HR: 0800h
AN: H41F-0346    [Abstracts]
TI: Techniques for Interpretation of Shallow Lake Metabolism
AU: * Pugh, H E
EM: heather.pugh@uconn.edu
AF: University of Connecticut, Department of Marine Sciences 1080 Shennecossett Road, Groton, CT 06340-6097 United States
AU: Torgersen, T
EM: thomas.torgersen@uconn.edu
AF: University of Connecticut, Department of Marine Sciences 1080 Shennecossett Road, Groton, CT 06340-6097 United States
AB: In shallow lakes, nutrients come from two sources; aerobic respiration in the water column and anaerobic respiration processes (by HNO$_{3}$ and Fe$_{2}$O$_{3}$) typically in the sediments. Because of the water column and sediment reactions, the net observable change in oxygen and carbon dioxide in the shallow lake may or may not follow the Redfield Ratio of -138O$_{2}$:106C. We define the Process Ratio (PR) as the rate of change in dissolved oxygen concentration divided by the rate of change in total dissolved inorganic carbon (TDIC) concentration. The PR can be used to evaluate net biogeochemical pathways contributing to lake metabolism. Mirror Lake, Storrs, Connecticut, has a maximum depth of 1.5 meters. During summer, Mirror Lake is thermally stratified during the day and may or may not destratify at night. Oxygen and TDIC were measured at six depths within the water column. Significant departures from the Redfield Ratio are observed in the bottom layers of Mirror Lake when oxygen is at or near depletion. Surface PR values for the same time period are close to the Redfield value of -1.3 (within error). These observed departures from the Redfield Ratio are consistent with shallow lake metabolism. Idealized PR values were modeled using stoichiometric equations for the oxidation reactions of organic matter by HNO$_{3}$ and Fe$_{2}$O$_{3}$ as end members. These are used to identify both the nitrate and the iron reduction nutrient pathways. The reduction of iron also implies the loss of a significant adsorption surface that may result in remobilization of adsorbed metals. PR may thus serve as a diagnostic tool for highly eutrophic lakes.
DE: 4805 Biogeochemical cycles (1615)
DE: 4239 Limnology
DE: 1806 Chemistry of fresh water
DE: 1871 Surface water quality
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting