Influence of land use on aquatic pollution in an urban wetland: a case study in ‘Kirala kale’, Matara District, Sri Lanka

Abstract

Kirala Kale is an urban wetland in southern Sri Lanka. This study examined the aquatic pollution status within the wetland in relation to the nearby land-use composition. Eight water sampling sites considering inlets and outlets, low flow rate, and easy access were selected to represent the whole wetland. Percentages of different land-use types (urban, forest, marshlands, paddy lands, sparse vegetation, and water bodies) within a 300m buffer area around each site were assessed via remote sensing and GIS. Temperature, Electrical conductivity (EC), Total Dissolved solids, Salinity, Dissolved Oxygen, pH, Nitrate (NO3-), Orthophosphate (PO43-), Heavy metals (Cu, Cd, Cr, Pb) in water and macro-benthos in sediment were analyzed at two sampling occasions with three replicates from each site. There were significant positive spearman rank correlations between the proportion (%) of Urban and settlement land cover and NO3-(r = 0.762, p < 0.01), PO43- (r = 0.738, p < 0.01), and EC (r = 0.833, p < 0.01). Similarly, Paddy land cover and NO3- (r = 0.994, p < 0.05), and PO43-(r = 0.994, p < 0.05) were positively correlated. Negative correlations were observed between forest cover and NO3-(r = - 0.708, p < 0.01), and sparsely distributed vegetation and NO3- (r = - 0.881, p < 0.05), and PO43- (r = - 0.905, p < 0.05). Cu and Cd concentrations (0.006-0.022 ppm) were below the accepted limits (0.05 ppm and 0.03 ppm, respectively) in Sri Lanka. The absence of pollution-sensitive EPT taxa and the presence of pollution-tolerant Glycera sp., Pomacea sp. Helisoma sp. etc. in sediment indicated moderate pollution at sites. Results showed urban setup has affected aquatic pollution levels in Kirala Kale wetland.