Researchers have drawn a new detailed map depicting the input and impact of human sewage on the world’s coastlines. The result is not beautiful, but very enlightening.
The lead author of the study, Cascade Tuholske, said that the motivation behind the study “is to have a detailed understanding of how wastewater affects coastal waters around the world.” A new paper Appeared in PLOS One magazine. He said that research on coastal marine ecosystems tends to focus on agricultural runoff from fertilizers and livestock manure, but few studies have focused on human sewage.
This is not the first study to generate a global wastewater model, but it is the first to map the input of nitrogen and pathogens in wastewater from 130,000 watersheds around the world. “This is important because there are trade-offs in the intervention space,” Tuhorsk said. He added that the information from this model can make these trade-offs clearer and make management decisions easier.
Excessive nitrogen and other nutrients can cause harmful algae to multiply. (Nicholas Aumen/US Geological Survey)
As a graduate student at the University of California, Santa Barbara, Tuholske conducted this research with colleagues. He is now a postdoctoral researcher at Columbia University. International Earth Science Information Network Center.
Most human wastewater is discharged into the oceans around the world from sewage, septic tanks and direct input sources in various treated and untreated states. Not surprisingly, the main source of wastewater has dense populations, which tend to gather around major watersheds.
Researchers estimate that only 25 watersheds contribute 46% of the global nitrogen input from wastewater into the ocean. They say that globally, the nitrogen content from wastewater is almost half of the nitrogen content from agricultural runoff. The paper stated that coastlines around the world are affected by the increase in nitrogen.
Tuholske and a team of interdisciplinary scientists at the University of California, Santa Barbara created a data visualization It maps the source and destination of nitrogen. It can lead to eutrophication, which is a phenomenon in which too much nutrients can cause phytoplankton to multiply in the coastal waters, thereby producing toxins and depriving waters of oxygen. These so-called dead zones not only suffocate marine life, but also cause problems in the food chain, including humans.
“Many coastal ecosystems, such as coral reefs and seagrass beds, are particularly sensitive to excess nutrients, even if you have no dead zones,” the study co-author said Ben Halpern, Professor at the University of California, Santa Barbara. “When the nutrient level is too high, the entire ecosystem may enter a highly degraded state. Coral reefs can turn into algae, which overgrowth and kill the corals below them. Our work here helps map out the nutrients in wastewater that may make These ecosystems face the most risky locations.”
For Tuholske, who focuses on food system research, this model has significantly alleviated the impact of modern diets on coastal ecosystems.
“What’s really surprising is how the shift in diet to animal-based protein affects marine ecology,” he said. He said that as countries become wealthier and consume more meat, in addition to the already high nitrogen content produced by agriculture, more and more nitrogen appears in wastewater. “The more burgers people eat, the more nitrogen enters the ocean,” he said.
Excessive nitrogen is not the only problem; where the waste water flows, so does the pathogen. But removing nitrogen or pathogens may require very different methods, which may make it difficult for decision makers with limited resources and different priorities to weigh their options between improving public health and protecting coastal ecosystems. The researchers said that the fine estimates of nutrients and pathogen inputs provided by the new model are intended to provide information on local solutions that can lead to complex global problems.
“These top-down high-resolution heat maps can be matched with the bottom-up approach,” Tuholske said. “Adaptation and mitigation are indeed bottom-up, and having a global map helps to set priorities and share knowledge.”
Adapted from a press release from the University of California, Santa Barbara.
