A multivariable approach for evaluating major impacts on water quality in Murrells and North Inlets, South Carolina.
ABSTRACT Urbanization poses a particular threat to the coastal areas of the southeastern United States United States, officially United States of America, republic (2005 est. pop. 295,734,000), 3,539,227 sq mi (9,166,598 sq km), North America. The United States is the world's third largest country in population and the fourth largest country in area. where uplands surrounding wetlands are still relatively undeveloped compared with other regions. Predictive models, which would correlate information on land use change and development, would be useful so that downgrades in water quality can be predicted before they occur to allow effective land management decisions to be made. The approach used for this study involved a historical comparison of land use change and fecal coliform coliform /col·i·form/ (kol´i-form) pertaining to fermentative gram-negative enteric bacilli, sometimes restricted to those fermenting lactose, e.g., Escherichia, Klebsiella, or Enterobacter. bacterial densities on Murrells Inlet (MI) (urbanized site) (n = 2026 samples) and North Inlet (NI) (pristine site) (n = 1656 samples), both bar-built estuaries located on the northern coast of South Carolina South Carolina, state of the SE United States. It is bordered by North Carolina (N), the Atlantic Ocean (SE), and Georgia (SW). Facts and Figures
Area, 31,055 sq mi (80,432 sq km). Pop. (2000) 4,012,012, a 15. south of Myrtle Beach. The microbiological and water quality data used in this research covered the period of 1967-1995 and the following parameters were used: date of sampling, most probable number (MPN MPN Master Promissory Note
MPN Most Probable Number
MPN Medical Provider Network
MPN Mobil Producing Nigeria
MPN Manufacturer's Part Number
MPN Military Personnel, Navy
MPN Mobile Private Network
MPN Managed Private Network
MPN Mode Partition Noise ) of fecal coliform bacteria coliform bacteria
Rod-shaped bacteria usually found in the intestinal tracts of animals, including humans. Coliform bacteria do not require but can use oxygen, and they do not form spores. They produce acid and gas from the fermentation of lactose sugar. , salinity, rainfall and water temperature. The regression models used the above parameters and a change in trend term that accounted for both instantaneous and gradual changes in water quality that may arise from a particular environmental intervention. For MI, the 1980 environmental intervention consisted of the construction of a jetty jetty: see coast protection. and the conversion from septic tanks to a main sewer line Noun 1. sewer line - a main in a sewage system
main - a principal pipe in a system that distributes water or gas or electricity or that collects sewage of approximately 92% of all residences. For NI, the 1973 and 1977 interventions were the construction of Baruch Laboratory and urban development of Debidue Island, respectively. For MI, the intervention, controlling for other environmental parameters, was found to be significant at the alpha = 0.05 level. There was a significant decrease in the increasing trend of fecal coliform bacteria for MI and the conversion to the sewage collection system had a beneficial effect on water quality and probably dominated the jetty effect. For NI, the laboratory construction had no overall impact on water quality so background natural sources of bacteria probably masked any small increases from human sources.
KEY WORDS: regression, Escherichia coli Escherichia coli (ĕsh'ərĭk`ēə kō`lī), common bacterium that normally inhabits the intestinal tracts of humans and animals, but can cause infection in other parts of the body, especially the urinary tract. , estuaries, southeast, septic system
Coastal marshes and estuaries serve as nursery and spawning grounds for numerous aquatic species. For instance, it is estimated that at least 70% of recreationally important and 96% of commercial shellfish and fish of the southeastern United States use estuaries and near-shore marine habitats at some point in their life cycle (Fulton et al. 1993). Specifically, marsh grasses in the wetlands provide shelter and nourishment for growing larvae Larvae, in Roman religion
Larvae: see lemures. and juvenile invertebrates and fishes (Charleston Harbor The Charleston Harbor is an inlet (8 sq mi/20.7 km²) of the Atlantic Ocean at Charleston, South Carolina. The inlet is formed by the junction of Ashley and Cooper rivers at . Morris and Moultrie Island. shelter the entrance. Project 1992). Also, the more than 300 estuaries in the southeastern and Gulf coasts of the United States, Puerto Rico Puerto Rico (pwār`tō rē`kō), island (2005 est. pop. 3,917,000), 3,508 sq mi (9,086 sq km), West Indies, c.1,000 mi (1,610 km) SE of Miami, Fla. and the Virgin Islands support $3.4 billion in recreational and over $850 million in commercial fisheries (Fulton et al. 1993). Over the last couple of decades, the United States has become increasingly dependent on imported shellfish. Specifically, United States imports of molluscan mol·lus·can also mol·lus·kan
Of or relating to the mollusks.
A mollusk. shellfish have grown from 20 million pounds in 1970 to 57 million pounds in 1990. In spite of inflation, the actual value of total United States harvests of scallops, clams and oysters has declined from $368 million in 1985 to $360 million in 1989. This pattern has held in spite of restoration efforts such as selective breeding
Selective breeding in domesticated animals is the process of developing a cultivated breed over time. , hatchery hatchery
a commercial establishment dedicated to the hatching of bird eggs to provide day old chicks and poults to the poultry industry.
the contents of unfertilized eggs. Used in petfood manufacture. operations and oyster reef replenishment (Leonard 1993, Leonard et al. 1991).
In addition, coastal areas of the United States are being rapidly developed. It had been estimated that by the year 2000, 75% of the United States population would live within 50 miles of the ocean coastline and the great lakes Great Lakes, group of five freshwater lakes, central North America, creating a natural border between the United States and Canada and forming the largest body of freshwater in the world, with a combined surface area of c.95,000 sq mi (246,050 sq km). (Vernberg et al. 1992). In the southeast, the number of people has more than doubled from 4 million in 1960 to 9.1 million in 1990 (Culliton et al. 1990). Encompassing the South Carolina (SC) study sites, Georgetown and Horry counties experienced a substantial growth in population during recent decades. Based on census data, population figures for Georgetown County in 10-year increments were 34,798 (1960), 33,500 (1970), 42,461 (1980) and 46,802 respectively (1990). For Horry County, analogous population figures were 68,247 (1960), 69,992 (1970), 101,419 (1980) and 144,053 (1990) respectively (United States Dept. of Commerce, Bureau of the Census Noun 1. Bureau of the Census - the bureau of the Commerce Department responsible for taking the census; provides demographic information and analyses about the population of the United States
Census Bureau 1960-1990). This change in population distributions is expected to have a harmful impact on coastal ecosystems Coastal ecosystems are considered to be one of the most productive ecosystems on Earth. They can be referred to as “the intertidal and subtidal areas above continental shelf (to a depth of 200m) and adjacent land area up to 100 km inland from the coast” (PAGE, 2001). . Most believe that, other things being equal, an increase in the concentrations of enteric enteric /en·ter·ic/ (en-ter´ik) within or pertaining to the small intestine.
1. Of, relating to, or within the intestine.
2. pathogens is typically associated with increasing densities of human populations (Maiolo & Tschetter 1981). Several large monitoring studies in coastal areas have shown increased contaminant contaminant /con·tam·i·nant/ (kon-tam´in-int) something that causes contamination.
something that causes contamination. concentrations near urban areas (O'Connor 1996, Daskalakis & O'Connor 1995, Sericano et al. 1993). One impact of urbanization on coastal wetlands is the loading of human bacterial pathogens into wetland waters and the subsequent contamination of aquatic species and the lowering of water quality (Blood et al. 1992, USEPA USEPA United States Environmental Protection Agency 1988). Consequently, there have been reductions in the amount of domestic seafood that can be harvested commercially and an increase in our dependence on imported seafood. Similarly, there have been restrictions of recreational uses of these nearshore near·shore
The region of land extending from the backshore to the beginning of the offshore zone.
near waters (e.g., recreational gathering of shellfish or swimming; Weiskel et al. 1996, Maiolo & Tschetter 1981).
Urbanization poses a particular threat to those coastal areas of the southeastern United States (i.e., parts of South Carolina and Georgia) where the lands surrounding the wetlands are still undeveloped compared with other regions. The estuaries there also tend to be shallow and the rivers are not of sufficiently large In mathematics, the phrase sufficiently large is used in contexts such as:
Area, 52,586 sq mi (136,198 sq km). Pop. 1974 (Maiolo & Tschetter 1981). Elevated levels of fecal coliform bacteria have been associated with urbanization and human activities. Some research has showed that fecal bacteria densities were directly related to housing density, population, development, apparent animal density and percent impervious area (Young & Thackston 1999). The coliform group consists of all the aerobic and facultative anaerobic anaerobic /an·aer·o·bic/ (an?ah-ro´bik)
1. lacking molecular oxygen.
2. growing, living, or occurring in the absence of molecular oxygen; pertaining to an anaerobe. gram negative, rod-shaped, nonspore forming bacteria, which ferment ferment /fer·ment/ (fer-ment´) to undergo fermentation; used for the decomposition of carbohydrates.
1. lactose with the formation of gas within a 48 h period at 35[degrees]C (Koren 1991). At the present time, the fecal coliform bacterial group is the standard for fecal pollution in surface waters and is comprised of species that reside in the intestines of warm-blooded mammals and birds (Dufour 1977). This group includes Escherichia coli (E. coli E. coli: see Escherichia coli.
in full Escherichia coli
Species of bacterium that inhabits the stomach and intestines. E. coli can be transmitted by water, milk, food, or flies and other insects. ), Escherichia aurescens, Escherichia intermedia Intermedia - A hypertext system developed by a research group at IRIS (Brown University). , Escherichia freundii, Aerobacter aloacae, Aerobacter aerogenes Aerobacter aerogenes
a name formerly used to describe some strains of klebsiellapneumoniae. and the biochemical intermediates between Escherichia and Aerobacter (Koren 1991). Fecal coliforms Fecal coliforms (sometimes faecal coliforms) are facultatively-anaerobic, rod-shaped, gram-negative, non-sporulating bacteria. They are capable of growth in the presence of bile salts or similar surface agents, oxidase negative, and produce acid and gas from lactose within are important indicators of public health. On the average, [10.sup.10) E. coli organisms are generated per human per day (Edberg et al. 1994). The threat to human health occurs when human and/or animal feces come in contact with and contaminate con·tam·i·nate
1. To make impure or unclean by contact or mixture.
2. To expose to or permeate with radioactivity.
con·tam·i·nant n. drinking water drinking water
supply of water available to animals for drinking supplied via nipples, in troughs, dams, ponds and larger natural water sources; an insufficient supply leads to dehydration; it can be the source of infection, e.g. leptospirosis, salmonellosis, or of poisoning, e.g. supplies, recreational waters and/or growing waters of filter-feeding shellfish (Gersberg et al. 1995, Zonderman & Shader 1993). Shellfish absorb food by means of a filtering process that has a low level of selectivity. Besides food, suspended sediments, toxic algae algae (ăl`jē) [plural of Lat. alga=seaweed], a large and diverse group of primarily aquatic plantlike organisms. These organisms were previously classified as a primitive subkingdom of the plant kingdom, the thallophytes (plants that , bacteria and viruses may also be absorbed. Thus, shellfish can be contaminated contaminated,
v 1. made radioactive by the addition of small quantities of radioactive material.
2. made contaminated by adding infective or radiographic materials.
3. an infective surface or object. with various disease-causing microorganisms residing in overlying overlying
suffocation of piglets by the sow. The piglets may be weak from illness or malnutrition, the sow may be clumsy or ill, the pen may be inadequate in size or poorly designed so that piglets cannot escape. water, especially in shallow water See:
ISSC Interstate Shellfish Sanitation Conference
ISSC International Social Sciences Council
ISSC Integrated Systems Solutions Corporation
ISSC Information Systems Steering Committee
ISSC Information Systems Sub-Committee 1997). In the United States, point and nonpoint non·point
Not found or located at a single, definable point, as pollution whose source cannot be ascertained. sources each account for about 38% of all closures of shellfish harvesting areas (Leonard et al. 1991). Pollutants of the latter category may be distinguished from the former because they seep or run off into waterways instead of entering the water through a discrete conduit or discharge (Nadakavukaren 1990). Examples of nonpoint sources of contamination include agricultural runoff, malfunctioning or poorly located septic systems, runoff from vegetated areas (e.g., wetlands) and deposition directly by waterfowl waterfowl, common term for members of the order Anseriformes, wild, aquatic, typically freshwater birds including ducks, geese, and screamers. In Great Britain the term is also used to designate species kept for ornamental purposes on private lakes or ponds, while in feces (Weiskel et al. 1996). Compared with point sources, nonpoint sources are more difficult to control because of problems in localizing and identifying their origins (Leonard et al. 1991). The most important nonpoint source of pollutants are septic systems, also known as ground absorption treatment, typically found in outlying rural and beach areas (Maiolo & Tschetter 1981). Both sources are associated with a seasonal population influx, an expansion in tourism and development in housing and accompanying infrastructure (e.g., roadways, solid waste and human waste disposal; Leonard et al. 1991).
