In 2017, the USGS National Water-Quality Assessment (NAWQA) project assessed streams in coastal California. The California Stream Quality Assessment (CSQA) covered most of the Central California Foothills and Coastal Mountains ecoregion, where fast urban growth and intensive agriculture in the big valleys raise concern for stream health. The goal: tell the public and policymakers which human and natural factors matter most, pointing toward ways to protect streams.
It was NAWQA's fifth regional stream assessment, following the Midwest (2013), Southeast (2014), Northwest (2015) and Northeast (2016) — see Regional Stream Quality Assessments.
Ecological sampling in a stream. Alan Cressler, USGS.
Objectives
- Describe stream quality — contaminants, nutrients, toxicity, sediment, flow, habitat and biological communities — across the region.
- Weigh how much each chemical and physical stressor affects stream life.
- Relate stressors and communities to the watersheds' natural and human characteristics.
- Build models and tools to predict stressors and ecological conditions in wadeable streams.
Approach
85 sites were provisionally chosen for up to 6 weeks of sampling in March, April and May 2017, ending with an ecological survey at every site; final choices depended on winter streamflow.
| Watershed land use | Sites |
|---|---|
| Urban | 44 |
| Mixed urban and agricultural | 28 |
| Agricultural | 2 |
| Undeveloped | 11 |
The wide range of stressors should clarify their effects on stream ecology.
What was sampled
| Component | What and how |
|---|---|
| Ecological condition | algae, benthic invertebrates and fish, plus physical habitat, once at all 85 sites in April or early May |
| Water | weekly for 6 weeks at most sites (and 4 weeks at the 12 reference sites) — nutrients, suspended sediment, major ions, pesticides and their breakdown products; some samples for mercury, pharmaceuticals and wastewater compounds |
| Integrated water samplers | POCIS devices at all 85 sites for 6 weeks, soaking up dissolved chemicals to show chronic exposure to pesticides and pharmaceuticals |
| Biofilms | ceramic tiles left 6 weeks to grow microbial films, analyzed for pesticides, especially pyrethroid insecticides |
| Streambed sediment | at all 85 sites — trace elements, radionuclides, pesticides, PAHs, halogenated compounds such as DDT, wastewater compounds and hormones |
| Suspended sediment sources | traps at 7 sites; geochemistry to trace where the sediment comes from |
| Toxicity tests | bed sediment tested on amphipods (Hyalella azteca, 28 days) and midge larvae (Chironomus dilutus, 10 days) for effects on survival and growth |
| Continuous monitoring | water level and temperature at all 85 sites; about 30 already had USGS real-time streamgages |
| Daily pesticides | automated samplers at seven streams (five CSQA sites and two in the Central Valley), analyzed by the EPA's Office of Pesticide Programs, to capture short-term peaks |
| Cyanobacterial toxins | a May 2017 survey of microcystins, little studied in small streams |
| Mercury in fish | total mercury in fish from most sites, and mercury isotopes at some to reveal its sources |
Collecting water samples. Amanda Egler, USGS.
Sediments collect different contaminants than water, adding to the picture; amphipods and fish are sensitive to many contaminants, notably some current-use insecticides and PAHs; and mercury is a well-known concern in California's coast ranges.
Sources
Based on The California Stream Quality Assessment, U.S. Geological Survey Fact Sheet 2017–3014 (DOI; publication page), National Water-Quality Program, citing Griffith and others (2016). The two photographs are restored from the fact sheet's PDF; its study-area map, on a licensed commercial basemap, is left out. A work of the United States government in the public domain.
Licence: CC0 1.0 (public domain) · Adapted from pubs.usgs.gov
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