Erik M. Smith

Temperature, Salinity, Nutrients, and the Covariation of Bacterial Production and Chlorophyll-a in Estuarine Ecosystems

Abstract The National Estuarine Research Reserve System represents a diverse collection of ecosystems among which environmental conditions differ dramatically, making it inherently difficult to determine the extent to which patterns and properties identified in one estuary are transferable to those of any other. The primary objective of our study was to develop a multivariate classification framework for comparison of these estuaries and identify the primary sources of environmental variability in each. Using a 4-year dataset from the National Estuarine Research Reserve System-Wide Monitoring Program, combined with principal components analysis, we identified distinct patterns among 21 reserves that allowed grouping based on the primary factors shaping physicochemical variability. Salinity and temperature were the primary factors shaping variability in the reserves, an observation that was corroborated by similar multivariate analysis of data from 33 published studies of non–National Estuarine Research Reserve systems representing a wide range of coastal and estuarine waters. We then investigated the effect of temperature and salinity on biological processes in these systems by using the ratio of bacterial production to chlorophyll-a as a response variable. Salinity and temperature had different but significant effects on bacterial production/chlorophyll-a ratios, suggesting in turn that these properties contribute to the balance between autotrophic and heterotrophic planktonic processes in estuarine ecosystems. Our study confirms the universal role of salinity and temperature in shaping the variability among even the most diverse systems and provides a valuable classification framework for comparison of reserves within the context of the entire National Estuarine Research Reserve System. Use of this classification approach may provide insight into the extent to which results from investigative studies in one reserve may be applicable to others, a valuable application when the effect of environmental stressors is considered.

Mesozooplankton Responses to Climate Change and Variability in a Southeastern U.S. Estuary (1981–2003)

Abstract Long-term trends and relationships between large mesozooplankton (1.5–20 mm) and the physical environment were used to investigate impacts of climate change and variability in the North Inlet estuary, South Carolina. Biweekly collections (365 μm) from 1981 to 2003 demonstrated distinct seasonal patterns and large interannual fluctuations in abundances. Significant long-term decreases in abundances were observed for total zooplankton and 12 taxa (e.g., Gobiosoma larvae, chaetognaths, and adult shrimps), whereas 14 others, including some of the most abundant constituents, did not change (e.g., mysids, amphipods, crab megalopae, and Palaemonetes larvae). The composition of the fauna was similar at the beginning and end of the 23-year period. A significant long-term increase in winter water temperature (2.6°C) and a decrease in summer salinity (3.2) were determined. Relationships between physical conditions and taxa varied in strength and direction, and most did not agree with their long-term trends. However, some major taxa appeared to respond to climate variability, including the timing and intensity of El Niño or La Niñ a events. Although changes in the North Inlet mesozooplankton were minor compared to fauna in northern waters in recent decades, a trend toward the freshening and warming of this system could alter processes including larval recruitment, secondary production, and trophic interactions. The design of long-term sampling programs must consider effects of tide and time of day on zooplankton. The National Estuarine Research Reserve System provides an ideal platform for the collection of time series measurements that are critical to the understanding of climate change on biological communities.

Spatiotemporal Variability in Dissolved Organic Matter Composition is More Strongly Related to Bacterioplankton Community Composition than to Metabolic Capability in a Blackwater Estuarine System

The composition and metabolic capability of bacterioplankton communities were examined over seasonal and spatial gradients and related to the source, composition, and quantity of dissolved organic matter (DOM) in the blackwater estuary Winyah Bay, Georgetown County, SC, USA and its tributary rivers. Bacterial community composition (BCC) was measured by terminal restriction fragment length polymorphism, and bacterial metabolic capability (BMC) was measured by defined substrate utilization patterns (Biolog GN2 plates). Spatial patterns were not important, despite the anticipated watershed effects and the well-documented influence of salinity gradients on estuarine bacterioplankton, but DOM, BCC, and BMC all showed varying degrees of temporal patterns; DOM-based groupings differentiated BCC samples better than spatiotemporal categories, but not BMC. BCC was closely related to properties describing DOM composition, particularly those related to DOM source (i.e., cypress swamps vs. in situ phytoplankton production, indicated by chlorophyll a, colored DOM spectral slope, α355/dissolved organic carbon (DOC), and DOC concentration), and to associated physicochemical variables, such as temperature, pH, and salinity. BMC was more strongly related to abiotic factors, such as temperature and dissolved nutrients, as well as to chlorophyll a and percent bioavailable DOC. In contrast with previous studies, BCC and BMC were significantly correlated in this highly heterotrophic estuary, suggesting that DOM source variability may select for specialist phylotypes above a background of generalists. This study, therefore, supports a causative pathway from DOM to BMC to BCC while suggesting that BCC and BMC may be simultaneously influenced by different suites of DOM characteristics and physicochemical parameters.

System-Wide Monitoring Program of the National Estuarine Research Reserve System: Research and Monitoring to Address Coastal Management Issues

Abstract The National Estuarine Research Reserve System (NERRS) consists of 28 coastal reserves located across the United States. A system-wide monitoring program was established in 1995 to develop quantitative measurements of short-term variability and long-term changes in abiotic and biotic properties of estuarine ecosystems for the purpose of informing effective coastal management. The hallmarks of this program are its two decades of data collection, the use of common protocols and instrumentation across all observing platforms, and a centralized approach to data quality assurance/quality control (QA/QC). By using standardized procedures at all reserves, this monitoring program generates a national database on estuarine ecosystems, and it creates a network of sentinel sites for detecting and understanding the effects of climate change. Examples of how these data inform coastal managers include water quality assessment, habitat mapping and change analysis, establishment of nutrient criteria for estuaries, and understanding the predicted impacts of climate change.

