Wetlands hydraulics scaling analyses Part 1: External influences on mixing processes. Setember 1994.

Abstract

Littoral vegetation is a sink for nutrients and other pollutants in wetlands. Mechanisms by which this removal of pollutants occurs are poorly understood. However, the transport through the wetland is thought to play a significant role in the removal process. This assesses the order of magnitude of transport processes in wetlands subjected to external forcings. These processes were evaluated for a hypothetical "typical" wetland with features representative of existing constructed wetlands. The most important processes causing mixing are found to be wind effects, and penetrative convection. Rain may also cause significant mixing. However mean flow velocities, inflow and outflow processes seem to be of little importance. The processes expected to cause significant mixing occur intermittently rather than continuously, so transport of substances within wetlands will be characterised by quiscent periods, during which mixing is limited, interspersed with periods of moderate to severe mixing. Density stratification is expected to affect mixing processes significantly; building up under the influence of solar radiation according to diurnal and seasonal patterns, and breaking down by the intermittent mixing processes