_________ is the movement of chemical in the upper layers of soil into lower layers or into groundwater by being dissolved in water.

Leaching is the process where soluble chemical substances, nutrients, or contaminants are washed dissolved in water and move downwards through the upper layers of soil into deeper horizons or into the groundwater system.
Infiltration refers specifically to the downward entry of water into the soil surface.

Salinisation is the accumulation of water-soluble salts in the soil.

Eutrophication is the over-enrichment of water bodies with nutrients leading to excessive plant/algal growth.