Primary production

In ecology, primary production is the synthesis of organic compounds from atmospheric or aqueous carbon dioxide. It principally occurs through the process of photosynthesis, which uses light as its source of energy, but it also occurs through chemosynthesis, which uses the oxidation or reduction of inorganic chemical compounds as its source of energy. Almost all life on Earth relies directly or indirectly on primary production. The organisms responsible for primary production are known as primary producers or autotrophs, and form the base of the food chain. In terrestrial ecoregions, these are mainly plants, while in aquatic ecoregions algae predominate in this role. Ecologists distinguish primary production as either net or gross, the former accounting for losses to processes such as cellular respiration, the latter not.

Seawifs global biosphere
Global oceanic and terrestrial photoautotroph abundance, from September 1997 to August 2000. As an estimate of autotroph biomass, it is only a rough indicator of primary-production potential, and not an actual estimate of it. Provided by the SeaWiFS Project, NASA/Goddard Space Flight Center and ORBIMAGE.
The maps above show Earth's monthly terrestrial net primary productivity from February 2000 to December 2013. The data come from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite. Values range from near 0 grams of carbon per square meter per day (tan) to 6.5 grams per square meter per day (dark green). A negative value means decomposition or respiration overpowered carbon absorption; more carbon was released to the atmosphere than the plants took in. In mid-latitudes, productivity obviously interacts with seasonal change, with productivity peaking in each hemisphere’s summer. The boreal forests of Canada and Russia experience high productivity in June and July and then a slow decline through fall and winter. Year-round, tropical forests in South America, Africa, Southeast Asia, and Indonesia have high productivity, not surprising with the abundant sunlight, warmth, and rainfall. However, even in the tropics, there are variations in productivity over the course of the year. For example, the Amazon basin exhibits especially high productivity from roughly August through October - the period of the area's dry season. Because the trees have access to a plentiful supply of ground water that builds up in the rainy season, they actually grow better when the rainy skies clear and allow more sunlight to reach the forest.[1]

Overview

Calvin-cycle4
The Calvin cycle of photosynthesis

Primary production is the production of chemical energy in organic compounds by living organisms. The main source of this energy is sunlight but a minute fraction of primary production is driven by lithotrophic organisms using the chemical energy of inorganic molecules.

Regardless of its source, this energy is used to synthesize complex organic molecules from simpler inorganic compounds such as carbon dioxide (CO2) and water (H2O). The following two equations are simplified representations of photosynthesis (top) and (one form of) chemosynthesis (bottom):

CO2 + H2O + light → CH2O + O2
CO2 + O2 + 4 H2S → CH2O + 4 S + 3 H2O

In both cases, the end point is a polymer of reduced carbohydrate, (CH2O)n, typically molecules such as glucose or other sugars. These relatively simple molecules may be then used to further synthesise more complicated molecules, including proteins, complex carbohydrates, lipids, and nucleic acids, or be respired to perform work. Consumption of primary producers by heterotrophic organisms, such as animals, then transfers these organic molecules (and the energy stored within them) up the food web, fueling all of the Earth's living systems.

Gross primary production and net primary production

Gross primary production (GPP) is the amount of chemical energy as biomass that primary producers create in a given length of time. (GPP is sometimes confused with Gross Primary productivity, which is the rate at which photosynthesis or chemosynthesis occurs.) Some fraction of this fixed energy is used by primary producers for cellular respiration and maintenance of existing tissues (i.e., "growth respiration" and "maintenance respiration").[2][3] The remaining fixed energy (i.e., mass of photosynthate) is referred to as net primary production (NPP).

NPP = GPP - respiration [by plants]

Net primary production is the rate at which all the plants in an ecosystem produce net useful chemical energy; it is equal to the difference between the rate at which the plants in an ecosystem produce useful chemical energy (GPP) and the rate at which they use some of that energy during respiration. Some net primary production goes toward growth and reproduction of primary producers, while some is consumed by herbivores.

Both gross and net primary production are in units of mass per unit area per unit time interval. In terrestrial ecosystems, mass of carbon per unit area per year (g C m−2 yr−1) is most often used as the unit of measurement.

Terrestrial production

Raunkiaer
An oak tree; a typical modern, terrestrial autotroph

On the land, almost all primary production is now performed by vascular plants, with a small fraction coming from algae and non-vascular plants such as mosses and liverworts. Before the evolution of vascular plants, non-vascular plants likely played a more significant role. Primary production on land is a function of many factors, but principally local hydrology and temperature (the latter covaries to an extent with light, specifically photosynthetically active radiation (PAR), the source of energy for photosynthesis). While plants cover much of the Earth's surface, they are strongly curtailed wherever temperatures are too extreme or where necessary plant resources (principally water and PAR) are limiting, such as deserts or polar regions.

Water is "consumed" in plants by the processes of photosynthesis (see above) and transpiration. The latter process (which is responsible for about 90% of water use) is driven by the evaporation of water from the leaves of plants. Transpiration allows plants to transport water and mineral nutrients from the soil to growth regions, and also cools the plant. Diffusion of water vapour out of a leaf, the force that drives transpiration, is regulated by structures known as stomata. These structure also regulate the diffusion of carbon dioxide from the atmosphere into the leaf, such that decreasing water loss (by partially closing stomata) also decreases carbon dioxide gain. Certain plants use alternative forms of photosynthesis, called Crassulacean acid metabolism (CAM) and C4. These employ physiological and anatomical adaptations to increase water-use efficiency and allow increased primary production to take place under conditions that would normally limit carbon fixation by C3 plants (the majority of plant species).

Oceanic production

Diatoms through the microscope
Marine diatoms; an example of planktonic microalgae

In a reversal of the pattern on land, in the oceans, almost all photosynthesis is performed by algae, with a small fraction contributed by vascular plants and other groups. Algae encompass a diverse range of organisms, ranging from single floating cells to attached seaweeds. They include photoautotrophs from a variety of groups. Eubacteria are important photosynthetizers in both oceanic and terrestrial ecosystems, and while some archaea are phototrophic, none are known to utilise oxygen-evolving photosynthesis.[4] A number of eukaryotes are significant contributors to primary production in the ocean, including green algae, brown algae and red algae, and a diverse group of unicellular groups. Vascular plants are also represented in the ocean by groups such as the seagrasses.

Unlike terrestrial ecosystems, the majority of primary production in the ocean is performed by free-living microscopic organisms called phytoplankton. Larger autotrophs, such as the seagrasses and macroalgae (seaweeds) are generally confined to the littoral zone and adjacent shallow waters, where they can attach to the underlying substrate but still be within the photic zone. There are exceptions, such as Sargassum, but the vast majority of free-floating production takes place within microscopic organisms.

Phytoplankton Intensity
Differences in relative photosynthesis between plankton species under different irradiance

The factors limiting primary production in the ocean are also very different from those on land. The availability of water, obviously, is not an issue (though its salinity can be). Similarly, temperature, while affecting metabolic rates (see Q10), ranges less widely in the ocean than on land because the heat capacity of seawater buffers temperature changes, and the formation of sea ice insulates it at lower temperatures. However, the availability of light, the source of energy for photosynthesis, and mineral nutrients, the building blocks for new growth, play crucial roles in regulating primary production in the ocean.[5] Available Earth System Models suggest that ongoing ocean bio-geochemical changes could trigger reductions in ocean NPP between 3% and 10% of current values depending on the emissions scenario.[6]

Light

Kelp forest Otago 1s
A kelp forest; an example of attached macroalgae

The sunlit zone of the ocean is called the photic zone (or euphotic zone). This is a relatively thin layer (10–100 m) near the ocean's surface where there is sufficient light for photosynthesis to occur. For practical purposes, the thickness of the photic zone is typically defined by the depth at which light reaches 1% of its surface value. Light is attenuated down the water column by its absorption or scattering by the water itself, and by dissolved or particulate material within it (including phytoplankton).

Net photosynthesis in the water column is determined by the interaction between the photic zone and the mixed layer. Turbulent mixing by wind energy at the ocean's surface homogenises the water column vertically until the turbulence dissipates (creating the aforementioned mixed layer). The deeper the mixed layer, the lower the average amount of light intercepted by phytoplankton within it. The mixed layer can vary from being shallower than the photic zone, to being much deeper than the photic zone. When it is much deeper than the photic zone, this results in phytoplankton spending too much time in the dark for net growth to occur. The maximum depth of the mixed layer in which net growth can occur is called the critical depth. As long as there are adequate nutrients available, net primary production occurs whenever the mixed layer is shallower than the critical depth.

Both the magnitude of wind mixing and the availability of light at the ocean's surface are affected across a range of space- and time-scales. The most characteristic of these is the seasonal cycle (caused by the consequences of the Earth's axial tilt), although wind magnitudes additionally have strong spatial components. Consequently, primary production in temperate regions such as the North Atlantic is highly seasonal, varying with both incident light at the water's surface (reduced in winter) and the degree of mixing (increased in winter). In tropical regions, such as the gyres in the middle of the major basins, light may only vary slightly across the year, and mixing may only occur episodically, such as during large storms or hurricanes.

Nutrients

WOA09 sea-surf NO3 AYool
Annual mean sea surface nitrate for the World Ocean. Data from the World Ocean Atlas 2009.

Mixing also plays an important role in the limitation of primary production by nutrients. Inorganic nutrients, such as nitrate, phosphate and silicic acid are necessary for phytoplankton to synthesise their cells and cellular machinery. Because of gravitational sinking of particulate material (such as plankton, dead or fecal material), nutrients are constantly lost from the photic zone, and are only replenished by mixing or upwelling of deeper water. This is exacerbated where summertime solar heating and reduced winds increases vertical stratification and leads to a strong thermocline, since this makes it more difficult for wind mixing to entrain deeper water. Consequently, between mixing events, primary production (and the resulting processes that leads to sinking particulate material) constantly acts to consume nutrients in the mixed layer, and in many regions this leads to nutrient exhaustion and decreased mixed layer production in the summer (even in the presence of abundant light). However, as long as the photic zone is deep enough, primary production may continue below the mixed layer where light-limited growth rates mean that nutrients are often more abundant.

