Capturing the impact of human sewage on Earth's coastal ecosystems
New worldwide mapping analysis identifies key exposure hotspots in unprecedented resolution

Date:
November 10, 2021
Source:
PLOS
Summary:
A new mapping analysis estimates the amounts of nitrogen and
pathogens released into coastal ecosystems from human wastewater
sources around the world.



FULL STORY ==========================================================================
A first-of-its-kind, high-resolution mapping analysis estimates the
amounts of nitrogen and pathogens released into coastal ecosystems
from human wastewater sources around the world. Cascade Tuholske (now affiliated with the Columbia Climate School) and colleagues at the
University of California, Santa Barbara, present this research in the open-access journal PLOS ONE on November 10, 2021.


========================================================================== Human sewage can introduce disease-causing pathogens and nitrogen
into the ocean, potentially impacting human health as well as coastal ecosystems and the communities that depend on them for such purposes as fishing. However, most research into humans' impact on coastal ecosystems
has focused on agricultural runoff, while investigations on human sewage
have been limited.

To better capture the impact of sewage on coastal ecosystems, Tuholske
and colleagues conducted a novel analysis in which they estimated and
mapped nitrogen and pathogen inputs into the ocean from sewage for about 135,000 watersheds around the world at a resolution of 1 kilometer. The assessment employed newly available, high-resolution data on global
human populations and modeled how wastewater plumes entering the ocean
would overlap with different ecosystems.

The analysis suggests that wastewater from human sewage introduces 6.2 teragrams of nitrogen into coastal ecosystems per year -- for comparison,
that is about 40 percent of estimated inputs from agriculture. Sixty-three percent of the nitrogen is from sewage systems, 5 percent from septic
systems, and 32 percent from untreated, direct input.

Of the watersheds that appear to release the most nitrogen from
sewage, most are located in India, Korea, and China, with the Chang
Jiang (Yangtze) River contributing 11 percent of the global total. The researchers also identified hotspots for coral reef exposure to nitrogen
in China, Kenya, Haiti, India, and Yemen. Seagrass exposure hotspots
were found in Ghana, Kuwait, India, Nigeria, and China. The Chang Jiang
and Brahmaputra Rivers have the highest input of pathogens.

Further research will be needed to refine the model and its estimates.

Nonetheless, this work provides a new resource that could play a key
role in efforts to mitigate harm to ecosystems and human health -- such
as by highlighting locations where tradeoffs between managing nitrogen
and pathogen levels are particularly important to consider.

The authors add: "The sheer scale of how much wastewater is impacting
coastal ecosystems worldwide is staggering. 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."
Note: The researchers have created a visual representation of their
research, available at: http://www.globalwastewatermodel.com/webmap.html ========================================================================== Story Source: Materials provided by PLOS. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Cascade Tuholske, Benjamin S. Halpern, Gordon Blasco, Juan Carlos
Villasenor, Melanie Frazier, Kelly Caylor. Mapping global inputs
and impacts from of human sewage in coastal ecosystems. PLOS ONE,
2021; 16 (11): e0258898 DOI: 10.1371/journal.pone.0258898 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/11/211110145428.htm

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