Groundwater-Dependent Ecosystems (or GDEs) are

ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syst ...

s that rely upon

groundwater Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidat ...

for their continued existence.

Groundwater Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidat ...

is water that has seeped down beneath Earth's surface and has come to reside within the pore spaces in soil and fractures in rock, this process can create

water table The water table is the upper surface of the zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with water. It can also be simply explained as the depth below which the ground is saturated. Th ...

s and

aquifer An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials ( gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characteri ...

s, which are large storehouses for

. An

is a community of living organisms interacting with the nonliving aspects of their environment (such as air, soil, water, and even

). With a few exceptions, the interaction between various

s and their respective

is a vital yet poorly understood relationship, and their management is not nearly as advanced as in-stream

Methods of identification

Isotopes

Examining the composition of stable

isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers ( mass number ...

s in the water found in soil, rivers,

, and

xylem Xylem is one of the two types of transport tissue in vascular plants, the other being phloem. The basic function of xylem is to transport water from roots to stems and leaves, but it also transports nutrients. The word ''xylem'' is derived fr ...

(or vein systems) of vegetation, using

mass spectroscopy Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are presented as a ''mass spectrum'', a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is use ...

, which measures and sort the masses in a sample, along with data on the changes in

depth coupled with the time and vegetative rooting patterns, shows spatial changes over time in the use of

by the vegetation in its respective

Plants

A groundwater-dependent ecosystem can also be inferred through plant water use and growth. In areas with high rainfall

reliance can be seen by monitoring the water use made by the plants of the

in relation to the water storage in the soil of the area. If the use of water in the vegetation exceeds that of the water being stored in the soil it is a strong indication of

utilization. In areas of prolonged drought the continuation of water flow and plant growth are highly indicative of a

reliant area.

Remote sensing/Geographical Information Systems (GIS)

Remote Sensing Remote sensing is the acquisition of information about an object or phenomenon without making physical contact with the object, in contrast to in situ or on-site observation. The term is applied especially to acquiring information about Ear ...

is the scanning of Earth by

satellite A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioiso ...

aircraft An aircraft is a vehicle that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines. ...

to obtain information.

GIS A geographic information system (GIS) is a type of database containing geographic data (that is, descriptions of phenomena for which location is relevant), combined with software tools for managing, analyzing, and visualizing those data. In a ...

is a system designed to capture, store, analyze and manage

geographic Geography (from Greek: , ''geographia''. Combination of Greek words ‘Geo’ (The Earth) and ‘Graphien’ (to describe), literally "earth description") is a field of science devoted to the study of the lands, features, inhabitants, and ...

data. Together the data collected (such as

elevation The elevation of a geographic location is its height above or below a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational surface (see Geodetic datum § ...

and bore holes measuring groundwater levels) can very accurately predict where groundwater-dependent ecosystems are, how extensive they are, and can guide field expeditions to the right areas for further confirmation and data collection on the GDEs.

Classification

Due to the high variety of

s and their individual fluctuation in dependency on

there is some uncertainty when it comes to defining an

strictly as groundwater-dependent or merely groundwater-using. Each

expresses a varying degree of dependency. An

can be directly or indirectly dependent, as well as have a variation in

use throughout the seasons. There are a variety of methods for classifying types of groundwater-dependent ecosystems either by their

geomorphological Geomorphology (from Ancient Greek: , ', "earth"; , ', "form"; and , ', "study") is the scientific study of the origin and evolution of topographic and bathymetric features created by physical, chemical or biological processes operating at or n ...

setting and/or by their respective

groundwater flow Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolida ...

mechanism (deep or shallow).

Terrestrial

Arid to humid environments

Arid A region is arid when it severely lacks available water, to the extent of hindering or preventing the growth and development of plant and animal life. Regions with arid climates tend to lack vegetation and are called xeric or desertic. Most ...

humid Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present. Humidity dep ...

terrestrial Terrestrial refers to things related to land or the planet Earth. Terrestrial may also refer to: * Terrestrial animal, an animal that lives on land opposed to living in water, or sometimes an animal that lives on or near the ground, as opposed to ...

environments with no standing water but deeply rooted vegetation relies upon

to support the producers of their

. The deeply rooted vegetation requires the

to maintain a consistent or semi-consistent level to allow for their continued health and survival.

