Full life cycle assessment of insect biomass allows estimation of bioflows across water, air, and land

Abstract

As global environmental change continues, animals face uncertain habitat availability and quality that influences life cycle phenology and population dynamics. For decades, the population abundance and emergence patterns of burrowing mayflies have been used as a sentinel for water quality changes in large freshwater systems around the world. Despite reduced point source pollutants, evidence is mounting that the interactions among habitat loss, contaminants, and changing climate could be causing declines in mayfly production and shifts in emergence timing. We combined radar observations with traditional field measures to identify changes in mayfly populations from nymph to adult. We studied Hexagenia sp. secondary production in a large reservoir, Lake Seminole, which has contrasting water sources and land use on each arm that could contribute to differences in emergence patterns. We predicted that mayfly secondary production would be higher, and emergence would be earlier in the Chattahoochee arm versus the Flint arm because of differences in available nutrients and temperature. Benthic declines in abundance and biomass followed radar observations of emergence. Mean annual water temperature was similar, with the Flint arm having less seasonal variation. Mayfly growth was similar across the lake, but production was higher in the upper Flint arm, perhaps because of temperature stability, higher nutrient concentrations, and more lotic conditions. The natural abundance of nitrogen-stable isotopes in mayflies showed distinct patterns between the arms and from nymph to adult. Linking benthic sampling with radar observations verified our capability to track mayfly biomass across the landscape and begin to calibrate previous measures of production with radar-derived abundance. Coupling radar observations with stable isotope and tissue nutrient measurements allowed us to further quantify the subsidies moving from aquatic to terrestrial ecosystems, setting the framework to examine both historic and future population changes and mayfly contributions to cross-ecosystem subsidies.