Causes and consequences of changing oxygen availability in lakes

Abstract

Changing oxygen availability in lakes and reservoirs is a fundamental limnological challenge of our time, with massive consequences for freshwater ecosystem functioning and water quality. Cross-lake surveys, paleolimnological studies, and long-term monitoring records indicate that many lakes are exhibiting declines in both surface and bottom-water oxygen availability due to climate and land use change, though a few lakes are exhibiting increases in oxygen. By analyzing time series of oxygen monitoring data from ~400 lakes, I find that some lakes may be experiencing a decoupling of surface and bottom oxygen dynamics: variability in surface oxygen concentrations is decreasing in some lakes while variability in bottom oxygen concentrations is increasing. Changes in both oxygen concentrations and variability have many implications for lake functioning because oxygen concentrations control many ecosystem processes. Consequently, lake ecosystem provisioning and cultural services (e.g., drinking water, fisheries, recreation) will likely be impaired by declining oxygen, whereas the effects of changing oxygen on regulatory and supporting ecosystem services (e.g., nitrate removal through denitrification,

Reduced greenhouse gas emissions from particulate organic matter degradation in iron-enriched sediments

“…Shallow, polymictic, and eutrophic lakes in such a system (in the Spree, Lake Neuendorfer See, Lake Glower See and Lake Müggelsee) could therefore be strong emitters of greenhouse gases, particularly when fresh POM, for example aer algal blooms in spring/summer and leaf litter input in autumn, is not permanently buried in deeper zones with lower microbial activity. 15,90 Additionally, during more pronounced anoxic phases in summer that can be anticipated with ongoing climate change, 98 CH 4 emissions might also increase considerably relative to CO 2 emissions. Already today, freshwater systems are releasing more CH 4 than oceans, even though they only cover approximately 3% of the Earth's surface.…”