What is meaning of Hydrosphere?

The hydrosphere’s mass is a mass of all water (including salt dilutions and excluding polar ice and glaciers).

The hydrosphere, including all the waters on the Earth’s surface, is interconnected with the other ‘spheres’ in the Earth system, that is the geosphere (lithosphere and atmosphere), the biosphere, and the human-related anthroposphere. Water, the most widespread substance in the environment of our planet, is available, in liquid, solid, and vapor states, everywhere on Earth, albeit its abundance largely differs in space and time.

Quantitative estimates of availability of water (and in particular, freshwater) in different Earth’s water stores (reservoirs) are given. The abundance of liquid water on Earth clearly distinguishes our unique planet from other planets in the solar system, where no liquid water can be found.

Water is a basic element of the life support system of the planet, being essential for self-reproducing life. It is a universal solvent and carrier of substances. Water has unique properties and behaves in an anomalous way. This plays a crucial role in many fundamental processes in the geosphere and biosphere. Climate and water on Earth are closely linked. Water influences the climate and is influenced by the climate. Discussion of observed and projected impacts of climate changes on the hydrosphere is offered, as well as a review of human interactions with the hydrosphere.

The Young Earth in Katarchaean was devoid of the hydrosphere and atmosphere. It is natural to suggest that these external and very mobile geospheres emerged only due to the Earth’s degassing. The degassing could only begin after the heating of the upper section and the emergence of melted matter nodes within it. The Earth depths’ heating at those distant times was only due to the release of the Moon-interaction tidal energy and radioactive decay. The tidal energy was released mostly in the Earth’s upper section. For this reason, first melts of the Earth’s matter appeared at relatively shallow depths of 200–400 km approximately 600 MMY after the emergence of Earth.

Immediately upon the appearance of first melts, the Earth’s matter differentiation began and first indications of the tectonomagmatic activity showed about 4 BY ago. After that, the Earth’s matter differentiation was fed by the most powerful gravitational energy process of high-density melted iron separation from the Earth’s matter silicates (see Section 4.3).

It is to be expected that the Earth’s—or rather the Earth’s mantle—degassing substantially depended not only on the mantle temperature (which determined the mantle convection flow intensity) but also on its chemical composition.

The emergence of the lithospheric plate tectonics and especially the development of the fundamentals of the Earth’s global evolution provided a real opportunity for a quantitative description of the ocean forming processes. Our quantitative models of the World Ocean water and the gas shell growth were based on the most general concept of the global evolution (Sorokhtin, 1974).

The concept included the lithospheric plate tectonics as its component. The models took into account the direct proportionality between the Earth’s degassing rates but the major contribution to the mantle convective mass exchange came from the most powerful energy process of the chemico-density differentiation of Earth’s matter into a high-density iron-oxide core and a residual silicate mantle.

These earlier studies, however, were still related to the end of the planet’s formation process about 4.6 BY ago.

Later models (Monin and Sorokhtin, 1984; Sorokhtin and Ushakov, 1991, 2002) were based on the aforementioned Earth’s matter zonal and barodiffusion differentiation mechanisms (see Sections 4.3 and 4.4). These models were more sophisticated and took into account that the primordial Earth after its emergence was a relatively cold planet. Thus, the degassing could have started only much later (about 600 MMY after the Earth’s emergence), after a preliminary heating of the originally cold Earth’s depths to the temperature when the silicate melting began in the upper mantle, and the emergence of the first asthenosphere.

The primary mantle degassing is apparently associated with the solubility decline of volatile components in the silicate melts under lowering temperature and relatively low pressure. As a result, the mantle melts erupted on the surface (mostly basalts, and in Archaean also komatiite lavas) boiled and released the excess volatile elements and compounds into the atmosphere. Some of these volatile components may have been released at the weathering of the erupted rocks after their sojourn on the surface. However, the main water degassing mechanism was the decline of its solubility under the cooling and crystallization of water-containing basalt melts at low pressure.

The mantle degassing rate is in direct proportion with the component content in the mantle, its mobility factor χi, and the rate of the mantle convective mass exchange.

