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 that 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 year^-1 and consumption from 0.44 to 1.47 Pg year^-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.