A recent study conducted by UMass Dartmouth School of Marine Science and Technology (SMAST) Dean Steven Lohrenz and an international team of scientists concludes that rising levels of atmospheric carbon dioxide, the compound that is emitted by coal plants and gasoline-burning automobiles, may act together with high nutrient run-off to damage coastal ocean habitats.
Low oxygen in bottom waters associated with high nutrient run-off has long been a concern in many coastal areas and is viewed as a threat to coastal fisheries. As high levels of nitrogen are flushed into the ocean by rivers, this can cause eutrophication -- the process of excessive plant growth and eventual depletion of oxygen -- in bottom waters as plants settle and decay, leaving too little oxygen for wildlife to survive. Now, according to the study published this week in Nature Geosciences, it appears that the combination of eutrophication-induced depletion of oxygen in ocean bottom waters and increasing levels of carbon dioxide absorbed from the atmosphere may be accelerating a condition known as ocean acidification.
"It's a double whammy," said Dr. Steven Lohrenz, dean of SMAST. "Ocean acidification is a condition that threatens many forms of marine life, including commercially important species of shellfish and other creatures that feed on them. This work provides some of the first evidence for a compounding effect of coastal eutrophication and rising atmospheric carbon dioxide levels on ocean acidification. This combination can push conditions to the edge of the natural ability of ocean waters to buffer changes to these fragile habitats."
The study was conducted in the Gulf of Mexico and South China Sea where the Mississippi River and the Changjiang (or Yangtze) River empty, respectively. While the study focused on the Gulf of Mexico and South China Sea ecosystems, the results have broader implications for other coastal zones including those in New England where increasing levels of nutrients are being released into the ocean. Given expectations that atmospheric carbon dioxide levels will continue to rise in the near future, the study predicts dramatic increases in ocean acidification in bottom waters with uncertain consequences for marine life. Future work will be needed to better understand the impacts on living marine resources and to develop strategies to manage or mitigate these impacts.
Besides Dr. Lohrenz, the scientific team included the following:
University of Georgia: Wei-Jun Cai, Xinping Hu, Wei-Jen Huang, James T. Hollibaugh, Yongchen Wang, Pingsan Zhao, Xianghui Guo.
Environmental Protection Agency, Gulf Breeze, Florida: Michael C. Murrell & John C. Lehrter.
National Taiwan Ocean University: Wen-Chen Chou, Gwo-Ching Gong
Xiamen University, China: Weidong Zhai, Xianghui Guo, Minhan Dai.
University of Southern Mississippi, Stennis Space Center: Kjell Gundersen.
National Taiwan Ocean University: Gwo-Ching Gong.