Land use
The health of a watershed can be related to a line of dominoes or a pebble thrown into a pool of water. When even one is pushed over a little bit, a chain reaction can start, collapsing the entire line. The pebble only impacts one area in the pool, but the ripples from the pebble hitting the water reach outward, effecting the entire pool. Every factor in a watershed is a domino and changing one or two can have far reaching effects. Realizing this interconnectedness can make it easier to understand the multiple impacts that various land uses can have on a watershed.
Industry
General industry
Any general industry can have a number of impacts on the watershed. Construction activities are a major change in the watershed. Not only does the placement of a building change run-off patterns and filtration areas, the heavy machinery needed takes its own toll by compacting the soil. Parking lots and roads create impervious surfaces that prevent percolation of water into the ground and increase run-off. There may also be factory discharge to be treated prior to its release into the environment. If the flow or temperature of this discharge is too great, there may also be impacts on the stream.
Extractive Industry
The most common extractive industry in Pennsylvania by far is coal mining. Legislative acts such as SMCRA have been passed to control and prevent current mining operations from impacting watersheds too adversely. Unfortunately, this does not touch the problem of the abandoned mines that contaminate our state's water supply. Abandoned mines collect groundwater which eventually seeps out of the mine at a lower pH and carrying toxic minerals. AMD is the number one source of NPS (non-point source pollution) in PA. Other problems, arise from surface mines which may act as sponges. these areas trap and hold water, releasing it a a much slower rate than usual. Erosion and sedimentation are also prominent problems associated it surface mining.
Other extractive industries include oil and natural gas removal. The construction of these wells often results in the collection of brine (salt water). Unless brine is handled correctly, it can seep into the watershed, contaminating the freshwater with high salt concentrations. In some streams, salt concentrations have been found to be higher than those found in the oceans! this waste water is often collected and spread over roads to decrease dust and stabilized roads. The Oil and Gas Act of 1984 is taking steps to control the collection and disposal of brine and other extraction wastes.
Agriculture
Agriculture effects the watershed in two very big ways: increasing erosion and increasing nutrients. Erosion is common from field run-off is crops aren't properly planted to minimize water flow. It is also possible that the crop may not have a root system particularly suited to preventing erosion. Corn is a necessary crop, but one of the most prone to erosion due to the tall, thin nature of the stocks and its characteristic root system. livestock also contribute to erosion by trampling stream banks that run through pastures. Fencing around these streams makes watering the animals more difficult, but is very effective in reducing erosion.'
Nutrient pollution is also a problem. Fertilizer run-off from field crops is very common. Livestock also tend to increase nutrients in streams if allowed free access. The extra nutrients may not seem to be harmful, but can have devastating effects. Excess nitrogen can lead to algae blooms which remove all of the oxygen from an area of aquatic habitat. the organisms in this habitat suffer massive deaths and losses due to the lack of oxygen. Once the water is circulated and oxygen concentrations rise, it is possible to repopulate the area. unfortunately the massive kill has already occurred. Preventing or reducing nutrient can have a significant effect in reducing the number of fish kills and loss of aquatic organisms.
Residential
Many of the effects of residential areas are the same as general industry: changes in run-off patterns, the addition of impervious surfaces. Residential areas do have the added danger of septic systems. Leaks and discharges from septic treatment plants can cause nutrient pollution in the watershed.
Recreational
Parks and recreational areas are a wonderful tourist attraction and great for relaxation. To truly get the most out of recreational facilities, though, they must be maintained and cared for. Campers and other outdoor recreationists leave their own marks on nature. The is often evidence of nutrient pollution around campsites. There can also be effects on vegetation from constant hiking.
Forestry
Proper forestry stewardship is essential to maintaining watershed health. Most of Pennsylvania's stream miles run through forested lands. These are the healthiest stream areas in the state. Forests serve to control erosion and nutrient leaching into the water. Trees are impart parts of a riparian buffer zone. Improper practices such as clear cutting (removing all of the trees) on a hill side or only leaving a few small trees can greatly increase erosion. There is also an increase in erosion from the presence of logging roads need to transport machinery into the forest and wood out.
The effects of timber harvesting can be decreased by following BMP's (best management practices). This is a list of guidelines designed to reduce the impact of harvesting on water quality.
Wildlife
Wildlife are an important part of the ecosystem and play their own part in
the maintenance of the watershed. It is important to recognize that
wildlife habitat must be preserved, not only for its filtering capacity, but
for its habitat value. Many reclamation projects have the added
benefit of providing additional wildlife habitat while rehabilitating the
watershed.