Tonle Sap ecosystem water quality index development and fish production

Abstract

The Tonle Sap ecosystem of Cambodia is situated in the lower part of the Mekong River basin (MRB), the TS ecosystem water environment is influenced by 181,035 km2 of its catchments and water inflow from 4000 km in length of the upper Mekong River. The water quality index (WQI) was developed based on seven environmental chemical factors of DO, NO3+NH4, TOTP, TSS, temperature, pH and conductivity at Kampong Luong monitoring station during the period 1995 - 2002. On PCA, among 15 candidate parameters, the six most variation parameters of 'concentration of TSS mg 1-1, 'temperature C degree', 'conductivity mS m-1, 'ratio between N and P', 'average monthly variation of NO3+NH4N', 'average monthly variation of pH', were identified and selected to constitute the WQI. Each parameter was scored as 1, 3 and 5 and narrated, in order, as poor, fair and good conditions. The yearly WQI score was calculated from these six parameter scores in the relative year. The WQI showed that the highest score of 4.3 was in 1996, while the lowest scores were of 1.3 and 1.0 in 2002 and 1998. Importantly, the WQI was significantly (P<0.05) correlated with the 'dai' fish catch (r2 = 0.858) and the fish biological group 4 (r-species) (r2 = 0.75) during the period 1995-2002 indicating that the index was sensitive to reflect the relation between water quality condition and fish production. Then the WQI should be considerably used as the biological monitoring tool for water quality - fish production assessment. The correlations (P<0.05) between WQI and fish families of Gyrinocheilidae and Cyprinidae indicated these fish families should be considered to be used as the TS ecosystem water quality bioindicators. © 2007 WIT Press.