HR: 08:30h
AN: NB31D-01 INVITED     [Abstracts]
TI: Hydrologic Control of Nitrate Loading and Transformation in Backwater Lakes of the Upper Mississippi River
AU: * Richardson, W
EM: wrichardson@usgs.gov
AF: US Geological Survey, Upper Midwest Environmental Sciences Center, 2630 Fanta Reed Rd, La Crosse, WI 54603 United States
AU: James, W
EM: jamesw1@svtel.net
AF: US Army Corps of Engineers, Eau Galle Limnological Research Lab, 250th St., Spring Valley, WI 54767 United States
AU: Strauss, E
EM: estrauss@usgs.gov
AF: US Geological Survey, Upper Midwest Environmental Sciences Center, 2630 Fanta Reed Rd, La Crosse, WI 54603 United States
AU: Bartsch, L
EM: lbartsch@usgs.gov
AF: US Geological Survey, Upper Midwest Environmental Sciences Center, 2630 Fanta Reed Rd, La Crosse, WI 54603 United States
AU: Cavanaugh, J
EM: jcavanaugh@usgs.gov
AF: US Geological Survey, Upper Midwest Environmental Sciences Center, 2630 Fanta Reed Rd, La Crosse, WI 54603 United States
AB: Floodplain backwater lakes (BWL) are biogeochemically active with potential to remove large quantities of transported nitrate (NO₃^-) from the Upper Mississippi River. We measured nitrate transformations in BWL receiving high NO₃^- water under natural flooding and controlled inflow conditions to determine: 1) patterns of NO₃^- loss; 2) biogeochemical processes affecting NO₃^- transformation; and 3) effect of loading rate on removal capacity. In a large (300 ha) BWL, floodwater NO₃^- concentrations dropped from 6.5 to < 0.5 mg-N L^-1 in 12 d, with a loss of >18 tons-N. Under controlled inflow another BWL (Third Lake, 15 ha) exhibited high rates denitrification (22 μg-N cm^-2 d^-1), limited by NO₃^- loading and tightly coupled with nitrification. Nitrate retention was linear with load (r²=0.95), with greatest retention occurring in late June. An average of 48 kg - N d^-1 NO₃^- was removed from Third Lake (43 % of total inflow load, 32 % via denitrification). These results show NO₃^- removal from backwater lakes is directly related to river-flood plain connectivity, river discharge, and NO₃^- loading rate. Engineered reconnection of backwaters to main channels could reduce downstream flux of NO₃^- while also restoring other ecologic functions and meeting multiple management goals.
DE: 0400 Biogeosciences
DE: 1806 Chemistry of fresh water
DE: 1821 Floods
DE: 1845 Limnology
DE: 1871 Surface water quality
SC: North American Benthological Society [NB]
MN: 2005 Joint Assembly