Causes and control measures for algae occurrence in a constructed wetland treating stream runoff from agricultural land use

摘要

The constructed wetland (CW) was designed to treat impacted runoff stream water coming from a 221 ha agricultural watershed. The CW was composed of 7 cells in series including a sedimentation zone, deep marsh and shallow marsh. Water quality, sediment and plant monitoring on the CW was conducted since October 2009 and additional analyses were performed to recognize the causes of algae occurrence since 2012. Large amounts of Haematococcus pluvialis species was observed in the first five cells of the CW but no algae was seen at the last 2 cells prior to the outlet. Results indicated that the proportion of plant coverage to surface area in Cells 1 to 5 was very low (less than 6%). Findings revealed that nutrients were being transported into the CW from the catchment area with the soluble nutrients degraded by microbial activities in the sediments and released to the water table. Relatively high potassium content was found in Cell 1 of the CW which originated from the chemical fertilizers used in the paddy field. Algal bloom control and better design methods in the CW were suggested to prevent and regulate the algal bloom in CWs.