4.3 How Much Change Occurs Over Time in the Water Cycle and Carbon Cycle? Flashcards
What is dynamic equilibrium in natural systems?
Dynamic equilibrium refers to a state where natural systems have continuous inputs, throughputs, outputs, and variable stores of energy and materials, maintaining stability over the long term.
In the short term, inputs, outputs and stores of water or carbon will fluctuate from year to year. In the long term, however, flows and stores usually maintain a balance, allowing a system to retain its stability.
How do negative feedback loops function in the water and carbon cycle?
Negative feedback loops restore balance in the water cycle. For example, heavy rainfall increases water stored in aquifers, raising the water table and flow from springs until normal levels are reached.
In the carbon cycle, burning fossil fuels increases atmospheric CO, but at the same time stimulates photosynthesis. This negative feedback response should remove excess CO, from the atmosphere and restore equilibrium.
What is urbanisation?
Urbanisation is the conversion of land use from rural to urban, replacing farmland and woodland with housing, offices, factories, and roads.
What is the issue with drainage from urbanisation?
Urban areas also have drainage systems designed to remove surface water rapidly (eg pitched roofs, gutters, sewerage systems) As a result a high proportion of water from precipitation flows quickly into streams and rivers, leading to a rapid rise in water level.
How does urbanisation affect water storage?
Urbanisation leads to impermeable surfaces that allow little infiltration and minimal water storage capacity, resulting in rapid runoff and increased flood risks.
In addition to changing land use, urbanisation also encroaches on floodplains. Floodplains are natural storage areas for water. Urban development on floodplains reduces water storage capacity in drainage basins, increasing river flow and flood risks.
What impact does urbanisation have on the carbon cycle?
Urbanisation reduces organic carbon storage by removing vegetation and increases carbon dioxide emissions from burning fossil fuels.
How does farming change the carbon and water cycles?
Farming reduces carbon storage through deforestation ,in the above and below biomass, and soil erosion. Soll carbon storage is also reduced by ploughing and the exposure of soil organic matter to oxidation. Further losses occur through the harvesting of crops, with only small amounts of organic matter returned to soils. Soil erosion invariably accompanies arable farming, Erosion by wind and water is most severe when crops have been ifted and soils have little protective cover.
Crop irrigation diverts water from rivers and groundwater, affecting the natural water cycle. . Some of this water is extracted by crops from soil storage and released by transpiration, but most is lost to evaporation and in soil drainage.
Interception of rainfall by annual crops is less than in forest and grassland ecosystems (Figure 4.22. page 124). So too is evaporation and transpiration from leaf surfaces. Ploughing increases evaporation and soil moisture loss, and furrows ploughed downslope act as drainage channels, accelerating run-off and soil erosion. Infiltration due to ploughing is usually greater in farming systems, while artificial underdrainage increases the rate of water transfer to streams and rivers. Surface run-off increases where heavy machinery compacts soils. Thus peak flows on streams draining farmland are generally higher than in natural ecosystems.
What are the effects of forest management on the water cycle?
- Higher rates of rainfall interception in plantations in natural forests in eastern England, interception rates for Sitka spruce are as high as 60 per cent in upland Britain, where temperatures and evaporation are lower, interception is about half this figure. In the UK, preferred plantation species are conifers. The needle- like structure of conifer leaves, their evergreen habit and high density of planting all contribute to high rates of interception.
- Increased evaporation. A large proportion of intercepted rainfall is stored on leaf surfaces and is evaporated directly to the atmosphere
- Reduced run-off and stream discharge. With high interception and evaporation rates and the absorption of water by tree roots, drainage basin hydrology is altered. Streams draining plantations typically have relatively long lag times, low peak flows and low total discharge. The effect of confer plantations in upland catchments is often to reduce water yield for public supply.
- Compared to farmland and moorland, transpiration rates are increased. Typical transpiration rates for Sitka spruce in the Pennines are around 350mm/year of rainfall equivalent.
- Clear felling to harvest timber creates sudden but temporary changes to the local water cycle, increasing run-off, reducing evapotranspiration and increasing stream discharge.
What is the impact of forestry on the carbon cycle?
