Human Impact on the environment

AH Biology

Unit 2 Environmental Biology

Changes to ecosystems

Human Impact on the environment– i Changes in complexity.– ii Effects of intensive food production.– iii Effects of increased energy

production.– iv Pollution.

Succession - Arrangements

• Autogenic succession (primary and secondary succession).

• The increase in complexity of ecosystems from pioneer through to climax communities.

• Facilitation of change in early stages.• Increase in complexity shown by increase in

– diversity of species, – variety of habitats and niches, – complexity of food webs. – Changes in stability and productivity through

succession.

Changes in complexityArrangements

• Reference to effects of external factors in allogenic succession and relatively short-term nature of degradative (heterotrophic) successions.

• Loss of complexity through human activity as illustrated by – monoculture, – eutrophication (algal bloom and its

consequences), – toxic pollution,– habitat destruction.

Succession

• This is the non-seasonal, directional and continuous pattern of colonisation and extinction at a site by populations of species.

• Pioneers Climax communityr-strategists K-strategistsRapidly changing stable communities

Categories of succession

• Autogenic succession – natural sequence– Primary succession– Secondary succession

• Allogenic succession

• Degradative succession

Changes in complexity

• Limited complexity is typical of naturally stressed communities

• Loss of complexity is also typical of stressed communities associated with polluted habitats that may result from– Eutrophication– Toxic

• Reduction in complexity can also be a result of – Monoculture– Habitat destruction

Eutrophication

• “Enrichment of waters by inorganic plant nutrients, usually nitrogen and phosphorous, which increases primary production”

• Freshwater ecosystems are classified by the status of nutrients in their waters.– Oligotrophic = nutrient poor and unproductive– Eutrophic = rich in nutrients and productive– Mesotrophic = waters that fall in between

Factors which influence the rate of eutrophication

• Natural eutrophication is caused by natural features of a lakes catchment, e.g. a lakes nutrient content rises with age.

• Cultural eutrophication – anthropogenic influences.• Most important factors in temperate lakes are:

– Fertility of drainage basin– Seasonal behaviour of the water– Depth of a lake– Temperature of the water– Rate of turnover of the water– Cultural eutrophication

Cultural Eutrophication of lakes and rivers

• Areas of concern for lakes and rivers– Acidification of lake water associated with acid rain– Introduction of toxic wastes– Eutrophication

• Effects of cultural eutrophication– Species diversity decreases and the dominant biota

change– Turbidity increases– Rate of sedimentation increases– Anoxic conditions may occur

Further problems caused by eutrophication

• Difficulties in the treatment of drinking water

• Growth of algae may leave unacceptable tastes or odours in the water supply

• Water may be injurious to health• Amenity value is reduced• Growth of plants may inhibit water flow and

navigation• Loss of salmonids and coregonids from

water may have economic consequences for fisheries

Causes of Cultural Eutrophication

• Soil erosion may increase phosphate levels in the water

• Nitrates from inorganic fertilizers or from sewage treatment facilities

• Phosphate from animal waste; sewage or manure

• Possible solution to eutrophication is to limit the amount of phosphorous going into watercourses, as it is cheaper to remove at sewage treatment plants.

Stages of Eutrophication

• Algal bloom – caused by the effect of fertilizers on the growth of microscopic green algae

• Rapid growth of algae causes death of higher plants

• Flow rate of river slows down• Older algae decompose, bacterial

populations increase (BOD increases)• Fish are killed and the entire food web of

the river is disrupted.

Toxic pollution

• E.g. pesticides, insecticides or heavy metals• Loss of diversity• Reduction in species richness• Species present in large numbers due to

lack of interspecific competition in polluted habitats

Toxic pollution

• Problems with pesticides– Kill non-target species– target species evolve resistance to the insecticide– some insecticides become concentrated up food

chains• PCB’s and heavy metals

– Egg shell thinning– Interference with mammalian reproduction– Damage to the immune system– Carcinogenic

Monoculture

• Loss of diversity by modern agricultural practices

• A single crop species is grown over a large area, reducing the complexity of the ecosystem to a single species.

• Unstable ecosystem, at risk from interspecific competition.

