Pollution discharged over a wide land area, not from one specific location. These are forms of diffuse pollution caused by sediment, nutrients, organic and toxic substances originating from land-use activities, which are carried to lakes and streams by surface runoff. Non-point source pollution is contamination that occurs when rainwater, snow melt or irrigation washes off plowed fields, city streets or suburban backyards. As this runoff moves across the land surface, it picks up soil particles and pollutants such as nutrients and pesticides. If more oxygen is consumed than is produced, dissolved oxygen levels decline and some sensitive animals may move away, weaken, or die. .
Cold water holds more oxygen than warm water and water holds less oxygen at higher altitudes.
Also, the sustained extraction of groundwater from an aquifer at a rate greater than the recharge rate of the aquifer, resulting in a drop in the level of the water table. The ability of a material to allow the passage of a liquid, such as water, through rocks. Permeable materials, such as gravel and sand, allow water to move quickly through them, whereas impermeable material, such as clay, does not allow water to flow freely. Perchlorate is an oxidizer used in the production of rocket fuel. A shorthand designation for the concentration of hydronium or hydrogen ions in a solution, defined as the negative log of the concentration of hydronium ions.