Ecosystem Characterization
Study Area Description
The area potentially affected by the proposed project includes riparian forest, freshwater marsh, saltwater marsh, and the lagoon near the river mouth. A map of the study area is shown in figure 1. The boundary farthest upstream is set by the City of Salinas Alisal wastewater treatment plant outfall, which discharges about 0.004 m3 per second (1.5 cfs) about 200 m. (220 yd.) upstream of the Highway 68 bridge. The reach of river just upstream from Alisal is normally dry during the summer; water releases from the two reservoirs upstream are regulated such that all surface flow has percolated into the ground above this point. The City of Salinas' main treatment plant discharges about
[1] Paper presented at the California Riparian Systems Conference. [University of California, Davis, September 17–19, 1981].
[2] Thomas T. Jones is Environmental Engineer with Engineering-Science, Inc., Berkeley, Calif. Bruce W. Snyder is Terrestrial Ecologist with Engineering-Science, Inc., Denver, Colo.
Figure l.
Map of the study area showing sampling locations
and significant point source discharges to the river.
0.24 m3 per second (8.5 cfs) about 2.5 km. (2.5 mi.) downstream from Alisal.
Except for the riparian corridor, the land on both sides of the river has been extensively cleared for agricultural use. The land north of the river is uniformly flat for several miles; just south of the river and inland from Highway 1, the land rises sharply to elevations of 40 to 100 m. (125 to 330 ft.).
The lagoon at the mouth of the river is part of the 210 ha. (518 ac.) Salinas River Wildlife Refuge and serves as a feeding and breeding ground for large numbers of birds. During high flow periods, the lagoon is open to the bay, and the river discharges to Monterey Bay. During the summer, sand dunes close off the mouth, and the river discharges through Moss Landing Harbor about 6.5 km. (4 mi.) to the north via the old Salinas River channel.
Baseline Study Plan
The first phase of the monitoring program was a baseline study, initiated in 1979. Its objectives were to: 1) characterize the study area with respect to hydrology, water quality, and ecology; and 2) determine if there was a need for detailed impact analysis because of the proposed project. The study was conducted during the summer of 1979. Nine sampling stations, shown in figure 1, were established. At each station except Station 6, which proved to be inaccessible, the flow, electrical conductivity (EC), and temperature of the water were measured biweekly; in addition, at Stations 7 and 8 the dissolved oxygen (DO), ammonia, total organic nitrogen, nitrite, nitrate, phosphorus, and major cation and anion concentrations were measured monthly. This was done to better identify impacts on the water quality in the lagoon. The ecological portion of the study identified the dominant plant and animal species within the study area; it consisted of a literature review and two week-long field trips to the area.
Hydrology and Water Quality
Sources of Water Flow
A major effort of the baseline study was to identify the sources of summertime flow in the lower Salinas River. There are three major point sources of discharge within the study area; the two City of Salinas treatment plants and the Blanco Drain, which discharges an average of about 0.11 m3 per second (4 cfs) approximately 8 km. (5 mi.) upstream from the mouth. This drain discharges agricultural irrigation water runoff from about 2,400 ha. (6,000 ac.) north of the river. In addition to these major point sources, there are numerous nonpoint sources of agricultural return water along both sides of the river and along the north side of the lagoon.
There are two other potential sources of water to the lagoon: groundwater inflow from the surrounding land, and seawater inflow from Monterey Bay. The magnitude of the groundwater inflow (or outflow) was measured by constructing groundwater wells around the periphery of the lagoon and calculating the magnitude and direction of flow based on soil permeability and water level difference in the wells. Seawater inflow was estimated by performing a salt balance on the lagoon water, and by a previous study which directly measured seawater inflow (Muckel etal . 1964).
Since it was impossible to measure the nonpoint flow into the river directly, it was calculated by performing a mass balance between the various sampling points on the river. The average nonpoint inflow between stations was estimated as the difference between the upstream flow and any known point source inflows within the reach. An average value for this flow per unit length of river was then computed and applied to the entire length of river and lagoon to give a total value for nonpoint inflow.
Using the data thus collected, an overall water budget for the river and lagoon was constructed. This is presented in figure 2. Surface flow into the lagoon accounted for about 92% of the inflow; of this, about 45% was from the treatment plants and the rest was from the Blanco Drain outfall and nonpoint sources. In the river, the quantity of flow from the treatment plants ranged from 100% in the upper reaches of the study area to about 45% at the head of the lagoon. Groundwater inflow from the periphery of the lagoon was negligible; seawater inflow was also very small. One source of water which was
Figure 2.
Low-flow water balance for the lower Salinas River and Lagoon.
not measured was subsurface flow in the river channel.