Changing land use from farmland, moorland and to forestry increases carbon stores in a typical in the UK, mature forest trees contain on average 200 tonnes C/ha. This is ten times higher than and 20 times higher than heathland. The so an even larger carbon pool. In England measurements of forest soil carbon are around 500 tonnes C/ha Forest trees extract CO, from the atmosphere and sequester it for hundreds of years.
Forestry plantations usually have a rotation period of 80 100 years. After this time the trees are felled and reforestation begins afresh- only an active carbon sink for this long.
What is water extraction on the River Kennet?
Water is extracted from surface and groundwater to meet public, industrial and agricultural demand Direct human intervention in the water cycle changes the dynamics of river flow and groundwater storage.
Water extraction on the River Kennet catchment The River Kennet in southern England drains an area of around 1200 km in Wiltshire and Berkshire. The upper catchment mainly comprises chalk which is highly permeable. Thus groundwater contributes most of the Kennet’s flow As a chalk stream, the river supports a diverse range of habitats and wildlife. Its water, filtered through the chalk, has exceptional clarity, high oxygen levels and is fast- Bowing Among the native fauna are Atlantic salmon, brown trout, water voles, otters and white-clawed crayfish
Within and close to the catchment, several urban areas rely on water from the Kennet basin to meet public supply Swindon, the largest, has a population of over 220,000. The Kennet also supplies water for local Industries, agriculture and public use. Thames Water abstracts groundwater from the upper catchment from boreholes. None of this water is returned to the river as waste water.
What is the impact of water extraction on regional water cycle?
- Rates of groundwater extraction have exceeded rates of recharge, and the falling water table has reduced flows in the River Kennet by 10-14 per cent
- During the 2003 drought, flows fell by 20 per cent and in the dry conditions of the early 1990s by up to 40 per cent.
- Lower flows have reduced flooding and temporary areas of standing water and wetlands on the Kennet’s floodplain between Marlborough and Hungerford
- Lower groundwater levels have caused springs and seepages to dry up and reduced the incidence of saturated overland flow on the chalk hills of the Marlborough Downs.
What is the role of aquifers in the water cycle?
Aquifers are permeable rocks that store groundwater, contributing to river flow and affected by extraction and recharge rates.
Groundwater is abstracted for public supply from aquifers by wells and boreholes. Emerging in springs and seepages, groundwater feeds rivers and makes a major contribution to their base flow. Within an aquifer the upper surface of saturation is known as the water table. Its height fluctuates seasonally and is also affected by periods of exceptional rainfall, drought and abstraction. In normal years in southern England, the water table falls between March and September as rising temperatures increase evapotranspiration losses. Recharge resumes in the late autumn.
What is an artesian aquifer?
When sedimentary rocks form a syncline or basin-like structure, an aquifer confined between impermeable rock layers may contain groundwater which is under artesian pressure. If this groundwater is tapped by a well or borehole water will Sow to the surface under its own pressure. The is known as an artesian aquifer. The level to which the water will rise-the potentiometric surface-is determined by the height of the water table in areas of recharge on the edges of the basin
In the past 50 years declining demand for water by industry in London and reduced rates of abstraction have allowed the water table to recover. By the early 1990s it was rising at a rate of 3 m/year and began to threaten buildings and underground tunnels. Since 1992 Thames Water has been granted abstraction licences to slow the rise of the water table which is now stable.
How do fossil fuels impact the carbon cycle?
In 2019 they accounted for 84 per cent of global energy consumption.
Fossil fuel consumption releases 10 billion tonnes of CO2 to the atmosphere annually increasing atmospheric CO concentration by over 1 ppm (parts per million). It is estimated that since 1750, cumulative anthropogenic CO2 emissions total nearly 2000 GT. Three-quarters of these emissions are from the burning of fossil fuels Since 1750, 879 GT of anthropogenic CO2 emissions have remained in the atmosphere ,raising CO2 concentrations from 280 ppm to 400 ppm. Today CO2 levels in the atmosphere are over 415 ppm; the highest for at least 800,000 years.