Iron

Another factor relatively recently discovered to play a significant role in oceanic primary production is the micronutrient iron.[7] This is used as a cofactor in enzymes involved in processes such as nitrate reduction and nitrogen fixation. A major source of iron to the oceans is dust from the Earth's deserts, picked up and delivered by the wind as aeolian dust.

In regions of the ocean that are distant from deserts or that are not reached by dust-carrying winds (for example, the Southern and North Pacific oceans), the lack of iron can severely limit the amount of primary production that can occur. These areas are sometimes known as HNLC (High-Nutrient, Low-Chlorophyll) regions, because the scarcity of iron both limits phytoplankton growth and leaves a surplus of other nutrients. Some scientists have suggested introducing iron to these areas as a means of increasing primary productivity and sequestering carbon dioxide from the atmosphere.[8]

Measurement

The methods for measurement of primary production vary depending on whether gross vs net production is the desired measure, and whether terrestrial or aquatic systems are the focus. Gross production is almost always harder to measure than net, because of respiration, which is a continuous and ongoing process that consumes some of the products of primary production (i.e. sugars) before they can be accurately measured. Also, terrestrial ecosystems are generally more difficult because a substantial proportion of total productivity is shunted to below-ground organs and tissues, where it is logistically difficult to measure. Shallow water aquatic systems can also face this problem.

Scale also greatly affects measurement techniques. The rate of carbon assimilation in plant tissues, organs, whole plants, or plankton samples can be quantified by biochemically based techniques, but these techniques are decidedly inappropriate for large scale terrestrial field situations. There, net primary production is almost always the desired variable, and estimation techniques involve various methods of estimating dry-weight biomass changes over time. Biomass estimates are often converted to an energy measure, such as kilocalories, by an empirically determined conversion factor.

Terrestrial

In terrestrial ecosystems, researchers generally measure net primary production (NPP). Although its definition is straightforward, field measurements used to estimate productivity vary according to investigator and biome. Field estimates rarely account for below ground productivity, herbivory, turnover, litterfall, volatile organic compounds, root exudates, and allocation to symbiotic microorganisms. Biomass based NPP estimates result in underestimation of NPP due to incomplete accounting of these components.[9][10] However, many field measurements correlate well to NPP. There are a number of comprehensive reviews of the field methods used to estimate NPP.[9][10][11] Estimates of ecosystem respiration, the total carbon dioxide produced by the ecosystem, can also be made with gas flux measurements.

The major unaccounted pool is belowground productivity, especially production and turnover of roots. Belowground components of NPP are difficult to measure. BNPP (below-ground NPP) is often estimated based on a ratio of ANPP:BNPP (above-ground NPP:below-ground NPP) rather than direct measurements.

Gross primary production can be estimated from measurements of net ecosystem exchange (NEE) of carbon dioxide made by the eddy covariance technique. During night, this technique measures all components of ecosystem respiration. This respiration is scaled to day-time values and further subtracted from NEE.[12]

Grasslands

Konza1
The Konza tallgrass prairie in the Flint Hills of northeastern Kansas

Most frequently, peak standing biomass is assumed to measure NPP. In systems with persistent standing litter, live biomass is commonly reported. Measures of peak biomass are more reliable if the system is predominantly annuals. However, perennial measurements could be reliable if there were a synchronous phenology driven by a strong seasonal climate. These methods may underestimate ANPP in grasslands by as much as 2 (temperate) to 4 (tropical) fold.[10] Repeated measures of standing live and dead biomass provide more accurate estimates of all grasslands, particularly those with large turnover, rapid decomposition, and interspecific variation in timing of peak biomass. Wetland productivity (marshes and fens) is similarly measured. In Europe, annual mowing makes the annual biomass increment of wetlands evident.

Forests

Methods used to measure forest productivity are more diverse than those of grasslands. Biomass increment based on stand specific allometry plus litterfall is considered a suitable although incomplete accounting of above-ground net primary production (ANPP).[9] Field measurements used as a proxy for ANPP include annual litterfall, diameter or basal area increment (DBH or BAI), and volume increment.

Aquatic

In aquatic systems, primary production is typically measured using one of six main techniques:[13]

  1. variations in oxygen concentration within a sealed bottle (developed by Gaarder and Gran in 1927)
  2. incorporation of inorganic carbon-14 (14C in the form of sodium bicarbonate) into organic matter[14][15]
  3. Stable isotopes of Oxygen (16O, 18O and 17O)[16][17]
  4. fluorescence kinetics (technique still a research topic)
  5. Stable isotopes of Carbon (12C and 13C)[18]
  6. Oxygen/Argon Ratios [19]

The technique developed by Gaarder and Gran uses variations in the concentration of oxygen under different experimental conditions to infer gross primary production. Typically, three identical transparent vessels are filled with sample water and stoppered. The first is analysed immediately and used to determine the initial oxygen concentration; usually this is done by performing a Winkler titration. The other two vessels are incubated, one each in under light and darkened. After a fixed period of time, the experiment ends, and the oxygen concentration in both vessels is measured. As photosynthesis has not taken place in the dark vessel, it provides a measure of ecosystem respiration. The light vessel permits both photosynthesis and respiration, so provides a measure of net photosynthesis (i.e. oxygen production via photosynthesis subtract oxygen consumption by respiration). Gross primary production is then obtained by adding oxygen consumption in the dark vessel to net oxygen production in the light vessel.

