Ecology of the Southern California Bight

A Synthesis and Interpretation

Murray D. Dailey, Donald J. Reish, and Jack W. Anderson, editors

Chapter 3. Chemical Oceanography and Geochemistry
Robert P. Eganhouse and M. Indira Venkatesan

Introduction

The Southern California Bight (SCB) comprises a network of deep sea basins close to shore that trap coastal sediments. Water circulation is constrained below the basin sills, some of which are at depths intersecting the oceanic oxygen minimum zone. Consequently, nearshore (inner) basin sediments are anoxic and preserve sedimentation records. In addition, upper water column motions are restricted by the land masses and by diminished local wind effects caused by coastal mountain topography. Because the California Current is an eastern rather than a western boundary current, the general circulation within the bight is dynamically restricted (Jackson et al. 1989). These complex circulation patterns influence the biological as well as geochemical environments in the region. The geochemistry of dissolved and particulate phases as discussed in this chapter pertains to the water column from the sea-air interface to water depths of about 2000 m. The sedimentary record under discussion is confined to a few hundred years. Chemical components are identified as autochthonous (formed in situ in the SCB, of marine origin) or allochthonous (not originally formed in the SCB, originating outside of the SCB, and mainly land derived).

The cycling and fate of chemical components and elements in the SCB are determined by a complex interplay of various biological, chemical, and physical processes (fig. 3.1). The elements most affected by biological activity are those used by organisms for their cellular, structural, and energetic needs. Among these are C, N, P, and Si. These elements are classified as "macronutrients" because they are assimilated in relatively large amounts (although sometimes present in low concentrations in the surrounding environment). One or more of these nutrients may become limiting, depending on the rates of supply and utilization. In the SCB the N:P ratio in surface water is about 6, whereas the (Redfield) ratio in living phytoplankton is 16. This suggests that nitrogen is limiting in bight waters (Eppley and Holm-Hansen 1986). Other elements whose behavior could potentially be affected by biological cycles are among the list of "micronutrients" (Fe, Mn, Cu, Zn, Mo, V, and Co). These elements are required by organisms only in trace amounts and typically occur at subnanomolar to micromolar concentrations. Recent studies have indicated that the cycling of other chemical constituents believed to be nonessential (for example, Cd and Ni) may also be directly affected by the activities of living organisms (Bruland et al. 1978; Bruland 1980). Finally, biological activity indirectly affects the cycling of a variety of other nonessential elements and compounds by numerous mechanisms (such as scavenging, complexation by biogenic ligands, and bioturbation). These processes, which together control the spatial and temporal distribution of chemical substances in the SCB, are discussed in this chapter. The distribution of trace metals, stable isotopes (¹³C and ¹⁵N), and anthropogenic elements (such as Pb, Cr, and Cu) are reviewed, along with sources and fluxes of specific organic compounds such as the anthropogenic pollutants DDT, PCBs, and PAHs. The coupling among biological, physical, and chemical components of the system is emphasized to embody the dynamics of the ecosystem.

Figure 3.1. Inputs and biogeochemical processes in the SCB. Arrows between boxes suggest flows of matter and energy. (Modified from Carlucci et al. 1986; Williams 1986a.)

The dissolved, suspended, and sinking organic and inorganic matter and the deposited sediments are dynamically interrelated in the marine ecosystem. The dissolved phase is arbitrarily defined as those materials passing through filters having nominal pore sizes of 0.5-1.2 μm, whereas the suspended particles are those retained by the same filters (Williams 1986a). These particles are too small to sink rapidly through the water column (sinking flux is \<1 m d^-1) (McCave 1975) and thus can be transported by currents to adjacent areas. The suspended particles are made up of organic detritus and clay minerals in addition to significant bacterial populations (Williams 1986a). Because of the ease of lateral advection, suspended particles may not reflect the true characteristics of the overlying surface waters.

Rapidly sinking materials are collected by sediment or particle interceptor traps deployed in the water column over various time intervals ranging from a few days to a few months. Large particles such as fecal pellets and "marine snow" are aggregates of living and detrital organic material (Silver and Alldredge 1981). These aggregates account for most of the vertical settling flux of organic and inorganic matter because of their high sinking rates (Deuser and Ross 1980; Honjo and Roman 1978). They constitute only a small part of the total particulate matter pool in seawater. Settling (sinking) particles can play a major role in removal of dissolved components (radionuclides, metals, organics, and other materials) from the euphotic zone into subsurface waters (Goldberg 1961; Lal 1977). Studies by Williams and Zirino (1964), Suess (1970), and Meyers and Quinn (1973) suggest that metal oxides scavenge some of the dissolved organic matter, whereas amino acids and lipids are probably adsorbed onto clay minerals and carbonates. Moreover, particles repackaged (metabolically altered) by bacteria and other microheterotrophs from dissolved and suspended organic material are believed to provide organic matter to zooplankton at depth (Fuhrman et al. 1980) (see fig. 3.1). Upwelling processes (from March to June in the SCB) can also transport fine particles to the surface, where they coalesce to form larger particles. These, in turn, can be ingested by zooplankton and expelled as sinking fecal pellets. Thus, some chemical components are found at enhanced concentrations farther offshore as a result of the remobilization and recycling of fine particles (Williams 1986a). Both dissolved material and suspended particles are also scavenged by marine snow (Silver and Alldredge 1981).

