The City of Sanibel’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 there and the marsh has been “turned off.” Because the water flowing through the marsh is pumped in from the Sanibel Slough (Sanibel River) 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. Over the past two years, the vegetation has matured and the exponential growth phase which occurs when the plants are young has passed. 

 

 

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.