A comparative study of nitrogen and phosphorus cycling in tidal and non-tidal riverine wetlands

This paper describes a study of nutrient dynamics in 17 tidal and non-tidal freshwater riverine wetlands in The Netherlands, Belgium, and Maryland (US A). The purpose of the study was to investigate the relationships between n utrient cycling processes in riverine wetlands that were geographically sep arated, that were dominated by different types of vegetation, and that had different hydrodynamics We also compared restored and natural riverine wetl ands. The results showed distinct differences in interstitial water chemist ry between the sites in Maryland and Europe. No such regional differences w ere found in the soil variables, except for soil phosphorus, which was high er in The Netherlands. Soil organic matte, total nitrogen and phosphorus co ntent, and bulk density were higher in tidal freshwater wetland soils. Fore sted wetland soils had higher organic matter and total nitrogen and lower b ulk density and total phosphorus than soils from wetlands dominated by herb aceous species. Restored wetlands had lower soil organic matter and total s oil nitrogen and phosphorus than similar types of natural riverine wetlands . There were no differences in nutrient-related process rates nor plant nut rient concentrations in tidal versus non-tidal riverine wetlands. Lower nit rogen and phosphorus concentrations in plants at the restored sites suggest that nutrient uptake by vegetation may be poorly coupled to rates of nutri ent cycling during early stages of vegetation development. A principal comp onents analysis of the data identified groupings of soil and water variable s that were similar to those that had been previously identified when we ap plied the same methods to peatlands that were also geographically widely se parated. Results of the study demonstrate that the techniques that we have been using are robust and repeatable. They are especially useful for making general comparisons of nitrogen and phosphorus cycling when there are limi tations on the number of wetland that can be sampled. The approach that we have developed may also be used to calibrate and refine nutrient cycling mo dels that are incorporated into wetland assessment procedures.