Browning could make lakes less productive, affecting food webs and fish

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As more dissolved organic matter enters lakes in the northeastern United States, darkening the lakes in a phenomenon called “browning,” new research shows these waters may become less productive and able to support less life. . In a study published today in Limnology and Oceanography Letters, scientists have found that, rather than enriching lakes with nutrients as previously assumed, water more loaded with dissolved organic matter blocks sunlight and restricts plant growth.

“A key question regarding the browning of lakes is what impact it will have on aquatic food webs, including algae growth and fisheries,” said Kevin Rose, co-author and assistant professor of biological sciences at the Polytechnic Institute. by Rensselaer. “These results demonstrate that browned lakes are increasingly limited by light. As a result, the algae and aquatic plants that grow in these lakes will be increasingly limited to shallower areas, restricting an important food resource for the lake. invertebrates that feed fish. This change could make it difficult for fish that typically rely on visual foraging, such as brook trout, to find prey. “

Browning is the result of environmental changes that include the recovery of acid rain, changes in land use and climate change. Scientists had previously speculated that as more dissolved organic matter poured into lakes, levels of nutrients like nitrogen and phosphorus would also rise, potentially offsetting the effects of reduced light. But according to Jonathan Stetler, the lead author and a graduate student working with Rose, nutrients don’t increase as the lakes darken over time. In the absence of an increase in nutrients, the models created by the authors predict that darker lakes will be less welcoming to plant and animal life.

Le brunissement pourrait rendre les lacs moins productifs, affectant les réseaux trophiques et les poissons

Peak summer average photosynthetic potential estimates for the entire lake for 28 study lakes during the period 1994-2012 in the Adirondacks (data from Leach et al. 2018b). The solid blue dots represent a significant long-term decrease while the solid red dots represent a significant long-term increase in the tendency of the Sen slope (p

“The lakes are turning brown, and across the region, there is a correlation that shows that the browner lakes have more nutrients. But when we look back in time, we see that the lakes that are turning brown have similar nutrient levels to those. that they had before turning brown, ”Stetler mentioned. “This tells us that the processes that control nutrients in space and time differ from each other.”

To reach their conclusions, the research team conducted an extensive spatial survey, collecting data on carbon, nutrient levels in water, and light penetration into lakes across the country, and s’ is also turned to one of the few long-term datasets with similar information. , which was collected from 28 lakes in the Adirondack Mountains from 1994 to 2012.

The spatial survey provides insight into how nutrients change with browning and was based on samples the team collected from 38 lakes in New York City, Pennsylvania, and Minnesota, and data from 90 lakes in across the country collected as part of the 2012 National Environmental Protection Agency. Lake Assessment. These data showed that browner lakes indeed have higher nutrient levels than lighter lakes.

But the Adirondack Mountains data set showed that these nutrient amounts don’t change. Researchers found that nitrogen levels actually decreased, a likely result of the Clean Air Act. Meanwhile, phosphorus levels have not changed, a finding that could be due to changes in soil pH or the effects of global warming.

“In the Adirondacks and other northern areas, acid rain recovery has seen a simultaneous increase in dissolved organic matter flowing into surface waters. We were surprised to find that nitrogen and phosphorus levels do not increase with dissolved organic matter, ”said Charles Driscoll, co-author and professor at Syracuse University. “Since limiting nutrients can reduce the productivity of the lake, this observation has important implications for the future structure and function of these aquatic ecosystems.”

Stetler said the results, which revealed a discrepancy between data collected in a spatial survey and long-term recordings, underscore the need for long-term continuous monitoring. Biological field stations are often the cornerstone of long-term monitoring efforts, but given the difficulty in securing funding for monitoring efforts, long-term data is scarce.

“As is often the case, the true value of these long-term data sets is not fully realized until decades later,” Stetler said. “Although useful inferences can sometimes be obtained from spatial surveys, there is no substitution for long-term data.”


Good news for anglers: “browning” has less of an impact on fish than expected.


More information:
Jonathan T. Stetler et al. “The browning of lakes generates a spatio-temporal shift between dissolved organic carbon and limiting nutrients” Limnology and Oceanography Letters. aslopubs.onlinelibrary.wiley.c… i / 10.1002 / lol2.10194

Provided by the Rensselaer Polytechnic Institute


Quote: Browning could make lakes less productive, affecting food webs and fish (2021, May 31) retrieved May 31, 2021 from https://phys.org/news/2021-05-browning-lakes-productive -affecting-food.html

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