The soft-bottom macrobenthos of North Carolina estuaries

The structure of macro infaunal (>0.5 mm sieve size) assemblages was examined in samples of unconsolidated substrates collected during the summers of 1994–1997 at 208 stations throughout North Carolina estuaries. Numerical classification (cluster analysis) of stations resulted in 14 distinct site groups that reflected discernible habitatrelated patterns in species distributions. Multiple discriminant analysis, performed on synoptic abiotic variables (depth, salinity, dissolved oxygen, pH, percent silt-clay), showed that the separation of site groups was related primarily to salinity. Percent silt-clay had a secondary influence on the separation of sites within similar salinity zones. Species diversity among site groups generally decreased with decreasing salinity and increasing mud content of sediment. Nodal analysis showed a wide range in constancy and fidelity of species assemblages within site groups. Some assemblages dominated by euryhaline species had no particular affinity with any one site group. The strongest affinities, as evidenced by high values of both constancy and fidelity, were displayed by an assemblage of oligochaetes, insect larvae, gammaridean amphipods, and the clamCorbicula fluminea in tidal freshwater muds; and an assemblage of haustoriid amphipods, the bivalveDonax variabilis, the polychaeteParaonis fulgens, and unidentified echinoids at high-salinity sites in outer Pamlico Sound near ocean inlets. A series of stations with impaired benthic assemblages in polluted habitats emerged from the cluster analysis and was distinguishable from other site groups that reflected a greater influence of natural controlling factors (such as salinity and sediment type) on species distributions. These results suggest that the interaction of both anthropogenic and natural environmental controlling factors is important in defining the structure of these infaunal assemblages.     

Phytoplankton ecology of North Carolina estuaries

Numerous phytoplankton-oriented ecological studies have been conducted since 1965 in the extensive North Carolina estuarine system. Throughout a range of geomorphological estuarine types, a basic underlying pattern of phytoplankton productivity and abundance following water temperature seasonal fluctuations was observed. Overlying this solar-driven pattern was a secondary forcing mechanism consisting of a complex interaction between meteorology and hydrology, resulting in periodic winter or early spring algal blooms and productivity pulses in the lower riverine estuaries. Wet winters caused abundant nitrate to reach the lower estuaries and stimulate the blooms, whereas dry winters resulted in low winter phytoplankton abundance and primary production. Dinoflagellates (Heterocapsa triquetra, Prorocentrum minimum, Gymnodinium spp.) and various cryptomonads dominated these cool-weather estuarine blooms. Sounds were less productive than the riverine estuaries, and were dominated by diatoms such asSkeletonema costatum, Thalassiosira spp.,Melosira spp., andNitzschia spp., as were the most saline portions of riverine estuaries. Nutrient-limitation studies found that nitrogen was the principal limiting nutrient in these estuarine systems over a range of trophic states, with phosphorus occasionally co-limiting. Freshwater and oligohaline portions of large coastal plain rivers were often subject to summer blue-green algal blooms. Formation of these blooms on a year-to-year basis was also determined by meteorology and hydrology: wet winters or springs and consequent nutrient loading, coupled with low summer flow conditions and regeneration of nutrients from the sediments. Dry winters or springs resulted in less available nutrients for subsequent summer regeneration, and high flow conditions in summer flushed out the blooms. In recent years, there has been a dramatic increase in reported fish kills attributed to toxic dinoflagellate blooms, particularly in nutrient-enriched estuarine areas. This issue has become a major coastal ecological and economic concern.     

