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Ecological cyclesAquatic ecosystems form a part of, and depend on the cycling of matter (such as nutrients and other important chemical elements) which is driven by energy. Without these cycles, there would be no life on Earth. Cycles integrate many essential processes of an ecosystem[10][17]. Equilibrium explains the balance between the inputs and outputs of energy or matter. If what comes into the system is the same as what goes out, then it is balanced or in equilibrium. Otherwise, there is net gain or loss of energy or matter. The concept of equilibrium may be applied in many different fields. In physics, the forces acting on an object need to be balanced for the object not to be moving. In chemistry, a reaction needs to have reached a state where the concentration of inputs and products are not changing. Geomorphologists take a different approach using equilibrium to describe long-terms fluxes and mass-balances to understand morphological changes[11].
Cycles are a collection of on-going repetitive processes in which components are continuously cycled in various forms (such as air, water, soil, organisms). Examples include the carbon, nitrogen and phosphorus cycles (nutrient cycles), energy cycles and the water cycle[10]. Boom and BustOne of the most interesting examples of adaptation to cycles of matter is the 'boom and bust' cycle of aquatic ecosystems in variable and arid flow regimes. These systems, such as those of the Lake Eyre Basin, go through long periods without rain and without any river flow for months or years. After periods of intense rainfall, usually in the northern part of Queensland, significant flooding can occur, inundating floodplains for extended periods. This flooding results in population explosions of algae, invertebrates, fish, waterbirds and other aquatic life. This 'boom' period supports large increases in biota in the region and continues until the water evaporates where the 'bust' then occurs. This bust results in the significant crash of some species, or the movement of species (for example, waterbirds) out of the region and the movement of some species into refugia as food supplies vanish. Many species adapted to this cycle have short life cycles that can be completed while floodplains and arid lakes are full of water, and at their lowest salinity. Some species such as the water flea Daphiniopsis queenslandensis and brine shrimps Artemia spp. produce drought-resistant eggs or larvae that will only hatch when water is present, and can survive for years through dry conditions. The crayfish Cherax destructor and some species of water snails and frogs, take refuge in burrows, underground, or under stones to avoid desiccation as wetlands dry out. Climate and weather cyclesWeather cycles are recurring patterns and variations in atmospheric conditions over specific periods of time. These cycles can occur on various timescales, ranging from short-term cycles like daily, seasonal, or annual patterns, to longer-term cycles that span decades and centuries[12]. Climate is the long term pattern of weather cycles in a particular area[8]. Climate can be classified into different groups using different attributes (for example, temperature, humidity and rainfall). Atmospheric conditions change according to a combination of components and processes which trigger weather cycles. Due to the constantly changing atmosphere, climate and weather cycles are variable, and infuence a number of components in ecosystems, such as temperature, evaporation, humidity and rainfall. One of the most familiar weather cycles that impact aquatic ecosystems in Australia is the El Niño-Southern Oscillation (ENSO), which affects weather patterns and sea surface temperatures in the Pacific Ocean and has global impacts on weather and climate[12]. Short term and variable weather events such as cyclones are not considered weather cycles, but are individual weather events that are driven by specific atmospheric conditions and oceanic temperatures[5]. Climate can be classified into zones using criteria such as rainfall, temperature, humidity, and vegetation. The Climate Classification of Australia from the Bureau of Meteorology website is recommended as the base map for this layer. Extra links and information
The water cycleThe water, or hydrological, cycle describes the journey of water as water molecules make their way from the above or below the surface to the atmosphere and back again[10]. This cycle is powered by energy from the sun, in a continuous exchange of moisture between the oceans, the atmosphere, and the land. The principal source of water is from the oceans, and radiant energy makes water evaporate into the atmosphere, where winds distribute it over the earth's surface - with precipitation as a process that brings water to the earth's surface, where it is stored (temporarily) in soils, waterways and wetlands[3]. This cycle involves an exchange of energy that leads to temperature changes and drives processes such as evaporation, transpiration, condensation, precipitation, infiltration and runoff. These processes differ in magnitude depending on location. Global patterns of water movement are influenced by temperature variations. Water retention in the atmosphere depends on two main processes - evaporation rate (increases with temperature), and air temperature (warm air holds more water vapour than cold air). Evaporation is higher in warmer regions, and precipitation is lower in regions with drier air. Major river systems are fed by precipitation carried from areas of high evaporation to terrestrial landscapes via prevailing wind patterns[7]. The main processes of the water cycle are:
