Sometimes it's not good to be green

March 26, 2019

The good news is global and local. Keeping inland lakes from turning green means less greenhouse gases entering the atmosphere and contributing to climate change. Healthy drinking water, fishing and recreation opportunities are also increased when waters are not green.

What's wrong with being green? Toxins released by algal blooms can ruin drinking water. When dense algae blooms die, the bacteria that decompose the algae also deplete oxygen in the water. Without oxygen, fish and other animals suffocate. Globally, such green waters are also an important contributor to atmospheric methane -- a greenhouse gas that is up to 34 times more potent than carbon dioxide.

"We estimate that the greening of the world's lakes will increase the emission of methane into the atmosphere by 30 to 90 percent during the next 100 years," said Jake Beaulieu of the United States Environmental Protection Agency and lead author of a paper on lake greening and greenhouse gas emissions published March 26, 2019 in the journal Nature Communications.

According to the authors, three distinct mechanisms are expected to induce increases in lake greening or eutrophication during the next 100 years. First, human populations are expected to increase by 50 percent by 2100. More people means more sewage and more fertilizers that runoff land. At current rates of population growth and climate change, eutrophication in lakes will increase by 25 to 200 percent by 2050 and double or quadruple by 2100.

Second, increased storms and stormwater runoff will increase the nutrient losses from land to inland waters. Third, as the climate warms, lakes will warm. Warmer waters produce more algae. Additionally, the area of the planet covered in water is expected to increase, which will result in more methane-emitting surface waters.

"It is really surprising how much eutrophication could increase in the next 50 to 100 years," said co-author John A. Downing of the University of Minnesota Sea Grant program. "People do four important things that affect eutrophication: they eat, they excrete, they make more people who eat and excrete, and they alter landscapes and climate," said Downing.

Using projected population growth and climate change, the authors simulated the eutrophication of lakes under four different and conservative scenarios of future phosphorus loading from low to high: 80, 130, 170, 200, and 220 percent of current levels.

"We used phosphorus because the relationship between phosphorus and plant or algae growth is well established," said co-author Tonya DelSontro of the University of Geneva. "Currently, the single largest source of atmospheric methane is wetlands. If the phosphorus in lakes triples, then methane emissions from lakes could be twice that of wetlands."

The authors used a statistical model they created in 2018 that correlates methane emissions with lake size and chlorophyll, which is a measure of high algal biomass stimulated by phosphorus. By using global distribution of lake size and total lake area, climatic heating of lakes, future phosphorus concentrations and storm-driven nutrient runoff they were able to estimate future lake methane emissions, which the authors say has not been done before.

The optimistic outcome is that improved nutrient management practices could reverse the greening or eutrophication of lakes and thereby reduce methane emissions. Additionally, local action to improve water quality could have important global consequences.

"In keeping and improving the quality of our fresh water we win twice," said Downing. "Once in the atmosphere and once back down here on Earth."
-end-
Contacts: Jake J. Beaulieu, biologist, U.S. Environmental Protection Agency, Office of Research and Development, Cincinnati, Ohio. Beaulieu.Jake@epa.gov.

Tonya DelSontro, Research and Teaching Fellow, University of Geneva, tdelsontro@gmail.com, tonya.delsontro@unige.ch, +41.22.379.03.12.

John A. Downing, Director, Minnesota Sea Grant; Professor of Biology, Department of Biology and Scientist, Large Lakes Observatory, University of Minnesota Duluth; downing@d.umn.edu, 218.726.8715.

Marie Thoms, Communications and Public Relations, Minnesota Sea Grant, methoms@d.umn.edu, office: 218.726.8710, mobile: 907.460.1841, @MNSeaGrant. http://www.seagrant.umn.edu

University of Minnesota

Related Climate Change Articles from Brightsurf:

Are climate scientists being too cautious when linking extreme weather to climate change?
Climate science has focused on avoiding false alarms when linking extreme events to climate change.

Mysterious climate change
New research findings underline the crucial role that sea ice throughout the Southern Ocean played for atmospheric CO2 in times of rapid climate change in the past.

Mapping the path of climate change
Predicting a major transition, such as climate change, is extremely difficult, but the probabilistic framework developed by the authors is the first step in identifying the path between a shift in two environmental states.

Small change for climate change: Time to increase research funding to save the world
A new study shows that there is a huge disproportion in the level of funding for social science research into the greatest challenge in combating global warming -- how to get individuals and societies to overcome ingrained human habits to make the changes necessary to mitigate climate change.

Sub-national 'climate clubs' could offer key to combating climate change
'Climate clubs' offering membership for sub-national states, in addition to just countries, could speed up progress towards a globally harmonized climate change policy, which in turn offers a way to achieve stronger climate policies in all countries.

Review of Chinese atmospheric science research over the past 70 years: Climate and climate change
Over the past 70 years since the foundation of the People's Republic of China, Chinese scientists have made great contributions to various fields in the research of atmospheric sciences, which attracted worldwide attention.

A CERN for climate change
In a Perspective article appearing in this week's Proceedings of the National Academy of Sciences, Tim Palmer (Oxford University), and Bjorn Stevens (Max Planck Society), critically reflect on the present state of Earth system modelling.

Fairy-wrens change breeding habits to cope with climate change
Warmer temperatures linked to climate change are having a big impact on the breeding habits of one of Australia's most recognisable bird species, according to researchers at The Australian National University (ANU).

Believing in climate change doesn't mean you are preparing for climate change, study finds
Notre Dame researchers found that although coastal homeowners may perceive a worsening of climate change-related hazards, these attitudes are largely unrelated to a homeowner's expectations of actual home damage.

Older forests resist change -- climate change, that is
Older forests in eastern North America are less vulnerable to climate change than younger forests, particularly for carbon storage, timber production, and biodiversity, new research finds.

Read More: Climate Change News and Climate Change Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.