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Groundwater seepage into northern San Francisco Bay: Implications for dissolved metals budgets
SPINELLI Glenn A. ; FISHER Andrew T. ; WHEAT C. Geoffrey ; ...
Nonconservative excesses of dissolved metals in northern San Francisco Bay indicate that there are internal sources of metals within the bay. We quantified groundwater seepage and bioirrigation rates in this area to determine their roles in transporting dissolved metals from benthic sediments to surface waters. We deployed seepage meters and collected sediment, pore water, and bottom water samples at three sites. We determined seepage rates from seepage meters and modeled the transport of water through the sediment using pore water data to constrain rates of diffusion, advection, and bioirrigation. A groundwater flow model incorporating sediment physical properties and local topography constrains more regional seepage estimates. The seepage meters indicate upflow rates from 7 to 56 cm yr-1 in March and April 1999 with some large (<50 cm yr-1) daily fluctuations that greatly exceed predictions based on sediment physical properties and tidally induced pore pressure variations. During this period, results from modeling pore water chemical data are consistent with a small bioirrigation rate (<1.5 x 10-7s-1) relative to values determined for southern San Francisco Bay, and an average groundwater upwelling speed of 15 cm yr-1. The speed and direction of flow changed throughout the year, with best fits to the data ranging from 20 cm yr-1 upflow to 34 cm yr-1 downflow and averaging 4 cm yr-1
American Geophysical Union
ISSN : 0043-1397 CODEN : WRERAQ
Water resources research A. 2002, vol. 38, n° 7, pp. 12.1-12.19
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