PARENT SESSION
Oral Session # 39: Limnology I: Ecosystems, Eutrophication, and Restoration.
Presiding: KL Cottingham
Wednesday, August 6. 8:00 AM to 11:30 AM, SITCC Meeting Room 101.
Effect of macrophytes on lake eutrophication and restoration in relation to lake morphometry.
Genkai-Kato, Motomi*,1, Carpenter, Stephen1, 1 University of Wisconsin-Madison, Madison, Wisconsin
ABSTRACT- In eutrophic lakes, phosphorus (a primary cause of algal blooms) is supplied internally from the lake's sediment, as well as externally from the lake's watershed. Phosphorus recycling from the sediment can cause two different states of water clarity: clear-water and turbid-water states. Since shifts between the states are often abrupt events, phosphorus recycling makes restoration management more difficult. In shallow lakes, an inverse relationship between water clarity and macrophyte dominance is often reported. Macrophytes in the littoral zone can prevent phosphorus from resuspension by stabilizing the sediment. However, the effect of macrophytes should depend on lake morphometry determining the proportion of the littoral zone. In addition, water temperature in the hypolimnion is known to be an important determinant of phosphorus recycling. Here we look at the effect of macrophytes on water clarity along a gradient of eutrophication, in relation to lake morphometry and water temperature. The macrophyte effect was critically dependent on mean depth and temperature, while lake area hardly altered the effect. Lakes with intermediate mean depth (∼10 m) are most susceptible to eutrophication. In these lakes, restoration by reducing phosphorus input is most likely to end in failure. Shallow lakes (<2 m in mean depth) are resistant to eutrophication due to the presence of macrophytes. A deep lake (>20 m) is also resistant because of its great water mass in the hypolimnion. Eutrophication is more likely and therefore restoration is more difficult in a warmer lake.
Key words: lake morphometry, hysteresis, macrophytes, phosphorus recycling