Abstract
Airborne pollutants such as SO42- and NO3- that cause acid rain may pollute water resources via acid deposition. However, such effects on the water quality of the upper Rio Grande River section in Texas have not been systematically studied. The objective of this study is to collect and analyze field data, and perform hydrological and water chemistry analyses to assess acid deposition effects on the river water quality. The analysis of the precipitation data indicates that the concentrations of ions decrease as the quantity of precipitation increases. The precipitation with higher concentrations of SO42- and NO3- has a lower pH while that with higher concentrations of Ca2+ and Na+ has a relatively higher pH value. The analysis of river data demonstrates that the pH value, Dissolved Oxygen (DO), and Total Dissolved Solid (TDS) generally decrease when the flow rate increases immediately following precipitation events. The drop in pH following a precipitation event is due to the low pH in the precipitation. The DO and TDS decrease after the precipitation due to the increased flow rate. The slightly higher pH and lower DO values in the eastern section of the river (where the basin is limestone-dominated) as compared to the western section is due to the limestone erosion caused by the acid deposition. The annual stone loss by the acid deposition is about 72,000 m3. The fluctuation between the pH value and the temperature suggests the effect of CaCO3 solubility on the pH value. The water chemistry analysis using Geochemist’s Work Bench (GWB) has been performed to estimate the effect on the oscillation of CaCO3 dissolution-precipitation process. The equilibrium pH decreases with decreasing temperature, but increases as the CaCO3 concentration decreases. The effect of limestone on observed daily pH fluctuations appears to be supported by the simulation.
Highlights
Acid deposition, commonly known as acid rain, is one of the important culprits for water quality and ecology system degradation in the USA [1,2,3]
To assess the acid precipitation impacts in the study area, the three years water quality data analysis indicates that the pH, Dissolved Oxygen (DO) and Total Dissolved Solid (TDS) decrease with the increasing flow rate followed by the precipitation event
The study has included the collection and analysis of field measurement data and the performance of hydrological and water chemical analyses to assess the impact of acid deposition on the water quality
Summary
Commonly known as acid rain, is one of the important culprits for water quality and ecology system degradation in the USA [1,2,3]. The acid deposition attaches to the beautifully etched limestone cliffs in the Sierra del Caballo Muerto and in Big Bend’s canyons to dissolve a tiny bit of calcite, which is transported away by rapid runoff and flash-flooding following summer thunderstorms [12] Such impact caused by the acid deposition in streams is a complex physical and chemical process [13]. It is accomplished through collecting and analyzing field measurement data and performing hydrological and water chemical analyses on river water. A geochemical analysis by Geochemist’s Work Bench (GWB) has been performed to estimate the effect of the oscillation of calcite dissolution-precipitation process on the equilibrium pH in the river
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