A Preliminary Analysis of Water Quality and Nitrogen and Phosphorus Pollution in the Main Canal of Guangli Irrigation District

Abstract

【Objective】 One challenge facing developing sustainable irrigation districts is to alleviate water deterioration. This paper is to present the results of a preliminary study on water quality and nitrogen and phosphorus contents in the main canal of Guangli irrigation district in Henan province, and propose strategy to prevent water from deterioration. 【Method】 We selected six sections along the canal from June to December 2019, and measured monthly changes in total nitrogen (TN), total phosphorus (TP), CODCr and BOD5. We then evaluated water quality and eutrophication in the canal using the comprehensive water quality identification index - suitable for comprehensive evaluation of river water quality in China - and the exponential universal formula of power function in logarithmic form. 【Result】 ①The comprehensive water quality identification index showed that 86% of the water in the irrigation district meets the Grade V standard for agricultural water usage. It was also found that the comprehensive water quality index varied spatiotemporally at significant level. In July, 66.7% of water in the canal deteriorated below Grade 5 standard, with black and odorous water (eutrophication) found at Gate 3 and the entry point to the canal. ②Eutrophication was widespread. The maximum eutrophication evaluation index was 80.5 and appeared in July at the entry point to the canal; approximately 41.6% of water in the district was seriously eutrophic. ③The average mass concentration of TN was 5.30 mg/L, 2.65 times the Grade V standard for surface water. The average mass concentration of TP was 0.156 mg/L and the ratio of total nitrogen to total phosphorus was 33.97∶1, an ideal environment for algae bloom. 【Conclusion】 Overall, the water quality in the irrigation district meets the requirements for irrigation, but it is highly eutrophic with high nitrogen content. The original earth canals with aquatic plants are able to purify the water and keep the district ecologically function. Keeping water from deterioration therefore should tighten control of pollutants from entering the irrigation district, and monitor the changes in nitrogen and phosphorus. Channel lining should consider its consequence for ecological functions. Alternating lining and earth canal bed, combining with aquatic plants to take up the pollutants such as nitrogen and phosphorus, can improve water quality in the irrigation district.

Keywords

• guangli irrigation district
• main canal
• water quality
• nitrogen and phosphorus pollution
• eutrophication