Hydrosphere is that component of the climate system that comprises all the liquid water on, over, and under Earth’s surface and subterranean water, such as oceans, seas, rivers, freshwater lakes, underground water, etc. (IPCC, 2013a, 2013c). Nearly all of that liquid water—in the oceans, lakes, streams, and groundwater—constitute a mere 1% of the hydrosphere. However small, these continental components of the hydrosphere, though small, are reservoirs for moisture on land and serve as facilitator for transport system for returning precipitation and transporting salt and other minerals to the ocean, and as such are called upon to play a vital role in the climate system (Grotizinger & Jordan, 2014, p. 410).

This vital role of the oceans in the climate system assumes significance because of the oceans’ ability of controlling the quantum of GHGs, including CO2, water vapor, and N2O, along with heat in the atmosphere. According to Rhein et al. (2013), up to now bulk of the net energy enhancement in the climate system from anthropogenic radiative forcing (RF) has been in the form of ocean heat.

This supplementary heat that accounts for nearly 60% is stored principally in the upper 700 m of the ocean (Johnson et al., 2016). According to Fahey, Doherty, Hibbard, Romanou, and Taylor (2017), ocean warming and climate-driven changes in ocean stratification and circulation change oceanic biological productivity and consequently CO2 uptake; combined, these feedbacks impact the rate of warming from RF.

Marine ecosystems absorb CO2 from the atmosphere in the similar manner that plants do on land. According to some scholars, nearly half of the world’s net primary production (NPP) is by marine plants (Carr et al., 2006; Chavez, Messié, & Pennington, 2011; Falkowski et al., 2004). It is also claimed that Phytoplankton NPP supports the biological pump that facilitates transportation of organic carbon ranging from 2 to 12 GtC/year to the deep sea (Doney, 2010; Passow & Carlson, 2012) where it is kept away from the atmospheric pool of carbon for longer durations ranging from 200 to 1500 years.

By virtue of the ocean being a vital carbon sink, climate-driven changes in NPP constitute a significant feedback owing to their potentiality to alter atmospheric CO2 abundance and forcing. While referring to multiple links between RF-driven changes in climate, physical changes to the ocean, and feedbacks to ocean carbon and heat uptake, Fahey et al. (2017) have opined that fluctuations in ocean temperature, circulation, and stratification driven by climate change modify phytoplankton NPP, along with the increase in acidity of the ocean owing to absorption of CO2 and that in turn entail the potential of impacting NPP and thus the carbon sink.

Occurrence of the bulk of surface evaporation and rainfall over the ocean enables the latter to assume a prominent role in the hydrological cycle, apart from being a significant carbon sink (Schanze, Schmitt, & Yu, 2010). Increase in the surface ocean salinity has been reported in areas of high salinity, such as the subtropical gyres, and diminution in surface salinity in areas of low salinity, such as the Warm Pool region, over decadal time scales (Good, Gregory, Lowe, & Andrews, 2013). This upsurge in stratification in select regions and mixing in other regions are feedback processes for the reason that they set in motion changed patterns of ocean circulation that entails the potential of influencing uptake of anthropogenic heat and CO2. Augmented stratification constrains surface mixing, high-latitude convection, and deepwater formation, and in so doing theoretically enfeebling ocean circulations, especially the Atlantic Meridional Overturning Circulation (AMOC) (Kostov, Armour, & Marshall, 2014). Lesser deepwater formation and gradual overturning are linked with diminished heat and carbon sequestration at greater depths. Rahmstorf et al. (2015) have observed that future projections demonstrate that the strength of AMOC could prominently decline as the ocean warms and freshens and as upsurge in the Southern Ocean gets enfeebled owing to the storm track moving poleward (Rahmstorf et al., 2015).