Aquatic

Springs

Springs, arguably, rely the most heavily on the continued contribution of

because they are a natural discharge from relatively deep

flows rising to the surface. Springs are often in association with uniquely adapted plants and animals. Wetlands in Donana

Wetlands

Wetland A wetland is a distinct ecosystem that is flooded or saturated by water, either permanently (for years or decades) or seasonally (for weeks or months). Flooding results in oxygen-free (anoxic) processes prevailing, especially in the soils. The ...

s require a shallow discharge of

, it flows as a seepage into depressions in the land surface, in some instances

wetland A wetland is a distinct ecosystem that is flooded or saturated by water, either permanently (for years or decades) or seasonally (for weeks or months). Flooding results in oxygen-free (anoxic) processes prevailing, especially in the soils. The ...

s feed off of perched groundwater which is

separated from the regular

by an impermeable layer.

Marsh A marsh is a wetland that is dominated by herbaceous rather than woody plant species.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p Marshes can often be found a ...

es are a type of

and though not directly reliant on

they use it as an area of recharge.

Bog A bog or bogland is a wetland that accumulates peat as a deposit of dead plant materials often mosses, typically sphagnum moss. It is one of the four main types of wetlands. Other names for bogs include mire, mosses, quagmire, and muskeg; a ...

s, are also a type of

that is not directly reliant on

but uses the presence of

to provide the area with recharge as well as

buoyancy Buoyancy (), or upthrust, is an upward force exerted by a fluid that opposes the weight of a partially or fully immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus the p ...

Rivers

River A river is a natural flowing watercourse, usually freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the ...

s collect

groundwater discharge Groundwater discharge is the volumetric flow rate of groundwater through an aquifer. Total groundwater discharge, as reported through a specified area, is similarly expressed as: :Q = \fracKA where :''Q'' is the total groundwater discharge ( 3·T� ...

from

s. This can happen seasonally, intermittently or constantly, and can keep an area's water needs stable during a dry season.

Coastal

Lagoons/estuaries

Lagoon A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into '' coastal lagoons'' (or ''barrier lagoons' ...

s and

estuaries An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environme ...

use

to help

dilute Dilution may refer to: * Reducing the concentration of a chemical * Serial dilution, a common way of going about this reduction of concentration * Homeopathic dilution * Dilution (equation), an equation to calculate the rate a gas dilutes * Trad ...

the

salinity Salinity () is the saltiness or amount of salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensionless and equal ...

in the water and helps support their distinctly unique coastal

Threats

Extraction

The extraction of groundwater in both large and smaller amounts lowers the areas water table, and in too large of quantities can even collapse parts of the

and permanently damage the quantity of water the

can store.

Urbanization

Pollution

Due to the increase in populated areas

and other

aquatic ecosystem An aquatic ecosystem is an ecosystem formed by surrounding a body of water, in contrast to land-based terrestrial ecosystems. Aquatic ecosystems contain communities of organisms that are dependent on each other and on their environment. The t ...

s face a greater threat of

pollution Pollution is the introduction of contaminants into the natural environment that cause adverse change. Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). Pollutants, the ...

. In many cases groundwater can become polluted through

toxin A toxin is a naturally occurring organic poison produced by metabolic activities of living cells or organisms. Toxins occur especially as a protein or conjugated protein. The term toxin was first used by organic chemist Ludwig Brieger (1849 ...

s, or even just excessive amounts of certain

nutrient A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excr ...

s seeping down to the

. This polluting of the groundwater can have many different effects on the related

s in the case of an

estuary An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environm ...

Cape Cod Cape Cod is a peninsula extending into the Atlantic Ocean from the southeastern corner of mainland Massachusetts, in the northeastern United States. Its historic, maritime character and ample beaches attract heavy tourism during the summer mon ...

it was noted that an influx of new

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at seve ...

had come from septic tank fields in the groundwater's flow path. Increased levels of

s can cause

eutrophication Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phytopla ...

which is the process of excessive introduction of

s causing an abundance of plant growth which can result in the death of a variety of aquatic life.

Recharge

Urbanization Urbanization (or urbanisation) refers to the population shift from rural to urban areas, the corresponding decrease in the proportion of people living in rural areas, and the ways in which societies adapt to this change. It is predominantly t ...

of land has significant effects on

groundwater recharge Groundwater recharge or deep drainage or deep percolation is a hydrologic process, where water moves downward from surface water to groundwater. Recharge is the primary method through which water enters an aquifer. This process usually occurs ...

deforestation Deforestation or forest clearance is the removal of a forest or stand of trees from land that is then land conversion, converted to non-forest use. Deforestation can involve conversion of forest land to farms, ranches, or urban area, urban ...

and urbanizing limits the amount of surface area viable for water to actually infiltrate and contribute to the

References

{{Reflist Hydrology Ecosystems Habitat