Study: MPAs are Unusually Vulnerable to Wastewater Runoff
Researchers have long understood that land-based pollution sources are a leading cause of environmental harm in the ocean, from plastic wastes to nutrient runoff. Land-based sewage is an issue as well, and it turns out that marine protected areas (MPAs) might be more affected by this form of pollution than the average acre of unprotected ocean, a new study in Ocean & Coastal Management has determined.
Working together, researchers from the University of Queensland and the New York-based Wildlife Conservation Society (WCS) evaluated the total nitrogen load at 1,855 coastal MPAs around the world in tropical latitudes. Excess nitrogen comes from agricultural fertilizer runoff, as well as sewage effluent; in river deltas it can cause algae blooms and eutrophication, and in reef habitats it is harmful to the growth of coral, supporting diseases and reducing light availability in the water column. In lieu of direct measurements, the team used
For the study, the researchers selected MPAs in regions with high concentrations of coral reefs, seagrass meadows, and mangrove forests - areas in Southeast Asia, Australia, the Indian Ocean, the Arabian Gulf and the Caribbean. Within these key regions for coral biodiversity, about nine out of 10 MPAs are affected by wastewater pollution, the authors found. Contamination levels within MPA boundaries often exceeded the levels in nearby, unprotected waters - sometimes by factor of 10.
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The authors warned that the effects of wastewater pollution could negate the value of MPAs in providing a safe refuge for marine life. While charitable donors and political actors pursue further MPA expansion, onshore wastewater leakage goes unaddressed in MPA governance: it occurs far outside of the geographical bounds and legal structures of MPAs. Without heavy investments in fixing wastewater runoff - the source of the excess nitrogen - MPAs could fall short as a conservation tool, they warned.
"The global push to achieve 30x30 will fail to deliver on its promise unless the effectiveness of protection from pollution is prioritized alongside extent. For MPAs to safeguard biodiversity, pollution sources that undermine their ecological integrity, such as wastewater, must be addressed," the authors concluded.
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