The health of terrestrial and estuarine biota in the ACE Basin is vulnerable to pollution, since many contaminants are toxic. A common definition of pollution is an undesirable change in the physical, chemical, or biological characteristics of air, water, soil, or food that can adversely affect the health, survival, activities of humans or other living organisms (Miller 1994). There is a wide range pollutants including chemical contaminants, nutrients, and biopollutants. This section will concentrate on chemical contamination of the ACE Basin. (See related section: Water Quality.)
The effects of chemical contaminants are often insidious, occurring at low concentrations, which may be difficult to observe directly in the environment. All chemicals can be toxic to an organism depending on the dose of chemical to which the organism is exposed. Contaminants can cause a range of biological effects including cellular abnormalities (dysplasia and lesions), reduced growth, declining fertility and reproductive rates, behavioral abnormalities, shortened life spans, and death. Some consequences may be as mild as having vegetation die over a limited geographical area or as severe as a population decline of one or more important estuarine species over a broad geographical area. Behavioral modifications may occur that could limit an animal's ability to avoid a predator or, conversely, to catch prey. In addition, some species may avoid chemical contaminants by leaving or avoiding a contaminated area.
A well-known example of a chemical effect on biota occurred with the wide use of the insecticide DDT. DDT was considered a wonder pesticide that was widely used to control insects in the United States until its ban in the 1970s (Leary and others 1946). DDT was found to cause mortality of non-target organisms, to be persistent in the environment, and to bioaccumulate in organisms. Application of DDT increased mortality in numerous bird species and reduced their reproductive success (Blus 1995). The brown pelican is one of the most sensitive species to DDT (and its metabolites DDD and DDE), which can cause embryo mortality from both tissue degradation and eggshell thinning. In the most extreme case of reproductive impairment reported, only five baby pelicans hatched on Anacapa Island in 1969 out of 1300 nesting attempts. The use of DDT was predominantly responsible for the decline in the brown pelican populations in the US (Blus 1995).
The chemicals of primary concern are trace metals and organic contaminants. Numerous trace metals are an essential dietary component at low concentrations for aquatic organisms; however, trace metals also pose a threat to organisms due to their persistence in sediments, toxicity at high concentrations, and tendency to bioaccumulate in biological tissue. Trace metals are naturally occurring elements that are influenced by the natural weathering of basement rock (Williams and others 1994). In addition, trace metal concentrations can be enhanced from industrial and urban associated activities. Lead, chromium, cadmium, copper, zinc, and mercury are trace metals that are commonly enriched in sediments due to anthropogenic activities (Bruland and others 1974, Erlenkeuser and others 1974, Goldberg et al. 1977, Kennish 1992). When a trace metal enters the environment from a natural process it is generally at low levels and not biologically harmful; however, when a trace metal enters the environment from anthropogenic processes, then the increased trace metal levels have the potential to cause biological harm.
The organic chemicals commonly associated with anthropogenic processes are polycyclic aromatic hydrocarbons (PAHs), pesticides, and polychlorinated biphenyls (PCBs ). PAHs are chronically toxic, carcinogenic, and mutagenic to a wide range of biota including aquatic organisms and humans. PAHs are a major component of lubricating oils and fossil fuels. They are released into the environment when these products are spilled or combusted to produce energy. PAHs are also produced during the combustion of naturally occurring organic matter such as during a forest fire. Potential sources of PAHs to streams, rivers, and estuarine tidal creek systems include runoff from highways and parking lots, vehicle exhaust, street dust, fuel spills, marina and recreational boating activities, and atmospheric fallout (Weinstein 1996).
Pesticides are organic contaminants of concern particularly in aquatic environments with watersheds that are used for agricultural production (Scott et al. 1994). Pesticides are used to produce a desired effect, usually death, on target organisms. The problem arises when these intentionally used chemicals produce a nondesired effect on non-target organisms. The effects that DDT had on birds as previously described, is one example. Pesticides can cause a wide range of adverse effects on non-target organisms. PCBs are another persistent organic contaminant banned in the 1970s that have been reported to accumulate in estuarine environments (Weinstein 1996). PCBs were commonly used in cooling agents and insulators for capacitors, transformers, gaskets, caulking compounds, paints, and oils (Hutzinger and others 1974, Kennish 1992). PCBs have been found to cause reproductive abnormalities, skin lesions, liver damage, and cancer in various organisms (Kennish 1997).
