A Model of Carbon and Nitrogen Dynamics for Temperate Grasslands and Forests

In the last two decades, the importance of hydrological processes for ecosystem dynamics and the effects of plants on hydrological processes has become increasingly apparent. A better understanding of the relationship between plant growth (carbon and nitrogen distribution) and the hydrological characteristics of a catchment would improve ecological assessments and management of forests and grasslands.

TOPDNDC, developed for this study, is a detailed, semi-distributed, quantitative, ecohydrological model for predicting carbon and nitrogen dynamics in small temperate catchments. TOPDNDC establishes an explicit linkage between the biogeochemical process and the hydrology of catchments using the well-known and tested biogeochemical model DNDC and hydrological model TOPMODEL. The new model’s ability to predict is assessed against field data.

The TOPDNDC computer model does not require use of high performance computers or large and expensive datasets, but it allows investigation in detail of how the locations and spatial patterns of biogeochemical processes shift across watershed topography in response to antecedent conditions and multiple temporal scales.

Application of the model to annual biomass production from a grassland shows very good agreement with the field data. The temperate forest simulation showed lesser agreement with field data collected along a transect in a watershed, but was able to reproduce the same patterns found in the field and with high correlations. The difference in the results between the grassland and forest simulations may result, in part, from the intentionally simple link between the lateral and vertical water distribution components of the model.