Water Quality
Important water quality parameters which would be most affected by the proposed project were total dissolved solids (TDS), nutrients, ammonia, DO, pesticides, and coliform levels. TDS was measured at each station biweekly; nutrients, ammonia, and DO were measured monthly at Stations 7 and 8 to assess their effects on the lagoon. Pesticides and coliform levels were not measured, but data from other sources were reviewed. The significant findings for each parameter are discussed below.
Total Dissolved Solids .—TDS was determined indirectly by measuring electrical conductivity (EC) and temperature. The TDS values for the treatment plant effluents were generally less than half those for the Blanco Drain outfall, which is representative of agricultural runoff water. As expected, therefore, the TDS values generally increased downstream as more agricultural water entered the river. In particular, the TDS at the lower end of the lagoon (Station 8) was substantially higher than anyplace else in the river, due largely to seawater inflow through the sand dunes. The result of removing the sewage effluents would be to generally raise the TDS level in the river and lagoon by about a factor of two, from 1,000–1,500 mg. per l. at present to about 2,500–3,000 mg. per l.
Nutrients .—Nutrients in the form of total nitrogen and total phosphorus were measured at the upper (Station 7) and lower (Station 8) ends of the lagoon. Total phosphorus (as P) values ranged from 3.20 to 20.26 mg. per l. at Station 7 and from 0.72 to 5.56 mg. per l. at Station 8. Total nitrogen (as N) values ranged from 14.7 to 21.0 mg. per l. at Station 7, and from 4.4 to 11.2 mg. per l. at Station 8. The data indicated that nutrient removal in the lagoon was high. In addition, there was a shift in nitrogen speciation from predominantly ammonia nitrogen and nitrate to predominantly organic nitrogen and nitrate forms. These effects were undoubtedly due to algal activity in the lagoon. The treatment plant effluents are major contributors of these nutrients; mass balance calculations indicated that the two treatment plants contributed at least half and often virtually all of the nutrients found at Station 7. The Blanco Drain water (and most likely, nonpoint agricultural return water as well) occasionally had high nutrient levels, due to over-application of fertilizer, but generally it had low nutrient concentrations.
Ammonia .—Ammonia levels at Station 7 ranged from 3.09 to 16.0 mg. per l. and at Station 8 from 0 to 4.8 mg. per l. The levels of ammonia were directly correlated with high levels of ammonia in the treatment plant effluents. Mass balance calculations indicated that the plants consistently contributed most or all of the ammonia found at Station 7. Presumably, the ammonia levels upriver were even higher since less dilution water for the plant effluents was available. At the pH and temperatures encountered, these ammonia levels would lead to unionized ammonia—which is its toxic form—considerably in excess of the US Environmental Protection Agency EPA criterion of 0.02 mg. per l. Fish sensitivity to un-ionized ammonia varies widely among species and within the same species depending upon other environmental stress parameters (Willingham 1976).
Dissolved Oxygen .—DO levels at Station 7 ranged from 5.9 to 21.5 mg. per l. and at Station 8 ranged from 9.0 to 24 mg. per l. These generally high values were undoubtedly due to algae photosynthesis. All measurements were taken in the late morning or early afternoon when photosynthetic production of DO would be relatively high. Usually, in environments with high algal productivity, such as this, values drop substantially at night or in very cloudy weather, and can even be reduced to zero, due to algae decay.
Pesticides .—Historical pesticide data for the Salinas River, treatment plant effluents, and Blanco Drain water were examined. All the Salinas River levels were well below 1 ppm with the exception of one measurement of over 30 ppm of Diazinon at Stations 2 and 3 in October 1978. Diazinon was used to contol mosquitoes in the river and was undoubtedly the source of the high levels. A fish kill also occurred at this time, and was attributed to either the pesticide or the high ammonia levels, or a combination of both (Greenfield and Grunt 1978). A few pesticide analyses from Blanco Drain water also showed levels consistently less than 1 ppm. No pesticides have ever been detected in the effluents of either treatment plant.
Coliforms .—Coliform levels at various locations in the river have been periodically monitored by various agencies, (e.g., Bureau of Sanitary Engineering 1971; Irwin 1976). These studies have consistently shown much higher coli-
form levels below the treatment plant discharges than above them. Although coliforms can be contributed by agricultural runoff water, it is likely that most of the coliforms in the river were due to the treatment plant effluents. High coliform levels indicate a health hazard, and they were one of the main factors in the decision to remove the treatment plant discharges from the river. Chlorination by the treatment plants has been subject to periodic breakdown in the past, which led to very high coliform levels in the effluent.