When regulators and scientists discuss "pollutants", they generally mean substances in the water that can
cause harm to people and the environment.
The Clean Water Act of 1987 defines pollution as man-made or man-induced
alteration of the chemical, physical, biological and radiological integrity of water.
Some of these contaminants may
include metals, bacteria, nutrients, organic waste, and organic compounds.
Not only are there different types of pollutants,
but there are different ways for these substances to get into rivers, lakes ponds and the ocean:
- Point sources discharge pollution into the water from specific, identifiable locations and can usually be measured.
Examples of point sources include wastewater treatment facilities and storm sewer outfalls.
- Non-point sources contribute pollution through more scattered means such as failed septic systems, atmospheric deposition,
and runoff from construction sites. Pollutants from non-point sources are usually harder to measure and regulate.
When monitoring water quality, one of the most frequent measures we wish to take is dissolved oxygen (DO). Just as with land plants and animals, most creatures in the water need a constant adequate supply of oxygen to survive. But life in the water provides additional challenges that we do not experience on land. The air we breathe contains about 21% oxygen, and this number changes very little unless access to fresh air is completely cut off. Water can only contain relatively low concentrations of oxygen.
A river system both produces and consumes oxygen. It gains oxygen from the atmosphere and from plants as they go through photosynthesis. Running water (because of its constant mixing action) will also have a higher concentration of dissolved oxygen than still water (such as in a reservoir) will. Aquatic organisms, decomposition, and natural chemical reactions consume portions of the oxygen present in a river or lake. Effluent from wastewater treatment plants can also contain organic materials that are decomposed by microorganisms, which use oxygen to in the process. The amount of oxygen consumed by these organisms breaking down waste is called biochemical oxygen demand. This parameter is often measured in conjunction with dissolved oxygen levels. Other sources of oxygen-consuming waste include stormwater runoff from urban streets or farmland and failing septic systems.
Oxygen is measured in its dissolved form, which is the form that is utilized in an aquatic environment. If more oxygen is consumed than is being produced in an ecosystem, then aquatic organisms may weaken or die, or move to a different area. Low DO levels threaten the overall health of a waterbody.
Dissolved oxygen levels fluctuate naturally with the change of seasons. Because colder water will hold more oxygen than warm water will, lower DO levels are expected during the summer months. However, monitoring is necessary to ensure that levels are not falling below healthy standards for the river or lake being sampled.
Aquatic organisms are most vulnerable to low DO conditions during the early morning hours of hot summer days when the flow of water is low, water temperatures are high, and aquatic plants have not been producing oxygen since sunset. MORE
Fecal coliform bacteria are generally used as indicators of potential water contamination, as these bacteria are found in human and animal feces. Though not harmful themselves, fecal coliform bacteria indicate the possible presence of other pathogenic bacteria, viruses, and protozoans that line in animal and human digestive systems. The presence of these organisms can make swimming or eating shellfish harvested from contaminated waters a health risk. Because it is costly, difficult, and time-consuming to test for each pathogen organism, water is general tested for just fecal coliform. The test for fecal coliform is a quick and effective method of detecting potential threats to human health.
Sources of fecal coliform contamination include combined sewer overflow (CSO) effluent, leaching septic systems, domestic and wild animal waste contained in runoff, and storm runoff.
The Narragansett Bay Commission
is currently working on a project to end CSO discharges to Rhode Island’s urban rivers and Narragansett Bay.
MORE.
pH is a measure of how acidic or basic (alkaline) a solution is. The pH scale ranges from 0 to 14.0, where a pH of 7.0 is considered neutral. Values below 7.0 are more acidic and values above 7.0 are more basic. Testing water for pH measures the capacity of the water to neutralize acids associated with pollution.
pH is one of the primary indicators used for evaluation of surface-water quality. Most aquatic plants and animals are sensitive to pH variations. Water's pH is affected by the minerals dissolved in the water, aerosols and dust from the air, and human-made wastes as well as by plants and animals through photosynthesis and respiration. Several factors affect the pH of the water, including:
- Algal blooms
- Bacterial activity
- Water turbulence
- Chemicals flowing into the waterbody
- Sewage overflows
- Impacts from land pollution, accidental spills, and acid rain
The pH of water is critical to the survival of most aquatic plants and animals. Many species have trouble surviving if
pH levels drop under 5.0 or rise above 9.0. MORE
Ammonia (NH 3 ), nitrates (NO 3), and nitrites (NO 2) are the biologically available forms of nitrogen found in water
bodies. Nitrogen is an essential plant nutrient, but can cause significant water quality problems if found in excess.