The technique of using 14C incorporation (added as labelled Na2CO3) to infer primary production is most commonly used today because it is sensitive, and can be used in all ocean environments. As 14C is radioactive (via beta decay), it is relatively straightforward to measure its incorporation in organic material using devices such as scintillation counters.

Depending upon the incubation time chosen, net or gross primary production can be estimated. Gross primary production is best estimated using relatively short incubation times (1 hour or less), since the loss of incorporated 14C (by respiration and organic material excretion / exudation) will be more limited. Net primary production is the fraction of gross production remaining after these loss processes have consumed some of the fixed carbon.

Loss processes can range between 10-60% of incorporated 14C according to the incubation period, ambient environmental conditions (especially temperature) and the experimental species used. Aside from those caused by the physiology of the experimental subject itself, potential losses due to the activity of consumers also need to be considered. This is particularly true in experiments making use of natural assemblages of microscopic autotrophs, where it is not possible to isolate them from their consumers.

The methods based on stable isotopes and O2/Ar ratios have the advantage of providing estimates of respiration rates in the light without the need of incubations in the dark. Among them, the method of the triple oxygen isotopes and O2/Ar have the additional advantage of not needing incubations in closed containers and O2/Ar can even be measured continuously at sea using equilibrator inlet mass spectrometry (EIMS)[20] or a membrane inlet mass spectrometry (MIMS).[21] However, if results relevant to the carbon cycle are desired, it is probably better to rely on methods based on carbon (and not oxygen) isotopes. It is important to notice that the method based on carbon stable isotopes is not simply an adaptation of the classic 14C method, but an entirely different approach that does not suffer from the problem of lack of account of carbon recycling during photosynthesis.

Global

As primary production in the biosphere is an important part of the carbon cycle, estimating it at the global scale is important in Earth system science. However, quantifying primary production at this scale is difficult because of the range of habitats on Earth, and because of the impact of weather events (availability of sunlight, water) on its variability. Using satellite-derived estimates of the Normalized Difference Vegetation Index (NDVI) for terrestrial habitats and sea-surface chlorophyll for the oceans, it is estimated that the total (photoautotrophic) primary production for the Earth was 104.9 petagrams of carbon per year (Pg C yr−1; equivalent to the non-SI Gt C yr−1).[22] Of this, 56.4 Pg C yr−1 (53.8%), was the product of terrestrial organisms, while the remaining 48.5 Pg C yr−1, was accounted for by oceanic production.

Scaling ecosystem-level GPP estimations based on eddy covariance measurements of net ecosystem exchange (see above) to regional and global values using spatial details of different predictor variables, such as climate variables and remotely sensed fAPAR or LAI led to a terrestrial gross primary production of 123±8 Gt carbon (NOT carbon dioxide) per year during 1998-2005 [23]

In areal terms, it was estimated that land production was approximately 426 g C m−2 yr−1 (excluding areas with permanent ice cover), while that for the oceans was 140 g C m−2 yr−1.[22] Another significant difference between the land and the oceans lies in their standing stocks - while accounting for almost half of total production, oceanic autotrophs only account for about 0.2% of the total biomass.

Estimates

Primary productivity can be estimated by a variety of proxies. One that has particular relevance to the geological record is Barium, whose concentration in marine sediments rises in line with primary productivity at the surface.[24][25][26]

Primary production and plant biomass for the Earth

Ecosystem type Area
(10⁶ km²)
Mean NPP
(g/m²/yr)
World NPP
(10⁹ tons/yr)
Mean biomass
(kg/m²)
World biomass
(10⁹ tons)
Tropical rainforest 17.0 2,200 37.4 45 763
Tropical seasonal forest 7.5 1,600 12.0 35 260
Temperate evergreen forest 5.0 1,300 6.5 35 175
Temperate deciduous forest 7.0 1,200 8.4 30 210
Boreal forest 12.0 800 9.6 20 240
Woodlands and shrublands 8.5 700 6.0 6 50
Savanna 15.0 900 13.6 4 60
Temperate grasslands 9.0 600 5.4 1.6 14
Tundra and alpine 8.0 140 1.1 0.6 5
Desert and semi-desert 18.0 90 1.6 0.7 13
Extreme desert and ice 24.0 3 0.07 0.02 0.5
Cultivated land 14.0 650 9.1 1.0 14
Swamp and wetland 2.0 2,000 4.0 12.3 30
Lakes and streams 2.0 250 0.5 0.02 0.05
Total Continental 149 773 115 12.3 1837
Open ocean 332.0 125 41.5 0.003 1.0
Upwelling zones 0.4 500 0.2 0.02 0.008
Continental shelf 26.6 360 9.6 0.01 0.27
Algal bed and reef 0.6 2,500 1.6 2.0 1.2
Estuaries 1.4 1,500 2.1 1.0 1.4
Total marine 361 152 55.0 0.01 3.9
Grand total 510 333 170 3.6 1841

From R.H. Whittaker, quoted in Peter Stiling (1996), "Ecology: Theories and Applications" (Prentice Hall).

