Robert B. Swanson1
Methods were developed to collect representative physical, chemical, and biological samples at 31 wetlands in the Platte River Basin from North Platte, downstream to the confluence with the Missouri River near Omaha, Nebraska, during May and August 1994. Transects were referenced with global positioning systems equipment and marked with iron pins. Ten equidistant points along the transect designated locations where samples were collected and composited. Water depth and air and water temperatures were measured and water-column samples were collected at each of these points, whereas bed material was collected at alternate points. A polytetra-fluoroethylene well bailer was used effectively for collecting undisturbed water-column samples as shallow as 2 cm. Wetland water columns consisting of standing water less than 2 cm deep were sampled with a polyethylene syringe and inlet tubing. Water-column samples were analyzed for nutrients, major ions, phytoplankton community composition, chlorophyll-a, and triazine herbicides; samples collected in August included analysis for trace elements at sites where tissue samples were collected for trace-element analyses. Dragonfly nymphs (Genus Anax) were collected for bioconcentrated trace-element analyses by sieving bed sediment and organic material though a fiberglass screen attached to a wooden frame. Bed-material samples were analyzed for triazine herbicides in May and for trace elements in August. The U.S. Geological Survey BMH-53 bed-material sampler was used to collect nutrient and herbicide samples in the substrate, and a polytetrafluoroethylene pipe was used to collect cores for trace-element analysis. A polytetrafluoroethylene or plastic spoon was used where dense organic matter in the substrate prohibited the use of other samplers. Qualitative macroinvertebrate and algae samples were collected from undisturbed areas near each transect. Vegetation was described at 1m intervals along two parallel plant transects one to two meters on either side of each water and bed-sediment sampling line.
