Journal of Experimental Marine Biology and Ecology,
213 (1997) 1-11
Kriging in estuaries: as the crow flies, or as the fish swims?

Laurie S. Little a, Don Edwards b,c,*, Dwayne E. Porter c
a Hughes Space and Communications Company, Los Angeles, CA 90009, USA
b Department of Statistics, University of South Carolina, Columbia, SC 29208, USA
c Belle W. Baruch Institute for Marine Biology and Coastal Research, University of South Carolina, Columbia, SC 29208, USA

Geostatistical methods are becoming an essential tool for understanding the spatial distribution of biological and chemical species in estuaries. At the heart of these methods are the spatial prediction/mapping methods known as “kriging”; these can construct statistically optimal predictions for data at unobserved locations using a relatively small, spatially explicit sample. The prediction at any given location is a weighted average of the sample values, where the weights depend on the distances between the sample sites and the target location. For most geostatistical settings, distances are computed “as the crow flies”, i.e. Euclidian distance. For measurements made in estuarine systems, however, intuition suggests that distances between sites should be measured “as the fish swims”, i.e. the length of the shortest in-water path between two sites. Our study evaluated the relative accuracy of eight kriging methods for predicting contaminant and water quality variables measured in an urban estuary in South Carolina. The eight methods were defined by all combinations of three factors, each at two levels: (a) Distance metric (Euclidian vs. in-water); (b) semivariogram type (spherical vs. linear) and (c) model trend component (distance to the inlet mouth; without vs. with). For four of the eight variables studied, the in-water distances provided prediction accuracy improvement on the order of 10-30% of prediction error variance. In two of these cases, the improvement only occurred when in-water distances were used together with a model trend component. Choice of semivariogram did not have much effect on prediction accuracy. Although the overall improvement in prediction accuracy was unpredictable and modest, considering the additional difficulties associated with in-water distances, the results suggest that the integration of Geographic Information System (GIS)-based network analysis with kriging using in-water distances merits further research. © 1997 Elsevier Science B.V.

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John R. Kucklick a,b,*, Scott K. Siversten a, Marion Sanders a, Geoffrey I. Scott a
a National Marine Fisheries Service, Southeast Fisheries Science Center, Charleston Laboratory, 219 Fort Johnson Road, Charleston, SC 29412-2607, USA
b Chesapeake Biological Laboratory, Center for Environmental and Estuarine Studies, University of Maryland, P.O. Box 38, Solomons, MD 20688, USA

Surface (2cm) sediment was collected from three South Carolina estuaries, Winyah Bay, Charleston Harbor and the North Edisto River estuary for a total of 64 samples. The sediment samples were analyzed for 24 individual polycyclic aromatic hydrocarbons (PAHs; two to six rings) by gas chromatography with ion trap mass spectrometric detection. Concentrations of total PAHs were extremely variable, ranging from 33 ng/g dry weight in the Edisto River estuary to 9600 ng/g dry weight in some areas of urbanized Charleston Harbor. The observed variability was not explained by total organic carbon or grain size, indicating that other factors were more important, such as the proximity of the sampling location to sources. Principal components analysis was performed on the percentage of total PAHs, to examine factors that account for the variability of distribution of individual PAHs in a sample. Considering this analysis, the first principal component accounted for 65% of the variability and was related to variations in perylene, a non-anthropogenically produced PAH. The principal components calculated on the PAH distributions in the absence of perylene were related to the fraction of pyrogenic and petroleum-based PAHs in the samples. The majority of the samples with pyrogenic PAH signatures were located adjacent to urban areas, suggesting that the source was urban runoff, whereas samples with petroleum signatures were generally from rural areas. © 1997 Elsevier Science B.V.

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Tomohiro Kawaguchi a,*, Alan J. Lewitus b,c, C. Marjorie Aelion a,c, and Henry N. McKellar a,c
a Department of Environmental Health Sciences, School of Public Health, University of South Carolina, Columbia SC 29208, USA
b Baruch Marine Field Laboratory, University of South Carolina, Georgetown SC 29442, USA
c Marine Science Program, University of South Carolina, Columbia SC 29208, USA