The measurement of the concentration of fecal coliforms in the vicinity of a given molluscan shellfish bed is currently the major criterion for deciding when and if shellfish harvesting should be approved for human consumption (Dufour 1977). However, the current regulations could be improved by incorporating existing meteorological me·te·or·ol·o·gy
The science that deals with the phenomena of the atmosphere, especially weather and weather conditions.
[French météorologie, from Greek and land use change data into predictive models. Moreover, they do not anticipate the potential downgrading of approved harvest areas that may arise from high rates of coastal development. What are needed are predictive methods that would correlate information on land use change/development so that downgrades in water quality can be predicted before they occur and corrective development/environmental management approach can be made to prevent water quality degradation. This approach used for this study involved an historical comparison of land use change and fecal coliform bacterial densities on Murrells Inlet (MI) and North Inlet (NI), determining important benchmark development dates, developing a database and appropriate models to which to test hypotheses or investigate research questions and then performing statistical analyses on these data.
MATERIALS AND METHODS
Study and Control Sites
Murrells Inlet (33[degrees]33'N, 79[degrees]01'W) is a highly suburbanized, bar-built estuary located approximately 32 km north of NI and 90 km north of Charleston, SC and covers sections of Horry and Georgetown Counties (Fig. 1, Table 1). The northern two-thirds of the estuary consist largely of commercial, residential and tourism related land uses, whereas the remaining part is predominantly undeveloped state park (Newell 1997). MI has experienced a high rate of development in recent years. Its population of permanent residents had increased 230% (from 1,000-3,300 people) during the 1980s and had one of the highest population densities in SC as of 1990. In MI there are neither discharges of standard industrial code industries nor agricultural runoff into shellfish harvesting waters. As a result, MI was selected for inclusion in this study because there is a negligible amount of inputs from these sources. Thus, the vast majority of closures would be because of fecal coliforms from suburban housing, marinas and service industries (Fulton et al. 1993), with wildlife sources being negligible, except on the southern end of the estuary that is maintained as a state recreational area.
North Inlet (33[degrees]20'N, 79[degrees]10'W) served as a pristine reference site, relatively free from human agricultural, urban or industrial development (Fig. 1). Nevertheless, wildlife there has significantly affected the numbers of fecal coliform bacteria that are loaded into the estuary through natural forest runoff. NI is a bar-built estuary that is bounded to the northeast by Debidue Island and to the southeast by North Island (Fulton et al. 1993, Vernberg et al. 1992, Newell 1990). It is made up of stable and temporary habitats that are linked by a tidally fluctuating water height. The major functional and structural habitats of NI consist of a water column (tidal creeks and pools), oyster reefs, a subtidal benthos benthos: see marine biology. (the whole assemblage of plants or animals living on the sea bottom) and a vegetated marsh surface and subsurface (Vernberg et al. 1992). NI is rather unique because private institutions (Yawkey Foundation and Belle W. Baruch Belle W. Baruch was the daughter of financier Bernard Baruch.
Her legacy is preserved in the Belle W. Baruch Institute for Marine Biology and Coastal Research established on Hobcaw Barony Foundation) own large tracts of this estuary (Vernberg et al. 1992). NI has also been designated by the national oceanic and atmospheric administration Noun 1. National Oceanic and Atmospheric Administration - an agency in the Department of Commerce that maps the oceans and conserves their living resources; predicts changes to the earth's environment; provides weather reports and forecasts floods and hurricanes and (NOAA NOAA
National Oceanic and Atmospheric Administration
Noun 1. NOAA - an agency in the Department of Commerce that maps the oceans and conserves their living resources; predicts changes to the earth's environment; ) as a national estuaries research reserve (NERR NERR National Estuarine Research Reserves
NERR Network Error
NERR New Error Type ) site. This has limited developmental activity and probably contributed to the overall pristine condition of NI. Because there is a negligible level of industrial or agricultural activity and because red tides are a very infrequent occurrence on the SC coastline, nearly all the closures of harvesting areas in this estuary could be attributed to fecal coliforms that were primarily from wildlife sources (Fulton et al. 1993).
The microbiological and water quality data used in this research covers the period of 1967-1995 and were available on a Storet CD-ROM CD-ROM: see compact disc.
in full compact disc read-only memory
Type of computer storage medium that is read optically (e.g., by a laser). that was compiled by the SC department of health and environmental control (DHEC DHEC Department of Health and Environmental Control
DHEC Deep Heat Energy Corporation ) this data was also utilized in (Nelson 1998) from which much of the present work is drawn. Among the parameters obtained were the time and date of sampling, most probable number (MPN) of fecal coliform bacteria, salinity (parts per thousand) and the water temperature (degrees Celsius). Daily rainfall records for the study period have been recorded by the national weather service at Brookgreen Gardens Brookgreen Gardens is a sculpture garden and wildlife preserve near Pawleys Island, South Carolina.
It is the creation of Archer and Anna Hyatt Huntington of Connecticut, who purchased the old Brookgreen rice plantation and some neighboring land to open the garden to the (BG) (near MI and NI) and at Beaufort, SC. These two stations were found to have a high correlation (r = 0.763, P < 0.0001) so it is likely that the precipitation patterns at BG were a better approximation to those at MI and NI because these sites are much closer to BG than is Beaufort. The BG site is approximately 4 km from MI and 28 km from NI. Moreover, the relevant information on the history of urban development of the respective estuaries came from Mary Culberson (Georgetown Water and Sewer) and Charles Newell (DHEC Myrtle Beach). The principal statistical method for analyzing the available data was intervention analysis. Because the data is of a temporal nature, it was important to focus on large-scale events in the developmental history of a given estuary and examine how the response variable (i.e., fecal coliform (FEC See forward error correction.