Habitat destruction

• Britain's wild orchids disappearing habitats

• Annualdeforestationestimates

Essay question

Give an account of the types of succession and

the changes in complexity of

ecosystems as a result of succession.

Effects of intensive food production.• Monoculture and its effect on

– soil condition, – field size, – shelter – habitats.

• Environmental impact of increased use of pesticides and chemical fertilisers in relation to species diversity and loss of stability.

Development of Farming in Britain

• 14, 000 y.a– domestication of dogs from semi-wild animals

• 9,000 – 10,000 y.a– domestication of cattle, sheep and goats– gatherer-hunters

• 5,000 – 6,000 y.a – Agriculture develops– lowland deforestation for crop growing

Intensive farming

• This is an open system; there is a net loss of nutrients as large yields are being exported from the farms, which then has to be replaced by fertilisers.

• Animals are farmed at high densities, which increase the chance of catching diseases due to stress, and overcrowding, this leads to antibiotics being added to their food.

Pupil Activity

• With the use of a highlighter, read the handout on intensive farming – advantages and disadvantages.

Monoculture

• Single species cultivated over a large area for economic efficiency

• Disadvantages– Replacement of naturally diverse communities

with a single species– Removal of nutrients (open system)– Leaching of nutrients from soil– Soil erosion– Invasions by pests

• Weeds, insects and animal pests, pathogenic fungi, bacteria and viruses.

Hedgerow Destruction

• Hedgerow – narrow belt of vegetation dominated by shrubs

and occasional trees.

• Traditionally hedgerows served two functions– A barrier to the movement of livestock.– Marking property boundaries.

Hedgerows have a high landscape and conservation value

• They are a traditional feature of the landscape and add diversity to it.

• Provide foraging, roosting and nesting sites for birds.

• Rich in plant and animal species.• Act as a source of beneficial insects.• Act as wildlife corridors through an increasingly

hostile agricultural landscape.

Hedgerow losses

• Estimated that between 1945 and 1970 there was an annual loss of about 8,000km year-1 in the U.K.

• In the 1990’s it is estimated that the U.K. was still losing 5,000 – 6,000 Km year-1.

Advantages of Hedgerow removal to the farmer

• Hedgerows act as a refuge for weeds, diseases and crop pests.

• Reduce the loss of crop yields adjacent to the hedge

• Bigger field sizes – decreases the amount of land needed for turning machinery.

Disadvantages of Hedgerow removal to the farmer

• Increases soil erosion• Reduce crop yields through the loss of

beneficial insect species– Predators for pest control– Pollinators

Pollution from farm wastes

• Fertilisers– Nitrogen from fertilisers can build up in the

soil. – Soil bacteria then convert this to nitrates. – The nitrates then get into stream and river

systems through surface run off.

• Pesticides– Bioaccumulation in food chains– Non specific

Major changes in agricultural activity in the U.K. since the 1940’s

• Increasing levels of farm mechanisation, energy inputs and decline in the labour force

• Development of highly productive strains of crops and livestock

• Increasing use of fertilisers and pesticides.• Changes in farm sizes.• Changes in farming practices and

significance of different crops.• Financial returns.

Pupil Activity

• Diagram – consequences of modernisation of agriculture on ecology and wildlife interests of farmland.– Stick the diagram into your book– Write out a paragraph discussing the diagram,

including any comments that you can draw form the diagram.

Essay question

Discuss the advantages and disadvantages of

intensive food production

Effects of increased energy production.• Fossil fuels as finite energy resources. • Need for conservation and use of alternative

sources of energy. • Air pollution from fossil fuels:

– acidic gases (sulphur dioxide, nitrous oxide, carbon dioxide) and greenhouse gases (carbon dioxide and water) produced.

– Other greenhouse gases include methane and CFCs. • Enhanced greenhouse effect and effects of global

warming on abundance and distribution of species – E.g. zooxanthellae and 'coral bleaching'.

Fossil fuels

Alternative energy sources

Atmospheric Pollution

• Atmospheric pollution can be attributed to anthropogenic causes; it causes harm to humans and other living organisms in the environment.

• By the late 20th C. atmospheric pollution effects can be seen in all nations of the world.

• Air pollution is a global problem as it ignores international boundaries, as does the wind that carries it. This had led to international co-operation and global legislation for air pollution.

