Simulation of the effects of nutrient enrichment on nutrient and carbon dynamics in a river marginal wetland

A computer simulation model was built to investigate the interactions of ca rbon, nitrogen and phosphorus in a riverine wetland, and to simulate the ef fects of management and other human influences in or outside the wetland on nutrient-related functions, such as nutrient retention or transformation. The purpose of this study was to examine the usefulness of the model in pre dicting the effects of nutrient enrichment on the system. This was done by performing a computer simulation of a fertilisation experiment and comparin g the results with a field fertilisation experiment that was performed at t he same site that the model simulated. The model simulations increased the understanding of the functioning of the system, but did not accurately pred ict the results of the field experiment. Both the field experiment and the model simulations indicated co-limitation of plant growth by N and P, but t he model simulations predicted a far greater role for N than was found in t he field experiment. This is likely due to the fact that environmental cond itions in the field at the time of the experiment were not exactly the same to those in the computer simulation, because of (1) probable losses of app lied N due to high denitrification during peak weather events in the field, and (2) the fact that the computer simulation is based on measurements of a larger area than the area in the held experiment. Furthermore, the field experiment showed a greater role for P limitation than could be explained b y the model; according to the model (which is based on experimental phospha te adsorption isotherms of the local soil, and held measurements), there is ample P in the soil. This could mean that P isotherms determined in a labo ratory do not give a true picture of the situation in the field. In the fie ld experiment it was difficult to find effects of the added N and P on the size of labile or more refractory soil nutrient pools due to the high heter ogeneity of the soil. Long term computer simulations showed a strong accumu lation of added N and P. Added N accumulated mainly in soil organic matter. Added P accumulated in the soil pool of adsorbed phosphorus. The nutrient accumulations predicted are in accordance with the nutrient storage functio n that have often been found in wetland studies, though sometimes a more ra pid P saturation has been found or expected. (C) 2000 Elsevier Science B.V. All rights reserved.