Map Shows Where Human Poop Is Entering The Oceans

'The sheer scale of how much wastewater is impacting coastal ecosystems worldwide is staggering,” the study authors write. Image credit: Weerayuth Kanchanacharoen/Shutterstock.com

New research has mapped out the impacts of human poop on coastal areas – and let’s just say trips to the beach will never be the same again.

As reported in the journal PLOS ONE, researchers found that wastewater from human sewage introduces 6.2 million metric tonnes of nitrogen into coastal ecosystems per year. Up to 63 percent of this nitrogen comes from treated sewage systems, 5 percent from septic systems, and 32 percent from untreated input (ie. poop just going straight into the sea). 

A) Global map of the terrestrial sources (green to blue) and coastal diffusion of inputs (yellow to purple) of total wastewater N, measured in log10(gN) in both. Coastal plumes have been buffered to line segments to exaggerate patterns to be visible at the global scale. Insets show zoomed-in views of the B) Ganges, C) Danube, and D) Chang Jiang (Yangtze) Rivers, showing wastewater plumes at high resolution. Credit: Tuholske et al., 2021, PLOS ONE, CC-BY 4.0
A) Global map of the terrestrial sources (green to blue) and coastal diffusion of inputs (yellow to purple) of total wastewater N, measured in log10(gN) in both. Coastal plumes have been buffered to line segments to exaggerate patterns to be visible at the global scale. Insets show zoomed-in views of the B) Ganges, C) Danube, and D) Chang Jiang (Yangtze) Rivers, showing wastewater plumes at high resolution. Credit: Tuholske et al., 2021, PLOS ONE, CC-BY 4.0

 

Just 25 watersheds contribute nearly half of all wastewater nitrogen. These watersheds were mainly concentrated in India, Korea, and China, with the notoriously polluted Yangtze River in China contributing 11 percent of the world's total. For most of the world, most sewage underwent some treatment, but raw sewage remained a prominent problem for certain countries including China, India, and a number of African nations 

"The sheer scale of how much wastewater is impacting coastal ecosystems worldwide is staggering,” the study authors said in a statement. “But because we map wastewater inputs to the ocean across more than 130,000 watersheds, our results identify target priority areas to help marine conservation groups and public health officials to work together and reduce the impacts of wastewater on coastal waters across the planet."

To reach these conclusions, scientists from the University of California, Santa Barbara, used geospatial modeling to map out the nitrogen and pathogen inputs into the ocean from sewage for about 135,000 points around the world.

This is likely to have an impact on public health, especially in areas where wastewater outflow is particularly severe. However, it’s very likely to also have a harsh effect on marine life. Although nitrogen is considered an important nutrient, it can be extremely harmful to the oceans in large amounts because it promotes harmful algal blooms, which result in eutrophication and ocean dead zones.

The researchers mapped out where areas with coral reefs and seagrass were also meeting hotspots of nitrogen output. They found parts of China, Kenya, Haiti, India, and Yemen are likely to have coral impacted by the outlaw of sewage, while seagrass exposure hotspots were identified in Ghana, Kuwait, India, Nigeria, and China. This, however, might just be the tip of the iceberg and is likely to be having a knock-on effect throughout the wider ecosystem.

Maps show where A) coral reefs and B) seagrass beds are heavily impacted (raster cells in top 2.5% of exposure; red dots), not impacted (no exposure to wastewater N; dark blue dots), or impacted but not in the top 2.5% (yellow dots). Raster cells are represented as points which visually over-represents the habitat; red is overlaid on top which makes it visually dominant; blue points are transparent and overlaid on green/yellow points such that higher densities of unimpacted areas are brighter blue. Credit: Tuholske et al., 2021, PLOS ONE, CC-BY 4.0 (
Maps show where A) coral reefs and B) seagrass beds are heavily impacted (raster cells in top 2.5% of exposure; red dots), not impacted (no exposure to wastewater N; dark blue dots), or impacted but not in the top 2.5% (yellow dots). Raster cells are represented as points which visually over-represents the habitat; red is overlaid on top which makes it visually dominant; blue points are transparent and overlaid on green/yellow points such that higher densities of unimpacted areas are brighter blue. Credit: Tuholske et al., 2021, PLOS ONE, CC-BY 4.0

 

“Wastewater inputs of pathogens and nitrogen into coastal oceans present clear challenges to coastal ecosystems, public health, and economies across the planet. Beyond these direct impacts, our results suggest that wastewater inputs are likely to interact with the plethora of anthropogenic stressors to coastal ecosystems, leading to declining fisheries, habitat loss and degradation, and human health impacts,” the study concludes.

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