While Fahey et al. (2017) have opined that such a deceleration of the ocean currents entail the likelihood of impacting the rate at which the ocean engrosses CO2 and heat from the atmosphere; according to Rignot and Thomas (2002), enhanced ocean temperatures also quicken ice-sheet melt, especially for the Antarctic Ice Sheet where basal sea-ice melting is significant compared to surface melting due to colder surface temperatures. Undersea melting at tidewater margins, particularly in the case of the Greenland Ice Sheet, is also contributing to volume loss (van den Broeke et al., 2009). Sequentially, alterations in the cold and freshwater inputs get affected by changes in ice-sheet melt rates thereby impacting ocean stratification. This, in turn, entails the potential of impacting ocean circulation and the ability of the ocean to absorb more GHGs and heat (Enderlin & Hamilton, 2014). Increased sea-ice export to lower latitudes enhances local salinity anomalies such as the Great Salinity Anomaly (Gelderloos, Straneo, & Katsman, 2012) and hence to changes in ocean circulation and air–sea exchanges of momentum, heat, and freshwater that successively could impact the atmospheric distribution of heat and GHGs. Despite prevailing variations across climate model projections, there is still good agreement that in the future there will be increasing stratification, decreasing NPP, and a decreasing sink of CO2 to the ocean via biological activity (Fu, Randerson, & Moore, 2016).

Freshwater amounts are essentially held at a constant level by the hydrologic cycle that is powered by the sun and continuously moves water around the planet by exchanging water molecules from the vegetation and oceans to the atmosphere and back around. Evapo-transpiration, condensation, precipitation, infiltration, runoff, and subsurface flow are the wheels on the hydrologic cycle that move water in and out of the hydrosphere. Water is transformed in these cyclical processes as liquid, solid, and gas (vapor). When it evaporates, the surroundings are cooled; as it condenses, water releases energy and warms its surroundings. Water sculpts landforms through erosion and the movement of minerals, it hydrates life on the planet, and plays a role in the transfer of energy from terrestrial to aquatic systems. Without these cycles, and water itself, life would cease to exist on this planet. In fact, about 60% or so of our body weight is water.

The hydrosphere (often referred to as the aquasphere) is generally defined by geochemists as the vapor, liquid, and solid water present at and near the land surface, and its dissolved constituents. Water vapor and condensed water of the atmosphere are usually included, but water that is immobilized by incorporation into mineral structures in rocks is usually not thought of as part of the hydrosphere. In fact, in the processes of the hydrological cycle on the Earth, connecting hydrosphere with atmosphere, lithosphere and biosphere, the chemical composition of water is formed.

The hydrosphere contains all the solid, liquid, and gaseous water of the Earth and ranges in thickness from (approximately) 6 to 12 miles. The hydrosphere extends from the surface of the Earth downward several miles into the lithosphere and upward approximately 7 miles into the atmosphere. A small portion of the water in the hydrosphere is fresh water (non-salty water, non-saline water). This water flows as precipitation from the atmosphere down to the surface of the Earth, as rivers and streams along the surface of the Earth and also as groundwater beneath the surface of the Earth. Most of fresh water of the Earth, however, is frozen in the form of ice sheets and glaciers.

The oceans constitute approximately 98% v/v of the hydrosphere, and thus the average composition of the river water. Sphere is, for all practical purposes, that of seawater. The Obviously, the chemical composition of surface runoff water of the ocean basins is generally fairly well mixed waters of the Earth is highly variable through both time with regard to major constituents, although concentrations and space, and this book discusses the variations and of most minor elements are not uniform with depth or reasons for them at some length. The average concentrations of the major dissolved global average has little significance except, perhaps, as a elements or ions, and of some of the minor ones, are baseline for comparison. On the basis of stability of each of the complex species, the predominant forms in which the dissolved constituents occur.

Substantial differences in concentration between water near the surface and water at depth, as well as on an area basis, are characteristic of solutes that are used as nutrients by marine life. Some of the minor elements have distributions that resemble those of the nutrients. In addition, the chemical composition of surface runoff water of the ocean basins is generally fairly well mixed waters of the Earth is highly variable through both time with regard to major constituents, although concentrations and space, and this book discusses the variations and of most minor elements are not uniform with depth or reasons for them at some length.

The average concentrations of the major dissolved global average has little significance except, perhaps, as a elements or ions, and of some of the minor ones, are baseline for comparison.

