TITLE:
Assessment of Acid Deposition Effects on Water Quality of the Upper Rio Grande River Section in Texas
AUTHORS:
Qin Qian, Badri Parajuli, Qi Fu, Kaiming Yan, John L. Gossage, Thomas Ho
KEYWORDS:
Acid Deposition; Precipitation; Rio Grande River; Water Quality
JOURNAL NAME:
Journal of Water Resource and Protection,
Vol.5 No.8,
August
14,
2013
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.