HR: 1400h
AN: H33B-06    [Abstracts]
TI: Nitrogen Dynamics Along a Headwater Stream Draining a Fen, Swamp, and Marsh in a Fractured Dolomite Watershed
AU: * Duval, T P
EM: duvaltp@mcmaster.ca
AF: School of Geography and Earth Sciences, McMaster University, 1280 Main St W, Hamilton, ON L8S 4K1, Canada
AU: Waddington, J M
EM: jmw@mcmaster.ca
AF: School of Geography and Earth Sciences, McMaster University, 1280 Main St W, Hamilton, ON L8S 4K1, Canada
AB: Stream-wetland interaction has been shown to have a significant effect on nutrient cycling and downstream water quality. Additionally, connection to regional groundwater systems can dilute or enrich stream water with a number of dissolved constituents. This study demonstrates the resultant downstream change in dissolved nitrogen species as a hardwater stream emerges from a calcareous aquifer and traverses a calcareous fen, a cedar swamp, and a cattail marsh over two growing seasons, a very dry 2006 and a very wet 2007. Upon emergence at a number of groundwater seeps, the water contained appreciable nitrate levels averaging 2.72±0.42 mg NO₃-N L^-1, minimal organic nitrogen, and ammonium below detectable levels. Through the gently sloping calcareous fen, with a stream residence time of ~ 5 hours, NO₃-N concentration decreases of 0.35 mg L^-1 were observed. Concomitantly, stream recharge into the dolomite bedrock depressed stream discharge values significantly, further removing nitrate from the stream system. This resulted in the fen-bedrock system acting as an estimated net sink of 432 kg of NO₃-N in the early summer of 2007, for example. In contrast, the hydrological-biogeochemical systems became decoupled through the swamp during the same period, where concentrations increased from 2.58±0.34 mg L^-1 entering the swamp to 2.65±0.58 mg L^-1 exiting, but streamflow decreased in general by 5 L s^{- 1}. This resulted in the swamp, with its large depression storage, acting as a small net sink of nitrate (75 kg through the early summer), which would not be detected simply from concentration changes. The concentration-discharge relation realigned through the marsh, where significant groundwater entered the wetland, increasing both concentration and discharge, yielding a small export of 93 kg over the same time period. A series of tracer injections in each wetland type will be presented to compare the streamflow- concentration patterns with the measured nutrient spiralling. This research highlights the complexity of surface-groundwater interactions and multiple landscape elements on the resultant downstream fate and transport of nutrients.
DE: 0469 Nitrogen cycling
DE: 0497 Wetlands (1890)
DE: 1830 Groundwater/surface water interaction
DE: 1871 Surface water quality
DE: 1879 Watershed
SC: Hydrology [H]
MN: 2009 Joint Assembly