STREAMBED PERMEABILITY AND WATER CHEMISTRY WITHIN THE HYPORHEIC ZONE OF STREAMBED GRAVELS
In the Cosumnes River of Sacramento, California, 87 mini-piezometers have been installed at 29 monitoring points along a one-mile stretch of the river. Each monitoring point consists of three nested mini-piezometers at depths of 1, 2, and 9 ft. In the spring, summer and fall of 2002, samples have and will be collected. High flows prohibit winter sampling. Parameters such as dissolved oxygen, pH, electrical conductivity, and temperature are measured at each mini-piezometer in the field. Water samples are collected and analyzed for dissolved organic carbon, dissolved metals, and dissolved anions. Permeability and vertical gradients are measured using a perforated standpipe and a manometer board, respectively.
Initial water chemistry results are available for the spring sampling. Dissolved oxygen during the spring averages 8.3 mg/L with a high of 10.0 mg/L (100% saturation) and a low of 1.7 mg/L. Electrical conductivity has a high of 241 uS/cm and averages 84.3 uS/cm. Dissolved organic carbon (DOC) from within the streambed was found to have an average of 1.2 mg/L; all samples contained less than 2 mg/L DOC. Of the four dissolved metals analyzed, Na+ had the greatest concentrations with an average of 4.0 mg/L. K+ had the lowest concentrations, averaging 1.0 mg/L. Ca2+ and Mg2+ averaged 2.7 mg/L and 3.4 mg/L, respectively. Cl- and SO42- were typically the only dissolved anions detected in the springtime samples, with average concentrations of 1.9 mg/L and 3.1 mg/L.
Results indicate that hyporheic flow has a significant effect in shallow pore water chemistry. Dissolved oxygen is a limiting environmental factor in areas with upwelling or low stream bed permeability, and concentrations of metals and anions tend to increase along subsurface flowpaths. These relationships can be used to target appropriate areas for future stream restoration projects.