A modified water quality index for intensive shrimp ponds of Litopenaeus vannamei

a b s t r a c t A modified water quality index (WQI) was used to evaluate the water quality of intensive culture ponds of Litopenaeus vannamei. Multivariate statistical technique, principal component analysis (PCA), was applied to interpret the large complex water quality data set generated over a span of 120 days (from 1st July to 28th October, 2008) with weekly monitoring of 11 variables in four different shrimp ponds. The PCA revealed three, four, three, and three latent factors that accounted for 82.843%, 81.6%, 81.629%, and 84.801% of the total variance in the water quality data sets from each of the four shrimp ponds, respec- tively. The varifactors indicated that the variables responsible for water quality deterioration were mainly related to organic matter group (COD and BOD5), natural condition group (pH and T), and nutrient group (TAN, Chl-a and DIP) in intensive shrimp ponds. A modified WQI based on the varifactors was applied to evaluate the water quality in shrimp culture ponds. The result revealed that the overall water quality in the shrimp ponds were mainly excellent during the early period and deteriorated in the mid to late period. The WQI evaluates water quality synthetically; furthermore, it reveals the outcome when some of the other variables deteriorate significantly. Thus, this study illustrates the necessity and usefulness of multivariate statistical techniques for interpreting large and complex data sets regarding water quality in shrimp culture pond. Furthermore, the evaluation results revealed that the modified WQI can be used as a tool for determining water quality.