Water Quality 1999-2000

     SCDHEC has developed State regulations to protect the water quality of the state for several of the parameters measured by the SCECAP program (SCDHEC, 2001a). These regulations are used for setting permit limits on discharges to waters of the State, with the intent of maintaining and improving surface waters to provide for the survival and propagation of a balanced aquatic community of flora and fauna and to provide for recreation in and on the water. Occasional short-term departures from these conditions will not automatically result in adverse effects to the community and these deviations may occur due solely to natural conditions that the aquatic community is adapted to. Therefore, one goal of SCECAP is to provide additional data on typical conditions observed during the summer months in South Carolina estuarine habitats, especially in those habitats such as tidal creeks that historically have not been sampled by SCDHEC as part of their long-term water quality monitoring program.

     As noted previously, the six primary water quality parameters used to develop an integrated measure of overall water quality within the state's coastal waters were dissolved oxygen (DO), biochemical oxygen demand (BOD₅), total nitrogen (TN), total phosphorus (TP), fecal coliform bacteria, and pH. The oxygen measures provide an indication of both oxygen availability (i.e. DO) and consumption (i.e BOD₅). The nitrogen and phosphorus measures provide the best indication of possible nutrient enrichment (eutrophication) in our estuaries. Fecal coliform bacteria concentrations provide an indication of the suitability of the water for shellfish harvesting and primary contact recreation with regard to the amount of potentially harmful bacteria in the water. Measures of pH provide additional information on conditions that may be stressful for many marine species.

     Values of each water quality parameter were compared to standards for the state's saltwaters (SCDHEC, 2001a) where possible. Because SCECAP sampling is limited to a summer index period and generally doesn't include multiple samples over time, the data are not appropriate for use in USEPA 303(d) or 305(b) reporting requirements. Additionally, only a few of the water quality parameters measured for SCECAP have state standards. When standards were not available, values were compared to data compiled over a 5-year period (1993-1997) by the SCDHEC Bureau of Water in their routine statewide Fixed Ambient Surface Water Monitoring Network (SCDHEC, 1998a). Values exceeding the 75th percentile of all historical values reported by SCDHEC in the state's saltwaters were considered to be evidence of elevated concentrations; values exceeding the 90th percentile of the historical values were considered to be extreme concentrations. Because the SCDHEC historical database was primarily obtained from larger open water bodies, caution should be used in interpreting data from tidal creek sites since high or low values observed for some parameters in that habitat may represent "normal" conditions. In the future, the SCECAP database will be used to identify normal conditions in tidal creeks using protocols similar to those described by SCDHEC (1998a).

The following water quality parameters were evaluated in the SCECAP Program:

Temperature:

     Temperature data are primarily collected to relate with other water quality variables that are affected by this parameter, such as dissolved oxygen conditions. The average of the continuous 25-hr water temperature data observed at tidal creek sites (29.9^oC) was comparable to the average observed at the open water sites (29.8^oC) and ranged from 25 to 33^oC (Appendix 2.1). The average temperature observed at sites sampled in 1999 was within 1 ^oC of the average values observed in 2000 for both habitats. Variations observed among sites within each year reflected the normal temperature variation typically observed between summer months. As expected, the average variation in bottom water temperature over the 25-hr monitoring period was greater in the shallow creek habitats (2.5^oC) than in the open water areas (1.3^oC). Instantaneous measures of water temperature correlated moderately well with the mean 25-hr measure obtained at each site (r² = 0.66). Additionally, the average difference between surface and bottom readings was <0.2^oC at both creek and open water sites. The fauna inhabiting both types of habitats are generally well adapted to the temperature ranges observed in this program.
 

Salinity:

     Salinity is measured because of its influence on the distribution and diversity of many invertebrate and fish species. Changes in salinity at a site can also provide a measure of stressful conditions if there is a large variation in concentrations over short time periods. The mean bottom salinity values observed in tidal creek sites during 1999-2000 was 31.3 ppt and ranged from 5.5 - 37.1 ppt based on the 25-hr instrument deployment data (Appendix 2.1). Mean bottom salinity values among the open water sites was 27.2 ppt and ranged from 2.1 - 36.7 ppt. Mean bottom values observed at each site showed a strong correlation to the instantaneous measures collected during the primary site visit (r² = 0.9). Mean instantaneous surface salinities observed in the creeks and open water sites were 30.4 and 26.0 ppt, respectively. As with temperature, the mean difference between the instantaneous surface and bottom salinities was < 0.5 ppt at both creek and open water stations within each year (Appendix 2.1).

