How Water Quality Impacts Climate Change—and Vice Versa
Although many studies look at how climate change impacts water quality, few turn that around and ask how water quality affects climate change. But a recent report published by the Environmental Protection Agency (EPA) did just that: It looked at how nutrients like phosphorous and nitrogen in surface waters can increase greenhouse gas emissions that contribute to global warming—and how reducing nutrients from agriculture, industry, stormwater, and wastewater treatment would benefit the environment and economy. Given the investment required to implement watershed management plans that reduce nutrient loading, it's crucial for cost-benefit analysis to include the payback from reducing greenhouse gas emissions.
"The Climate Benefits of Improving Water Quality" investigated greenhouse gas reductions from a program to manage nutrients in America's largest estuary and the accompanying climate benefits. The authors estimated the monetary value for the estuary would exceed $300 million over 50 years, then extrapolated those results to America's largest river basin—a primary contributor to the low-oxygen dead zone in the Gulf of Mexico.
Progress depends on implementing effective water management plans and monitoring to ensure cleaner drinking water, healthier ecosystems, better groundwater quality, and lower greenhouse gas emissions. Here's a closer look at how nutrient management plans can mitigate climate change and the role of water testing in developing viable water management plans.
Counteracting the Damaging Effects of Excess Nutrients
Over-enrichment of inland and coastal waters due to nitrogen and phosphorous is one of the greatest threats to water resources worldwide, according to the EPA. Over half of U.S. stream miles and an estimated 40% of freshwater lakes and reservoirs suffer from eutrophication—defined as excessive nutrient enrichment—and associated growth of algae, low dissolved oxygen, and loss of underwater vegetation.
Nutrients impact the availability of carbon and oxygen to microbes in surface water. The algal blooms that nutrients stimulate can generate carbon—and microorganisms metabolize it, increasing methane production in aquatic environments. The carbon may also deplete oxygen by stimulating microbes to decompose, processes that can produce greenhouse gases in low-oxygen environments.
Assessing the Climate Benefits of Reducing Nutrients
The study aimed to quantify the climate benefits of reducing nutrients in surface waters. Scientific advances enabled the researchers to develop models predicting greenhouse gas emissions from individual water bodies based on factors including nutrient levels and algal abundance. Researchers used these models to estimate global greenhouse gas emissions from lakes and reservoirs, the effects of watershed management on greenhouse gas emissions, and changes in global methane emissions over the next century.
The research initially evaluated the impacts of a nutrient management program in the Chesapeake Bay Watershed, which spans six states and Washington, D.C. In 2010, the EPA established a Total Maximum Daily Load (TMDL) for nitrogen and phosphorus in the estuary to achieve standards for dissolved oxygen, chlorophyll a, and water clarity for fishing and swimming. The TMDL impacts roughly 4,200 water bodies.
The current study estimated the economic benefits of managing nutrient loading, modeling annual reductions in greenhouse gases. The authors then applied a set of updated social cost estimates that the EPA developed to put a dollar value on climate benefits. The researchers extrapolated the results to a nutrient management program for the Mississippi/Atchafalaya River Basin (MARB), which drains parts of 31 states from Pennsylvania to Montana, Minnesota to Louisiana, and contains nearly 200,000 water bodies.
Monetizing Water Quality Improvements
The total monetized climate benefits of the Chesapeake Bay TMDL will be about $6 million in 2025, estimated to rise to over $16 million by 2075, and with a value of $333 million over those five decades, according to the study. That depends on reducing nutrients by 24%.
The Gulf of Mexico Watershed Nutrient Task Force has targeted a 45% reduction in nitrogen and phosphorus from historic levels (1980-1996) from the MARB into the Gulf of Mexico by 2035. The researchers estimated annual climate benefits of $290 million in 2035 and $10.6 billion over the first four decades of the program. They based the estimates on methane only, although they anticipate carbon dioxide and nitrous oxide reduction as well.
Testing to Evaluate Improvements
Resource managers worldwide are implementing plans to manage nutrients and curtail the harmful effects on surface waters. The researchers concluded the climate benefits of nutrient management could be substantial at regional, national, and global scales and should be considered in the cost-benefit analysis of regulations to protect resources.
Water testing can provide the parameters needed to gauge water body health, including dissolved oxygen, alkalinity, pH, conductivity, nutrient levels, secchi depth, and bacteria counts. This data can help guide measures to reduce nutrients, whether that means aeration systems, nutrient remediation, or prescriptions to eliminate algae and aquatic weeds. Sampling and testing to establish baseline values are essential to develop an ecologically balanced approach to managing water bodies.
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