2014 Volume 5 Issue 2 Pages 57-62
The Namphong river catchment in NE Thailand, part of the Mekong River catchment, has agro-industrial activities, dry land farming, rice cultivation and river cage aquaculture. Most utilize irrigation while larger industrial activities extract groundwater. The tropical wet and dry seasons cause variation in river flow. Potential effects of water quality may arise annually from constituents introduced by agricultural and other practices. Nutrients are added to soil to improve agricultural production and directly to the river in cage aquaculture from fish feed. The seasonal variations were considered from heavy metals (cadmium, copper, iron, manganese, lead and zinc) and nutrients in the Namphong River during one annual cycle and their relationships to water quality. Water samples were collected from 10 sites along the Namphong River in January 2012 (dry season mean flow 8 sec/m) and 9 sites in September 2012 (wet season mean flow 28 sec/m). Labile metals estimated by the Diffusive Gradient in Thin Films (DGT) technique showed no toxicity to aquatic biota. Most metals showed concentration and location consistency in both seasons. Iron and manganese in pulp mill discharge and vegetable cultivation downstream showed high concentrations in September indicating a groundwater or saturated soil seepage source from reducing conditions. Nutrients decreased by half from January to September; total N was higher at upstream sites in January while nitrate and orthophosphate were not significant and pH and electrical conductivity were consistent for both seasons. Hardness and alkalinity increased in September and were highest in pulp mill discharge indicating a groundwater source. Total and suspended solids were affected by wet season runoff. Variations in metals and nutrients in January and September were attributed to differences in Namphong River flow and from seasonality and agricultural activities. Large agro-industries, particularly pulp, contributed the highest concentrations of nutrients and metals to the river.
