In 2015 the U.S. Geological Survey's National Water-Quality Assessment (NAWQA) programme set out to assess stream quality in the Pacific Northwest. The study measured many water-quality factors that stress aquatic life and looked at how they relate to the living communities in the streams, focusing on the effects of urban development and agriculture in the Puget Lowlands and the Willamette Valley. The aim: tell the public and policymakers which human and natural factors matter most for stream quality, and so point to ways of protecting or restoring the region's streams.
It was NAWQA's third regional study, designed like the first two — the Midwest in 2013 and the Southeast in 2014.
Objectives
- Establish the state of stream quality across the region: contaminants, nutrients, sediment, the toxicity of streambed sediment, streamflow, habitat and biological communities.
- Work out how much each of those — contaminants, nutrients, sediment, toxicity, streamflow and habitat — influences the biological communities.
- Relate the measured stressors and communities to the natural and human characteristics of each watershed.
- Build statistical models and tools to predict stressor levels, and where possible ecological conditions, in wadeable streams throughout the region.
The design
Eighty-eight sites were to be sampled in April, May and June 2015, weekly for 4 or 10 weeks depending on land use in the watershed, for contaminants, nutrients and sediment. That water-quality "index" period would end with an ecological survey of habitat, algae, bottom-dwelling invertebrates and fish at every site, with sediment collected at the same time.
Fast urban growth, especially around Seattle and Portland, raises water-quality concerns, so 80 sites spanned a wide range of urbanisation, from dense urban watersheds to undeveloped reference ones. Eight more represented the region's main kinds of agriculture. Covering such a range of stressors should show more clearly how each affects stream life.
What was measured
| Component | What it involves |
|---|---|
| Ecological condition | Algae, benthic macroinvertebrates and fish sampled, and physical habitat assessed, once at all 88 sites in late June 2015, along several transects of each reach, by NAWQA protocols |
| Water | Depth- and width-integrated samples weekly — for 10 weeks at 70 urban and agricultural sites, 4 weeks at reference and rural sites — through spring runoff, a time of concern for chemical runoff. Analysed for nutrients, suspended sediment, major ions and about 230 dissolved pesticides and their breakdown products; some also for mercury, pharmaceuticals and wastewater compounds |
| Integrated sampling | Passive POCIS samplers left in streams at about 75 sites for about 7 weeks, to capture longer-term, chronic exposure to water-soluble pesticides, pharmaceuticals and wastewater compounds |
| Sediment | About an inch of surface streambed sediment from depositional areas at all 88 sites, analysed for trace elements, PAHs, halogenated compounds such as DDT, pharmaceuticals, wastewater compounds and hormones — sediment gathers different contaminants from water and can pass them to organisms. Suspended-sediment samplers at about 13 sites traced where sediment comes from (radionuclides and trace elements) |
| Toxicity | Bed sediment from some urban sites tested on amphipods (Hyalella azteca, 28 days), midge larvae (Chironomus dilutus, 10 days) and freshwater mussels (Lampsilis siliquoidea, 28 days) for effects on survival and growth |
| Continuous monitoring | Water level and temperature at all 88 sites; full water-quality monitors at 6, tracking dissolved oxygen and nitrate alongside periodic nutrient and periphyton sampling |
| Daily pesticides | Small automated samplers at 7 streams collecting daily and weekly samples for the ~230 pesticides, analysed by the EPA's Office of Pesticide Programs, to capture short-term, acute exposure and refine sampling schedules |
| Fish health | A "Juvenile Salmonid Scorecard" tested at about 15 sites with University of Washington researchers |
The toxicity tests matter here because amphipods, mussels and fish are sensitive to many contaminants — notably some insecticides in current use and PAHs — and several salmon and trout species are threatened or endangered in Pacific Coast streams.
The salmon scorecard
The Juvenile Salmonid Scorecard rates young salmonids on average growth rate, fat content and total calories, plus the activity of about two dozen genes, measured by quantitative PCR, that can reveal a fish's genetic response to particular stressors. It is built in tiers of cost and complexity, so that state and local agencies can adopt it as a standard way to judge salmonid health.
Sources
- Van Metre, P.C., Morace, J.L., and Sheibley, R.W., 2015, The Pacific Northwest Stream Quality Assessment: U.S. Geological Survey Fact Sheet 2015–3020. https://pubs.usgs.gov/publication/fs20153020
- Earlier regional studies: Midwest (Fact Sheet 2012–3124) and Southeast (Fact Sheet 2014–3023). More: NAWQA.
- The fact sheet's study-area map sits on an Esri basemap used under licence, and its one photograph is credited to the Portland Bureau of Environmental Services; both are left out.
- Rewritten in hubnx's own words.
Licence: CC0 1.0 (public domain) · Adapted from pubs.usgs.gov
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