FEC - Forward Error Correction ) bacteria concentration) was affected by important developmental events. There are several types of intervention models that are summarized in Table 2. Figure 2 A depicts a theoretical example of the Mean-Shift intervention model. This is a sudden-impact model with no trend before the date of interest (the intervention date). The striking feature of this model is that there is no chronologic trend but there is abrupt increase in the parameter of interest (e.g., fecal coliform bacterial density, coinciding with a 1980 intervention). Its form may resemble the following equation:
[log.sub.10] (FEC) = [[alpha].sub.1] Salin + [[alpha].sub.2] Temp + [[alpha].sub.3] [[log.sub.e] (Rain) + [[alpha].sub.4] Il + [epsilon] (1)
[log.sub.10] (FEC) = transformed MPN fecal coliform concentration
Salin = salinity
Temp = water temperature
Rain = rainfall
[FIGURE 2 OMITTED]
Il = indicator variable of date (1 if the date occurs after the intervention, 0 otherwise)
The Il term of the equation captures the effect of this jump. Bacterial MPN concentration and rainfall are logarithmically log·a·rithm
The power to which a base, such as 10, must be raised to produce a given number. If nx = a, the logarithm of a, with n as the base, is x; symbolically, logn a = x. transformed because they are skewed skewed
curve of a usually unimodal distribution with one tail drawn out more than the other and the median will lie above or below the mean.
skewed Epidemiology adjective Referring to an asymmetrical distribution of a population or of data to the right and deviate substantially from normality.
Figure 2B depicts an example of the Trend-Plus-Jump Model.
This is a sudden impact model with an underlying increasing trend. Again, there is an abrupt increase in the parameter of interest mean [Log.sub.10] FEC because of the 1980 intervention. The general equation for this model has the following form:
[log.sub.10] (FEC) = [[alpha].sub.1] Salin + [[alpha].sub.2] Temp + [[alpha].sub.3] [log.sub.e] (Rain) + [[alpha].sub.4] Date + [[alpha].sub.5] Il + [epsilon] (2)
Here, the additional Date term captures the trend effect, whereas the Il term is representative of the sudden increased effect.
Figure 2C depicts the Change-In-Trend model. This model allows for the assessment of a sudden impact and/or change in trend. Figure 2C shows an abrupt increase in the parameter of interest mean [log.sub.10] FEC with the 1980 intervention. At the same time, an increasing pattern of [log.sub.10] FEC ceases after 1980. A general equation for this would take a form as follows:
[log.sub.10] (FEC) = [[alpha].sub.1] + [[alpha].sub.2]Temp + [[alpha].sub.3] [log..sub.e] (Rain) + [[alpha].sub.4]Date + [[alpha].sub.5] Il + [[alpha].sub.6] Il Date + [epsilon] (3)
Here, the interaction term I1Date accounts for the change in trend. Equation 3 is a desirable model for the water quality data because it is the most general and powerful as the following cases demonstrate:
a) If [[alpha].sub.4] [not equal to] 0, [[alpha].sub.5] = 0 and [[alpha].sub.6] = 0, then there is a Constant-Trend Model (no intervention).
b) If [[alpha].sub.4] = 0, [[alpha].sub.5] [not equal to] 0 and [[alpha].sub.6] = 0, then we have a Mean-Shift Model (no trend).
c) If [[alpha].sub.4] [not equal to] 0, [[alpha].sub.5] [not equal to] 0 and [[alpha].sub.6] = 0, then we have a Trend- Plus-Jump Model.
d) If [[alpha].sub.4] [not equal to] 0, [[alpha].sub.5] [not equal to] 0 and [[alpha].sub.6] [not equal to] 0, Change in-Trend Model
After evaluating fecal coliform data compiled before the intervention date of 1980 in MI, it was concluded that the Change-in-Trend Model was the appropriate focus in the analyses because it is the only model that accounts for long-term trends in water quality and short-term changes that are attributable to an intervention. It accommodates the instantaneous and gradual changes that a given intervention would have on the concentration of fecal coliform bacteria. All models used the logarithm logarithm (lŏg`ərĭthəm) [Gr.,=relation number], number associated with a positive number, being the power to which a third number, called the base, must be raised in order to obtain the given positive number. transformation for normalizing the right-skewed distributions of coliform bacteria and rainfall. Some of the observations were outside the detectable range of the microbiologic multiple tube dilution test (generally 2 to 2,400 MPN bacteria per 100 mL). For convenience, extreme readings outside the detectable range of the fecal coliform estimates were conservatively estimated by adding or subtracting one unit above or below, respectively, the limits of detection. Thus, a measure that was <2 MPN was coded as 1, whereas a reading that was >2400 MPN was coded as 2401.
On MI, three land use development events in the period 1967 to 1995 were identified as having the potential to affect coliform concentrations (Table 3). The first was the completion and conversion of most of the septic tanks to the central sewer line by April 1980 (Fred Earnhart, Georgetown Water and Sewer, Georgetown, SC, pers. comm.). This would be expected to decrease E. coli concentrations because septic tanks periodically leak and thus discharge fecal coliform bacteria into the waterways. Second, there was a completion of the construction of a large jetty by August 1981 that had begun in September 1977 (Dr. Dave Bushack, Belle W. Baruch Laboratory, Georgetown, SC, pers. comm.). In contrast to the sewer conversion, the jetty construction was predicted to increase coliform and decrease salinity levels by reducing the tidal amplitude of the estuary because the jetty blocks some of the intrusion of clean ocean water into the estuary. Offshore oceanic water dilutes and thus reduces the concentration of fecal coliform contaminants in the estuary. It was not clear which of these events was dominant. Because both events were so close, chronologically, and because there were few samples taken between them, the date 6/15/80 was selected to account for both events. The third key intervention event was the completion of the construction of public boat ramp in January 1986. A boat ramp increased the volume of boat traffic and would probably be an important source of pollutants because many boats may potentially release marine sanitation debris into estuarine es·tu·a·rine
1. Of, relating to, or found in an estuary.
2. Geology Formed or deposited in an estuary.
Adj. 1. estuarine - of or relating to or found in estuaries
estuarial surface water. Thus, 1/15/86 was selected as the intervention date for assessing effects of boat ramp construction.
