Bhatt, M. P., and W. H. McDowell (2007), Controls on major solutes within the drainage network of a rapidly weathering
27 tropical watershed, Water Resour. Res., 43, XXXXXX, doi:10.1029/2007WR005915.
Abstract:
Surface water chemistry in the main stem and source points of the Rio Icacos basin
7 (Luquillo Experimental Forest, Puerto Rico) was studied to investigate the factors
8 regulating spatial variability in major solutes in a rapidly weathering landscape. We
9 sampled along the main stem as well as at small source points at high elevation where
10 fresh bedrock is frequently exposed, and at low elevation in the floodplain/colluvial
11 plain of the main stem. Concentrations of silicon, alkalinity, and the sum of base
12 cations were lower at the source points than in the main stem, and were lowest in low-
13 elevation source points. Calcium and sodium were the dominant cations at all sampling
14 points after sea-salt correction, reflecting the weathering of plagioclase feldspar
15 throughout the basin. The partial pressure of carbon dioxide (pCO2) tended to be higher,
16 and HCO3
concentrations were lower, in the low-elevation source points than at other
17 positions in the landscape. When coupled with the relatively low concentrations of Si and
18 base cations, this suggests that the availability of primary reactive minerals, rather than
19 carbonic acid concentrations, limits weathering in these low-elevation sources.
20 Mechanical denudation appears to enhance chemical weathering rates not only by
21 refreshing reactive mineral surfaces but also by contributing carbon dioxide from the
22 decomposition of organic-rich material in landslides, which occur frequently. The spatial
23 variability of major solutes appears to depend primarily on the availability of fresh primary
24 reactive minerals, carbon dioxide concentrations, and hydrolysis conditions.