Denise Sanger

Linkages between tidal creek ecosystems and the landscape and demographic attributes of their watersheds

Twenty-three headwater tidal creeks draining watersheds representative of forested, suburban, urban, and industrial land cover were sampled along the South Carolina coast from 1994 to 2002 to: (1) evaluate the degree to which impervious land cover is an integrative watershed-scale indicator of stress; (2) synthesize and integrate the available data on linkages between land cover and tidal creek environmental quality into a conceptual model of the responses of tidal creeks to human development; and (3) use the model to develop recommendations for conserving and restoring tidal creek ecosystems. The following parameters were evaluated: human population density, land use, impervious cover, creek physical characteristics, water quality, sediment chemical contamination and grain size characteristics, benthic chlorophyll a levels, porewater ammonia concentration, fecal coliform concentration, and macrobenthic and nekton population and community characteristics. The conceptual model was developed and used to identify the linkages among watershed-scale stressors, physical and chemical exposures, and biological responses of tidal creeks to human development at the watershed scale. This model provides a visual representation of the manner in which human population growth is linked to changes in the physiochemical environment and ultimately the nursery habitat function of tidal creeks and the safety of seafood harvested from headwater tidal creeks. The ultimate stressor on the tidal creek ecosystem is the human population

Responses of tidal creek macrobenthic communities to the effects of watershed development

This study examined the effects of watershed development on macrobenthic communities in tidal creeks of Charleston Harbor, South Carolina, U.S. Two types of creeks were evaluated: upland creeks which drained watersheds consisting of at least 15% terrestrial land cover, and salt marsh creeks which drained no upland habitat (i.e., only intertidal habitat). Samples of macrobenthic organisms were taken along the longitudinal axis of twenty-three primary (first order) tidal creeks. Water and sediment quality data were also collected including measurements of dissolved oxygen, salinity, temperature, sediment characteristics, and toxic chemicals in the creek sediments. Hypoxic conditions occurred more than 15% of the time in both reference and developed creeks and were a natural attribute of these systems. The most severe and frequent hypoxia occurred in impacted salt marsh creeks. Salinity fluctuations were the greatest in developed upland creeks and salinity range was identified as a potentially reliable indicator of the degree to which watershed development has altered hydrodynamic processes. The creeks draining urban and industrial watersheds were degraded environments characterized by watersheds with high (>50%) levels of impervious surface, broad fluctuations in salinity, severe hypoxia, and potentially toxic levels of chemicals in the sediment. These creeks had low macrobenthic diversity and abundance and were numerically dominated by the oligochaeteMonopylephorus rubroniveus in mud sediments, and the polychaeteLaeoreis culveri in sand sediments. Suburban watersheds had 15–35% impervious surface and creeks draining them were exposed to frequent hypoxia and broad salinity fluctuations. The levels of chemical contaminants in sediments of suburban and impacted salt marsh creeks were generally not different from the levels in reference creeks. Macrobenthic diversity and abundance were higher for suburban and impacted salt marsh creeks than for urban and industrial creeks. However, suburban and salt marsh impacted creeks were numerically dominated by a few pollution indicative species including the oligochaetesM. rubroniveus andTubificoides brownae and the polychaeteL. culveri. These creeks appear to be exhibiting early signs of degradation (e.g., a simplified food web). Two promising community-level macrobenthic metrics for assessing environmental quality were identified: the proportional abundance of pollution indicative taxa, and the proportional abundance of pollution sensitive taxa. These indicators were significantly (p<0.05) correlated with the salinity range, the level of chemical contaminants in sediments, and amount of impervious surface in the watershed.

The transcriptomic responses of the eastern oyster, Crassostrea virginica, to environmental conditions

Understanding the mechanisms by which organisms adapt to environmental conditions is a fundamental question for ecology and evolution. In this study, we evaluate changes in gene expression of a marine mollusc, the eastern oyster Crassostrea virginica, associated with the physico‐chemical conditions and the levels of metals and other contaminants in their environment. The results indicate that transcript signatures can effectively disentangle the complex interactive gene expression responses to the environment and are also capable of disentangling the complex dynamic effects of environmental factors on gene expression. In this context, the mapping of environment to gene and gene to environment is reciprocal and mutually reinforcing. In general, the response of transcripts to the environment is driven by major factors known to affect oyster physiology such as temperature, pH, salinity, and dissolved oxygen, with pollutant levels playing a relatively small role, at least within the range of concentrations found in the studied oyster habitats. Further, the two environmental factors that dominate these effects (temperature and pH) interact in a dynamic and nonlinear fashion to impact gene expression. Transcriptomic data obtained in our study provide insights into the mechanisms of physiological responses to temperature and pH in oysters that are consistent with the known effects of these factors on physiological functions of ectotherms and indicate important linkages between transcriptomics and physiological outcomes. Should these linkages hold in further studies and in other organisms, they may provide a novel integrated approach for assessing the impacts of climate change, ocean acidification and anthropogenic contaminants on aquatic organisms via relatively inexpensive microarray platforms.

Effects of changing land use on the microbial water quality of tidal creeks

Population growth along the southeastern United States coast has precipitated the conversion of forested watersheds to suburban and urban ones. This study sampled creeks representing forested, suburban, and urban watersheds along a longitudinal gradient for indicators of water quality, including traditional indicator bacteria (fecal coliforms and enterococci) and alternative viral indicators (male-specific and somatic coliphages). Tested microorganisms were generally distributed with highest concentrations in creek headwaters and in more developed watersheds. The headwaters also showed the strongest predictive relationship between indicator concentrations and urbanization as measured by impervious cover. A seasonal pattern was observed for indicator bacteria but not for indicator viruses. Coliphage typing indicated the likely source of contamination was nonhuman. Results suggest that headwater creeks can serve as sentinel habitat, signaling early warning of public health concerns from land-based anthropogenic activities. This study also implies the potential to eventually forecast indicator concentrations under land use change scenarios.

A transcriptomic analysis of land-use impacts on the oyster, Crassostrea virginica, in the South Atlantic bight.

Increasing utilization and human population density in the coastal zone is widely believed to place increasing stresses on the resident biota, but confirmation of this belief is somewhat lacking. While we have solid evidence that highly disturbed estuarine systems have dramatic changes in the resident biota (black and white if you will), we lack tools that distinguish the shades of grey. In part, this lack of ability to distinguish shades of grey stems from the analytical tools that have been applied to studies of estuarine systems, and perhaps more important, is the insensitivity of the biological end points that we have used to assess these impacts. In this study, we will present data on the phenotypic adjustments as measured by transcriptomic signatures of a resilient organism (oysters) to land‐use practices in the surrounding watershed using advanced machine‐learning algorithms. We will demonstrate that such an approach can reveal subtle and meaningful shifts in oyster gene expression in response to land use. Further, the data show that gill tissues are far more responsive and provide superior discrimination of land‐use classes than hepatopancreas and that transcripts encoding proteins involved in energy production, protein synthesis and basic metabolism are more robust indicators of land use than classic biomarkers such as metallothioneins, GST and cytochrome P‐450.

On the Ecology of Oligochaetes: Monthly Variation of Community Composition and Environmental Characteristics in Two South Carolina Tidal Creeks

In the tidal creeks of the southeastern United States, the numerically and ecologically dominant macrobenthic organisms are typically oligochaetes. Due to their relatively small size and difficult taxonomy, little is known about the short-term and seasonal changes in the oligochaetes of tidal creeks. This study presents a report of the spatial and temporal changes of the oligochaete taxa within and between two tidal creeks in southern South Carolina, at monthly intervals over a 13-month period. These changes are framed within the reference of monthly changes in benthic chlorophylla, sediment composition, and porewater ammonia, as well as in the perspective of seasonal changes in the entire tidal creek macrobenthic community. The most abundant oligochaete found in this study was the tubificidMonopylephorus rubroniveus, followed by the naidParanais litoralis and the tubificidsTubificoides heterochaetus andT. brownae. All of the oligochaetes exhibited strong month-to-month and spatial changes, indicative of changes in water quality and sediment habitat characteristics (e.g., low dissolved oxygen, high benthic chlorophylla). There were significant correlations between the abundance of most species and either benthic chlorophylla concentration or the silt-clay fraction of the sediment. Looking at short-term changes in this rapidly changing component of the macrobenthic community provides insight not only into the ecology of the oligochaetes, but also into the changes in the tidal creek ecosystem and their potential effects on other biota.

Variability in Dissolved Oxygen and Other Water-Quality Variables Within the National Estuarine Research Reserve System

Abstract Shallow estuarine habitats are normally characterized by wide interannual and intraannual fluctuations in water-quality variables, including dissolved oxygen; however, the short-term variability in water-quality variables is seldom measured and characterized. Water-quality data collected semicontinuously by automated data sondes from 1995 to 2000 at 55 sites among 22 National Estuarine Research Reserves (NERR) were analyzed to characterize temporal variability and compare conditions among estuarine systems and regions. Three-way analysis of variance (ANOVA) models revealed several significant interannual and seasonal differences for water-quality variables for many sites sampled within a reserve; however, interannual trends with respect to reserve or region were not readily apparent. Salinity and hypoxic events (dissolved oxygen [DO] < 28% saturation [sat]) were generally greatest in summer or fall. Evapotranspiration and precipitation appeared to influence seasonal salinity patterns at reserve sites. Abrupt short-term decreases and sustained long-term decreases in salinity associated with precipitation events were documented during the passage of tropical systems. An abrupt decrease in water temperature prior to storm passage was noted, with increasing cooling effects related to increasing storm intensity. Although hypoxia occurred over a broad geographic range, it was primarily experienced at sites with sustained warm water conditions. Hypoxia was strongly influenced by latitude and climate. Duration of hypoxia at most reserves persisted less than 12 hours. Increased deployment duration was shown to increase the percentage of time with hypoxic conditions (DO < 28% sat) and decrease the percentage of time with supersaturation (DO > 120% sat) at many sites. The large fluctuations in dissolved oxygen that occur over short time periods in estuaries demonstrate the need for long-term continuous measurements to estimate the frequency and duration of exposure to low DO. Without continuous monitoring, many low-DO events would have been missed, thus underestimating the potential impacts from this type of water-quality variability. The synthesis of water-quality data from the NERR sites indicates that reserves have not experienced many of the problems found in other more populated locales.