Ferry-based monitoring of surface water quality in North Carolina estuaries

Several interrelated factors affect, water quality in the Albemarle-Pamlico Estuarine System (APES) including land use change in the upland and coastal watersheds, legislatively mandated basin-wide nutrient management plans, intense storms, and global and local changes in sea level. Despite its importance as an essential fish habitat, the APES has not been monitored as intensively or extensively for habitat impacts associated with decreased water quality as other estuaries have been, such as with the North Carolina tributary estuaries or Chesapeake Bay. To support the sustainable use of these estuaries, we are developing an automated water quality monitoring system aboard ferries that traverse the APES. This program, FerryMon, provides a unique, long-term, and cost-effective monitoring system to evaluate status and trends in APES water quality. Intensive temporal and spatial data obtained from all ferry routes provide an environmental baseline and are used to assess the patterns and variability in surface water hydrography, dissolved constituents, and particulate matter. The data are useful to calibrate estimates of ocean color and sea surface temperature from aircraft and satellite sensors. We are creating a searchable geographic database that is intended for scientists, managers, and the general public. Using ferries as sampling platforms to monitor estuarine water quality is a tractable approach and FerryMon represents a model for use in other large bodies of water traversed by ferries.     

Short-term variability of water quality parameters in two shallow estuaries of North Carolina

We quantified the effects of nutrient loading following precipitation events (≥ 1.25 cm) in 2 tidal creeks varying in size and anthropogenic input during the winter and summer seasons of 1996. Several water quality parameters were repeatedly measured in the water column every 3 h for several days after each event (4–5 per season). Total nitrogen (TN) and total phosphorus (TP) behaved nonconservatively with salinity and appeared as pulsed additions, occasionally doubling within 1 to 2 tidal cycles following significant rain events. Average values for TN, TP, and chlorophylla were 10–15 μM, <4 μM, and <7 μg l⁻¹, respectively for winter events and 30–35 μM, >4 μM, and ≥ 7 μg l⁻¹, respectively for summer events. However, response times were variable, depending on the magnitude and duration of the event as well as temperature. Chlorophylla biomass often increased after nutrient additions, especially in the summer when increased nutrient loading took place. Dissolved silica (DSi) behaved conservatively with salinity; low values were observed at high tide and vice versa. Average DSi ranges for winter and summer events were 5–45 μM and 10–85 μM, respectively. DSi range values increased proportionally with the amount of freshwater loaded into the system. Recovery times for salinity were usually greater than the recovery times for nutrients. Dissolved oxygen displayed a diel pattern, increasing after daytime productivity and decreasing during nighttime. In conclusion, each rainfall event was unique and responses were variable depending upon rainfall history, seasonality, and the duration and intensity of the rainfall event. Several other variables, such as water viscosity, percolation rates, and evapotranspiration rates which were not quantified in this study, could have also explained parameter responses.     

Paleoecological evidence of human impacts on the Neuse and Pamlico estuaries of North Carolina,USA

Sediment cores were collected from the Neuse and Pamlico River estuaries, North Carolina, at seven different sites, and the data show strong anthropogenic influence on water quality. The sediments from these cores were dated using²¹⁰Pb,¹³⁷Cs,¹⁴C, and pollen horizon techniques. Specific parameters investigated include bulk density, sedimentation rates, diatom assemblage changes, nutrient and trace metal flux, and vegetation changes as recorded in the pollen record. The greatest increases in sedimentation, nutrient and metal flux and changes in diatom assemblages have occurred in the past 50–60 yr in the Pamlico and Neuse. Diatom diversity has decreased and small planktonic forms have become dominant over time, most likely due to eutrophication and increased turbidity and sedimentation. Major changes occur before phytoplankton surveys and monitoring were initiated. Overall trends are similar to those found in Chesapeake Bay, although the time frame of major changes is more recent. Dominant small planktonic diatom species differ between Chesapeake Bay and the Neuse and Pamlico. Variance in paleoecological indicators between these mid-Atlantic estuaries may be due to geomorphology and land use history.     

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.     

