Effects of hurricane floyd inland flooding,September–October 1999, on tributaries to Pamlico Sound,North Carolina

Hurricane Floyd in September 1999 caused disastrous flooding from South Carolina to Massachusetts in the United States, with particularly severe and prolonged flooding in eastern North Carolina resulting in record flood-flow loadings of freshwater and contaminants to Pamlico Sound, North Carolina. The inland flooding, water quality, and loadings to Pamlico Sound were determined as part of a multi-agency response to the floods and in an effort to understand the effects of the floods on the greater Pamlico Sound Basin. All major river basins draining to Pamlico Sound experienced floods at the 500-yr recurrence level. The volume of flood waters entering Pamlico Sound during September–October 1999 was estimated to be equivalent to about 95% of the volume of Pamlico Sound, meaning that flood waters could have essentially displaced most of the water present in Pamlico Sound. Nitrogen and phosphorus loads to the Pamlico River estuary and Neuse River estuary, the two principal estuaries draining to Pamlico Sound, in a 36-d period during the flooding were between 50–90% of the long term average annual loads. Pesticide concentrations in flood waters were surprisingly high, given the amount of dilution produced by the floodwaters.     

Rapid Holocene coastal change revealed by high-resolution micropaleontological analysis, Pamlico Sound, North Carolina, USA

Foraminiferal analyses of 404 contiguous samples, supported by diatom, lithologic, geochronologic and seismic data, reveal both rapid and gradual Holocene paleoenvironmental changes in an 8.21-m vibracore taken from southern Pamlico Sound, North Carolina. Data record initial flooding of a latest Pleistocene river drainage and the formation of an estuary 9000 yr ago. Estuarine conditions were punctuated by two intervals of marine influence from approximately 4100 to 3700 and 1150 to 500 cal yr BP. Foraminiferal assemblages in the muddy sand facies that accumulated during these intervals contain many well-preserved benthic foraminiferal species, which occur today in open marine settings as deep as the mid shelf, and significant numbers of well-preserved planktonic foraminifera, some typical of Gulf Stream waters. We postulate that these marine-influenced units resulted from temporary destruction of the southern Outer Banks barrier islands by hurricanes. The second increase in marine influence is coeval with increased rate of sea-level rise and a peak in Atlantic tropical cyclone activity during the Medieval Climate Anomaly. This high-resolution analysis demonstrates the range of environmental variability and the rapidity of coastal change that can result from the interplay of changing climate, sea level and geomorphology in an estuarine setting.     

Water quality and phytoplankton as indicators of hurricane impacts on a large estuarine ecosystem

Three sequential hurricanes in the fall of 1999 provided the impetus for assessing multi-annual effects on water quality and phytoplankton dynamics in southwestern Pamlico Sound, North Carolina. Two and a half years of post-hurricane data were examined for short- and long-term impacts from the storms and >100 year flooding. Salinity decreased dramatically and did not recover until May 2000. Inorganic nitrogen and phosphorus concentrations were briefly elevated during the flooding, but later returned to background levels. Dissolved organic carbon concentrations declined through the whole study period, but did not appear to peak as was observed in the Neuse River estuary, a key tributary of the Sound. Light attenuation was highest in the fall to spring following the storms and was best correlated with chlorophylla concentrations. Phytoplankton biomass (chla) increased and remained elevated until late spring 2000 when concentrations returned to pre-storm levels and then cycled seasonally. Phytoplankton community composition varied throughout the study, reflecting the complex interaction between physiological optimal and combinations of salinity, residence time, nutrient availability, and possibly grazing activity. Floodwater advection or dilution from upstream maxima may have controlled the spatial heterogeneity in total and group-specific biomass. The storms produced areas of shortterm hypoxia, but hypoxic events continued during the following two summers, correlating strongly with water column stratification. Nitrogen loading to the southwestern sound was inferred from network analysis of previous nitrogen cycling studies in the Neuse River estuary. Based on these analyses, nutrient cycling and removal in the sub-estuaries would be decreased under high flow conditions, confirming observations from other estuaries. The inferred nitrogen load from the flood was 2–3 times the normal loading to the Sound; this estimate was supported by the substantial algal bloom. After 8-mos, the salinity and chla data indicated the Sound had returned to pre-hurricane conditions, yet phytoplankton community compositional changes continued through the multi-year study period. This is an example of long-term aspects of estuarine recovery that should be considered in the context of a predicted 10–40 yr period of elevated tropical storm activity in the western Atlantic Basin.     

