Preliminary assessment and spatial distribution of selected water quality parameters at Kalmadu tank in Vavuniya District of Sri Lanka

This research on Kalmadu tank aims to analyze the horizontal and vertical profiles of selected water quality parameters. Twenty randomly selected sampling points on surface and corresponding vertical depths of 30 cm and 60 cm were measured for temperature, pH, TDS, EC and ORP using intended electronic probes. The measured values were statistically analyzed with t-test, paired t-test and Pearson correlation. Kriging interpolation technique was used to visualize the spatial distribution. Results revealed non-compliance of TDS and EC with existing permissible limits for irrigable water. Except the temperature with pH, all the other measured parameters resulted positive correlation and TDS trend resembled the spatial pattern of EC. The mean values of pH at 30 cm & 60 cm depth significantly differed with surface, similarly surface ORP varied from 30 cm depth. There are no significant vertical wise changes observed in the other tested parameters. Significant spatial variations were observed in the selected parameters from the kriging map.  Reflection and shading of existing plants, microbial organic degradation, anthropogenic water usage, and small water current movements may be some of the influencing factors for this variation. This study suggests to policy makers and relevant management authority, to pay more attention to irrigation tanks in terms of maintaining irrigable water.
In-depth investigation is imperative to identify the reason behind the changes in the tank water quality and would also yield further information to initiate appropriate strategies for the management of this tank.