Use of geomorphic, hydrologic, and nitrogen mass balance data to model ecosystem nitrate retention in tidal freshwater wetlands

[摘要] Geomorphic characteristics have been used as scaling parameters to predict water and other fluxesin many systems. In this study, we combined geomorphic analysis with in-situ mass balance studiesof nitrate retention (NR) to evaluate which geomorphic scaling parametersbest predicted NR in a tidal freshwater wetland ecosystem. Geomorphiccharacteristics were measured for267 individual marshes that constitute the freshwater tidal wetland ecosystem of the PatuxentRiver, Maryland. Nitrate retention was determined from mass balance measurements conducted at theinlets of marshes of varying size (671, 5705, and 536 873 m²) over a period of severalyears. Mass balance measurements indicate that NR is proportional to total water flux over thetidal cycle. Relationships between estimated tidal prism (calculated water volume) for spring tides andvarious geomorphic parameters (marsh area, total channel length, and inletwidth) were defined using measurements from air photos and compared to fielddata. From these data, NR equations were determined for each geomorphicparameter, and used to estimate NR for all marshes in the ecosystem fora reference spring (high) tide. The resulting ecosystem NR estimates wereevaluated for (a) accuracy and completeness ofgeomorphic data, (b) relationship between the geomorphic parameters and hydrologic flux, and (c)the ability to adapt the geomorphic parameter to varying tidal conditions. This analysis indicatedthat inlet width data were the most complete and provided the best estimate of ecosystem nitrateretention. Predictions based on marsh area were significantly lower than the inlet width-basedpredictions. Cumulative probability distributions of nitrate retention indicate that the largest3–4% of the marshes retained half of the total nitrate for the ecosystem.

[学科分类] 地球化学与岩石