Groundwater-dependent ecosystems

Groundwater-Dependent Ecosystems (or GDEs) are ecosystems that rely upon groundwater for their continued existence. Groundwater 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 tables and aquifers, which are large storehouses for groundwater. An ecosystem is a community of living organisms interacting with the nonliving aspects of their environment (such as air, soil, water, and even groundwater). With a few exceptions, the interaction between various ecosystems and their respective groundwater is a vital yet poorly understood relationship, and their management is not nearly as advanced as in-stream ecosystems.[1]

Groundwater flow
Graphic on Groundwater Flow

Methods of identification

Isotopes

Examining the composition of stable isotopes in the water found in soil, rivers, groundwater, and xylem (or vein systems) of vegetation, using mass spectroscopy, which measures and sort the masses in a sample, along with data on the changes in groundwater depth coupled with the time and vegetative rooting patterns, shows spatial changes over time in the use of groundwater by the vegetation in its respective ecosystem.[1]

Plants

A groundwater-dependent ecosystem can also be inferred through plant water use and growth. In areas with high rainfall groundwater reliance can be seen by monitoring the water use made by the plants of the ecosystem 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 groundwater utilization. In areas of prolonged drought the continuation of water flow and plant growth are highly indicative of a groundwater reliant area.[1]

Remote sensing/Geographical Information Systems (GIS)

Remote Sensing is the scanning of Earth by satellite or aircraft to obtain information.[2] GIS is a system designed to capture, store, analyze and manage geographic data.[3] Together the data collected (such as elevation 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.[4][5]

Classification

Due to the high variety of ecosystems and their individual fluctuation in dependency on groundwater there is some uncertainty when it comes to defining an ecosystem strictly as groundwater-dependent or merely groundwater-using.[6] Each ecosystem expresses a varying degree of dependency. An ecosystem can be directly or indirectly dependent,[7] as well as have a variation in groundwater use throughout the seasons.[1] There are a variety of methods for classifying types of groundwater-dependent ecosystems either by their geomorphological setting and/or by their respective groundwater flow mechanism (deep or shallow).[6]

Terrestrial

Arid to humid environments

Arid to humid terrestrial environments with no standing water but deeply rooted vegetation relies upon groundwater to support the producers of their ecosystem. The deeply rooted vegetation requires the groundwater to maintain a consistent or semi-consistent level to allow for their continued health and survival.[6]

Aquatic

Springs

Springs, arguably, rely the most heavily on the continued contribution of groundwater because they are a natural discharge from relatively deep groundwater flows rising to the surface.[6] Springs are often in association with uniquely adapted plants and animals.[7]

Wetlands in Donana
Wetlands in Donana

Wetlands

Wetlands require a shallow discharge of groundwater, it flows as a seepage into depressions in the land surface,[6] in some instances wetlands feed off of perched groundwater which is groundwater separated from the regular water table by an impermeable layer.[8] Marshes are a type of wetland and though not directly reliant on groundwater they use it as an area of recharge.[6] Bogs, are also a type of wetland that is not directly reliant on groundwater but uses the presence of groundwater to provide the area with recharge as well as buoyancy.[7]

Rivers

Venice Lagoon December 9 2001
Venice lagoon

Rivers collect groundwater discharge from aquifers. This can happen seasonally, intermittently or constantly, and can keep an area's water needs stable during a dry season.[6]

Coastal

Lagoons/estuaries

Lagoons and estuaries use groundwater flow to help dilute the salinity in the water and helps support their distinctly unique coastal ecosystems.[6]

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 aquifer and permanently damage the quantity of water the aquifer can store.[9]

Urbanization

Pollution

Due to the increase in populated areas estuaries and other aquatic ecosystems face a greater threat of pollution. In many cases groundwater can become polluted through toxins, or even just excessive amounts of certain nutrients seeping down to the water table. This polluting of the groundwater can have many different effects on the related ecosystems in the case of an estuary in Cape Cod it was noted that an influx of new nitrogen had come from septic tank fields in the groundwater's flow path.[10] Increased levels of nitrogen in aquatic ecosystems can cause eutrophication which is the process of excessive introduction of nutrients causing an abundance of plant growth which can result in the death of a variety of aquatic life.[11]

Recharge

Urbanization of land has significant effects on groundwater recharge, deforestation and urbanizing limits the amount of surface area viable for water to actually infiltrate and contribute to the groundwater.[12]

References

  1. ^ a b c d Murray, Brad R.; Zeppel, Melanie J. B.; Hose, Grant C.; Eamus, Derek (August 2003). "Groundwater-dependent ecosystems in Australia: It's more than just water for rivers". Ecological Management & Restoration. 4 (2): 110–113. doi:10.1046/j.1442-8903.2003.00144.x.
  2. ^ Administration, US Department of Commerce, National Oceanic and Atmospheric. "What is remote sensing?". oceanservice.noaa.gov. Retrieved 2017-05-12.
  3. ^ "What is GIS? | The Power of Mapping - Esri". www.esri.com. Retrieved 2017-05-12.
  4. ^ Münch, Zahn; Conrad, Julian (2007-02-01). "Remote sensing and GIS based determination of groundwater dependent ecosystems in the Western Cape, South Africa". Hydrogeology Journal. 15 (1): 19–28. doi:10.1007/s10040-006-0125-1. ISSN 1431-2174.
  5. ^ Doody, Tanya; Barron, Olga; Dowsley, Kate; Emelyanova, Irina; Fawcett, Jon; Overton, Ian; Pritchard, Jodie; van Dijk, Albert; Warren, Garth (2017). "Continental mapping of groundwater dependent ecosystems: A methodological framework to integrate diverse data and expert opinion". Journal of Hydrology: Regional Studies. 10: 61–81. doi:10.1016/j.ejrh.2017.01.003.
  6. ^ a b c d e f g h Foster, Stephen; Koundouri, Phoebe; Tuinhof, Albert; Kemper, Karin; Nanni, Marcella; Garduno, Hector. "Groundwater Dependent Ecosystems the challenge o balanced assessment and adequate conservation" (PDF). The World Bank.
  7. ^ a b c Kløve, Bjørn; Ala-aho, Pertti; Bertrand, Guillaume; Boukalova, Zuzana; Ertürk, Ali; Goldscheider, Nico; Ilmonen, Jari; Karakaya, Nusret; Kupfersberger, Hans (2011-11-01). "Groundwater dependent ecosystems. Part I: Hydroecological status and trends". Environmental Science & Policy. Adapting to Climate Change: Reducing Water-related Risks in Europe. 14 (7): 770–781. doi:10.1016/j.envsci.2011.04.002.
  8. ^ Cecil, L. DeWayne; Orr, Brennon R.; Norton, Teddy; Anderson, S.R. (November 1991). "Formation of Perched Ground-Water Zones and Concentrations of Selected Chemical Constituents in Water" (PDF). Water Resource Investigations Report.
  9. ^ USGS, Howard Perlman. "Groundwater depletion, USGS water science". water.usgs.gov. Retrieved 2017-05-12.
  10. ^ Charette, Matthew A.; Buesseler, Ken O.; Andrews, John E. (23 March 2001). "Utility of radium isotopes for evaluating the input and transport of groundwater-derived nitrogen to a Cape Cod estuary". Limnology and Oceanography. 46 (2): 456–470. doi:10.4319/lo.2001.46.2.0465.
  11. ^ Administration, US Department of Commerce, National Oceanic and Atmospheric. "NOAA's National Ocean Service Education: Estuaries". oceanservice.noaa.gov. Retrieved 2017-05-12.
  12. ^ Foster, S. S. D.; Morris, B. L.; Lawrence, A. R. (1994-01-01). Groundwater problems in urban areas. Thomas Telford Publishing. pp. 43–63. doi:10.1680/gpiua.19744.0005. ISBN 978-0727740168.
Fen-meadow

A Fen-meadow is a habitat that occurs in numerous locations throughout northern and western Europe. This habitat is generally found in damp lowland areas. The hydrology of fen-meadows are typically groundwater-dependent ecosystems.There are several distinct plant associations that may comprise a fen-meadow including the Juncus subnodulosus-Cirsium palustre association.

