Using Fractal Interpolation to Evaluate Eutrophication at Pingzhai Reservoir in Guizhou Province

Abstract

【Background】Water eutrophication has become prevalent in China and the underlying mechanism is the imbalance between nutrients inflow and consumption, which boosts overgrowth of some species. Eutrophication could undermine functions of the aquatic ecosystem, and understanding development of the eutrophication and its determinants is therefore important to ameliorate it. 【Objective】The Pingzhai reservoir in the karst plateau of Guizhou province is an important water source for irrigation and drinking in the province, and the objective of this paper is to unveil its eutrophication and the factors affecting it. 【Method】Water samples were collected from late November 2018 (autumn), January (winter), May (spring) and July (summer) 2019, and for each sample we measured the contents of chlorophyll a (Chla), total phosphorus (TP), total nitrogen (TN), permanganate index (CODMn) and transparency (SD) in it. A model derived based on the fractal interpolation was used to evaluate eutrophication in the reservoir. 【Result】①The TP and CODMn contents in the reservoir meet Class II water quality standard, and the TN content exceeds the class V water quality standard and is the main determinant of the eutrophication. The contents of TN, CODMn and Chla were highest in summer, while the TP content was highest in winter and the SD content was lowest in spring. ②Eutrophication in the reservoir is moderate or above, and the data measured from different locations showed that the reservoir was not oligotrophic, indicating that the reservoir has been eutrophic. ③The reservoir is most eutrophic in summer and least in autumn, with other seasons between. The eutrophication degree was highest at the BS2 and HJ2 monitoring sections, and least at the ZW8 and SG1 sections, with NY3, SG3 and PZ4 sections between. 【Conclusion】In general, the reservoir is highly eutrophic with the increased TN being the main determinant. Controlling inflow and accumulation of nitrogen in the reservoir is hence the top priority to remediate its eutrophication.

Keywords

• fractal interpolation model
• water eutrophication
• comprehensive evaluation
• karst plateau
• reservoir