Although a number of data sets are available on the vertical distribution of soluble and suspended particulate inorganic and organic components in the SCB, especially from the nearshore environment (see references in Eppley 1986; Johnson et al. 1988; Williams and Druffel 1987), the chemistry of these phases is complex and only poorly understood. Information regarding sinking particulate matter is just beginning to accumulate (Crisp et al. 1979; Nelson et al. 1987; Small et al. 1989; Venkatesan and Kaplan 1992; Williams et al. 1992).

The fate of chemical (inorganic and organic) components in the SCB sediments has been both studied and reviewed extensively by a limited number of groups such as Southern California Coastal Water Research Project (SCCWRP), the University of California at Los Angeles and at San Diego, the Los Angeles County Sanitation Districts (Joint Water Pollution Control Plant, JWPCP), and the Department of Energy California Basin Study (CaBS) Program (Eganhouse and Kaplan 1988; Eppley 1986; Katz and Kaplan 1981; Finney and Huh 1989a; Jackson et al. 1989; Mankiewicz et al. 1978; Stull et al. 1986; Thompson et al. 1986; Venkatesan et al. 1980). Dissolved inorganic nutrients and other hydrographic properties have also been measured in coastal waters of the SCB since the early part of this century (Williams 1986a). Major research programs in progress or recently completed in the SCB are listed in table 3.1.

Table 3.1 Major Studies in Oceanography and Geochemistry in the SCB

This chapter is presented in four sections. The first section discusses sources of inorganic and organic components to the SCB and attempts to provide budgets of the various inputs (organic carbon, water, suspended, and sinking particles). The dynamics of the water column are treated in the second section which concludes with an overview of the transport and fate of anthropogenic contaminants in the water column. The third section focuses on the distribution and post-depositional fate of organic and trace inorganic substances in sediments of the SCB. Major findings are summarized in the last section, where gaps in current knowledge are identified and recommendations are made concerning areas for future research.

Sources of Organic Matter and Trace Elements

The organic matter and trace elements in marine ecosystems are contributed by autochthonous (marine) as well as allochthonous (terrestrial) sources. The marine component in the SCB derives from primary production and submarine oil seepage. The major inputs of terrestrial origin include domestic and industrial waste discharges, surface runoff from rivers and urban storm drains, dry and wet atmospheric fallout, ocean dumping, and shales eroded from coastal areas. The nature and magnitude of waste discharges and runoff are better characterized than diffuse sources such as atmospheric fallout and ocean dumping. Data on erosion of the Monterey Shale along the coast of California are scant. Oil seepage is both episodic and chronic, whereas inputs from sewage are essentially constant (see table 12.1 in chap. 12). In contrast, storm runoff is episodic and mostly active during winter months (December to February, but occasionally extending from September to March). Strong northeasterly Santa Ana winds during spring and summer (March to July) blow seaward down slopes and valleys from the deserts and influence aerial fallout in the SCB. An attempt is made here to evaluate and estimate the input of organic and trace metal constituents from these various recognizable sources to the SCB. (For a more detailed treatment of spatial and temporal distribution of selected anthropogenic inputs, see chap. 12.)

Autochthonous Sources

The mean primary production (P) of the SCB is calculated to be 390 mg C m^-2d^-1 based on the empirical algorithm developed by Eppley and Holm-Hansen (1986):

P = exp(-3.78 -0.372T + 0.227D)

where D is the day length set at 12 hours and T is the temperature anomaly assumed to be zero. Using this expression, one arrives at a total production over the approximate area of the SCB (78,000 km²) (after Emery 1960) that ranges from 1.1 to 1.6 × 10⁷t C yr^-1 (table 3.2). This compares with the average global oceanic production of approximately 3 × 10¹⁰t C yr^-1. Primary production in the SCB (approximately 400 mg C m^-2 d^-1) is nearly twice the average oceanic value, and it falls between ranges estimated for the Peru upwelling region (approximately 1000 mg C m^-2d^-1) and the Scotia Sea of the Antarctic Ocean or the central subtropical gyre of the North Pacific (approximately 200 mg C m^-2d^-1) (Eppley and Holm-Hansen 1986). The study by Eppley and Holm-Hansen (1986) covered a region encompassing the San Diego Trough, the Santa Monica and San Pedro basins, and the narrow coastal strip of continental shelf between Los Angeles and San Diego (fig. 1.4 in Carlucci et al. 1986). It did not extend offshore beyond 107 km or north toward Santa Barbara Basin and Point Conception where primary productivity is generally higher (Owen and Sanchez 1974). The total bight-wide production estimate is, therefore, probably at the lower limit.

