Study maps sewage inputs to coastal ecosystems
S. Himmelstein | February 14, 2022The impacts of sewage inputs on coastal ecosystem health were gauged by Columbia University and University of California Santa Barbara researchers with a global wastewater model and map that identify inputs of nitrogen and pathogens from wastewater across 130,000 watersheds worldwide.
The analysis indicates that treated as well as untreated wastewater discharges collectively contribute a much larger fraction of total nutrient pollution to oceans than previously understood. The wastewater discharges from about 130,000 watersheds add about 6.2 trillion grams of nitrogen to coastal waters annually, about double that originating in agricultural runoff. About 63% of total nitrogen is contributed by sewered systems, 5% by septic systems and 32% by direct sources.
Total nitrogen input into Exclusive Economic Zone (EEZ) waters of coastal countries, by source type (sewer, septic, direct). Source: Cascade Tuholske et al.
Just 25 watersheds contribute 46% of global nitrogen and 51% of fecal indicator organisms inputs from wastewater into the ocean, with watersheds in India, Korea and China identified as the largest contributors. Modeling the plume of wastewater nitrogen into coastal waters reveals that about 58% of all coral reefs globally and 88% of all seagrass beds experience at least some anthropogenic nitrogen input from wastewater.
A data visualization map that depicts specific points associated with high surface-level nitrogen concentrations in coastal waters can be accessed to help stormwater infrastructure managers prioritize areas for local runoff control interventions.
The research is published in PLoS ONE.