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Developing methods for assessing water quality in streams when there’s no water
Citation:
Fritz, K., C. Nietch, AND R. Burke. Developing methods for assessing water quality in streams when there’s no water. 2019 Annual Meeting of the Society for Freshwater Science, Salt Lake City, Utah, May 19 - 23, 2019.
Impact/Purpose:
Intermittent streams lack year-round flow and are often dry when perennial streams are monitored. Intermittent streams represent much of the U.S. stream length and because most are connected to downstream perennial waters, they collectively affect downstream water quality. Under the Clean Water Act, states, territories, and tribes (hereafter, collectively called “states”) must develop, revise and adopt water quality standards for their jurisdictional waters. However, states lack water quality methods, standards, and data for intermittent streams because of their flow regime. Methods have been developed to distinguish intermittent from perennial streams for different regions and to assess the ecological integrity of intermittent streams. While these methods are useful, they do not provide sufficient insight on the chemical nature or quality of the water in these systems when they are flowing, nor do they provide any characterization of chemical inputs to downstream waters. Developing methods to characterize recent water quality will enable a better understanding of stressor-biotic relationships. Water quality in streams is an integration of a watershed’s landscape processes and the processes within channel corridors. Evaporative crystallization is an abiotic retention process in intermittent streams that may provide insight into recent water quality. This process occurs when water is evaporated during the drying phase of intermittent streams and water-soluble minerals are taken out of solution and crystallized on the streambed. Common evaporite minerals include chlorides, sulfates, nitrates, phosphates, and carbonates. Biotic assimilation by the biofilms covering the channel substrates in all flowing waters is another retention process. However, resuming flow in the stream channel results in a pulse of available nutrients which has been attributed to death of bacteria, algae and other organisms associated with the dry biofilm and subsequent mineralization and evaporite dissolution. We propose that retention processes provide a signal of recent water quality for intermittent streams and may be a useful means of water quality assessment for these systems that would otherwise be difficult to monitor because of their flow regimes. To investigate this assessment approach we conducted a stream mesocosm experiment to determine if, upon rewetting, dry substrates (unglazed tiles and gravel) will release nitrogen and phosphorus that reflect 2-month experimental dosing concentrations (nominal N/P ppb range: 240/40 to 3300/400).
Description:
Non-perennial streams lack year-round flow, represent much of the U.S. stream length, and collectively affect downstream waters. Under the Clean Water Act, states, territories, and tribes must have water quality standards for their jurisdictional waters. Evaporative crystallization and biotic assimilation on benthic surfaces are retention mechanisms that may signal recent water quality for non-perennial streams that are often dry when water quality would otherwise be monitored. We conducted a stream mesocosm experiment to determine if, upon rewetting, dry substrates (unglazed tiles and gravel) will release nitrogen and phosphorus that reflect 2-month experimental dosing concentrations (nominal N/P ppb range: 240/40 to 3300/400). Substrates were dried for 69d before rewetting with deionized water. Water was collected from all 6 treatments at 2 and 48h after rewetting and after 72h for the lowest and highest concentrations. Rewetted-nutrient concentrations were generally linear with dose 2h after rewetting and remained so after 48h among the 3 lower doses for tiles and at least the 4 highest doses for gravel. Dose-response modeling is presented to characterize the resolution of the method. Our results indicate rewetting substrates from non-perennial streams has potential as a rapid monitoring method.