Table 3.2. Particulate, Water, and Total Organic Carbon Budgets for the SCB

In addition to phytoplankton, microzooplankton contribute particular organic matter to the ocean. On average, about 132 mg C m^-2 d^-1 of particulate organic carbon were produced by microzooplankton in 1967 (Beers and Stewart 1970). Carbon from microzooplankton composed about 20% of total zooplankton carbon in the upper 100 m. Extrapolating froma this value, the carbon contribution from total zooplankton of the SCB is estimated to be about 1.9 × 10⁷ t yr^-1 (table 3.2), assuming again the area of the SCB to be 78,000 km². Zooplankton and phytoplankton apparently contribute equally to the organic carbon and particulate matter pools in the ocean. Only a small fraction of these inputs is eventually deposited in the sediments. While about two-thirds of the primary production may be recycled in the euphotic zone, the remaining third sinks into deeper waters. The sinking flux of particles appears to be correlated with surface primary production (Deuser and Ross 1980; Honjo 1982).

The carbon derived from primary production is augmented by inputs from local natural oil seeps in the SCB that have been active throughout Holocene time (Wilson et al. 1974). The circum-Pacific belt, including the SCB, is estimated to contribute approximately 48% of the total global marine petroleum seepage (0.27 × 10⁶ of 0.6 × 10⁶ t) (Wilson et al. 1974). Of the 190 seepages cited by Wilson et al. (1974), about 60 zones were located by Wilkinson (1972) within the 2600-km² offshore California area from Point Conception to Long Beach. Some zones are continuously active while others are only sporadically active. Estimates of seepage rates range from 16 m³ d^-1 to more than 160 m³ d^-1 (Allen et al. 1970; Wilson 1973). Surprisingly little comprehensive compositional information on these natural oil seeps exists except for the reports of Delaney (1972), Sivadier and Mikolaj (1973), and Reed and Kaplan (1977). Since direct information pertaining to seepage rates from many areas is limited and of uncertain quality (Kvenvolden and Harbaugh 1983), the input of organic matter from seeps can only be crudely estimated. The active areas in the SCB from Point Conception to Long Beach are believed to have contributed seep material in the 1970s at rates of 2-56 × 10³t yr^-1, which is based on multiplying the volume of seep (2.3-58 × 10³ m³ yr^-1) (Wilson et al. 1974; Fischer 1978) by the average specific gravity (0.97 g cm^-3) of California oils (Tissot and Welte 1984). Assuming that seep oil contains approximately 85% organic carbon, the total organic carbon (TOC) input to the SCB is approximated to be 1.7 × 10³-4.8 × 10⁴t yr^-1 (table 3.2). This represents an upper limit estimate of the TOC contribution from seeps because a significant portion of nearshore seepage oil is probably gradually incorporated into the local food web (Spies and DesMarais 1983).

Advection via the California Current could play a significant role in mobilizing autochthonous as well as allochthonous materials in different regions of the SCB (Drake et al. 1985). However, limitations of the available data currently make it difficult to calculate the input of various constituents to the bight from advection. Mass transport rates of some trace components were estimated by SCCWRP (1973). Assuming that the trace metal and chlorinated hydrocarbon concentrations of open ocean waters are representative of California Current waters and that the advective transport of the California Current is about 2 × 10¹³ m³ yr^-1, SCCWRP (1973) estimated that the mass transport rates of trace metals, DDT, and PCB by advection far exceeded the mass emission rates from all other sources. Measurements by Hickey and Kachel (pers. comm. 1989) indicate that the actual mass transport rates could be even higher since advective transport of the California Current is greater by a factor of about 10 (1.8-2.5 × 10¹⁴ m³ yr^-1). On the other hand, estimates of mass transport rates such as these probably represent upper limits because the California Current generally flows outside of the Santa Rosa-Cortes Ridge and thus largely bypasses the SCB. The mean circulation in the SCB is dominated by the poleward surface flow (the Southern California Countercurrent) and the subsurface flow (the California Undercurrent) (see chap. 2). Considering the magnitude of this poleward transport (which varies from 2.5 to 5.7 × 10¹³ m³ yr^-1), we have recalculated mass transport rates of several trace metals, DDT, and PCB here using the concentrations reported by SCCWRP (1973). These estimates are presented in table 3.3. An estimate of the organic carbon introduced and/or transported by current advection is included in table 3.2. Note again that the advective flow of the Southern California Countercurrent could transport enormous quantities of land-derived components to the entire SCB.

