NITRATES (NO 3 – )
Nitrates are water soluble. Nitrates that are found in fertilizers can remain on
fields and accumulate, leach into groundwater, or end up in surface runoff.
Nitrates can cause algal blooms in surface waters, resulting in decreased
dissolved oxygen levels. They can also contaminate drinking water supplies by
reducing the effectiveness of hemoglobin (“blue baby” syndrome), and they
contribute to acid rain by forming nitrous and nitric acid. The bacterial
decomposition of nitrogen-based fertilizers produces nitrous oxide (N 2 O), which
contributes to global warming and the depletion of stratospheric ozone.
PHOSPHATES (PO 4 3–)
Phosphates are also a component of inorganic fertilizers. However, they are not
water soluble, and they adhere to soil particles. Soil erosion contributes to the
buildup of phosphates in water supplies. Phosphate levels in water supplies are
75% higher than they were during pre-industrial times. Phosphate buildup is
more damaging in freshwater systems because it may contribute to algal blooms,
and it may also provide an advantage to certain invasive species that are more
tolerant of higher phosphate levels in the water (e.g., cattails replacing endemic
sawgrass).
Steps Involved in Algal Blooms
■ An increase in algae occurs due to increased nitrate and/or phosphate
concentrations and results in decreased light penetration and the killing off
of deeper plants and their supply of oxygen to the water.
■ The oxygen concentration decreases in the water due to the consequences
of increased material for decomposers (consumers of dissolved oxygen).
■ Lower oxygen concentrations cause fish and other aquatic organisms to
die and contaminate the water at a high rate.
■ Decaying fish and algae produce toxins in the water.MICROBIOLOGICAL
Disease-causing (pathogenic) microorganisms, such as bacteria, viruses, and
protozoa, can result in swimmers getting sick and fish and shellfish becoming
contaminated. Examples of waterborne diseases include cholera, typhoid,
shigella, polio, meningitis, and hepatitis.