Breath of Clarity

Salt Marshes and Tidal Freshwater Marshes

1. The hydrologic complexity of salt and tidal freshwater marshes was clear from the websites and in the power points. The onset of global warming is now almost universally accepted (except maybe for Exxon/Mobil). What will happen to both kinds of marshes as sea level rises? Describe the hydrology then pick 2 other aspects of these wetlands to discuss the changes we will see in North America.

Researchers created model simulations using the Intergovernmental Panel on Climate Change (IPCC) mean and maximum estimates of sea level rise to show its impact on salt and tidal freshwater marshes. The range they used to derive the IPCC’s mean and maximum values is a sea level rise of 30-100 cm for the year 2100 (Craft et al. 2009). The data suggested that salt marshes will respectively decline in area by 20% and 45% (Craft et al. 2009). Similarly, the area of tidal freshwater marshes will decline by 39% under the maximum scenario (Craft et al. 2009). Evidently, the hydroperiod of a salt marsh is tidal dependent and sea level rise brings powerful pulses that ultimately leads to instability and interferes with wetland survival (NOAA 2021). Insofar as there is sea level rise, the hydroperiod is extended. Salt marshes are built by salt- and inundation-tolerant plants that exist in a limited elevation range relative to mean sea level (Crosby et al. 2016). Due to limits in the inundation tolerance of these plants, salt marshes must gain elevation at a rate equal to or exceeding relative sea-level rise to resist drowning and conversion to mudflats without vegetation (Crosby et al. 2016). In terms of ecosystem structure, rising sea levels may result in tidal freshwater marsh submergence and habitat migration, as salt marshes transgress landward and replace tidal freshwater marshes (Craft et al. 2009). Eventually, tidal freshwater marshes will decline in area as saltwater intrudes and brackish marshes migrate inland to replace them (Craft et al. 2009). Insofar as there is not action to combat sea level rise, salt marshes will convert to open water because their low rate of vertical accretion relative to tidal freshwater marshes may prevent them from keeping pace with sea level rise (Craft et al. 2009). Human modification and development of shorelines worldwide has limited the area available for upland migration by salt marshes as sea level rises, and coastal populations and development pressures continue to grow (Crosby et al. 2016). In terms of ecosystem function, tidal freshwater marsh delivery of services associated with productivity, such as macrophyte biomass will decline. Additionally, in terms of nutrients, waste treatment, such as nitrogen accumulation in soil and potential denitrification, will also decline (Craft et al. 2009). Below is a graphic that illustrates the changes. Impacts due to sea level rise also result in flooding the ecosystems that neighbor the wetland areas.

You are the manager of a wetland area that includes a salt marsh. You have noticed a portion of your marsh is dead and it happened suddenly. So you go to check the water and find the pH is 3, the salinity is low, and no crabs are present. You send a sediment sample to be tested and it comes back high in arsenic, cadmium, and chromium. What is the problem and how do you find the culprits?

The important pieces of information are that the wetland area was originally a salt marsh, death in the marsh happened suddenly, the pH is acidic, salinity dropped, and a form of waterborne wildlife was eliminated. Sediment sampling also indicates presence of heavy metal pollutants. Typically, salt marshes are not able to absorb the plethora of metals. The heavy metal pollutants were somehow transferred into the wetland, captured by the clay sediment and then absorbed by the vegetation as a result of nutrient uptake. Considering it was originally a salt marsh and is now the salinity is low, there are freshwater inputs that diluted the salt water of the marsh. The high peat content in freshwater would also explain the low pH value. Since it happened suddenly, cameras can be used to determine the cause and culprits as the timeframe would be narrow. However, the challenge is that the metals could have been derived from a multitude of sources and are difficult to detect due to a range of non-point pollution sources. Still, even without the cameras, the management team can identify potential areas where runoff may have flowed into the wetland. Runoff would be responsible for lowering the pH balances as it decreases amount of salinity in the water. It is important to trace the streams and other drainage into the salt marsh. Also, the cameras can be used to further monitor the flora and fauna as well as survey industrial companies in the area and any current construction projects.


Craft, Christopher, Jonathan Clough, Jeff Ehman, Samantha Joye, Richard Park, Steve Pennings, Hongyu Guo and Megan Machmuller. 2009. “Forecasting the Effects of Accelerated Sea-Level Rise on Tidal Marsh Ecosystem Services”. Frontiers in Ecology and the Environment. 7(2): 73-78.

Crosby, Sarah, Dov F. Sax, Megan E. Palmer, Harriet S. Booth, Linda A. Deegan, Mark D. Bertness, Heather M. Leslie. 2016. “Salt marsh persistence is threatened by predicted sea-level rise”. Estuarine, Coastal and Shelf Science. 181: 93-99.

NOAA. 2021. What is a salt marsh?

Comment by Jenny Kelley:

Hi Mary – (responding to Q2)

Great sleuthing and deductive reasoning for your answer to question 2. The use of cameras to monitor the area, the flora and fauna in order to find out what might be contributing to the degradation is such a good one. It reminded me of our last class together and how the Petrified Forest management implemented cameras to monitor visitors after a series of thefts of pieces of petrified wood. Also, your point that low pH could be a result of input from freshwater seems plausible and worth further examination. Overdevelopment, the ensuing construction, and sewage drainage could contribute to your idea of freshwater influx. I say this because the southeast, where many salt marshes are in this country, has seen a population rise in the last decade or so. At least, this is what I observed when I lived there – if it was not a subdivision being built it was another hotel chain along the coastline. Developments such as these encroach on space and limit the marsh’s ability to move and grow (and flow for that matter). The increase in human population – the increase in sewage, run off, lawn chemicals, etc, could be culprits in the marsh’s demise too.


My Reply:

Hi Jenny,

I appreciate the comment! Using cameras to monitor the flora and fauna would definitely be beneficial. To reap the most fruit from the cameras, managers need to go into the filming with some hypotheses about causes of the degradation and observe the footage with the predictions in mind. That way, they are going to have some sort of direction while deriving patterns that may help determine the cause. Also, great connection to Impacts of Recreational Use! Not only would the cameras help in finding the culprits, but it would also play a role in adaptive management as it would inform the managers how to be proactive going forward so that a similar contamination does not occur again.

Comment by Carmen Valencia:

Mary, in response to question 2, you made a thorough analysis of what the problem/s could be. In the book, clay is discussed heavily as a sink of chemicals and heavy metals, which can cause long-term damage to the ecosystem. Unfortunately, these types of remediation projects can be expensive and time-consuming, although the losses were quick and extensive in this case. Although cameras can be set up near dump sites, wildlife cameras may be an additional help in order to identify what parts of the marsh they are avoiding. Perhaps this could give an indication of which direction the contaminants are coming from and where they are accumulating. Certain regulations also allow organizations to increase their water output in order to decrease the percentage of pollution in their wastewater. I cannot track down whether or not this is an EPA regulation or another agency’s, although I know this action is not always permitted.

My Reply:


Fantastic point in viewing animals as a clear identifier of subareas related to the problem. Researching tendencies of the animals at the site can help understand the camera footage even better as each type would respond to specific conditions in particular ways. Insight about this location’s water flow also needs to go hand in hand with any findings about where the contaminants are entering the wetland. From there, the managers can track how the contaminants spread after determining the source.

Comment by Carmen:

Mary, tracking animal behavior and migration is a huge field that has allowed researchers to understand not only animals, but other parts of the ecosystems such as the abiotic systems. The flow of the water can indicate how fast and frequent the heavy metals are being cycled through the clay, soil, and water.