HR: 0800h
AN: H31D-1329    [Abstracts]
TI: Sources of Solutes in Hawaiian Stream Waters and Their Spatial Variability
AU: * Schopka, H H
EM: hhs22@cornell.edu
AF: Cornell University, Department of Earth and Atmospheric Sciences , Ithaca, NY 14853-1504 United States
AU: Derry, L A
EM: lad9@cornell.edu
AF: Cornell University, Department of Earth and Atmospheric Sciences , Ithaca, NY 14853-1504 United States
AB: The mechanical denudation rates of mountainous islands in the tropics are much higher than the global average. This is largely due to high rainfall, steep slopes and elevated temperatures. Basaltic terranes have higher chemical denudation rates than other crystalline areas (e.g. Dessert et al., 2003). Studies of river geochemistry in the tropics are severly hampered by a lack of chemistry and runoff data. In order to circumvent this problem, we are investigating methods of using variables related to topography, vegetation type, bedrock geology and precipitation to estimate the rates of chemical denudation of tropical basalt terranes. The islands of Hawai'i (less than 150 kyr) and Kaua'i (av. age ~4 Myr) represent the extremes in bedrock age, topographic development and soil maturity on the Hawaiian islands. Samples were collected from nearly thirty streams and rivers on Hawai'i and Kaua'i and from 11 groundwater wells on Hawai'i. All samples were analyzed for major elements and are being analyzed for DIC δ¹³C and Sr isotopes. Preliminary results show that the TDS (mg/L) is high compared to major world rivers, i.e. (62 ± 30) mg/L on Hawai'i and (92 ± 33) mg/L on Kaua'i. Solutes in streams derive from both weathering and precipitation inputs and the rain signal must be removed before making inferences about chemical denudation. We need better constraints on Hawaiian rain chemistry but make the general assumption that [X]/[Cl] in rain is identical to seawater. After correcting for input of recycled marine aerosols, we find the weathering contribution to the dissolved load to be higher on Hawai'i than on Kaua'i. On both islands, most of stream Na is supplied by rain and most of stream Ca comes from weathering. On Kaua'i all stream sulfate is derived from precipitation while approximately half of it comes from weathering on Hawai'i. Seasalt-corrected K/Ca-values indicate weathering of primary mineral sources on Hawai'I, but point to significant mixing of primary weathering solutions with rainwater on Kaua'i. These preliminary results show first-order differences in stream geochemistry across bedrock age gradients on the Hawaiian islands. Further work investigating the links between stream geochemistry and topographic, climatic and landcover variables will be presented.
DE: 1719 Hydrology
SC: Hydrology [H]
MN: Fall Meeting 2005