The Relation of Lotic Fish and Benthic Macroinvertebrate Condition Indices to Environmental Factors Across the Conterminous USA

National and regional ecological assessments are essential for making rational decisions concerning water body conservation and management. We analyzed data from 4597 samples collected from 3420 different sites across the conterminous USA during the U.S. Environmental Protection Agency’s 2008-2009 and 2013-2014 National Rivers and Streams Assessment. We evaluated the relationship between both fish and macroinvertebrate multimetric index (MMI) condition scores and 38 environmental factors, and to quantify the relative importance of natural versus anthropogenic predictors, site-scale versus watershed-scale predictors, and ecoregional and assemblage differences. We found that most of the environmental factors we examined were related to either fish and/or macroinvertebrate MMI scores in some fashion and that the factors involved, and strength of the relationship, varied by ecoregion and between assemblages. Factors more associated with natural conditions were usually less important in explaining MMI scores than factors more directly associated with anthropogenic disturbances. Local site-scale factors explained more variation than watershed-scale factors. Random forest and multiple regression models performed similarly, and the fish MMI-environment relationships were stronger than macroinvertebrate MMI-environment relationships. Among ecoregions, the strongest environmental relationships were observed in the Northern Appalachians and the weakest in the Southern Plains. The fish and macroinvertebrate MMIs were only weakly correlated with each other, and they generally responded more strongly to different groups of variables. These results support the use of multiple assemblages and the sampling of multiple environmental indicators in ecological assessments across large spatial extents.

Impact/Purpose

Indicators derived from biomonitoring data, such as multimetric indices (MMIs), are important tools in assessing the condition of aquatic resources to address the reporting objectives of the Clean Water Act. Limited information is available regarding how these types of indicators respond over larger geographic regions to environmental variables (e.g., those associated with natural gradients vs. stressors associated with human activity) or at different scales (local influence vs. cumulative impacts within a watershed or catchment. In this journal article, we used data from the EPA’s National Rivers and Stream Assessment (NRSA) to evaluate the relationship MMI scores developed for fish and benthic macroinvertebrate assemblages and 38 environmental variables. We applied multiple statistical approaches to quantify the relative importance of the type of variable (natural versus stressor-related), and the scale of the variable (derived from local-scale data versus variables derived from watershed-level data) in predicting an MMI score. In addition, we evaluated how the relationships between environmental variables and MMI scores might vary across geographic regions and the type of biological assemblage (fish vs. benthic invertebrates). Our results suggest that for data produced by NRSA and applied over large regional or national geographic areas, environmental variables that are more associated with natural conditions were usually less important in explaining MMI scores than stressor variables more directly associated with human activity. Variables derived from local-scale data were more important in explaining MMI scores than variables derived from watershed-scale data. The MMIs for fish and benthic macroinvertebrates were not strongly correlated with each other, and generally responded more strongly to different groups of environmental variables. These results support the use of multiple assemblages and the sampling of multiple environmental indicators in ecological assessments across large spatial extents Our findings provide additional knowledge to improve the capability of the NRSA assessments to evaluate the importance of various types of human activities in explaining ecological condition of the Nation’s river and stream resources. The results help assessments for NRSA to advance from associative to more causal-based relationships between stressors and biological condition as measured by MMI scores. NRSA data, indicators, and assessment results are of interest to the EPA Office of Water, EPA Regions, State water quality agencies, and other organizations interested in assessing status and trends in the condition of their river and stream resources. This effort supports ORD research related to NRSA that are identified in the strategic research action plan for the Safe and Sustainable Water Resources program to support EPA strategic goals. This research includes 1) identifying and explaining the geographic patterns existing in the physical .chemical. and biological data acquired for NRSA; 2) examining new approaches to ranking the impact of environmental stressors on aquatic biota; 3) evaluating how various human activities in watersheds relate to explaining physical, chemical and biological condition of rivers and streams; and 4) . advancing beyond using NRSA data to simply rank stressors based on their spatial extent to develop approaches

Citation

Herlihy, A., J. Sifneos, R. Hughes, D. Peck, AND R. Mitchell. The Relation of Lotic Fish and Benthic Macroinvertebrate Condition Indices to Environmental Factors Across the Conterminous USA. Elsevier Science Ltd, New York, NY, 112:105958, (2020). [DOI: 10.1016/j.ecolind.2019.105958]

DOI: The Relation of Lotic Fish and Benthic Macroinvertebrate Condition Indices to Environmental Factors Across the Conterminous USA