1. What is the geologic history of the US that gave this continent so many wetlands? Do you think that the eastern seaboard of the US which is a passive margin attributes to the huge coastal wetland complex there? Why?
There have been multiple ancient and more modern events that have created many wetland complexes in the United States. The primary reason is due to the subsistence of Earth along structural fault boundaries, which allowed swamps to exist for millions of years. Additionally, the retreat of continental glaciers has been a massive phenomenon that has resulted in many long-lived wetlands. During the Eocene, the Powder River Basin was formed when the mountains uplifted and the earth’s crust bowed. This created a hole that sedimentation created a swamp from as it accepted subsidies. The balance between sediments and subsidence of the basin produced great swamps. The Carboniferous period saw the formation of many deltas. Ecosystems were able to blend and move across the landscape during this period millions of years ago, allowing wetlands to disappear and reform repeatedly (Flanagan 2021).
I think that the passive margin across the eastern seaboard of the US has contributed to the huge coastal wetland complex. Wetlands have two necessities: being able to move locations and to be short lived environments; these two factors are not amenable to human activity, but wetlands had plentiful options across the US landscape. Additionally, passive fault lines allow for the formation and movement or expansion of wetlands, with their only real hindrance being hurricanes. There are not any significant barriers to limit the development of wetland complexes, allowing for great expansion over time (Flanagan 2021).
2. What is the hydroperiod of the wetland you have observed?
The wetland that I have observed is one of the mangrove forests along the shores of central and southern Florida. A wetland’s hydroperiod is the combined result of water inflows and outflows (water budget), landscape surface contours, and subsurface soil, geology, and groundwater conditions. Mangrove forests are inflow dominated wetlands, and are characterized by their high salinity and protection from high potential wave action (Mitsch and Gosselink 2015, 119-124).
The water budget of mangrove swamps is significantly affected by tides, with one to two tidal periods per day (Mitsch and Gosslink 2015, 122). Tides have bimonthly patterns of stresses and subsidies; these pulses include submergence and bringing new nutrients, increasing and decreasing soil salinity, and changing from anaerobic to aerobic conditions (Mitsch and Goddlink 2015, 142). It has been found that the freshwater hydroperiod of mangrove wetlands has also been significantly altered by human activity. Water management practices, such as mosquito control and water flow changes, have resulted in variable inputs of freshwater that can alter the saline processes of mangrove wetlands (Fish and Wildlife Service 1999).
3. I worked in a cypress-hardwood, forested wetland where the Army Corps of Engineers wanted to dam to make permanent, standing water for recreation. With your knowledge of the hydroperiod and primary production – why did we stop the project?
Creating a dam to make a permanent standing water wetland for recreation would have directly impacted both the hydroperiod and primary production of the cypress hardwood wetland. Firstly, hydrological modifications to wetland environments directly impact biota. The biota may respond with species composition, richness, or productivity changes to the ecosystem (Mitsch and Gosselink 2015, 112). Additionally, the flowing water pulses stimulate species diversity; more and longer flooding leads to less species richness. The resulting waterlogged soil and chemical changes limit types and number of rooted plants that are able to survive, which will result in significant detriment to the cypress trees of the wetlands that attract many visitors for recreation (Mitsch and Gosselink 2015, 146).
Primary productivity levels and ecosystem services in wetlands are depressed by stagnant conditions, and long flood durations increase stresses caused by anaerobic root zones (Mitsch and Gosselink 2015 146-148). Nutrient cycling and availability are additionally affected significantly by hydrology. Nutrient inflows and outflows are the result of water flows, which allow the ecosystem to continue supporting a diverse array of life. Both productivity and decomposition are slowed in stagnant water, which also slows nutrient cycling (Mitsch and Gosselink 2015, 153). The lack of water flow will ultimately result in a buildup of sediment, which over time will fill in the wetland and alter the ecosystem to be a terrestrial forest. All of these actions will result in the loss of the wetland that the Army Corps was attempting to protect and draw recreation to.
References
Mitsch, William J., and James G. Gosselink. 2015. Wetlands. John Wiley & Sons, Inc.
Flanagan, Kathryn. 2021. “Geology and Wetlands.” Wetland Ecology and Management. Lecture, June 21. https://canvas.du.edu/courses/128480/pages/week-2-geology-and-wetlands?module_item_id=2329213.
US Fish and Wildlife Service. 1999. “Multi-Species Recovery Plan for South Florida: Mangroves.” Updated May 3, 2019. https://www.fws.gov/verobeach/msrppdfs/mangroves.pdf.
My Comment:
Hi Megan (Question 2),
Mangrove wetlands are definitely crucial to protecting the offshore coral reefs from sedimentation.
I found a video showing how mangrove roots provide a nursery for certain types of fish in Mexico. Drones are used to estimate the area and volume of the remaining mangrove forests, as well as the quantity and type of animals living there. With that information, scientists can create conservation priorities to protect biodiversity.
Here is the video:
Another video describes the benefits of mangroves and a strategy to protect them through a case study in Gazi Bay, Kenya. Its mangrove forest stores 1,500 tons of carbon/hectare.
Here it is: