Global inland-water oxygen cycle has changed in the Anthropocene

Inland waters are an important resource, a highly diverse habitat, and a key component of global biogeochemical cycles. Oxygen plays a major role in inland-water ecosystem functioning, but long-term changes in its cycling remain unknown. Here we quantify global inland-water oxygen production, consumption, and exchange with the atmosphere during 1900-2010 using a spatially-explicit, mass-balanced, mechanistic model which takes into account changes in climate, hydrology, human activities, and the coupled biogeochemical (oxygen-nutrient-organic matter) dynamics. The model results show that global inland-water oxygen turnover increased during 1900-2010: production from 0.16 to 0.94 Pg yr-1 and consumption from 0.44 to 1.47 Pg yr-1. Inland waters overall remained heterotrophic and a sink of atmospheric oxygen. Direct human perturbations (changes in hydrology and nutrient supply) were more important in increasing oxygen turnover than indirect effects via warming.