Finally, the property of water known as wettability is an important aspect of the properties of water. Briefly, the wettability of a solid surface is the ability of a solid surface to reduce the surface tension of the liquid in contact with the surface such that the liquid spreads over the surface and wets it. Thus, wettability refers to the interaction between fluid and solid phases. in a reservoir rock the liquid phase can be water or oil (gas is also included within the “oil” term), and the solid phase is the rock mineral assemblage.

Advances in technology continue to provide smaller and more robust sensors, smaller data-acquisition packages with innovative data-transmission capabilities, and better analytical instrumentation for accurate and precise measurement of low elemental and solute concentrations on small samples. In addition, new tools are evolving in the areas of nanotechnology, remote sensing, and biosensor technology, which are providing new and innovative ways to evaluate processes linking hydrology and biogeochemistry. In addition, computer-technology advances and new visualization software with much higher computation and processing speeds provide a platform for innovative designs in data analysis and modeling. Interdisciplinary research incorporating some of these new technologies for data collection and processing coupled with the computer processing and visualization may provide new ways of data mining and testing of hydrological, biological, and biogeochemical process interactions.

Though the hydrosphere continues to operate in response to the same forces it always has, humans have had an unmistakable role in altering some of its balances. In general, these impacts have had relatively little effect on the overall global water balance, and there is little chance that direct manipulation of the hydrosphere will alter water storage and cycling on a global basis.

On regional scales, however, people have spent the last several thousand years trying to redistribute water resources temporally and spatially. Weirs, canals, and reservoirs have been built to control the timing of runoff and, more recently, to relocate surface water supplies, with the unintended result of greater evaporation losses from reservoir surfaces. Irrigated agriculture also diverts ocean-bound flow, much of which is then returned to the atmosphere through evapotranspiration. Thus, people pay for the privilege of redistributing water with greater losses to the atmosphere.

Dams and reservoirs represent some of the largest engineering projects of the 20th century, and they play a major role in the alteration of the hydrologic cycle on a regional scale. The Columbia River system in the northwestern United States and southwestern Canada is one of the most extensively dammed river systems in the world, with more than 50 dams providing irrigation, hydroelectric power, flood protection, and water supply for the Pacific Northwest. The dams have significantly altered the natural annual hydrograph, as shown in Fig. 6-12. The May-June runoff peaks, 2 to 2.5 times the annual average runoff in the 1915–1924 period prior to dam construction, were barely 1.5 times the average flow between 1985 and 1994. Meanwhile, autumn low flows during the 1985–1994 period are close to the mean annual flow, compared to low flows at about half the mean prior to river regulation.

The consequences of this regulated system include significantly lower total discharge (beyond what would be expected from climate variability), ecological effects of altered freshwater inputs to the Pacific, and altered sediment budgets due to sediment trapping behind dams. One unintended result of the changed hydrograph has been reduced autumn and winter surface salinity from the mouth of the Columbia along the North American coast to the Aleutian Island chain, which has potentially negative ecological consequences for endangered salmon runs.

Regional water balances are also altered by agricultural and domestic water uses drawing on underground aquifers, increasingly at rates that exceed natural recharge capability and result in groundwater overdraft. Pollution of surface and groundwaters, though it has no physical effect on the water cycle itself, results in a loss of freshwater resources in addition to the effects on balances in other biogeochemical cycles.

One of the largest human influences on the hydrologic cycle results from changes in land use. Alteration of the land surface and natural vegetation disrupts the natural balance of precipitation, evapotranspiration, and runoff at a given location. This effect tends to be exaggerated by the fact that land use change (e.g. agriculture and urbanization) is often associated with the direct physical changes discussed above.

These and other direct human impacts on the hydrosphere are unlikely to affect the global hydrologic cycle, particularly since humans have not had a great deal of success in manipulating the water balances of the ocean and atmosphere, the largest and most sensitive reservoirs in the system, respectively. Significant anthropogenic effects on the hydrologic cycle are much more likely to arise from indirect changes, most notably human-induced climate change.