    Due to the drought conditions experienced in both years, approximately 95% of the state's tidal creek habitat and 87% of the open water habitat represented polyhaline waters (> 18 ppt; Appendix 2.5). Salinity ranges observed at each site were also generally small during the sampling period (< 10 ppt) except at five open water locations (Appendix 2.1). Until additional data are available, no criteria have been established by the SCECAP program to identify stressful conditions using salinity. However, the five open water sites with high salinity ranges (10.3 - 21.3 ppt) may represent stressful conditions to the organisms inhabiting those areas.

Comparison of the average salinity concentrations observed in tidal creek and open water habitats during 1999-2000, and estimates of the percent of the state's coastal habitat that represented various salinity ranges based on the average of measurements obtained over 25-hours at each station.

Dissolved Oxygen:

    Dissolved oxygen (DO) is one of the most critical water quality parameters measured in this program. Low dissolved oxygen conditions can limit the distribution or survival of most estuarine biota, especially if these conditions persist for extended time periods. Dissolved oxygen criteria established by the SCDHEC for "Shellfish Harvesting Waters" (SFH) and tidal saltwaters suitable for primary and secondary contact recreation (Class SA saltwaters) is a daily average not less than 5.0 mg/L with a low of 4.0 mg/L (SCDHEC, 2001a). Tidal saltwaters suitable for primary and secondary contact recreation, crabbing and fishing, except harvesting of clams, mussels, or oysters for human consumption (Class SB waters) should have dissolved oxygen levels not less than 4.0 mg/L. Since the SCECAP program was designed to sample only during a summer index period when DO levels would be at their lowest, DO measurements collected in this program approximate short-term worst-case conditions that may not necessarily occur for long time periods. Therefore, these measurements should not be used for regulatory purposes. However, SCECAP data does provide useful measures of average DO concentrations occurring in both tidal creek and open water habitats during a period when DO levels may be limiting, and it identifies areas within the state where this is occurring. Based on the state water quality standards, average DO concentrations > 4 mg/L are considered to be good and values > 5 mg/L are considered to be very good for this time of year. Average DO concentrations < 4 mg/L but > 3 mg/L are considered to be marginal (i.e. does not meet one portion of the state standards). Average DO concentrations < 3 mg/L are considered to be potentially stressful, especially since most of the sites with DO levels in this range had many measurements that were < 2 mg/L which represents hypoxic conditions known to be limiting to many estuarine and marine biota.

    The primary measure of dissolved oxygen used for SCECAP was based on a 25-hr average of measurements collected every 15 minutes by water quality meters deployed in the bottom waters of each site. During 1999 and 2000, the average DO concentration at open water stations was 4.9 mg/L and the average DO concentration in tidal creek habitats was only 4.1 mg/L. Approximately 91% of the state's open water habitat had good to very good DO levels that should not be limiting to most species of concern. Only 9% of the open water habitat had marginal DO conditions and none of the open water sites had poor DO concentrations. In contrast, only 54% of the state's tidal creek habitat had good to very good DO conditions, 39% of this habitat had marginal DO concentrations, and 7% had poor DO concentrations which may be limiting to many species.

    Since tidal creek habitats generally supported a greater density and diversity of fish and crustaceans than the open water sites (see biological summary), DO measures traditionally obtained by SCDHEC in larger open water may not be indicative of stressful conditions in creeks. However, creeks with poor DO levels (< 3 mg/L on average) may not fully support biological assemblages inhabiting those sites, especially during periods when DO levels are less than 2 mg/L (hypoxic conditions).
 

Comparison of the average dissolved oxygen concentrations observed in tidal creek and open water habitats during 1999-2000, and estimates of the percent of the state's coastal habitat representing various DO conditions.
 

pH:

    Measures of pH provide another indicator of water quality in estuarine habitats. The pH measurements are based on a logarithmic scale, so even small changes in the value can result in significant stress to estuarine organisms (Bamber, 1987, 1990; Ringwood and Keppler, 2002). Low pH values can indicate the presence of pollutants (e.g. release of acids or caustic materials) or high concentrations of carbon dioxide (Gibson et al., 2000).

