This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Along a quarter of the planet's coastal waterways, humans contribute more harmful nitrogen—via agricultural runoff, wastewater discharges and other activities—than all natural sources combined. That is a key finding from a new study led by Washington State University that measured and mapped the human impact on nitrogen, phosphorus and silicon inputs to the planet's coastal waters, which can harm marine life and pose health risks to people.
"Coastal ecosystems provide food, jobs, and recreation for billions of people worldwide, but these coastal waters are threatened by nutrient pollution that can fuel harmful algal blooms, oxygen-depleted dead zones, and biodiversity shifts," said John Harrison, the corresponding author of the new publication and Edward R. Meyer Distinguished Professor in WSU's School of the Environment, where he directs the Global Change and Watershed Biogeochemistry Laboratory. The study, published in the journal Global Biogeochemical Cycles, found that human activities outpace all natural nutrient sources in many coastal waterways and that land-based sources of the nutrients—both natural and human-caused—contributed more than marine sources in roughly half the planet's coastal waters.
The good news: Reducing nutrient discharge can make a big difference, and the research pinpoints where such steps may be most effective. "Getting a handle on nutrient inputs to the coastal zone and mitigating them is important, but we need to be sure that we invest our resources where it's going to make a difference," Harrison said. "This work provides a first cut at a framework for using resources to manage coastal zones efficiently." Harrison's co-authors included scientists from Utrecht University in the Netherlands and Zhejiang University in China.
Levels of nitrogen, phosphorus and silicon, as well as their ratios to each other, are key to healthy marine life. The nutrients occur naturally in both the ocean and on land, but human activities also contribute substantially. Among some oceanographers, Harrison said, the idea that land-based sources are a dominant factor was considered unlikely, given the vast size of the ocean.
"I really wanted to understand whether that worldview was correct or whether the community of scientists that studies coastal impacts of land-based nutrients was correct in thinking that these nutrient inputs were really important," Harrison said. "So, this is a first attempt to put together what we know about what's coming from land with what we know about what comes from offshore sources." Humans add nitrogen and phosphorus to rivers in several ways, including fertilizer and manure runoff from farms, wastewater emissions from sewage systems, urban runoff from city lawns and streets, and emissions from cars and power plants. Past studies have evaluated the overall global effects of human activity on nutrient levels; the new study is the most comprehensive to date because it includes both land-based and marine sources of multiple nutrients.
Researchers developed a novel database of global nitrogen, phosphorus and silicon sources across preindustrial and contemporary time spans and evaluated the contribution of land-based human activities, as well as the impact on nutrient ratios and the potential for eutrophication, a condition that promotes algal growth. Discover the latest in science, tech, and space with over 100,000 subscribers who rely on Phys.org for daily insights. d research that matter—daily or weekly. While natural marine sources were still the largest overall contributor of nutrients, land-based sources accounted for the majority of nutrients for more than half the world's coastlines, the researchers found.
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