Surface and groundwater interactions: Methodology and changing chemical processes

Abstract

In the recent times, there is a growing demand for creating sustainability in both groundwater and surface water bodies in order to optimize water uses and for reaching a good ecological state. Hydrologically, both surface and groundwater interact with one another, and therefore, there is a continuous exchange of nutrient and pollutants taking between the two systems. When the groundwater reaches the river as base flow, it changes the chemical characteristics of the river water. Similarly, groundwater can also get contaminated by the recharges from the polluted surface water bodies (Krishan et al., 2016, 2017). Thus, an understanding of groundwater-surface water interactions is of great importance. The groundwater and surface water interactions are controlled by the relative positions of surface water bodies, hydrogeological characteristics of the aquifer beds, and the climatic settings (Winter, 1999). Both the directionality of interactions and quantification of exchanges are important for ensuring robust water management practices (Brunke and Gonser, 1997; Kalbus et al., 2006; Kidmose et al., 2013; Malik and Bhagwat, 2020). Apart from water budgeting, these interactions generate enormous ecological influence through physiochemical and biological processes taking place at hyporheic zone and at the interface of sediment-water interactions (Triska et al., 1993; Dahm et al., 1998; Mugnai et al., 2015). For instances, the change in nitrate concentration in hyporheic zone has been reported in several studies (Pinay et al., 2008; Zarnetske et al., 2011). The surface and groundwater exchanges vary both spatially and temporally. The spatial variability is governed by hydraulic conductivity of surface water bodies (Kalbus et al., 2009), and the temporal variability is determined by the groundwater fluctuations and recharge rate (Winter, 1981). Thus, it becomes essential to map the flux exchanges on large areas. Regional approaches like hydrograph separation and satellite imaging quantify the interactions at very course level. For example, in semiarid terrain of north-west India, sustained growth in the agricultural sector has only been possible through the use of irrigation from shallow local groundwater sources as well as an extensive canal network redistributing water from the Himalayan watershed to the plains (Bonsor et al., 2017; MacDonald et al., 2016). Satellite-based observations by Rodell et al. (2009), Tiwari et al. (2009), and Wada et al. (2012) have shown that there is a significant net loss in terrestrial water storage (TWS) in this region, but the spatial variability in groundwater recharge processes is not captured by these regional approaches. Looking at the limitations of regional approach, it becomes necessary to explore more robust methods/tracers like Radon, temperature, ions, chlorofluorocarbons (CFCs) and sulfur hexafluoride (SF6), noble gases, stable isotopes, environmental tritium, etc. to map the interaction and understand the processes controlling the chemical exchanges. Thus, this chapter focuses on exploring the above-mentioned tracers and presenting the chemical exchange or processes taking place between surface and groundwater.