The treatment marsh relies on vegetation such as cattails to remove nutrients from the water as it slowly flows through the system. Over the past two years, the vegetation has matured and the exponential growth phase which occurs when the plants are young has passed.
Because of the absence of the rapid growth phase of the younger plants, nutrient removal in the marsh has dropped significantly over the last six months as indicated by SCCF’s water quality monitoring.
The City of Sanibel’s Dana Dettmar explained: “The Jordan Marsh has been in operation since March 2019, and the wetland vegetation responsible for most of the nutrient removal processes has now matured and begun to senesce (deteriorate with age). As vegetation matures, it is not as effective at nutrient removal, and the senescent plants can add to unwanted nutrient additions to the marsh. Recognizing the need to manage vegetation to sustain effective nutrient removal, the city has allocated funds to perform routine maintenance on the marsh that includes the harvest of mature vegetation as well as the installation of additional plants.”
Constructed wetlands have been used for decades to treat domestic wastewater, stormwater, and industrial wastes. The experience of other treatment marsh operators has found that periodic harvesting of a portion of the marsh vegetation (cattails) will improve nutrient removal efficiency in the marsh.
The U.S. Environmental Protection Agency recommends harvesting and removing mature plants from treatment wetlands every few years. This eliminates nutrients that are bound up in the biomass. It also encourages new plant growth, which uses nutrients at a much greater rate than mature, senescent plants. “After the harvest is complete, we hope to see an almost immediate improvement in water quality from the marsh,” said SCCF Research Associate Mark Thompson.
Thompson noted that “it is difficult to watch the wildlife move away, and the floating vegetation die off during this harvest period, but soon the marsh will be turned back on, and the vegetation and the wildlife it supports will return.”
The city plans to add floating vegetation, such as water lilies, to the pond area of the marsh. The floating vegetation will add another layer of nutrient removal capacity to the system.
“Plants are our best mechanism for removing excess nutrients from the landscape and preventing algae blooms, red tide, and wildlife deaths downstream,” Thompson said. SCCF encourages residents to do their part by making their yard look as natural as possible with plenty of native vegetation. “If it looks like a golf course, your yard is part of the local water quality problems,” he cautioned. “If it looks like an SCCF preserve, you are doing a great job.”
Drone Photo by Leah Reidenbach
(Funding for Drone Provided by CHNEP)