Some Aspects of Pollution in San Diego County Lagoons
Total Page：16
File Type：pdf, Size：1020Kb
Calif. Mar. Res. Comm., CalCOFI Rept., 16 : 84-94, 1952 SOME ASPECTS OF POLLUTION IN SAN DIEGO COUNTY LAGOONS JOHN S. BRADSHAW University of Son Diego Son Diego, California ond PETA J. MUDlE Foundation for Ocean Research Scripps Institution of Oceanogrophy La Jolla, California INTRODUCTION tween August 22 and October 17, 1970; we have also Water is considered polluted if it is not suitable for drawn on the data of Gannon (1967), and on the its intended use, whether that be a water supply, prop- records of the San Diego County Regional Water agation of fish and wildlife, or recreation. Water pol- Quality Control Board. Our preliminary analyses are lution thus covers a diversity of events, such as oil based on limited data, but we hope that the broad spills, pesticide accumulation, heavy metal contami- trends shown by them will spark more detailed and nation and sewage discharge. Since the most serious exacting studies in the future. pollutant in the lagoons of San Diego County appears to be sewage efluent, we shall confine ourselves to this Description of the Lagoons topic. The distribution of the coastal lagoons in San Diego Almost all of the coastal lagoons in San Diego County is shown in Figure 1. These partially land- County have a history of use as sewage disposals. locked water bodies have resulted from the drowning Most of the effluent now entering the lagoons is sec- of river mouths and the subsequent development of ondarily treated, that is, the solids have been removed, protective sand bars, a process thought to have begun and most of the organic matter has been oxidized. approximately one million years b.p. Evidence from However, even after secondary treatment, the effluent Indian kitchen middens indicates that all of these still contains large quantities of nitrogen and phos- lagoons supported rich marine faunas from approxi- phorus. The effluent adds a large nutrient load to the mately 9,000 to 800 years ago (Miller, 1966). naturally nutrient-rich lagoon water, and results in Some aspects of the recent ecology and geology of a stimulation of excessive plant growth. Phytoplank- these lagoons have been studied by Carpelan (1964, ton in some lagoons may be so prolific that the water 1969), Miller (1966) , Gannon (1967), Bradshaw turns pea green ; other lagoons become covered with (1968) , Ford (1968), Damon (1969), Fairbanks rafts of filamentous algae (Enteromorpha spp.). Fol- (1969) , and Mudie (1970). The most important factor lowing an algal bloom, the decomposition of plant ma- affecting the lagoon ecosystems appears to be the size terial may result in the lowering of dissolved oxygen of the tidal prism, which is the volume of water ex- to such low concentrations that fish and other aquatic changed by the tide. If the tidal prism is reduced organisms can no longer survive; the death of these below a critical volume (due to obstruction of the en- organisms further adds to the organic load and the trance channel, or to decrease of river inflow or la- oxygen deficiency. Other undesirable effects of this eu- goon volume) , long-shore transported sand fills in the trophication process include the accumulation of lagoon mouth, and tidal exchange ceases until the en- sludge from the partially decomposed organic matter, trance barrier is breached by river flooding or by the development of foul odors, and a lowering of the artificial means. If the lagoon remains closed for an esthetic and recreational values of the lagoons. extended period of time, the ecosystem changes from Some of the features of this eutrophication process one characteristic of protected inshore ocean water in the San Diego County lagoons have previously to one dominated by brackish water (when the volume been described by Bradshaw (1968), Carpelan (1964, of fresh water inflow is high) or by hypersaline water 1969), Gannon (1967), the California Department of (when the fresh water inflow is small). Fish and Game (1951) and the California Depart- The tidal prism of a lagoon is determined by the ment of Public Health (1951). The primary purpose surface area, the height of the sill at the lagoon en- of our study was to measure several chemical indi- trance, and the tidal range. Large lagoons (tidal prism cators of eutrophication (specifically, inorganic nitro- > 1 x lo7 cu.ft.) generally remain open to the ocean gen and phosphorus) in lagoons receiving different (Inman and Frautschy, 1965), and, in Southern Cali- amounts of nutrient-rich effluent, and to compare fornia, where river flows are relatively small, the sa- these nutrient levels with the background values of linity of the water in these open lagoons is similar to non-polluted lagoons in the same area. We also at- that of the ocean 33.5%0.At the other extreme, small tempted to