A constructed surface flow wetland for treating agricultural waste waters.

A study was conducted between December 1997 and December 1998 in NE Italy on a 3,200 m2 surface flow vegetated wetland receiving agricultural drainage water from a cultivated field of about 6 ha and occasional applications of organic wastes. The study aimed at evaluating: 1) biomass and seasonal nitrogen dynamics in above- and below-ground biomass of Phragmites australis Cav. (Trin.) and Typha latifolia (L.) grown in separate zones; 2) the effectiveness of the wetland in removing nutrients and sediments coming from the fields; 3) the possibility that wetland could treat occasional applications of organic wastes and 4) to collect some general information on whether the wetland can receive heavy loads coming from storm water runoff. Monthly observations showed that, in both species, aboveground biomass, nitrogen concentration and nitrogen content reached maximum values in summer and minimum values in winter. The contrary occurred in below-ground biomass. The total input of water in the wetland was 66,000 m3 ha(-1), of which 7,700 were drained. Total nitrogen input was 526 kg ha(-1), of which 58 were discharged out of the wetland.