Lyle M. Varnell

An assessment of ecological conditions in a constructed tidal marsh and two natural reference tidal marshes in coastal Virginia

Abstract A comparison of a constructed tidal marsh with two adjacent natural tidal marshes was conducted. The marshes were sampled for fish, shellfish, benthic infauna, marsh surface utilization, vegetation community type, stem density and cover, salinity, temperature, dissolved oxygen, organic carbon, bird utilization, and zooplankton. The proximity of study sites permitted simultaneous sampling to test for marsh preference by fish and shellfish. Subsurface organic carbon, Spartina alterniflora stem density, low marsh zone surface utilization, zooplankton abundance and bird nesting sites were all greater in the natural marshes. Other attributes such as stem density of the high marsh, high marsh zone surface utilization, surface organic carbon, and benthic infauna community structure and abundance were similar between the constructed and natural marshes. Seasonal differences were observed for fish and shellfish abundance between the constructed and natural marshes. The study is among the first to use simultaneous sampling techniques to investigate fish and shellfish use between constructed and adjacent natural reference wetlands.

Maturation of a constructed tidal marsh relative to two natural reference tidal marshes over 12 years

Abstract Habitat functions of a constructed tidal marsh and two adjacent natural tidal marshes were compared between marshes and with similar data collected in the same marshes 7 years earlier. The marshes were sampled for fish, blue crabs, benthic infauna, vegetation community type, stem density and cover, salinity, temperature, dissolved oxygen, organic carbon, and bird utilization. The constructed marsh has progressed to a general level of function similar to that of nearby natural marshes. Some morphological differences remain, such as the differences in community type ratios. Significant differences in habitat function remain in three areas: sediment organic carbon at depth, mature saltbush density, and bird utilization (related to saltbush density). The addition of organic soil amendments and mature saltbush in the construction of tidal marshes will help in the progression of constructed marshes to functional equivalency with natural marshes. Specific functions can be enhanced for fish utilization (more subtidal habitat) and for birds (more shrub habitat) depending on management priorities.

An integrated habitat enhancement approach to shoreline stabilization for a Chesapeake Bay island community

Shore protection and habitat enhancement along a residential island werethe main goals of this shoreline study. The physical and geological factorsnecessary to design shoreline stabilization structures capable of confidentlysupporting suitable and stable habitat enhancement/restoration substrate areemphasized since this area of study generally may be unfamiliar to wetlandresource managers. Erosion along the targeted shoreline is influenced by aunidirectional wave field from the south-southwest. Results of our analysesshowthat a headland control system comprised of headland breakwaters could be usedsuccessfully to stabilize the existing shoreline and provide resource managersflexibility in habitat restoration decisions. Headland breakwaters are designedto diffract wave energy so that shore planform equilibrium is attained and canbe sized and positioned to maximize the length of stabilized shoreline.Maximization of the new shoreline length provides increased subaerial,intertidal, and subaqueous environments for flexible habitat restorationalternatives. The final restoration design developed through this study willcreate approximately 69,000 m2 of new habitat includingstable beach, dune, tidal marsh, scrub shrub, and submersed aquatic vegetation.An additional 2,000 m2 of rock substrate habitat isprovided directly by the headland control structures.

Daily variability in abundance and population characteristics of tidal salt-marsh fauna

Nekton and macrocrustacean population levels and characteristics were studied in two similar tidal marsh creeks. Absolute and area-adjusted data were analyzed to determine variability resulting from daily population fluctuations. Two sampling schemes—intensive 3-d seasonal and periodic 1-d—were examined by constructing probability matrices to compare the accuracy of data comparisons resulting from each scheme. The probability of inaccuracies in comparisons of abundance using nonreplicated sampling schemes ranged from 0% to 100%. Significant differences between consecutive day data were observed for population characteristics such as blue crab (Callinectes sapidus) sex ratios, spot (Leiostomus xanthurus) length-weights, killifish: sciaenid ratios, and killifish: blue crab ratios. These data support the need to account for short-term variability when assessing mobile aquatic fauna abundance in estuarine wetlands.

