The Mahi: An Important West Flowing River of Central India

Rivers are lifeline of terrestrial biodiversity including humans. Freshwater is a basic natural resource, and therefore, the areas situated close to the river banks witnessed great cultural and economic progress since ancient times. It is essential for human, agricultural, and industrial activities; India is bestowed by a network of large and small rivers receiving water mainly through glacier melt and monsoon clouds. ~20% of the Indian rivers flow in the westward direction eventually drains into the Arabian Sea. Compared to large rivers, e.g. the Indus, which flows over a variety of lithological units under a variety of climatic conditions, therefore, the behavior of natural processes is rather complex. To understand the natural processes in relatively simplistic but comprehensive manner, a west flowing and comparatively smaller river—the Mahi River has therefore been identified to understand the role of natural earth-surface processes. The Mahi is flowing in central part of western India; it originates in the western Vindhyan mountains in the state of Madhya Pradesh and starts flowing through Rajasthan and Gujarat states before joining the Cambay Bay. The overall drainage area of the Mahi River is 34,842 km2. The hydrogeochemistry of the Mahi River water suggests that the water is slightly acidic to alkaline in nature. Na+ and Ca2+ are the major cations, and \( {\text{HCO}}_{3}^{ - } \) and CI− are the dominant anions. Rock weathering is largely controlling the water chemistry; however, anthropogenic and marine sources contributions are rather meager (Sharma et al. 2012). The Mahi basin sediments fall under the litharenite category and composed of quartz, basalt fragments, pyroxene, biotite, and feldspar with little calcite, smectite, and illite. The overall composition of the bulk Mahi sediments suggests ~70–75% contribution from the Deccan basalts and ~25–30% contribution from the biotite-rich granitoids from the upland Aravalli ranges (Sharma et al. 2013). Biologically, the Mahi River basin is dominated by the bottom-dwelling pinnate forms of diatoms over the floating centric forms suggesting control of physicochemical conditions in determining the diatom distribution (Sharma et al. 2011).