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Life Along the Salt Marsh: Troubleshooting Salt Marsh Decline

Introduction

The salt marsh is a landscape feature that defines the South Carolina Lowcountry. Kim Morganello, ©2021, Clemson Extension

The salt marsh is a landscape feature that defines the South Carolina Lowcountry.
Kim Morganello, ©2021, Clemson Extension

The seemingly endless salt marsh horizon, interwoven with tidal creeks and rivers, defines a sense of place in coastal South Carolina. The aesthetic beauty and seasonal variation of the salt marsh is an economic driver for communities and a reason many residents seek to live near the coast. The recreational and wildlife viewing benefits associated with the salt marsh provide a way of life unique to coastal living.

The salt marsh provides many ecosystem services to humans. It serves as a buffer during major storm events providing flood control and stormwater conveyance. The salt marsh filters pollutants protecting water quality and sequesters carbon during photosynthesis. The salt marsh supports the local economy in commercial and recreational fisheries, tourism, and the culinary arts. Furthermore, the salt marsh ranks as one of the most biologically productive ecosystems on earth.

Natural conditions, human activities, or a combination of both can have negative impacts on the health of the salt marsh. The salt marsh may decline, leaving dead or dying patches behind. Salt marsh die-off is concerning to stakeholders, in particular, those who have invested in property near or adjacent to the afflicted area. If salt marsh decline is observed, residents can use the following guidelines to help identify the cause and potential management solutions.

A degraded salt marsh is evident when patches are dead or dying. Kim Morganello, ©2021, Clemson Extension

A degraded salt marsh is evident when patches are dead or dying.
Kim Morganello, ©2021, Clemson Extension

As impervious surface areas associated with the built environment increase, so does the potential for negative impacts on the salt marsh. Kim Morganello, ©2021, Clemson Extension

As impervious surface areas associated with the built environment increase, so does the potential for negative impacts on the salt marsh.
Kim Morganello, ©2021, Clemson Extension

Document Existing Conditions

The first step is to identify the type of vegetation present in the salt marsh. A South Carolina salt marsh is typically dominated by a monoculture of Sporobolus alterniflorus, typically referred to as Spartina, in reference to the previous scientific name Spartina alterniflora, or referred to by the common name Smooth Cordgrass. This plant can withstand the dynamic conditions created by the twice-daily ebb and flow of the tides. Spartina goes dormant in the winter months in a healthy system, it turns brown and dies back resulting in decaying plant material that forms the base of a complex food web. However, year-round die-off of Spartina is indicative of a stressed, unhealthy salt marsh.

Spartina and Black Needlerush create a brown and green patchwork in a South Carolina salt marsh during the summer months. Kim Morganello, ©2021, Clemson Extension

Spartina and Black Needlerush create a brown and green patchwork in a South Carolina salt marsh during the summer months.
Elizabeth Vernon Bell @2007 SC SeaGrant Consortium

Another dominant plant in the salt marsh is Black Needlerush (Juncus romarieanus). Needlerush occurs in areas that receive less salt water inundation due to a slightly higher elevation, a further distance from a creek bed, or located further upstream at a greater distance from the ocean. The name Needlerush refers to the sharp, needle-like points located on the top of the plant. Needlerush remains brown throughout the year and should not be confused with Spartina.

Document extent of die-off accurately; select a landmark, such as a dock piling, to define the area of salt marsh decline. Take photographs of the site consistently and refer back to photo documentation over time. If possible, measure the length and width of the area of concern every year. To identify whether the die-off may be seasonal or persist year-round, observe and record the months when the marsh is dying back.

Pollution Detection

The following are a few pollution sources that can impact your salt marsh by creating an imbalance in this critical area. If pollution sources are present, adjust behavior and management practices to reduce stress on your local salt marsh and help regain a healthy ecosystem.

