The Shasta River below Dwinnell Reservoir receives water from creeks, springs, agricultural returns, and a small discharge from Dwinnell Reservoir. The water from Dwinnell Reservoir had elevated levels of nitrogen and phosphorus compounds, as shown in chemical analysis of samples from the canal and the river immediately downstream of the dam. Proceeding downstream to East Louie Road and then to Highway A-12, there was a decrease in total nitrogen concentrations. This is most probably due to the high volume of spring water inflows and relatively low volume of agricultural return water in this section. Proceeding downstream from A-12 to Montague-Grenada Road, Highway 3, and Ager Road, there was an upward trend in both nitrogen concentrations and flow volume. This was believed to be from agricultural return water bearing organic matter. After peaking out at Ager Road, concentrations of nitrogen dropped slightly, such that the median concentration at Highway 263 was roughly equivalent to that at the Canal station, i.e., water from Dwinnell Reservoir. While the concentrations were equivalent, the volume of flow was significantly higher at the downstream station, thus the actual amount of nitrogen was higher. This was indicative of loading of nitrogen from the Shasta Valley.
Phosphorous loading was also observed, although this was not as dramatic. As a relationship to these changes in water chemistry, there was an obvious variability in the growth and composition of aquatic vegetation masses. Increases in nutrients result in increases in plant mass. In the upper study section, currents are somewhat swift, clarity is high, and gravel bottoms are generally visible, with a variety of rooted and attached vegetation growing near the banks. In the lower reaches, currents were often indiscernible, clarity low, and deep pools characterized by thick, muddy bottom deposits predominated. Thick mats of attached filamentous algae, macrophytes, and duckweed were typical in late spring through early winter, particularly in the slack water section in the vicinity of Highway 3 and Ager Road. The pools appear to have been formed by in-stream diversions which blocked the flow, allowing suspended matter to become deposited and allowing luxuriant growths of aquatic vegetation to become established. While lush aquatic vegetation was also observed in the vicinity of the Montague-Grenada Road bridge, the duckweed and surface matting did not occur.
Decomposition of organic matter in sediment exerts a high oxygen demand. This was masked during daylight when dissolved oxygen levels were driven up by plant photosynthesis in the presence of high sunlight plus high nutrient conditions. However, as soon as sunlight became faint, there was an almost instantaneous sag in dissolved oxygen, frequently below Basin Plan objectives. In addition to loading of nitrogen into the system, temperatures increase downstream from East Louie Road. During the irrigation season, it was not uncommon to observe large amounts of agricultural return water flowing unrestrained off the fields into the river.
Initial studies detected significant nutrient loading in Yreka Creek in close proximity downstream of the Yreka POTW. This condition is being addressed by Regional Board Northern District staff.
As stated in the introductory section of this report, in 1985 the U.S. Department of the Interior reported threats to the recovery of anadromous fish populations in the Shasta River due to low flows and high summer water temperatures; unscreened water diversions; degraded spawning gravel; and possible hydroelectric projects. Relatively rapid in-stream flow reductions at the start of the irrigation season were seen as a possible contribution to juvenile fall chinook, coho, and steelhead losses by stranding them in pools and side channels. Additional 1985 information from California Department of Fish and Game reported observations of depressed levels of dissolved oxygen, high temperatures, and mortality of large numbers of young of the year. During the period covered in this report, field observations confirmed the occurrence of a majority of the above water quality conditions. Hydroelectric projects were not considered. Also during the period of this report, staff of CDFG observed at least one instance of an estimated several hundred dead juvenile fish in the vicinity of a screened diversion (May/June, 1992).
Generally, water quality was determined by inflow upstream of ELR and remained stable until the area downstream of Highway A-12. Water temperature, nutrients, dissolved solids, and alkalinity increased, and night time dissolved oxygen decreased in that area of the lower river. Those changes in the presence of increasing stream flow rate suggest significant loading to the river downstream of Highway A-12.
