Earth Science Lecture 15 - Human Impacts on the Biosphere

Introduction

Humans are a part of the biosphere, so some of our impacts are a natural part (Nutrient flows, carbon cycle, respiration, etc)

But, there are ways in which we are separate, so many impacts get termed anthropogenic; it reflects the scale, importance and uniqueness of our impacts

Some of these are unintentional, i.e. air pollution

Some of these are intentional, i.e. agriculture

History

Tend to imagine we have only been affecting ecosystems etc for the last few hundred years, but not true.

•  Discovery of fire
•  Domestication in the Neolithic
•  Industrial and agricultural revolutions
•  Also major historical civilisations – north Africa becoming deforested during the Roman era, Iceland under the Vikings vs the Inuits, etc.
•  Great Green Wall, and similar projects, vs large scale farming/mining/deforestation.

Problem is the scale of impacts, and how reversible they are (things like extinctions are, obviously, irreversible)

Is It All Bad?

A fair question, because a lot of it is. But, no - it's more complicated than that.

Human activity has created new habitats:

• Canals
• Urban areas
• Brownfield sites
• Soft engineering habitats

We have also created new species, enabled others, and are capable of protecting many more

Footpaths and Access

Use of countryside for recreation grown substantially since the 1960s (post war movements), throughout the developed world.

• More mobility (cars)
• More income
• More leisure time

Generally, recreation is restricted to specific areas (paths are easier to traverse than An Entire Marsh). Tend to also be restricted to areas with fragile ecosystems – that’s sort of the appeal.

Stress-tolerant organisms aren’t disturbance-tolerant, and vice-versa (biosphere)

Upland Paths

Most are pre-existing paths; agricultural tracks, forest paths, etc; so, not designed for heavy recreational use. Lot of land managers now engineer paths, either building from scratch or amending old (boulders, for example)

Vegetation is stripped away by footfall; exacerbated on steep slopes, and ‘toe-steps’ can form. Underlying substrate compacted.

Obvious implications for drainage, which encourages erosion – a natural process, but accelerated by human action. This leads to gully formation, so walkers begin walking around the path, so the process starts anew over a wider area.

Upland Paths - the Process

Sort of like reverse succession?

First to go – plant species vulnerable to crush damage (usually herbaceous flowering plants). Followed by more resistant, grasses and mosses. Eventually, whole surface is devegetated.

Then compaction in the upper soil profile – surface drainage impeded. Erosion follows, soil washed away.

Low levels of use can be weirdly beneficial in one sense - Mineralisation rate of organic matter increased, and disturbance-tolerant grasses: a lightly used path will become grassy. But heavy use – bare ground.

Horses, bikes, 4x4s all similar, but faster.

Management

Path improvements – gully filling, improved drainage.

Boardwalks and steps.

Paving (can be done to look ‘natural’)

Reseeding; path diversions to rest areas.

Reducing entry.

Eutrophication

This is where a natural nutrient deficiency of a water body (usually nitrogen, phosphorus or potassium) is overcome by human activity; in other words, fertilisers get into water courses they shouldn’t.

This leads to an explosion in primary productivity – plant life. Specifically, organisms like algae, cyanobacteria and waterweeds. They grow faster than the water’s ability to replenish oxygen, and block sunlight from plants lower down the water column, preventing photosynthesis for those and depleting oxygen.

The deoxygenation can be severe enough to effectively sterilise the whole water body.

Causes

Two main sources:

Fertilisers

Globally, we use a lot, and they cost less to buy than the profit made from their results, so economically, you’re going to use it.

Fertilisers are soluable, so they easily leach into water courses. Contain nitrogen, phosphorus and potassium.

(Side note: high nitrate levels in drinking water are harmful to humans.)

Sewage

More Causes

Rich in phosphorus, which is generally the nutrient in shortest supply in water bodies naturally.

May be deliberate or accidental.

Ecological Impacts

For higher trophic levels, deoxygenation, pH alteration, chemical changes and prey availability all impact vitality and reproduction for lots of fishes.