Hydrographic characterization of two tidal creeks with implications for watershed land use, flushing times, and benthic production

Many coastal ecosystems are undergoing anthropogenic stress from large increases in population and urbanization. In many regions changes in freshwater and material inputs to the coastal zone are altering the biogeochemical and biological capacities of ecosystems. Despite increased watershed inputs, large tidal volumes and flushing indicative of macrotidal estuaries can modulate the fate of introduced materials masking some of the symptoms of eutrophication. The Land Use Coastal Ecosystem Study (LU-CES) examined linkages between land use and environmental properties of Malind and Okatee Creeks in South Carolina from 2001 to 2004. The objectives of this particular study were to assess the hydrography of the two macrotidal creek ecosystems, explore differences in dissolved oxygen (DO), and develop a better understanding of the variations in primary and benthic secondary production in southeastern creek ecosystems. Depth, pH, salinity, and DO were reduced and more variable in Malind Creek than in Okatee Creek, although both creeks had strong semidiurnal frequencies in salinity time signatures. While time series analyses of DO saturation in Malind Creek revealed a dominant semidiurnal pattern, Okatee Creek had a distinctly diel DO pattern. The strongly semidiurnal fluctuations in DO and reduced flushing time indicated that biological processes were not fast enough to influence DO in Malind Creek. The Okatee Creek system had a much greater storage volume, a wider marsh, and a dominant 25-h DO frequency. These attributes contributed to an estimated 8–10 times more phytoplankton-based carbon in Okatee Creek and twice the annual benthic production. As expected from their proximity to the upland, low surface area, and high organic content, both ecosystems were net heterotrophic. This fundamental understanding of tidal creek hydrography is being used to help define linkages among differential watershed land uses, flushing characteristics, and levels of biological production in coastal ecosystems of the southeastern United States.

Comparative tolerance of two estuarine annelids to fluoranthene under normoxic and moderately hypoxic conditions

The tolerance of the oligochaete Monopylephorus rubroniveus and the polychaete Streblospio benedicti to sediment-associated fluoranthene was characterized under normoxic (>80% dissolved oxygen saturation) and moderately hypoxic ( approximately 50% dissolved oxygen saturation) conditions. Under both conditions, M. rubroniveus was highly tolerant of fluoranthene. Streblospio benedicti was considerably less tolerant of fluoranthene compared with M. rubroniveus. In addition, S. benedicti was less tolerant to fluoranthene under moderately hypoxic conditions, although no differences in sensitivity between the two oxygen conditions were observed based upon median lethal tissue residues. Bioaccumulation factors were higher for S. benedicti exposed to moderate hypoxia, suggesting that behavioral adaptations to compensate for the lower dissolved oxygen increased its bioaccumulation of fluoranthene. The results of the present laboratory study demonstrate that (1). changes in annelid tolerance to fluoranthene under varying oxygen conditions is a species-dependent phenomenon and (2). the differential tolerance of these two annelids to these combined stressors is consistent with their relative abundances in the field.

Bioaccumulation and toxicity of fluoranthene in the estuarine oligochaete Monopylephorus rubroniveus

The tolerance of the estuarine oligochaete Monopylephorus rubroniveus to fluoranthene was characterized both in the presence and absence of ultraviolet (UV) radiation. Using waterborne exposures, the 72-h median lethal concentration (LC(50)) and median lethal dose (LD(50)) were 0.7 (95% CI, 0.4-0.8) microg/L and 8.0 (5.6-9.6) microg/g worm dry weight, respectively, in the presence of UV radiation [UV-A=64.7+/-1.0 mu W/cm(2) (mean+/-standard deviation)]. In the absence of UV radiation, little mortality was observed, even at the water solubility limits of fluoranthene (120.4 microg/L). Mean bioconcentration factors across all treatments was 10,893+/-2828. Using sediment exposures, little mortality was observed following 10 days at concentrations as high as 3912 microg fluoranthene/g sediment dry weight in both the presence of UV radiation (UV-A=108.4+/-1.3 mu W/cm(2)) and its absence. Bioaccumulation of sediment-associated fluoranthene was comparatively high and varied little among the five sediment treatments. The results of the present study demonstrate that M. rubroniveus is (1) sensitive to waterborne fluoranthene in the presence of UV radiation and (2) highly tolerant of fluoranthene in the presence of sediment, despite the ability to bioaccumulate fluoranthene to comparatively high levels. These findings suggest that those environmental factors which could potentially increase their exposure to UV radiation need to be considered when assessing the overall risk of fluoranthene to M. rubroniveus.