Geographic signatures of North American West Coast estuaries

West Coast estuaries are geologically young and composed of a variety of geomorphological types. These estuaries range from large fjords to shallow lagoons; from large to low freshwater flows. Natural hazards include E1 Niños, strong Pacific storms, and active tectonic activity. West Coast estuaries support a wide range of living resources: five salmon species, harvestable shellfish, waterfowl and marine birds, marine mammals, and a variety of algae and plants. Although populations of many of these living resources have declined (salmonids), others have increased (marine mammals). West Coast estuaries are also centers of commerce and increasingly large shipping traffic. The West Coast human population is rising faster than most other areas of the U.S. and Canada, and is distributed heavily in southern California, the San Francisco Bay area, around Puget Sound, and the Fraser River estuary. While water pollution is a problem in many of the urbanized estuaries, most estuaries do not suffer from poor water quality. Primary estuarine problems include habitat alterations, degradation, and loss; diverted freshwater flows; marine sediment contamination; and exotic species introductions. The growing West Coast economy and population are in part related to the quality of life, which is dependent on the use and enjoyment of abundant coastal natural resources.     

Sulfate enrichments in estuarine waters of North Carolina

Sulfate concentrations in the mesohaline surface waters of the Pamlico and Neuse River estuaries were enriched, relative to the conservative seawater ratio with Cl^? (0.0517 (M)), by 5 to 43% between late winter and early summer. During this period, sulfate concentrations increased to a maximum excess of 3.5 mM in the bottom waters (0.5 m deep) through intermittent periods of both very low river flow and bottom water anoxia. The calculated net sulfate production rate for this period was 18 mmol per m² per d in the bottom waters. By late summer, the excess sulfate (an average of 12 mol per m²) had been removed from the water column, presumably due to SO₄ ^?2 reduction in anoxic bottom waters and sediments. Qualitative laboratory experiments with slurries of mud exposed to excess O₂ and treated with inhibitors of cytochrome oxidase showed that it was possible to produce the excess SO₄ ^?2 under these conditions via biochemical (not chemical) oxidation of pyride that occurs within the top 5 cm of mud (ca. 100 mmol pyrite-S per g dry mud). Whether the in situ substrate for SO₄ ^?2 production was pyrite, S⁰, or S⁺², is unknown, but the predominance of aqua regia extractable pyrite-Fe and the accumulation of excess SO₄ ^?2 in slurries with insufficient other sources of oxidizable S, indicates that it may be an important substrate for biochemical production of SO₄ ^?2.     

A geochemical atlas of North Carolina, USA

A geochemical atlas of North Carolina, U.S.A., was prepared using National Uranium Resource Evaluation (NURE) stream-sediment data. Before termination of the NURE program, sampling of nearly the entire state (48,666 square miles of land area) was completed and geochemical analyses were obtained.The NURE data are applicable to mineral exploration, agriculture, waste disposal siting issues, health, and environmental studies. Applications in state government include resource surveys to assist mineral exploration by identifying geochemical anomalies and areas of mineralization. Agriculture seeks to identify areas with favorable (or unfavorable) conditions for plant growth, disease, and crop productivity. Trace elements such as cobalt, copper, chromium, iron, manganese, zinc, and molybdenum must be present within narrow ranges in soils for optimum growth and productivity. Trace elements as a contributing factor to disease are of concern to health professionals. Industry can use pH and conductivity data for water samples to site facilities which require specific water quality.The North Carolina NURE database consists of stream-sediment samples, groundwater samples, and stream-water analyses. The statewide database consists of 6,744 stream-sediment sites, 5,778 groundwater sample sites, and 295 stream-water sites. Neutron activation analyses were provided for U, Br, Cl, F, Mn, Na, Al, V, Dy in groundwater and stream water, and for U, Th, Hf, Ce, Fe, Mn, Na, Sc, Ti, V, Al, Dy, Eu, La, Sm, Yb, and Lu in stream sediments. Supplemental analyses by other techniques were reported on U (extractable), Ag, As, Ba, Be, Ca, Co, Cr, Cu, K, Li, Mg, Mo, Nb, Ni, P, Pb, Se, Sn, Sr, W, Y, and Zn for 4,619 stream-sediment samples. A small subset of 334 stream samples was analyzed for gold.The goal of the atlas was to make available the statewide NURE data with minimal interpretation to enable prospective users to modify and manipulate the data for their end use. The atlas provides only very general indication of geochemical distribution patterns and should not be used for site specific studies. The atlas maps for each element were computer-generated at the state's geographic information system (Center for Geographic Information and Analysis [CGIA]). The Division of Statistics and Information Services provided input files. The maps in the atlas are point maps. Each sample is represented by a symbol generally corresponding to a quartile class. Other reports will transmit sample and analytical data for state regions. Data are tentatively planned to be available on disks in spreadsheet format for personal computers.During the second phase of this project, stream-sediment samples are being assigned to state geologic map unit names using a GIS system to determine background and anomaly values. Subsequent publications will make this geochemical data and accompanying interpretations available to a wide spectrum of interdisciplinary users.     

