Theme 3-9-Effects of irrigated agriculture on groundwater quality in North-West Bangladesh

Abstract

The emerging problem of groundwater contamination due to agricultural land use changes with increased use of fertilizers and pesticides has created a need for information which can be supplied by properly designed groundwater quality monitoring programmeme. The effective design of such monitoring programmemes and subsequent use of data obtained depends upon an understanding of spatial and temporal variability of groundwater quality parameter concentrations. Herein an attempt is made to assess the spatial and temporal variability of groundwater quality based on available data in northwest region of Bangladesh. Data from about 40 observation wells in the northwest Bangladesh were used in this study. Results of investigation on nine parameters are presented and compared to standards, criteria and other guidelines for assessing groundwater quality. These initial results suggest that parameter concentrations are well within permissible limits. To assess the parameter concentration values at the regional level and to examine if statistically any significant difference in values exists between the periods 1977-83 and 1992-94, data series from all the wells were combined. Empirical distributions were compared and chi-square tests were employed. Also selected parameter concentration variation with depth was looked into in a regional scale. To evaluate the differential effects of agricultural practices, hydro geologic and climatic factors, site specific analyses were also performed using data for five representative well locations, one in each district in the study area. Spatial variability appeared to be more pronounced than temporal difference. At present the quality of groundwater in the northwest region of Bangladesh may be considered adequate for domestic and agricultural use. However, this observation is based on limited time series that were available at the time of this study. Obviously there is a time lag between the activities on the land surface and concomitant deterioration of groundwater supplies. Degradation of groundwater quality may not be readily apparent given the extent of current monitoring activities. Suggestions and comments made should be considered as tentative only and need to be verified by more exhaustive studies and research.