Abstract
Understanding the hydrologic and hydrochemistry processes in the riparian area is of great importance for managing and protecting riparian water resources. This paper took a highly disturbed and polluted Shaying River Basin (SRB) of China as the study area. In this research, environmental tracers (hydrochemical and isotopic data of222Rn, δ18O, and δD) and corresponding models (two-component mixing model and 222Rn mass balance model) were employed to investigate the hydrologic and associated hydro-chemical process of riparian groundwater. The results indicated that rivers received groundwater discharge located at Xihua (J8), Zhoukou (Y1), Luohe (S2), and Shenqiu (SY2), and the mixing extent with groundwater was greater in wet seasons than in dry seasons. The 222Rn mass balance model showed that the flux of river water leakage was 3.27 × 10−4 m3/(s·m) at the front of Zhoukou sluice while groundwater discharge was 3.50 × 10−3 m3/(s·m) at the front of Shenqiu sluice during the sampling period. The cation exchange and the dissolution/precipitation of aquifer minerals (including calcite, dolomite, gypsum, and halite) were dominated by geochemical processes. The untreated sewage discharge and fertilizer usage were the main anthropogenic activities affecting the hydrochemistry process in surface water and riparian groundwater. Additionally, our results found that nitrate pollutants derived by riparian groundwater were potential threats to river quality at the lower reaches of Jialu River and Shenqiu county of Shaying River, where the nitrate inputs could be larger during the wet seasons because of higher groundwater discharge.
Highlights
Riparian zones are defined as transition areas between terrestrial and aquatic ecosystems and are important for residents and for the industrial and agriculture sector
Equation (1) is determined under the following condition: (i) two end-members consist of groundwater and surface water not including other sources of water bodies, (ii) CD lies within the range delimited by the end-member CU and CD, and (iii) the changes in radon activities are influenced only by infiltration of surface water/groundwater, and evaporation, gas exchange, radioactive decay, and hyporheic exchange terms to be neglected
The statistical summary of hydro-chemical parameters was shown in Figure 4. pH value is an essential parameter reflecting the characteristics of hydro-chemical balance in water [48]
Summary
Riparian zones are defined as transition areas between terrestrial and aquatic ecosystems and are important for residents and for the industrial and agriculture sector. Surface water and groundwater in riparian zones are not completely independent but are interconnected components of the river basin system [1]. Water quality and quantity in riparian zones are controlled by the hydrogeological settings and by the human activities in the watershed. Water 2020, 12, 1939 rapid urbanization, intensive agriculture, and industrial activities have greatly threatened the quality in surface water and riparian groundwater mainly due to increased nitrogen pollution [2,3]. Elevated nitrate concentration in water bodies has caused severe harm to ecosystems (eutrophication and toxic algal blooms), and threaten residents’ health (methemoglobinemia and stomach cancer) [4,5]
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