Eutrophication concern: A case study on several lakes in Dong Ha city

Abstract

Three representative lakes in Dong Ha city, Quang Tri province (Khe San, Dai An and Khe May) were selected for sampling and analysis of water quality parameters, including temperature, pH, DO, transparency, TSS, conductivity (EC), COD, BOD5, TN, NH4+, NO3–, NO2–, TP, PO43–, and chlorophyll-a (Chl-a) during the period from June to August 2017. The results show that organic pollution levels (BOD5 and COD) and nutrients levels (Tuy nhiên, and TP) at Khe San and Dai An were higher than those at Khe May lake (p < 0.05); Chl-a concentrations in the lake water were also high with an average of 9–84 μg/L, considered as the eutrophication level. Phosphorus was a limiting factor for the eutrophication at the three lakes: 90% of the ratios of TN/TP is higher than 6. The eutrophic status at thelakes was assessed on the basis of Carlson trophic index (TSI) and Wollenweider trophic index (TRIX): Dai An and Khe San lakes are at the eutrophic status with the TSI values higher than 60 and TRIX values in the range of 6–8; Khe May lake is at the level from mesotrophic to eutrophic with TSIs higher than 50 and TRIX = 5÷6. The correlations between the TSI, TRIX, and the water quality parameters were also analyzed.