The terrestrial hydrosphere likely formed early and rapidly, probably through degassing during accretion and/or rapid degassing of the interior, in the first roughly ∼100 My of Earth history. The most important contributors of water to the early Earth were likely carbonaceous chondrites or objects possessing D/H ratios identical to both carbonaceous chondrites and the Earth. In contrast to the apparent constancy of the oceans through time, the atmosphere has transitioned from an early atmosphere far richer in CO2 and CH4 to our current oxygen-bearing atmosphere. Abundant mechanisms exist by which the deep Earth could hold significant quantities of water, varying from separate crystalline hydrous phases, to water-bearing nominally anhydrous phases, to iron hydride within Earth’s core: accordingly, there are ample means by which subducted water could be taken up in Earth’s mantle. But, at least the portion of the upper mantle represented by the mid-ocean ridge basalts (MORB) source region is fairly dry: of order 100 ppm of water. More deeply derived upwellings (hot spot associated magmas) are somewhat wetter, but not hugely so. The importance of water transcends its rather small abundance in the silicate portion of the planet: its effect on melting relations (and thus crustal generation) is profound; and its role in dramatically lowering the viscosity of silicates is likely critical for our current style of mantle convection.

The groundwater hydrosphere is generally regarded as an oligotrophic environment regarding the abundance and bioavailability of organic material. Due to the complete absence of light, an important energy source for primary production is missing. Even though chemoautotrophic organisms, for instance, as part of microbial biofilms, can sometimes contribute substantially to biomass production in groundwater, most of the energy is derived from the land surface (Herrmann et al., 2020). This includes organic material mainly in the form of allochthonous DOM (dissolved organic matter), which is supplied with seepage water. The availability and composition of DOM and essential nutrients are crucial for the survival and flourishing of the fungal communities in groundwater. In groundwater, the input of organic material will usually change dynamically during periods of precipitation and subsequent recharge or drought. Likewise, the quality and quantity of DOM that ultimately reaches the saturated zone is influenced by various biotic and abiotic factors, such as the surface land cover, surface water to catchment connectivity, the porosity, and the geology of the unsaturated zone, as well as the distance of the land cover to the aquifer (groundwater table depth). It is also dependent on the chemical and physical properties (e.g., polarity) of the dissolved organic compounds, if they have undergone photodegradation on the surface, and the degree of biodegradation by resident microbial communities in the soil layers through which the DOM passes (Shen et al., 2015). As a result, typical groundwater DOM is largely deprived of lignin-derived phenols, which are derivatives of secondary metabolites of vascular plants, and higher molecular weight (HMW) compounds (Shen et al., 2015). These fractions of DOM are highly reactive and have the ability to readily adsorb to the surface of solids (Rutlidge et al., 2021; Singh et al., 2016). Therefore, in terms of DOM composition, groundwater is similar to the deep ocean (Shen et al., 2015).

In contrast, in rivers, streams, and lakes, POM (particulate organic matter), e.g., animal and plant detritus, is an essential energy source. However, POM is not present in significant quantities in groundwater, as it is attenuated or degraded already within the pedosphere. From this point of view, groundwater represents a rather hostile environment for fungal organisms. On the other hand, some limiting factors such as UV-irradiation, competition for food or host species, or extreme temperature fluctuations do not exist or are less pronounced, which in turn may prove advantageous for the survival of various fungal species and their spores.

Not surprising, groundwater is different to surface water systems in several other aspects, such as high-water residence times (sometimes decades or millennia) and limited space, mainly in the form of (interconnected) pore cavities in unconsolidated sediments or fractures in the rock matrix. As a result, the groundwater hydrosphere may only serve to a limited extent as a vector for (long-distance) dispersal of fungal taxa and their spores. In summary, groundwater, represented by water in various types of aquifers, underground streams, and cave waters, forms a unique ecosystem with some potential limitations and advantages for its fungal and overall microbial life, on which the stability of this ecosystem is founded. Since groundwater is usually recharged by rain and snowmelt, as well as surface water passing through soil and sediment zones, this ecosystem provides a rare opportunity to study both transient and resident fungi in their natural settings.


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