Atmospheric Pollution

• The increase in pollution over the last 150 years can be attributed to the increasing human population and increases in urban and industrialised societies.

• There are 3 main concerns of atmospheric pollution– Acid rain– Greenhouse effect– Climate change / global warming

Acid Rain

• Explain the production of acid rain and it’s effect on lakes and forests

• 1872 - The Scottish chemist, Robert Angus Smith, first used the term “Acid rain”.

• Acid rain is used to describe the acidity of wet and dry deposition– Wet deposition = rain, snow, hail, sleet, mist or

fog– Dry deposition = gases and particles

Acid Rain

• Natural precipitation is weakly acidic (pH 5.6), as carbon dioxide dissolves in rainwater it forms weak carbonic acid.– In Britain, Europe and North America, often find

pH of 4 or 4.5– 10th April 1974 – Rainstorm in Pitlochry,

Scotland, pH 2.4• The increasing acidity of rainwater has been

attributed to the production of sulphur dioxide (SO2) and nitrogen oxides (NOX) during the burning of fossil fuels.

Pupil Activity

• Read the Aric Fact sheet “What is Acid Rain?

• Answer the following questions– What are the natural sources of sulphur dioxide

and nitrogen oxides?– Compare the quantities of natural sources of

these gases, and those released from emissions.

Formation and Deposition of Acid Rain

Formation and Deposition of Acid Rain

• Washout – when acids present below the clouds are taken up by the falling rain or snow.

• Rainout – when cloud water droplets or ice crystals containing acids grow to sufficient size to fall.

Effects of Acid Rain Terrestrial Ecosystems

• The most noticeable symptom of acid rain in terrestrial ecosystems is in trees– Conifers most at risk, as they do not shed there

pines all at once.– Deciduous trees only have a few months to

intercept acid rain, so only a seasons growth is damaged

• As a result trees need extra energy to grow extra leaves, which can lead to a failure to reproduce, increasing susceptibility to disease, pests, drought and frosts.

The Effects of Acid Rain on Trees

Effects on trees include

• Poor growth• Lower productivity• Discolouration of needles• Shallow roots• Dieback of crown

• In Europe, deterioration can be seen in Norway spruce, Scots pine and beech.

• In areas affected by acid rain populations of wildlife have declined (h/out impacts of air pollution and acid rain on wildlife)

Pollution of the Air

Structure of the atmosphere, and absorption of ultraviolet and infrared light

Carbon DioxideThe Greenhouse Effects

• Outline roles of carbon dioxide and methane in enhanced greenhouse effect and global warming.

• Appreciate international efforts to reduce carbon dioxide emissions.

Carbon Dioxide

• Carbon dioxide is naturally occurring in the atmosphere at a concentration of less than 0.05%.

• CO2 Levels– Constant 2,500 – 200 ya 270ppm– Since industrial revolution risen to 360ppm

• Since 1960 levels have been slowly rising

Carbon dioxide concentrations in the Northern Hemisphere

Seasonal variations in CO2 concentrations

• Spring & summer – CO2 levels fall, as plants make new leaves and grow

• Autumn & winter – CO2 levels rise as leaves fall and decay, producing CO2

• 2 reasons for overall rise in CO2 levels– Global use of fossil fuels as energy source; fossil

fuels act as sinks in the carbon cycle, carbon would not naturally escape.

– Increase in the destruction of the world’s forests. Trees act as carbon reservoirs

Rate of CO2 fixation by trees

• Tropical rainforest – between 1-2 kg/m2 carbon per year

• Deciduous forest– 0.2 – 0.4kg/m2/year

• Increasing CO2 levels caused by deforestation is reversible. As regrowth of forests would use CO2 and release O2

• Forests can be renewable energy resources if allowed to grow.

Greenhouse Effect

• The presence of the atmosphere increases the Earth’s surface temperature by an average of about 33oC.

• Sun’s energy travels through the atmosphere and warms the Earth’s surface.

• Some heat is radiated back into the atmosphere where the gases prevent heat energy from escaping into outer space.

