4.6 - Watersheds

Question 1

Watersheds

Answer 1

• All of the land that drains into a specific body of water (river, lake, bay, etc.)
• Determined by slope; ridges of land divide watersheds (diff. runoff directions)
• Vegetation, soil composition, slope play a large role in how watersheds drain
  - More vegetation = more infiltration & groundwater recharge
  - Greater slope = faster velocity of runoff & more soil erosion
  - Soil permeability determines runoff vs. infiltration rates
• Human activities of a watershed impact H2O quality
  - Ex: ag, clearcutting, urbanization, dams, mining

Question 2

Chesapeake Bay Watershed

Answer 2

• 6 state region that drains into a series of streams/rivers & eventually into Chesapeake Bay
• Mix of fresh & salt water + nutrients in sediment make estuary habitats like the salt marshes in the bay highly productive
• Estuaries & wetlands provide ecosystem services:
  - Tourism revenue - hotels, restaurants, permits
  - Water filtration (grass roots trap pollutants)
  - Habitats for food sources (fish & crabs)
  - Storm protection (absorbing & buffering floods)

Question 3

Human Impacts on Chesapeake Bay

Answer 3

• Nutrient pollution (N & P) leads to eutrophication in the Bay
• Algae bloom due to increase of N/P → decreased sunlight → plants below surface die → bacteria use up O2 for decomp. → hypoxia (low O2) & dead zones
• Major N/P sources:
  - Discharge from sewage treatment plants (N/P levels from human waste)
  - Animal waste from CAFOS
  - Synthetic fertilizer from ag. fields & lawns
• Other major pollutants:
  - Endocrine disruptors (from sewage treatment)
  - Sediment pollution (deforestation, urbanization, tilling ag. fields)
  - Increases turbidity (reduced photosynth) & covers over rocky streambed habitats

Question 4

Direct Effects of Clearcutting

Answer 4

Soil Erosion
- Caused by loss of stabilizing root structure
- Removes soil organic matter & nutrients from forest
- Deposits sediments in local streams
- Warms water & makes it more turbid (cloudy)

Increased soil and stream temperature
- Loss of tree shade increases soil temperature
- Soil has lower albedo than leaves of trees
- Loss of tree shade along rivers & streams warms them
- Erosion of sediments into rivers also warms them

Question 5

Solutions to Watershed Pollutants

Answer 5

• Cover crops absorb the nutrients that are not needed
• Riparian buffers prevent runoff
• Septic Tank Upgrades have a drain field that nutrients are filtered and purified before entering the soil and groundwater