Bioavailable forms of iron are highly unstable in oxygenated saline water, but one way in which iron bioavailability to algae can be enhanced is by chelation to dissolved organic matter (DOM). We hypothesized that urbanization-associated deforestation in Murrells Inlet, South Carolina caused a reduction of iron bioavailability to estuarine phytoplankton by decreasing the supply of forest derived DOM (i.e. the iron chelation source). Bioassay experiments were conducted comparing the potential for iron depletion by phytoplankton in natural populations and Cylindrotheca closterium (Ehr.) Reimann et Lewis cultures, transferred to Murrells Inlet and North Inlet (an undeveloped estuary) water. Chelated iron addition to incubated natural populations transferred to Murrells Inlet water resulted in increased abundances of phototrophic microplankton (accounted for by Cylindrotheca), nanoplankton, and picoplankton (dominated by Synechococcus spp.). In North Inlet water, iron enrichment to natural populations only enhanced Synechococcus growth, but this stimulation was much less than in Murrells Inlet water. The effect of iron on Synechococcus growth in Murrells Inlet was striking (up to 34-fold greater abundance in iron-enriched treatment), suggesting that estuarine Synechococcus may be sensitive to iron stress. The results indicate that iron could be depleted much more readily in Murrells Inlet water, and suggest that iron availability to estuarine phytoplankton may be reduced by urbanization related practices such as coastal forest clearcutting. © 1997 Elsevier Science B.V.

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G. Thomas Chandler*, Michelle R. Shipp, Teresa L. Donelan
Marine Science Program, Department of Environmental Health Sciences, School of Public Health, University of South Carolina, Columbia SC 29208, USA

Macrobenthos of the pristine North Inlet, SC estuaries are predominated by the cosmopolitan spionid polychaete Streblospio benedicti. (Webster) Laboratory experiments were conducted to measure larval settlement and metamorphosis, and sub-adult bioaccumulation/growth rates of S. benedicti when exposed to controlled concentrations of sediment-associated polynuclear aromatic hydrocarbons. Larval settlement/metamorphosis was reduced, but not significantly affected (relative to controls) by 1X, 5X and 10X background PAH mixture concentrations of the six most abundant sediment-associated PAHs found in urbanized Murrell’s Inlet (1X = 0.9 mg PAH per g dry sediment). Bioaccumulation of the most abundant sediment-associated PAH, fluoranthene (FL), was very high in this PAH tolerant species ---9.5-13.7X FL sediment concentrations after 28-day exposures. 28-day exposures to 0.26 and 2.4 mg FL-g-1 caused no significant mortality, and significantly effected positive average weight gains in S. benedicti up to 18 days exposure. However, dramatic and significant weight declines occurred from days 18-28 in both FL treatments. Such a strong tolerance of PAH may explain why these polychaetes are not limited to pristine geographic areas, but can, as numerous field studies have shown, recruit well into hydrocarbon-contaminated and organically enriched sediments. © 1997 Elsevier Science B.V.

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M.H. Wahl a,*. H.N. McKellar a,b, T.M. Williams c
a Department of Environmental Health Sciences, School of Public Health, University of South Carolina, Columbia, SC 29208
b Belle W. Baruch Institute for Marine Biology and Coastal Research, University of South Carolina, Columbia, SC 29208, USA
c The Belle W. Baruch Forest Science Institute, Clemson University, P.O. Box 596, Georgetown, SC 29442, USA

As part of a larger investigation of the effects of coastal urbanization on estuaries, stream nutrient loading was examined over a range of hydrologic and seasonal conditions for an urbanized and a forested watershed (11 ha versus 37 ha). Despite the smaller size, the urbanized stream produced 72% greater annual streamflow volume (162 versus 194 X 103 m3-yr-1), and 66% greater annual sediment load than the forested stream (1796 versus 1082 kg-yr-1). This was due to the longer period of groundwater interception at the urbanized site (increased drainage), and the elevated sediment production resulting from deep excavation (2.1 versus 0.4 m), bank instability, and resuspension of sediment. Mean annual DOC concentration in the urbanized stream (13 mg C-l-1) was only half as concentrated as the forested stream (26 mg C-l-1-yr-1). However, the annual DOC load between streams was within 10% (urban 2.25 X 103 versus forest 2.5 X 103 kg-C-yr-1) due to the greater runoff volume at the urbanized stream. More than twice the amount of dissolved inorganic nitrogen (NOx-N and NH4-N) flowed out of the urbanized watershed than from the forested watershed (34 versus 14 kg-N-yr-1). An even bigger difference between sites was observed with respect to the NOx-N load. Greater runoff volume at the urbanized stream combined with higher mean annual concentration of NOx-N (130 versus 43 mg N-l-1-yr-1) resulted in 11 X more NOx-N loading at the urbanized stream than the forested stream (18.0 versus 1.6 kg N –yr-1). Near channel soil aeration brought on by deep excavation may have promoted more oxidized (and mobile) forms of mineral N. Transport patterns of the two forms of mineral nitrogen varied substantially between streams, with the urbanized site exhibiting a steady release of the NH4-N and NOx-N the effects of an extensive unsaturated soil. In contrast, nitrogen loading of NH4-N and NOx-N at forested Oyster Creek was more episodic, with spring pulses generating much of the load of NOx-N (47%), and summer periods of high concentration resulting in most of the annual load of NH4-N (32%). © 1997 Elsevier Science B.V.