estimate the impact of sewage effluent dis- lagoons normally remain closed and are connected posal via the lagoons on the nutrient levels of the with the ocean only during times of severe winter adjacent coastal waters. Our data was collected be- flooding. Fresh water predominates in these lagoons, REPORTS VOLUME XVI, 1 JULY 1970 TO 30 JUNE 1971 85 the salinity generally being less than 5 parts per thou- plankton flora dominated by marine diatoms. Sewage sand (%o). Lagoons with tidal prisms in the "critical effluent discharge rates in these lagoons are presently range" (defined empirically here as 1 X lo7 to 1 X relatively low, the duent constituting raw sewage lo5 cu.ft.) tend to remain open only a few months of contributed directly from watercraft. Up until 1962, the year but can be kept open artificially by annual however, large volumes of raw and primary sewage small-scale dredging of the entrance channel. The sa- were discharged into San Diego Bay (1962 discharge linity of the water in these variable lagoons is subject rate was approximately 60 X lo6 gals/day) . Buena to great seasonal variation, the maximum range being Vista is a closed lagoon with a limited brackish water approximately 10 to 65%0. fauna and flora. Prior to 1966, approximately 2 X IO6 The pertinent characteristics of the San Diego gals/day of secondary sewage effluent were discharged County lagoons are summarized in Table 1. San Diego into this lagoon. In recent years, however, this dis- Bay, Mission Bay and Agua Hedionda Lagoon are charge has stopped and at present only a small volume open lagoons which support a high diversity of in- of irrigation runoff enters the lagoon from Buena shore marine fish and invertebrates, and a phyto- Vista Creek. I I7O30' 117' 33O30' 33'30 r.- * . g,.. Buena Vista Creek BUENA VISTA LAGOON .' .Agua Hed ionda Creek I San Marcos Creek AGUA HEDIONDA LAGOON V:.. 2.- Escond i do Creek BATIQUITOS LAGOON + San Dieguito River SAN ELI JO LAGOON 33O - 33O DEL MAR LAGOON LOS PENASQU I TOS LAGOON '- Los Penasqu itos Creek .. A San Diego River c: 1 - MISSION BAY SAN DIEGO BAY 32O30' 32O30' 117°30'.. I17O FIGURE 1. Distribution of the Son Diego County lagoons sampled in this study. 86 CALIFORNIA COOPERATIVE OCEANIC FISHERIES INVESTIGATIONS Los Penasquitos, San Elijo, Batiquitos and Del Mar illustrate typical late-summer nutrient profiles of an lagoons are variable lagoons. Prior to the inflow of unpolluted and heavily polluted lagoon, respectively. significant volumes of sewage effluent (commencing Mission Bay is a tidally-flushed lagoon receiving an between 1955 and 1960), these lagoons probably sup- insignificant sewage input, and thus can be considered ported a limited euryhaline biota, with brackish as representing the background nutrient levels of an water elements appearing temporarily during periods open lagoon. The phosphate levels were generally low of fresh water accumulation. The biology of these var- (0.3-1.2 pg-at P/1), although occasional higher val- iable lagoons has undoubtedly been altered by their ues (up to 6 pg-at P/1 were found. Nitrate and ni- history of secondary duent discharge. At present, trite levels were also uniformly low (< 2.5 pg-at sewage enters the Los Penasquitos and Del Mar la- N/1). In contrast, ammonia values were relatively goons in ditches from treatment plants located within high and variable, with a total range of 17-720 pg-at ' one mile of the lagoons. In contrast, the sewage enter- N/1. The two extremely high ammonia values appear ing San Elijo Lagoon originates as effluent discharged atypical and comparable values were found in no into the Escondido Creek approximately eleven miles other lagoons. upstream. The effluent entering Batiquitos Lagoon Figures 3 and 4 show the distribution of nutrients now comprises a relatively small volume of irrigation in San Elijo Lagoon and in Escondido Creek below runoff and overflow from a sewage effluent storage the entry point of the sewage effluent. This lagoon is dam. However, extensive sludge beds still exist in the open for only one to two months of eaoh year follow- lagoon from an earlier period of greater sewage dis- ing winter flooding. Between these major openings, charge. Most of these polluted lagoons presently sup- the lagoon is usually closed except for sporadic short- port an impoverished aquatic fauna comprising a few term artificial openings (2-7 days duration). species of fish and large populations of Tubificidae, Approximately 3 X lo6 gals/day of secondary sew- chironomids and ostracods. The phytoplankton is usu- age effluent enters the creek from the City of Escon- ally dominated by unicellular or colonial green algae, dido, 14 miles inland ; roughly two-thirds of this reaches several species of which commonly number well over the lagoon 11 miles downstream. Above the sewage 100,000 cells/ml during bloom periods.