Human impact and appropriation

Human societies are part of the Earth's NPP cycle, but exert a disproportionate influence in it.[27] In 1996, Josep Garí designed a new indicator of sustainable development based precisely on the estimation of the human appropriation of NPP: he coined it "HANPP" (Human Appropriation of Net Primary Production) and introduced it at the inaugural conference of the European Society for Ecological Economics.[28] HANPP has since been further developed and widely applied in research on ecological economics as well as in policy analysis for sustainability. HANPP represents a proxy of the human impact on Nature and can be applied to different geographical scales and also globally.

The extensive degree of human use of the Planet's resources, mostly via land use, results in various levels of impact on actual NPP (NPPact). Although in some regions, such as the Nile valley, irrigation has resulted in a considerable increase in primary production, in most of the Planet there is a notable trend of NPP reduction due to land changes (ΔNPPLC) of 9.6% across global land-mass.[29] In addition to this, end consumption by people raises the total HANPP [27] to 23.8% of potential vegetation (NPP0).[29] It is estimated that, in 2000, 34% of the Earth's ice-free land area (12% cropland; 22% pasture) was devoted to human agriculture.[30] This disproportionate amount reduces the energy available to other species, having a marked impact on biodiversity, flows of carbon, water and energy, and ecosystem services,[29] and scientists have questioned how large this fraction can be before these services begin to break down.[31] Reductions in NPP are also expected in the ocean as a result of ongoing climate change, potentially impacting marine ecosystems and goods and services that the oceans provide [6]

See also

References

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Bathyal zone

The bathyal zone or bathypelagic – from Greek βαθύς (bathýs), deep – (also known as midnight zone) is the part of the pelagic zone that extends from a depth of 1,000 to 4,000 m (3,300 to 13,100 ft) below the ocean surface. It lies between the mesopelagic above, and the abyssopelagic below. The average temperature hovers at about 4 °C (39 °F). Although larger by volume than the euphotic zone, the bathyal zone is less densely populated. Sunlight does not reach this zone, meaning primary production, if any, is almost nonexistent. There are no known plants because of the lack of sunlight necessary for photosynthesis. It is known as the midnight (also twilight or dark) zone because of this feature.

Biological pump

The biological pump, in its simplest form, is the ocean's biologically driven sequestration of carbon from the atmosphere to the ocean interior and seafloor sediments. It is the part of the oceanic carbon cycle responsible for the cycling of organic matter formed mainly by phytoplankton during photosynthesis (soft-tissue pump), as well as the cycling of calcium carbonate (CaCO3) formed into shells by certain organisms such as plankton and mollusks (carbonate pump).

Biomass (ecology)

The biomass is the mass of living biological organisms in a given area or ecosystem at a given time. Biomass can refer to species biomass, which is the mass of one or more species, or to community biomass, which is the mass of all species in the community. It can include microorganisms, plants or animals. The mass can be expressed as the average mass per unit area, or as the total mass in the community.

How biomass is measured depends on why it is being measured. Sometimes, the biomass is regarded as the natural mass of organisms in situ, just as they are. For example, in a salmon fishery, the salmon biomass might be regarded as the total wet weight the salmon would have if they were taken out of the water. In other contexts, biomass can be measured in terms of the dried organic mass, so perhaps only 30% of the actual weight might count, the rest being water. For other purposes, only biological tissues count, and teeth, bones and shells are excluded. In some applications, biomass is measured as the mass of organically bound carbon (C) that is present.

The total live biomass on Earth is about 550–560 billion tonnes C, and the total annual primary production of biomass is just over 100 billion tonnes C/yr. The total live biomass of bacteria may be as much as that of plants and animals or may be much less. The total number of DNA base pairs on Earth, as a possible approximation of global biodiversity, is estimated at (5.3±3.6)×1037, and weighs 50 billion tonnes. In comparison, the total mass of the biosphere has been estimated to be as much as 4×1012 tonnes of carbon.

Canary Current

The Canary Current is a wind-driven surface current that is part of the North Atlantic Gyre. This eastern boundary current branches south from the North Atlantic Current and flows southwest about as far as Senegal where it turns west and later joins the Atlantic North Equatorial Current. The current is named after the Canary Islands. The archipelago partially blocks the flow of the Canary Current (Gyory, 2007).