Stormwater Runoff: As more humans move to the coast, factors that stress the salt marsh increase. The addition of roads, bridges, rooftops, and other impervious areas increases the amount of stormwater runoff that enters the salt marsh. Stormwater runoff carries pollutants left on land, such as excess fertilizers, sediment, pet waste, and litter, to nearby water bodies. Polluted stormwater runoff causes water quality to degrade and salt marsh health to decline. In some instances, the sheer volume of freshwater entering the salt marsh can be a form of pollution.

Stormwater best management practices reduce the amount of runoff that enters the salt marsh. Practices such as rain gardens, rain barrels, vegetative buffers, and native plant landscaping can slow water down and provide an opportunity for water to infiltrate on-site. Learn more about actions you can take at Clemson’s Carolina Clear and Carolina Yards programs.

Pool maintenance best practices can help to protect adjacent tidal creeks and salt marsh areas from harm. Kim Morganello, ©2021, Clemson Extension

Pool maintenance best practices can help to protect adjacent tidal creeks and salt marsh areas from harm.
Kim Morganello, ©2021, Clemson Extension

Pool Discharge: For humans, life along the salt marsh may also include a swimming pool. It is sometimes necessary to drain a swimming pool for maintenance or safety. Pool water is treated with chlorine and other chemicals and can be toxic to aquatic life if discharged improperly. Before discharge, contact your local government to learn about ordinances and recommendations; a pool professional can further assist. Before the water leaves the pool, do not add chlorine for several days to dechlorinate. Chlorine will dissipate, and test kits are available at pool supply stores to check concentrate before draining; the recommended amount is 0 mg/L. Check the pH, which should be between 6.5 and 7.5; a pH less than 5.0 or greater than 8.5 can negatively impact aquatic life. Filter cloudy water to remove suspended solids. Check local ordinances, and if allowable, drain pool slowly to avoid erosion and direct water towards a vegetated area as far away from the salt marsh as possible.

Drain field installation at a coastal property close to the salt marsh. Knowledge of drain field location will help identify if septic system issues exist. Kim Morganello, ©2021, Clemson Extension

Drain field installation at a coastal property close to the salt marsh. Knowledge of drain field location will help identify if septic system issues exist.
Kim Morganello, ©2021, Clemson Extension

Septic Tank Systems: Coastal properties often utilize septic systems for wastewater treatment. If not properly maintained, septic systems can be a source of bacteria pollution, pose a risk to human health, and degrade water quality in nearby water bodies. Generally, septic systems should be inspected by a service professional once every one to two years and pumped, on average, every three to five years. Proper use of a septic system will help ensure it is functioning as intended; system users should be aware of what can and cannot go down the drain or toilet and implement best water efficiency practices. The drainfield is part of your septic system; identify the location on your property and, if possible, that of your neighbors. After heavy rainfall or household use, note if standing water is present in the drainfield area. Standing water may transport harmful bacteria from the septic system to unintended areas such as a nearby salt marsh. Consult a service provider to determine appropriate action. To learn more about septic system management, see Be Septic Safe.

Lawn Fertilization: The desire for the perfect lawn can lead to increased fertilizer application. When fertilizer is misused in the landscape, plants are unable to absorb the excess nutrients, and these nutrients runoff into a nearby water body. For many coastal properties, the nearby water body is a salt marsh or tidal creek. The plant community may collapse from excess nutrients in the salt marsh if conditions are sustained over several years. A soil test is a useful tool to determine the amount and type of fertilizer needed for your lawn based on its soil chemistry. Learn more at Clemson Extension’s Home and Garden Information Center, see HGIC 1652 Soil Testing.

Consider establishing a 10 to 30 foot “no fertilizer, no pesticide” buffer zone along shorelines.