Table 3.3. Estimated Mass Emission or Transport Rates (t Yr^-1) of Selected Organic Compounds and Trace Metals to the SCB

Allochthonous Sources

The four largest municipal waste dischargers (Hyperion, JWPCP, County Sanitation Districts of Orange County, and Point Loma) currently release 1.6 × 10¹² 1 of water and 8.3 × 10⁴ t of suspended solids into the coastal waters of the SCB annually (SCCWRP 1991). In addition, petroleum, metals, fish cannery, and other industries when combined with power plants discharge wastes and cooling waters on the order of 8 × 10¹² 1 yr^-1. The volume of surface runoff from storm drains and rivers that enters the coastal waters is comparable to that from municipal wastes (2.4 × 10¹¹ 1 yr^-1), but during episodic flooding, flows can be one or two orders of magnitude greater (Schwalbach and Gorsline 1985). A flow of about 1000 times as great as the total combined flows just listed is also estimated to be contributed by advected ocean water (2.5-5.7 × 10¹⁶ l yr^-1) to the SCB (chap. 2). It is therefore pertinent to estimate the influences of these important external sources on chemical balances in the SCB.

About three quarters of the municipal effluent produced in the coastal counties of southern California is directly discharged into the coastal waters of the SCB (SCCWRP, unpublished data). Part of the one-third not directly discharged to the ocean is reused. The remainder is released in drainage channels at different inland locations and transported to the bight via "dry weather" surface runoff. Consequently, significant amounts of suspended solids (rtable 3.2) from the effluents containing a wide spectrum of organic and inorganic constituents are probably deposited along the coastline or find their way to deeper parts of the offshore basins.

Municipal waste is a major contributor of anthropogenic heavy metals and chlorinated hydrocarbons to shelf sediments (e.g., Brown et al. 1986; Eganhouse and Kaplan 1988; Kettenring 1981; Stull et al. 1988; Young et al. 1977a). Quantitative estimates of inputs of these various components from waste discharges have been computed since 1971, much of this work emanating from the systematic studies at SCCWRP (Biennial and Annual Reports). Since 1971, the flow of water has increased by approximately 30%, while suspended solids have been reduced by approximately 68% (see fig. 12.2 in chap. 12) (SCCWRP 1991). Sharp decreases in emissions of trace contaminants from the outfalls have also been observed since monitoring began in 1971 (SCCWRP 1991). For example, the total input of DDT appears to have reached a plateau at around 20 kg yr^-1 in 1989 from 21,600 kg yr^-1 in 1971, and PCBs have declined steadily from 6200 kg yr^-1 to essentially zero over this time period (figs. 3.2 and 12.3) (SCCWRP 1991). With the exception of Cd and Se, eight of the ten measured metals (As, Ag, Cr, Cu, Hg, Ni, Pb, and Zn) are being discharged at lowest reported rates (fig. 3.3).

Figure 3.2. Mass emission rates (t yr^-1) of DDT and PCBs to the SCB. (From SCCWRP 1991.)

Figure 3.3. Emission rates (t yr^-1) of (a) silver and cadmium and (b) chromium, copper, and zinc to the SCB from four largest municipal waste dischargers from 1971 to 1989. (From SCCWRP 1991.)

Municipal wastewater particles are composed of as much as 30-35% organic carbon (Hendricks and Eganhouse 1992; Myers 1974). Considering that the average annual mass emission of total suspended solids from major discharges to the SCB during 1989 was approximately 8.4 × 10⁴ t (SCCWRP 1991), municipal outfalls should contribute at least 2.9 × 10⁴ t yr^-1 of particulate organic carbon (POC) to the ocean. This estimate falls within the range of organic carbon possibly contributed to the SCB from oil seeps but is three orders of magnitude less than that from primary productivity. It is interesting to compare the input of particulate organic carbon from wastewater discharge with the natural flux of particles from planktonic and pelagic food web debris. While the emission rate of sewage-derived carbon is presently 2.9 × 10⁴ t yr^-1, the natural flux of POC sinking out of the euphotic zone was estimated to be 25.6 g C m^-2 yr^-1 (Williams 1986b). Thus, the POC input from wastewater discharge is approximately equivalent to the natural planktonic flux calculated for an area equivalent to 1130 km². However, the input of municipal waste is localized. Recently improved wastewater treatment technologies and source controls to be implemented in the near future should further reduce sewage-derived contaminant emissions into the SCB (Schafer 1989).

