In rivers, the microbial loop explains how microbes oxidize DOC to obtain energy making carbon available to higher trophic levels in the river foodweb. DOC biodegradability, however, is variable depending on its source. Its concentrations and quality can be affected by allochthonous sources, but can also be affected by anthropogenic sources such as wastewaters and runoff from urban or agricultural areas. Anthropogenic carbon inputs to rivers can increase the concentration of labile DOC (Balakrishna, 2006).