Gases are not the only atmospheric components influencing water chemistry. Particles from numerous sources also occur in water. These can be insoluble, unreactive dust particles or relatively soluble compounds, such as gypsum (calcium sulfate) or limestone (calcium carbonate). Numerous compounds are found in both gaseous and particulate forms. One example is mercury, which can also be introduced via natural sources, industrial outfalls, sewage discharges, and via the atmosphere from incinerators (Windom and others 1975). Mercury is a very toxic compound, which has been linked to a wide range of toxic effects including nervous system damage, reduced growth, and inhibited reproduction (Wren and others 1995). The mercury problem has been well documented in a number of freshwater environments throughout North Carolina and South Carolina. Freshwater environments typically have low pH levels that keep the mercury in solution and hence, bioavailable. The mercury threat to the marine or estuarine environment is less clear due to higher pH values that reduce mercury solubility.
The hydrochemistry influencing the level of contamination and partitioning of contaminants in the environment is complex. All of the research examining the contamination of the ACE Basin has primarily been conducted in the aquatic environment. In general, contaminants that are deposited on land can leach into groundwater or enter an aquatic system through runoff from the terrestrial environment during a rain event. Once pollutants enter the aquatic environment, particularly an estuarine environment, a series of complex factors determine the location of the contaminants in the environment. Most contaminants do not remain dissolved in water, instead they will adsorb to particle surfaces present in the bottom sediment or within the water column, which eventually settle to the bottom sediments. A change in the environmental condition or hydrochemistry can alter the partitioning of contaminants in the environment (e.g., water, sediment, tissue) and the ultimate fate of the contaminant.
For example, the solubility and stability of many compounds are affected by pH, which is a measure of the acid balance of a solution and is defined as the negative log to the base 10 of the hydrogen ion concentration (-log10[H+]). The pH is considered neutral at 7, acidic between 0 and 7, and basic between 7 and 14. The pH of seawater averages 8.3, while a blackwater river like the Edisto River may have a pH of 5.5 to 6.0. Estuaries naturally reflect their source waters. A lower pH is found near the river input and a higher pH is found near the ocean. In general, the pH is above 7 throughout an estuary. The pH of the water can affect chemical contaminant concentrations in water and sediments of a system. In basic water (pH>7), many metallic hydroxides are either insoluble or only slightly soluble. These compounds usually form precipitates that settle out with the bottom sediments. For example, iron hydroxide is a precipitate with an enormous surface area that tends to adsorb other compounds on its surface as it settles out of the water column. Iron is present at relatively high concentrations in most river water and forms the hydroxide when acidic river water meets basic seawater. In addition, basic water encourages the breakdown of a number of organic chemicals, particularly pesticides. Malathion is a classic example of a pesticide which breaks down faster in basic water (~ 48 hours).
Relatively high concentrations of metals are found in acidic water, since most metals are soluble at low pHs. The so-called blackwater rivers are black or dark brown due to the presence of humic acids, which come from leaves and other sources. In these environments, some metals are found at concentrations hundreds of times greater than those in seawater. For example, the iron concentration in river water is 670 ppb, but in seawater it is <5 ppb (Goldberg 1967).
Most of the data presented in this section will involve the level of sediment contamination present in the ACE Basin. Emphasis on sediment chemical contamination is related to the fact that sediments are an environmental sink for chemical contaminants. In order to understand what the level of contamination in the ACE Basin indicates, the chemical concentrations found in the ACE Basin will be compared to the contaminant concentrations in other estuarine systems as well as to contaminant concentrations known to cause biological effects. This potential for a biological effect from sediment chemical concentrations will be described using the effects range-low (ER-L ) and the effects range-median (ER-M ) as defined by Long and Morgan (1990) and Long and others (1995). The ER-L and ER-M are concentrations associated with biological effects from a large collection of biological experiments and field assessments. The ER-L and ER-M values are defined as the concentrations at which 10% and 50% of the studies showed a biological effect at specific concentrations, respectively. Values below the ER-L would rarely be expected to be associated with measurable biological effects. Values between the ER-L and ER-M represent a range in which there are possible biological effects for a wide range of organisms. Values above the ER-M represent a range above which there are probable biological effects for a wide range of organisms. In the description of data for the ACE Basin, ER-L and ER-M values will be used to identify those sites with the highest potential for biological effects.
