Lecture 10 - (Freshwater Ecosystems) - Human Impacts on Freshwater Systems

What are some human threats to freshwater ecosystems?

• Demands for space - channelisation, flood protection = disruption between biota and the flood channel

• land use changes - agriculture, forestry, urban pollution 

  • Climate change 

How much freshwater is used for agriculture currently?

approx 70%

What are some ways channels can be modified?

flood control, erosion control, navigation, urbanisation

Give an example of why temporary relocation of channels would happen

For contamination clean up - e.g in Idaho

Why would a channel need to be permanently relocated?

Coal mining - e.g NSW in Australia

What are some characteristics of natural channels?

Rich riparian zone, high inputs of CPOM (course particulate organic matter), shading

What are characteristics of natural catchments?

• infiltration through soils

• increased storage in catchment

explain the effects of a modified channel would be straight

• increased slope

  • loss of riffle / pool structure ex

explain the impacts of reinforced banks on modified channels

• reduced erosion / deposition

  • loss of undercut banks = loss of fish habitat

explain the effects of the loss of the riparian zone for modified channels

• reduced CPOM

• reduced cover for fish

  • high temperature variability

What are the characteristics of modified urban catchments

• hard surfaces - through man made drain systems

• rapid runoff = increased flood risk

  • washes more pollution / sediment into rivers from the urban environment

What is the ‘Urban Stream Syndrome’ (Walsh, 2005)

The steeper rising limb on a hydrograph in modified catchments, due to decreased lag time from impermeable surfaces

Name types of pollutants

acids and alkalis, detergents, dissolved organic matter

• However new contaminants such as microplastics, nanomaterials etc.

describe urban waste waters as a main source of river pollutants

• combined sewer overflows - carries untreated sewage at times of high volume

• many leakages occur due to lack of investment

  • sewage contains organic material and detergents, heavy metals and emerging contaminants

describe agricultural wastes as a main source of river pollutants

• slurry, dairy washings, fertilisers etc.

• animal waste sometimes utilised for fertilising fields - yet runoff causes river pollution

  • slurry from animals = more concentrated than sewage

describe industrial waste as a main source of river pollutants

• heat pollution, oxygen depleting substances, carcinogens

  • can alter reproductive characteristics of fish

describe transport systems and impermeable surfaces as a main source of river pollutants

• road waste, de icer run off etc. 

  • many invertebrates have evolved to live without salt - so this would greatly impact them 

What is organic pollution?

organic compounds that act as a substrate for microorganisms - e.g proteins, carbohydrates, fats etc.

What is labile organic carbon (LOC)?

the portion of soil organic carbon that is easily decomposed by microorganisms, and has a short ‘turnover time’.

What is recalcitrant organic carbon (ROC)?

the stable, slow decomposing fraction of soil organic carbon, which has a slow turnover compared to LOC

What is the biochemical oxygen demand (BOD)?

the amount of oxygen comsumed by microorganisms in decomposing organic matter

• the more polluted the water = the higher the BOD demand can be

Describe the standard test to test for BOD required in water

1. Collected water sample measured for dissolved oxygen (day 0)

2. incubated in the dark for 5 days

3. dissolved oxygen measured again

4. dissolved oxygen (day 0) - dissolved oxygen (day 5) = the BOD

What are some sources of organic waste

• domestic sewage

• industrial - brewing, dairy etc.

  • agricultural - slurry, dairy washings etc.

What are the impacts of organic pollution in rivers

• reduction in dissolved oxygen

• extent of organic pollution depends on - BOD of the discharge, sensitivity of receieving river water, temperature

What does ‘The biology of Polluted Waters’ (Hynes, 1960) describe?

how water pollution affects aquatic life, and identifies how species can indicate different levels of pollution

What species can indicate sewage fungus?

algae

What is Cladophora?

‘blanket weed’ - can indicate eutrophication

• decaying algae reduce oxygen

What is tubifcidae?

red worms - contain pigment similar to haemoglobin

• thrives on abundant food and absence of predators

describe bloodworms

a non biting midge larva

• adapted to low oxygen - have pigment similar to haemoglobin

Why are fish not inherently an indicator of aquatic pollution?

• fish can easily swim away from polluted areas

What are the advantages and disadvantage of using algae for biological monitoring

advantages

• pollution tolerances well documented

• indicates eutrophication

• disadvantages

  • not useful for severe organic pollution

What are the advantages and disadvantages of using macroinvertebrates as an indicator of biological monitoring

Advantages

• long lived species - can indicate integrated pollution effects over time

• Disadvantages

  • quantitative sampling difficult

What are the advantages and disadvantages of using macrophytes for biological monitoring

advantages 

• easy to see and identify 

• disadvantages

  • responses to pollution not well documented

What are the advantages and disadvantages of using fish for biological monitoring

advantages

• ease of identification

• disadvantages

• species may migrate to avoid pollution

What are BMWP scores

biological monitoring Working party scores = way of assessing river water quality based on types of macroinvertebrates found in it

How does BMWP scores work?

1. each aquatic invertebrate is given a score 1-10 based on pollution tolerance

2. the BMWP score for a site is the sum of all the scores of the different families present

3. Higher total = cleaner water (e.g 100+ = good water quality)