Metabolic Responses of Estuarine Microbial Communities to Discharge of Surface Runoff and Groundwater from Contrasting Landscapes

Groundwater discharge is increasingly recognized as a significant source of nutrient input to coastal waters, relative to surface water inputs. There remains limited information, however, on the extent to which nutrients and organic matter from each of these two flowpaths influence the functional responses of coastal microbial communities. As such, this study determined dissolved organic carbon (DOC) and nutrient concentrations of surface water runoff and groundwater from both an urbanized and a relatively pristine forested drainage basin near Myrtle Beach, South Carolina, and quantified the changes in production rates and biomass of phytoplankton and bacterioplankton in response to these inputs during two microcosm incubation experiments (August and October, 2011). Rainwater in the urbanized basin that would otherwise enter the groundwater appeared to be largely rerouted into the surface flowpath by impervious surfaces, bypassing ecosystem buffers and filtration mechanisms. Surface runoff from the developed basin was most enriched in nutrients and DOC and yielded the highest production rates of the various source waters upon addition to coastal waters. The metabolic responses of phytoplankton and bacterioplankton were generally well predicted as a function of initial chemical composition of the various source waters, though more so with bacterial production. Primary and bacterial productivities often correlated at reciprocal time points (24-h measurement of one with the 72-h measurement of the other). These results suggest human modification of coastal watersheds enhances the magnitude of dissolved constituents delivered to coastal waters as well as alters their distributions between surface and groundwater flowpaths, with significant implications for microbial community structure and function in coastal receiving waters.

A Case History of the Science and Management Collaboration in Understanding Hypoxia Events in Long Bay, South Carolina, USA

Communication of knowledge between the scientific and management communities is a difficult process complicated by the distinctive nature of professional career goals of scientists and decision-makers. This article provides a case history highlighting a collaboration between the science and management communities that resulted from a response to a 2004 hypoxia, or low dissolved oxygen, event in Long Bay, off Myrtle Beach, South Carolina. A working group of scientists and decision-makers was established at the time of the event and has continued to interact to develop a firm understanding of the drivers responsible for hypoxia formation in Long Bay. Several factors were found to be important to ensure that these collaborative efforts were productive: (1) genuine interest in collaboratively working across disciplines to examine a problem; (2) commitment by agency leadership, decision-makers, and researchers to create successful communication mechanisms; (3) respect for each others’ perspectives and an understanding how science and management are performed and that they are not mutually exclusive; (4) networking among researchers and decision-makers to ensure appropriate team members are involved in the process; (5) use of decision-maker input in the formulation of research and monitoring projects; and (6) commitment of resources for facilitation to ensure that researchers and decision-makers are communicating effectively.

An Environmental Assessment of the North and South Carolina Coasts

Abstract Coastal waters of the Carolinas include some magnificent resources that are increasingly degraded from upstream pollution and poorly controlled local development. Escalating water demands have rapidly depressed coastal water tables. Upper watershed industries, cities, and croplands contaminate coastal riverine potable source waters with a wide array of unregulated/poorly regulated toxic substances, and with nutrients that fuel nuisance algal blooms. Industrialized livestock production adds fecal microbes and many other contaminants to surface and groundwaters. Toxic cyanobacteria blooms have spread into newly affected freshwaters including potable source waters. Physical reengineering of coastal landscapes with numerous detention ponds has created ideal incubation sites for noxious estuarine/marine dinoflagellate and raphidiophycean blooms. Stormwater runoff from sprawling coastal development alters the sediment composition and benthic fauna of receiving waters, while also adding toxic chemicals and fecal contaminants that threaten human health and seafood safety. These impacts are expected to be exacerbated by warming trends in climate change.

Author Correction: Accuracy and Precision of Tidal Wetland Soil Carbon Mapping in the Conterminous United States

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has not been fixed in the paper.

Quantifying Groundwater Export from an Urban Reservoir: A Case Study from Coastal South Carolina

Climatic and anthropogenic factors can have a significant influence on groundwater resources, calling into question the future quality and quantity of the commodity. In this chapter, we discuss current and emerging issues concerning groundwater scarcity. These concepts are demonstrated using a case study from an urban reservoir that serves as a stormwater conduit to the nearshore ocean. Quantitative estimates of groundwater interaction with the reservoir were determined via direct tracer techniques which are rarely, if ever, used by urban hydrologists. Continuous time-series records of dissolved 222Rn were collected to evaluate the volumetric percentage of groundwater within the reservoir from 2012 through 2013. Using high-resolution sampling, we are able to characterize groundwater and reservoir response on event and seasonal time scales, while also offering general assessments of the hydrologic conditions during the study. When rainfall was not occurring, evapotranspiration served as the primary driver of overall hydrologic characteristics, directly influencing the water table and subsequent groundwater discharged from the reservoir. However, during storm events, hydrologic factors influencing the amount of groundwater within the reservoir were found to be more complex, including event duration, magnitude, and antecedent conditions. Seasonally, rainfall patterns were largely responsible for the magnitude of groundwater present within the reservoir and quasi-related to peak export to the coastal ocean. Most notably, we observed a decline in the volumetric percentage of groundwater within the reservoir as a result of increased groundwater residence time within the aquifer—a likely function of reduced aquifer recharge that would result from more efficient stormwater management.