Most industrial wastes originate from petroleum-related industries of onshore and offshore oil production, shipping, and other tanker activities. Petroleum waste discharges occur in the vicinity of Santa Barbara Channel and Santa Monica Bay and off Orange County coastal areas. The discharge of particles and water from other industries, such as metal-working plants and fish canneries (table 3.2), is approximately of the same order of magnitude as that from petroleum industries. The effluent flow from industrial wastes comprises about 9.1% of the total municipal wastewater discharge in the SCB, and the estimated mass emission rate of suspended solids from the former sources is 6.6% of that released from the latter dischargers (as of 1989). Practically no data exist in the open literature regarding the contribution of organic and inorganic constituents from industrial wastes to the California coastal waters.

Fourteen major thermal power generating stations and one nuclear power generating station (San Onofre) together discharge approximately 8 × 10¹² l yr^-1 of cooling water into the southern California coastal regime (including bays and estuaries) (table 3.2). Cooling water is indeed the largest type of discharge to the SCB. Young et al. (1977b) investigated the input of six trace metals (Cd, Cr, Cu, Ni, Pb, and Zn) in both seawater influent and effluent of eight major generating stations located along the Ventura, Los Angeles, and Orange county coastlines. The annual inputs of these trace metals from cooling waters were estimated to range from 0.3 to 2.1 t yr^-1. At that time, this constituted less than 1% of the combined input from storm runoff, aerial fallout, municipal wastewater, and thermal discharge. Retention basin waters (consisting of acid-cleaning wastes, fireside boiler wash water, and floor drainings) were not discharged during the sampling period. The release of basin waters would be expected to contribute additional trace metals (as much as four orders of magnitude) (Young et al. 1977b) as well as organic contaminants to the effluent cooling water. However, data pertaining to organic constituents are not readily available.

Approximately 300 rivers, streams, and storm drains discharge into the SCB, and 6 of these—all major rivers with tributaries (Ventura, Santa Clara, Calleguas, Los Angeles, San Gabriel, and Santa Ana)—make large contributions to coastal sediments. Using the data of Brownlie and Taylor (1981) and Taylor (1981), Schwalbach and Gorsline (1985) estimated the "actual" input of sediments from Point Conception to Baja California into the SCB to be about 9 × 10⁶ t yr^-1 (table 3.2). Taking into account the reduction in sediment yields by flood control and damming, Brownlie and Taylor (1981) projected "natural" discharge rates (which could be systematically higher in drainages accompanying urban developments) to be around 13 × 10⁶ t yr^-1 during the Holocene. This is probably an underestimate of modern sediment inputs because agricultural land use and progressive deforestation tend to enhance natural sediment yields (Meade 1969). The discharge from streams could range up to one or two orders of magnitude greater than that observed during normal years (e.g., during the exceptional flood events of 1941 and 1969). These two major events alone contributed more than half of the influx of sediment from small streams during the past 50 years (Brownlie and Taylor 1981). Yet, very limited data exist to correlate storm flow characteristics with the mass emission rates of numerous constituents that are washed into the SCB during storm runoff and in dry weather flows (Eganhouse and Kaplan 1981; SCCWRP 1987).

As much as 70% of the total contemporary surface runoff could derive from storm flows, and a major portion of the suspended silt (94%) and total organic carbon (86%) are discharged into the SCB during the winter storm season lasting from November through April (SCCWRP 1973; Water Resources Data for California 1986). Mass emissions of oil and grease are apparently of equal magnitude in storm and dry weather flows (SCCWRP 1973).

The emission of suspended silts in storm runoff ranges from 1.5 to 6.0 × 10⁵ t yr^-1 (Eganhouse and Kaplan 1981; SCCWRP 1973; SCCWRP 1992) and appears to be fairly constant over a decade (table 3.2). The lower end of this range is nearly double the present-day suspended solids discharge rates from municipal wastewater outfalls, but the chemical composition of the two types of solids is quite different (Eganhouse and Kaplan 1982b; Eganhouse et al. 1981). Over time scales of decades to centuries, the Santa Clara River is the single most important source of sediment in southern California, although it discharges only about 10% of the total surface runoff flows from the Los Angeles Basin (SCCWRP 1973). During water years 1986-1987 and 1987-1988, the Los Angeles and San Gabriel rivers carried the greatest amounts of suspended solids to the northern part of the bight. Ballona Creek and the Los Angeles River contained silt concentrations in the range of 300-400 mg l^-1 during the storm in 1970-1971. This is comparable to the average concentration of suspended solids (715 mg l^-1, ranging from 30 to \>1000 mg l^-1) determined for the Los Angeles River after a storm event in 1978 (Eganhouse and Kaplan 1981). Apparently the stringent flood control measures on rivers such as the Los Angeles and Santa Ana have greatly reduced the mass emission rates of silt, although the Los Angeles River has averaged about 77% of the total storm runoff carried from the Los Angeles Basin over the decade (Young et al. 1980).

