Policy ForumENVIRONMENTAL REGULATION

Dissolved oxygen and pH criteria leave fisheries at risk

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Science  24 Apr 2020:
Vol. 368, Issue 6489, pp. 372-373
DOI: 10.1126/science.aba4896

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Summary

Changes in human population centers and agricultural fertilizer use have accelerated delivery rates of nitrogen and phosphorus to coastal waters, often stimulating rapid accumulations of primary production (1). Whereas resulting eutrophication processes are of less environmental relevance in well-mixed, ocean ecosystems, when they occur in warm, stratified, and/or poorly mixed waters, they can result in hypoxia [depletion of dissolved oxygen (DO)] and acidification (decrease in pH), both of which individually can have adverse effects on aquatic life, affecting a suite of physiological processes and increasing mortality rates (2, 3). Only recently, however, have studies of aquatic hypoxia begun to consider coeffects of low pH (4). Many ecologically and/or economically important shellfish and finfish that experience decreased survival and/or growth when exposed to hypoxia are further impaired by concurrent acidification (4). Yet although scientific understanding of DO and pH variability and documentation of coastal hypoxic and acidification events have improved, regulatory reform has not kept pace. We suggest that more stringent DO and pH numeric criteria be considered to account for the negative effects of low pH on marine life and the combined impairment from low DO and low pH.

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