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Christopher W. Corbett a,c,*, Matthew Wahl b, Dwayne E. Porter a,c, Don Edwards a,d, Claudia Moise d
a Belle W. Baruch Institute for Marine Biology and Coastal Research, University of South Carolina, Columbia, SC 29208, USA
b Environmental Health Sciences, School of Public Health, University of South Carolina, Columbia, SC 29208, USA
c Marine Science Program, University of South Carolina, Columbia, SC 29208, USA
d Department of Statistics, University of South Carolina, Columbia, SC 29208, USA

Storm water runoff volumes, flow rates and sediment loads from a forested watershed and an urbanized watershed draining into adjacent estuaries were compared using the distributed parameter (grid cell) agricultural nonpoint source runoff (AGNPS) model. The comparisons were based 10 simulated rainfall events. Effects of impervious surfaces on runoff and sediment transport were also investigated with the model. The 38 ha forested watershed, representing undeveloped land in coastal South Carolina, was covered with mixed second growth hardwoods and pines with interspersed cypress wetlands. The urbanized watershed was 15 ha of single-family residential and commercial land and included a four-lane interstate highway segment. Both watersheds had sandy soils and low stream-bed slopes (<0.5%). This paper shows that the model equations, although intended for agricultural watersheds, also applied to forested and urban land use. The hydrologic submodel was calibrated with 10 rain events from 19-102 mm total rainfall. Simulation results indicated runoff volume was on average 5.5X (±2.7) and sediment yield 5.5X (±2.3) greater from the urban watershed than from the forested watershed. The ratio of rainfall volume to runoff volume was on average 14.5% higher in the urban watershed compared to the forested watershed. IN the AGNPS model, runoff volumes were governed by the total impervious area and were independent of other impervious surface spatial characteristics (size, shape, location, contiguity). Simulation results indicated eroded sediment from both watersheds originated predominantly within the channels. Adding simulated impervious surface area increased runoff runoff volumes linearly and peak flow rates exponentially, flow rates and sediment loads were controlled by impervious surface spatial characteristics. Maximum sediment loads from the urban watershed occurred when disconnected patches of impervious surface covered 35% of the watershed. Maximum differences between the forested and urban watersheds occurred at low rainfall depths (<75 mm). Future nonpoint source runoff modeling should incorporate groundwater dynamics, the spatial and temporal variability of rainfall, and accumulation and wash-off of specific pollutants. © 1997 Elsevier Science B.V.

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*D.L. White 1,2, D.E. Porter 1,2,3, A.J. Lewitus 2,4
1 Marine Science Program, University of South Carolina, Columbia, SC 29208
2 Baruch Institute for Marine Biology and Coastal Research, University, South Carolina,
Columbia, SC 29208
3 Department of Environmental Health Sciences, Norman J. Arnold School of Public Health, USC, Columbia, SC 29208
4 Marine Resources Research Institute, SCDNR, PO Box 12559, Charleston, SC 29422

Nutrient availability and primary productivity in shallow well-mixed estuarine systems vary over time and space. However, temporal studies are usually the primary focus, and information on spatial variability within these systems is generally insufficient. The robust growth of coastal communities in the southeast is putting unique pressures on estuarine resources. Urbanization of estuarine systems may alter ecosystem function, and thus affect the spatial scale and magnitude of nutrient concentrations and primary production in both a temporal and spatial manner. We examine the spatial and temporal patterns of nutrients and primary productivity in two well mixed estuarine systems, (1) a developed estuary, Murrells Inlet (MI), SC, and (2) a relatively pristine estuary, North Inlet (NI), SC. Results indicate that the urbanized estuary may be under some eutrophication stress as primary production was significantly higher during the summer
maxima when compared to NI. Nitrogen (N) and phosphorous (P) were also found to be greater following stochastic storm events in MI, and a model is presented to explain the spatial distribution of nitrate and phosphorous in MI.

