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Development and refinement of benthic indices to assess coastal waters for U.S. EPA’s National Coastal Condition Assessment
Citation:
Pelletier, M., D. Gillett, A. Hamilton, T. Grayson, V. Hansen, E. Leppo, S. Weisberg, A. Borja, T. Angradi, E. Hinchey, B. Lubya, AND H. Sullivan. Development and refinement of benthic indices to assess coastal waters for U.S. EPA’s National Coastal Condition Assessment. National Water Quality Monitoring Conference 11th Conference, CO, Denver, March 25 - 29, 2019.
Impact/Purpose:
The National Coastal Condition Assessment (NCCA) monitors estuaries every 5 years to evaluate condition. Measurements include water quality, ecological fish condition (fish contaminant load), sediment condition, and benthic (organisms living on the sea bottom) condition. In estuaries, benthic condition has been evaluated using individual regional indices, where available, and salinity adjusted diversity on the West Coast. This approach has been criticized because of the concern that the indices were not comparable with each other. Because the indices were locally calibrated, ‘bad condition’ in the northeast might not be comparable to ‘bad condition’ in the west. For this reason, a development of a nationwide index was desired. The new index performed well in assessing benthic coastal condition when compared to well-calibrated local indices from three different areas of the country. This new index appears to be an acceptable index for comparing condition across broad-scales such as estuarine and coastal waters surveyed by NCCA, and for application to the many parts of the US coast that do not already have a locally derived benthic index. Preliminary work is being conducted to try to improve the current index being used in Great Lake waters.
Description:
The National Coastal Condition Assessment (NCCA) is part of the National Aquatic Resource Surveys (NARS). NCCA assesses the condition of estuaries every 5 years using a variety of characteristics including the condition of the benthic invertebrates, which are good indicators of the health of coastal waters. Benthic condition has historically been evaluated using multimetric benthic indices, which combine different summary characteristics into a single number that can be characterized as Good, Fair or Poor. In estuaries, these indices were developed with different individual metrics using different statistical methods. Because of this there was concern that the indices might not be comparable, there was a need to develop a comparable nationwide benthic index. In the Great Lakes, the Oligochaete Trophic Index (OTI) was applied to the 2010 NCCA survey, but there were many missing values (~50%). This was due in part to a lack of oligochaetes in the sample, or lack of tolerance values for the oligochaetes that were present, so an improvement of this index or development of a better index was desired. In estuaries, a multi-year effort was initiated to develop a benthic index that could be applied nationwide using the AMBI/M-AMBI approach, a tolerance-based index first developed in European waters for use under the Water Framework Directive. Tolerance values (Ecological groups or EGs) for estuarine taxa were assembled to calculate AMBI. These results were compared to locally calibrated indices from southern California, the southeast and mid-Atlantic region. The index performed reasonably well, but had a salinity bias. To reduce this bias, M-AMBI, the multivariate version of AMBI was implemented. This index was calculated separately for individual habitats (salinity zone). The new index performed well, without a salinity bias. In the Great Lakes, a similar effort was initiated to either improve the OTI or implement the modified Trophic Index (mTI). This presentation will describe the development of the M-AMBI index as well as provide an update on the Great Lakes index development.