Which of the following is/are the possible consequence/s of heavy sand mining in riverbeds ? 1. Decreased salinity in the river 2. Pollution of groundwater 3. Lowering of the water-table Select the correct answer using the code given below :

Lists factors controlling surface salinity, explicitly naming freshwater flow from rivers as a major influence on coastal salinity.

A student could check whether sand mining changes river freshwater discharge or the relative freshwater input to a coastal/estuarine zone to infer likely salinity change.

States surface salinity decreases with input of fresh waters (such as from rivers), giving a direct rule linking river inflow to lower salinity.

Use local data on river fresh-water volume before/after mining to see if mining reduces or increases effective fresh-water input and thus salinity.

Provides concrete examples (Bay of Bengal, Baltic, Black Sea) where large river influx lowers salinity, showing how riverine input dilutes seawater.

Compare estuaries with varying river inflow and consider whether sand mining that alters river geometry could change that diluting effect.

Describes how sand stripping deepens rivers and estuaries, enlarges mouths and alters channel bed — physical changes that can affect mixing between river and seawater.

Combine this with a map/tidal information to evaluate if deeper/enlarged estuary from mining would increase seawater intrusion (raising salinity) or alter freshwater retention.

Notes salinity is linked to density, temperature and currents, implying that changes in depth/flow or circulation (which mining can alter) affect local salinity patterns.

A student could consider whether mining-induced changes in flow or circulation would change stratification and thereby increase or decrease surface salinity.