This wide and slow moving current is thought to have been exploited in the early Phoenician navigation and settlement along the coast of western Morocco. The ancient Phoenicians not only exploited numerous fisheries within this current zone, but also established a factory at Iles Purpuraires off present day Essaouira for extracting a Tyrian purple dye from a marine gastropod murex species.

Ecoforestry

Ecoforestry has been defined as selection forestry or restoration forestry. The main idea of Ecoforestry is to maintain or restore the forest to standards where the forest may still be harvested for products on a sustainable basis. Ecoforestry is forestry that emphasizes holistic practices which strive to protect and restore ecosystems rather than maximize economic productivity. Sustainability of the forest also comes with uncertainties. There are other factors that may affect the forest furthermore than that of the harvesting. There are internal conditions such as effects of soil compaction, tree damage, disease, fire, and blow down that also directly affect the ecosystem. These factors have to be taken into account when determining the sustainability of a forest. If these factors are added to the harvesting and production that comes out of the forest, then the forest will become less likely to survive, and will then become less sustainable.

Since the forest is considered an ecosystem, it is dependent on all of the living and non-living factors within itself. This is a major part of why the forest needs to be sustainable before it is harvested. For example, a tree, by way of photosynthesis, converts sunlight to sugars for respiration to keep the tree alive. The remains of the converted sugars is left in roots for consumption by the organisms surrounding the tree in the habitat. This shows the productivity of an ecosystem with its inhabitants. Productivity within the ecosystem cannot come to fruition unless the forest is sustainable enough to be harvested. If most individual organisms of the ecosystem vanish, the ecosystem itself is at risk. Once that happens, there is no longer any forest to harvest from. The overall productivity of a system can be found in an equation where the Net Primary Production, or NPP, is equal to the Gross Primary Production, or GPP, minus the Respiration, or R. The formula is the NPP = GPP - R. The NPP is the overall efficiency of the plants in the ecosystem. Through having a constant efficiency in NPP, the ecosystem is then more sustainable. The GPP refers to the rate of energy stored by photosynthesis in plants. The R refers to the maintenance and reproduction of plants from the energy expended.

Ecoforestry has many principles within the existence of itself. It covers sustainable development and the fair harvesting of the organisms living within the forest ecosystem. There have been many proposals of principles outlined for ecoforestry. They are covered over books, articles, and environmental agencies. All of the principles relate to the idea that in ecoforestry, less should be harvested, and diversity must be managed. Through harvesting less, there is enough biomass left in the forest, so that the forest may stay healthy and still stay maintained. It will grow at a sustainable level annually, and thus it will be able to still be harvested the following year. Through management of the diversity, species may cohabitate in an ecosystem where the forest may feed off of other species in its growth and production. The Principles of Ecoforestry may be found below.

Ecology of the San Francisco Estuary

The San Francisco Estuary together with the Sacramento–San Joaquin River Delta represents a highly altered ecosystem. The region has been heavily re-engineered to accommodate the needs of water delivery, shipping, agriculture, and most recently, suburban development. These needs have wrought direct changes in the movement of water and the nature of the landscape, and indirect changes from the introduction of non-native species. New species have altered the architecture of the food web as surely as levees have altered the landscape of islands and channels that form the complex system known as the Delta.This article deals particularly with the ecology of the low salinity zone (LSZ) of the estuary. Reconstructing a historic food web for the LSZ is difficult for a number of reasons. First, there is no clear record of the species that historically have occupied the estuary. Second, the San Francisco Estuary and Delta have been in geologic and hydrologic transition for most of their 10,000 year history, and so describing the "natural" condition of the estuary is much like "hitting a moving target". Climate change, hydrologic engineering, shifting water needs, and newly introduced species will continue to alter the food web configuration of the estuary. This model provides a snapshot of the current state, with notes about recent changes or species introductions that have altered the configuration of the food web. Understanding the dynamics of the current food web may prove useful for restoration efforts to improve the functioning and species diversity of the estuary.

Ecosystem

An ecosystem is a community of living organisms in conjunction with the nonliving components of their environment, interacting as a system. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the system through photosynthesis and is incorporated into plant tissue. By feeding on plants and on one-another, animals play an important role in the movement of matter and energy through the system. They also influence the quantity of plant and microbial biomass present. By breaking down dead organic matter, decomposers release carbon back to the atmosphere and facilitate nutrient cycling by converting nutrients stored in dead biomass back to a form that can be readily used by plants and other microbes.Ecosystems are controlled by external and internal factors. External factors such as climate, parent material which forms the soil and topography, control the overall structure of an ecosystem but are not themselves influenced by the ecosystem. Unlike external factors, internal factors are controlled, for example, decomposition, root competition, shading, disturbance, succession, and the types of species present.

Ecosystems are dynamic entities—they are subject to periodic disturbances and are in the process of recovering from some past disturbance. Ecosystems in similar environments that are located in different parts of the world can end up doing things very differently simply because they have different pools of species present. Internal factors not only control ecosystem processes but are also controlled by them and are often subject to feedback loops.Resource inputs are generally controlled by external processes like climate and parent material. Resource availability within the ecosystem is controlled by internal factors like decomposition, root competition or shading. Although humans operate within ecosystems, their cumulative effects are large enough to influence external factors like climate.Biodiversity affects ecosystem functioning, as do the processes of disturbance and succession. Ecosystems provide a variety of goods and services upon which people depend.

