Carbon supply and the regulation of enzyme activity in constructed wetlands

Regulation of extracellular enzyme activity in constructed wetlands (i.e. artificial wetlands for wastewater treatment) has not been elucidated; the objective of this work was to investigate the contribution of one possible regulator (carbon supply) to rates of activity of three enzymes involved in organic matter decomposition. Soil samples from a constructed wetland were supplied with carbon (cellulose or glucose) at different concentrations (10 and 100 mg l−1) and with carbon-free water (control) or sewage effluent. The activities of β-d-glucosidase, phosphatase and arylsulphatase in the soil were monitored over a 54-day period using methylumbelliferyl substrates, which are cleaved only extracellularly (Jones 1990). When compared to controls receiving no carbon, phosphatase activity under all treatments showed no significant differences over the course of the experiment. Sulphatase activities over the course of the experiment were significantly reduced by glucose (10 and 100 mg l−1), cellulose (10 and 100 mg l−1) and sewage effluent addition, to between 53 and 79% of the activity in controls. β-glucosidase activity gradually increased by 127–161% over the 54 d in response to cellulose addition (10 and 100 mg l−1), and decreased after sewage effluent addition to 84% of the activity in controls. These findings suggest that by manipulating the quantity and quality of carbon supply in constructed wetlands, it may be possible to modify extracellular enzyme activities in order to maximize the efficiency of water treatment.