Pabich, W. J. Massachusetts Institute of Technolgy, wjpabich@mit.edu
Valiela, I. Boston University Marine Program, valiela@bio.bu.edu
Hemond, H. F. Massachusetts Institute of Technology, hfhemond@mit.edu

 
VADOSE ZONE THICKNESS AS A CONTROL ON DISSOLVED ORGANIC CARBON (DOC) DELIVERY TO GROUNDWATER, WAQUOIT BAY WATERSHED, CAPE COD
 
The concentration of DOC in groundwater impacts numerous watershed processes, including loss of groundwater nitrogen through denitrification, which, especially is systems receiving significant amounts of anthropogenically-derived nitrogen, is often limited by the availability of DOC. As part of a larger study to model groundwater nitrogen delivery to Waquoit Bay at the watershed scale, we investigated the relationship between thickness of the vadose zone through which DOC must percolate during recharge to its concentration in the underlying groundwater. Using both multi-level sampling wells and drive point piezometers, we collected water samples at various sites where the thickness of the vadose zone varied from less than 1 to 6 meters. We analyzed acidified, Ar-purged water samples for total organic carbon using a Shimadzu TOC analyzer. These data, combined with published data on groundwater DOC concentrations from wells with vadose zones as thick as 17 m, suggest that depth of the vadose zone exerts a significant control on the amount of DOC reaching groundwater, presumably due to immobilization and oxidation during transport through the oxic zone. DOC concentrations in shallow water also vary substantially, but this spatial pattern is temporally stable.
 
Day: Tuesday, Feb. 2
Time: 09:00 - 09:15am
Location: Eldorado Hotel
 
Code: CS56TU0900E