The Effect of Land Use on Water Quality in Lam Takong Basin, Nakhon Ratchasima Province, Thailand

The water quality assessment of Lam Takong River and tributaries, from 20 stations, 6 times (October and December, 2008; February, April, June and August, 2009), revealed that overall water quality was in class 3 of Thailand surface water standard, except NH3-N, P and BOD. The maximum of NH3-N (12.6 mg/L), Phosphate 2.7 mg/L and BOD (8.7 mg/L) were found at Quartermaster Department Royal Thai Army Bridge, Nakhon Ratchasima Municipality pump in Lam Takong reservoir and Ban Ta Krasang, respectively, causing class 4 surface water standard in these areas. Moreover, trophic level of Lam Ta Khong River was mesotrophic; except they were meso-eutrophic after passing through Nakhon Ratchasima Municipality, Ban Ta Krasung, and Kan Pom dam before reaching Mool River. The season also affected on water quality. The value of pH, DO, BOD and NH3-N were significantly higher in dry season (p<0.01), while temperature, salinity and TSS were significantly lower in dry season (p<0.01). However, turbidity, TOC, NO3, NO2 and Chlorophyll-a in rainy season were higher than dry season but not statistically different. Pearson’s Correlation of 9 land use types on water quality showed that urban area was correlated with BOD, DO, NH3-N, PO4 and Chlorophyll-a (0.425, 0.380, -0.259, 0.445, and 0.339, respectively) higher than industrial area, scrub forest and water body. However, nitrate was mostly correlated with water body. Later, statistical models were developed from these results. WAPS was used to predict water quality in Lam Takong River. Three scenarios (present, 10 years, and 10 years with 25% BOD reduction) were simulated. The model predicts that water quality still decreases when flow through Nakhon Ratchasima Municipality. The minimum DO would reach 1 mg/L in ten years. However, if 25% BOD are reduced by future wastewater treatment plant and septic tank construction, the minimum DO would be 2.75 mg/L.