Phytoplankton forcing by a record freshwater discharge event into a large lagoonal estuary

We report here the response of the water column and phytoplankton biomass of a large lagoonal estuary to a record freshwater discharge event which followed from extraordinary hurricane activity. In the fall of 1999, three hurricanes passed over eastern North Carolina coast in a 7-wk period: Hurricane Dennis (August 24–September 5), Hurricane Floyd (September 14–17), and Hurricane Irene (October 13–16). The hurricanes delivered record rainfall to the watersheds of the Pamlico Sound, North Carolina, the second largest estuary in North America. Hurricane Floyd was followed by a 500-yr flood that displaced 80% of the volume of the Sound and delivered half the annual nitrogen (N)-nutrient load to this N-limited system.After Hurricane Floyd, buoyancy stratification restricted the mixed layer depth, dissolved inorganic nitrogen (DIN) in surface waters increased, and surface chlorophyll biomass increased up to 4-fold. Chlorophyll biomass did not increase to the potential indicated by residual DIN because of light-limitation attributable to suspended particulates, phytoplankton pigments, and colored dissolved organic material (CDOM).The discharge waters created hydrological conditions and supplied materials that we interpret to have both stimulated and restricted phytoplankton blooms. The effects of the discharge event on the hydrology and phytoplankton of the Pamlico Sound persisted about 6 months, after which it returned to its pre-event condition, attesting to the resilience of the system.     

Ecological response to hurricane events in the Pamlico Sound system, North Carolina, and implications for assessment and management in a regime of increased frequency

Since the mid 1990s, the Atlantic and Gulf Coast regions have experienced a dramatic increase in the number of hurricane landfalls. In eastern North Carolina alone, eight hurricances have affected the coast in the past 9 years. These storms have exhibited individualistic hydrologic, nutrient, and sediment loading effects and represent a formidable challenge to nutrient management aimed at reducing eutrophication in the Pamlico Sound and its estuarine tributaries. Different rainfall amounts among hurricanes lead to variable freshwater and nutrient discharge and variable nutrient, organic matter, and sediment enrichment. These enrichments differentially affected physical and chemical properties (salinity, water residence time, transparency, stratification, dissolved oxygen), phytoplankton primary production, and phytoplankton community composition. Contrasting ecological responses were accompanied, by changes in nutrient and oxygen cycling, habitat, and higher trophic levels, including different direct effects on fish populations. Floodwaters from the two largest hurricances, Fran (1996) and Floyd (1999), exerted, multi-month to multi-annual effects on hydrology, nutrient loads, productivity, and biotic composition. Relatively low rainfall coastal hurricanes like Isabel (2003) and Ophelia (2005) caused strong vertical mixing and storm surges, but relatively minor hydrologic and nutrient effects. Both hydrologic loading and wind forcing are important drivers and must be integrated with nutrient loading in assessing short-term and long-term ecological effects of these storms. These climatic forcings cannot be managed but should be considered in the development of water quality management strategies for these and other large estuarine ecosystems faced with increasing frequencies and intensities of hurricane activity.     

Geographic Variability in Salt Marsh Flooding Patterns may Affect Nursery Value for Fishery Species

Flooding of salt marshes controls access to the marsh surface for aquatic organisms and likely regulates the value and use of this habitat for juvenile fishery species. We examined geographic variability in marsh access by measuring tidal flooding characteristics in 15 Spartina alterniflora marshes in the southeastern US between South Texas and lower Chesapeake Bay. Flooding duration and flooding frequency were correlated with the elevation of the marsh edge in relation to mean low water and with the tidal range. Mean annual flooding duration over the years 2006–2008 was highest in Texas (91.5% in Aransas Bay) and North Carolina (89.3% in Pamlico Sound) and lowest in Timbalier Bay, LA (54%) and the lower Carolinas and Georgia (55–57%). We used published data on densities of blue crabs and penaeid shrimps as a measure of habitat selection, and there was a positive relationship between marsh selection and flooding duration.     

