4 years later, wastewater a boon to wetlands


March 17, 2010 at 8:52 am  | Mobile Reader | Pring this storyPrint 

4 years later, wastewater a boon to wetlands
In a resolution issued by the Louisiana Wildlife Federation, the effectiveness of discharging wastewater into wetlands was called into question because of the perceived negative impacts the practice has caused in the Hammond area.

But in St. Charles Parish, discharging treated effluent has revitalized the Luling wetlands, according to an ecologist studying the area.

The parish began discharging secondarily treated effluent from the Luling Oxidation Pond into the adjacent wetlands in 2006. The wetlands in the vicinity of the pond are composed of freshwater forested wetlands. Because these wetlands are isolated from the Mississippi River, there was inadequate freshwater, sediment, and nutrient input.

The parish began the wetland discharge program to not only introduce nutrients and freshwater intended to enhance vegetative growth, but also to meet more stringent water quality standards that were introduced by the Department of Environmental Quality.

Wetland ecologist Dr. Rachael Hunter said that the program is a win-win for both the parish and the Luling wetlands.

“The Luling site is working great and it’s a very healthy wetland,” she said. “Those wetlands are starved for fresh water and nutrients, and this process gives those wetlands what they need to be more productive.”

Hunter said studies of the Luling wetlands have shown that vegetation productivity has increased significantly since the program began.  In fact, productivity is twice as high in the discharge area as it is in a similar wetland that is not receiving the discharge.

To make sure that continues, the Luling wetlands are strictly monitored to ensure that the discharge of treated effluent is helping, and not hurting, them.

“We have to monitor the site continuously in order to keep the Louisiana Pollutant Discharge Elimination System permit that allows us to discharge the treated effluent,” Hunter said.

The site is so intensely monitored, she added, that scientists collect fallen leaves monthly and water samples quarterly to really gauge the effect the process is having on the wetlands.

But in Hammond, some say there have been significant problems with discharging treated effluent into the wetlands.

Hammond has the largest and most highly-touted wastewater assimilation project in the state. The effluent is pumped into a 700-acre marsh in the Manchac wetlands just south of Ponchatoula. Less than three years after the 4.1 million gallons-per-day of effluent discharge into this marsh began, the Hammond project has caused the destruction of emergent vegetation and the creation of over 400 acres of open water, according to the LWF resolution.

It has also altered much of the remaining areas of vegetation by replacing vegetation with extensive root systems with floating or invasive vegetation that has little or no useful root systems for holding soil together.

Scientists studying effluent assimilation by wetlands attribute the change in this wetland primarily to the consumption and destruction of vegetation by nutria. 

“Nutria are a huge problem and they can actually mow down a wetland,” Hunter said. “They are a lot bigger problem than people believe.”

Critics counter by saying that nutria cause only minor problems. Instead, they blame excessive nutrient loads, other toxic constituents and a continuous discharge that prevents normal wet and dry cycles that are important to maintain healthy wetlands.

Hunter doesn’t believe that’s the case.

“I know some people are saying that the discharge increases the water levels, which in turn hurts the vegetation, but we constantly monitor those levels,” she said. “We have recorders set up that monitor daily water levels.”

Hunter said that problems at the Hammond site are unique to that wetland because the vegetation there has undergone a transformation that is not directly related to effluent discharge.

“There are people out there who say that discharging treated effluent into the wetlands is not a good thing to do, but I strongly believe that it has a positive effect,” she said. “One thing that people don’t understand is that the effluent that is discharged is secondarily treated, which means that it’s safe to be discharged into canals or other water bodies.”

Prior to discharge, the municipal effluent is analyzed for volatile compounds, metals, and hazardous substances  and Hunter said that the Luling effluent was below the EPA minimum required concentrations. That means that the pollutant would not be a problem in the receiving water body.

“All sewage treatment plants are required to test for priority pollutants prior to discharging into any water body,” she added. “I think referring to the process as sewage going into the wetlands affects the public’s perception of what is going into the wetlands.

“This effluent is disinfected prior to discharge and so no harmful microorganisms are present.”




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