PARENT SESSION
Tuesday, August 8, 1:30-5:00 pm
COS 43 - Aquatic ecology III: lake ecosystems
Mississippi, Mezzanine Level, Cook Convention Center
Presiders: O Sarnelle
A 23-year record of cascading limnological effects of a shifting light environment in a monomictic seepage lake in central Florida.
Gaiser, Evelyn*,1, Deyrup, Nancy2, Bachmann, Roger 3, Battoe, Larry4, Swain, Hilary2, 1 Florida International University, Miami, FL2 Archbold Biological Station, Lake Placid, FL3 University of Florida, Gainesville, FL4 St. John's River Water Management District, Palatka, FL
ABSTRACT- We examined a 23-year limnological dataset from Lake Annie, a small (37 ha), relatively deep (21 m) sinkhole lake in central Florida. Unlike most lakes in the state, Lake Annie is relatively protected from direct anthropogenic impacts, being located on the property of Archbold Biological Station. It is historically nutrient poor, monomictic and primarily groundwater fed. The most striking change in the period of record is a decrease in transparency; a relatively stable photic zone (1% surface light) depth of 8-12m characterized earlier years (1983-1993) while successive years contained several shifts that reduced the zone to 1-3 m at present. More of the variance in transparency was explained by color than chlorophyll a (75 vs. 20%), indicating DOC, rather than excess production, was responsible for the change. Decreased transparency was followed by a cascade of changes including reduced thermocline depth and number of mixing days, increased aerial hypolimnetic oxygen deficit and decreased sulfate concentrations, constituting a significant regime shift in the lake. The decline in transparency followed increases in lake stage, and we hypothesize that reduced recharge of surface water into the surface aquifer is promoting overland flow and wet-season transport of highly concentrated DOC from surrounding wetlands into the lake. Increased stage levels are similarly reported for other lakes regionally. Stage levels at Lake Annie are correlated with increased water table height in two groundwater wells on Archbold indicating a regional hydrologic shift has occurred that had significant limnological consequences.
Key words: Lake, Dissolved organic carbon, Regime shift