HR: 0800h
AN: H51B-0441    [Abstracts]
TI: Benthic Fluxes of Dissolved Macro- and Micronutrients to the Water Column of Upper Klamath Lake, Oregon
AU: Kuwabara, J S
EM: kuwabara@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Road, MS439, Menlo Park, CA 94025, United States
AU: * Topping, B R
EM: btopping@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Road, MS439, Menlo Park, CA 94025, United States
AU: Lynch, D D
EM: ddlynch@usgs.gov
AF: U.S. Geological Survey, 2130 SW Fifth Avenue, Portland, OR 97201, United States
AU: Murphy, F
EM: fmurphy@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Road, MS465, Menlo Park, CA 94025, United States
AU: Carter, J L
EM: jlcarter@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Road, MS465, Menlo Park, CA 94025, United States
AU: Lindenberg, M
EM: mlinden@usgs.gov
AF: U.S. Geological Survey, 2795 Anderson Avenue, Suite 106, Klamath Falls, OR 97603, United States
AB: Hypoxic, environmentally stressful conditions for endangered fish populations have been generated over the past century by an annual phytoplankton bloom in Upper Klamath Lake, OR. The bloom is consistently dominated by the nitrogen-fixing cyanophyte Aphanizomenon flos–aquae (AFA), thus a quantitative understanding of processes affecting the transport of biologically available phosphorus (P), presumably the limiting nutrient, is critical for resource management in the lake. This work was undertaken to help develop sound remediation or restoration strategies, and to set realistic expectations for water-quality improvements. Particle-reactive phosphate can adsorb or complex onto particles that settle and accumulate in the lake bed. Biogeochemical processes near the sediment-water interface can remobilize particle-bound P and generate a benthic flux of bioavailable P. This study provides estimates of the benthic flux of dissolved macronutrients (i.e., phosphorus and nitrogen species) before, during and after the period of: (1) increased water-column nutrient concentrations that cannot be accounted for by riverine inputs, and (2) the annual bloom of AFA. Benthic flux of dissolved orthophosphate was consistently positive (i.e., out of the sediment into the overlying water column) and ranged between 0.5 and 6.1 mg m^-2 d^-1. Assuming a lake area of 200 km², this converts to a mass flux to the entire lake of 8,000 to 100,000 kg over a 3-month AFA bloom season which is comparable in magnitude to riverine inputs. An additional concern related to fish toxicity was that dissolved ammonium also displayed consistently positive benthic fluxes of 4 to 100 mg m^-2 d^-1; also comparable to riverine inputs. In contrast, dissolved nitrate exhibited a consistently negative flux (consumed by the sediment) with values ranging between -20 to -0.1 mg m^-2 d^-1. Macroinvertebrate densities of the order of 10⁵ individuals-m^-2 suggest that the diffusive-flux estimates may be significantly lower than actual values due to bioturbation. Although phosphorus is a logical choice for the limiting nutrient when nitrogen-fixing cyanophytes dominate, initial trace-metal results in the form of coordinated benthic flux, water-column and tributary-inlet data suggest that iron availability to primary producers in the lake is possibly a limiting factor.
UR: http://wwwrcamnl.wr.usgs.gov/solutetransport/index.htm
DE: 1806 Chemistry of fresh water
DE: 1845 Limnology (0458, 4239, 4942)
DE: 1871 Surface water quality
DE: 4804 Benthic processes, benthos (0408)
DE: 4845 Nutrients and nutrient cycling (0470, 1050)
SC: Hydrology [H]
MN: 2007 Fall Meeting