Hydrologic control of dissolved organic matter in low-order Precambrian Shield Lakes

Concentrations of dissolved organic carbon (DOG) and color were measured as a function of time in enclosures and lakes at the Experimental Lakes Area, to calculate their net loss rates. Loss rates in enclosures were first order for both DOC and color, with half-times for loss of 166 and 122 d, respectively. Thus, the colored, light-attenuating component of the DOC pool is lost from water more rapidly than is bulk DOG. Loss rates in lakes, calculated from a steady state model, were similar to values for color in enclosures, but for DOC in lakes were four times slower than in enclosures. In lakes, loss rate for DOC increased rapidly with decreasing water residence time (tau(w)) but was independent of tau(w) when it was greater than 3 years. In lakes, the loss rate for color was independent of water residence time. The difference in losses of DOC and color between lakes and enclosures could be from release of low-color DOC from sediments.