Relationship between nitrate concentration and chemical oxygen demand (COD) of a stream in vegetable farm area in Cameron Highlands

Excessive fertiliser application in agricultural activities, especially in vegetable farms, can be washed into the streams and decline the water quality. Nitrate from fertiliser may increase organic loading in the river and indirectly increase the oxidising activity especially chemical oxygen demand (COD). This research aims to determine the relationship between Nitrate concentration and COD of a stream flows within the vegetable farm area. This study used a cross-sectional study design. Water samples were collected at seven sampling points of Sungai Ulung, Cameron Highlands representing the river upstream and downstream. The COD and nitrate were analysed by using HACH-DR 2400 datalogging spectrophotometer. The concentration for nitrate and COD in the stream was slightly increased, where the concentration for both parameters at downstream was higher than those in the upstream river. The mean concentration of nitrate and COD upstream was 1.5 mg/L and 11.5 mg/L, respectively, while the mean concentration downstream after the river through the vegetable crop was 2.0 mg/L and 14.0 mg/L. The increases of both parameters have resulted on decline of dissolve oxygen (DO) of the river. Besides, the result also shows a positive correlation of nitrate with COD (r = 0.865), R-square = 0.62 with p value of 0.012. The degradation river quality of Sungai Ulung was probably due to the agricultural activity near the river. Farmers can practice Best Management Practices (BMPs) for their crop to reduce the chance of nutrient losses to the impaired water bodies.