Primary producers grow out of balance – plants lower in the water column may be shaded out, and algae, cyanobacteria and water weeds may grow out of control and choke a water system.

Competition can eliminate important natural species.

If water flow is blocked/interrupted, floods and droughts are a risk.

Algal blooms can be fatally toxic even to humans.

Can it be fixed?

Happily, yes

Eutrophication is completely reversible if you cut off the pollution source, flush the water body with oxygenated water, and sustain aeration (artificially for a time, if necessary.)

Case Study - Argentina

The CORFO region – arid and semi-arid areas, where farmers use irrigation systems and fertilise the crops.

The warmth, high sunlight and fertilisers combine to make the perfect growing conditions for sago pondweed – Potamogeton pectinatus. It therefore grows out of control in the irrigation channels.

This, in the early 1990s, meant crops would be either drought damaged (as the water was blocked), or flooded (as it over-spilled).

They initially tried to either use expensive machines to cut the weed (costly, and also inefficient), or extremely toxic herbicides (costly, and only short-term success – so constant poisoning needed.)

Case Study: the Fix

BUT THEN they hit on the idea of using nature’s weird-ass water pig – the carp (Cyprinus carpio).

Carp root when they feed, thus uprooting the sago pondweed. They also therefore stir up the water column and make it murky, which helps to limit the sunlight reaching the plants, thus reducing their growing rates. And, they’re big enough that they can be easily fished out and chucked into new areas that need their attention.

The need for cutting or herbicides is thus reduced or sometimes eliminated each year.

But, of course, reducing fertilisers would be the actual fix.

Deforestation

When natural forest areas are replaced by other types of ecosystems; very often agricultural, though not always.

As old as our species. Primitive humans used fire; later, tools.

• Grass species are almost always better at dealing with repeated burning cycles than trees (slower-growing, longer lived).
• Seedling trees are vulnerable to grazing/trampling, whereas grasses have intercalary meristems that let them be competative
• Some grassland types (e.g. savannah) are partly anthropogenic, for all that they’ve then developed an ecosystem themselves.

The Main Triggers - Agriculture

Including clearance and overgrazing

Overgrazing is a particular problem in the third world, and leads to desertification

The Main Triggers - Wood Products

Fuel, pulp, construction material.

Increased hugely during 20th century. To counter, softwood plantations have replaced hardwoods; softwoods grow faster and straighter

Often no natural destruction; BUT, other issues:

• Soil acidification. Obvious implications to soil degradation.
• Ecosystem change. Different organisms are adapted to different types of forest cover; pH, moisture, light availability all different.
• Sometimes, stressed ecosystems are toppled by healthy tree removal; tropical forests are very vulnerable to exotic-type timber (e.g. teak, mahogany) being removed, and can trigger ecosystem collapse. A particular problem to indigenous peoples living there.

Ecological Impacts

Species loss in forests is not confined to primary producers (i.e. trees); species at every trophic level are impacted.

Biodiversity loss. Tropical forest biodiversity is amongst the highest of any ecosystem type – when we assess current extinction rate (one estimate: 4,000 species of mammal and 250,000 species of flowering plants extinct since 1600, making the rate about the same as the Triassic dinosaur thing) is, to a considerable extent, the result of tropical deforestation.

Regional climate change affects ecosystem composition and functions

Physical Impacts

Soils

• Raindrop impact is increased with no canopy to intercept.
• Reduced/no leaf litter – soil surface exposed, plus structure impaired.
• Surface runoff accelerated.
• With no trees to intercept, winds grow stronger, increasing aeolian action
• Kinetic energy from impact, infiltration reduced, increased fluvial action = increased erosion.

Hydrology

• In addition to previous, water now reaches drainage basins all at once rather than a bit at a time – flooding becomes much more likely.
• Sediment budgets in deforested river catchments are disrupted, meaning increased sedimentation of water courses. This blocks human anti-flood measures, such as ditches and dams; it can also block aquatic turbines, thereby impacting renewables
• The last few decades have seen an increase in severely damaging floods in Bangladesh, which has been linked to huge deforestation in the upper courses of the Padma – Meghna – Jamuna rivers flowing into the Bay of Bengal.