Greenhouse gas Source or origin

Water vapour (H2O) Evaporation and transpiration

Carbon Dioxide (CO2) Combustion of fossil fuels, wood

CFC’s Refrigerators, aerosol spraysMethane

(CH4)Cattle, rice fields, bogs and

rubbish tipsNitrous oxide

(N2O) DenitrificationOzone

(O3)Secondary pollutant from car

exhausts

Sources of Greenhouse Gases

Carbon dioxide and Methane

• Due to human activity CO2 and CH4 are increasing in abundance. This may be causing global warming by enhancing the natural greenhouse effect of the atmosphere.

• Methane (CH4)– Primarily from the breakdown of cellulose– Animal emissions exceed 100 million tonnes– 10 times more effective as a greenhouse gas than CO2– Concentration in the atmosphere is lower than carbon

dioxide– Increase 800ppbv to 1720ppbv in last 200 years

• Carbon dioxide contributes about 60% to the greenhouse effect, methane contributes about 15%.

Climatic Effects

• Climate in naturally variable, last 100 years seen an average world temperature rise of 0.5oC– Predicted a 1oC – 5oC rise in the next 50 years

• What evidence?– The effects of global warming are not known,

and many scientists remain unconvinced that it is occurring.

Present Situation

– Oceans surface is warmer at the equator – More water evaporates– Warm air rises faster causing stronger winds– Moisture laden air is carried further from the

tropics– Less rain in the tropics– Floods in temperate regions

• Last 30 years seen more extremes of weather and more droughts in the tropics

El Nino

• Warms surface waters off the coast of South America

• Causing drought and conditions in Australia and Indonesia

• Torrential rain in Peru and Ecuador. • If El Nino lasts for 12 months or longer, it

severely disrupts populations of plankton, fish and seabirds in upwelling areas and can trigger extreme weather changes over much of the globe.

Normal Conditions

El Nino Conditions

Future

• Death and destruction from hurricanes and floods

• Ice caps melt – rise in sea levels• Polar meltdown would switch the path of the

Gulf Stream – colder climate in the North Atlantic and UK.

Effects of Global Warming on British Flora

• Increasing the northwards range of rare orchids

• Plants adapted to the cold would suffer e.g. bluebells rely on a cool spring

• Due to the complexity of ecosystems it is very difficult to predict how changes in climate will affect biodiversity. However the combination of this and habitat loss is not looking good for biodiversity.

International efforts to reduce carbon dioxide emissions

• 1998 – international panel on climate change formed to report on the global situation

• 1992 – climate change convention was signed at the Rio Earth Summit in 1992 (greenhouse gas emissions to go back to 1990 levels by 2000)

• 1997 - Kyoto Protocol• Recognised this was unachievable• Targeted CO2, methane, nitrous oxide, some

fluorocarbons and sulphur hexafluoride.• Aim to cut emissions to 5% below 1990 by 2010• Each nation given a specific target – allowing countries

to trade in carbon emissions

Montreal vs. Kyoto Protocol

Montreal Protocol Kyoto Protocol

Ozone depletion was evident Uncertainty about the actual consequences of global warming.

Technology existed to replace CFC’s with less damaging products

Developed world is reliant on fossil fuels, no easy alternative energy source.- Developed countries need to make the major contribution to lowering greenhouse gas emissions.

• Another reason for lack of success is the current political climate.

• To stabilise atmospheric CO2 at 560ppm

(which is two time the natural level), requires a reduction to 60% below 1990 levels.

Approaches to reducing Emissions

• Less reliance on fossil fuels, switch to renewable energy resources

• Energy saving measures – insulating houses • Lower expectations about the standard of living• Plant more trees (CO2 sink)• Alternatives to petrol and diesel for a fuel – “clean

sources of energy”• Pump CO2 underground or down to ocean floor• Encourage massive oceanic algal blooms to trap

CO2 in organic matter.

Example – zooxanthellae and “coral bleaching”

• Communities of coral polyps in a symbiotic relationship with a single celled algae called zooxanthellae.

• Corals can only tolerate a narrow range of temperatures

Temperature rise and coral bleaching

• Rising water temperatures block the photosynthetic reaction that converts carbon dioxide into sugar.

• This results in a build-up of products that poison the zooxanthellae.

• To save itself, the coral spits out the zooxanthellae and some of its own tissue, leaving the coral a bleached white.

• The bleached coral can recover, but only if cooler water temperatures return and the algae are able to grow again.

