A modeling approach to couple leaf decomposition and nutrient dynamics in forested headwater streams

We synthesized previous studies of nutrient processes in streams at Coweeta to construct a series of decomposition models for Hugh White Creek in Coweeta, a stream dominated by heterotrophic processes.  The models simulated the biotic processes affecting dissolved nutrients and leaf detritus and predicted nutrient dynamics in stream, as well as detritus dynamics and microbial pool.  In our models, we consider two mechanisms of nutrient acquisition by microbes: immobilization and mining.  Microorganisms use nutrients from stream water as the secondary nutrient source when immobilization predominates, while in mining they obtain nutrients from the leaves by increasing the decay rate and respiring the excess carbon.  Numerical solution of the model is accomplished using the fractional-steps method and simulated with parallel processing.  Simulated nutrient concentration patterns were similar to observed patterns.  Nutrient mining by microbes may be important when nutrients limit decomposition.  It is also important to consider different quality components of leaf material for predicting nutrient dynamics in the late stage of decomposition.