More Physical Impacts

Air

• Trees provide a massive service in purifying our air – not just CO2 conversion, but also in removing particulate matter. A loss of tree cover sees a rise in air pollution.

Climate

• A feedback loop! Deforestation causes climate change (reduced sequestration, C cycled to atmosphere), which then causes drier/harsher conditions, reducing growth. Global climate.
• Evapotranspiration leads to drier areas (tree transpiration is greater than any other vegetation type). Tropics become arid. Cloud forest ceases to function. Regional climate.

Large Reservoirs

These have been increasingly constructed (in some cases, forming the largest man-made structures ever built) through the 20th/21st centuries, and for a number of reasons:

• Water supply, for agriculture, domestic or industrial consumption
• Flood control
• Navigation improvement
• Hydroelectric generation
• Recreational use

Large schemes tend to be a combination of these.

Reservoir is constructed by building a dam to modify stream hydrology, so water can be collected and then released as needed; it therefore can’t not have an impact environmentally.

Impacts

Modification of Downstream Flow

Literally the point of the exercise, of course.

River flow volume is reduced – less water in the river means fewer organisms, as the habitat is smaller

Flood frequency/intensity reduced – many biological communities need regular inundation.

If a river has a pronounced seasonal flow regime, the river might be a glorified stream during the dry season now, with obvious disastrous consequences for the shit living in it.

Impacts

Change to Sediment Budgets

Reduced flow below a dam – reduced kinetic energy.

BUT, the water dumps sediment in the reservoir – so, below the dam, it can carry more sediment as it now has nothing.

This means although the flow is reduced, erosion and sediment transport is INCREASED.

Deltas especially damaged, by both reduced sediment input and higher erosive power

Also impacts fish breeding sites and vegetation

Impacts

Submergence of Land

An area is drowned under the new reservoir – both people and environment affected.

Habitats vanish, so many species disappear or reduce – new come in (this can be a good thing, of course.)

Spp are particularly vulnerable to invasives, here

Impacts

Disease Risk Increase

Still water where previously there was none – more mosquitos, or other river flies. Diseases such as malaria can therefore thrive.

This does not exclusively affect humans – animals can also be affected, by both diseases and creepy asphyxiation

Impacts

Micro-Climate Impacts

The super big ones can even have regional effects.

Atmospheric moisture increases (evaporation), and temperature lowers (thermal sink, and also evaporation again.)

Not always a terrible thing, but can cause problems to natural ecosystems like hyper-arid deserts with specially adapted species; a significant number of these are in such zones.

In areas that SHOULDN’T be arid, of course, they can help restore natural function (for a given value).

Case Study: the Aswan High Dam

96% of Egypt is desert; remaining 4% is almost all on the Nile or its delta. So the dam was to boost food production in the 60s/70s, and created Lake Nasser

Reservoir reached its planned size - >400km in length, storage capacity of >2 years’ worth of flow of the Nile – in 1978. It holds the annual flood surge for the White Nile. This is then used for irrigation.

Also generated 15 – 20% of Egypts energy by the late 90s

This has caused farming-related problems – no fertiliser, as silt is now trapped in Lake Nasser, so synthetic used instead. This causes eutrophication in the Nile.

River bed and delta erosion now increased

Fisheries lost/impacted. Some evidence of disease outbreaks increased, and of regional climate change.

CHEMICALS

WATER DEMAND

BIODIVERSITY

Overfishing

Where more fish are removed than can naturally replenish through reproduction.

Fish are a vital part of aquatic ecosystems, AND a staple food for ~2 billion people worldwide.

Last 50 years have seen fishing go well beyond sustainable levels; partly through increased efforts, and partly through fishing practices. And not just fish – by-catch is a serious problem.

