Salient ecological functions of a tropical freshwater wetland

Abstract

AbstractAn ecological survey was carried out for the Iriyawetiya freshwater wetland in Sri Lanka. The goal was to characterize this unique wetland, about which little ecological information was available. The areal extent of the wetland was 87 ha, with a marshy cover of approximately 52 ha. Water samples to assess physico‐chemical parameters were collected at monthly intervals for six months from four study sites along the stream length through the wetland. A 1 m × 0.5 m quadrat was used for vegetation sampling at 5 m intervals along a 50‐m transect, aligned perpendicular to a reference shore line. Constituent plant species of each quadrat, both floating and attached, were identified and enumerated. Multivariate analysis using PC‐ORD4 software (MJM software, Gleneden Beach, Oregon, USA) was performed to identify plant associations. Four distinguishable clusters of plant associations were identified using a TWINSPAN analysis; namely (i) bank side floral community, (ii) dense marginal stand, (iii) graminoid and (iv) reed cyperous communities. The water in bank side floral association had a high biological oxygen demand (BOD). The reed plant community was confined to stream outlet and exhibited high dissolved oxygen (DO) levels. The two stream inlets displayed high nitrate concentrations, whereas the outlet and mid‐wetland sampling sites exhibited low nitrate levels. In this study, the DO concentrations increased downstream, while the phosphate, nitrate and BOD concentrations, and turbidity gradually declined towards the outlet, indicating the purifying effect of the wetland. In this preliminary analysis, it was ascertained that the proximity of this wetland to an urban area is propitious, as the wetland could be ecologically engineered to provide water that would need less treatment.