Dissolved organic carbon (DOC) is defined as the organic matter that is able to pass through a filter (filters generally range in size between 0.7 and 0.22 um). Conversely, particulate organic carbon (POC) is that carbon that is too large and is filtered out of a sample. If you have ever seen a body of water that appears straw, tea, or brownish in color, it likely has a high organic carbon load. This color comes from the leaching of humic substances from plant and soil organic matter. This organic matter contributes acids to the stream, resulting in the yellow-brown coloration as well as weathering the soils. Organic carbon can be allochthonous, or sourced from outside the system (e.g. by atmospheric deposition or transported long distances via stream flow) or it can be autochthonous, or sourced from the immediate surroundings of the system (e.g. plant and microbial matter and sediments/soils within the catchment). High amounts of organic matter are common in low oxygen areas, such as bogs and wetlands.