Distributive Characteristics of Riverine Nutrients in the Mun River, Northeast Thailand: Implications for Anthropogenic Inputs

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.

Distribution, Sources and Water Quality Evaluation of the Riverine Solutes: A Case Study in the Lancangjiang River Basin, Tibetan Plateau

“…In the sample site LCJ-1, 3.8% of the total cations are derived from the rain inputs, while the contributions of the halite dissolution, gypsum dissolution, silicate weathering and carbonate weathering make up 19.2%, 24.7%, 17.4% and 34.9% of the total cations, respectively. Similar to many studies [5,6,7,8,12,13], the carbonate weathering is the predominant sources of the riverine solutes. As mentioned before, the estimate regarding the contribution of gypsum should be the maximum value because this estimated contribution value involves the contribution of sulfate oxidation to the SO 4 2 − .…”

“…Because Cl − is conservative in river, the Cl − contents in river water derived from rain should keep the same level. The widely accepted method is assuming that the sample with the lowest Cl − concentration acquired all its dissolved Cl − completely from the atmospheric inputs, thus other ions derived from the rain can be calculated by the elemental ratio in rain [5,6,7,8,9,12,13,14]:[X] rain = [Cl] lowest × (X/Cl) rain where [X] rain is the element X concentrations in rain waters, [Cl] lowest is the concentrations of Cl − which is assumed completely from the precipitation, (X/Cl) atm is the X/Cl − molar ratio in rain waters. The sample LCJ-25 (Langcangjiang River-25) with the lowest Cl − concentration (3.5 μmol/L) is collected in the tributaries in pristine areas, the bedrock in the sampling site LCJ-25 is Precambrian rocks consisting of medium-highly granodioritic-granitic metamorphic rocks, in which the chloride contents are limited.).…”

“…River water is the important component of hydrosphere and draws great attention in geological and environmental research, for it constitutes the lateral channels transporting the territorial matters towards the ocean [1,2]. The riverine dissolved loads transported along river waters are derived from both natural processes and anthropogenic perturbations [3,4,5,6], among which the chemical weathering is considered as the dominant source [1,7,8]. Thus, estimating the contributions of the different minerals during chemical weathering to the riverine solutes can help researchers to better understand the chemical composition of river water and regular patterns of matter cycling [9,10].…”

Distribution, fractionation and sources of rare earth elements in suspended particulate matter in a tropical agricultural catchment, northeast Thailand

“…The data of REE in soils quoted from the previous study, and the information of six soil profile location and REE analysis can be found in Zhou et al (2020) . The dissolved organic carbon (DOC) concentrations of river water quoted from Liu et al (2019) .…”

The Mercury Behavior and Contamination in Soil Profiles in Mun River Basin, Northeast Thailand

“…The monthly average temperature is from 25 to 30 °C [25], and the highest temperature is in April. The fluvial deposit area where the Mun River flows through is primarily dominated by cretaceous claystone and sandstone with some halite and gypsum spread around the basin, while there is less than 10% coverage of tertiary basalt in the south of basin [22,26].…”