The estimate made by Schwalbach and Gorsline (1985) of the suspension (natural) discharge (12 × 10⁶ t yr^-1) from rivers in southern California is an order of magnitude greater than recent storm runoff estimates (Eganhouse and Kaplan 1981; SCCWRP 1973, 1992). This is probably because Schwalbach and Gorsline (1985) have integrated the data over the entire Holocene. A large range in values is conceivable because terrigenous silt could enter in large pulses during exceptional events, as previously described. Furthermore, note that the data of Eganhouse and Kaplan (1981) are based on only one storm event.

The particulate organic carbon emission rate from surface runoff to the SCB in modern times is of the same order of magnitude as that from municipal waste outfalls (table 3.2). This emphasizes the potential importance of surface runoff to the ecosystem of the SCB. The limited data available on chlorinated hydrocarbons (SCCWRP 1973) suggest that the mass emission rate of these compounds from runoff during the early 1970s was roughly 1% of that observed from municipal wastewaters at that time, although the rates are similar a decade later (table 3.3) (Young et al. 1980). A comparative study of storm runoff in the Los Angeles River by Young et al. (1980) showed that most of the trace metals investigated (Ag, Cd, Cr, Cu, Hg, Ni, Zn, Fe, and Mn) exhibited only a minor decline in flow-weighted mean concentrations over the decade. However, total PCBs decreased by about a factor of eight (Los Angeles River storm runoff in 1971-1972 was 2.6 mg l^-1, while in 1979-1980 it was 0.31 mg l^-1). This trend is to be expected because the use of PCBs was banned in the mid-1970s. Similarly, the concentration of lead decreased by a factor of six (Los Angeles River storm runoff in 1971-1972 was 940 mg l^-1, while in 1979-1980 it was 160 mg l^-1). This probably reflects federal regulation (initiated in 1975) of leaded gasoline and other fuel additives (National Research Council 1980). Comparison of trace metal concentrations in runoff and wastewaters during 1979 and the entire decade (1970-1979) shows that the annual mass emissions of most constituents via wastewater discharge exceed (by an order of magnitude) runoff emissions from Los Angeles Basin storm channels (Young et al. 1980). Lead and zinc are exceptions because of their automotive uses.

Harmful wastes have been barged farther out into the sea and dumped, either without packaging or after encapsulation in metallic drums. Few data are available in the open literature on the contaminants contained in these wastes, but they include radioactive and industrial wastes, oil drilling muds and cuttings, garbage, and military explosives. Drums could probably corrode in a decade, gradually releasing the enclosed materials. Only oil refinery and chemical wastes are believed to contribute significant amounts of pollutants in the SCB (SCCWRP 1973). Practically all dumping ceased as of 1972-1975 (Chartrand et al. 1985), with the exception of sediments dredged from the Los Angeles, Long Beach, and San Diego ports and from the naval station at San Diego. Currently, site LA-5 (at the outer edge of the continental shelf at a depth range of 130-190 m and 14 km from the entrance to San Diego Bay) is an active interim site for disposing of dredged material. Sites LA-2 (off Point Fermin, 9 km from the breakwater at San Pedro) and LA-3 (8 km to the south, southwest of Newport Beach Harbor) are inactive because their site designations have lapsed. The latter two sites will probably be designated as permanent sites in the future (Patrick Cotter, EPA, pers. comm. 1989).

The average amount of dredge spoils allowable for disposal at these three sites is 200,000-500,000 yd³ (2.62-6.54 × 10⁵ m³) per site per year. Assuming that the dredged sediments from the southern California harbors have an average total organic carbon content of 1.65% (based on three replicate samples from 12 harbor locations extending from San Diego Bay to Los Angeles Harbor) (Anderson and Gossett 1987), we can estimate the potential organic carbon input from the allowable volume of dredged material dumped into a single dumpsite. An average specific gravity of 2.2 is also assumed in the calculations. About 9.5 × 10³-2.4 × 10⁴ t yr^-1 of organic carbon is estimated to be contributed to the SCB environment from a single dumpsite (table 3.2).

Sedimentary rocks such as those of the western Transverse Ranges generally disintegrate to produce fine-grained debris. Surface runoff should therefore receive sizeable contributions from eroded shales such as the Monterey Shale (Miocene) along the coast of California. Unfortunately, data on the input of eroded shale to the SCB do not exist. However, the sediment budgets discussed by schwalbach and Gorsline (1985) from southern California drainages obviously encompass contributions from shale erosion. Taylor (1983) estimated that an average of approximately 12 × 10⁶ m³ of sedimentary debris is eroded annually from the southern California coastal drainage systems. Fifty percent of this volume is composed of fine silt and clay, and a sizeable fraction is most likely derived from the eroding coastal shales. Thus, a gross estimate of mass emissions from shale erosion can be attempted here.