For NI, there has been little anthropogenic an·thro·po·gen·ic
1. Of or relating to anthropogenesis.
2. Caused by humans: anthropogenic degradation of the environment. activity during the time of data collection. Nonetheless, two potential sources of contamination are outlined in Table 3. These were the completion of the construction of Baruch Laboratory in June 1973. Thus, the date 6/15/73 was selected. Later, the construction of the Debidue housing development began in the middle part of the 1970s. An intervention date of 1/15/77 was selected to approximate the completion of the initial phase of residential development at Debidue Island near NI. Whereas pristine, it is important to realize that adjacent to NI, and to the south is Winyah Bay Winyah Bay is a coastal estuary that is the confluence of the Waccamaw River, the Pee Dee River, the Black River and the Sampit River in Georgetown County in eastern South Carolina. (WB). Unlike NI, WB is a partially mixed and low salinity estuary that receives fresh water from the Black, Pee Dee Pee Dee or Great Pee Dee, river, c.435 mi (700 km) long, rising in the Blue Ridge, W N.C., and flowing NE then SE to Winyah Bay, S.C. It is called the Yadkin until it is joined by the Uharie River W of Troy, N.C. and Waccamaw Rivers that drain extensive agricultural areas. The relatively high flow rates of these rivers enables anthropogenic wastes to be readily transported from nearby industrialized in·dus·tri·al·ize
v. in·dus·tri·al·ized, in·dus·tri·al·iz·ing, in·dus·tri·al·iz·es
1. To develop industry in (a country or society, for example).
2. Georgetown (Lackland et al. 1982). In the analysis, some water sampling stations To enhance water quality monitoring in a drinking water network sampling stations are installed along the route of the water network. Water sampling stations are connected to next water main and have a little sink. on the southern end of NI near WB were excluded because they were located within the tidal node for WB.
Descriptive statistical outputs (monthly/yearly) of fecal coliform bacteria and rainfall data were coupled for NI and MI to indicate the trend in each parameter over time. In addition, regression analysis In statistics, a mathematical method of modeling the relationships among three or more variables. It is used to predict the value of one variable given the values of the others. For example, a model might estimate sales based on age and gender. was conducted to assess the variables affecting fecal coliform bacteria densities such as rainfall and physiochemical physiochemical /phys·io·chem·i·cal/ (fiz?e-o-kem´ik-il) pertaining to both physiology and chemistry.
pertaining to both physiology and chemistry. water quality.
Yearly Trends in Fecal Coliform Bacteria
It is of interest to visually describe the yearly distributions of mean coliforms for each inlet with the distributions for rainfall at BG. Because BG is close to both study sites, one can see how the distribution of bacteria compares to that of rainfall depicted in Figure 3 and Figure 4. To avoid confusion, it should be noted that the zero bacteria concentration readings for MI in 1968 and for NI in 1969 and 1971 are caused by a lack of measurements taken during those years, rather than pristine water quality. In MI, note that fecal coliform densities were generally higher after the intervention than before. However, levels were not statistically different. In NI, fecal coliform densities were similar before and after the intervention dates. For these graphs, it is a bit difficult to visually assess the intervention. For instance, in MI mean annual bacteria levels were somewhat higher in the period following the intervention. However, the standard deviation In statistics, the average amount a number varies from the average number in a series of numbers.
(statistics) standard deviation - (SD) A measure of the range of values in a set of numbers. for this variable is sufficiently large that one cannot say for certain how bacteria levels were affected by the intervention (i.e., there was no statistically significant response). Because the analytic approach accounts for the potential influence of other variables and underlying trends in the data, it should be given more emphasis than the graphical approach depicted in Figures 3 and 4. These data show inconsistencies regarding the effect of the interventions. For NI, the limited number of sampling years before and after the intervention, respectively, makes it more difficult to draw conclusions about trends in the data. As mentioned, large rainfall events have been observed to elevate bacterial concentrations. The correlation coefficients (r) between loge (rainfall) and [log.sub.10] (coliform) concentrations generally support this observation, although some of these are weak but significant. For the MI station Main Creek at Atlantic Ave Bridge, r was found to be 0.363 (P = 0.0004) and for MI station Main Creek at Mickey Spillane's Home, an r = 0.436 (P < 0.0001) was observed. Similarly, for NI station North Inlet, an r = 0.251 (P = 0.0408) was observed and for NI station Town Creek at Debidue Creek, an r = 0.255 (P = 0.0388) was found. It should be noted that the correlations between rainfall and fecal coliform counts were considerably stronger and more significant for MI than for NI. This is suggestive of suggestive of Decision making adjective Referring to a pattern by LM or imaging, that the interpreter associates with a particular–usually malignant lesion. See Aunt Millie approach, Defensive medicine. a land use effect. In more developed areas rainfall/runoff would have more of an effect than a largely wooded area like North Inlet. Developed areas have more impervious surface Impervious surfaces are artificial structures, such as pavements and building roofs, which replace naturally pervious soil with impervious construction materials. They are an environmental concern because, with their construction, a chain of events is initiated that modifies urban coverage and less opportunity for rainfall to percolate percolate /per·co·late/ (per´kah-lat)
1. to strain; to submit to percolation.
2. to trickle slowly through a substance.
3. a liquid that has been submitted to percolation. into the ground; thus, greater pollution impacts.
[FIGURES 3-4 OMITTED]
Monthly Trends in Fecal Coliform Bacteria
For the monthly trends in fecal coliform bacterial density graphs (Figs. 5, 6), it can be seen that for MI, the before intervention (BI) fecal coliform bacteria densities peak in January, April and July and the after intervention (AI) densities peak in June and October. Rainfall appears to peak in January and the summer, a time when there is peak tourism. In comparison, for NI, the BI bacteria concentrations peak in January, April and September, whereas AI bacteria concentrations peak in March, April and November. The January and April coliform peaks may be attributed in part to winter waterfowl, a high water table condition, high wildlife activity, low wildlife feces degradation rates and a low rate of plant transpiration transpiration, in botany, the loss of water by evaporation in terrestrial plants. Some evaporation occurs directly through the exposed walls of surface cells, but the greatest amount takes place through the stomates, or intercellular spaces (see leaf). . Paired t-tests were run to compare the monthly mean coliform concentrations before and after the intervention. For MI, significant differences in coliform levels were found for January (P = 0.0188, BI > AI), March (P = 0.0051, BI > AI), May (P < 0.0001, AI > BI), June (P < 0.0001, AI > BI), October (P < 0.0001, AI > BI) and November (P = 0.0053, AI > BI). For NI, the mean bacterial densities also differed significantly for January (P = 0.0026, BI > AI), March (P = 0.0056, AI > BI), April (P = 0.0058, BI > AI) and September (P < 0.0001, BI > AI). The temporal similarity of January and March differences before and after the intervention indicated that similar variables (e.g., seasonal rainfall, high water table conditions and low feces degradation rates for wildlife) may affect fecal coliform densities in each estuary. Although the months where significant differences in the means varied in each inlet, the interventions seemed to influence the seasonal distributions of coliforms for MI and NI. As with the yearly plots, there were apparently 0 bacterial concentration readings for May and June during the period before the intervention, because no samples were collected for those months.