Short-term effects of a low dissolved oxygen event on estuarine fish assemblages following the passage of hurricane Charley

Hurricane Charley, a category 4 storm, passed directly over the Charlotte Harbor estuary and Peace River watershed on August 13, 2004. Following the storm's passage, dissolved oxygen in the Peace River fell below 1 mg l⁻¹ and hypoxic conditions (<2mgl⁻¹) extended into Charlotte Harbor. A long-term fisheries-independent monitoring program (1989 to present) was already in place in Charlotte Harbor, and sampling was intensified during the month after the storm. Changes in fish assemblages that resulted from the hypoxic event were determined using nonmetric multidimensional scaling and similarity percentages analysis. At the mouth of the Peace River and upper Charlotte Harbor, fish abundance decreased dramatically after the hurricane, and typical estuarine fish assemblages were replaced by those dominated by a few resilient estuarine and freshwater species, including the nonindigenous brown hoplo (Hoplosternum littorale) and sailfin catfish (Pterygoplichthys spp.). Fish assemblages in the estuarine portion of the Maykka River, located only a few kilometers west of the Peace River, were unaffected. The hypoxic event was short lived; dissolved oxygen and estuarine fish assemblages in the Peace River and upper Charlotte Harbor recovered within a month. The results of this study are consistent with other hurricane-related hypoxic events in the literature which have reported acute effects to estuarine systems in the short term, rapid recoveries, and long-term resilience.     

An estuarine benthic index of biotic integrity for the Mid-Atlantic region of the United States. I. Classification of assemblages and habitat definition

An objective of the Mid-Atlantic Integrated Assessment Program (MAIA) of the U.S. Environmental Protection Agency is to develop an index for assessing benthic community condition in estuaries of the mid-Atlantic region of the United States (Delaware Bay through Pamlico Sound). To develop such an index, natural unimpaired communities must first be identified and variability related to natural factors accounted for. This study focused on these two objectives; Lnansó et al. (2002) describe the index. Using existing data sets from multiple years, classification analyses of species abundance and discriminant analysis were employed to identify major habitat types in the MAIA region and evaluate the physical characteristics that structure benthic infaunal assemblages. Sampling was restricted to soft bottoms and to the index development period, July through early October. The analyses revealed salinity and sediment composition as major factors structuring infaunal assemblages in mid-Atlantic estuaries. Geographical location was a secondary factor. Nine habitat classes were distinguished as a combination of 6 salinity classes, 2 sediment types, and the separation of North Carolina and Delaware-Chesapeake Bay polyhaline sites. The effect of sediment types on faunal assemblages was restricted to polyhaline sites, which were separated into two sediment groups above and below 90% sand content. Assemblages corresponding to each of these 9 habitats were identified in the context of widely recognized patterns of dominant taxa. Differences between North Carolina and Delaware-Chesapeake Bay polyhaline assemblages were attributed to the relative contributions of species and not to differences in species composition. No zoogeographic discontinuities could be identified. Our results reinforce the findings of recent studies which suggest that, with respect to estuarine benthic assemblages, the boundary between the Virginian and the Carolinian Provinces be moved to a new location south of Pamlico Sound.     