>30% of fisheries are now beyond their biological limits.

Causes

Open access areas. Fisheries are basically ‘open access’ because there are few/no property rights (unlike a terrestrial farm, for e.g.). This means a lack of incentive to leave fish in the water.

Poor fisheries management. Ongoing for a long time; limited/no oversight, governmental regulations, and tracibility (hard to trace if someone is doing something they shouldn’t when they’re in the middle of the ocean.) We need to limit fishing capacities to sustainable levels, but current rules and regulations aren’t strong enough; on the high seas, they may not exist at all, or may go unenforced.

Causes

Illegal fishing. An obvious problem, since it sabotages attempts by legitimate fishers to limit catches. WWF estimates that 20% of the world’s catch is illegal, spanning across 50% of fisheries. Pirate fish products are estimated at $10-23.5 billion annually.

Subsidies. Many governments still give fishers subsidies to keep fishing, which directly increases overfishing. Today’s worldwide fleet is about 2.5X what it needs to be to feed us all.

MPAs. Only 1.6% of the global oceans are MPAs, and 90% of those allow fishing. So there aren’t enough protected areas where fish can restock before spilling over to others.

Impacts

Decreased food security: given that fish are a staple food source for 2 billion, their decline causes famine, malnutrition and major economic downturn in affected areas.

But biospherically, it’s a disaster. Large predator species, such as tuna, sharks and billfish, are preferentially targeted; this causes an imbalance in the ecosystem, allowing smaller animals to become adundant. This leads to other problems, like coral reef decline and increased algal growth.

Impacts

By-catch and ghost fishing. The former is where non-target species are taken and killed by non-specific traps, lures, hooks and nets. The latter is where a net (or other equipment) breaks off a boat and drifts away through the ocean, trapping and killing things as it goes. Cetaceans and sharks are especially vulnerable to both.

Habitat destruction. In addition to the organisms being caught, some fishing techniques are sufficiently destructive to kill other things. Trawling involves dragging a weighted net along the sea floor to catch bottom-dwelling fish like tuna and plaice; the net utterly destroys coral communities.

Pollinator Impacts

 Bees are our most important pollinators – 80% of our wildflowers, >90% of leading crop types (food, cotton, etc), are pollinated by them.

 Hoverflies, wasps, mosquitoes, butterflies etc as well; but mostly bees.

 In the UK alone, the services provided by bees are worth £691m a year annually; if we had to pollinate by hand, it would cost £1.8b a year.

 And they are declining. In the UK, we’ve lost 13 species, 35 are at risk of extinction, and all are threatened.

Causes

Habitat loss.

• Naturally, trees; but hedgerow-lined flower meadows do great, too, and they’re pretty adaptable.
• But,we’ve lost 97% of our wildflower meadows since WW2.
• Insensitive urban development + intensive farming. Habitat is destroyed, or the remainder is fragmented.

Pesticides

• Breeding success and disease resistance are both affected by even correctly-applied pesticides; honeybees can’t navigate properly, bumblebees can’t reproduce well, and solitary bees can’t produce young at all.
• The particular bastards: neonocotinoids. These guys affect the nervous systems of bees; essentially, it’s a nerve gas. Monsanto has been fighting efforts by lobbyists to ban them in the EU.
• Not just farms, though – garden herbicides also terrible.

Causes

Climate Change

• Nesting behaviour/post-winter emergence is off because of seasonal change. Plus, many forage plants are flowering at odd times.
• Tawny mining bee has managed to move northwards, but bumblebees really struggle with that.

Invasive species

• Sometimes an accidental import, sometimes intentional. Often brought unintentionally in larval form through the gardening trade.
• Some aren’t a problem (non-invasive.) Carpenter bees and tree bumblebees have both come and adapted beautifully to Britain without any displacement of natives, for example.
• Others really are, like the Asian giant hornet – we’re hoping it won’t establish, because while Asian honeybees can deal with it, ours can’t.

Generally, though, these all work together.