Chemical habitat quality is an increasingly important conservation issue, particularly in watersheds affected by urban stormwater runoff. Regulatory and restoration efforts typically evaluate a limited suite of conventional parameters and chemical pollutants. However, complex urban chemical mixtures contain hundreds to thousands of organic contaminants that are currently unidentified, unmonitored, unregulated and/or have poorly understood fate and toxicity outcomes. Additionally, identifying water quality metrics or specific contaminants that delineate land-use activities or key chemical sources, and can also effectively correspond to diverse ecotoxicological impacts, remains difficult. The objective of this study was to provide a framework for developing more holistic approaches and metrics for water quality impairment associated with biological degradation. Sampling occurred across an urbanization gradient defined by landscape characteristics, with stream samples collected during baseflow conditions in September/October 2017, with repeat sampling during storm events in November through June 2017-2018 in 15 regional watersheds (Puget Sound, WA, USA). Surface water chemical composition was characterized via liquid chromatography coupled to non-target high resolution mass spectrometry (LC-HRMS) analyses (7,068 unique chemical detections across 65 water samples). Observed water sample chemical composition was highly correlated with landscape-based urbanization gradient (p&lt;0.01), season (p&lt;0.01) and storm events (compared to baseflow conditions) (p&lt;0.01). Chemical composition was similarly aligned with two anchors of biological decline: coho salmon mortality (p&lt;0.001) and macroinvertebrate richness (p&lt;0.001). We isolated and identified 32 chemical indicators capable of effectively resolving urbanization-associated water quality degradation, including well-known anthropogenic contaminants (e.g., caffeine, organophosphates, vehicle-derived chemicals), two parent-transformation product pairs, and a previously unidentified (methoxymethyl)melamine compound. Study outcomes validated use of spatial landscape modeling to evaluate a geographic gradient of chemical water quality. Outcomes also support data-directed selection of next-generation chemical water quality indicators for integration with existing metrics used to prioritize and evaluate watershed management efforts for aquatic ecosystem protection.

Characterizing the chemical profile of biological decline in stormwater-impacted urban receiving waters

ACS Spring Meeting 2021

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