Stable Isotope Indicators and NARS: Linking Landscape Processes to Stressor Levels
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In partnership with states and tribes, EPA assess the condition of the nation’s waters through EPA’s National Aquatic Resource Surveys (NARS). EPA is interested in using new technologies to gain more information to aid the goals of NARS, and one of those technologies being tested is stable isotopic ratios obtained from NARS samples. This presentation introduces states and tribes to ORDs research into two potential stable isotopic indicators for NARS: a lake hydrological indicator and a nitrogen indicator.
Hydrologic water balance measurements are often excluded from spatially extensive lake monitoring programs because they require detailed gauging and monitoring of lake inflows and outflows. Yet, lake flow-through status, and water residence time are important parameters for understanding a lake’s chemical, physical and biological condition. We briefly introduce how lake water isotopes can be used to calculate the proportion of inflowing water that evaporates (evaporation:inflow ratios) and water residence time.
For the nitrogen isotopic indicator, nitrogen (N) pollution represents a major threat to aquatic ecosystems globally. Here, we introduce research into using the nitrogen isotope ratio (d15N) of chironomids, a family of aquatic insects that is abundance and collected as part of NARS. We found that chironomid d15N values can be a valuable tool to assess integrated watershed-level N sources, input rates, and processing for water quality monitoring and assessment at large scales.
These isotopic indicators are relatively low cost and make use of existing samples collected as part of NARS. They indicate key ecological processes, and integrate them over space and time, and that information is recorded in the samples collected. Isotopic indicators can be a valuable tool to assess integrated watershed-level sources, and processing for water quality monitoring and assessment at large scales.