Gnangara Mound

The Gnangara Mound is an area north of Perth, Western Australia where a large mound of sandy soil reaches an elevation of about 60 metres. It stores about 20 cubic kilometres of fresh water, about one hundred times Perth's current annual water usage. It is currently the single most important source of potable water for the city. Together with the Jandakot Mound south of Perth it supplies about 35%-50% of the city's drinking water.However, studies have shown that water levels in the Gnangara Mound have fallen substantially in recent times. This has had a significant impact on nearby groundwater-dependent ecosystems such as the Wanneroo wetlands and the Yanchep Caves. The problem has also been causing acidification of the nearby Lakes Gnangara, Jandabup, Wilgarup and Mariginiup. The remaining mound springs of the Swan Coastal Plain depend on the aquifer and are susceptible to any dramatic change in hydrology. It is widely recognised that sustainability of the Mound as a water resource is under threat. Depletion has been blamed on a combination of climate change and excessive drawing of water.

Groundwater

Groundwater is the water present beneath Earth's surface in soil pore spaces and in the fractures of rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock become completely saturated with water is called the water table. Groundwater is recharged from and eventually flows to the surface naturally; natural discharge often occurs at springs and seeps, and can form oases or wetlands. Groundwater is also often withdrawn for agricultural, municipal, and industrial use by constructing and operating extraction wells. The study of the distribution and movement of groundwater is hydrogeology, also called groundwater hydrology.

Typically, groundwater is thought of as water flowing through shallow aquifers, but, in the technical sense, it can also contain soil moisture, permafrost (frozen soil), immobile water in very low permeability bedrock, and deep geothermal or oil formation water. Groundwater is hypothesized to provide lubrication that can possibly influence the movement of faults. It is likely that much of Earth's subsurface contains some water, which may be mixed with other fluids in some instances. Groundwater may not be confined only to Earth. The formation of some of the landforms observed on Mars may have been influenced by groundwater. There is also evidence that liquid water may also exist in the subsurface of Jupiter's moon Europa.Groundwater is often cheaper, more convenient and less vulnerable to pollution than surface water. Therefore, it is commonly used for public water supplies. For example, groundwater provides the largest source of usable water storage in the United States, and California annually withdraws the largest amount of groundwater of all the states. Underground reservoirs contain far more water than the capacity of all surface reservoirs and lakes in the US, including the Great Lakes. Many municipal water supplies are derived solely from groundwater.Polluted groundwater is less visible and more difficult to clean up than pollution in rivers and lakes. Groundwater pollution most often results from improper disposal of wastes on land. Major sources include industrial and household chemicals and garbage landfills, excessive fertilizers and pesticides used in agriculture, industrial waste lagoons, tailings and process wastewater from mines, industrial fracking, oil field brine pits, leaking underground oil storage tanks and pipelines, sewage sludge and septic systems.

Nambung River

The Nambung River is a river in the Wheatbelt region of Western Australia, 170 kilometres (106 mi) north of Perth. The river drains an area between the towns of Cervantes and Badgingarra. In its lower reaches the Nambung River forms a chain of waterholes in the Nambung Wetlands where it disappears underground into a limestone karst system 5.5 kilometres (3 mi) from the Indian Ocean.

Wetland

A wetland is a distinct ecosystem that is inundated by water, either permanently or seasonally, where oxygen-free processes prevail. The primary factor that distinguishes wetlands from other land forms or water bodies is the characteristic vegetation of aquatic plants, adapted to the unique hydric soil. Wetlands play a number of functions, including water purification, water storage, processing of carbon and other nutrients, stabilization of shorelines, and support of plants and animals. Wetlands are also considered the most biologically diverse of all ecosystems, serving as home to a wide range of plant and animal life. Whether any individual wetland performs these functions, and the degree to which it performs them, depends on characteristics of that wetland and the lands and waters near it. Methods for rapidly assessing these functions, wetland ecological health, and general wetland condition have been developed in many regions and have contributed to wetland conservation partly by raising public awareness of the functions and the ecosystem services some wetlands provide.Wetlands occur naturally on every continent. The main wetland types are swamp, marsh, bog, and fen; sub-types include mangrove forest, carr, pocosin, floodplains, mire, vernal pool, sink, and many others. Many peatlands are wetlands. The water in wetlands is either freshwater, brackish, or saltwater.

Wetlands can be tidal (inundated by tides) or non-tidal. The largest wetlands include the Amazon River basin, the West Siberian Plain, the Pantanal in South America, and the Sundarbans in the Ganges-Brahmaputra delta.The UN Millennium Ecosystem Assessment determined that environmental degradation is more prominent within wetland systems than any other ecosystem on Earth.Constructed wetlands are used to treat municipal and industrial wastewater as well as stormwater runoff. They may also play a role in water-sensitive urban design.

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