    Because salinity and alkalinity affect the pH of estuarine waters, SCDHEC has established water quality standards that account for these effects. The pH in Class SA and SB tidal saltwaters should not vary more than one-half of a pH unit above or below effluent-free waters in the same geologic area having a similar salinity, alkalinity and temperature, and values should never be lower than 6.5 or higher than 8.5. Shellfish harvesting waters (SFH) shouldn't deviate more than 0.3 units from pH levels in effluent-free waters.

    The pH measurements used to characterize each site were collected from water quality meters deployed for 25 hrs. There were a sufficient number of sites in pristine areas having moderate to high salinities (18 - 40 ppt) to establish pH criteria for the SCECAP program. The majority of these stations were located in areas considered to be pristine environments (e.g. Cape Romain National Wildlife Refuge, North Inlet and Ashepoo, Combahee, and Edisto [ACE] National Estuarine Research Reserves, SFH class saltwaters). Only a few stations were sampled in 1999-2000 that had lower salinities. These stations were not evaluated for pH since we do not yet have a sufficient database to set criteria for what represents good, marginal, and poor pH levels in that salinity regime. For the SCECAP program, pH values below 7.4 were considered to represent marginal pH conditions and values below 7.1 represented poor conditions (see Van Dolah et al., 2002 for criteria methodology).

    The 1999 - 2000 average of pH values measured at tidal creek stations was lower than the average pH value measured at open water stations. Based on the SCECAP criteria, approximately 24% of the open water sites sampled had marginal or poor pH concentrations compared to about 42% of the tidal creek sites. The pH at these stations may be causing stress for some organisms, particularly at sites with values <7.1.

Comparison of the average pH concentrations observed in tidal creek and open water habitats during 1999-2000, and estimates of the percent of the high salinity stations having poor, moderate, or good pH values.

Errata:  The pH values shown in the pie figure and text are in error. The correct values are as follows: RO, 90% ≥7.4, 8% >7.1&<7.4, 2% <7.1; RT, 69% ≥7.4, 27% >7.1&<7.4, 4% <7.1.  Mean values apply to all stations statewide.

Nutrients:

    Nutrient loading into estuarine waters has become a major concern due to the rapid development that is occurring in the coastal zone of South Carolina and other states. This development results in increased nutrient input from wastewater treatment facilities, some industrial facilities, urban and suburban runoff of fertilizers, vehicle exhaust, etc. Other sources of nutrients include runoff from agricultural fields adjacent to estuarine habitats, riverine input of nutrient-rich waters from inland areas, and atmospheric deposition. High nutrient levels can lead to enrichment or eutrophication of estuarine waters resulting in excessive algal growth including harmful algal blooms (HAB), decreased dissolved oxygen, and other undesirable effects that adversely affect estuarine biota (Bricker et al., 1999).
There are no State or USEPA standards for the various forms of nitrogen (except ammonia) and phosphorus in estuarine waters. Therefore, the SCECAP data were compared to SCDHEC's historical database (SCDHEC, 1998a) to identify waters showing evidence of elevated nutrients. Values were also compared with guidelines published by NOAA for estuarine waters (Bricker et al., 1999), although it should be noted that those values represent dissolved rather than total nutrient concentrations.

Nitrogen:

    The average total nitrogen (TN) concentration measured at tidal creek sites was significantly higher than the average concentration measured at open water sites. Approximately 12% of the creek habitat and only 4% of the state's open water habitat had TN concentrations that were considered to be enriched. In 2000, total dissolved nitrogen (TDN) was also measured. None of those samples had high TDN concentrations (> 1.0 mg/L) based on the guidelines developed for coastal waters by NOAA (Bricker et al., 1999) and there was no significant difference in TDN between creek and open water sites.

Comparison of the average total nitrogen (TN) concentrations observed in tidal creek and open water habitats during 1999-2000, and estimates of the percent of the state's coastal habitat with TN values that represent normal or enriched values relative to SCDHEC historical data.