Effects of hypoxic disturbances on an estuarine nekton assemblage across multiple scales

Disturbances influence ecological communities over a wide range of scales. We investigated the effects of localized hypoxic disturbances on an estuarine fish assemblage at several spatial (m² and 10s km²) and temporal (days, seasons, years) scales in a multivariate framework (temperature, salinity, depth, dissolved oxygen). We examined whether seasons, years) scales in a multivariate framework (temperature, salinity, depth, dissolved oxygen). We examined whether there were consistent changes in fish and crustacean estuarine assemblage characteristics along environmental gradients and whether these relationships were altered by hypoxic disturbances. We also investigated at what scale dissolved oxygen concentration may be influencing the structure of motile estuarine assemblages and whether the size of the hypoxic zone altered its effects on the estuarine assemblage. Hypoxic disturbances altered fish and crustacean assemblages along the depth gradients that were present during well-oxygenated periods. Species diversity, richness, and catch rates were lower in hypoxic patches than in oxygenated areas. Dissolved oxygen concentration remained an important explanatory variable for patch-level assemblage dissimilarity, species richness, and diversity when data were aggregated across seasons. When we examined the data at a larger scale, by aggregating information across the study area, we did not detect influences of hypoxia on assemblage structure. Fish moved out of local hypoxic zones, but remained within the estuary even in years with extensive hypoxia. There was no effect of size of the hypoxic distrubance on whether organisms responded to hypoxia or on diversity or richness of the study site. These results suggest that these local disturbances play an important role in structuring motile species assemblages at a patch-level within an estuary, but regional factors such as recruitment and migration are important in influencing species assemblages for the entire estuary over months and years.     

Airborne detection of ecosystem responses to an extreme event: Phytoplankton displacement and abundance after hurricane induced flooding in the Pamlico-Albemarle Sound system,North Carolina

Airborne laser-induced fluorescence measurements were used to detect and monitor ecosystem wide changes in the distribution and concentration of chlorophyll biomass and colored dissolved organic matter in the Pamlico-Albemarle Sound system, North Carolina, U.S., following massive flooding caused by a series of three hurricanes in the late summer of 1999. These high-resolution data provided a significantly more detailed representation of the overall changes occurring in the system than could have been achieved by synoptic sampling from any other platform. The response time for the distribution of chlorophyll biomass to resume pre-flood conditions was used as a measure of ecosystem stability. Chlorophyll biomass patterns were reestablished within four mo of the flooding, whereas higher chlorophylla biomass concentrations persisted for approximately 6 mo. The primary trophic level in the Pamlico-Albemarle Sound system returned to equilibrium in less than a year of a major perturbation.     

Presence of Fish on the Shallow Flooded Margins of a Small Intermittently Open Estuary in South Eastern Australia under Variable Flooding Regimes

Shallow water habitats within estuarine systems are believed to be important areas for small fish. While a wide variety of shallow habitats have been studied, the land that becomes inundated by the damming effect after the closure of intermittently open mouths has previously been overlooked. Fish were sampled monthly from both the main channel and flood zone of an intermittently open estuary between July 2004 and June 2005 using minifyke nets during the day and at night. A total of 7,787 fish were collected during the study representing 13 species and 11 families. Philypnodon grandiceps was the most abundant species and, together with Atherinosoma microstoma, Pseudogobius olorum, and Galaxias maculatus, made up 94% of the total catch. Inundation of the flood zone occurred in two discrete forms associated with mouth condition, which consisted of sporadic flooding while the mouth was open, to long-term flooding for 6 months after its closure. Large numbers of fish were captured on the flood zone, which included nine species; however, A. microstoma dominated the catch. A distinct shift in the flood zone fish assemblage occurred between the two mouth conditions, which is likely associated with changes in hydro-period and food availability of the flood zone and physico-chemical parameters in the main channel. There was no longitudinal variation in the fish assemblage in both the main channel and flood zone; similarly, the diel period was found to have little effect on the fish assemblage. The total catch per unit effort did not vary across seasons and suggests that fish abundance within the estuary is stable throughout the year. Unlike other estuarine systems where shallow water fish assemblages may be structured by variations in tide and elevation within the Surrey, freshwater inflow and, more importantly, mouth condition appear to have the greatest influence in composition of the shallow water flood zone fish assemblage of intermittently open estuaries.     

