4.6 watersheds

watershed

all land that drains into particular body of water

stream, river, lake, wetland

runoff

surface water from rainfall, snowfall, etc. that didn’t infiltrate or percolate through ground/ evaporate

watershed

aka basin or catchment

everyone lives in watershed

drainage divide

elevated terrain that separates neighboring watersheds

rugged, hilly land drainage divide is along RIDGELINE or TOPOGRAPHICAL RIDGES

vegetation, soil composition, slope

__, __, __ play role in how watershed drains

vegetation cover

more vegetation cover slows flow of water, increases infiltration and groundwater recharge

reduces flooding

vegetation

retains nutrient in soils, protects against soil erosion

slope/topography

slope is greater → velocity of runoff is greater

reduces infiltration + increases erosion

soil type

sandy soils = more permeable → reduce flood risk by increase infiltration/ reduce runoff

clay soils = impermeable → contributes to flood volumes bc less infiltration/ more runoff

clearcutting

causes soil erosion and increased soil/stream temperature on watershed

soil erosion

• caused by loss of stabilizing root structure

• removes soil organic matter + nutrients from forest

• deposits sediments in local streams (warms water and makes 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 river/stream → increase water temperature

  • erosion of sediments into rivers also warms river

chesapeake bay watershed

6 state region that drains into streams/rivers → chesapeake bay

mix of fresh/salt water + nutrients in sediment make estruary habitats like salt marshes HIGHLY productive

cultural ecosystem service

tourism revenue - hotels, restaurants, permits

provisioning ecosystem service

food - crabs and fish

regulating ecosystem service

water filtration - grass roots trap pollutants

storm protection - absorb excess flood waters

supporting

habitats - maintain biodiversity

human impact on chesapeake bay

nutrient pollution of N and P leads to eutrophication

algae bloom → decreased sunlight → plants die → bacteria use up oxygen for decomposition → hypoxia → dead zone

major N/P sources

discharge from sewage treatment (N and P from human waste)

animal waste from concentrated animal feeding operations (CAFOS)

synthetic fertilizers from agriculture fields & lawns

other major pollutants

endocrine disruptors - sewage treatment

sediment pollution - deforestation, urbanization, tilling agriculture fields

• increases turbidity (reduced photosynthesis) and covers over rocky stream bed habitats

precipitation

water that falls onto earth as rain or snow, flows into streams and gets absorbed by plants to soak into their roots

headwater

place where stream begins, usually highest point

tributaries

streams that flow into one another to make larger stream which makes river

floodplain

area thats easily flooded when river or stream overflows

estuary

where river meets ocean and freshwater and saltwater mixes

ridgeline

top edge of mountain that divides one watershed from another