Salt consists of sodium chloride. Through primary and secondary salinization, it intrudes into freshwater and damages the health of humans and other organisms.
Freshwater salinization is the process of salty runoff contaminating freshwater ecosystems, which can harm aquatic species in certain quantities and contaminate drinking water.[1] It is often measured by the increased amount of dissolved minerals than what is considered usual for the area being observed.[2] Naturally occurring salinization is referred to as primary salinization; this includes rainfall, rock weathering, seawater intrusion, and aerosol deposits.[3] Human-induced salinization is termed as secondary salinization, with the use of de-icing road salts as the most common form of runoff.[4] Approximately 37% of the drainage in the United States has been affected by salinization in the past century.[1] The EPA has defined two thresholds for healthy salinity levels in freshwater ecosystems: 230mg/L Cl− for average salinity levels and 860mg/L Cl− for acute inputs.[5]
Salinity plays a major role in a freshwater organism's attempts to maintain an osmotic balance between ion concentration and their internal fluids. Salinization increases osmotic pressure, thus negatively affecting the chance of an organism's fitness and survival.[3] Higher levels of salinity present in freshwater environments can lead to declining species richness in general observations, though toxicity varies among freshwater species and the identity of the ions that are causing the salinization.[6] Excluding an organism's death, excess salinity may also lead to a decrease in both individual and population fitness via stunted growth during adolescence,[7] decreased feeding ability,[8] oxidative stress,[9] and overall bodily disfigurement.[10]
Excess amounts of saline water in freshwater areas also play a significant role on larger population scales; they may alter trophic interactions within ecosystems[11] and transform pre-existing biochemical cycles into 'new' ones by changing the flow of compound direction. The altercation of ecosystems may facilitate the intrusion of invasive species that are able to handle brackish to saline water conditions[12]
Effects on human health
Most of the water that humans use and consume everyday originate from freshwater sources.[13] High salt concentrations within drinking water sources can result in many harmful effects on human health.[14] A study on two coastal villages in Bangladesh showed that when freshwater contaminated with high salinity concentrations is consumed, it can result in health issues such as hair loss, skin diseases, gastric problems, diarrhea, and high blood pressure.[15] High salinity levels in drinking water also has been found to be highly associated with cardiovascular diseases (CVD).[14] Freshwaters that are alkaline and salty can also mobilize and release a variety of chemicals that travel together throughout watersheds, contaminate human water sources, and can cause a variety of negative health effects on humans if consumed.[16] These toxic chemicals, often consisting of metals and nitrogen containing compounds, are either forced out of streambed soils by the salt ions,[16] or the salinity within the water corrodes the pipes through passing, releasing the chemicals into the water source.[17] An example of this occurring was in Flint, Michigan. Due to the high salt concentrations in the Flint River water source from nearby road salt runoffs, the water passing through the resident's pipes contributed to corrosion and the release of lead into their drinking water.[17]
Secondary salinization
Colder climates use mixtures of salt to keep ice from forming along roads, which increases saline runoff to nearby freshwater locations.
Human interaction accelerates rates of primary salinization. Land development, like construction and mining, causes compounds found in bedrock to be released from their tight locations and come to the surface, which are then exposed to accelerated rates of weathering, eventually leading to leaching ions in nearby water sources. Agricultural practices also generate highly saline irrigation that may enter freshwater through the introduction of various pesticides or husbandry-related runoff, and naturally saline groundwater can be brought to the surface via land clearing.[3]
Chlorine in the form of chloride is recognized as the most common type of anthropogenic salts exposed to an environment.[2] In agricultural practices, chlorine is mixed together with other compounds to produce an antibacterial solvent used to treat water. This treated water moves from fields into watersheds where it may remain present for long periods of time. Aggregation of chlorine is especially prevalent where improper irrigation occurs. Raised chloride levels may lead to acidification, movement of metalloid compounds via ion exchange with the stream bed, tampering with lake mixing schedules, and modifications of freshwater biotic relationships.[18]
Effects on freshwater organisms
Due to body permeability, the salinity of the organism's aquatic environment can have a huge influence on cellular stability.[3] Organisms residing in freshwater ecosystems need to maintain an osmotic balance between their body fluids and the ion concentrations within their cells.[3] Changes in osmotic pressure requires large amounts of energy and can result in cellular damage and cellular death within the organisms.[3] Changes within salinity levels affect organisms within freshwater ecosystems both directly and indirectly.[19] The toxic levels of salt ions can directly result in physiological changes in species which can cause harmful effects to not only the individual, but also the species population.[19] The various effects on these organisms can then indirectly affect the overall freshwater ecosystem by modifying the aquatic community structure and function.[19] As salinity increases within a freshwater ecosystem, often this results in a decrease of biota diversity and richness.[19] The extinction rate for freshwater organisms are among the highest worldwide,[3] and as salinity levels in these aquatic ecosystems continue to increase, more species and their environments will become threatened.
