Drowning wetlands in Chesapeake Bay

Date: 15 September 2016

Introduction: A new study by Lennert Schepers shows how a coastal marsh area along the Chesapeake Bay (USA) has been converted to open water over the last 80 years.

Although many coastal marshes have the ability to build themselves up with sea level rise, in some areas of the world coastal marshes are nonetheless disappearing on a large scale. This has potentially large implications for the protection of the hinterland against storm floods. Lennert Schepers (Global Change Ecology Excellence Centre, Research Group Ecosystem Management), together with international and national colleagues investigated the decline of coastal marshes along the Chesapeake Bay (USA East Coast). This area is frequently confronted with severe storms. A good example is the storm Hermine along the east coast of the USA (early September 2016).

Figure 1: Early September floodings near Chesapeake Bay, during and after the passage of Hermine (photo Lennert Schepers)

Lennert specifically investigated the decline of coastal marshes in the Blackwater National Wildlife Refuge, since the 1930s. Lennert: “The first signs of massive marsh loss are small, shallow ponds. After this stage, a continued expansion enlarges the ponds, which become connected with each other and with the tidal channels. We found that marsh plants were unable to recover their lost habitats, so the process of vegetation loss is a one-way evolution towards marsh loss.” Interestingly, marshes bordering the river that dissects the marsh were more stable, possibly due to direct sediment input during tidal inundation and improved drainage. Also on a larger scale, there are areas that more vulnerable with increased vegetation die-off. Lennert: “Marshes close to the Chesapeake Bay are stable and intact, but vegetation die-off increases more upstream the Blackwater River, up to Lake Blackwater, where all the marshes have disappeared.”

Based on these results, the researchers are now studying the processes that lead to the initial vegetation die-off, and how ponds can expand. This is important, since there are several processes that can fasten the degradation of the marshes such as wave or tidal erosion. Lennert has just returned from a research stay at the renowned Virginia Institute of Marine Science (VIMS) to collect new data. He’s working with colleagues from VIMS and the US Geological Survey.

You can read the Limnology & Oceanography paper at http://dx.doi.org/10.1002/lno.10381

Figure 2: Map, aerial image and different marsh die off stages. On the middle figure, the main bay is on the right. Marshes are still prominent (red color) closest to the main bay. On the right, different stages are visualized. The top stage shows complete drowning; the lower stage is that of an intact tidal marsh.

Figure 3: Lennert @ work in the Blackwater National Wildlife Refuge.