Channel Adjustment and Floodplain Development Following Dam Removal

Abstract

Dam removal is being used to experimentally investigate hydrologic, geomorphic and ecological links in streams, particularly riparian vegetation and floodplain wetlands as mediated by channel adjustment. Damming leads to accumulation of organic matter and nutrient-rich sediments and altered hydrology and geomorphology. Following dam removal, altered hydraulics will drive upstream channel evolution which will determine the spatial relationship between the channel and the floodplain. Channel wetted perimeter will decrease exposing nutrient-rich sediments for floodplain ecosystem succession. In this paper preliminary results are shown from an experimental dam removal. Due to the progress of the dam removal particular emphasis will be focused on the fate of interstitial nutrients within the developing floodplain and floodplain plant community succession. Initial data show floodplain wetland interstitial water N and P concentrations 10-20X greater than adjacent surface water which initially will likely compromise floodplain nutrient retentive capacity. Here, floodplain nutrient retentive capacity is defined as the system’s ability to attenuate surface water nutrient concentrations during flood events. Secondary succession is primarily measured using biomass of macrophytes (AFDM) and benthic algae (chl a), and within the rooting-zone using fungal biomass and bacterial productivity. Field nutrient data from the floodplain wetland are being collected throughout the successional process (surface water, interstitial and sediment surface). In addition to the field studies, development of floodplain retentive capacity is being simulated via floodplain wetland mesocosms within a greenhouse under variable hydrologic conditions in the presence and absence of wetland floodplain vegetation. These contrasting experimental techniques will elucidate fundamental links between geomorphology, hydrology, and ecosystem processes in streams, as well as provide novel data on environmental response following dam removal.