Isle of Wight Coastal Marsh Restoration Assessment
A standard practice in the management of coastal salt marshes was to dredge series of ditches throughout the marsh for mosquito control. While these practices proved useful initially, the modification to the natural environment and long term usefulness of these ditches were never tracked.
Time has shown that these ditches have not provided the benefits that their initial objectives posed, and that in fact their effect on the tidal regimes and the organisms that reside in natural salt marshes in the area have been altered. Because of this, the Maryland Department of Natural Resources (MD DNR) has begun a project in the Isle of Wight watershed to begin plugging these ditches to restore salt marshes to a more natural habitat.
As part of a larger ecosystem study quantifying the changes that occur as a result of the salt marsh restoration program, Ecosystem Solutions scientists have been asked to monitor the changes that are occurring to both fish and invertebrate populations and in situ water quality. Additional data that are being tracked as part of the larger study include salt marsh vegetation and waterfowl usage. Together with their collaborators, ESI will help draw conclusions as to the benefits of restoring salt marshes in the Maryland Coastal Bays watershed.
Experimental Design
As with many of our research projects, we are employing a Before-After-Impact-Control (BACI) design. This type of experimental design will allow us to determine changes occurring both temporally and spatially as a result of ditch plugging effort. Initial samples were collected this past September and will depict a “before” shot of the marsh prior to plugging to be done this fall and winter (2008). We have worked the MD DNR to determine the most suitable sites in which to carry out our experiments. In total, 5 sites were chosen around the marsh area to track fish and invertebrate population changes. To get a wholistic picture of organisms using the marsh habitat, scientists sampled three main areas within the salt marsh.
- Ditch – Area of standing water routinely dredged to ensure drainage of the marsh. These areas are being plugged at their outlets to the larger body of water so that the rest of the marsh will hold water in a more natural way during normal tidal flow.
- Low Marsh – The low marsh is an area within the marsh that is routinely flooded during normal tidal flow. These areas are characterized by standing pools of water where many fish and invertebrates tend to gather during low tide. The normal vegetation in these areas includes: smooth cordgrass (Spartina alterniflora), Saltwort (Salicornia spp.), black needlerush (Juncus roemarianus), big cordgrass (Spartina cynosuroides).
- High Marsh - The high marsh is an area further “upstream” or “upland” in the marsh that is usually only flooded during the highest of tides or from storm action. These areas have very little standing water, and are home to a variety of plants. The most common of these are black needle rush, salt meadow hay (Spartina patens), short-form smooth cordgrass (Spartina alterniflora), salt grass (Distichlis spicata), sea lavender (Limonium spp.), salt marsh aster (Aster tenuifolius), marsh orach (Atriplex patula) amongst others.
Fish and Invertebrate Sampling Method
To sample fish and invertebrate populations in the above mentioned habitats, ESI scientists used an innovative methodology called drop rings. The drop rings, made of galvanized metal, are thrown on the marsh surface to encompass a known area of marsh in which to collect organisms. Click here to view a movie of how these were deployed. Once deployed, scientists pump out as much water as possible, and sweep the enclosed area with a net until no organisms are found for 10 straight sweeps. We deployed two rings per habitat at the five sites chosen with the MD DNR for a total of 30 total samples.
Samples were collected at high tide to ensure maximum water present on the marsh, and therefore the maximum achievable diversity. Once organisms were collected from the drop ring area, they were placed in sample jars and preserved for further laboratory analysis. Once back in the lab, ESI scientists will be identifying organisms to species, and measuring and weighing each organism. This data will provided information on the density, size and biomass of groups represented on the marsh and in the ditches prior to the ditch plugging restoration. In addition to organismal data, scientist collected in-situ water quality data which included: water temperature, dissolved oxygen, conductivity, and salinity readings.
Accomplishments to Date
Ecosystem Solutions scientists, in conjunction with MD DNR personnel have collected all field data for the “pre-restoration” snap shot. These data were collected in September of 2008 and are awaiting laboratory processing. Initial field identification of organisms has provided us with the following observations:
- Fish using the ditches include: bay anchovies (Anchoa mitchili), atlantic silversides (Menidia menidia),
- Fish using the low marsh include: atlantic silversides, mummichogs (Fundulus heteroclitus), sheepshead minnow (Cyprinodo variegatus)
- Fish using the high marsh include: sheepshead minnow
- Macro-invertebrates using the ditches: grass shrimp (Palaemonetes), blue crabs (Calinectes sapidus),
- Macro-invertebrates using the low marsh: grass shrimp, mud crabs (Xanthidae spp), fiddler crabs (Uca spp), marsh snails (Melampus bidentatus), marsh mussels (Geukensia demissa)
- Macro-invertebrates using the high marsh: mud crabs, fiddler crabs, marsh snails
Further Work
Scientists will continue identifying organisms and taking length and weight measurements this fall and winter, and will analyze these data through the winter. We will be providing the Maryland Department of Natural Resources with an initial report in the late winter before the next sampling season begins. Because this is a five-year project, we will continue collecting data following restoration during the early summer (June) and later summer (August/September) through 2012. Check back during each field season to see the progress of our results and the changes that are occurring on the march following restoration.
Learn more about our restoration and assessment programs.