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.

Estimating lake-wide sediment accumulation from historic bathymetry and radiometrically dated cores.

Keller, Troy^*,1, Martinez, Maria¹, ¹ St Johns River Water Management District, Palatka, FL, USA

ABSTRACT- Heterogeneity caused by water circulation patterns, lake morphometry, and nutrient loading results in spatial variation in sedimentation. Sedimentation rates are can be calculated from individual sediment cores by measured mass accumulation and dating using radiometric analysis. Often the accuracy of lake-wide estimates of sedimentation is limited by the density and spatial distribution of radiometrically-dated cores. To improve the spatial accuracy of sedimentation rate estimates, we calculated sedimentation from bathymetric surveys (1939 and 1996) of Lake Jesup, a 32 km² lake, hydrologically linked to the St. Johns River. Results from 8 ²¹⁰Pb dated cores show that 21.1 - 56.2 cm of sediment accrued over the 57 year period. Mass sedimentation rates for these cores ranged from 6.13 to 92.3 dry mg*cm^-2*yr^-1. Bathymetric comparisons indicated a mean sediment accumulation of 25.6 cm of muck (22 SD). The accumulation was highly variable and greatest in the deepest portions of the lake. A preliminary lake-wide estimate of 55 mg*cm^-2*yr^-1 is nearly equivalent to the 58 mg*cm^-2*yr^-1 mean calculated from the dated cores. This spatial analysis technique provides a powerful approach for estimating lake-wide sedimentation and generates a detailed picture of the within basin heterogeneity of sediment accumulation.

Key words: Deposition, Spatial, Sedimentation, Eutrophication