Although anthropogenic carbon emissions comprise less than 10 per cent of the natural influx from the biosphere and oceans to the atmosphere, they impact significantly on the size of the atmosphere, ocean and biosphere carbon stores. Despite international efforts to limit human carbon emissions, in the period 2000-09 they grew faster than in any previous decade, although by 2019 they had stopped rising. Without increased absorption of anthropogenic carbon by the oceans and biosphere, today’s atmospheric CO2 concentrations would exceed 500 ppm
What is carbon capture and storage (CCS)?
CCS is a technology that captures CO2 emissions from power plants, compresses it, and stores it underground to reduce greenhouse gas emissions.
It is a form of carbon sequestration. In US 40% of all CO2 emissions are from coal and gas, CCS has the potential to reduce these by 80-90%.
The Drax project in North Yorkshire, designed to capture 2 million tonnes of CO2 per year commenced operation in 2019. The plan is for the carbon to be transported by pipeline to the North Sea and stored in depleted gas reservoirs CO, gas can also be pumped into mature oilfields to extract of that would otherwise be uneconomic to recover.
Although the technology of CCS is feasible, its effectiveness is limited by economic and geological factors. This is because CCS:
- involves big capital costs-the Drax and Peterhead projects will cost at least £1 billion
- uses large amounts of energy-typically 20 per cent of a power plant’s output is needed to separate the CO, and compress it
- requires storage reservoirs with specific geological conditions, ie, porous rocks overlain by impermeable strata
What are the human CO2 emissions flows and stores?
Atmospheric CO2 concentration (ppm):
- 1750- 280
- 2012- 393
Influx CO2 to atmosphere (ppm):
- Coil- +86
- Oil- +64
- Gas- +26
- Cement- +5
- Land Use- +76
Absorption of CO2 from atmosphere (ppm)
- Biosphere sink: -68
- Ocean sink: -76
Net gain CO2 in atmosphere= 113 ppm
What are positive and negative feedback loops?
Feedback is an automatic response to changes which disturb a system’s balance or equilibrium Change in natural systems can produce either positive or negative feedback responses. Positive feedback occurs when an initial change causes further change. Negative feedback is the opposite: it counters system change and restores equilibrium.
How does rising temperature create positive feedback in the water cycle?
Rising temperatures affect the water cycle at the global scale. In a warmer world, evaporation increases and the atmosphere holds more vapour. The result is greater cloud cover and more precipitation. These changes create a positive feedback effect. Because water vapour is a greenhouse gas, more vapour in the atmosphere increases absorption of long-wave radiation from the Earth, causing further rises in temperature.
Alternatively, more atmospheric vapour can induce negative feedback. This works as follows more vapour creates greater cloud cover which reflects more solar radiation back into space. And as smaller amounts of solar radiation are absorbed temperatures fall. by the atmosphere, oceans and land, average global temperature falls.
What are the feedback loops present in a drainage basin?
In drainage basins in the longer term, inputs and outputs of water are in equilibrium. The main input, precipitation, is balanced by outputs of evapotranspiration and run-off. However, this balance varies from year to year. The system responds to above average precipitation by increasing river flow and evaporation, and excess water recharges aquifers, increasing water storage in permeable rocks. Both responses are example of negative feedback. During droughts the system adjusts to lower precipitation by reducing run-off and evapotranspiration. Meanwhile, as the wate table falls, springs and seepages dry up, helping to conserve groundwater stores.
Feedback in the water cycle also takes place at the smallest scale. In most years precipitation is sufficient to satisfy an individual tree’s demand for water However, in drought years, shallow rooted trees like silver birch become stressed: water lost in transpiration is not replaced by a similar uptake of water from the soil. The tree responds, reducing transpiration losses by shedding some or all of its leaves. This negative feedback loop restores the water balance and ensures the tree’s survival
What are the feedback loops present in the carbon cycle?
The global carbon cycle is currently in a state of disequilibrium. Human activity primarily through burning fossil fuels has increased the concentration of CO2 in the atmosphere, the acidity of the oceans and the flux of carbon between the major stores. Within the carbon cycle there are feedback loops which could either restore equilibrium or induce further disequilibrium
Negative feedback could neutralise rising levels of atmospheric CO2 by stimulating photosynthesis. This process is called carbon fertilisation in this way excess CO2 is extracted from the atmosphere and stored in the biosphere Eventually much of this carbon would find its way into long-term storage in soils and ocean sediments, allowing the system to return to a steady state
However, increased primary production through carbon fertilisation is conditional on the availability of other requirements for photosynthesis such as sunlight, soil nutrients, nitrogen and water. So, although there is evidence that primary production has indeed increased in recent years it is not possible to say with certainty that this is due to increased atmospheric CO2 for instance, recently significant increases in primary production have been observed in the Amazon rainforest but this could be explained by lower rainfall with less cloud cover and more sunlight rather than an increase in CO2.