F-ratio

In oceanic biogeochemistry, the f-ratio is the fraction of total primary production fuelled by nitrate (as opposed to that fuelled by other nitrogen compounds such as ammonium). The ratio was originally defined by Richard Eppley and Bruce Peterson in one of the first papers estimating global oceanic production. This fraction was originally believed significant because it appeared to directly relate to the sinking (export) flux of organic marine snow from the surface ocean by the biological pump. However, this interpretation relied on the assumption of a strong depth-partitioning of a parallel process, nitrification, that more recent measurements has questioned.

Forest

A forest is a large area dominated by trees. Hundreds of more precise definitions of forest are used throughout the world, incorporating factors such as tree density, tree height, land use, legal standing and ecological function. According to the widely used Food and Agriculture Organization definition, forests covered 4 billion hectares (9.9×109 acres) (15 million square miles) or approximately 30 percent of the world's land area in 2006.Forests are the dominant terrestrial ecosystem of Earth, and are distributed around the globe. Forests account for 75% of the gross primary production of the Earth's biosphere, and contain 80% of the Earth's plant biomass. Net primary production is estimated at 21.9 gigatonnes carbon per year for tropical forests, 8.1 for temperate forests, and 2.6 for boreal forests.Forests at different latitudes and elevations form distinctly different ecozones: boreal forests around the poles, tropical forests around the Equator, and temperate forests at the middle latitudes. Higher elevation areas tend to support forests similar to those at higher latitudes, and amount of precipitation also affects forest composition.

Human society and forests influence each other in both positive and negative ways. Forests provide ecosystem services to humans and serve as tourist attractions. Forests can also affect people's health. Human activities, including harvesting forest resources, can negatively affect forest ecosystems.

List of countries by gold production

This is a list of countries by gold production in 2017.

For many years until 2006, South Africa was the world's dominant gold producer, but recently other countries have surpassed South Africa: China, Russia, Canada, the United States, Peru and Australia. Albeit, none of these countries have approached South Africa's peak production which occurred in the apartheid-era 1970s.Note the figures are for primary production. In the US, for example, for the years 2010–14, new and old scrap exceeded both primary production and reported domestic consumption.

Photic zone

The photic zone, euphotic zone (Greek for "well lit": εὖ "well" + φῶς "light"), or sunlight (or sunlit) zone is the uppermost layer of water in a lake or ocean that is exposed to intense sunlight. It corresponds roughly to the layer above the compensation point, i.e. depth where the rate of carbon dioxide uptake, or equivalently, the rate of photosynthetic oxygen production, is equal to the rate of carbon dioxide production, equivalent to the rate of respiratory oxygen consumption, i.e. the depth where net carbon dioxide assimilation is zero.

It extends from the surface down to a depth where light intensity falls to one percent of that at the surface, called the euphotic depth. Accordingly, its thickness depends on the extent of light attenuation in the water column. Typical euphotic depths vary from only a few centimetres in highly turbid eutrophic lakes, to around 200 meters in the open ocean. It also varies with seasonal changes in turbidity.

Since the photic zone is where almost all of the photosynthesis occurs, the depth of the photic zone is generally proportional to the level of primary production that occurs in that area of the ocean. About 90% of all marine life lives in the photic zone. A small amount of primary production is generated deep in the abyssal zone around the hydrothermal vents which exist along some mid-oceanic ridges.

The zone which extends from the base of the euphotic zone to about 200 metres is sometimes called the disphotic zone. While there is some light, it is insufficient for photosynthesis, or at least insufficient for photosynthesis at a rate greater than respiration. The euphotic zone together with the disphotic zone coincides with the epipelagic zone. The bottommost zone, below the euphotic zone, is called the aphotic zone. Most deep ocean waters belong to this zone.

The transparency of the water, which determines the depth of the photic zone, is measured simply with a Secchi disk. It may also be measured with a photometer lowered into the water.

Phytoplankton

Phytoplankton are the autotrophic (self-feeding) components of the plankton community and a key part of oceans, seas and freshwater basin ecosystems. The name comes from the Greek words φυτόν (phyton), meaning "plant", and πλανκτός (planktos), meaning "wanderer" or "drifter". Most phytoplankton are too small to be individually seen with the unaided eye. However, when present in high enough numbers, some varieties may be noticeable as colored patches on the water surface due to the presence of chlorophyll within their cells and accessory pigments (such as phycobiliproteins or xanthophylls) in some species.

Planktology

Planktology is the study of plankton, various small drifting plants, animals and microorganisms that inhabit bodies of water. Planktology topics include primary production, energy flow and the carbon cycle.

Plankton drive the "biological pump", a process by which the ocean ecosystem transports carbon from the surface euphotic zone to the ocean's depths. Such processes are vital to carbon dioxide sinks, one of several possibilities for countering global warming. Modern planktology includes behavioral aspects of drifting organisms, engaging modern in situ imaging devices.