Phosphorus:

    The average total phosphorus (TP) concentration measured at tidal creek sites was significantly higher than the concentration measured at open water sites. Approximately 47% of the state's tidal creek habitat showed moderate phosphorus enrichment and an additional 8% of that habitat was very enriched with respect to total phosphorus. In contrast, only 20% of the open water habitat showed moderate enrichment and none of the sites had highly enriched phosphorus levels. The higher phosphorus concentrations may represent natural conditions in creek habitats since the historical database was based on sampling in larger open water systems. Additional data collected through this program will help to resolve whether new guidelines for TP enrichment should be considered for creek habitats. Until those data are available, the historical SCDHEC database provides the best record of deviations from normal estuarine water quality conditions.
The average total dissolved phosphorus (TDP) concentration measured in the creek versus open water stations in 2000 was not significantly different. Using the NOAA guidelines (Bricker et al., 1999), none of the open water sites and only two of the creek sites were enriched.

Comparison of the average total phosphorus (TP) concentrations observed in tidal creek and open water habitats during 1999-2000, and estimates of the percent of the state's coastal habitat with TP ranges that represent normal, enriched, or highly enriched values relative to SCDHEC historical data.

Silica:

    Dissolved silica (DS) measurements are primarily collected for the National Coastal Assessment Program and therefore were not collected in 1999. Low silica levels can be a limiting factor in the production of certain forms of phytoplankton, primarily diatoms. Average silica concentrations in 2000 were 2.1 mg/L at tidal creek sites and 1.5 mg/L at open water sites (Appendix 2.3). All of the DS concentrations measured in 2000 represent relatively high values that should not be a limiting nutrient for phytoplankton species in South Carolina waters since the ratio of dissolved inorganic nitrogen to dissolved silica at all sites (mean ratio = 0.05) was well below the 1:1 ratio considered to be critical (Day et al., 1989).

Biochemical Oxygen Demand:

    The five-day biochemical oxygen demand (BOD₅) is a measure of the amount of oxygen consumed by the decomposition of organic matter, both natural and man-made wastes, in the water column. Although BOD₅ is regulated by National Pollutant Discharge Elimination System (NPDES) permits to protect instream dissolved oxygen, there are no freshwater or saltwater standards for natural waters. Both the SCDHEC water quality monitoring program and the SCECAP program include measurements of BOD₅ in order to obtain information on areas where unusually high values may be occurring. Average BOD₅ concentrations sampled in 1999-2000 were similar at creek and open water sites. However, a slightly higher percentage of the state's tidal creek habitat had BOD₅ levels that exceeded the 75th and 90th percentiles of historical observations when compared to open water habitat. High BOD₅ concentrations may be indicative of poor water quality.

Comparison of the average five-day biochemical oxygen demand (BOD5) concentrations observed in tidal creek and open water habitats during 1999-2000, and estimates of the percent of the state's coastal habitat representing BOD5 ranges that were normal, enriched, or highly enriched values relative to SCDHEC historical data.

Fecal Coliform Bacteria:

    Coliform bacteria are present in the digestive tracts and feces of all warm-blooded animals. Public health studies have established correlations between adverse human health effects and concentrations of fecal coliform bacteria in recreational, drinking, and shellfish harvesting waters. State fecal coliform standards to protect primary contact recreation require a geometric mean count that does not exceed 200 colonies/100 mL based on five consecutive samples in a 30 day period and no more than 10% of the samples shall exceed 400 colonies /100 ml. To protect for shellfish consumption, the geometric mean can not exceed 14 colonies/100 mL and no more than 10% of the samples shall exceed 43 colonies/100 mL (SCDHEC, 1998b). Since only a single fecal coliform count was collected at each site, compliance with the standards cannot be strictly determined, but the data can provide some indication of whether the water body is likely to meet standards. For the SCECAP program, we consider any sample with > 43 colonies / 100 mL to represent marginal conditions (i.e. potentially not supporting shellfish harvesting) and any sample with > 400 colonies / 100 mL to represent poor conditions (i.e. potentially not supporting primary contact recreation).