• Without the zooxanthellae, the coral slowly starves to death.

Essay question

Give an account of the need for conservation and use of alternative energy

sources, including the greenhouse effect and

global warming.

Pollution.

• Biodegradable organic pollutants and changes in biochemical oxygen demand (BOD).

• Major types of toxic pollutants and their sources – DDT – heavy metals.

• Bioaccumulation. – Consequences of biological magnification in food chains. – Biotransformation. – Toxicity and persistent/non-biodegradable nature of DDT.

• Susceptible and favoured species – the use of indicators in the monitoring of quality of fresh

water ecosystems.

Biodegradable organic pollutants

• Biodegradable organic pollutants include:– Sewage– Farm waste– Industrial waste

• Problems arise when the system becomes overloaded and eutrophication ocurs.

Biological Oxygen Demand (BOD)

• Definition– The mass of dissolved oxygen, in grams per

cubic metre or milligrams per cubic decimetre, taken out of solution by a water sample incubated in darkness at 20oC for five days.

Biological Oxygen Demand

• BOD is a common measure of organic pollution

• Calculation of BOD– How much oxygen is taken up by a sample of

water when it is kept in the dark for 5 days at 20oC.

– Kept in the dark to prevent photosynthesis.– Therefore the oxygen used up is by the micro-

organisms breaking down organic matter.

The table below shows the BOD of some organic pollutants, the figures are for before the pollutants enter a river (once in a river the pollutant will become diluted).

Indicator Species of Water Pollution

• In order to use indicator species as a measure of organic pollution you must first understand the tolerance levels of different species to pollution.

• A level for pollution is estimated depending on the presence or absence of certain organisms from a habitat.

• Biological monitoring gives a summary of the recent history of the environment.

Indicator Species of Water Pollution

• In 1964, Trent River Authority devised a recording system for monitoring the pollution of watercourses.

• BMWP Score Sheet – points are allocated on the presence of invertebrate families. The score is totalled them divided by the number of groups present. The lower the score, the more polluted the river.

• Aquatic plants and invertebrates complement each other as biological indicators, as they have different tolerance levels to certain chemicals.

Pupil Activity

• Explain why the use of biochemical oxygen demand and indicator species may give different measures of water pollution.

The effects of an organic effluent on a river at different distances downstream from the outfall

A + B = physical and chemical

changesC = changes in micro-

organismsD = changes in larger

animals

(based on Hynes, 1960)

Events affecting quality of water in a river

• In a given stretch of river, there is continual exchange of water, so that events at some distance upstream can affect the river much lower down.

Pupil Activity

• Sewage – inadequate treatment leading to pollution

– Using the information given in the handout, in the table and in the graphs, explain as fully as possible the changes of water quality, and plant and animal populations in a river after the introduction of sewage

Pesticides and Toxins

• Appreciate the need for pesticides and explain the consequences of pollution by DDT.

• Pesticides are an important group of agricultural chemicals, which are designed to kill organisms, therefore their use has health and environmental concerns.

• Need for pesticides– Necessary in intensive farming regimes to;

• prevent damage of crops whilst growing• give a longer shelf life to fruits and vegetables by

reducing decay from surface micro-organisms• reduce the infection of farm animals

The Ideal Pesticide

• effective at low dosage against its specific target

• inexpensive to manufacture• non-polluting• Plentiful• easy to apply• breakdown products should be harmless to

non-target organisms in air, soil and water

Problems associated with certain pesticides

• pose a risk to human health• herbicides have a rapid breakdown and are

only toxic when absorbed or ingested in high concentrations

• fungicides not known to have environmental effects?!

Insecticides

• Early insecticides include:– stomach poisons– tar oils– plant extracts

• Since 1940’s 3 main types of insecticides come into use– Organochlorines (chlorinated hydrocarbon

compounds)• Examples – DDT, Dieldrin• Ecological effects of DDT, accumulation of toxin in food

chains– Organophosphate compounds

• Examples – malathion and diazion• Very toxic to insects and humans

Insecticides

– Carbamates• Examples – carboxyl, aldicarb• Do not leave long lasting residues in environment• Lethal to non-target organisms

• Problems with pesticides– Kill non-target species– target species evolve resistance to the

insecticide– some insecticides become concentrated up food

chains

Bioconcentration

• Materials are absorbed whilst being used for feeding or respiration/

• Materials then may move to storage sites within the body where it can accumulate and concentrate.