Rock cycleThe rock cycle describes a set of processes that explains how each of the three major rock types (igneous, metamorphic, and sedimentary) form and break down, depending on heat, pressure and sediments fluxes over long geological timespans[13][15]. The rock cycle processes transforms rock types and substrates, from one kind into another, changing their physical and chemical characteristics. The diagram below applies to rocks that originate on land (terrigenous lithologies), rather than those formed by animals and plants (biogenic substrate/rock), such as limestones. Geological processes occurring underground (such as heat and pressure, melting and crystallization) transform a rock type respectively into metamorphic or igneous rocks:
Both geological and geomorphological processes occuring on the surface of the earth are involved in the formation of sedimentary rock. Rocks can break down from their consolidated (hard) form into unconsolidated fragments or sediments, due to energy from surface processes of weathering and erosion (processes influenced from the climate, weather and the water cycle). The unconsolidated fragments or sediments are transported and deposited by hydrodynamic, aeolian and gravitational processes. Following deposition, the sediment can undergo various physical and chemical changes at low temperatures, known as diagenesis. The sediment layers may be buried and compacted, turning back into (consolidated) sedimentary rock through the process of lithification. Unconsolidated sediments remain uncovered on the surface of the substrate. Sediments on the surface and buried may also undergo chemical and physical processes (e.g. soil forming processes[18]) sometimes prior to lithification, and this may influence their lithology/substrate composition[14].
Biogenic substrates/sediments have slightly different formation processes. Calcareous biogenic substrates include limestones formed by corals, such as those described below. Corals reefs accrete through corals growing on limestone platforms beneath them formed by old coral reefs, i.e., over the ‘bones of their ancestors’[1]. The depth of the growing reef and its resultant shape modify hydrodynamic (wave and current) energy, driving processes of sediment transport, erosion and deposition that result in different geomorphological patterns (zones). The formation of reefsIn the last ice age, 20,000 years ago, sea levels were 120 metres lower than they are today[18], islands were hills, and the edge of Australia’s continental shelf was the seashore, as also described in First Nations’ creation stories[1]. As the sea level rose and the water flooded the land, coral reefs growing along the outer edge could recolonize the old limestone platforms formed by outer and mid shelf reefs during previous interglacial periods. Some inshore and fringing coral reefs are as young as 5,000 years old and formed when the sea rose to its present level. Factors influencing coral reef substrates include these thousands of years of sea level rise and fall, position on the continental shelf, width of the continental shelf, erosion, chemical dissolution, sediment transport, deposition, calcification, and lithification (into sedimentary limestones). The resulting coral reef is composed both of a consolidated carbonate framework and large areas of unconsolidated (generally carbonate) sediments. Most modern coral reefs grow on old carbonate reefs, so it is important to distinguish what is the composition of antecedent substrate within the Great Barrier Reef (i.e. whether Terrigenous or carbonate). Nutrient cycleNutrients are moved over vast distances by wind and fresh and marine waters. A nutrient cycle is the movement and exchange of nutrients within and between various biotic or abiotic components of the environment. During nutrient cycles, nutrients get absorbed, transformed, transferred, released and reabsorbed. Wetland ecosystems function as sinks and/or sources of nutrients due to various conditions and interactions between physico-chemical and biological components, such as climate and tropic interactions. Nutrients are consumed by plants and animals, and returned to the environment. Soil microbes also contribute to nutrient cycling by decomposing organic matter to release nutrients[6][3]. Some examples of nutrient cycles include:
Life cyclesBiological life cycles are a generation to generation sequence of stages in the life history of an organism, including conception, birth, growth, reproduction, and death.[4]. The main types of reproductive life cycles are the haploid and diploid life cycles[17]. The haploid life cycle is found in many single celled organisms, which contain only one set of chromosomes, such as bacteria and protists. The diploid life cycle is found with organisms with two chromosomes, one from each parent, through the process of meiosis. Meiosis is a two-stage type of cell division, where a single cell divides twice to produce four cells containing half the original amount of genetic information. Animals, plants and fungi undergo meiosis, however in many different ways (such as spawning, seed dispersal) to achieve fertilisation (combination of gametes) and ultimately reproduction. References
Last updated: 22 March 2013 This page should be cited as: Department of Environment, Science and Innovation, Queensland (2013) Ecological cycles, WetlandInfo website, accessed 18 March 2024. Available at: https://wetlandinfo.des.qld.gov.au/wetlands/ecology/components-processes-drivers/cycles/ |
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— Department of Environment, Science and Innovation