Some planktology projects allow the public to participate online, such as the Long-term Ecosystem Observatory.

Plankton

Plankton are the diverse collection of organisms that live in large bodies of water and are unable to swim against a current. The individual organisms constituting plankton are called plankters. They provide a crucial source of food to many large aquatic organisms, such as fish and whales.

These organisms include bacteria, archaea, algae, protozoa and drifting or floating animals that inhabit—for example—the pelagic zone of oceans, seas, or bodies of fresh water. Essentially, plankton are defined by their ecological niche rather than any phylogenetic or taxonomic classification.

Though many planktonic species are microscopic in size, plankton includes organisms over a wide range of sizes, including large organisms such as jellyfish.

Technically the term does not include organisms on the surface of the water, which are called pleuston—or those that swim actively in the water, which are called nekton.

Primary producers

Primary producers convert an abiotic source of energy (e.g. light) into energy stored in organic compounds, which can be used by other organisms (e.g. heterotrophs). The primary producers can convert the energy in the light (phototroph and photoautotroph) or the energy in inorganic chemical compounds (chemolithotrophs) to build organic molecules, which is usually accumulated in the form of biomass and will be used as carbon and energy source by other organisms (e.g. heterotrophs and mixotrophs). The photoautotrophs are the main primary producers, converting the energy of the light into chemical energy through photosynthesis, ultimately building organic molecules from carbon dioxide, an inorganic carbon source. Examples of chemolithotrophs are some archaea and bacteria (unicellular organisms) that produce biomass from the oxidation of inorganic chemical compounds, these organisms are called chemoautotrophs, and are frequently found in hydrothermal vents in the deep ocean. Primary producers ares at the lowest trophic level, and are the reasons why Earth is sustainable for life to this day.

Primary sector of the economy

The primary sector of the economy includes any industry involved in the extraction and collection of natural resources; such as farming, forestry, mining and fishing.The primary sector tends to make up a larger portion of the economy in developing countries than it does in developed countries. For example, animal husbandry is relatively more common in countries in Africa than it is in Japan.Mining in 19th-century South Wales provides a case study of how an economy can come to rely on one form of activity.In developed countries primary industry has become more technologically advanced - witness for instance the mechanization of farming as opposed to hand-picking and -planting. More developed economies may invest additional capital in primary means of production. As an example, in the United States' corn belt, combine harvesters pick the corn, and sprayers spray large amounts of insecticides, herbicides and fungicides, producing a higher yield than is possible using less capital-intensive techniques. These technological advances and investment allow the primary sector to employ a smaller workforce - in this way, developed countries tend to have a smaller percentage of their workforce involved in primary activities, instead having a higher percentage involved in the secondary and tertiary sectors.Developed countries are allowed to maintain and develop their primary industries even further due to the excess wealth. For instance, European Union agricultural subsidies provide buffers against fluctuating inflation-rates and prices of agricultural produce. This allows developed countries to export their agricultural products at extraordinarily low prices. This makes them extremely competitive against those of poor or underdeveloped countries that maintain free-market policies and low or non-existent tariffs to counter cheap goods. Such price differences also come about due to more efficient production in developed economies, given farm machinery, better information available to farmers, and (often) larger scale.

Some economies exhibit a particular emphasis on the basic food-providing parts of the primary sector (farming and fishing), wishing to guarantee via autarky in food-production that citizens can eat even in extreme circumstances (such as war,blockade,

or sanctions).

The agricultural revolution may not have preceded the industrial revolution entirely by chance.

Productivity (ecology)

In ecology, productivity refers to the rate of generation of biomass in an ecosystem. It is usually expressed in units of mass per unit surface (or volume) per unit time, for instance grams per square metre per day (g m−2 d−1). The mass unit may relate to dry matter or to the mass of carbon generated. Productivity of autotrophs such as plants is called primary productivity, while that of heterotrophs such as animals is called secondary productivity.

Stratification (water)

Water stratification is when water masses with different properties - salinity (halocline), oxygenation (chemocline), density (pycnocline), temperature (thermocline) - form layers that act as barriers to water mixing which could lead to anoxia or euxinia. These layers are normally arranged according to density, with the least dense water masses sitting above the more dense layers.

Water stratification also creates barriers to nutrient mixing between layers. This can affect the primary production in an area by limiting photosynthetic processes. When nutrients from the benthos cannot travel up into the photic zone, phytoplankton may be limited by nutrient availability. Lower primary production also leads to lower net productivity in waters.

Zacoalco de Torres

Zacoalco de Torres, formerly Zacoalco (Nahuatl languages: Tzacoalco; "place of closed water"), is a town and municipality in Jalisco, Mexico. The municipality covers an area of 491.27 km². It is the primary production region of the equipal-style wood and pigskin furniture.

As of 2005, the municipality had a total population of 25,529.To the east lies the largest lake in Mexico, Lago de Chapala.

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