Biomagnification

• Materials are concentrated through ingestion, and incorporation into the body of the consumer (aquatic food chains)

• Substances which are harmless at original environmental concentrations may concentrate to levels at which toxic effects are significant.

• E.g. The DDT story and its warnings

Case Study: DDT

• The story of dichlorodiphenyltrichloroethane (DDT to its friends)

• In 1939 DDT was first used as an insecticide. – DDT and other Organochlorines last for 10-25

years in the environment. – As they are more soluble in fat than water, once

they have been ingested they remain in fatty tissues (lipids).

• DDT and Organochlorines have been found to accumulate in food chains.

Case Study: DDT

• In the 1950’s the numbers of peregrine falcons in Europe halved over 20 years, this was traced to DDT dressing put on seeds, eaten by pigeons, eaten by the Falcons.

• The DDT caused the falcons to lay eggs with thinner shells, so when they were sat on they were smashed.

• In the 1980’s, after restrictions on the use of DDT, falcon numbers returned to normal.

Pupil Activity

• Read through the information, answer the questions on “pesticides and Bioaccumulation”.

Case Study: Clear Lake, California

• The earliest example of Bioaccumulation comes from Clear Lake in California.– 1949

• lake was sprayed with DDD, 99% of non-biting phantom midge larva died.

– 1951 • swarms of midge recover

– 1954 • second dose of DDD, this time more concentrated• 100 Western Grebes dead on lake (bioconc. X 30 000)

– 1957 • population fell 30 000 to 30 pairs, most of which were

sterile– 1960’s

• switch to substitute organophosphorous insecticide and Grebe populations are slowly recovering.

Transfer of an organochlorine pesticide through the food chain of Clear Lake.

PCB’s and Heavy Metals

• Outline the sources of polychlorinated biphenyls (PCBs) and heavy metals and the consequences of their release on the environment.

• PCBs– There are over 200 different types of PCB; they

were first released in the US in 1929.– Their use includes electrical insulators and the

manufacture of paint, ink and plastics.– Effects of PCBs were first noticed in the 1960’s

and their use was banned in the 1970’s.

Environmental Concerns

• Egg shell thinning• Interference with mammalian reproduction• Damage to the immune system• Carcinogenic

• Since 1988, over 20 000 seals in the North Sea have died of viral infections, these are thought to have been enhanced by PCB poisoning.

• In Canada, Inuit nursing mothers have five times more PCB in their milk than mothers in southern Canada.

Heavy Metals

• Heavy metals become pollutants when found in high concentrations in water and soils.

• There has been an increase in heavy metal concentrations since the industrial revolution, but they have been around for over 3000 years.

• Effects at high Concentrations– 1.    Toxic to animals– 2.    Developmental defects– 3.    Cancers– 4.    Kidney failure– 5.    Immune system failure

Biotransformation

• Biotransformation occurs during the degradative metabolic processes of organisms.

• This process is vital to the sustainability of life if part of natural degradation.

• It can be deleterious– Example – mercury

• Inorganic mercurial ions with low toxicity can be transformed into the highly toxic methyl mercury ions by microbial activities.

• Minimata bay, Japan

Case Study: Mercury Poisoning• Mercury is a serious pollutant in the Amazon Basin,

where it is used to extract gold.

• In the 1950’s in Minimata Bay in Japan, high concentrations of Methyl Mercury was released into the river, this concentrated in the marine food chain. – The Japanese ate fish and shellfish; over 1000 people were

killed or disabled between 1950 and 1970.

• Some plants can develop tolerance to heavy metals, for example Leadwort near the abandoned lead mines in Yorkshire and Derbyshire.

Differential sensitivity

• Not all species respond in the same way to a pollutant, and it is important to recognise that for any particular pollutant there will be very sensitive and less sensitive species.

• TBT (organic tin) has devastating effects on oysters and other molluscs (dog whelk) whilst having negligible effects on most other species.

Essay Question

•Give an account of monitoring water quality particularly the uses of indicator species and biological oxygen demand.