Lecture 3; HUman impacts on freshwater systems Flashcards
Name some threats to freshwater systems (4)
- demands for water and energy
- demand for space
- pollution
- exploitation of species
What are the main uses of water?
- public and private water supply
- agricultural
- electricity
- fish farming
What are the reasons for channel modification?
- flood control
- navigation
- urbanization
- relocation
- prevention of erosion
How do modified channels vary from natural channels in shape and size?
- straightened
- shortened
- increased slope
How do modified channels vary from natural channels in riffle/pool structure?
loss of riffle/pool structure
- mainly shallow riffle run
How do modified channels vary from natural channels in the banks?
- reduced erosion/deposition
- loss of undercut banks
How does modifying channels affect the diversity of species?
loss of heterogeneity of habitats, more simple systems so a lack of species diversity
What is water pollution?
a contaminant of river water that causes potential harm to human health or well-being
Name the 4 main sources of river pollutants
- urban wastewater
- agricultural wastes
- industrial wastes
- transport systems
Name some organism compounds which act as substrate for microorganisms?
- proteins
- carbohydrates
- fats
What is the standard test to determine amount of oxygen consumed by microorganisms in decomposing organic matter?
- oxygen consumed over a 5 day period at 20C
why is it tested over a 5 dya period?
it take 5 days for water to travel from headwaters to the sources
what is CSO and when does it occur?
a combined sewer overflow when there is heavy rainfall, sewers go over the capcity and flow directly into river system
BOD?
Biological oxygen demand
what is the BOD of natural rivers?
<10mg/l
what is the BOD of raw sewage?
200-800 mg/l
what is BOD of treated sewage?
10-50 mg/l (not a problem)
Name 3 sources of organic waste?
- domestic sewage
- industrial;
- agricultural
impact of the breakdown of organic material?
- reduction in DO
what does the reduction of DO due to breakdown of organic material depend on?
- BOD of discharge
- BOD of receiving river water
- dilution
- temperature
what is the effect of a loss of riparian zone in modified channels?
- reduced CPOM & woody debris
- reduced cover for fish
- reduced shade (more variable temperatures)
Overall effects of river modification?
- loss of heterogeneity
- extremes of flow
- increased sediment inputs
- extreme temperature regime
what is outfall?
The discharge point of a waste stream into a body of stream
physical impacts of sewage outfall on sedimentation?
sediments increase, then gradually decline as they settle out downstream
