challenges of using benthic assessments in san francisco estuary bruce thompson and sarah lowe san...
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CHALLENGES OF USING
BENTHIC ASSESSMENTS
IN SAN FRANCISCO ESTUARY
Bruce Thompson and Sarah Lowe
San Francisco Estuary Institute
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PURPOSE
• Summarize our understanding of benthic assemblages in the Estuary
Relationships to key abiotic factors:
- Salinity- Sediment-type- Sediment contamination
• Conceptual models of benthic response
• Application of science to benthic assessments
• Information needs: What does RMP need to do?
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WHAT IS AN ASSEMBLAGE ?
The group of organisms collected within a common habitat-type; aka community.
• Key attribute is relatively stable species composition and abundances within the assemblage
• Variations may be due to: – life histories – ecological interactions – disturbances
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IDENTIFICATION OF ASSEMBLAGES
Multivariate methods were used to determine similarities in species composition and abundances among samples
1. Principal Coordinates Analysis
– Relationships among samples along environmental gradients
2. Classification (Cluster) Analysis
– Data was edited, transformed, and standardized – Bray-Curtis Index: ecological distance, etc. – Clustered sites and species– Produces a dendrogram, and two-way table
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DATA USED
Program Dates N. sites N. samples
RMP 1994 – 2001 12 80
BACWA LEMP 1994 – 1997 6 42
BPTCP 1992, 94, 97 22 24
DWR 1994 – 1998 15 436
CISNet 1999 – 2000 6 18
NOAA-EMAP 2000 – 2001 50 50
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7 6 5 4 3 2 1 0
OLIGOHALINE MUDDY SEDIMENTS ASSEMBLAGE 192 SAMPLES
OLIGOHALINE SANDY SEDIMENTS ASSEMBLAGE 18 SAMPLES
ESTUARINE TRANSITION SUB-ASSEMBLAGE 72 SAMPLES
POLYHALINE SANDY SEDIMENTS SUB-ASSEMBLAGE 6 SAMPLES
MESOHALINE ASSEMBLAGE 68 SAMPLES
ESTUARINE MARGINS SUB-ASSEMBLAGE 8 SAMPLES -
POLYHALINE MUDDY SEDIMENTS ASSEMBLAGE 60 SAMPLES
ECOLOGICAL DISTANCE
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Oligohaline (muddy)
Oligohaline-Mesohaline (transition)
Mesohaline (muddy)
Polyhaline (muddy)
Major Benthic Assemblages
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Oligohaline (muddy) Oligohaline (sandy)
Oligohaline-Mesohaline (transition)
Mesohaline (muddy)Mesohaline (margin)
Polyhaline (muddy)Polyhaline (sandy)
Major Assemblage Designations
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Species Taxon Muddy Sandy Transition Main Marginsn = 192 18 72 6 68 8 60
Cyprideis sp. A C 15 (27)Manayunkia speciosa P 117 (103)Corbicula fluminea Pe 50 (191) 19 (18) 1 (17)Limnodrilus hoffmeisteri O 36 (180) 1 (5) 2 (10)Varichaetadrilus angustipenis O 30 (188) 1 (12) 1 (19)Corophium spinicorne A 20 (120) 1 (3) 1 (4) 1 (1)Corophium stimpsoni A 57 (162) 2 (12) 4 (19) 1 (1)Gammarus daiberi A 36 (172) 4 (15) 4 (32) 1 (4)Marenzelleria viridis P 6 (70) 2 (11) 20 (57) 2 (21)Corophium alienense A 1 (3) 26 (33) 5 (9) 16 (4) 1 (1)Potamocorbula amurensis Pe 5 (3) 1 (5) 28 (67) 1 (2) 162 (67) 3 (4) 4 (28)Neanthes succinea P 1 (4) 3 (54) 1 (1) 1 (8)Nippoleucon hinumensis T 1 (38) 3 (26) 22 (49) 145 (8) 8 (31)Grandidierella japonica A 1 (6) 1 (9) 4 (29) 46 (6) 3 (19)Gemma gemma Pe 1 (4) 70 (4) 1 (2)Streblospio benedicti P 1 (1) 3 (37) 116 (8) 1 (2)Glycera tenuis P 2 (4)Hesionura coineaui difficilis P 3 (3)Heteropodarke heteromorpha P 18 (4)Corophium spp. A 1 (1) 92 (5) 53 (23)Corophium acherusicum A 1 (1) 1 (17) 6 (1) 745 (34)Ampelisca abdita A 1 (14) 135 (52) 55 (4) 697 (56)Corophium heteroceratum A 1 (7) 9 (42) 133 (55)Tubificidae O 1 (5) 1 (3) 3 (13) 404 (4) 9 (54)Nematoda N 8 (3) 1 (2) 37 (4) 25 (53)Mediomastus spp. P 1 (1) 1 (1) 1 (3) 37 (52)Euchone limnicola P 1 (1) 58 (26)
Mean No. Taxa 13 4 4 7 10 16 36Mean Tot. Abundance 443 33 89 38 362 1130 2110Mean Biomass - - 3.05 0.18 42.2 - 9.91
MuddyOligohaline Estuarine Polyhaline Polyhaline Mesohaline
Sandy
Most Common and Abundant Bay Benthosmean abund. per sample (frequency)
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Abiotic Variable
n Axis 1 Axis 2 Axis 3
Salinity 336 .808** -.123* -.072 Temperature 306 -.113* .061 .074 Depth 284 .176** .164 -.544** % Sand 422 -.062 -.121* -.558** % Fines 422 .047 .122* .555** % Gravel 422 .306** .002 -.151** TOC 419 -.496** .346** .390** TSS 52 -.572** -.538** .550** mERMq 115 .350** .262** .278** Dflow 394 -.009 -.031 -.081 Dissolved O2 58 .112 -.126 -.145
ABIOTIC VARIABLESTHAT INFUENCE ASSEMBLAGES
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Main Mesohaline
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Oligohaline muddy
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CONCEPTUAL MODELS OFBENTHIC RESPONSE
• Expected field responses for response to contaminant mixtures by:
– Number of Species, Abundances, Biomass– Higher Taxa (e.g. amphipods)– Sensitive and Tolerant Taxa
• Interactions of key abiotic factors (e.g.salinity, TOC, grain-size)
• Biological and ecological mechanisms
• Guides development of assessment methods
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Sediment Contamination / TOC Gradient
Sen
sitiv
e &
Tol
eran
t ta
xa
CONCEPTUAL MODEL
• Based on Pearson-Rosenberg response model• Response to contamination is similar to TOC• Position along gradient differs among assemblages
Sensitive taxa
Species, Abundances, Biomass Tolerant taxa, Higher taxa
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HYPOTHESIZED MECHANISMS
• Interactions of toxicity and TOC enrichment affect taxa with varying tolerances, affects ecological interactions
• Contamination, TOC, and physical disturbance have similar effects on assemblages.
• Low contamination,TOC: - Sensitive taxa abundant, few tolerant/opportunists (t-o)
• Moderate contamination,TOC: - Sensitive taxa decrease due to toxicity - t-o taxa increase (persist) due to increased organic material,
below most toxic thresholds
• High contamination TOC: - Sensitive taxa absent due to acute toxicity - t-o taxa reduced, most effects thresholds exceeded
• Extremely high contamination:
- Acutely toxic to all organisms
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1. Evaluation of benthic indicator metrics: What do they indicate?
2. Identification of “reference” samples 3. Evaluation of assessment results: Do results properly
reflect reference and impacted conditions?
KEY ISSUES
DEVELOPMENT OF
BENTHIC ASSESSMENTS METHODS
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A) Partial Coefficients Independent Variables Prop. R2 from Candidate Indicator Salinity Fines TOC mERMq Total R2 mERMq Log number of taxa 0.006 0.191A 0.026 0.589* 0.679* 0.87 Log total abundance 0.024 0.068 A <.001 0.394* 0.449* 0.88 Log number amphipod taxa 0.094 0.066A 0.018A 0.332* 0.445* 0.75 Oligochaete abundance 0.042 0.021A 0.007 0.030L 0.095 0.32 Log C. capitata abundance 0.075 0.026 A 0.001 0.028 0.125* 0.22 B) No. taxa 0.140 0.016A 0.332A 0.081* 0.481* 0.17 Total abundance 0.087 0.005A 0.431A 0.078L 0.525* 0.15 Number molluscan taxa 0.047L 0.006A 0.215 0.150* 0.368* 0.41 Oligochaete abundance 0.028 0.052 0.158 0.825* 0.865* 0.95 S. benedicti abundance 0.027L <0.001A 0.541 0.197* 0.642* 0.31
EVALUATION OF CANDIDATE INDICATOR METRICS
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REFERENCE SITES
1. Reference samples
• Not toxic• Mostly sensitive species• Oligochaete proportion
2. Reference ranges
Assessment Assemblage Indicator Polyhaline muddy Mesohaline
No. Taxa 21 - 66 6 - 18Tot. Abund. 97 - 2931 20 - 1090Molluscan Taxa 1 - 4 Amphipod Taxa 2 - 11 Oligochaete abund. 0 - 47C. capitata 0 - 13 Streblospio benedicti 0 - 38
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Site Date N. Taxa Total Abundance Amphipod Taxa C. capitata AV
BB15 2/15/1994 24 81 0 1 2
EBMUD4 9/23/1994 60 4866 11 16 2
ZM-2 12/3/1997 0 0 0 0 4*
EXAMPLE OF BENTHIC ASSESSMENTPolyhaline Muddy Assemblage
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EVALUATION OF ASSESSMENT METHOD
A) Polyhaline Assemblage Reference (n) Impacted (n) Probability
Sediment Contamination (mERMq) 0.0800 (19) 0.3491 (9) 0.013*Total Organic Carbon (%) 0.86 (20) 1.08 (9) 0.131Fine Sediments (% silt+clay) 58.5 (20) 80.8 (9) 0.013*Salinity (psu) 27.3 (19) 28.8 (9) 0.942Sediment Toxicity (percent of samples)0 (20) 100 (4) not tested
B) Mesohaline Assemblage
Sediment Contamination (mERMq) 0.0694 (8) 0.3190 (16) 0.011*Total Organic Carbon (%) 0.91 (9) 2.46 (16) 0.004*Fine Sediments (% silt+clay) 63.6 (9) 85.2 (16) 0.255Salinity (psu) 22.2 (9) 23.6 (12) 1.0Sediment Toxicity (percent of samples)0 (9) 85.7 (14) not tested
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CONCLUSIONS
• We know the species composition and abundances in the major benthic assemblages in the Estuary.
• We have a basic understanding of the spatial and temporal scales of change in these assemblages
• Benthic assessment methods exist and have been shown to accurately distinguish reference from impacted benthic conditions and reflect increasing sediment contamination
• Most benthic impacts in SF Estuary occur near the Estuary margins
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INFORMATION NEEDS
• Develop benthic assessment methods for other assemblages: mesohaline, oligohaline Delta, wetlands
• Which contaminant(s) cause observed benthic impacts?
• Investigate contaminant specific responses in species composition
• Better links between sediment toxicity and benthic response
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SUGGESTED RMP PROPOSALS
1. Include benthos in RMP status and trends program in collaboration with other programs
2. Conduct special studies to identify causes of observed benthic impacts
• multivariate analysis of existing data• lab, field, mesocosm experimental studies