LECTURE 29 - The Human Footprint Flashcards
silent spring
Rachel Carson 1962,
warned of synthetic chemicals accumulating in mammals and birs (DDT, 2,4-D, chlordane, Heptachlor etc)
–> apparent in raptors (Birds of prey) but people and other organisms were also being affected (bioaccumulation)
e.g. american bald eagle : chemicals weakened egg shells so they would break when the birds sat on it, populations of predatory birds were nose diving
toxic inputs
toxics are entering in the natural environment in increasingly big quantities
* pesticides
* manufacturing
* industral accidents
* chemical spills
* atmospheric pollution
* plastics
* nanoparticles
bioaccumulation
- Occurs when an organism absorbs a toxic
substance at a rate greater than that at which
the substance is lost accumulation - Persistent and mobile in the environment. This means that they do not break down easily and can move through air, water, or soil.
- Accumulation occurs in body tissues
- Particularly in higher predators at the top of
food chains and webs - Diverse group of toxins introduced in 1940-50s for
different reasons – especially pesticides - Many were used because they work quickly and so effective
- 2,4-D & 2,4,5-T (herbicides)
- DDT, dieldrin, lindane (organochlorine insecticides)
- PCBs (polychlorinated biphenyls, chlorinated organic
compounds used as insulation in electrical
equipment, e.g. transformers, coolants – very stable) - Heavy metals (mercury, lead, cadmium etc)
long lives and do not break down at all, once released in the environment, they stay
impacts on human wellbeing of the human footprint
Context
* PCBs found in breast milk of mothers in
southern Quebec in the mid 1980s that were thought they were away from PCBS in environment –> need for a control (“pristine milk”)
* Obtained milk from Inuit mothers and 5 times the PCB levels!!!
(also toxaphene and chordane)
* children had unacceptably high levels
of PCBs (figure surpassed 95% where
whale consumption was high) [PCB in the contaminated fish]
* Older people had higher levels
Impact :
* 11-year olds exposed to PCBs in
the womb had:
* lower IQ
* poor memory
* shortened attention span
* learning difficulties
* Hostility between indigenous people and researchers in trying to uncover what was going on
why were the inuit people who were far from PCS in canada being impacted?
- Inuit use almost every bit of the 100s
of narwhal and beluga whales taken
every year. Preference for muktuk
(skin and surface fat) - Also consume bits of ringed seals
(livers), caribou (kidneys) and fish
These foods are top of their food chains and thus toxins accumulate in certain body
parts, particularly fat
–> getting PCBs in their diets
how were the inuit people who were far from PCS in canada being impacted?
- “Global distillation” & “global fractionation” – processes
whereby volatile chemicals are transported long distances
–> Heavy usage in tropics, where they evaporate from soils,
carried on winds (fractionation) and then condense out in the
cold as toxic snow and rain (distillation)
–> Systematic transfer from warm to cold - Very slow breakdown in cold climates [persist for a long time in colder environments. Cold temperatures slow down the breakdown or degradation of these chemicals, leading to their accumulation over time.]
solutions to this inuit problem
PCBs are now banned worldwide
* Monitoring and regulation
–> showing declines in the warmer areas and should work
problems with lead
- Condors ingest lead after feeding on the carcasses of animals
that hunters have shot, leading to chronic lead poisoning - 2008 California ban –> but feather and blood samples from trapped birds found no
discernible difference in lead levels before and after the ban [lead takes a long time to work its way out of the tissues]
–> Many have dangerous levels of lead in their bodies
–> Lead poisoning severely damages birds’ nervous systems and
impairs liver and kidney function - recovering slowly
effects of bioaccumulation
- lethal effects, radically affected
- developmental problems in jaw morphology, leg morphology, any part of the organisms
what have we learned about oil spills
- 40 million litres in Alaska in 1989
- 795 million litres in Gul of Mexico in 2010
The old wisdom: Acute mortality through short-term toxic exposure to oil deposited on shore [aggressive clean-up is always the best approach.]
The new wisdom:
* Clean-up attempts can be as damaging as the oil itself, with impacts recurring as long as clean-up (chemical and physical
methods) continues.
* Strong pervasive biological interactions in rocky
intertidal and kelp forest communities contribute to cascades of delayed,
indirect impacts and expand the scope of damages well beyond the
initial direct losses and thereby also delay recoveries
–> Need for development of ecosystem-based toxicology;
monitoring may be needed for > 100 years
habitat loss and fragmentation
- Habitat loss is one of the major contributors to biodiversity loss, [destroyed or changed into something else, lose different types of species.]
- Fragment size and isolation are primary drivers of diversity [it can reduce the number and variety of living things that can survive there. So, bigger, connected natural areas are better for diversity.]
- Edge effects are prevalent [When we change the edge of a natural area (like a forest or a lake), it can affect the species living inside. So, we need to be careful about what happens at the edges.]
- Shape matters [Some shapes are better for different types of species, so it’s not just about size but also the form of the area.]
- Connectivity and corridors enhance
landscapes [When we link natural areas together with things like green corridors or pathways, it helps animals and plants move around. This helps biodiversity because it connects different habitats.] - Role of the matrix – hospitable or
not? [The “matrix” refers to the areas between habitat fragments. Depending on what’s in this matrix – whether it’s suitable for wildlife or not – it can either help or hinder the movement and survival of species.]
Two classic effects of fragmentation
- Biomass collapse [Fragmentation can lead to a significant reduction in the total amount of living organisms (biomass) in an ecosystem. This means there are fewer plants and animals in fragmented areas.]
- Irreversible shifts (‘ecological meltdown’) [Fragmentation can cause long-lasting and often harmful changes in an ecosystem. These shifts can be difficult or impossible to reverse, leading to what is sometimes called an ‘ecological meltdown,’ where the ecosystem loses its original structure and function.]
why does biomass collapse occur during habitat fragmentation
when you fragmented a patch of continuous forrest, you expose the edges to strong winds, it is less moist, there are changes in the microclimatic factors [small-scale weather and environmental conditions. Things like wind and water flow can be very different on the edges of an area compared to the center.]
can significantly impact the ecosystem –> these may favour woody vines but the established trees, which were adapted to the original climate state or equilibrium are lost because they cannot cope with the new conditions, disrupted and altered the climate state or equilibrium
more fragmentaiton –> more biomass loss
ecological meltdowns and predator free fragments
Small and medium islands do not support
>75% of vertebrates from mainland and
control sites
–> mostly large animals and
predators lost
affects trophic cascades –> increasing prey that should’ve been eaten
what is the effect of ecological meltdown and predator free fragemnts
- Predators of vertebrates are absent, –>
prey that predators normally limit them exploded–> disrupting the balance of the ecosystem. - Densities of seedlings and saplings of
canopy trees are severely reduced on
herbivore-affected islands: forest cannot recover without the regulatory influence of predators.
The evidence of a trophic cascade is observed, where the removal of top-down regulation (predators) , herbivore populations surge, leading to increased herbivory on vegetation and subsequent repercussions for plant communities.
Losing predators – loss of crucial ecological processes. Predators play a vital role in shaping ecosystem dynamics, controlling prey populations, and influencing community structure. The removal of these processes can trigger a chain reaction, contributing to the ecological meltdown.
–> Ecological meltdown [all the vegetation being consumed by the abundance of herbivores]