Erosion: The salt marsh is a dynamic ecosystem; constant change is due to tidal flow, storm surge, wind, rain, and other forces of nature. Human actions may exacerbate erosion, a change in the salt marsh resulting in the loss of marsh, pluff mud, and land. If erosion is of concern to you, note the salt marsh’s length and width each season, or select a landmark for yearly comparison. Identify signs of erosion such as “shelfing off” in which the salt marsh transitions dramatically to the tidal creek in cliff-like formations. Understanding the extent and rate of erosion helps identify a management strategy.

If an adjacent tidal creek or river is present, note creek orientation as straight or on a curve. Tidal marshes on creek bends may shift with the natural migration of the channel. Boat traffic can bring added stress to an eroding salt marsh in the form of boat wake. Contact the SC Department of Natural Resources to report concerns or to gain information on obtaining a “No Wake” sign for communication with local boaters.

Residents can promote vegetative buffers along tidal creeks to stabilize shorelines and help to protect water quality. Kim Morganello, ©2021, Clemson Extension

Residents can promote vegetative buffers along tidal creeks to stabilize shorelines and help to protect water quality.
Kim Morganello, ©2021, Clemson Extension

High volume and velocity of stormwater runoff can cause erosion in the salt marsh. A vegetative buffer incorporated as a functional landscape feature can help to dissipate runoff energy. Learn more at Clemson Extension’s Home Garden Information Center, see, HGIC 1856, Life Along the Salt Marsh: Protecting Tidal Creeks With Vegetative Buffers.

If erosion continues and threatens personal property, contact the SC Department of Health and Environmental Control-Office of Ocean and Coastal Resource Management (SC DHEC-OCRM) to determine potential shoreline stabilization methods. The salt marsh is a designated critical area; as such, any area below the high tideline requires a permit for land disturbance activities in addition to local ordinances. Living shorelines, including marsh grass and oyster reef plantings, and coastal structures, including revetments and bulkheads, are methods to stabilize shorelines. Living shorelines are encouraged in appropriate locations as they provide added ecological benefits of marsh growth and habit for marine life.

Environmental Stressors

The salt marsh is part of a dynamic system, complex in nature. The following are environmental stressors that may occur in your local salt marsh; overarching, systematic factors cause these. Management strategies for residents are at times limited; however, understanding the present conditions is helpful. Environmental stressors compounded with localized pollution can increase the rate and area of salt marsh decline. The best management practices mentioned in this fact sheet can help to reduce stress and ideally help maintain a healthy salt marsh.

If wrack becomes trapped, it can collect into thick mats that shade out salt marsh. Kim Morganello, ©2021, Clemson Extension

If wrack becomes trapped, it can collect into thick mats that shade out salt marsh.
Kim Morganello, ©2021, Clemson Extension

Wrack: As previously noted, the salt marsh’s dominant plant is Spartina, which grows and dies back each year. When it dies, Spartina eventually becomes detached and can create a floating mat as it attaches to other dead pieces, often referred to as “wrack.” This process is significant in building sand dunes along barrier islands and adding elevation in the salt marsh as the material decomposes. However, if wrack becomes trapped by uplands, a dock, causeway, or other structure, the wrack can cover the living salt marsh causing it to die as sun exposure is limited. Effectively, the wrack has formed a blanket over the salt marsh. Remove the wrack using a rake, net, poll, or another available method. You can attempt to break up a thick entanglement to reduce potential issues for boaters or other salt marsh areas nearby.

Periwinkle snails are a natural part of the salt marsh ecosystem. A healthy salt marsh may readily support the number of periwinkle snails seen here; however, a stressed salt marsh may degrade under such pressure. Kim Morganello, ©2021, Clemson Extension

Periwinkle snails are a natural part of the salt marsh ecosystem. A healthy salt marsh may readily support the number of periwinkle snails seen here; however, a stressed salt marsh may degrade under such pressure.
Kim Morganello, ©2021, Clemson Extension

Periwinkles: A periwinkle is a snail that lives in the salt marsh and spends most of its life attached to a salt marsh blade. The snails move up and down the salt marsh with the tides’ ebbs and flows, creating tiny notches with their radula or toothed tongue. Abundant periwinkle snails can add stress to an already stressed or degrading salt marsh. Blue crab, among other animals, eat periwinkles. If a localized blue crab population is in decline, periwinkle snails in the area may thrive and multiple. Unfortunately, there is not much a resident can do about this system stressor. The salt marsh is a dynamic ecosystem with a complex food web. At times, life along the salt marsh requires humans to accept these changes as part of the salt marsh’s larger cyclical ebbs and flows.