Vesicular-arbuscular mycorrhizae in salt marshes in North Carolina

The primary objective of this research was to determine if vesicular-arbuscular (VA) mycorrhizal fungi are associated with the roots of common plant species found in North Carolina salt marshes. Root samples of Spartina alterniflora, S. patents, S. cynosuroides, Distichlis spicata, and Juncus roemerianus were collected from eight salt marsh sites. With the exception of S. alterniflora, all plant species were mycorrhizal. A greenhouse experiment was conducted to determine whether unfavorable soil conditions or inherent resistance by the plant inhibited development of mycorrhizal infection in field-collected S. alterniflora. Spartina alterniflora and S. patens were grown from seeds in soil collected from a pure stand of S. alterniflora (soil A) or a mixed stand of S. patens and D. spicata (soil P). Seedlings were harvested weekly for 8 wk, and roots were evaluated for infection by mycorrhizal fungi. Seedlings of S. patens were infected when grown for 2 wk in either soil A or soil P, indicating that soil collected from stands of S. alterniflora did not inhibit mycorrhizal infection in a susceptible host. Percent root length infected in S. patens was always greater in soil P than in soil A. Seedlings of S. alterniflora were not infected by mycorrhizal fungi in either soil A or soil P. Results of the greenhouse study indicate that S. alterniflora may be resistant to infection by vesicular-arbuscular mycorrhizal fungi.     

Petrology of the Mecklenburg gabbro-metagabbro complex,North Carolina

The Mecklenburg complex, which crops out in the Carolina Piedmont, consists of older metagabbro and metafelsic rocks of upper amphibolite grade, and a younger postmetamorphic gabbro. On the evidence of field data and gravity measurements, the younger gabbro appears to be a plug-like body with steeply dipping contacts that may converge inward at relatively shallow depth; the pluton may extend only 8,000–15,000 feet into the subsurface.Gabbroic rocks contain plagioclase, olivine, orthopyroxene, clinopyroxene, hornblende, and biotite, and display hypidiomorphic textures characterized by numerous reaction relations among the mafic phases; hydrous minerals are commonly abundant, comprising up to 37% of the rock, and indicate the fugacity of H₂O was relatively high during primary crystallization. In contrast metagabbro lacks olivine and exhibits textures that range from relict igneous varieties to crystalloblastic types that appear to represent equilibrium assemblages. A less common metagabbro type, associated with local zones of deformation, is characterized by faint banding and only trace amounts of anhydrous mafics. Varieties of metagabbro are complexly intermingled in the field, and resultant assemblages and textures largely reflect whole-rock composition and differences in initial H₂O contents, slightly modified locally by addition of fluid along favorable channelways.In general metagabbro is slightly higher in TiO₂, Na₂O, and K₂O, and lower in MgO relative to gabbro; regardless of the degree of recrystallization, the chemistry of the various metagabbro types is nearly identical, thus indicating metamorphism was essentially isochemical.     