Of the mainland shoreline distance of 327 km, 87% is estimated to be erosional (Emery 1960), and exposures of the Monterey Shale are found almost continuously along this shoreline (Obradovich and Naeser 1981). Assuming that up to a 1-m depth of this shale is eroded at a rate of approximately 10 cm yr^-1, the volume of sediment input to the SCB from shale erosion amounts to 2.9 × 10¹⁰ cm³yr^-1. Using an average specific gravity of 2.2 (for diatomite, which is common in Monterey Shale), we estimate the sediment input from shale erosion to be about 6.4 × 10⁴ t yr^-1. This constitutes roughly 1% of the contribution of sediment load from surface runoff, or 77% from waste discharge. The total organic carbon (TOC) input from the shale is approximately 6.4 × 10²-1.2 × 10⁴ t yr^-1 (table 3.2) when estimates are based on the TOC percentage for shale (1-18%) (Curiale et al. 1985). The upper limit of shale-derived TOC leads to an estimated input that roughly equals the contribution from surface runoff or waste discharge.

Thousands of different organic compounds are emitted to the atmosphere from natural and pollution sources (e.g., Finlayson-Pitts and Pitts 1986; Kawamura and Kaplan 1987; Gagosian et al. 1987; Mazurek and Simoneit 1984). It is estimated by the South Coast Air Quality Management District (SCAQMD) that, in 1985, 1637 t d^-1 of particles were emitted into the atmosphere in the south coast air basin (SCAQMD 1988). These particles undergo photochemical reactions that generate numerous compounds and adsorb sulfate, nitrate, and other reactive species (Arey et al. 1989; Finlayson-Pitts and Pitts 1986).

There have been suggestions that some of these species, especially PAHs, may accumulate in lipid-containing films on the ocean surface. These could become toxic to eggs and larvae (Hardy and Gucinski 1988). However, studies of atmospheric nitrogen budgets in the Pacific Ocean suggest that atmospheric nitrate deposition may add to the nutrient content of this oceanic regime (Logan 1983; Uematsu et al. 1985; Prospero and Savoie 1989) and affect productivity. Each of the airborne compounds has its own characteristic chemical and physical properties and associated atmospheric sources, residence times, and sinks. Unfortunately, data on aerial fallout rates of trace components into the SCB are very limited. In view of the restricted rainfall in southern California (approximately 20-40 cm yr^-1) (National Climate Data Center 1988), dry aerial fallout rather than wet deposition is expected to be the dominant airborne mechanism in the SCB. Strong north-easterly Santa Ana winds transport fine material from the nearby arid terrain into the SCB from March through July. As evidence of the importance of dry deposition, ships offshore have been found coated with fine dust during these episodes (Emery 1960).

Gray et al. (1986) have described the spatial and temporal distribution of aerosol carbon concentrations over an entire annual cycle in the Los Angeles area using a reference site on San Nicolas Island. Their island data are used here to compute the flux of total suspended particles, total fine organic carbon, and elemental carbon in the SCB. The fine carbonaceous particles emitted from most combustion processes (Cass et al. 1982; Muhlbaier and Williams 1982; Siegla and Smith 1981) contain organic compounds as well as black nonvolatile soot that has a chemical structure akin to impure graphite (Rosen et al. 1978). The black soot is referred to as elemental carbon, light absorption by which plays a significant role in the earth's radiation budget (Cess 1983; Patterson et al. 1982).

Assuming that the concentration of components measured by Gray et al. (1986) for San Nicolas Island is representative of the entire SCB area of 78,000 km², a gross estimate of the fluxes is computed as follows (after the method of Duce and Gagosian 1982). Dry deposition of atmospheric particulate matter is estimated, using the deposition velocity vd, as

vd = F/M

where M is the mass of aerosol in the atmosphere in micrograms per cubic centimeter, F is the flux of atmospheric particles to the surface (g cm^-2 s^-1) and vd is the deposition velocity (cm s^-1). For particles collected by Gray et al. (1986) that are less than 2.1 μm, a deposition velocity (vd) range of 0.05-0.5 cm s^-1 at wind speeds of 5-10 m s^-1 should be applicable (Slinn and Slinn 1980). With this velocity range and the known concentration of particles (Gray et al. 1986), F can be calculated. The estimated annual dry deposition for the SCB is presented in table 3.2. Data are available only for fine particles, which compose approximately 31% of the total suspended load. If these parameters are equally valid for the total suspended particles by analogy with the fine particles, the flux of the former can be estimated.

This computation shows that the total suspended particulates and the total fine organic carbon fluxes to the SCB from dry fallout are one or two orders of magnitude less than that of wastewater discharge or surface runoff. Similarly, by the extrapolation of LaJolla fallout, Chow and Earl (1970) found that lead from combustion of leaded gasoline could account for as much as 2400 t of fallout over the SCB. The annual dry fallout of chlorinated hydrocarbons in February 1972, however, has been estimated to be approximately 2-4 t, which at that time was lower than from municipal wastewaters (SCCWRP 1973; Young et al. 1976).

