Life forms present – certain species require very clean water (trout), or others such as clams or cattails can be chemically analyzed for chemicals, metals, pesticides)
Point sources are specific locations such as sewer discharges. In most developed countries, these discharges are regulated, but in most undeveloped countries, that are uncontrolled.
Non-point sources cannot be traced to a specific discharge site. Usually coming from large land areas or “airsheds” that pollute large areas. In US, non-pt pollution is estimated to account for about 60% of pollutants entering lakes and streams.
Interesting stat – 25% of people in developing countries do NOT have access to clean drinking water. Also some frightening stats about China, Russia, Africa.
14-6 Pollution of streams, lakes, aquifers
flowing stream exhibits an oxygen sag curve
no major oxygen demand upstream of pollution source, but downstream, DO is pulled out of water by aerobic bacteria feeding upon the water. Organisms requiring DO can not survive, so other “trash fish” predominate in the decomposition zone. After this comes the septic zone, which supports little life because there is so little DO. Beyond this is a recovery zone, where trash fish come back, and finally back to a clean zone.
Lakes are even more vulnerable to contamination, mostly because they don’t flow, so clean water doesn’t come in quickly to dilute pollutants
Nutrient enrichment causes eutrophication of lakes, a loss of oxygen. Nutrients cause algae to grow. Algae use up oxygen during respiration at night, and they also are decomposed by aerobic bacteria when they die, which also uses up DO.
Once the DO is depleted, anaerobic bacteria will take over the job of decomposing the algae, but with byproducts including H2S, and CH4, both dangerous gases.
Groundwater pollution is also a serious problem
GW is not cleaned up as readily as surface water, because flow rates are very slow (1 foot per day is FAST) and there are less bacteria to decompose waste.
Some stats suggest that 25% of usable GW in US is contaminated (Miller claims that every major aquifer in NJ is contaminated)