Event Title

Is stormwater harming our streams? Long-term monitoring of metals in stream stormflow

Presentation Abstract

Water-quality problems in urban and suburban streams are commonly blamed on stormwater pollution -- but actual stormflow pollutant data are much more limited. We analyzed 18 years (1993-2010) of stormflow metals concentrations from 33 stream stations across King County. We tested for long-term trends, compared stormflow and baseflow concentrations, and assessed aquatic and human-health toxicity. Five metals had long-term trends, all beneficial. Lead, nickel, and zinc concentrations have decreased over time. Calcium and magnesium concentrations have increased, which can reduce the adverse effects of toxic metals. In comparison to baseflow, 13 metals had discernably higher concentrations in stormflow (during 2001-2003 when metals were measured in baseflow). We assessed toxicity using state and federal regulatory water quality standards (WQSs), plus non-regulatory salmonid-specific screening values (SSVs). For aquatic toxicity, several samples were above WQSs for copper or lead, and 84% of streams had samples above the mercury chronic WQS. Ratios to WQSs were <10, indicating that adverse effects on the overall aquatic community were possible but uncertain. In contrast, all samples in all streams were above SSVs for lead and zinc, with ratios 10-100 indicating that adverse effects on salmonids were likely. There were also samples with cadmium, copper, or silver concentrations above SSVs. For human-health toxicity, several samples were above WQSs for nickel or thallium, and all samples in all streams had arsenic concentrations above the new arsenic WQS. Many metals in stormflow were well-correlated with iron, indicating they were predominantly weathering-derived; this included nearly all metals above WQSs/SSVs or with higher concentrations in stormflow than baseflow. This suggests that the major source of these metals of concern was increased erosion during storms, rather than other types of pollutants. The iron-correlation analysis also identified a few streams that had multiple metals from non-weathering sources and would benefit from detailed pollution tracking.

Session Title

Stormwater Characterization and Management Using a Watershed Approach

Conference Track

SSE3: Fate, Transport, and Toxicity of Chemicals

Conference Name

Salish Sea Ecosystem Conference (Seattle, WA : 2018)

Document Type

Event

SSEC Identifier

SSE3-375

Start Date

6-4-2018 10:30 AM

End Date

6-4-2018 10:45 AM

Type of Presentation

Oral

Contributing Repository

Digital content made available by University Archives, Heritage Resources, Western Libraries, Western Washington University.

Geographic Coverage

Salish Sea (B.C. and Wash.)

Rights

This resource is displayed for educational purposes only and may be subject to U.S. and international copyright laws. For more information about rights or obtaining copies of this resource, please contact University Archives, Heritage Resources, Western Libraries, Western Washington University, Bellingham, WA 98225-9103, USA (360-650-7534; heritage.resources@wwu.edu) and refer to the collection name and identifier. Any materials cited must be attributed to the Salish Sea Ecosystem Conference Records, University Archives, Heritage Resources, Western Libraries, Western Washington University.

Type

text

Language

English

Format

application/pdf

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Apr 6th, 10:30 AM Apr 6th, 10:45 AM

Is stormwater harming our streams? Long-term monitoring of metals in stream stormflow

Water-quality problems in urban and suburban streams are commonly blamed on stormwater pollution -- but actual stormflow pollutant data are much more limited. We analyzed 18 years (1993-2010) of stormflow metals concentrations from 33 stream stations across King County. We tested for long-term trends, compared stormflow and baseflow concentrations, and assessed aquatic and human-health toxicity. Five metals had long-term trends, all beneficial. Lead, nickel, and zinc concentrations have decreased over time. Calcium and magnesium concentrations have increased, which can reduce the adverse effects of toxic metals. In comparison to baseflow, 13 metals had discernably higher concentrations in stormflow (during 2001-2003 when metals were measured in baseflow). We assessed toxicity using state and federal regulatory water quality standards (WQSs), plus non-regulatory salmonid-specific screening values (SSVs). For aquatic toxicity, several samples were above WQSs for copper or lead, and 84% of streams had samples above the mercury chronic WQS. Ratios to WQSs were <10, indicating that adverse effects on the overall aquatic community were possible but uncertain. In contrast, all samples in all streams were above SSVs for lead and zinc, with ratios 10-100 indicating that adverse effects on salmonids were likely. There were also samples with cadmium, copper, or silver concentrations above SSVs. For human-health toxicity, several samples were above WQSs for nickel or thallium, and all samples in all streams had arsenic concentrations above the new arsenic WQS. Many metals in stormflow were well-correlated with iron, indicating they were predominantly weathering-derived; this included nearly all metals above WQSs/SSVs or with higher concentrations in stormflow than baseflow. This suggests that the major source of these metals of concern was increased erosion during storms, rather than other types of pollutants. The iron-correlation analysis also identified a few streams that had multiple metals from non-weathering sources and would benefit from detailed pollution tracking.