Positive feedback could tip the carbon cycle into greater disequilibrium. For instance, global warming will intensify the carbon cycle, speed up decomposition and release more CO2 to the atmosphere, thus amplifying the greenhouse effect Another positive feedback effect is seen in Arctic tundra where global warming is occurring faster than in any other region (1.5-2.5°C in the past 30 years). As the Arctic sea ice and snow cover shrinks large expanses of sea and land are exposed. This means that more sunlight is absorbed, warming the tundra and melting the permafrost. This is significant for the global carbon cycle because the tundra stores an estimated 1600 GT of organic carbon in the permafrost.
How can we monitor changes to the global water and carbon cycle?
Given the potentially damaging impact of climate change, accurate monitoring of changes in global air temperatures, sea surface temperatures (SST) sea ice thickness and rates of deforestation is essential. Because ground-based measurements of environmental change at the global scale are impractical, monitoring relies heavily on satellite technology and remote sensing. Continuous monitoring by satellite on a day-to-day, month-to-month or year-to-year basis allows changes to be observed on various time scales. Using Geographic Information Systems (CIS) techniques these data can then be mapped and analysed to show areas of anomalies and trends, and regions of greatest change.
What are diurnal changes in the water and carbon cycle?
Significant changes occur within a 24-hour period in the water cycle. Lower temperatures at night reduce evaporation and transpiration, Convectional precipitation, dependent on direct heating of the ground surface by the Sun, is a daytime phenomenon often falling in the afternoon when temperatures reach a maximum. This is particularly significant in climatic regions in the tropics where the bulk of precipitation is from convectional storms
Flows of carbon vary both diurnally and seasonally During the daytime CO2 flows from the atmosphere to vegetation. At night the flux is reversed. Without sunlight, photosynthesis switches off, and vegetation loses CO, to the atmosphere. The same diurnal pathway is observed with phytoplankton in the oceans.
What are seasonal changes in the two cycles?
Ultimately the seasons are controlled by variations the intensity of solar radiation. In the UK, G in southern England is around 800 Wim; in Deca intensity peaks in mid-June. A typical solar input the input fails to little more than 150 Win As a result, evapotranspiration is highest in the s months and lowest in winter (Table 4.14) in the driest parts of lowland England up to 60 percent of precipitation may be lost to evapotranspiration w large losses of precipitation to evapotranspiration the exhaustion of soil moisture, river flows in England are normally at their lowest in late summer.
Seasonal variations in the carbon cycle are shown by month-to-month changes in the net primary productivity of vegetation (NPP). In middle and high latitudes, day length or photoperiod, and temperature drive seasonal changes in NPP. Similar seasonal variations also occur in the tropics, though there the main cause is water availability.
During the northern hemisphere summer, when trees are in full foliage, there is a net global flow of CO2 from the atmosphere to the biosphere. This causes atmospheric CO2 levels to fall by 2 ppm. At the end of summer, as photosynthesis ends, the flow is reversed with natural decomposition releasing CO2 back to the atmosphere. Seasonal fluctuations in the global CO2 flux are explained by the concentration of continental land masses in the northern hemisphere. During the growing season, ecosystems such as the boreal and temperate forests extract huge amounts of CO2 from the atmosphere, which has a global impact.
In the oceans phytoplankton are stimulated into photosynthetic activity by rising water temperatures, more intense sunlight and the lengthening photoperiod. Every year in the North Atlantic there is an explosion of microscopic oceanic plant life which starts in March and peaks in mid-summer. The resulting algal blooms are so extensive, they are visible from space.
What other management strategies are there?
Arctic sea ice:
- NASA’S Earth Observing System(EOS) satellites have monitored sea ice growth and retreat since 1978
- Measures microwave energy radiated from Ea surface. Comparison of time series images to th changes.
