Submitted to: Environmental Monitoring and Assessment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/4/2010
Publication Date: 7/1/2011
Citation: Schwartz, J.S., Simon, A., Klimetz, L.A. 2011. Use of fish functional traits to associate in-stream suspended sediment transport metrics with biological impairment. Environmental Monitoring and Assessment. 179:347-369. Interpretive Summary: Streams are “listed” as in need of water-quality improvement (a TMDL) by States, Territories and Tribes if their designated use is impaired. In many cases the designated use is “aquatic life support”. With sediment being one of the principle sources of water-quality impairment, there is very limited information on the functional links between the magnitude, frequency and duration of suspended-sediment concentrations, and aquatic indices. Sediment-transport relations for stable and unstable streams in Northwestern Great Plains were combined with biologic data at 58 sites to test for statistically significant relations. Concentration data were transformed to “dosage” by multiplying by the average duration that a given concentration is expected to occur in a given year. A functional-traits analysis was used to quantify functional links between biologic and sediment-transport processes (using sediment-transport magnitude, frequency and duration), resulting in a range of water-quality “targets” for fish in Ecoregion 43. This marks advancement from earlier work where a single target value was determined, but not linked to biotic indices.
Technical Abstract: Loss of ecological integrity due to sediment is a major cause of water quality impairment in the United States. Numeric criteria for total maximum daily loads (TMDLs) must be generated and attained to regain ecological integrity of listed streams. Current assessment protocols lack a means to link temporally variable sediment transport rates with specific losses of ecological functions as loads increase. This study located in Northwestern Great Plains Ecoregion co-located 58 USGS gauging stations with existing flow and suspended sediment data, and fish data from federal and state agencies. Suspended sediment transport rates were quantified into exceedance frequencies of a given concentration, duration as the number of consecutive days a given concentration was equaled or exceeded, dosage as concentration x duration, and mean annual suspended sediment yields. Functional traits fish species present were used to investigate biological impairment. Twenty fish traits were organized into four main trait groups: preferred rearing habitat, trophic structure, feeding habits, and spawning behavior. Through the use of a functional traits analysis, ten traits were identified with possible impairment responses, and enumerated by either concentration frequency and duration, and dosage. Three principal responses were observed: 1) traits correlated with a broad range of concentration exceedance frequencies, 2) traits correlated at the upper range of concentration exceedance frequencies, i.e., 90 to 95% events occurring at moderate flows; and 3) traits correlated at the lower range of concentration exceedance frequencies, i.e., 0.01% to 10% events likely occurring during floods. Specific to these responses, impairment linked traits included habitat preferences for stream pool and river shallow waters; feeding generalist, omnivores, piscivores; and several spawning behaviors. These responses provide some evidence as to the potential loss of ecological function, related to fish, from elevated suspended-sediment loads. In addition, unstable channels, found to be greater in transported suspended sediment than stable channels over a range of concentration exceedance frequencies, likely influence physical habitat quality. Preferred habitat traits are likely co-impacted by habitat loss from morphological instabilities and elevated sediment loads. Overall, a functional traits approach was successful in identifying potential “thresholds” for biological impairment due to excessive suspended sediment, and will aid in developing sediment TMDLs.