Watersheds and Their Characteristics

Watersheds

• Definition: Area of land that drains into a specific water body (stream, river, lake, wetland).

Characteristics of a Watershed

• Key Factors:
  • Area: Watershed size can range from a few hectares to thousands (e.g., Mississippi River encompasses one-third of the U.S.).
  • Length: Measured along the main flow of water; longer length increases travel time to the outlet.
  • Slope:
  • Gentle slopes = slow water movement and low erosion.
  • Steep slopes = faster water movement, resulting in substantial erosion (e.g., landslides).
  • Soil Type:
  • Sandy soils allow rapid permeability.
  • Clay soils result in surface runoff as they are less permeable.
  • Vegetation Type:
  • Plants stabilize soil and facilitate water percolation.
  • Removal of vegetation increases erosion and runoff, negatively impacting water quality.

Human Impacts on Watersheds

• Alterations: Building dams, increased impermeable surfaces, mining activities.
• Case Studies:
  • Hubbard Brook Watersheds: Studied the effects of logging; increased nitrates in water after tree removal led to algal blooms and ecological disruption.
  • Chesapeake Bay Watershed:
  • Large area (17 million hectares) with diverse human activities.
  • Receives pollutants (pesticides, nitrogen, phosphorus) contributing to algal blooms and dead zones.
  • Annual nutrient inputs significantly affect the ecosystem, showcasing the need for integrated watershed management.

Summary of Findings

• Understanding watersheds reveals the interconnectedness of land use and water quality.
• Restoration efforts (e.g., vegetation cover) are crucial for mitigating human impact.