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R. HEATH KELSEY 1, 2*, GEOFFREY I. SCOTT 3, 4, DWAYNE E. PORTER 1, 4,
BRIAN THOMPSON 3, AND LAURA WEBSTER 3
1 Belle W. Baruch Institute for Marine Biology and Coastal Research, University of South Carolina, Columbia, SC
2 University of South Carolina, Institute for Public Service and Policy Research,
Center for Environmental Policy, Columbia, SC
3 National Oceanic and Atmospheric Administration Center for Coastal Environmental Health and Biomolecular Research, Charleston, SC
4 Department of Environmental Health Sciences Norman J. Arnold School of Public Health University of South Carolina, Columbia, SC

Multiple Antibiotic Resistance (MAR) analysis and regression modeling techniques were used to identify surface water areas impacted by fecal pollution from human sources, and to determine the effects of land use on fecal pollution in Murrells Inlet, a small, urbanized, high-salinity estuary located between Myrtle Beach and Georgetown, South Carolina. MAR analysis was performed to identify areas in the estuary that are impacted by human-source fecal pollution. Additionally, regression analysis was performed to determine if an association exists between land use and fecal coliform densities over the ten-year period from 1989 to 1998. Land-use variables were derived using Geographic Information System (GIS) techniques and were used in the regression analysis.
MAR analyses were conducted by comparing the frequency and patterns of antibiotic resistance found in Escherichia coli isolates derived from surface water samples and from sewage sources in the Murrells Inlet sewage collection system. The MAR results suggest that the majority of the fecal pollution detected in the Murrells Inlet estuary may be from non-human sources, including fecal coliforms isolated from areas in close proximity to high densities of active septic tanks. A MAR Index, which measures the frequency of antibiotic resistance, was calculated for each of twenty-three water samples and nine sewage samples. The antibiotic resistance pattern comparisons were performed using cluster analysis. Although the MAR indices indicated that several surface water sites had potential human- source contamination, the cluster analysis suggests that only one sampling site had MAR patterns that were similar to those found in the sewage samples. This site was in close proximity to several large pleasure boats as well as a sewage collection system lift station, but was not near areas with active septic tanks. The
results of the regression analysis also suggest that sewage sources and rainfall runoff from urbanized areas may contribute to fecal pollution in the estuary.

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Alan J. Lewitus 1,2, Laura B. Schmidt 3, Larissa J. Mason 2, Jason W. Kempton 2, Susan B. Wilde 1, Jennifer L. Wolny 2, B. Jamie Williams 2, Kenneth C. Hayes 1,4, Sabrina N. Hymel 1 Charles J. Keppler 2, Amy H. Ringwood 2

1 Belle W. Baruch Institute for Marine Biology and Coastal Research, University of South Carolina
2 Marine Resources Research Institute, South Carolina Department of Natural Resources
3 North Inlet-Winyah Bay National Estuarine Research Reserve, National Oceanic and Atmospheric Administration
4 South Carolina Department of Health and Environmental Control

The adverse impacts of harmful algal blooms (HABs) on environmental and human health are a global concern. With recent heightened attention given to the potential influence of anthropogenic nutrient loading on promoting estuarine HAB formation, a concerted statewide effort to evaluate the status of the problem in South Carolina’s estuarine waters was initiated in 2000. The SC coastal zone is among the fastest growing areas in the U.S., and population epicenters such as Myrtle Beach, Charleston, Kiawah Island, and Hilton Head Island are marked by dense brackish water pond (lagoon) coverage closely associated with housing complexes and golf courses. Surveillance efforts in spring 2001 through spring 2002 documented the widespread and common occurrence of several types of potentially or measurably toxic HABs in these ponds. A total of 1456 ponds > 1 acre in the SC coastal zone were documented from 1994 aerial images, the majority of which were brackish. Potentially harmful algal species were observed in 37 of 45 SC brackish-to-marine ponds sampled, and HAB species were in high abundance (i.e. “bloom” proportions) in 21 of these ponds. All of the observed HABs have precedence for toxicity and causing fish kills. These man-made retention ponds were constructed in order to serve as a buffer between developed areas and open estuaries or for aesthetic reasons. However, the combination of restricted tidal flow and nutrient and/or contaminant deposition creates a stimulatory environment for potential HAB formation. In addition to their potential environmental or human effects within or near pond boundaries, tidal transport of harmful algal cells, cysts, or toxins may adversely affect fish or shellfish in adjacent tidal creeks or open estuaries. The recent discovery of widespread, frequent, and often dense HABs in SC residential and golf course ponds introduces the need to consider mitigation measures to existing ponds and HAB preventive strategies for future pond construction associated with coastal zone development.

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