[FIGURES 5-6 OMITTED]
The intervention Change-in-Trend model was applied to MI where the individual station data were pooled. Several runs were done for the reduced model and models with different combinations of interactions. The 1986 intervention (boat ramp) proved not to be significant. The criterion that was used for determining a good model fit was a comparatively high adjusted [R.sup.2] (>0.25) and a low P value (<0.05) for the intervention parameter. After running regressions with the reduced model and models involving several interaction terms, the best-fitting model included rain-salinity interaction and found a significant change in trend resulting from the 1980 intervention. Table 4 gives a table of these analytic results. Here, date was significant (P = 0.0001), indicating an increasing trend in bacteria concentration over the period of data collection. I1 Date was also significant (P = 0.0001), suggesting a decrease in the increasing trend of coliform bacteria. I1 was marginally significant (P = 0.0573) suggesting the possibility for an instantaneous decline in bacteria concurrent with the intervention. When the earlier mentioned model was applied to the individual sampling stations, the following sites were found to have significantly changed (decreased fecal coliforms) after the intervention: Main Creek at Marlin Quay Marina (P = 0.0323), Main Creek at Inlet Range Marker A single calibration blip fed onto the time base of a radial display. The rotation of the time base shows the single blips as a circle on the plan position indicator scope. It may be used to measure range. (P = 0.0337), Allston Creek at Weston Flat (P = 0.0001), Allston Creek at Pogs Head Landing (P = 0.0017) and Parsonnage Creek at Nance's Dock (P = 0.0008). These stations can be seen spatially in Figure 7. Note that, spatially, most of the improved water quality was observed at stations nearest the mouth of the estuary, closest to clean, higher salinity oceanic seawater seawater
Water that makes up the oceans and seas. Seawater is a complex mixture of 96.5% water, 2.5% salts, and small amounts of other substances. Much of the world's magnesium is recovered from seawater, as are large quantities of bromine. . When stratified stratified /strat·i·fied/ (strat´i-fid) formed or arranged in layers.
Arranged in the form of layers or strata. by locality (inner [farthest], middle and outer [closest]), salinity was observed to increase approaching the open ocean: the mean salinity levels (parts per thousand) were 30.9 (inner), 34.3 (middle) and 35.0 (outer). Although regression analyses point out anticipated changes in water quality in response to a given intervention, in reality one would expect estuarine systems to respond nonlinearly to a given intervention. Figure 8 shows a possible interpretation for how water quality may have changed at Murrells Inlet. Here, a cubic function In mathematics, a cubic function is a function of the form
where a is nonzero; or in other words, a polynomial of degree three. was used to fit the yearly mean coliform concentrations:
MLFEC = -904078.2 + 1364.51 x Year - 0.686469 x [Year.sup.2] + 0.000115 x [Year.sup.3] (4)
[FIGURES 7-8 OMITTED]
This shows a gradual rather than sudden decrease in bacteria concentrations after the intervention and this seems reasonable given what is known about the geophysical nature of water quality in coastal South Carolina. However, extrapolation (mathematics, algorithm) extrapolation - A mathematical procedure which estimates values of a function for certain desired inputs given values for known inputs.
If the desired input is outside the range of the known values this is called extrapolation, if it is inside then outside the range of available data is uncertain because the wide 95% confidence limits for the mean predicted values in the plot illustrate. Figure 9 shows the plot of what MLFEC concentrations would have been assuming that no intervention had taken place. This takes on the following linear function:
MLFEC = -90.96471 + 0.046591 x Year (5)
[FIGURE 9 OMITTED]
Compared with the previous figure, it is clear that bacteria concentrations would have been higher in the absence of the septic tank/sewer convergence compared with that of the intervention. In particular, the expected MLFEC for 1995 without the intervention would be 1.98, whereas the corresponding value for the cubic model would be 1.08 with the intervention (a 45% reduction).
The methodology outlined earlier was also applied to NI where all the individual station data of estuaries were combined. Initially, a model was run containing the Date, I1, and I1 Date terms. However, this model had high variance inflation for some of the terms in the model. This indicated a probable multicollinearity among the independent parameters and the results would have to be interpreted with caution. At this point, the sudden impact term I1 was dropped, whereas I1 Date was retained because estuaries would be expected to respond gradually instead of instantaneously to a given intervention. The 1977 intervention proved not to be significant (P = 0.9191). The best-fitting model included rain-salinity interaction and found a marginally insignificant change in trend resulting from the 1973 intervention (P = 0.1189). Hence the 1973 intervention was used, whereas the 1977 intervention was not. The results from the regression model for the 1973 intervention may be found in Table 5. When the earlier mentioned model was applied to the individual sampling stations, only Town Creek at Sixty Bass Creek was statistically significant (P = 0.0285) (Fig. 10). This site is close to the tidal node from Winyah Bay and may indicate an increase in the rate of decrease in fecal coliform densities since 1973.
For MI, the overall inlet results are generally what one might expect. For an urbanized estuary, it was easier to detect improvements in water quality than for a pristine inlet. These results were consistent with the current water quality classification scheme in that rainfall was found to be an important variable in determining coliform concentrations and large rainfall events may contribute to closure of shellfish harvesting waters immediately after an event. When there was such a high level of development, anthropogenic inputs to the system may dominate over natural sources. Vernberg et al. (1997, 1999) found that fecal coliform bacteria in MI bad a much higher percentage of E. coli comprising the coliform group (83%) and only a small percentage of samples were free of coliforms (<5%) when compared with NI (53% E. coli and 23% coliform free respectively). This implies that MI is a greater potential source of human bacterial pollution than NI. Chestnut et al. (2000) have also shown that other urban areas of South Carolina also have high levels of E. coli comprising the fecal coliform group. Thus, the model was able to pick up an improvement in water quality resulting from the septic tank to sewer conversion. Although the jetty construction would be expected to act in the opposite direction (e.g., increase coliform counts caused by poorer flushing conditions), our data suggested that the septic tank to sewer conversion would likely have had a more pronounced impact on water quality than the jetty construction, because fecal coliform counts decreased based on our nonlinear model. Additionally the improvements in water quality in MI were most pronounced at the stations near the mouth of the estuary, near cleaner oceanic water.
