Cultural eutrophication

DEFINITION: Unwanted increase in nutrient concentrations in sensitive waters caused by human activities

Cultural eutrophication causes the degradation of productive aquatic environments, which has prompted state and federal governments to regulate point and nonpoint source pollution in surrounding watersheds.

Eutrophication (from the Greek term meaning “to nourish”) is the sudden enrichment of natural waters with excess nutrients, such as nitrogen, phosphorus, and potassium, which can lead to the development of algae blooms and other vegetation. In addition to clouding otherwise clear water, some algae and protozoa (namely, Pfiesteria) release toxins that harm fish and other aquatic wildlife. When the algae die, their decomposition produces odorous compounds and depletes dissolved oxygen in these waters, which causes fish and other organisms to suffocate.

Eutrophication is a naturally occurring process as an environment evolves over time. Cultural eutrophication is a distinct form of eutrophication in which the process is accelerated by human activities, including wastewater treatment disposal, runoff from city streets and lawns, deforestation and development in watersheds, and agricultural activities such as farming and livestock production. These activities contribute excessive amounts of available nutrients to otherwise pristine waters and promote rapid and excessive plant growth.

Eutrophication of the Great Lakes, particularly Lake Erie, was one of the key factors that prompted the passage of the Clean Water Act and various amendments during the 1970s. This act specifically addressed the disposal of sewage into public waters, a major contributor to cultural eutrophication. However, it did not specifically address nonpoint source pollution, which comes from sources that are not readily identifiable. Agricultural activities such as farming, logging, and concentrated livestock operations all contribute to nonpoint source pollution through fertilizer runoff, soil erosion, and poor waste disposal practices that supply readily available nutrients to surrounding watersheds and lead to eutrophication in these environments.

The Chesapeake Bay is an excellent case study in cultural eutrophication. As development surrounding the bay dramatically increased, wetland and riparian buffers that helped reduce some of the impact of additional nutrients were destroyed. Eutrophication in the bay during the 1980s threatened the crabbing and oyster industry. Consequently, in 1983 and 1987, Maryland, Pennsylvania, and Virginia, the three states bordering the Chesapeake Bay, agreed to a 40 percent reduction of nutrients by the year 2000 from point and nonpoint sources in all watersheds contributing to the bay. These reductions were to be accomplished through such actions as the banning of phosphate detergents, the implementation of management plans to control soil erosion, the protection of wetlands, and the institution of controls on the production and management of animal wastes. Although these steps reduced phosphorus levels in the Chesapeake Bay and kept nitrogen levels constant, regulators remained unsure how much nutrient reduction must take place for the bay and its surroundings to resemble their original condition. Although this is optimal, in the early 2020s, researchers at the Center for Environmental Science, University of Maryland, were considering implementing nutrient reduction strategies to stop eutrophication from continually occurring, especially as the water temperature continues to rise because of climate change. Into the mid-2020s, researchers continued to work on the project, although progress was slow. Researchers employed new technology, such as machine learning, improved sensors, remote sensing, and eutrophication indices, to better predict and monitor nutrient dynamics. However, climate warming, altered rainfall patterns, more frequent extreme storms, and warmer water temperatures are intensifying eutrophication. Other stressors—including sedimentation, habitat degradation, and hydrological modifications—interact with nutrient loading to worsen conditions, prompting revisions of monitoring frameworks to account for these multiple pressures.

Bibliography

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