Mattole River

Figure 9 Storm flow samples from the Mattole River, California, have and 5D values that do not plot along the mixing line (solid line) between the two supposed sources new rain and pre-storm base flow. Therefore, there must be another source of water, possibly soil water derived from a previous storm, contributing significant amounts of water to storm flow. The stream samples plot along a mixing line (dashed line) between the composition of average new rain and the composition of previous rain (after Kennedy et aL, 1986).

TABLE 10.6 Cation exchange capacity and time for 50% exchange of K onto Mattole River sediments of increasing size from clay to fine gravel... 

Kennedy, V. C., and R. L. Malcolm. 1978, Geochemistry of the Mattole River in northern California. U.S. Geol. Survey Open-File Report 78-205. 

Figure 2. View of lower Mattole River basin showing bridge from which...

The average composition of precipitation falling in the Mattole River basin is shown in Table I. Samples were collected near Petrolia, Honeydew, Ettersburg, and Thom during part of the 1966-67 rainy... 

Table I. Composition of Atmospheric Precipitation in the Mattole River Basin...

Chemical Composition of Stream Water. Streams in the Mattole River basin contain relatively low concentrations of dissolved salts, as might be expected because of the high rainfall. Representative analyses of the river water are presented in Table II. Calcium, magnesium, and sodium are the major cations, and bicarbonate and sulfate are the major anions. Mean discharge for a 20-year period (1912-13, 1951-68) was 1331 ft3 sec 1 (37.69 m3 sec 1) and mean annual discharge was 1.189 X 109m3 (37). 

Diurnal Variation During Low Flow. The silica concentration in the Mattole River shows small but consistent diurnal changes, as do pH and specific conductance (Figure 3). Silica concentration reaches a maximum in the late afternoon along with pH, whereas specific conductance is at a minimum then. A minimum in silica occurs between 8 and 11 a.m. Both silica and specific conductance show about a 4% diurnal variation. 

Table II. Composition of Mattole River Water Collected under Various Flow Conditions...

Calculated from relation between specific conductance and dissolved solids for the Mattole River reported in U.S. Geological Survey publications. 

Variations for a Single Storm Event. An intensive study of one small stream rise was made during the period November 7-15, 1969 for the Mattole River and Conklin Creek (Figure 4). Conklin Creek is a tributary to the Mattole River which enters from the north about 2 miles upstream from the main sampling site on the Mattole. Its drainage area is 5-6 square miles. 

Figure 5. Variation in discharge and chemical composition of the Mattole River, November 7-15, 1969...

Figure 6. Water quality variation with discharge of the Mattole River, November 24 to December 19,1966...

Figure 9. Variation of the ratio silica specific conductance with discharge in the Mattole River, Humboldt County,...

Figure 10. Monthly mean discharge and mean silica concentration for the 1967 water year, Mattole River near Petrolia, California...

Silicon—Cation Ratios in Solids and Stream Water. During low-flow periods of the Mattole river, the ratio of silicon (equivalents/liter) to alkalis plus alkaline earths (equivalents/liter) in solution is approximately 0.15-0.2, and following high flows it is in the range 0.8-0.9. These ratios can be compared with those in various common rock-forming minerals, as listed in Table IV. 

Factors Controlling Silica Concentration in the Mattole River... 

Silica concentration in the Mattole River displays a consistent pattern with respect to stream flow, specific conductance, and sediment concentration. However, the silica variation is out of phase with respect to both discharge and dissolved electrolytes, and silica varies inversely with sediment concentration. Any explanation of the silica variation must account for these facts. 

The fact that the pattern of silica variation in Conklin Creek is very similar to that in the Mattole River, even though the stream basins are different by a factor of about 40 in size, indicates that the observed variation in the Mattole basin is not owing to travel time effects. 

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