Life Histories, Salinity Zones, and Sublethal Contributions of Contaminants to Pelagic Fish Declines Illustrated with a Case Study of San Francisco Estuary, California, USA

Human effects on estuaries are often associated with major decreases in abundance of aquatic species. However, remediation priorities are difficult to identify when declines result from multiple stressors with interacting sublethal effects. The San Francisco Estuary offers a useful case study of the potential role of contaminants in declines of organisms because the waters of its delta chronically violate legal water quality standards; however, direct effects of contaminants on fish species are rarely observed. Lack of direct lethality in the field has prevented consensus that contaminants may be one of the major drivers of coincident but unexplained declines of fishes with differing life histories and habitats (anadromous, brackish, and freshwater). Our review of available evidence indicates that examining the effects of contaminants and other stressors on specific life stages in different seasons and salinity zones of the estuary is critical to identifying how several interacting stressors could contribute to a general syndrome of declines. Moreover, warming water temperatures of the magnitude projected by climate models increase metabolic rates of ectotherms, and can hasten elimination of some contaminants. However, for other pollutants, concurrent increases in respiratory rate or food intake result in higher doses per unit time without changes in the contaminant concentrations in the water. Food limitation and energetic costs of osmoregulating under altered salinities further limit the amount of energy available to fish; this energy must be redirected from growth and reproduction toward pollutant avoidance, enzymatic detoxification, or elimination. Because all of these processes require energy, bioenergetics methods are promising for evaluating effects of sublethal contaminants in the presence of other stressors, and for informing remediation. Predictive models that evaluate the direct and indirect effects of contaminants will be possible when data become available on energetic costs of exposure to contaminants given simultaneous exposure to non-contaminant stressors.     

The disruption and recovery of fish communities in the Indian River Lagoon, Florida, following two hurricanes in 2004

During the summer of 2004, four hurricanes (Charley, Frances, Ivan, and Jeanne) affected Florida between August 13 and September 27. Two storms (Frances: category 2 and Jeanne: category 3) made landfall in the southern portion of the Indian River Lagoon (IRL) on the east-central coast of Florida. The presence of Florida Fish and Wildlife Conservation Commission's long-term fisheries monitoring program in the IRL provided a unique opportunity to examine the effects of large tropical events on estuarine fish communities. Increased sampling efforts to monitor the effects of tropical disturbances on the fish community within the IRL and one of its major tributaries (St. Sebastian River) were initiated within days after the passing of the last hurricane (Jeanne). The objectives of the study were to characterize changes to the composition of the fish community within the lagoon and river immediately after the passage of two hurricanes, and to examine the recovery of the fish communities. Analyses indicated that immediately after the last hurricane passed, community diversity within the estuary decreased following these storms due to the absence of many marine species, whereas the fish community within the St. Sebastian River shifted to one containing a greater percentage of freshwater species. Recovery of the community structure to pre-hurricane conditions was evident within several weeks following the last hurricane, and by mid December 2004 (ca. 3 mo after the last storm), there was little difference between the pre-hurricane and post-hurricane fish communities.     

The abundance of fish larvae in estuaries: Within-tide variability at inlet and immigration

The larvae of winter spawning fishes immigrating through Beaufort Inlet into the Pamlico Sound estuarine system (North Carolina, United States) were passively sampled during 14 flood tides and nine of the following ebb tides. Five taxa were abundant in the catches. Pelagic species were represented by Atlantic menhaden, Brevoortia tyrannus. Nonpelagic taxa were represented by Atlantic croaker, Micropogonias undulatus, spot, Leiostomus xanthurus, pinfish, Lagodon rhomboides, and flatfishes of the genus Paralichthys. The sampling was continuous and the sample duration varied between 4 min and 32 min. The longest samples furnished the most accurate and precise estimates of the mean tidal abundance. Sampling 10 min each hour of the tide was the most efficient protocol for determining the mean tidal abundance. The abundance patterns was shown to differ according to the pelagic or nonpelagic behavior of the larvae. Analyses suggested the nonpelagic taxa rely on astronomical tides and vertical migrations synchronous with the direction of the tide flow to be transported upstream in the estuary. These larvae were not dependent upon the strength of the tide to penetrate the inlet. In contrast, menhaden larvae seemed to rely primarily on strong food tides to enter the estuarine area, probably because the vertical positioning of the species within the water column is not dependent upon the direction of the tide. However, if larvae were present outside of the inlet, strong flood tides indiscriminately brought pelagic and nonpelagic species into the estuary.     

