Quantifying lake allochthonous organic carbon budgets using a simple equilibrium model

We quantify the allochthonous organic carbon (OC) budgets for seven north temperate lakes, using diverse information about their land cover, hydrology, and limnological characteristics. We develop a simple equilibrium model within a Bayesian framework that exploits the differences among the lakes to estimate three key rates: aerial loading (A(OC)) and wetland loading (W-OC) from adjacent ecosystems and whole-lake mineralization of OC (RDOC). Combined with observational data, these rates allow for estimates of the total OC loads, mineralization, and sedimentation within lakes and export to downstream ecosystems. A(OC) was 1.15 g C m(-1) (shoreline) d(-1), W-OC ranged from 0.72 to 3.00 g C m(-1) (shoreline) d(-1), and RDOC, normalized to 20 degrees C, ranged from 0.00083 to 0.0015 d(-1). Total loads ranged from about 5 to 55 g C m(-2) yr(-1). Ecosystems immediately adjacent to lakes accounted for one-half or more of total OC loads for some lakes. Whether a lake processed and stored more allochthonous OC than it exported depended primarily on hydrologic residence time. Our equilibrium model provides a parsimonious approach to quantifying allochthonous OC budgets in lakes with relatively minimal baseline data.