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Bedded Sediment Conditions and Macroinvertebrate Responses in New Mexico Streams: A First Step in Establishing Sediment Criteria
Citation:
Jessup, B., Phil Kaufmann, F. John, L. Guevara, AND S. Joseph. Bedded Sediment Conditions and Macroinvertebrate Responses in New Mexico Streams: A First Step in Establishing Sediment Criteria. JAWRA. American Water Resources Association, Middleburg, VA, 50(6):1558-1574, (2014).
Impact/Purpose:
Bedded fine sediment remains one of the most widespread agents of habitat degradation and impairment of biotic integrity in US streams and rivers. Natural variability in the amount of fine sediments in streambeds complicates the determination of acceptable levels of fine sediments in these waters. Jessup et al. illustrate a systematic process (using New Mexico as an example) for deriving numeric benchmarks of fine and unstable sediments in sreambeds that could be used by state environmental agencies like New Mexico Environmental Department (NMED) to translate their narrative sediment standards and ultimately to protect their state's stream ecosystems. Their suggested benchmarks are based on analysis of state and National Aquatic Resource Survey data on sediment, relative bed stability, and benthic macroinvertebrates. The recommended benchmarks and supporting analyses provide a strong basis for NMED to make final selections of biologically-relevant sediment thresholds and to establish procedures for their application. Their approach may serve as a template for application in other states where similar data sets are available.
Description:
Aquatic life protection was the impetus for a New Mexico Environment Department (NMED) effort to define bedded sediment conditions in streams that were natural and tolerable, especially to benthic macroinvertebrates. Sediments were measured using surveys of streambed particles to find percentages of sand and smaller substrates and the geometric mean diameter of bed sediments. Bankfull Relative Bed Stability (RBS) is a measure of particle stability calculated as the ratio of observed mean sediment diameter to the critical diameter. Critical diameter is an estimate of the maximum diameter of sediments that can be mobilized at bankfull flows, calculated from stream slope, channel morphology, and hydraulic roughness. Through multivariate analysis of environmental factors and sediment measures, we identified three sediment site classes based on physiographic regime; the Mountains, Foothills, and Xeric areas. The approach for identifying benchmarks of sediment impact was based on sediment characteristics in minimally disturbed reference sites and benthic macroinvertebrate metric responses within the site classes. Change-point analysis and quantile regression were used to assess stressor-response relationships. Sediment benchmarks were based on evidence from the multiple analytical techniques. Thresholds for two sediment indicators, percent sand & fines and RBS, were recommended to NMED for translating narrative criteria to benchmarks for protection of aquatic life uses.
