Modelling dissolved organic carbon turnover in humic Lake Ortrasket, Sweden

The organic carbon balance of a lake with high input of allochthonous organ ic carbon is modelled integrating physical, chemical and biological process es. The physical model captures the behaviour of real thermal stratificatio n in the lake for different flow situations during the period 1993-1997. Th e dissolved organic carbon model is based on simulated trajectories of wate r parcels. By tracking parcels, account is kept of environmental factors su ch as temperature and radiation as well as DOC quality for each parcel, The DOC concentration shows seasonal variations primarily dependent on inflow. The organic matter degradation (bacterial- and photodegradation) in the la ke amounts to 1.5-2.5 mg C l(-1) yr(-1), where photooxidation is responsibl e for approximately 10%. The estimated DIC production in the lake is large compared to sediment mineralisation and primary production. The main conclu sion is that the model with the selected parameterisations of the degradati on processes reasonably well describes the DOC dynamics in a forest lake.