Breath of Clarity

Comment #2: Salt Marshes and Tidal Freshwater Marshes

Original Post by Hannah Claycomb:

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.

Global warming is intensifying sea level rise, bringing destruction to many ecosystems near the tide including salt and tidal freshwater marshes. Salt marshes are wetlands that are flooded and drained resulting from tidal inundation (NOAA 2021). Salt marshes provide habitat for numerous species and serve as a common habitat in estuaries. These wetlands protect the shoreline from erosion by buffering wave action and trapping sediments. These wetlands also help with flood control, water purification, and nutrient metabolization. Tidal freshwater marshes experience regular lunar tidal or irregular wind tidal flooding with water less salty than brackish (NCNHP nd). These wetlands are subject to salt water flooding during storm tides. The water is usually fresh or can be oligohaline because of the limited exchange with seawater combined with fresh precipitation and river flow. Sea level rise is causing salt marsh migration inward at a slow rate, detrimentally affecting freshwater marshes. Freshwater marshes are transitioning into wetter and saltier communities, leading to large amounts of vegetation to die out. Because freshwater marshes contain species that are not tolerant to saltwater, a single saltwater intrusion can damage a lot of vegetation. Sea level rise changes soil salinity, promoting the growth of halophytic vegetation inward. Saltwater “flooding can affect the soil structure, deplete soil O2, accumulate CO2, reduce Fe, and Mn, produce potentially toxic compounds, and induce anaerobic decomposition of organic matter (Fagherazzi et al 2019)”. Further, pulse disturbance from storms is increasingly becoming more common to coastal wetlands due to global warming (Fagherazzi et al 2019). According to NASA, researchers estimate extreme storms may increase 60% by the year 2100 (Buis, Alan 2020). Storm surges and sea level rise are in correlation with one another, thus, when sea levels rise so will the occurrence of storms. Tree canopy is an important characteristic of freshwater marshes. When storms destroy trees, light enters the marshes and promotes growth of invasive species (Fagherazzi et al 2019). Geomorphic effects can result from extreme storms, tampering with the saltwater and freshwater marsh boundaries through erosion and sediment deposition (Fagherazzi et al 2019).

2. 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?

Anthropogenic activities have been contaminating waterways in the United States for decades. If I was the manager of a salt marsh wetland and a portion of it suddenly dies and suffers from the effects listed above, I would think it was from urban development or unsustainable dumping of wastewater upstream, such as agricultural waste, construction waste, or sewage. If the salinity is decreased that would mean the salt water marsh is being flooded with freshwater. Urban development enhances erosion and sediment displacement in proximal wetlands, and improper dumping also causes increased pollution in waterways. The acidic pH indicates increased development nearby the wetland or improper disposal of waste in nearby waterways. Further, pH and metal pollution is negatively correlated (Hu et al 2015). Because there are more vegetation decomposing in this partly dead marsh, the high levels of organic carbon and total nitrogen also act as sinks for heavy metals and in turn increases heavy metals in the sediment (Hu et al 2015). The crabs could have died off due to the heavy metal uptake in the specie’s food chain through sediment deposition of the metals. The culprits of killing this marsh are involved in industrial, municipal, agricultural, or residential discharging. I would take samples of upstream soils and determine where the most concentrated metals are resulting. Afterwards, I would research new development in the area or install a wildlife camera near the nonpoint source like Dr. Flanagan mentioned above.

Buis, Alan. 2020. “How Climate Change May Be Impacting Storms Over Earth’s Tropical Oceans.” NASA.,percent%20by%20the%20year%202100.&text=Its%20data%20can%20also%20be,scientists%20maintain%20long%20data%20records.

Fagherazzi, Sergio, Shimon C. Anisfeld, Linda K. Blum, Emily V. Long, Rusty A. Feagin, Arnold Fernandes, William S. Kearney, and Kimberlyn Williams. 2019. “Sea Level Rise and the Dynamics of the Marsh-Upland Boundary.” Frontiers in Environmental Science.

Hu, Chong, Zheng-miao Deng, Yong-hong Xie, Xin-sheng Chen, and Feng Li. 2015. “The Risk Assessment of Sediment Heavy Metal Pollution in the East Dongting Lake Wetland.” Journal of Chemistry.

NCNHP. nd. Freshwater Tidal Wetlands.

NOAA. 2021. What is a salt marsh?

My Comment:

Hi Hannah (Question 1),

Excellent post!

I specifically appreciate the way it ties together how sea level rise leads to changes in water flow, soil components, and vegetation in tidal freshwater marshes. The beginning of the post also mentioned a benefit of wetlands being that they provide habitat for numerous species. One strategy to advocate for wetland management in the face of sea level rise is to bring the rare species existing in these areas to attention.

I found a video discussing the wetlands surrounding the Chesapeake Bay in Maryland. The video described the bird communities in the Somerset-Wicomico Marshes as there are a few species that live no where else. Among these are some rare and declining species including the Saltmarsh Sparrow. Other species, such as the Clapper Rail, the Willet and the Seaside Sparrow only breed in salt marshes.