Abstract
The nutrient contents of Mun River water in northeast Thailand during the dry season were measured to investigate the effect of human activities on dissolved load species. Dissolved organic carbon (DOC) values varied from 2.5 to 17.1 mg/L, averaging 9.0 mg/L; dissolved inorganic nitrogen (DIN) ranged between 0.12 and 0.11 mg/L; Cl− values ranged from 1.7 to 668.6 mg/L, with an average value of 84.8 mg/L; dissolved silicon (DSi) varied from 1.7 to 9.9 mg/L; and SO42− values averaged 8.9 mg/L. DOC, Cl−, and SO42− contents decreased with the flow direction. The high concentrations of DOC, K+, Cl−, and SO42− in the upper reaches were closely related to anthropogenic inputs, specifically industrial sewage. The covariation demonstrated that these dissolved loads may have the same sources. In other regions, Cl− contents were derived from weathering products. DIN contents maintained the same level on the river, and few sampling sites with high concentrations of DIN were influenced by point source pollution. The extremely low P concentrations limited algal growth, and the DSi showed no clear relationship with N and K, indicating that DSi in the Mun River was controlled by the weathering input rather than biological effects. The exact reverse spatial distributions of DOC between the wet and dry seasons (which increased with the flow direction in the wet season) were due to different precipitation rates, and the rare rainfall in the dry season had difficulty flushing the soil and transporting soil organic matter into the rivers. The local government should control sewage discharge and optimize farming methods.
Highlights
River waters, though constituting only a fairly small proportion of the hydrosphere, are the fundamental links between territorial matters and the ocean [1,2,3]
Our previous study [31] reported the dissolved carbon and nitrogen species in the wet season, which emphasized that agricultural activities have a significant impact on organic matter contents and that the Mun River water chemistry was influenced by human activities
The river water chemistry canand be topographic controlled by bothmay natural geochemical processes and of anthropogenic precipitation [30]
Summary
Though constituting only a fairly small proportion of the hydrosphere, are the fundamental links between territorial matters and the ocean [1,2,3]. Rivers transfer both natural weathering products and anthropogenic materials to the sea and influence the seawater composition [4,5,6]. The river chemistry can be affected by numerous natural geochemical processes, such as climate, tectonics, weathering, vegetation cover, and so forth [7,8,9,10], among which the dominant. Studies on river water chemistry can reveal the geochemical processes and provide policy considerations for comprehensive watershed management
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