A low-cost three-dimensional sample collection array to evaluate and monitor constructed wetlands

Artificially constructed wetlands are gaining acceptance as a low-cost treatment alternative to remove a number of undesirable constituents from water. Wetlands can be used to physically remove compounds such as suspended solids through sedimentation. Dissolved nutrients, biochemical oxygen demand, heavy metals, and potentially harmful anthropogenic compounds can all be removed in constructed wetlands through geochemical and biological processes. Sample collection to evaluate the effectiveness of treatment and to monitor the status of wetlands is usually only conducted at the inlet and outlet of the wetland due to cost constraints. To better understand the internal hydrology and biogeochemical processes operating within the wetland more intensive sampling is needed that does not interfere with the hydraulics of the system. A new relatively low-cost sample collection design has been developed using mostly off-the-shelf parts that allows for permanent, internal, three-dimensional sample collection in wetlands. The design has been used to construct a permanent three-dimensional array of 60-sample locations that can be sampled simultaneously throughout a 1.2 ha constructed wetland for less than US$ 5000. The sampling array was used in a tracer study and showed spatial and temporal differences in tracer concentration within the wetland. Concentration differences were seen and measured in all three dimensions. The basic features of the system are described and an example how to construct an array that can suit any wetland design is given.