Seasonal Occurrence of Cownose Rays (Rhinoptera bonasus) in North Carolina’s Estuarine and Coastal Waters

The seasonal occurrence of cownose rays (Rhinoptera bonasus) within North Carolina’s estuarine and coastal waters was examined from aerial surveys conducted during 2004–2006. Generalized linear models were used to assess the influence of several variables (month, year, habitat type, sea surface temperature, and turbidity) on predicted counts of cownose rays. The spatial distributions of rays were compared by season, and differences in group size were tested as a function of season and habitat. Cownose ray data associated with the North Carolina Division of Marine Fisheries (NCDMF) fishery independent gill net sampling program in Pamlico Sound was also examined as a function of season and year, and compared with aerial observations. Rays immigrated into the region in mid-spring (April), dispersed throughout the estuary in the summer (June–August), and emigrated by late autumn (November). Predicted counts were highest in the spring (April, May) and autumn (September–November) for coastal habitats and highest in the summer for estuarine habitats. Predicted counts were also higher in the coastal region than estuarine and higher when sea surface temperatures were above average. Comparison of group size by habitat type revealed substantially larger group sizes in the coastal habitat than the estuarine. In addition, for the estuary, spring surveys had larger group sizes than summer surveys; for the coastal habitat, autumn group sizes were significantly larger than spring or summer group sizes. The NCDMF gill net sampling surveys indicated similar trends in monthly migration patterns as well as increased ray abundance in 2008 and 2009 compared with 2003–2007. These results suggest that North Carolina’s waters serve as important habitat during the seasonal migration of cownose rays, as well as during the summer when the species may utilize the estuarine region as a nursery and/or for foraging.     

Catchability coefficients for coastal fishes caught in 366-meter and 732-meter long trammel nets struck with noise and rotenone

Catchability coefficients (q) of 366-m and 732-m trammel nets set along the shore in a rectangular shape were determined for selected fish species, utilizing noise and sublethal rotenone strike methods. Catachbility coefficients ranged from 0 to 1 for both trammel nets; 65% and 75% of the values for the 366-m and 732-m nets, respectively, were less than 0.1. Only the perpendicular strike method may have affected the catch efficiency of the nets, but the effect was not consistent among all species. Catchability coefficients were slightly higher when fish too small to be caught in the net were removed from the calculations. Despite the wide range of catchability coefficients among species, trammel nets struck with noise can be used to detect gross changes in abundance (standing stock) of many estuarine fishes. Increases in trammel net efficiency may be obtained by improvement in striking techniques or changes in net design, such as use of less visible monofilament webbing.     

Effects of Tidal Flooding on Juvenile Willows

Tidal wetlands are affected by sea level rise. In the tidal freshwater stretches of estuaries in the temperate zone, willows (Salix spp.) form tidal freshwater forests above the mean high water level. Willows tolerance to prolonged periodic flooding in riverine systems is well documented, whereas effects of tidal flooding on willows are largely unknown. Flooding stress may play a major role in regeneration failure of willows in tidal forest stands along estuarine shores, and juvenile willows might be specifically affected by partial or total submergence. To assess the tolerance of juvenile willows to tidal flooding, we conducted a mesocosm experiment with cuttings from Salix alba and Salix viminalis, which are both characteristic species for tidal freshwater forests in Europe. Cuttings originating from either fresh or brackish tidal forest stands were grown under four tidal treatments with up to a tidal flooding of 60 cm. A general tolerance to a tidal flooding of 60 cm was observed in chlorophyll fluorescence, growth rates, and biomass production in both willow species. Overall, S. alba showed higher leaf and shoot growth, whereas S. viminalis produced more biomass. S. alba with brackish origin performed worst with increasing tidal flooding, suggesting a possible pre-weakening due to stressful site conditions in tidal wetlands at the estuarine brackish stretch. This study demonstrates that juvenile willows of S. alba and S. viminalis tolerate tidal flooding of up to 60 cm. It is concluded that tidal inundation acts as a stress by causing submergence and soil anaerobiosis, but may also act as a subsidy by reestablishing aerobic conditions and thus maintaining willows performance. Therefore, we suggest investigations on Salix tidal flooding tolerance and possible effects of willows on tidal wetland accretion under estuarine field conditions.     