In 1994 to 1996, a study funded by the ACE Basin National Estuarine Research Reserve (NERR) and the National Oceanic and Atmospheric Administration, National Ocean Service (NOAA-NOS) was performed to determine recent sediment contamination in the ACE Basin NERR (Scott et al. 1998). Data collected for this study were designed to serve as a baseline of chemical concentrations in the relatively undeveloped and pristine ACE Basin. The chemical concentrations are expected to increase as development in the ACE Basin occurs. The study design involved sampling eight sites in the Combahee River, eight sites in the Edisto River, eight sites in the Ashepoo River, three sites in St. Helena Sound, and seven sites in the Intracoastal Waterway or adjoining small tidal creeks in the region for both trace metals and organic contaminant concentrations. Two of these sites, A and B, are located in Big Bay Creek and St. Pierre Creek, respectively. These two sites are part of the ACE Basin NERR long-term monitoring stations for water quality (See sediment sampling sites ).
The level of sediment contamination was low throughout the Basin study area; however, there was some variability in the contaminant concentrations among sites (Scott et al. 1998). In general, the sites with the highest contaminant concentrations were also the sites with high clay content. These findings are not surprising since contaminants preferentially bind to clay over sand particles. Therefore, the increased contaminant levels at these sites is probably due to the sediment type and not a contaminant source. For example, 62% and 55% of the sediment in Big Bay Creek (A) and St. Pierre Creek (B), respectively, was clay particles. These two sites generally had higher contaminant concentrations compared to the majority of sites sampled. Water quality research at these two sites has not found any abnormal values for the various variables measured.
Scott et al. (1998) found the level of sediment trace metal contamination in the ACE Basin NERR to be low. Only arsenic was found in high enough concentrations to exceed the ER-L level. Ten of the 34 sites had sediment arsenic concentrations exceeding the ER-L level but not the ER-M level (Comparison of bottom sediment contaminants ). This indicates that there is the possibility for some adverse biological effects from the levels of arsenic found in the ACE Basin; however, arsenic concentrations are naturally high in the southeastern United States. Several studies in pristine systems have also found high arsenic concentrations in the southeastern United States (Scott et al. 1994, Long et al. 1998, Sanger 1998). These naturally high levels are due to the high arsenic concentrations in the basement rock within the region. Therefore, these findings generally indicate that trace metal concentrations in the ACE Basin are indicative of that which one would expect from the natural weathering of basement rock within the region (Scott et al. 1998).
The overall level of sediment organic contamination in the ACE Basin was also found to be low. Sediment concentrations of PAHs were similar to concentrations reported at other pristine NERR sites (i.e., North Inlet NERR). Scott et. al. (1998) concluded the concentrations of PAHs found in the ACE Basin are reflective of atmospheric inputs into the region. None of the PAHs were found to exceed the ER-L or ER-M levels. The maximum total PAH concentration found in the ACE Basin was only 299 ppb while the ER-L level is 4,022 ppb. This indicates that there is little potential for a toxic effect in the ACE Basin due to PAHs. The PCB and organochlorine pesticide concentrations were also found to be very low in the ACE Basin. All 34 of the sites sampled had PCB and organochlorine pesticide concentrations well below the ER-L or ER-M levels. There appears to be little input of these types of contaminants into the ACE Basin (Scott et al. 1998). This is not surprising considering PCBs are an urban-derived contaminant that was banned in the US in the 1970s. Organochlorine pesticide use also appears to be very low in the area considering the level of contamination found in the sediment. Therefore, there is a low likelihood that any biological effects would be observed in relation to the organic contamination of the sediment.
