Try ...
Published by John R. Ackerman, P.E., P.G., BCEE, F.NSPE, President / Chief Engineer at Twin Oaks Water Systems, Inc.
Try http://water.epa.gov/type/wetlands/restore/cwetlands.cfm for descriptive material on constructed wetlands and http://water.epa.gov/type/wetlands/constructed/upload/guiding-principles.pdf for details.
If you are trying this yourself, I caution you that wetland design is more art than engineering and selection of the plants and their number is critical to nutrient removal. It is better to find a professional that has designed and constructed successful wetlands and contract with for their services.