Iron isotope systematics in estuaries: The case of North River, Massachusetts (USA)

Recent studies have suggested that rivers may present an isotopically light Fe source to the oceans. Since the input of dissolved iron from river water is generally controlled by flocculation processes that occur during estuarine mixing, it is important to investigate potential fractionation of Fe-isotopes during this process. In this study, we investigate the influence of the flocculation of Fe-rich colloids on the iron isotope composition of pristine estuarine waters and suspended particles. The samples were collected along a salinity gradient from the fresh water to the ocean in the North River estuary (MA, USA). Estuarine samples were filtered at 0.22 μm and the iron isotope composition of the two fractions (dissolved and particles) were analyzed using high-resolution MC-ICP-MS after chemical purification. Dissolved iron results show positive δ⁵⁶Fe values (with an average of 0.43 ± 0.04‰) relative to the IRMM-14 standard and do not display any relationships with salinity or with percentage of colloid flocculation. The iron isotopic composition of the particles suspended in fresh water is characterized by more negative δ⁵⁶Fe values than for dissolved Fe and correlate with the percentage of Fe flocculation. Particulate δ⁵⁶Fe values vary from −0.09‰ at no flocculation to ∼0.1‰ at the flocculation maximum, which reflect mixing effects between river-borne particles, lithogenic particles derived from coastal seawaters and newly precipitated colloids. Since the process of flocculation produces minimal Fe-isotope fractionation in the dissolved Fe pool, we suggest that the pristine iron isotope composition of fresh water is preserved during estuarine mixing and that the value of the global riverine source into the ocean can be identified from the fresh water values. However, this study also suggests that δ⁵⁶Fe composition of rivers can also be characterized by more positive δ⁵⁶Fe values (up to 0.3‰) relative to the crust than previously reported. In order to improve our current understanding of the oceanic iron isotope cycling, further work is now required to determine the processes controlling the fractionation of Fe-isotopes during continental run-off.     

Hydrologic equilibrium status of a disturbed Eastern North Carolina watershed

Evaluation of the impacts of artificial drainage systems on wetlands requires an assessment of the hydrologic equilibrium status of the surface hydrologic system. Hydrologic equilibrium is characterised by a high correlation between surplus moisture (as calculated by Thornthwaite's methodology) and stream discharge. A qualitative stability analysis shows that deterioration of artificial drainage channels is the process allowing the surface hydrologic system to adjust to the disturbances. The model is tested by examining the correlation between surplus and discharge for a small watershed altered by forestry drainage which is periodically rehabilitated. With hydrologic equilibeium arbitrarily defined as a surplus-discharge correlation coefficient 0.8, it is shown that the original, largely undisturbed watershed was in hydrologic equilibrium. Disequilibrium was induced by artificial drainage-ways, with a return to equilibrium over time. Subsequent renovations of ditches and canals were associated with a recurrence of disequilibrium. The surface hydrologic system is metastable, and cannot be expected to return to previously-existing states following a disturbance. Consistently maintained artificial drainage system appears to preclude any return to any type of hydrologic equilibrium.     

Habitat utilization by small flatfishes in a North Carolina estuary

Distribution and abundance of flatfish species (<150 mm standard length) were related to habitat characteristics in the Newport River and Back Sound estuaries in North Carolina. Salinity, turbidity, depth, distance from marsh edge, benthic composition, and grain size were used to describe the different shallow water habitats from April through October 1994. One Scophthalmidae, seven Paralichthyidae, one Achiridae, and one Cynoglossidae species were collected during the study including juvenileParalichthys albigutta (gulf flounder),P. dentatus (summer flounder), andP. lethostigma (southern flounder) along with multiple age classes ofCitharichthys spilopterus (bay whiff),Etropus crossotus (fringed flounder),Symphurus plagiusa (blackcheek tonguefish), andTrinetes maculatus (hogchoker). Incidental catches ofAncylopsetta quadrocellata (ocellated flounder),C. macrops (spotted whiff), andScopthalmus aquosus (windowpane) were also made. Flatfish distributions among habitats varied by species, size within species, and season. Regardless of season, the highest densities of flatfishes were found in the upper estuary. All habitats were used by one or more species and most species occurred at several habitats. Some species were significantly more abundant at specific habitat types. Ontogenetic shifts in habitat utilization were found for several species. High densities of smallP. lethostigma, C. spilopterus, S. plagiusa, andT. maculatus occurred in the upper estuary on muddy substrates. LargeP. dentatus, C. spilopterus, S. plagiusa, andT. maculatus utilized sand flats and channels in the lower estuary.     

