Lateral flow routing into a wetland: Field and model perspectives

As part of a plant succession/landscape ecology study of small, confined, emergent wetlands (boreal beaver meadows in northern Minnesota), we carried out an investigation of diffuse lateral flow of water and nutrients into the wetland from the local forested upland catchment. These local catchments may be very small (5-15 ha); flow routing is rarely considered at such a fine scale. Tape and compass surveying methods were successfully combined with GPS reference points to construct a detailed (10×10-m resolution) map of upland topography and vegetation. Analysis and modeling software were developed to trace flow from the local catchment into the meadow. Simplistic flow routing algorithms (D8) predicted uniform sheet flow with many artifacts in the predicted flow pattern, whereas a more sophisticated procedure (DEMON) suggested multiple hot spots of lateral input into the meadow along its perimeter. The flow model incorporated storage based on cover type. When considering the importance of flow from different zones in the catchment area, a simultaneous simulation of all flow to the meadow was found to be necessary to avoid serious execution order dependence. A number of edge flow collection devices were designed and installed. Collectors trapped flow across 2-3 m of meadow perimeter, and after rainfall, depending on placement, recorded flow values typically between 0 and 5-20 l/day, with peak flows in excess of 100 l/day. Concentrated points of water and nutrient input into the meadows may have a role in plant distribution and diversity.