Stormwater Treatment by
Natural Systems

Abstract

In the past few decades, it has become apparent that nonpoint source discarges of pollutants, primarily in the form of stormwater runoff, can contribute significantly to pollutant loadings in receiving water bodies. Nonpoint sources of pollution have been found to contribute significantly to receiving water loadings of nutrients and heavy metals (Wanielista 1982). As a result, efforts have been undertaken in the State of Florida to control nonpoint sources of pollution, particulary those associated with stormwater runoff.

As a means of protecting waters from further deterioration, several states have established regulations which require new developments to treat stormwater runoff before discharge from the property. In most cases, this treatment involves retention or detention of specified amounts of runoff volume in shallow ponds. Recently, a major interest has risen in the application of natural treatment systems, such as wetlands, for assimilation of stormwater pollutants in order to minimize the loss of valuable land in meeting these regulations.

Although numerous studies have been conducted on the treatment efficiency of controlled inputs of secondary effluent in wetland systems, with varying results, few detailed studies have been conducted on the feasibility of wetland systems in treating sporadic inputs of stormwater runoff in spite of the fact that numerous wetland areas are currently being used for this purpose. If natural systems such as isolated wetlands and bayheads could be effectively utilized in assimilating stormwater pollutants, then developers would have an incentive to preserve and incorporate them into their stormwater management systems. As a result, wetland areas may come to be viewed as valuable resources to developers rather than wasted land.

The purpose of this research was to investigate the fate and movement of runoff-related inputs of nutrients and heavy metals in a hardwood in a hardwood wetland north of Orlando, Florida. This research, which began in August 1984 and continued until July 1986, was funded initially by a STAR grant from the Florida Institute of Government and later extended by a subsequent grant from the Florida Department of Environmental Regulation. The major objective was to determine the feasibility of using a hardwood wetland as a stormwater management system. To accomplish this, the following tasks were undertaken:

1. Characterization of rainfall and runoff inputs into the wetland system.
2. Monitoring of hydrologic inputs into and out of the wetland.
3. Characterization of surface and groundwaters along the wetland flowpath and in isolated control areas.
4. Investigate the horizontal and vertical migration of nutrients and heavy metals in wetland sediments.
5. Determine the chemical speciation of phosphorus and heavy metals in the sediments and the effect on the ability of the sediments to retain inputs of pollutants.
6. Determine the influence of pH and redox potential on the chemistry and stability of phosphorus and heavy metals in the sediments.
7. To examine the rate of uptake and removal of nutrients and heavy metals during flow through the wetland.
8. To examine the physical mechanisms and characteristics which enhance pollutant removal in the wetland to aid in development of specific design suggestions.
9. Examine changes in algal productivity on stormwater inputs during flow through the wetland using a series of algal bioassay experiments.

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