ARS | Publication request: IN-STREAM WETLAND DESIGN FOR NON-POINT SOURCE POLLUTION MITIGATION

Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 2, 2003
Publication Date: June 1, 2003
Citation: STONE, K.C., HUNT, P.G., NOVAK, J.M., JOHNSON, M.H. IN-STREAM WETLAND DESIGN FOR NON-POINT SOURCE POLLUTION ABATEMENT. TRANSACTIONS OF THE AMERICAN SOCIETY OF AGRICULTURAL ENGINEERS. 2003. v. 19.p. 171-175.

Interpretive Summary: Nonpoint source (NPS) pollution occurs when nutrients from fertilizers and other sources wash from the fields into streams and rivers. This NPS pollution is a major concern throughout the world. The most effective way to reduce NPS pollution in streams is to attempt to prevent it from reaching the stream, but even then some nutrients may still reach streams. Streams can usually tolerate a small amount of nutrients, but high levels of nutrients can cause problems such as excessive algae blooms. Once excess nutrients are in a stream, it can be difficult to remove them. We investigated the use of an in-stream wetland (ISW) to reduce nutrients that were in a stream in eastern North Carolina. We found that over 50% of the nitrogen was removed by the ISW. To see how effective ISW's could be if used elsewhere, we analyzed these data and calculated parameters that could be used by engineers and environmentalists to design ISW's to reduce nutrients in other streams. We found that the models currently used for calculating constructed wetland size and treatment were able to adequately describe the nutrient treatment in the in-stream wetland.

Technical Abstract: Nonpoint source (NPS) pollution of rivers and streams is a major concern throughout the world. Most methods for NPS mitigation focus on source reductions, however, absolute prevention of stream impact is very difficult in natural systems. In-stream wetlands (ISW) have been shown to be effective in renovating, rejuvenating, and reducing nitrogen in streams. The objectives of this research were to evaluate the effectiveness of an ISW and to determine if design approaches used in constructed wetlands could be applied to predict ISW effectiveness in treating NPS pollution. The 3.3-ha ISW studied was located in a 425-ha watershed in eastern North Carolina. The ISW was effective in reducing Total Nitrogen (TN) and Nitrate-N (NO3-N) by 56 and 71%, respectively. First-order rate constants (K20 and theta) were calculated for the k-C* model and were found to be in close agreement with literature with TN K20=19-20 m/yr and theta =1.0-1.03. .The NO3-N rate constants were K20=38-54 m/yr and theta =1.07-1.13. These results indicate that engineers and environmentalists can predict the impact of ISW prior to their implementation with reasonable confidence in the design equations for constructed wetlands.