The Environmental Monitoring and Assessment Program Carolinian Province (EMAP-CP) is another study that sampled in the ACE Basin. One of the objectives of the EMAP-CP was to assess the estuarine sediment contamination from North Carolina to Florida (Hyland et. al. 1996 and 1998). Over a two-year period, the EMAP-CP sampled six sites located in the ACE Basin for trace metals and organic compounds. Overall, the level of sediment contamination was low. In general, the chemical contamination in the ACE Basin is less than the contamination found in the other estuarine areas studied. One of the 6 sites sampled had 5 chemical concentrations that exceeded the ER-L level (Comparison of bottom sediment contaminants ). The five chemicals that exceeded the ER-L were arsenic, chromium, nickel, P,P-DDD, and Total DDT, which indicates that there is some possibility of an adverse biological effect at this site. As previously described, arsenic concentrations are generally higher in the southeastern United States and may not constitute a problem. The reason for the elevated levels of chromium and nickel are unknown, but they may have come from mining activities or industrial activities upstream from this site. DDT and its derivative (PP-DDD) have soil half-lives of at least several years. These pesticides were banned in the US in 1972, but their residues tend to be very stable and reside in bottom sediments. As a consequence, these residues probably date from applications made decades earlier and do not reflect any recent activities. The site with slightly elevated levels of some contaminants is located in the South Edisto River near Bear Island Wildlife Management Area (CP95156). This site also had a high silt-clay content of the sediment indicating that the contaminants may have preferentially deposited there. As mentioned previously, the upland area around the upper Edisto River has increased in urban land cover by 31% from 1977 to 1989 (Marshall 1993). The chemical contamination will potentially increase in the aquatic environment as development continues.
Alexander and Wenner (1995) evaluated the historical record of trace metal flux into the ACE Basin from nonpoint sources of pollution. To perform this study, 40 to 55 cm (16 to 22 in) deep sediment cores were collected at two different sites. The first site was subtidal in the Fenwick Cut, which joins the South Edisto and Ashepoo Rivers. The second site was intertidal on a nearby salt marsh. The sediment accumulation rate (> 5 cm/mo, > 2 in/yr) at the subtidal site limited the historical record to the last year of metal and sediment flux. This subtidal core indicated that there were pulses of sediment and metals, especially chromium and zinc, throughout the year. The intertidal core showed approximately 130 years of sediment and metal accumulation at a rate of 0.42 cm/yr (0.17 in/yr). This core demonstrates a gradual increase in trace metal concentrations to the region for the last 80 years. The fluxes of all metals, except arsenic, exhibit a 1.5 to 3.0 times increase in metal concentrations over the length of the core (Alexander and Wenner 1995).
In addition to these large-scale studies, several other research projects on contaminants have been performed in the ACE Basin. Both sediment and oyster tissues collected in St. Helena Sound were generally lower in all contaminants than those from the Charleston Harbor system (Mathews unpubl. data). Similar results were reported for pesticides in samples taken on St. Helena Island (Knowles 1983). Although pesticides might be expected to be reasonably high in St. Helena Sound due to farming in the area, this does not appear to be the case. One explanation for lack of pesticide contamination is that circulation in the sound may not allow for their accumulation. The volume of freshwater flowing into St. Helena Sound is 362 m3/s (1188 ft3/s) (NOAA 1985). This flow rate is the third highest in the state following Charleston Harbor and Winyah Bay. Such a high volume of water may effectively flush the sound of contaminants. In addition, the pesticides used by agricultural operations may have naturally degraded over time. A decrease in the agricultural industry in the ACE Basin will presumably keep the level of pesticide contamination in the area low. (See related section: Agriculture.) However, an increase in urban development may counteract the decrease in agriculture considering pesticides are applied to lawns and golf courses.