Together with phosphorous, nitrogen in excess amounts can accelerate eutrophication, causing dramatic increases in aquatic
plant growth.
Phosphorous, like nitrogen, is an essential nutrient for the plants and animals that make up the aquatic food chain.
However, phosphorous is generally found in short supply in fresh water systems. As a result, even a modest increase in
phosphorous can trigger accelerate plant growth, algal blooms, low dissolved oxygen, and create unlivable conditions
for certain fish, invertebrates, and other creatures.
Salinity is affected by weather, especially at the surface of the water. During dry seasons, water evaporates, making salty water. When it rains, salty water is diluted by the added fresh water.
Salinity is measured as a ratio of salts to water, and is expressed in parts per thousand (ppt), which means the number of units (parts) of salts per thousand units of water. There are three main categories of salinity: fresh water (0-0.5 ppt), brackish water (partly salty, or 0.5-30 ppt), and salt water (full seawater, greater than 30 ppt).
Coastal waters are measurably more diluted than ocean water, so that the waters off the mouth of Narragansett Bay may have a salinity of only 32 ppt. The Bay is an estuary, so by definition, the waters there are further diluted, and there is a gradient of dilution from the mouth up to the head at each of the various rivers and streams that enter the Bay. Even at a single place in the estuary, salinity will fluctuate with movement of the tides, dilution by rain or snow, and mixing of the water by wind. MORE
The rates of biological and chemical processes depend on temperature. Temperature affects the oxygen content of water (oxygen levels become lower as temperature increases); the rate of photosynthesis by aquatic plants; the metabolic rates of aquatic organisms; and the sensitivity of organisms to toxic wastes, parasites, and diseases.
Causes of temperature change include weather, removal of shading streambank vegetation, impoundments (a body of water confined by a barrier, such as a dam), discharge of cooling water, urban storm water, and groundwater inflows to the stream.
Thermal pollution is a way that the temperature of water can increase. Thermal pollution is an increase in water temperature caused by adding relatively warm water to a body of water. Thermal pollution can come from stormwater running off warmed urban surfaces (streets, sidewalks, parking lots) and industries that discharge warm water from their facilities that was used to cool machinery.MORE
Turbidity is a measure of the relative clarity of water: the greater the turbidity, the murkier the water. Turbidity increases as a result of suspended solids in the water that reduce the transmission of light. Suspended solids are varied, ranging from clay, silt and plankton, to industrial wastes and sewage.
With higher levels of turbidity, water loses its ability to support a diversity of aquatic organisms. Water becomes warmer as suspended particles absorb heat from the sunlight and cause oxygen levels to fall. Remember- warm water holds less oxygen than cooler water. Photosynthesis decreases because less light penetrates the water, resulting in even further drops in oxygen levels. The combination of warmer water, less light and oxygen depletion makes it impossible for some forms of aquatic life to survive.
Suspended solids affect aquatic life in other ways as well. Suspended solids can clog fish gills, reduce growth rates, decrease resistance to disease and prevent egg and larval development. Particles of silt, clay and organic materials settle to the bottom, especially in areas of a river or stream that are slow moving. These settled particles could smother the eggs of fish and aquatic insects, as well as suffocate newly hatched insect larvae. Material that settles into the spaces between rocks makes these microhabitats unsuitable for mayfly and stonefly nymphs, caddisfly larvae and other aquatic insects living there. MORE
The velocity of a river also impacts the types of organisms that are found in the water. Some aquatic organisms need fast-flowing, highly-aerated areas, while others need quiet pools to survive. Velocity also has an affect on the water column. Fast-flowing streams will hold suspended sediments in the water column longer, while quiet, slow-moving rivers will allow suspended sediments to settle out to the bottom quickly.
Finally, velocity has an impact on the dissolved oxygen levels in a river or stream. Fast-moving sections of a river tend to have higher levels of dissolved oxygen than comparatively slower parts of a river because they are better aerated.
River or stream flow is the amount of water that moves over a designated point in a fixed period of time. This measurement is usually expressed in cubic feet per second (ft 3/s).
The flow of a river is directly related to the amount of water moving off of the watershed into the stream channel. It is a function of water volume and velocity, and is important because it has an impact on organisms living in the stream, as well as the overall water quality. Flow can affect the river’s ability to assimilate pollutants; larger, swiftly-moving streams and rivers can receive pollutants with a diminished negative effect. Smaller rivers with low flow have less of a capacity to dilute and degrade potentially harmful pollutants.
