Abstract
The Nilwala River is the third largest in the southern province of Sri Lanka which runs through 72 km along its cause. Conversion of forest lands to agricultural lands, expansion of urban areas and clearing of land for construction purposes in the catchment are major issues affecting water quality in Nilwala River. The water quality of the Nilwala River lower basin at 16 locations was estimated for 4 months from September2010 to December 2010 in two-week intervals. Water quality parameters pH, Electrical conductivity(EC), Dissolved oxygen (DO), Biochemical Oxygen demand (BOD5), turbidity, colour, Total Dissolved Solids (TDS), total hardness, alkalinity, Nitrite-N (NO2--N), Nitrate -N (NO3--N), Phosphate (PO43- -P), Sulphate (SO43-), Total Fe, Ca2+, F- and Cl- were evaluated in the sampling locations. The spatial and temporal variation of water quality associated with different land use categories were analyzed using Two-way ANOVA. Principal Component Analysis (PCA) and Cluster Analysis (CA) were also conducted to determine the association between water quality variation and land use impacts of the catchment. A significant (p <0.05) spatial variation of water quality parameters, except the hardness, Fluoride and Ca+2among sites were observed to be associated with different land use categories. No significant (p >0.05) temporal variability in water quality parameters except Nitrite and hardness was detected. PCA and CA also indicated a strong association between the water quality variables and the land use types of the river basin. Urban impacts, land clearance in the catchment and sand mining activities of the river bed were found to be the most significant impacts to the water quality of the river and areas with forest cover having positive impact to the water quality. These findings emphasize the need of better catchment management approaches and remediation of urban impacts on river water quality.
Highlights
Despite being the life supporting systems of the earth aquatic ecosystems around the world are increasingly affected by various anthropogenic impacts (Alamet al. 2006)
All physical and chemical water quality parameters, except total hardness, F- and Ca+2 detected in sites associated with different land use categories indicated significant differences (p
The observation of physical and chemical water quality parameters in selected locations in Nilwala River indicated significant (p
Summary
Despite being the life supporting systems of the earth aquatic ecosystems around the world are increasingly affected by various anthropogenic impacts (Alamet al. 2006). Loss of terrestrial vegetation and an increased area of impervious surfaces can influence evapotranspiration and infiltration, and alter natural flow regimes (Changnon and Demissie 1996). These land use practices increase the sediment inputs to streams and may alter substratum characteristics and channel morphology (Lake et al 1985; Bunn et al 1986). Altered catchment hydrology and land use can influence inputs of inorganic nutrients from terrestrial sources and may enhance in-stream primary production, resulting in change of the trophic structure of aquatic communities. Processing complex, large data sets collected through monitoring programmes and determination of underlying trends of water quality variation are crucial for taking decisions related to pollution prevention and catchment management efforts. Application of multivariate techniques to analyse water quality data has been successfully applied in many situations (Pearce et al 2013; Ndungu et al 2014; Wang et al 2014; Zeng and Arnold 2014)
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