freshwater ecology - human issues

ways humans have misused water resources

• Eutrophication

• Chemical pollutants

• Acidification

• Drainage systems

• Irrigation systems

• Landfilling

• Invasive species

extinction rates

• 15% of all animal species are freshwater species (70K species)

• Extinction rate is alarming, NA freshwater mussels/clams – most at risk

  
  

what effects biodiversity the most

1. changes in land use

2. climate change

3. nitrogen deposition

why was there a rise in acidification in the 70’s

• lots of factories burn chemicals for fuel and to rid of waste products

• caused acid rain that entered freshwater ecosystems making them acidic

how does acidification occur

• production of sulphur oxides (SOx) from the burning of coal and oil in power
  stations and other industrial plants

• SOx is oxidized to sulphuric acid and once on the ground reacts with soil minerals removing bases like calcium.

• Reaction also mobilizes metals, particularly aluminum, and leaves a lot of
  hydrogen ions (protons) that run into the stream lowering the pH

direct effects of acidification

• Interferes with enzyme needed by fish embryos to break through egg
  (fail to hatch)

• Mucus is produced around the gills of adult fish (they asphyxiate)

• Crustaceans fail to form calcareous components of the exoskeleton

• Insects disappear

• Aluminum accumulates in invertebrates and then further in
  insectivorous birds (interferes with eggshell formation)

indirect effects of acidification on fish

• fish have less fat deposits

• makes them thin

• due to food source dying off

US response to acidification

• Clean air act (1990)

• Environmental Protection Act (1995)

Clean air act

• Dramatically reduced emissions of sulfur dioxide and oxides of nitrogen

• by 2005, emissions for SO2 were 41% below 1980 levels (used a market-based cap and trade approach)

• Plants are given “allowances” and are worth one ton of SO2 emissions from
  their smokestacks...can buy allowances

Environmental protection act

• Required emitters to reduce emissions by permanently limiting to levels set in
  the 1990 CAA.

• Provides bonus allowances to plants installing clean coal technology or using
  renewable energy

  
  
  
  

how else might stream chemistry be altered

• hurricanes

• logging

• drought

• deforestation

• ice storms

what is considered a water pollutant

• Can be anything from nutrients to microplastics to chemicals

• The level or amount of a substance is usually considered (particularly in reference to background concentrations)

  
  
  
  

point vs non-point water pollution

• point source: originates from a single identifiable source

• nonpoint: diffuse sources that are hard to trace

examples of point source pollution

• waste water treatment plants

• mines

• thermoelectric plants

• hospitals

• leaks in sewage system

• pulp mills

• manufacturing plants

• landfills/ waste dumps

where is waste water held (before treatment)

• piles

• pits

• septic tanks

• lagoons

primary wastewater treatment

1. raw sewage run through screens

2. comminutor breaks down raw sewage more

3. goes through grit chamber to separate grit from liquid and sludge

4. primary clarifier separates sludge to be treated and disposed of from effluent (liquid)

secondary wastewater treatment

1. primary effluent (liquid) sent through an aeration tank supplied by air with a compressor

2. effluent then sent to a secondary clarifier where secondary effluent is separated from activated sludge

3. secondary effluent is treated with disinfectant while activated sludge goes through a pump and sends left over effluent back to the aeration tank and the left over sludge to sludge treatment and disposal

4. disinfected secondary effluent is either sent to tertiary treatment or discharged to surface water

what type of sewage system did winnipeg have pre-1960’s

• combined sewage system - water from housing and overland runoff treated together

• overflow from heavy rain and snow causes sewage to enter river

what type of sewage system does winnipeg have now

• separate sewer system - rainwater runoff caught in storm sewer sent to river while household wastewater sent to treatment plant

what human activities cause mercury to enter freshwater ecosystems

• historic mining particularly in mountainous regions where silver and gold are mined

• direct mercury production by mining cinnabar

• indirect mercury production from mine spoils (mercury used to recover gold and silver)

• Flooding of reservoirs and burning of fossil fuels also increase the amount
  of inorganic mercury in the environment

how does mercury bioaccumulate in freshwater ecosystems

• Microbes in aquatic environments and in soil react with inorganic
  mercury and methylate it (add a methyl group (CH3-) to mercury
  ion

• this form of mercury can then be taken in by fish and other organisms causing it to bioaccumulate

negative impacts of methyl mercury

• Acute exposure at high levels has neurotoxic effects and can cause
  death

• Also linked to developmental deficits in children

• accumulates lots in large fish (that humans eat)

mercury case study on the American dipper

• heavy mining near bird habitat

• eggs and nestling feathers collected

• larval forms of 3 aquatic macroinvertebrates collected

• 3 sites studied: 1 cinnabar mining, 1 gold mining, 1 no mining

• no impact b/c levels of methylmercury were low

water diversion

Capturing and re-directing water flow for human-use

why does agricultural irrigation have so much impact on freshwater ecosystems

• Arid and semi-arid ecosystems require water to be productive

• 70% of freshwater used by humans is for agricultural irrigation

• Most dryland rivers experience extensive diversion or groundwater use

• great plains (25% of world’s grains)

impacts of irrigation on great plain streams

• Require groundwater because snowmelt runoff is low

• Groundwater mining has resulted in stream habitat fragmentation and loss

• Most important factors causing population declines in aquatic ecosystems

impact of stream fragmentation on fish

• disrupt fish populations

• restrict genetics because cannot breed with each other

restoration ecology

• Returning headwaters to exact former ecosystem

• impossible

why is restoration impossible

• former ecosystem existed previously with low human populations and low impact technologies

• some components of the former ecosystem may be extinct

• no exact instructions in how to exactly replicate former ecosystem

rehabilitation ecology

the recreation of a semi-natural system that resembles the
natural ones but is inevitably not the same and is more limited in scope

examples of rehabilitation techniques fir stream ecology

• Straightening stream

• Gravel can be dumped to create new riffles

• Remove small dams and weirs

• Restock native fish

• Control invasive species

• Dig side channels for fish habitat

• contour ploughing

• keeping livestock from streams (fences)

  
  
  
  

landscape changes required for rehabilitation

• Reducing nutrient loss from land

• Water treatment

• Agricultural fields need management

• Restore connectivity

way to manage agriculture

• Recover manure quickly and spread on fields

• Drain into fields rather into waterways

• Minimize use of additional fertilizers

• Plough fields along contours rather than across them

• Leave wide strips of grassland within ploughed land

• Use buffer zones to absorb phosphate and denitrify nitrogen