Drought: The salt marsh thrives in brackish water, which is a mix of freshwater and saltwater. Drought may stress the salt marsh, causing die-off, especially during the summer months when temperatures are highest. Rainfall frequency and amounts can be highly variable across a region; therefore, noting localized rainfall will help to understand better if a drought is a factor. Track the rain with a rain gauge in your yard; make sure to record rainfall amount and date. Or use the Community Collaborative Rain, Hail, and Snow Network (CoCoRaHS); find a station near you at https://www.cocorahs.org. You can also check the drought status in South Carolina at http://www.scdrought.com.

As sea level rises, existing Spartina may spend more time under water and decline. Management strategies mentioned in this factsheet can help. Kim Morganello, ©2021, Clemson Extension

As sea level rises, existing Spartina may spend more time under water and decline. Management strategies mentioned in this factsheet can help.
Kim Morganello, ©2021, Clemson Extension

Sea Level Rise: As a result of longer term data collection, the extent of sea level rise has been documented. The average of all measurements taken during a specific time period is called a mean. In the Charleston Harbor, Charleston, SC; the mean sea level rise has risen 1.07 feet in the past 100 years. The National Oceanic and Atmospheric Administration (NOAA) uses research to provide potential sea level rise scenarios; this information is adjusted regionally based on factors such as land subsidence and ocean currents. For Charleston, SC; the intermediate projection has been accepted by decision makers for land use planning purposes; this projection is 2-3 feet of sea level rise over the next 50 years. Regardless of the amount, we know sea level rise will occur. Spartina requires space and time above the water; therefore, parts of the salt marsh may drown as the sea level rises. Naturally, the salt marsh will begin to migrate landward; leaving room for this movement is critical for the future of the salt marsh. Living shorelines and other land management strategies can assist.

For More Information

To gain information on the status of water quality in your area, reference the SC Watershed Atlas provided by SCDHEC. The tool can be found at https://gis.dhec.sc.gov/watersheds/. Locate the search engine at the top of the map and enter an address. The map will pan to the area searched. Next, check the “Impaired Waters- 303(d)” in the layers table located on the left-hand side. Zoom out to view water quality information of upstream and surrounding water bodies. The points that appear on the map indicate a water quality impairment; click on a point to view the type of impairment.

If salt marsh decline continues or if a pollution source is identified and not corrected, contact your local government, SC DHEC and South Carolina Department of Natural Resources. You may also call your County Clemson Extension office for further information on troubleshooting topics covered in this factsheet.

Visit https://www.saltmarshguide.org to learn more about the salt marsh and tidal creek systems in Southeastern United States.

References:

  1. City of Charleston , 2020, All Hazards Vulnerability and Risk Assessment, www.charleston-sc.gov/DocumentCenter/View/27994/All-Hazards-Vulnerability-Assessment-Full-Report.
  2. “Be Septic Safe.” Be Septic Safe | College of Agriculture, Forestry and Life Sciences | Clemson University, South Carolina, 25 Nov. 2020, www.clemson.edu/extension/water/be-septic-safe.html.
  3. Sanger, Denise, and Catherine Parker. Guide to the Salt Marshes and Tidal Creeks of the Southeastern United States. South Carolina Department of Natural Resources, 2016.

If this document didn’t answer your questions, please contact HGIC at hgic@clemson.edu or 1-888-656-9988.

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