| Virginia's Water Quality |
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| A Primer and Toolkit for Virginia's Citizens | ||
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This Section Contains the Following InformationWhat are the threats to Water Quality Within A Watershed?
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A Day in the Life of a WatershedThe purpose of this section is to define watersheds, why we care about watersheds and what watersheds have to do with water quality in our streams and rivers.
The land area through which water flows and drains to the lowest point, in a stream, river, lake or estuary, is known as a watershed. Watersheds collect precipitation and accumulate water into “flows” that course across the landscape. Streams start as a trickle of water and go downhill, gathering more water as they go, then join with other streams to form a larger river. A watershed may be large or small, may occupy sloping, mountainous or nearly flat terrain and cover many landscapes, including forests, farmland, small towns and cities. Watersheds include not only the waterway itself but also the entire land area that drains to it. Watersheds are natural boundaries without regard for political boundaries or communities. Watersheds are also nested – small watersheds are within larger watersheds; the land that drains to the small stream is the stream's watershed, the stream drains into a river and so joins the rest of the land draining to the river in the river's watershed, and so on.
Why should we care about our watersheds? We all live in a watershed. Watersheds are the places we call home, where we work and where we play. Everyone relies on water and other natural resources to exist. What you and others do on the land impacts the quality and quantity of water and our other natural resources. Human activities in a watershed eventually affect the water quality downstream. Healthy watersheds are vital for a healthy environment and economy. Our watersheds provide water for drinking, irrigation and industry. Many people also enjoy lakes and streams for their beauty and for boating, fishing and swimming. Wildlife also needs healthy watersheds for food and shelter.
What are the threats within watersheds that can impact water quality? All activities within the watershed have an impact on its natural resources. Cities, homes, roads and factories modify the watershed and affect its natural resources. Farming, recreation, mining, construction and forestry can also significantly affect a watershed. There are six major types of pollutants:
Materials that are necessary for plant growth, primarily forms of nitrogen or phosphorus, are known as nutrients. When too many nutrients end up in an aquatic system, they alter the natural plant community and can cause massive plant growth known as algal “blooms” which deplete oxygen concentrations in the water. Excess nitrates in drinking water have been linked to human health problems, including heart conditions and birth defects. Dirt and sand are natural substances that become pollutants when they end up in the water in excessive quantities. Sediment changes the shape of streambeds, smothers feeding and nursery areas of aquatic animals, and carries other pollutants into the water. Erosion from poorly managed construction sites, agricultural fields, or suburban gardens are major sources of sediment pollution. Another major source is road sand applied to improve winter driving conditions. Non-degradable trash, mostly plastic, when carelessly disposed of, will often end up in a nearby water body. Humans find it ugly, as well as hazardous when it entangles boat propellers. Aquatic animals can also become entangled, or mistake plastic for food, and strangle or starve. Pathogens are the bacteria and viruses that cause disease. They generally come from fecal material from humans and their pets, or from wild animals and birds. When the potential concentration of pathogens in the water exceeds certain limits, areas must be closed to shellfishing or swimming in order to prevent infections or disease outbreaks. Major sources of pathogens include: failing septic systems, leaky sewer lines, and concentrations of animal waste from pets, farm animals or wildlife. Many of the tens of thousands of chemicals in use today are harmful to both humans and aquatic organisms. Some of these chemicals can be passed through the food chain and concentrate in top predators (like humans). Extremely small concentrations of some toxic materials in the water can kill the eggs and larvae of many animals. Sources of toxic contaminants range from the exhaust and fluids that come from automobiles to the cleaning and disinfectant products used in homes to the pesticides used in yards, farms and parks. During summer months, thermal pollution can make the water in critical aquatic habitats too warm for sensitive native plants and animals to survive, as well as allowing the spread of non-native species. Overheated water can result from the removal of vegetation that shaded the stream, runoff from hot roofs and parking lots, or the collection of water in shallow unshaded ponds.
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