Food of Paralichthys dentatus and P. lethostigma (Pisces: Bothidae) in North Carolina estuaries

The diets of the spatially segregated summer flounder, Paralichthys dentatus, and southern flounder, P. lethostigma, in Pamlico Sound, North Carolina, were composed of crustaceans and fishes. Young flounders fed mainly on mysids and fishes throughout the year, but the ratios of these items differed between species. Feeding was minimal during winter, but summer flounder from near-inlet stations had a high frequency of stomachs with food. Older summer flounder fed equally on shrimp and fishes, while southern flounder fed almost solely on fishes. This difference was probably related to food availability.     

The responses of Patuxent River upper trophic levels to nutrient and trace element induced changes in the lower food web

As a result of human activities, coastal waters can be exposed to multiple stressors that affect primary producers and their interactions with higher trophic levels. Mesocosm experiments were conducted during spring and summer 1996–1998 to investigate the responses of natural populations of primary producers to multiple stressors and the potential for these responses to be transmitted to higher trophic levels (i.e., copepods, bivalves, anemones, and fish). The effects of two stressors, elevated nutrient and trace element loadings, were examined individually and in combination. Nutrient additions had a positive effect on biomass, productivity, and abundance of primary producers (Breitburg et al. 1999; Riedel et al. 2003). Growth or abundance of consumers increased with nutrient additions, but the magnitude of the response was reduced relative to that of their prey. Responses to trace element additions varied seasonally and among taxa. The responses of zooplankton and bivalves to stressor additions were affected by the biomass and changes in species composition of phytoplankton assemblages. The presence of fish predators did not alter zooplankton responses to stressor additions. These results suggest that the extent to which nutrient and trace element effects are transmitted from primary producers to higher trophic levels depends on the capacity of consumers to respond to stressor-induced changes in abundance and species composition of prey, on the absolute abundance of prey, and on the ability of predators to feed on alternative prey. The magnitude of the effects of stressors on estuarine food webs may depend on seasonal variability in species composition of phytoplankton assemblages, whether sensitive species dominate, and whether these species are important prey for secondary consumers. Because spatial and temporal patterns in nutrient and trace element loadings to the estuary can affect species composition of primary producers, it is critically important to examine the magnitude, timing, and spatial relationships of loadings of multiple stressors to coastal waters in order to understand the impacts of these stressors on higher trophic levels.     

Influence of artificial channels on the source and extent of saline water intrusion in the wind tide dominated wetlands of the southern Albemarle estuarine system (USA)

Saline water intrusion is degrading water quality in the channelized coastal wetlands of the southern Albemarle estuarine system (AES). The source, transport and fate of the saline water in the southern AES was determined by monitoring specific conductivity and water levels in small artificial channels, the Alligator River, the Alligator–Pungo Canal and the groundwater system for ~12 months. Results indicate that water levels are affected by wind tides which trigger the movement of saline water into the interior of the wetlands via the small canals. The wind tides are mostly driven by episodic southerly winds pushing saline water into the canal network and the groundwater regime proximal to the Alligator River. The saline waters persist in the canals as long as the wind tide events last. Specific conductivities from canals and groundwater are shown to be unexpectedly higher closer to the source of the Alligator River than toward the Albemarle Sound, suggesting that the large Alligator–Pungo Canal facilitates the northward migration of saline water from the Pamlico Sound to the Alligator River. Overwash and reversals in the flow directions between groundwater and surface water bodies suggest that saline water that is present during wind tide events may migrate into the groundwater system from surface water bodies. The results of this study reveal that whereas the large Alligator–Pungo Canal channels saline water to the AES, small artificial channels may also play significant roles in degrading water quality in the interior of channelized coastal wetlands.