Recent research by Kelsey et al. (2003) used multiple antibiotic resistance antibiotic resistance,
n the ability of certain strains of microorganisms to develop resistance to antibiotics.
antibiotic resistance (MAR) at MI to help identify fecal coliform by source. This research suggests that most of the fecal coliform pollution detected in MI estuary may be from nonhuman sources, including fecal coliforms found in areas adjacent to high densities of active septic tanks. For this study, human and pet wasteloads were ascertained for MI and it is estimated that the human to pet wasteload is 0.14. The process by which this figure was found is highlighted in Table 6. It has also been estimated that about 90% of residences in MI are currently connected to sewer lines. The product of these two coefficients is about 0.12 that is strikingly similar to the sudden decrease in bacteria concentrations highlighted in Table 4 (-0.12). This helps to validate our model and shows that manmade changes in land use for MI can affect water quality in spite of the fact that domestic animals and wildlife account for most of the bacteria concentration in this system.
Similarly, the findings at NI were not too surprising. Here, the construction of Baruch Laboratory and Debidue development only accounted for a small number of septic tanks and human inputs into the ecosystem. Thus, the background levels of bacteria contamination from natural wildlife sources would clearly outweigh the magnitude of contamination from any limited watershed development. In analyzing fecal coliform data for NI and MI over the entire 1967 to 1995 period, the fecal coliform density of NI should reflect primarily bacterial inputs from wildlife sources. Based on NI levels of fecal coliform representing wildlife sources (mean [log.sub.10] 0.83), mean fecal coliform densities in urbanized MI (mean [log.sub.10] 1.052) were only elevated by 27%. This implies the anthropogenic sources of fecal coliform bacteria may only account for 27% of the total fecal coliform burden in MI and NI. Also, natural fluctuations resulting from seasonal patterns in rainfall, salinity and temperature would potentially confound the effects from the intervention itself. Evidence of this was seen in the fact that the same monthly differences were seen before and after the interventions in NI and MI (January, March, April and September). Thus, rainfall and water table level(s) should be considered to be major factors affecting fecal coliform densities in each estuary.
Improved data collection and analysis may improve validity and applicability of the models in other ways. For example, localized variability in water currents may have affected how the coliforms responded to an intervention and other parameters, and this may also account for some of the unexplained variation of the models. Utilizing spatial procedures such as kriging could overcome some of these difficulties. Also, excluded variables for which there were no data, could account for much of the unexplained variation. For example, pH can affect the survival of bacteria. Generally, coliforms die more readily under alkaline than acidic conditions. The combination of salinity and the 8.0 pH of seawater contribute to the rapid death of coliforms that enter the oceans via sewage outfalls and land drainage Land drainage may concern:
An agent that destroys bacteria (e.g. efficiency of seawater is influenced by season, being highest in the summer and lowest in the winter (Vaccaro et al. 1950). Second, deficiencies of the inorganic nutrients of phosphorous phos·pho·rous
Of, relating to, or containing phosphorus, especially with a valence of 3 or a valence lower than that of a comparable phosphoric compound. and nitrogen are known to limit matter decomposition and bacteria development in sea water. In particular, a medium made of high levels of the inorganic nutrients of [(N[H.sub.4]).sub.2]HP[O.sub.4] and [(N[H.sub.4]).sub.2]S[O.sub.4] enable E. coli to survive (Carlucci & Pramer 1960). It is also well known that coliforms are facultative anaerobic organisms that do not directly depend on oxygen for their survival. Nonetheless, dissolved oxygen may be an important excluded variable because it has a high negative correlation Noun 1. negative correlation - a correlation in which large values of one variable are associated with small values of the other; the correlation coefficient is between 0 and -1
indirect correlation with water temperature and a high negative correlation with time of year (Gross & Folts 1973).
Clearly, the earlier mentioned findings are most applicable to estuaries and intercoastal in·ter·coast·al
Relating to, involving, or connecting two or more coastlines: intercoastal trade. waterway along the South Carolina coastline. It would be most useful for those regulators in the region who may be concerned that a high level of housing development, over a relatively small area, may lead to a larger proportion of shellfish harvesting water closures. Results from this study have clearly indicated the utility of intervention analysis for assessing long-term water quality trends of fecal coliform pollution in shellfish harvesting areas, in both pristine and urbanized estuaries. The usefulness of this method is quite obvious and the potential to forecast future trends in bacterial water quality may be possible, especially if linkages between fecal coliform density trends and urban census tract A census tract, census area, or census district is a particular community defined for the purpose of taking a census. Usually these coincide with the limits of cities, towns or other administrative areas and several tracts commonly exist within a county. data can be established with statistical accuracy. Future studies should attempt to better line (via GIS) fecal coliform trends with other land use data such as percentage impervious surface and percentage vegetative vegetative /veg·e·ta·tive/ (vej?e-ta?tiv)
1. of, pertaining to, or characteristic of plants.
2. concerned with growth and nutrition, as opposed to reproduction.
3. cover data. To be able to apply this methodology to other areas, other information may need to be incorporated into the model such as freshwater input from rivers and streams, toxic chemicals discharged from non-point sources, housing census tract data and other land use data.
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The study of bacteria, especially in relation to medicine and agriculture.
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Any of several enzymes produced chiefly by fungi, bacteria, and protozoans that catalyze the hydrolysis of cellulose. activity as a measure of environmental perturbation perturbation (pŭr'tərbā`shən), in astronomy and physics, small force or other influence that modifies the otherwise simple motion of some object. The term is also used for the effect produced by the perturbation, e.g. in salt marsh Salt marsh
A maritime habitat characterized by grasses, sedges, and other plants that have adapted to continual, periodic flooding. Salt marshes are found primarily throughout the temperate and subarctic regions. ecosystems. Botanica bo·tan·i·ca
A shop that sells herbs, charms, and other religious or spiritual items, especially those associated with Santeria.
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UMI United States Minor Outlying Islands (ISO Country code)
UMI University of Miami
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Golfo de Mexico
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KEVIN A. NELSON, (1) * GEOFF I. SCOTT (2) AND PHILIP F. RUST (3)
(1) Michigan Department of Community Health, Bureau of Epidemiology Administration, Lansing, Michigan 48909; (2) National Ocean Service, Charleston, South Carolina 29412; (3) Department of Biostatistics, Bioinformatics and Epidemiology, Medical University of South Carolina “MUSC” redirects here. For Abel Santa María airport in Santa Clara, Cuba (ICAO code MUSC), see Abel Santa María Airport.