Rabinowitz (1972) noted that although the concentrations of lead in wild oats (7-22 μg g^-1) from the islands in the SCB were lower by an order of magnitude than those found on the mainland, the island concentrations were above natural levels (2-3 μg g^-1). This indicates a significant flux in the past of atmospheric lead, other trace metals, and probably also organic constituents to waters of the SCB from urban centers. However, emissions of certain inorganic and organic components into the atmosphere have been curtailed by source controls such as the regulation of leaded gasoline from 1975 (National Research Council 1980) and the cessation of DDT production after 1982 by Montrose Chemical Corporation of Los Angeles County.

The particle flux from dry fallout just computed may be a realistic estimate. Fleischer (1970) attributes the increasing fine silt- and clay-sized quartz offshore to eolian deposition superimposed on the fluvial gradient offshore. The range in the particle input rate quoted in table 3.2 is consistent with the estimate of Fleischer (1970), who reported the eolian contribution to be less than 10⁶ t yr^-1.

Lazrus et al. (1970) determined the concentration of different metals in rainfall over Santa Catalina Island from September 1966 to January 1967. Assuming an average annual rainfall rate of 40 cm over the SCB (National Climate Data Center 1988), their rough estimate indicates that the mass deposition rates of mercury, lead, and manganese exceed the flux from wastewater and runoff (for example, mass deposition rate of lead was approximately 400 t yr^-1 from rainwater versus 243 t yr^-1 from municipal discharge in 1971) (after SCCWRP 1987). These results are consistent with the findings of Bruland et al. (1974), who noticed enhanced fluxes of lead, zinc, and copper in more recently deposited sediments as opposed to iron, nickel, and manganese whose concentrations are uniform with depth. A close similarity in anthropogenic sedimentary fluxes and rainfall washout fluxes for many elements was also obvious. This implies a significant atmospheric transport mechanism for these metals (Bertine and Goldberg 1977). Further measurements of anthropogenic metal fluxes in the outer basins would help confirm this observation.

Although numerous organic compounds (over 300) have been measured in air, rainwater, fog, and mist in and around Los Angeles (Grosjean 1982; Kawamura and Kaplan 1983; Kawamura and Kaplan 1986; Steinberg and Kaplan 1984), no similar studies have been conducted to date from the islands off coastal southern California. Hence, the task of computing fluxes of various organic constituents from rainfall into the SCB is currently impossible. Reductions in ocean discharges from municipal outfalls over the last decade (Schafer 1989) and consequent combustion of sludge for energy recovery undoubtedly warrant a more important role of atmospheric deposition than ever before in contaminant inputs to the SCB. Yet, research efforts involving wet and dry deposition over the SCB have not been extensive to date.

Table 3.3 presents a summary of mass emission rates of organic carbon and trace constituents from various sources to the SCB. All data under advective transport, except organic carbon, were calculated from concentration data compiled by SCCWRP (1973). Mass transport rates of organic carbon were calculated from the depth-integrated concentration of dissolved organic carbon in bight waters (approximately 75 μM) (Hansell et al. 1990) for Santa Monica Basin on the assumption that these values are representative of Southern California Countercurrent waters. The last column in table 3.3 represents the total constituent mass emission rates from municipal wastewater, surface runoff, oil seeps, shale erosion, vessel coating, ocean dumping, rainfall washout, and dry fallout.

For organic carbon and all listed trace components, the contribution from advective transport is far greater than the sum from all other sources. Of the nonadvective sources, municipal wastewaters, surface runoff, and atmospheric deposition are the primary inputs. A few other trace metals such as cobalt, iron, and manganese (not listed in table 3.3) from surface runoff exceed the contribution from municipal wastewaters (SCCWRP 1973). It is clear from these data that vessel coating has contributed major amounts of copper in the past, while ocean dumping may be a significant source of DDT and PCB to the SCB. Unfortunately, these latter estimates have great uncertainties at the present time. Dry and wet deposition probably contributed significant amounts of lead to the SCB until the late 1970s. This compilation (table 3.3) also indicates that data on contributions of such constituents as hydrocarbons and total organic carbon from other sources are lacking. Further study is required to determine the net advective transport of various constituents and to understand the influence of advective transport on the spatial distribution of these compounds.

The environmental fate of organic carbon is governed by the physical and chemical characteristics of individual organic constituents. These characteristics ultimately control their reactivity, mobility, and stability within the water and sedimentary columns. Although the relative magnitudes of contributions of organic carbon from different sources are compared here, it should be noted that organic carbon from various inputs is not equally reactive.