Courtney T. Hackney

Use of oligohaline marshes by fishes and macrofaunal crustaceans in North Carolina

Fishes and invertebrate macrofauna (nekton) inhabiting three low salinity, intertidal rivulets were sampled biweekly from July 1981 through June 1982. Twenty-nine species of fishes (24,335 individuals, 9.671 kg wet weight) representing 19 families and four species of invertebrates (6,812 individuals, 4.708 kg wet weight) were collected. The most abundant species were spot (Leiostomus xanthurus), grass shrimp (Palaemonetes pugio), bay anchovy (Anchoa mitchilli) and Atlantic menhaden (Brevoortia tyrannus). Only a few large predacious fish (e.g., largemouth bass,Micropterus salmoides) were collected in the rivulets although largemouth bass and longnose gar (Lepisosteus osseus) were abundant in a nearby permanently flooded area. The number of species was greatest during the warmer months and lowest, during the winter. There were three seasonal peaks of numerical abundance: spring peak attributed to the influx of junvenile spot Atlantic menhaden, Atlantic croaker (Micropogonias undulatus), and southern, flounder (Paralichthys lethostigma); summer peak due to grass shrimp; and fall peak to bay anchovy and grass shrimp. The occurence of these species was not correlated with salinity in the study area. Average densities of spot and Atlantic menhaden in the oligohaline rivulets at the peak of juvenile recruitment were similar to the average densities of these species reported for salt marshes. The results suggest that oligohaline estuarine areas contain important nursery habitat for some euryhaline species.

In Situ Decomposition of Roots and Rhizomes of Two Tidal Marsh Plants

In situ decomposition of roots and rhizomes of the marsh plants Juncus roemerianus and Spartina cynosuroides was investigated using litter bags. The decomposition rate was greatest in the top 10 cm (20%o mass loss/yr) of the marsh soil. There was no apparent decomposition below 20 cm depth. Belowground tissues of S. cynosuroides decomposed faster than those of J. roemerianus during the first 4 mo. The rhizome decomposition rate of 27%/yr (mass loss) was faster than the 16%o/ yr of the roots of J. roemerianus. There was no difference between the decomposition rate of mixed root and rhizome materials between experiments initiated in winter and those started in the spring. This indicates a relatively constant decomposition rate during the year in the 0-10 cm soil zone. There was no apparent trend in the hydrogen, carbon, phosphorus, nitrogen, or caloric content changes of the decomposing roots and rhizomes during the study.

Flux of dissolved organic carbon and pore water through the substrate of a Spartina alterniflora marsh in North Carolina

Abstract The export of dissolved organic carbon (DOC) from a sandy substrate Spartina alterniflora marsh in North Carolina was studied from August 1982 to July 1983. DOC of the pore water was determined using a total organic carbon analyzer and was reliably estimated by measuring the absorbance of the pore water. DOC ranged between 1 and 6 mg l −1 and was highest during summer and lowest in winter. Based on hydraulic conductivity calculations, over 34 000 1 year −1 of pore water was exported through the 1×25 m transect perpendicular to a tidal creek. Most of this flux (over 90%) occurred within 2 m of the creek bank. Based on this pore water flux, belowground DOC export was only 1·52 g Cm −2 year −1 .

Enegry Value, Elemental Composition, and Productivity of Belowground Biomass of A Juncus Tidal Marsh

Belowground standing crop of a Juncus roemerianus marsh in Mississippi ranged from 9.7 to 12.4 kg dry wt/m2 with the peak biomass occurring in April. Annual productivity estimated from expected maximum minus expected minimum biomass fitted into a periodic regression model was 1.36 kg/m2. Ninety—four percent of the productivity was within the top 20 cm indicating that the bulk of the materials found beyond this depth consisted of dead tissues. Energy, carbon, hydrogen, nitrogen, and phosphorus contents of belowground materials did not vary significantly during the year, but patterns of differences in samples taken from different depths were evident. The productivity of belowground materials in Juncus marshes is comparable with aboveground productions reported in the literature with respect to dry biomass. The probability that large portions of the underground production enter the aqueous system and become incorporated in estuarine energetics merits further consideration. See full-text article at JSTOR

Distribution ofJuncus roemerianus in North Carolina tidal marshes: The importance of physical and biotic variables

The physical habitat ofJuncus roemerianus was examined at nine sites along a salinity gradient in the Cape Fear River Estuary, North Carolina. Soil salinity, drainage, redox potential, pH, elevation, percent sand, percent organic matter, and above-ground plant biomass and height were measured at each site, and from these data, the habitat ofJuncus roemerianus was determined. All parameters varied over the salinity gradient, with soils at upriver sites having, a high sand fraction, low organic fraction, and highest redox potentials. Downriver, well-established marshes had low sand fractions, high organic fractions, and lowest redox potentials. Canonical Discriminant Analysis indicated that each site was statistically different from other sites due to salinity, elevation, and percent organic matter.Mean standing live biomass was 688 g m−2 and, despite differences in physical and chemical factors among sites, biomass ofJuncus roemerianus did not vary.Juncus roemerianus was found to grow equally well within a broad range of physical and chemical habitats but did not occupy the total expanse of its potential habitat at any one site.Extensive overlap in physical habitat occurred betweenJuncus-dominated communities and adjacent communities dominated by other species, especially in the more established marshes. However, Canonical Discriminant Analysis statistically separated short and tall formSpartina alterniflora, Distichlis spicata, Scirpus robustus, andJuncus roemerianus microhabitats based on elevation and redox potential. Thus, we found zonation in tidal marshes of the Cape Fear, River Estuary was based on abiotic factors, but we recognize the importance of plant species interactions and marsh position within the landscape.