Summer meroplanktonic prosobranch larvae occurring off Beaufort,North Carolina

The occurrence of planktonic prosobranch larvae identified during the summers of 1977, 1979 and 1981 off Beaufort, North Carolina is given. Forty-two species were recorded; 29 of these were found each summer. Observations and identifications were made on 12 newly described larvae: Lacuna sp, Epitonium sp. 1 (apiculatum), Epitonium sp. 2, Strombus alatus, Erato maugeriae, Simnia acicularis, Natica sp. 1, Natica sp, 2, Natica sp. 3, Natica sp. 4, Olivella adelae, Mangelia sp. and Sp.? Turridae. A key for the identification of planktonic prosobranch veligers occuring in summer months is included.     

Coastal saltmarsh development at Southern Topsail Sound,North Carolina

Topsail Sound is a marsh-filled barrier lagoon in southeastern North Carolina. This study quantified changes within a 477-ha tidal marsh located landward of Lea and Coke islands in southern Topsail Sound. Aerial photographs from 1949, 1966, and 1984 were enlarged, and sample areas of salt marsh were digitized and compared. Since 1949, Old Topsail Inlet has migrated southwest 1.2 km. As the inlet migrated, new Spartina alterniflora marsh colonized 33.2 ha of intertidal sand flats within the inlet flood tidal delta, adjacent islands, and primary tidal creeks. Landward of the flood tidal delta, site specific gains and losses of marsh were recorded. It is estimated that since 1949, approximately 34.1 ha of the marsh area occupying the zone landward of the flood tidal delta has drowned. This loss of marsh, combined with the colonization of marsh mentioned above, resulted in a net decrease of 1 ha in the total area of marsh. This study provides evidence that, although lagoonal marshes may be drowning as a result of soil waterlogging, reduced sediment supply, and sea-level rise, potential marsh environments are created by oceanic inputs of sand when inlets migrate.     

Transverse structure of residual flow in North Inlet,South Carolina

Transverse distributions of the depth-averaged, axial residual current across the mouth of North Inlet are computed. A numerical model is used in which the acceleration at any point of the section is governed by a balance between surface slope forcing, friction, and viscous drag. Computed velocities are compared with observations taken over three tidal cycles. The transverse structure of residual flow is similar to that described by the model. However, an additional circulation pattern is present in the data and may be due to advective effects.     

Dynamics of nutrient elements in three estuaries of North China: The Luanhe, Shuangtaizihe, and Yalujiang

Concentrations of nutrients (NO₃ ^?, NO₂ ^?, NH₄ ⁺, PO₄ ^3?, and dissolved SiO₂) were examined in three North China estuaries—the Luanhe, Shuangtaizihe, and Yalujiang. These riverine-estuarine systems provide distinct geographic and hydrodynamic conditions, that is, a shallow water zone embraced by shoals and sandbars (Luanhe), the confluence of two streams in the upper estuary with different water and sediment loads, and a turbidity maximum in the upper estuarine mixing zone (Yalujiang). Nutrient element concentrations in these rivers are high in comparison with large, less disturbed systems but similar to those from polluted and/or eutrophic European and North American rivers. This is attributed to intensive weathering and erosion and extensive use of chemical fertilizers. In the fresh-marine waters mixing zone, nutrient species can behave either conservatively or nonconservatively, or both. Wherever nonconservative behaviours of nutrient elements are observed, remobilization from solid phases is probably the predominant mechanism. The extrapolation of dilution curves to the fresh water end-members gives estimated riverine concentrations, which can be between two and ten times higher than those from field observations. Taking into account the high N:P ratios (10²–10⁴) from North China rivers and very low concentrations of nitrogen species in the Northwest Pacific coastal oceans (e.g., Yellow Sea), the estuaries in this study may act as regions in which production is limited by phosphorus to regions in which production is limited by nitrogen.