Organic nitrogen is the largest component of nitrogen in the system. Organic nitrogen is not elemental nitrogen or nitrate fertilizer, but rather is the result of biological processes. The possible inputs of organic nitrogen include algae, aquatic macrophytes, and plant and animal wastes washed into the river. Based on the light bottle/dark bottle studies done to date, the organic nitrogen appears to be mostly dissolved, indicating the source is decomposition of the above noted inputs.
Nutrient loading of Yreka Creek, a tributary downstream of Highway 5, was documented from the Yreka POTW. That situation is being addressed by the Northern District personnel.
Dissolved oxygen and pH exhibited daily fluctuations in response to benthic algal and aquatic macrophyte production. Plant respiration did not fully account for the nighttime lows in dissolved oxygen. It appears that sediment oxygen demand plays a large part in that relationship.
The Basin Plan minimum dissolved oxygen objective of 7.0 mg/L was not attained in 15% of the measurements. The median objective of 9.0 mg/L (50% of the measurements must equal or exceed) was attained in 61% of the measurements.
Arsenic was measured downstream of Dwinnell Reservoir in virtually all samples, well below the ISWP objectives for the protection of aquatic life, but exceeding the ISWP objective of 5 mg/L for surface waters used as drinking water sources. This was not unexpected with the history of volcanism in the area.
Focus springtime sampling on:
1) sediment oxygen, pH, and nutrient relationships;
2) continue light bottle/dark bottle experiments to provide supporting information for the sediment interactions;
3) nutrient, temperature, dissolved solids, and pH in the area downstream of Highway A-12, possibly doing up- and downstream sampling of agricultural tailwater runoff; and
4) perform at least one set of total vs. dissolved nutrients samples.
Present the interim report and recommendations to the Shasta Valley CRMP group, Dept. of Fish and Game, and interested agencies and parties with continued involvement at the local level by water quality staff to push for improvements.
We recommend looking at discharge rates, water column and bottom sediment oxygen demand relationships, aquatic vegetation biomass and productivity (particularly for attached vegetation), and fish population estimates, to pin down effects from agricultural return water nutrient levels and subsequent biological effects on water quality. Focusing assessment activities on ponded diversion areas and irrigation returns will provide information on these specific situations, and provide useful information to the agricultural community with regard to causes and solutions.
California Department of Fish and Game. 1960s. Miscellaneous data on fish populations.
________. 1985, 1987, 1988. Memoranda in NCRWQCB Shasta River File.
________. 1993. Mark Pisano, personal communication: 13.3° C is fully supportive of most life stages, 19.7° C is chronic stress threshold for salmonids.
California Department of Water Resources. 1951. Investigation of Effects of High Ground Water Table on Disposal of Sewage by Septic Tanks Near Montague, Siskiyou County. Water Resources Investigation 52-1-2.
________. 1959. Water Quality Investigation. Shasta Valley.
________. 1961. Preliminary Report - Shasta Valley Investigation.
________. 1964. Shasta Valley Investigation, Bulletin No. 87.
________. 1976. Miscellaneous data as reported in DWR 1990.
________. 1990. Shasta Valley Water Quality Literature Review.
________. 1980. Environmental Atlas - Klamath and Shasta Rivers Spawning Gravel Enhancement Study.
________. 1986. Shasta/Klamath Rivers Water Quality Study.
California Regional Water Quality Control Board, Central Valley Region. 1990. Trace Element Concentrations in Selected Streams in California: A Synoptic Study. Wescott, Dennis.
________. 1991. A Compilation of Water Quality Goals. Marchack, Jon B.
California Regional Water Quality Control Board, North Coast Region. Water Quality Control Plan for the North Coast Region. 1989.
United States Department of the Interior. 1985. Klamath River Basin Fisheries Resource Plan. Prepared by CH2M Hill.
United States Geological Survey. 1960. Geology and Ground Water Features of Shasta Valley, Siskiyou County, California. Water Supply Paper, 1484.
