Fundamental processes within natural and constructed wetland ecosystems: short-term versus long-term objectives

Use of wetland ecosystems for water pollution control consists essentially of sustained induced disturbances as pollutants are loaded to complex biological communities. Objectives are to maximize pollutant loading, incorporation, and retention while maintaining highest levels of community metabolism and minimal alteration of community structure. Several basic processes are emphasized: (a) macrophyte productivity in relation to shoot:root ratios, and nutrient availability; (b) macrophyte life history strategies, succession, and biodiversity under constant pollutant stress; (c) importance of standing dead and particulate detritus; (d) functions and controlling mechanisms of heterotrophic and autotrophic periphyton in pollutant retention and recycling; (e) coupling of microbial metabolism to macrophyte retention of pollutants; (f) gaseous losses to the atmosphere; (g) losses of dissolved organic matter and its utilization; and (h) water losses by evapotranspiration and effects on wetland efficacy. Short-term wetland removal efficiencies are confounded by massive variations in retentive capacities diurnally, seasonally, and spatially, in exceeding physiological tolerance levels, and in species succession. Problems of channelization, altered microhydrology, and assimilation/retention are major in natural and non-engineered ecosystems. Wetlands are highly ephemeral and variable in their capabilities for sequestering and retention of nutrients and other pollutants.