The Medical University of South Carolina , Charleston, SC 29425
* Corresponding author. E-mail: firstname.lastname@example.org
TABLE 1. Description of sampling stations at NI and MI. DHEC Location Station# NI 1 Jones Creek at Nancy Creek 2 Noble Slough 3 North Inlet 4 Town Creek at Debidue Creek 5 Oyster Bay near Cut-off Creek 6 No Man's Friend Creek and Mud Bay 7 Jones Creek and Mud Bay 8 Town Creek at Sixty Bass Creek 9 Town Creek at Southern Entrance 10 Jones Creek at Duck Creek 11 Town Creek at Bread and Butter Creek MI 01 Main Creek at Atlantic Ave Bridge OIA Main Creek at Stanley Drive 2 Main Creek at Mickey Spillane's Home 3 Main Creek at Captain Dicks' Marina 4 Main Creek at Marlin Quay Marina 5 Murrells Inlet-Range Marker 6 Allston Creek at Weston Flat 7 Allston Creek at Pog-Hughes Landing 8 Parsonnage Creek at Nance's Dock 16 Parsonnage Creek at Chicken Farm Ditch DHEC Coordinates Station# NI 1 33[degrees]17'34.0", 79[degrees]10'51.0" 2 33[degrees]18'00.0", 79[degrees]11'05.0" 3 33[degrees]19'30.0", 79[degrees]09'50.0" 4 33[degrees]20'02.0", 79[degrees]10'00.0" 5 33[degrees]18'32.0", 79[degrees]12'09.0" 6 33[degrees]18'06.0", 79[degrees]12'12.0" 7 33[degrees]16'15.0", 79[degrees]12'04.0" 8 33[degrees]19'21.0", 79[degrees]11'35.0" 9 33[degrees]19'32.0",79[degrees]11'48.0" 10 33[degrees]18'35.0",79[degrees]10'50.0" 11 33[degrees]19'53.0",79[degrees]11'17.0" MI 01 33[degrees]34'46.0", 79[degrees]00'14.0" OIA 33[degrees]34'30.0", 79[degrees]00'31.0" 2 33[degrees]24'02.0", 79[degrees]01'17.0" 3 33[degrees]33'17.0", 79[degrees]01'49.0" 4 33[degrees]33'10.0", 79[degrees]01'19.0" 5 33[degrees]31'50.0", 79[degrees]02'12.0" 6 33[degrees]32'16.0", 79[degrees]02'54.0" 7 33[degrees]31'48.0", 79[degrees]03'01.0" 8 33[degrees]34'20.0", 79[degrees]03'01.0" 16 33[degrees]32'28.0", 79[degrees]02'53.0" TABLE 2. Types of intervention models. Model Type Equation Mean-Shift [Log.sub.10]FEC = [[alpha].sub.1],Salin + [[alpha].sub.2]Temp + [[alpha].sub.3] [Log.sub.e]Rain + [[alpha].sub.4]I1 + [epsilon] Trend-Plus-Jump [Log.sub.10]FEC = [[alpha].sub.1],Salin + [[alpha].sub.2]Temp + [[alpha].sub.3] [Log.sub.e]Rain + [[alpha].sub.4]Date + [[alpha].sub.5]I1 + [epsilon] Change-in-Trend [Log.sub.10]FEC = [[alpha].sub.1],Salin + [[alpha].sub.2]Temp + [[alpha].sub.3] [Log.sub.e]Rain + [[alpha].sub.4]Date + [[alpha].sub.5]I1 + [[alpha].sub.6]Il Date + [epsilon] Constant-Trend [Log.sub.10]FEC = [[alpha].sub.1],Salin + (no intervention [[alpha].sub.2]Temp + [[alpha].sub.3] effect) [Log.sub.e]Rain + [[alpha].sub.4]Date + [epsilon] TABLE 3. Major anthropogenic interventions that had the potential to modify water quality for Murrells Inlet and North Inlet during the period 1967-95. Estuary Intervention Date Murrells Conversion of Septic Tanks to Sewer Line 6/15/80 Inlet Construction of Jetty 6/15/80 Construction of Boat Ramp 1/15/86 North Construction of Baruch Laboratory 6/15/73 Construction of Debidue Housing Development 1/15/77 TABLE 4. Analytical results Murrells Inlet, 1980 intervention, rain-salinity interaction. Source DF SS MS F P-value Model 7 392.72801 56.1040 116.93 < 0.0001 Error 2018 968.24982 0.47981 Total 2025 968.24982 Adjusted [R.sub.2] = 0.2861 Variable DF Param Est SE T P-value Intercept 1 2.496136 0.16 15.751 0.0001 Date 1 0.000126 0.00 7.348 0.0001 II 1 -0.117380 0.00 -1.902 0.0573 11 Date 1 -0.000130 0.00 -6.27 0.0001 Salin 1 -0.070463 0.00 -19.022 0.0001 Lrain 1 0.364628 0.04 9.537 0.0001 Temp 1 0.011213 0.00 4.703 0.0001 Lrain x Sal 1 -0.008687 0.00 -7.209 0.0001 Variance Variable DF Inflation Intercept 1 0.00 Date 1 11.83 I1 1 3.77 I1 Date 1 7.61 Salin 1 1.62 Lrain 1 30.11 Temp 1 1.05 Lrain x Salin 1 32.18 TABLE 5. Analytical results North Inlet, 1973 intervention, rain-temperature interaction. Source DF SS MS F P-value Model 6 370.25754 61.7096 229.066 -0.0001 Error 1650 444.50507 0.26940 Total 1656 814.76261 Adjusted [R.sub.2] = 0.4525 Variable DF Param Est SE T P-value Intercept 1 2.194261 0.13 16.914 0.0001 Date 1 0.000043 0.00 1.673 0.0946 11 Date 1 -0.000046 0.00 -1.579 0.1146 Salin 1 -0.041880 0.00 -33.782 0.0001 Lrain 1 0.169005 0.02 8.805 0.0001 Temp 1 -0.015172 0.00 -5.077 0.0001 Lrain x Sal 1 -0.004506 0.00 -4.81 0.0001 Variance Variable DF Inflation Intercept 1 0.00 Date 1 39.78 11 Date 1 40.27 Salin 1 1.02 Lrain 1 9.95 Temp 1 2.52 Lrain x Salin 1 10.97 TABLE 6. Wasteload calculations Murrells Inlet (humans and domestic animals) Human All (19,819) = 0.43 x [10.sup.14] MPNs/day Septic tank (1,585) = 0.03 x [10.sup.14] MPNs/day Domestic animals Dogs (3,993) = 1.33 x [10.sup.14] MPNs/day Cats (4,472) = 2.40 x [10.sup.14] MPNs/day Total human and pet wasteload = 2.56 x [10.sup.14] to 2.99 x [10.sup.14] MPNs/day Human/pet wasteload = 0.43/2.99 = 14%