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Development of a Zooplankton Assemblage Indicator for the 2012 National Lakes Assessment: Performance in the Western U.S.
Citation:
Peck, D. AND K. Blocksom. Development of a Zooplankton Assemblage Indicator for the 2012 National Lakes Assessment: Performance in the Western U.S. 2015 meeting: PNW chapter of the Society for Freshwatere Science, Coeur d'Alene, ID, November 03 - 05, 2015.
Impact/Purpose:
Zooplankton are an important biological component of lake and reservoir ecosystems. Biological-based indicators of ecological condition for lakes are limited in number, especially to assess condition at regional scales. We used zooplankton count data collected as part of the 2012 National Lakes Assessment (NLA) to develop candidate metrics and multimetric indices (MMIs) for five aggregated ecoregions of the conterminous USA, including the Western Mountains and Xeric West. We were able to develop MMIs that were sufficiently responsive to human disturbance and sufficiently repeatable to assess ecological condition for the NLA without the need to reduce the effects of natural variation using models. We did not observe strong effects of either lake size, lake origin, or site depth on the MMIs at the regional scale. The MMIs appear to respond more strongly to increased nutrient concentrations than to shoreline habitat conditions. This indicator allows for a more comprehensive assessment of the ecological condition of lake and reservoir populations in the USA.
Description:
We used zooplankton count data collected as part of the 2012 National Lakes Assessment (NLA) to develop candidate metrics and multimetric indices (MMIs) for five aggregated ecoregions of the conterminous USA (Coastal Plains, Eastern Highlands, Plains, Upper Midwest, and Western Mountains and Xeric [“West’]). We classified candidate metrics into six categories: Richness/biomass/density, diversity/dominance, trophic guild, and taxonomic composition of the three major components of the assemblage (cladocerans, copepods, and rotifers). In each aggregated ecoregion, we evaluated candidate metrics for range, responsiveness to disturbance (comparison of least-disturbed sites to more highly disturbed sites), and repeatability (variability among sites [signal] vs. variability within sites [noise]). We used metrics that had passed these screens to calculate all possible candidate MMIs that included at least one metric from each category. We evaluated each candidate MMI for responsiveness, repeatability, and pairwise correlation (maximum and mean) among component metrics. We selected the candidate MMI that had high responsiveness, a reasonable value for repeatability, low mean pairwise correlation among component metrics, and, when possible, a maximum pairwise correlation among component metrics that was <0.7. The performance characteristics of the MMI selected for use in the Western Mountains and Xeric region were as follows: responsiveness (least-disturbed vs. more highly disturbed sites; t=6.30), repeatability (Signal:Noise=3.2), maximum pairwise correlation of 0.63, and mean pairwise correlation of 0.21). We were able to develop MMIs that were sufficiently responsive and repeatable to assess ecological condition for the NLA without the need to reduce the effects of natural variation using models. We did not observe effects of either lake size, lake origin, or site depth on the MMIs. The MMIs appear to respond more strongly to increased nutrient concentrations than to shoreline habitat conditions. Improving our understanding of how zooplankton assemblages respond to increased human disturbance, and obtaining more complete autecological information for zooplankton taxa would likely improve MMIs developed for future assessments.