Predicting alterations in organic matter dynamics due to global change in freshwater ecosystems

Freshwater ecosystems are important sites for carbon storage and processing and can contribute significantly to the global carbon cycle.  However, global environmental changes, such as increased nutrient mobilization, rising surface temperatures, and altered biotic diversity and hydrology, are predicted to alter carbon processing rates and storage potentials. Other ubiquitous aspects of global change, including land-use change and elevated CO_2, further alter carbon dynamics through changes in the quality (e.g., low nutrient to carbon content) and quantity of detrital inputs. Our synthesis of the literature suggests that net directional change in organic matter dynamics due to global change will result in 1) reduced inputs and reach-scale retention of organic matter, 2) modified rates of export of detritus to the oceans (strongly affected by reservoirs), and 3) increased losses of organic matter via increased processing rates and respiration. Largely because of predicted reduced quantity and quality of organic matter inputs, overall system dependence on detrital pathways is likely to be reduced based on current and accelerated rates of global change.  Additionally, global change may indirectly reduce carbon flow to higher trophic levels and increase atmospheric carbon concentrations as a larger proportion of available carbon is predicted to be lost to microbial respiration.