Oh, In Case You Were Wondering, Rivers & Lakes Are Acidifying Too
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In the new study researchers reported a significant increase of CO2 and a correlating pH decrease of about 0.3 in four reservoirs in Germany over 35 years. They analyzed data collected from 1981 to 2015 by the local Ruhr region agency that monitors drinking water, and were able to document the rising carbon dioxide levels over time by factoring in changes in temperature, water density, pH, ion species distribution and total inorganic content.
A crucial reason why the study of freshwater acidification has lagged until now is because determining how atmospheric carbon affects these ecosystems requires complex modeling, and is much less clear than that occurring in oceans, according to study author Linda Weiss, an aquatic ecologist at Ruhr University Bochum in Germany. In oceans CO2 from the atmosphere dissolves into seawater’s surface, forming carbonic acid. Freshwater such as lakes, though, receive various sources of carbon dioxide from decomposing organic and inorganic matter swept into them, which makes it hard for scientists to distinguish between the direct effects of rising atmospheric CO2 and these other elements.
Carbon dioxide levels in lakes are often high and vary widely from lake to lake based on factors such as the type of nearby ecosystem, land use such as agriculture, sizes of the lake and watershed, amount of precipitation, and because some types of soils and rocks absorb more CO2 than others. Levels of CO2 also shift seasonally, changing as leaves drop in fall and ice forms in winter or as animals go through their life cycles, and even daily, rising at night due to temperature changes and algae’s inability to photosynthesize at night. All of this makes it harder to discern long-term trends. The data set Weiss used was unusual in that it monitored these myriad factors over the 35-year period, allowing the researchers to conclude the increase in CO2 they saw in the reservoirs was indeed due to increased carbon dioxide in the atmosphere.
The primary way freshwater ecosystems absorb CO2 created by humans burning fossil fuels is likely different than what happens in oceans. In lakes and reservoirs the extra atmospheric CO2 feeds the surrounding vegetation and the rising global temperature lengthens the growing season. As plants in and around the lake grow larger and/or proliferate, the amount of organic carbon available when they die and the rate at which they break down in soil increases. Precipitation then washes it into lakes and other freshwater systems.
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https://www.scientificamerican.com/article/like-oceans-freshwater-is-also-acidifying/