    Average fecal coliform concentrations were higher in creeks than in open water during 1999 - 2000. Approximately 17% of the state's creek habitat was marginal and 1% was poor with respect to fecal coliform concentrations. In contrast, only 5% of the open water habitat was marginal and 1% was poor. The higher fecal coliform counts observed in creek habitats is most likely due to the proximity of these small drainage system to upland runoff from both human and domestic as well as wildlife sources, combined with the lower dilution capacity compared to larger water bodies. Greater protection of tidal creek habitats is warranted in areas where upland sources of waste can be controlled.

Comparison of the average fecal coliform concentrations observed in tidal creek and open water habitats during 1999-2000, and percent estimates of the state's coastal habitat representing concentrations that are acceptable (green), possibly unsuitable for shellfish harvesting (yellow), or possibly unsuitable for primary contact recreation (red).
 

Turbidity:

    Measures of water clarity provide an indication of the amount of suspended particulate matter in the water column. South Carolina's estuarine waters are naturally turbid compared to many other states. Exceptionally high turbidity levels may be harmful to marine life. SCDHEC has recently developed a maximum saltwater state standard for turbidity of 25 NTU. This corresponds to the 90th percentile of the SCDHEC saltwater database, which was obtained primarily from the larger estuarine water bodies. The 75th percentile, representing partially elevated levels, is 15 NTU (Appendix 2.5).

    Average turbidities measured in 1999-2000 by this program were 21 NTU in the tidal creeks and 14 NTU in the open water habitat (Appendix 2.4). This difference was statistically significant (p < 0.001). Based on the single measure of turbidity taken at each station, approximately 23% of the tidal creek habitat exceeded the State standard, whereas only 8% of the open water habitat exceeded the standard (Appendix 2.4, 2.5). Turbidity levels in tidal creeks may be naturally higher due to the shallow depths of these systems (i.e. surface samples are often within 1-2 m of the bottom) combined with re-suspension of the bottom sediments due to tidal currents. Further sampling by this program will determine whether the turbidity criteria accurately reflect excessive conditions in tidal creeks.

Comparison of the average turbidity concentrations observed in tidal creek and open water habitats during 1999-2000, and estimates of the percent of the state's coastal habitat representing various turbidity ranges that represent normal, enriched, or highly enriched values relative to SCDHEC historical data.

Alkalinity:

    Alkalinity measurements were collected for the SCECAP program to be consistent with SCDHEC's larger water quality monitoring program. There are no state standards for alkalinity in saltwater and research is lacking on how high or low alkalinity values affect estuarine biota. Until additional data are gathered for this parameter in the SCECAP program, combined with better information on how alkalinity should be interpreted, the data are only summarized in Appendix 2.4.

Integrated Water Quality Measure:

    The integrated water quality score developed for the SCECAP program incorporates six of the water quality measures described above: Dissolved Oxygen, Biochemical Oxygen Demand, Fecal Coliform Bacteria, Total Nitrogen, Total Phosphorus, and pH. An explanation of the scoring process is provided by Van Dolah et al. (2002). Sites coding as poor (red) generally had four to six of the individual water quality variables coding as poor or marginal. Approximately 5% of the state's creek habitat had poor water quality in 1999-2000, whereas none of the open water habitat had poor water quality. Sites with marginal water quality (yellow) generally had 2-3 parameters coding as marginal or poor. Approximately 33% of the state's creek habitat had marginal water quality conditions compared to approximately 11% of the open water habitat. The higher percentage of poor and marginal water quality conditions in creeks indicates that these habitats are often more stressful environments and may, in part, reflect the relatively greater effect of anthropogenic runoff into these smaller water bodies due to their proximity to upland sources and their lower dilution capacity. However, since many of the creeks with poor water quality were in relatively pristine locations, some of the differences observed between creek and open water sites may simply be the result of using thresholds derived form SCDHEC's historic database, which is composed predominantly of data from open water habitats. Once a larger database is available, our threshold criteria for some of the water quality parameters measured in creek habitats may be changed from those used in this report to reflect the greater natural variability in these habitats.

Proportion of the South Carolina's estuarine habitat that ranks as good (green), marginal (yellow), or poor (red) using the integrated water quality score developed for the SCECAP program. The left portion of the figure shows examples of how individual stations coded for each of the six water quality parameters and the average integrated score for each station based on the combined numerical ratings of the six parameters (Van Dolah et al., 2002). The right portion of the figure shows the estimated proportion of water quality conditions for the entire coastal zone of the state.