Ice caps/glaciers:
- As well as ground-based estimates of mass balance, satellite technology
- Measures surface height of ice sheet and glaciers using laser technology. Shows extent and volume of ice changes
Sea surface temperatures (SSTS):
- NOAA satellites
- Radiometers measure the wave band of radiation emitted from the ocean surface. Changes in g SSTS and areas of upwelling and downwelling Measures cloud liquid water, total precipitate water, etc. Long-term trends in cloud cover and water vapour in the atmosphere.
Water vapour:
- NOAA polar orbiters
- Measures cloud liquid water, total precipitable water etc. Long term trends in cloud cover and water vapour in the atmosphere.
Deforestation
- ESA Albedo (reflectivity) images from various satellites
- Measurements of reflectivity of earth surface and land use changes
Atmospheric CO
- NASA’s orbiting carbon observatory. Ground based measurements at Mauna Loa, Hawaii since 1958.
- New satellite measurements of global atmospheric CO2 from NASA’s Orbiting Carbon Observatory (OCO-2). The satellite also measures the effectiveness of absorption of CO2 by plants
Primary production in oceans
- NASA’s MODIS/AQUA
- Measures net primary production in oceans and on land
What are long term changes?
The climate record over the last million years shows the Earth’s climate has been highly unstable, with large fluctuations in global temperatures occurring at regular intervals in the past 400.000 years, there have been four major glacial cycles with cold glacials followed by warmer inter-glacials. Each cycle lasted around 100.000 years. At the height of the last glacial 20.000 years ago, average annual temperatures in the British Isles were 5°C lower than today, and Scotland, Wales and most of northern England and Ireland were submerged by ice up to 1 km thick.
During the warm inter-glacial periods, temperatures were similar to those of today. However, on much longer time scales global temperatures have been even more extreme. For example, 250 million years ago average global temperatures reached 22°C-at least 7-8°C higher than today’s. These climatic shifts had a major impact on the water and carbon cycles.
What are long term changes in the water cycle?
During glacial periods the water cycle undergoes a number of changes. The most obvious is the net transfer of water from the ocean reservoir to storage in ice sheets, glaciers and permafrost. As a result, in glacials the sea level worldwide falls by 100-130 m: and ice sheets and glaciers expand to cover around one-third of the continental land mass. As ice sheets advance Equator-wards they destroy extensive tracts of forest and grassland. The area covered by vegetation and water stored in the biosphere shrinks. Meanwhile, in the tropics, the climate becomes drier and deserts and grasslands displace large areas of rainforest
Lower rates of evapotranspiration during glacial phases reduce exchanges of water between the atmosphere and the oceans, biosphere and soils. This together with so much freshwater stored as snow and ice, slows the water cycle appreciably.
What are long term changes in the carbon cycle?
The most striking feature of the carbon cycle during glacial periods is the dramatic reduction in CO, in the atmosphere. At times of glacial maxima, CO2 concentrations fall to around 180 ppm while in warmer inter-glacial periods they are 100 ppm higher.
No clear explanation exists for the drop in atmospheric CO2 during glacial periods. It is, however possible that excess CO2 finds its way from the atmosphere to the deep ocean. One mechanism is changes in ocean circulation during glacials that bring nutrients to the surface and stimulate phytoplankton growth. Phytoplankton fix large amounts of CO2 by photosynthesis before dying and sinking to the deep ocean where the carbon is stored. Lower ocean temperatures also make CO2 more soluble in surface waters.
Other changes occur in the terrestrial biosphere. The carbon pool in vegetation shrinks during glacials as ice sheets advance and occupy large areas of the continents. In this process deserts expand tundra replaces temperate forests and grasslands encroach on tropical rainforests. With much of the land surface buried by ice, carbon stored in sols will no longer be exchanged with the atmosphere. Meanwhile expanses of tundra beyond the ice-limit sequester huge amounts of carbon in permafrost. With less vegetation cover, fewer forests, lower temperatures and lower precipitation, NPP and the total volume of carbon fixed in photosynthesis will decline. The implications are an overall slowing of the carbon flux and smaller amounts of CO2 returned to the atmosphere through decomposition.