The Potential Role of Roots and Rhizomes in Structuring Salt-Marsh Benthic Communities

The density of the Carolina marsh clam,Polymesoda caroliniana (Bosc), was determined in three adjacent tidal marsh communities which differed only in plant species composition. Clam density was inversely related to the density (biomass) of plant roots and rhizomes in sediments and directly related to density of plant stems (numbers). Clam abundance was not related to the basal area of plant stems. Each plant community contained clams of various ages from juvenile to adult indicating continued recruitment and survival. These data suggest thatP. caroliniana is most abundant inJuncus roemerianus marshes because there are fewer roots and rhizomes (mean of 2.5 kg m−2) to hamper burrwing as compared toSpartina alterniflora andcynosuroides (5.1 and 6.3 kg m−2, respectively) dominated marshes. Salinity, floding frequency, distance from flooding water, and sediment type were essentially constant among the three plant communities. Root/rhizome density should be collected along with other environmental parameters during studies of benthic organisms on marshes because it potentially limits the occurrence or abundance of some species.

Restoration of coastal habitats: expectation and reality

Abstract Restoration today must satisfy a wide array of societal goals. In the past, success or failure of a project was dependent on minimal, measurable criteria. Simplistic designs and compliance criteria are being replaced by technically sophisticated projects and design goals that have variable criteria for success. Instead of a being static target, success criteria can be altered through a process termed Adaptive Management. Natural resource damage can be assessed accurately through a Habitat Equivalency Analysis. Acceptable progress toward compliance criteria is best measured by trends approaching a desired end point. An approach using natural variation of similar habitats also shows promise as a means of assessing compliance. Large-scale restoration projects are underway, directly and indirectly underwritten by the public. If the public is to continue support for restoration it must be a part of the decision-making process. This can be best accomplished through landscape management plans with clear objectives and goals that the public understands and that benefit the public at large. Technical problems in accomplishing and evaluating restoration projects will be solved if the experience gained at each site is used in future projects.

Sediment quality of North Carolina estuaries: an integrative assessment of sediment contamination, toxicity, and condition of benthic fauna

Sediment quality of North Carolina estuaries was evaluated using synoptic data on sediment chemistry, toxicity, and macroinfaunal community structure from 175 subtidal stations sampled during the summers of 1994–1997. The study area included Currituck, Albemarle, and Pamlico Sounds; estuarine portions of major rivers (e.g., Chowan, Roanoke, Tar-Pamlico, Neuse, New, Cape Fear); and numerous smaller tributaries and coastal embayments between the Virginia and South Carolina borders. A probabilistic sampling design permitted statistical estimation of the spatial extent of degraded versus non-degraded condition across these estuaries. Over half (54 ± 7%) of the surveyed area had high sediment quality characterized by healthy benthic assemblages and low levels of sediment contamination and toxicity. The remaining 46% showed evidence of significant stress in one or more of the above sediment-quality-triad components. While this is a sizable area, portions of it (27 ± 6%) were represented by sites with no connection between presence of stressors and adverse biological responses. Only 19% of the total area showed evidence of an impaired benthos coupled to significant pollution exposure (high sediment contamination, toxicity, or both). Impaired benthic condition was more closely linked to sediment contamination than to low dissolved oxygen (based on instantaneous oxygen measurements). The most pervasive contaminants were the metals arsenic, mercury, chromium, and nickel; the pesticides lindane, dieldrin, DDT, and DDT derivatives; and total PCBs. Degraded condition in all three components of the sediment quality triad co-occurred in <10% of the study area, suggesting that strong contaminant-induced effects on the benthos are limited to a small (yet ecologically significant) percentage of total estuarine area. The spatial extent of sediment contamination and toxicity was much less in these estuaries in comparison to other U.S. coastal regions where similar studies have been performed.

DOES INTERTIDAL VEGETATION INDICATE SPECIFIC SOIL AND HYDROLOGIC CONDITIONS

Six distinct plant zones were identified within a mesohaline tidal marsh in the Cape Fear Estuary, North Carolina. USA. All six vegetative zones were found within an 18-cm portion of the 1.35-m tidal range. Aerial photographs show that these six zones have existed within the marsh for the past 20 years. A monotypicJuncus roemerianus stand occupied soils with the highest salinity porewater (17 ppt), while stands dominated (>90%) by eitherScirpus robustus orTypha angustifolia were found associated with the least saline soil water (7 ppt) in areas of the marsh least flooded by tidal waters.Spartina cynosuroides dominated areas of the marsh at lowest elevations. In general, Eh was highest in theJuncus zone and lowest in theSpartina alterniflora zone. Four of the six vegetative zones represented distinct physical and chemical environments and could be statistically separated via canonical discriminate analyses. We suggest that established vegetation may be an accurate analog for specific hydrogeomorphic conditions.

The importance of oligohaline estuarine wetland habitats to fisheries resources

Oligohaline estuarine wetlands are found at the upper reaches of most estuaries. These wetlands are composed of several habitat types including tidal marshes, tidal creeks, and open-water areas. Twenty-five species of fish representing 11 families and three species of invertebrates were identified as economically important and abundant in oligohaline habitats along the northern Gulf and southeastern Atlantic coasts. These include anadromous and catadromous species which use low salinity habitats as migratory corridors and freshwater, estuarine and marine organisms which use these habitats as nursery and feeding areas. The few comparative data available suggest that some oligohaline wetland habitats may be of equal importance to higher salinity marshes for at least two important estuarine species (spot and Atlantic menhaden). Until detailed studies are available for specific estuaries, oligohaline habitats should be considered as valuable as salt marsh habitats. The value of these habitats as nursery areas should be considered by managers and regulatory agencies when reviewing proposals to modify them.