Water quality of Nilwala River, Sri Lanka in relation to land use practices

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 (PO4 3--P), Sulphate (SO4 3-), Total Fe, Ca 2+ , 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 +2 among 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.

Analysis of physicochemical parameters and selected potentially toxic elements to assess the water quality of Kattakaduwa reservoir in Hambanthota district, Sri Lanka

“…Abeysinghe et al (2017) have reported that the pH varied from 6.7-5.9 along the Kelani river, Sri Lanka during the study period of March-August in 2017. It was also reported that the pH varied between 5.8 and 7.3 along the Nilwala river in Sri Lanka (Jayawardana et al 2016). The pH of the water body at Kattakaduwa reservoir lies within a limited range (7.1-7.9).…”

“…Abeysinghe et al (2017) has reported turbidity values within the range of 11.84 -4.54 NTU along the Kelani river of Sri Lanka during the year 2017. It was also reported that along the Nilwala river, Sri Lanka, turbidity varied from 5.23 to 149.86 NTU (Jayawardana et al (2016).…”

“…It seems like carbonate, bicarbonate, hydroxyl anions present in water samples were precipitated with heavy metal ions and other cations in water during April to June. Jayawardana et al (2016) have reported that the alkalinity along the Nilwala river, Sri Lanka in 2016 varied from 19.5 -177 mg/L.…”

“…Sulphate ion concentration near the pump house before purification (site 3S) was within the range of 30.0 -104.0 mg/L with a mean of 57.40 ± 23.60 mg/L while the treated reference water sample has sulphate ion concentration of 43.0 -145.0 mg/L with a mean value of 86.0 ±35.80 mg/L which revealed that there is no change in sulphate ion concentration during the purification. Sulphate ion concentration varied from 4.0 -404.0 mg/L along the Nilwala river of Sri Lanka in 2016 (Jayawardana et al 2016).…”

Spatio-temporal variation of water quality and bio indicators of the Badulu Oya in Sri Lanka due to catchment disturbances

“…Aquatic ecosystems around the world are increasingly occurring in the respective catchment landscapes (Allan, 1995;Alam et al, 2006;Jayawardana et al, 2016). Alteration of land cover on the catchments of rivers and aquatic fauna in a number of ways.…”