A long-term perspective of dissolved organic carbon transport in Sycamore Creek, Arizona, USA

Abstract

Dissolved organic carbon (DOC) dynamics were examined over five years (1989–1993) in Sycamore Creek, a Sonoran Desert stream, specifically focusing on DOC concentration in surface and hyporheic waters, and rates of export. In 1989 and 1990, the years of lowest stream discharge (0.08 and 0.04 m3 s−1 annual mean of daily discharge, respectively), DOC was high, averaging 7.37 and 6.22 mgC l−1 (weighted annual means). In contrast, from 1991 through 1993, a period of increased flow (1.1, 1.2 and 4.3 m3 s−1), concentration was significantly lower (P<0.001) with annual mean concentrations of 3.54, 3.49 and 3.39 mgC l−1. Concentration exhibited little spatial variation between two sampling stations located 6 km apart along the mainstem or between surface and hyporheic waters. Annual export of DOC from Sycamore Creek varied 100-fold over the five-year period from a mean rate of only 24 kgC d−1 in 1990 to 2100 kgC d−1 in 1993. Ninety percent of DOC was exported by flows greater than 2.8 m3 s−1, and 50% during flows greater than 27 m3 s−1; flows of 2.8 and 24 m3 s−1 occurred only 9 and 1% of the time. The export of organic matter in Sycamore Creek appears to be coupled to El Nino-Southern Oscillation phenomena. The years of highest export, 1991–1993, had El Nino conditions while 1989 and 1990 had medial conditions.