.0 0.0 1 0.3 2 0.7 2Closterium 2 0.7 0.0 4 1.3 0.0 6 2.0 3Coelastrum 4 1.3 9 3.0 12 4.0 0.0 2 0.7 4Cosmarium 0.0 3 1.0 8 2.7 0.0 0.0 2Desmidium 0.0 0.0 3 1.0 1 0.3 0.0 2Euastrum 0.0 0.0 0.0 3 1.0 2 0.7 2Golenkinia 6 2.0 2 0.7 11 3.7 2 0.7 0.0 4Hydrodictyon 0.0 0.0 0.0 0.0 1 0.3 1Oedogonium 0.0 0.0 0.0 3 1.0 0.0 1Oocystis 15 5.0 8 2.7 20 6.7 18 6.0 14 4.7 5 1

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Pediastrum 7 2.3 0.0 6 2.0 2 0.7 4 1.3 4Scenedesmus 33 11.0 56 18.7 53 17.7 28 9.3 13 4.3 5 4Selenastrum 0.0 5 1.7 0.0 3 1.0 2 0.7 3Spirogyra 2 0.7 0.0 0.0 0.0 0.0 1Staurastrum 4 1.3 13 4.3 6 2.0 0.0 4 1.3 4

18 TOTAL 31 42 55 25 19

Ochrophyta Asterionella 28 9.3 12 4.0 3 1.0 41 13.7 55 18.3 5 3Cocconeis 7 2.3 9 3.0 0.0 2 0.7 0.0 3Cymbella 0.0 3 1.0 0.0 0.0 8 2.7 2Diatoma 0.0 0.0 9 3.0 0.0 0.0 1Epithemia 0.0 1 0.3 7 2.3 0.0 0.0 2Fragilaria 9 3.0 6 2.0 18 6.0 12 4.0 17 5.7 5 1Gomphonema 0.0 0.0 0.0 3 1.0 0.0 1Gyrosigma 2 0.7 0.0 0.0 3 1.0 1 0.3 3Melosira 27 9.0 19 6.3 8 2.7 20 6.7 29 9.7 5 4Navicula 4 1.3 8 2.7 4 1.3 6 2.0 0.0 4Synedra 9 3.0 3 1.0 3 1.0 0.0 5 1.7 4

11 TOTAL 29 20 17 29 38

Euglenophyta Euglena 9 3.0 2 0.7 0.0 0.0 2 0.7 3Phacus 23 7.7 18 6.0 2 0.7 4 1.3 9 3.0 5 1Trachelomonas 3 1.0 0.0 7 2.3 3 1.0 6 2.0 4

3 TOTAL 12 7 3 2 6

Cryptophyta Chroomonas 11 3.7 3 1.0 0.0 0.0 2 0.7 3Cryptomonas 36 12.0 20 6.7 21 7.0 13 4.3 6 2.0 5 3

2 TOTAL 16 8 7 4 3

300 300 300 300 300 46 300 100.0 300 100.0 300 100.0 300 100.0 300 100.0

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phytoplankton - web viewthey are all fairly tasty and easy to digest so their ... in those...

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