Potential Impacts to Water Systems
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POINT SOURCE POLLUTION: Discharge pollutants at specific locations through pipes, ditches or sewers into bodies of water. Includes a wide range of organic and inorganic substances, including chemical spills, oil spills, illegal dumping of debris and discharge from wastewater treatment facilities, at which the source of entry into the water column can be accurately pinpointed. Typically, this type of pollution results from the wastes or byproducts of public and private commercial facilities, which are purposely deposited into the water column and eventually into our estuaries.
NONPOINT SOURCE POLLUTION: Sources that cannot be traced to any single site of discharge; usually large runoff areas, subsurface flow or deposition from the atmosphere. Includes a wide range of organic and inorganic substances, sediments, toxic chemicals, petroleum products and bacteria, in which the exact point of entry into the water column cannot be determined. Generally, NPS is created through everyday occurrences in places where pavement, sidewalks, agricultural fields and flattened lawns have been constructed and where naturally occurring porous landscapes once existed. When precipitation falls, these substances are mixed into storm water and eventually make their way into estuaries. The concentration of NPS may be sufficient to significantly affect estuarine water quality and cause habitat destruction.
ALTERED FRESHWATER INFLOWS: Manmade structures like dams and water diversion facilities, which capture water for use in homes, businesses, and agriculture, reduce the natural flow of freshwater that is available for use in estuaries. Reduced freshwater inflow results in higher saline environments, reduced sediment flows, lower nutrient levels, and increased coastal erosion.
DROUGHT: The overall impacts which arise from reductions of freshwater inflow to estuaries (such as dams and reservoirs) are increased by the natural tendency for some weather patterns to produce below normal levels of precipitation.
DEVELOPMENT: Land development and the conversion of land for agricultural purposes reduce the total water holding capacity of a watershed and increases habitat loss. Large accumulations of water from heavy rainfall may rush into and through a watershed, thereby reducing its natural ability to hold and slowly release water. The resulting floods may cause millions of dollars in damage.
DREDGING: Dredging is the digging of channels through shallow bodies of water to allow the passage of larger ships and boats than would otherwise be naturally possible. Local examples of dredged channels include the Gulf Intracoastal Waterway (GIWW) which runs along the coastline of the Gulf of Mexico, the Corpus Christi ship channel, and the Aransas ship channel. These channels serve as transit systems for both industry and private use. Private citizens use these channels as a means of getting from one place to another for recreation. Industry uses channels to haul cargo including oil, grain, and industrial supplies. Dredging is necessary for the economy of the Coastal Bend because these channels enable a less expensive, efficient, and safer method of transportation for goods and supplies.
Channels dug by large ships called "dredges" remove bottom sediment, which may be stored in its hull or piped (in a water suspended state) to adjacent areas. Sediment removed by this process may be used to create "dredge material islands". Sometimes these materials are deposited back into the water in adjacent areas where they spread out with the aid of natural water circulation patterns. Dredge material islands can be seen as small linear islands along the Laguna Madre. Over a period of time, these islands become vegetated and provide nesting and roosting areas for shorebirds. However, dredging can also create problems for the plants and animals that inhabit our estuaries. Here are some potential impacts to estuaries as a result of dredging:
- Destruction of Seagrass Beds: Large amounts of dredge material deposited on certain areas of our estuaries can bury seagrass beds and the organisms that live in them. Increased turbidity resulting from dredging causes reductions in light penetration and the ability of seagrass to photosynthesize.
- Destruction of Oyster Beds: Large amounts of dredge material deposited on or near oyster beds cause clogging in the siphons of oysters reducing their ability to feed and may eventually cause death.
- Resuspension of Toxic Materials: Materials which are toxic to humans and wildlife and have been contained in bottom sediments can become resuspended in the water column as a result of dredging.
- Increased Water Flow: The flow of water in dredge channels is much greater than in the surrounding shallow areas. Fish and other animals may benefit from these deeper areas by using them as a means to escape shallow areas which become too hot or cold or contain low levels of dissolved oxygen. However, increased water flow in contact with channel sediments also elevates turbidity levels.
