Sediment and Temperature:
Excessive fine sediment, common in storm water runoff, may impact stream systems in several ways:
- Filling in the stream channel and thus reducing the number and depth of pools and complexity of stream habitat features;
- Creating a shallower stream environment that is more susceptible to increased temperature;
- Increasing nutrient loading, shallow pools, impaired flows, all of which contribute to nuisance algal conditions; and
- Smothering of spawning gravels and benthic macroinvertebrate communities.
Natural peak flows may be beneficial to stream systems by transporting sediment and promoting deeper pools with cooler water. Storm water flows however, may directly impact the natural temperature regime of receiving waters by changing the channel morphology and altering the temperature of the natural flows. Often, runoff from developed areas is much warmer than the receiving water, which can lead to temperature stress in many cold water aquatic species. For example, increased runoff from impervious surfaces, such as paved areas and rooftops, may increase the temperature of receiving waters.
The impact of warmer flows can also be less direct. For example, they can cause the stream to have less dissolved oxygen because warmer water has a lower oxygen saturation potential and, therefore, lower dissolved oxygen. These temperature changes can impact the biotic community within an aquatic ecosystem. Additionally, stream and aquatic ecosystems may already be stressed in summer due to lack of vegetated cover and lack of groundwater infiltration.
Pathogens such as bacteria, viruses, and protozoa are naturally occurring in soil and water, as well as in the gastrointestinal tracks of animals and humans. Some waterborne pathogens can cause human illnesses, ranging from typhoid and dysentery to minor skin diseases. These pathogens may enter waters through a number of routes, including inadequately treated sewage from improperly maintained onsite water treatment systems, storm water drains, malfunctioning septic systems, runoff from livestock pens, pastures or feedlots, illicit discharges from private drains, and sewage dumped overboard from recreational boats.
Because it is impossible to test waters for every possible disease-causing organism, regulatory agencies usually measure e. coli indicator bacteria which are found in great numbers in the stomachs of warm blooded animals. The presence of these indicator bacteria suggests that the water body may be contaminated with untreated sewage and that other, more dangerous organisms may also be present. Bacterial criteria are frequently used to determine if waters at beaches, rivers, creeks, estuaries, lagoons, and marinas are safe for contact recreation or for shellfish harvesting. Epidemiological studies indicate a causal relationship between recreational water quality, as measured by bacterial indicator densities, and adverse health effects.
pH is the standard measure of the concentration of hydrogen ions in a liquid. A pH value of 7 represents a neutral condition; a low pH value (less than 5) indicates acidic conditions; and a high pH (greater than 9) indicates alkaline conditions. Many biological processes, such as reproduction, cannot take place in acidic or alkaline waters. Differences in pH levels, therefore, contribute to shifts in composition of aquatic species that are a primary component of beneficial use. Acidic conditions also aggravate toxic contamination problems because sediments release toxicants in acidic waters. Common sources of acidity include mine drainage, runoff from mine tailings, and atmospheric deposition.
Low Dissolved Oxygen:
Dissolved oxygen is a basic requirement for a healthy aquatic ecosystem. Most fish and beneficial aquatic insects “breathe” oxygen dissolved in the water column. Some fish and aquatic organisms are adapted to low oxygen conditions, but most desirable fish species suffer if dissolved oxygen concentrations fall below 3 to 4 mg/L. Larvae and juvenile fish are more sensitive and require even higher concentrations of dissolved oxygen. Many fish and other aquatic organisms can recover from short periods of low dissolved oxygen availability, but prolonged episodes of depressed dissolved oxygen concentrations of 2 mg/L or less can result in complete loss of fish and other desirable aquatic life. Oxygen concentrations in the water column fluctuate under natural conditions, but severe depletion usually results from human activities that introduce large quantities of biodegradable organic materials into surface waters. In these polluted waters, bacterial degradation of organic materials can result in a net decline in oxygen concentrations in the water. Oxygen depletion can also result from chemical oxygen demand, chemical reactions of inert organic matter that is not biologically available for use by organisms. Other factors (such as temperature and salinity) influence the amount of oxygen dissolved in water. Prolonged hot weather can warm water, which will depress oxygen concentrations (because warm water cannot hold as much oxygen as cold water) and may cause fish kills, even in clean waters.
Low Dissolved Oxygen Resources:
Like many environmental pollutants, mercury bioaccumulates, leading to toxic levels within organisms such as fish. This effect is compounded the longer an organism lives. Mercury accumulates specifically in the muscle tissue of fish, so it cannot be filleted or cooked out of consumable game fish.
Various forms of mercury can be converted from one to another, including methylmercury, which is the most toxic form. Studies have shown that bacteria that process sulfate in the environment take up mercury in its inorganic form, and through metabolic processes, convert it to methylmercury. The conversion of inorganic mercury to methylmercury is important for two reasons: (1) methylmercury is much more toxic than inorganic mercury, and (2) organisms require considerably longer to eliminate methylmercury. During this time, the methylmercury-containing bacteria may be consumed by an organism that is higher in the food chain, or the bacteria may release the methylmercury into the water, where it can quickly adsorb to plankton, which are also consumed by organisms higher in the food chain. High levels of acidity (decreasing pH) and dissolved organic carbon enhance the mobility of mercury in the aquatic environment, making it more likely to enter the food chain.
Urban runoff, atmospheric deposition, alkali and metal processing, incineration of coal, and mining of gold and mercury contribute greatly to mercury concentrations in some areas, but in the Russian River watershed, geologic sources predominate. Natural sources of atmospheric mercury include volcanoes, geologic deposits of mercury, and volatilization from the ocean. All sediments, water, soils and many rocks naturally contain small but varying amounts of mercury, and scientists have found some local mineral occurrences and thermal springs that are naturally high in mercury. Other sources of mercury include compact fluorescent light bulbs, older thermometers, dental “silver” fillings, and some types of batteries.
Organic nitrogen (nitrogen combined with carbon) is found in proteins and other compounds. Inorganic nitrogen may exist in its free state as a gas, as ammonia (when combined with hydrogen), or as nitrite or nitrate (when combined with oxygen). Nitrites and nitrates are produced naturally as part of the nitrogen cycle, when bacteria break down toxic ammonia wastes first into nitrite, and then into nitrate.
Excess nitrogen in stormwater occurs as ammonia and nitrates, which are biostimulatory substances that can cause or contribute to eutrophism. In eutrophism, algae and water weeds become too stimulated by the excess nitrogen, thus choking the waterway and using up large amounts of oxygen. This, consequently, will kill off fish and other aquatic organisms. Nitrate is a major ingredient of farm fertilizer. Runoff due to rainfall or excessive irrigation can wash nitrate from the fertilized land (i.e. landscaped areas, farmland) into nearby waterways. Nitrates also get into waterways from leaking septic tanks and cesspools, manure from farm livestock, animal wastes (including fish and birds), and discharges from car exhaust. Ammonia – a product of decay of dead organisms – is highly toxic to fish and other aquatic life.
Phosphorous is a necessary element for plant and animal growth. Most fertilizers contain phosphates (a chemical compound containing the element) which can be washed into waterways. Other sources include pesticides, industry, cleaning compounds, solid or liquid wastes, and phosphate-containing rocks. Phosphates also are used widely in power plant boilers to prevent corrosion and the formation of scale. Phosphates enter waterways from human and animal wastes (the human body releases about a pound of phosphorus per year), phosphate-rich rocks, wastes from laundries, cleaning and industrial processes, and farm fertilizers. If too much phosphate is present, eutrophism can occur, killing off fish and other aquatic organisms.
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