Despite the low level of contamination in the ACE Basin, a few studies have found limited areas of sediment contamination. Marcus and Mathews (1987) found a mixture of PCBs in the sediments of Campbell Creek on Whale Branch, which connects with St. Helena Sound via the Coosaw River. A chemical plant is located near this creek. Sediment PCB concentrations at this site were up to 24,200 ppb, or almost 2500 times greater than those found downstream near the sound (Marcus and Mathews 1987). This concentration of PCBs is over a 130 times higher than the ER-M value. An adverse biological effect from PCB concentrations in the sediment is highly probable. PCB concentrations in blue crabs ranged from an average of 861 ppb near the chemical plant outfall to below detection limits <20 ppb for those from the South Edisto River (Marcus and Mathews 1987). In addition, a wide variety of synthetic organic chemicals rarely found along our coast were detected both in the sediments and oyster tissues of Campbell Creek, including diphenyl-methanone, 1,2,3-trichlorobenzene, and 9,10-anthracendione (Marcus and Swearingen 1985). This indicates that controlling the levels of chemical contaminants entering the aquatic environment from industrial development is very important as the ACE Basin continues to be developed.
Wood for docks and bulkheads is usually treated with an antifouling agent to increase the longevity of the structure. One antifouling agent is chromated copper arsenate or CCA. Weis and Weis (1995) explored the impacts of CCA on the biota adjacent to CCA-treated docks and bulkheads in four NERR sites, including the ACE Basin. Sediment and polychaete tissue samples were taken immediately adjacent to the treated surface and at intervals of 1, 3, and 10 m (3.3, 9.8, and 32.8 ft) from the structure to determine whether chromium, copper, or arsenic concentrations could be detected. Elevated levels of the three constituents, chromium, copper, and arsenic (CCA) were found in some sediments and polychaetes near a CCA-treated bulkhead in a residential canal in the North Inlet, SC NERR. They also recorded reduced diversity and biomass of benthic organisms. In the same area, but near an aluminum bulkhead, these deleterious effects were not observed. In the three other NERRs, including the ACE Basin NERR, with only docks and no bulkheads, the negative effects of the CCA-treated wood were absent. Therefore, it appears if only pilings are present and the system is well flushed, then there are no negative biological effects (Weis and Weis 1995).
Other Contaminant Data
An additional area of concern is eutrophication, especially in zones where agriculture or housing developments are common and fertilizers are frequently utilized . (See related sections: Water Quality and Water Quality Synthesis Module.) As mentioned in the water quality section, nutrient-rich runoff from agricultural fields and yards may enter sluggish tidal streams, resulting in algal blooms and fishkills. Data from NOAA's eutrophication study indicate medium levels of nitrogen (>0.1, <1 mg/L) and phosphorus (>0.01, <0.1 mg/L) in St. Helena Sound with a downward trend for nitrogen and no trend for phosphorus since 1970 (NOAA 1996). This might be due to lack of development and decreasing numbers of working farms in the ACE Basin. Whether the trend towards constant or decreasing nutrient concentrations will continue or reverse is difficult to predict. However, as pressure for development increases, inputs of nutrients and other chemicals that promote eutrophication will likely increase.
The ACE Basin is a unique system that is presently a pristine environment with regard to its levels of chemical pollution. The potential for pollution is, however, present due to the likelihood of chemical contaminants entering the ACE Basin from outside sources. The two main outside sources of contaminants are atmospheric inputs and aquatic inputs from upstream anthropogenic activities. These external pressures cannot be controlled to any great extent from within the Basin. In the near future, there is also the potential for pollution to enter the ACE Basin from development of the terrestrial environment in the surrounding watershed. Unlike outside sources, these internal contaminant sources can be regulated by land use planning and government regulations. As pressure for more residential and industrial development increases, controlling point and nonpoint sources of pollution will need to be a high priority. A study by the SCDNR/Marine Resources Research Institute (SCDNR/MRRI) found adverse effects on the South Carolina tidal creek biological community when the amount of impervious surface was greater than 30-35% (Holland and others 1997, Lerberg 1997). In addition, this study found a significant correlation between the amount of impervious surface and contaminant concentrations in the sediments of tidal creeks (Sanger 1998). This indicates that as impervious surface on land increases, then contaminant loadings in creek sediments increase. Therefore, land use planning in the ACE Basin study area will be a very important aspect of keeping chemical concentrations low.
T. Mathews, SCDNR Marine Resources Research Institute
D. Sanger, SCDNR Marine Resources Research Institute
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