Can Constructed Wetlands Reduce the Diffuse Phosphorus Loads to Eutrophic Water in Cold Temperate Regions?
- B. C. Braskerud *a,
- K. S. Tonderskib,
- B. Weddingc,
- R. Bakked,
- A.-G. B. Blankenberga,
- B. Uléne and
- J. Koskiahof
- a Jordforsk, Frederik A. Dahls vei 20, NO-1432 Ås, Norway
b Linköping University, IFM/Biology, SE-581 83 Linköping, Sweden
c Ekologgruppen i Landskrona AB, Järnvägsgatan 19B, SE-261 32 Landskrona, Sweden
d Telemark University College, Box 203, NO-3901 Porsgrunn, Norway
e Division of Water Quality Management, Swedish University of Agricultural Sciences, Box 7072, SE-750 07 Uppsala, Sweden
f Finnish Environment Institute, Integrated River Basin Research, P.O. Box 140, FIN-00251 Helsinki, Finland
Construction of wetlands is a possible supplement to best management practices (BMP) at the field level to mitigate phosphorus (P) pollution from agricultural areas. In this paper, annual results from 17 intensively studied wetlands in the cold temperate or boreal climatic zone are reported and analyzed. Surface areas varied from 0.007 to 8.7% of the catchment area. The average total phosphorus (TP) retention varied from 1 to 88%, and the dissolved reactive phosphorus (DRP) retention from −19 to 89%. Retention varied substantially from site to site, indicating the existence of site-specific factors in the catchment and wetlands that influenced the P removal. Factors important for P retention in wetlands were evaluated through multiple statistical analyses by dividing P into two fractions: particulate phosphorus (PP) and DRP. Both relative (%) PP and DRP retention increased with wetland surface area. However, PP retention was not as sensitive as DRP in terms of wetland size and retention: specific PP retention (gram P retention per m2 and year) decreased as wetland area (A w) increased, suggesting the existence of a site-specific optimal wetland to catchment area (A c) ratio. Particulate P retention decreased with increasing DRP to TP ratio, while the opposite was found for DRP. Dissolved reactive P retention was higher in new than in old wetlands, while increasing age did not influence PP retention negatively. Effective BMP in the catchment is important to keep the P loss low, because the outlet concentration of P from wetlands is often positively correlated to the input concentration. However, wetlands act as the last buffer in a catchment, since the retention often increases as the P concentration in streams increases.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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