City harvesting vegetation, replanting at Jordan Marsh
The city’s Jordan Marsh Water Quality Treatment Park on Casa Ybel Road has been in operation for more than two years. If you have ridden your bike there lately, you have noticed a big change.
The discharge pipe in the ditch next to the bike path is dry. The birds are no longer sitting there waiting for a fish. The fish in the ditch are mostly gone. The plants growing over the water are drying up, and the marsh itself is much lower and dry in some places. Even the baby gators and snakes that inhabit that spot are missing now.
It looks like an ecological disaster, and it is on some scale. But the city is in the process of harvesting vegetation and the marsh has been “turned off.” Because the water flowing through the marsh is pumped in from the Sanibel Slough and flows back into the slough, it is easy to turn off the marsh at the flick of a pump switch.
The treatment marsh relies on vegetation, such as cattails, to remove nutrients from the water as it slowly flows through the system. In 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, nutrient removal in the marsh has dropped significantly over the last six months.
“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,” Dana Dettmar, environmental specialist with the city, said. “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.
The U.S. Environmental Protection Agency recommends harvesting and removing mature plants from treatment wetlands every few years. It eliminates nutrients that are bound up in the biomass and 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,” SCCF research associate Mark Thompson said, adding 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,” he said.
The SCCF encourages residents to do their part by making their yard look as natural as possible with native vegetation.
“If it looks like a golf course, your yard is part of the local water quality problems,” Thompson said. “If it looks like an SCCF preserve, you are doing a great job.”