Adverse environmental conditions that may have human influences and may affect the benthic community 

 can be grouped into five general categories (Karr 1991, 1993; Fig. 3-1): 



1 . Water & Sediment Quality - hypoxia, salinity, temperature, contaminants 



2. Habitat Structure - substrate type, water depth, complexity of physical habitat 



3. Flow Regime - water volume and season flow distributions 



4. Energy Source - characteristics of organic material entering waterbody 



5. Biotic Interactions - competition, predation, disease, parasitism. 



For the purposes of this assessment, we sought to evaluate the effects of water and sediment quality 

 (specifically, contaminants and hypoxia) on the benthic community. While the other factors are equally 

 important in determining benthic community structure, they were not included in this assessment. Figure 3- 

 1 illustrates the primary pathways by which contaminants enter estuaries. Contaminants enter the estuary 

 primarily via land-based non-point sources (e.g., runoff from agricultural or livestock operations or urban 

 runoff) and point sources (e.g., industrial effluent or municipal wastewater). Contaminant stress is evident if 

 the sediments are toxic to test organisms or if the levels of certain chemicals are high when compared to 

 established guidelines. The benthic community responds to contaminant stress by an overall reduction in 

 abundance and number of species, an increase in the proportion of pollution-tolerant or opportunistic species, 

 or both. 



Non-point 

 Sources 



Waslev*/ater 



Point 

 Sources 



Industry 



Marsh 



Seagrass 



Components 



of the 

 Benthic Index 



Diversity 



Tubificids 



Benthic Coiniiumity 



Capitellids 



Bivalve 



Anipltipods 



Figure 3-1. Conceptual diagram of a typical estuary showing the environmental stressors 

 that may contribute to altering benthic macroinvertebrate community structure 

 and the components of the benthic index. 



3-5 