A comparison of dimension-adjusted catch data methods for assessment of fish and crab abundance in intertidal salt marshes

Sample collection methods and data standardization techniques accounting for marsh physiography were tested for mobile aquatic fauna in two intertidal pocket salt marshes in Sarah’s Creek, a tributary to the York River in Virginia. Fish and blue crab populations were described and compared as numbers per cubic meter of total marsh volume and numbers per square meter of total marsh area. These methods increase the accuracy of the analyses of sampled populations by relying on fewer assumptions than traditionals random sampling methods. Depending upon the season and the species compared, statistical differences were observed between dimension-adjusted data within the same sampled populations. Our data suggest that accurate population profiles can be determined if collection methods and data adjustments are based on the ecology, behavior, and life-history stage of the target species.

A geomorphological model of intertidal cove marshes with application to wetlands management

Abstract Detailed topographic and hydrologic surveys were conducted in five intertidal cove marshes in an outer coastal plain landscape to test the hypothesis that the equilibrium geologic state of intertidal habitats residing in similar landscape situations conforms to a consistent geometric form. The equation V=1571.84A1.70 (R2=96.2%) describes the relationship between hectares of marsh (A) and cubic meter volume at mean high tide (V). An empirical relationship between tide height and volume was found to obey the power series Vp=L2.38 (R2=99.6%), where Vp is volume as a percent of full pool and L is water height as a percent of mean high tide. A dimensionless index describing the relationship between area and volume is consistent for each marsh and approaches 0.10. A channel form parameter describing width to channel depth ratios is of consistent value for four of the five marshes. These provide evidence of deterministic rather than stochastic geologic development. The benefits of applying natural basin shape patterns in the design and engineering of created/restored intertidal marshes are highlighted and a generic basin is modeled (based on the geometrical section of a paraboloid retained by simple integration) as an example of the potential applicability of the study.

The relationship between inundation history and baldcypress stem form in a Virginia floodplain swamp

Algorithms that quantitatively define the stem buttress and the magnitude of stem hypertrophy were developed and used to determine the relationship between tree form and surface water hydrologic regime in baldcypress (Taxodium distichum). Regression analysis using inundation index (I; defined as the average number of inundation days per year over a 49-year period) as the independent variable and extent of buttress (Be) as the dependent variable described the relationship byBe=52.84+0.111I. The equation (P<0.001) explains approximately 68% of the variation in the relationship. Mean stem form of upland control populations was not significantly different from the stem form predicted from the equation for inundation indices equal to zero (the y-intercept, which corresponds to an upland situation). The use of stem form algorithms ofT. distichum shows promise as a source of historical hydrologic information useful in research and management situations.

Classification of fetch limited dunes in the lower Chesapeake Bay: evidence of morphologic equilibrium.

Abstract As part of a comprehensive assessment of dunes and beaches in the Virginia portion of the Chesapeake Bay, U.S.A., we developed a classification system for dunes that incorporates historical shoreline dynamics, shoreline reach setting, local geomorphologic situation, and shoreline use. Our classification system demonstrates the broad diversity of sandy shorelines in the lower Bay; however, we present a geomorphologic relationship between dunes and beaches that appears to act independently of geologic diversity. Cross-shore profiles revealed that the height of the primary dune crest above mean low water relates to the lateral distance between the point of mean low water and the normal line through the dune crest (termed the estuarine dune index [EDI]) in a 1 : 10 ratio. Mean EDIs showed no statistically significant differences between shoreline classes, which provides firm evidence of an equilibrium condition for fetch limited dunes (termed the point-one rule) and promises to be useful for shoreline assessments and the sustainable engineering of nourished shorelines.

Mathews County Shoreline Management Plan

National Fish and Wildlife Foundation through Grant Number 2007-0081-014 Virginia Institute of Marine Science College of William & Mary