Freshwater salinization can negatively effect the species richness, diversity, and community composition across multiple trophic levels. Competitive interactions between zooplankton can change as salinity increases, leading species such as Simocephalus vetulus to outcompete the normally-dominant Daphnia galeata under high salinity treatments.[20] Species richness and diversity declines as salinity increases for most macro-invertebrate species as well.[21]Mayflies, stoneflies, and caddisflies, which are considered to be good indicators of stream health, exhibited particularly sharp declines due to increased salinity.[21] Some fish species are negatively effected by salinization. In the lower Pecos River, 13 of the 44 native fish species have disappeared in areas of high salinization.[22] However, some fish only exhibit declines when salinity reaches extreme levels.[23]
A study performed in Baltimore revealed that at low concentrations, increased levels of chloride hinders the denitrification process within lakes, which is crucial for removing nitrate, the byproduct of ammonia from fish and other aquatic organisms. Chloride levels in the Northeastern USA increase seasonally to around 5 grams a liter from street salt use in the winter. This vacillation causes freshwater communities closer to urban areas to have reduced biodiversity and trophic complexity.[24]
A depiction of freshwater salinization syndrome (FSS). Many different factors contribute to FSS, making it difficult for scientist to quantify. Anthropogenic and biological outputs mix together to create unique effects in freshwater systems.
Biomodification of salt toxicity
Due to numerous concurrent stressors present in freshwater communities, increased levels of salinization may have unforeseen effects caused by interactions with other compounds. Freshwater salinization syndrome (FSS) is cited to be a familiar threat to freshwater located in North America and Europe.[3] The interactions between salt and pH, nutrients, metals, and base cations is not adequately known, though may exacerbate existing issues to negatively effect water quality, carbon dioxide concentrations, and biodiversity. The ion concentration of salt toxicity may change the level of reactivity a species will respond with. To be able to properly recognize the threat salinity plays requires the proper proportions of each ion present to be accounted for. Sensitivity also varies between species. Studies focusing on the abiotic interactions with freshwater organisms found that salinity had an additive effect on the detrimental compounds being observed for the majority of the time, but not always, which makes the prediction process difficult for scientists.[3]
Salinization and alkalization have been linked through the study of arid regions across North America and have negatively effected 37% and 90% of freshwater drainage areas, respectively. Their interaction is best noted by the levels of rising pH in streams and rivers measured in 232 USGS sites in 2018. Among these sites, 66% have shown a significant escalation of pH, the most commonly affected area being heavily populated cities in the east and mid-west. Along with the usual salinization offenders of agricultural runoff and road ice, lime and concrete quickly weather down to contribute base ions and salts into water streams. Noticeable signs of FSS include infrastructure deterioration, lowered biodiversity, and the increased mobilization of pollutants within an aquatic system. In conjunction with photosynthetic organisms, basic levels of pH can enter a positive feedback loop via the deficiency of dissolved carbons in the water in relation to the amount of dissolved carbon dioxide, thus further exacerbating FSS.[1]
Prevention and remediation
Remediation may occur through the creation of a national standardized data base where local governments and companies can report the quantity and chemical concentration of the road salts that are released for de-icing purposes.[25] This would help regulate and monitor the ions being released into the environment so nearby freshwater sources can be monitored for exposure more carefully.[25] There also needs to be a standardized reference developed by reputable scientists that shows what the average expected levels of salt ions for a normal freshwater ecosystem are.[25] A Canadian study suggested the use of halophyte plants to help remediate the salt exposure within the soils and prevent its infiltration into ground water.[26] Halophytes are plants that have a high salt tolerance, and the purpose of the study was to see if they could be planted around areas with high road salt usages to prevent infiltration into water sources.[26] The results showed that when the surrounding soil was tested, 11% of Cl ions and 87% of Na ions were retained within the top soil layers when halophytes were present.[26] This shows potential in the prevention of road salt runoff from accessing freshwater sources. If halophytes were potentially planted around freshwater sources maybe salt ions will be less likely to runoff into freshwater sources and salinity can be limited or prevented. In regards to other harmful human practices such as mining, conservationists and volunteers are planting species of native Appalachian trees and plants on sites used previously for mining activities. Replanting these native plants will hopefully remediate the land that was destroyed by the mountain top mining practices and increase the biodiversity in Appalachia.[27] The red spruce was one native species that was reintroduced due to its important ability to filter and capture water from a deep organic layer within its surrounding soil.[27] 90% of the red spruce trees planted survived,[27] which shows promise towards remediation efforts through the use of native species.
↑ Kaushal, S. S. (2009-01-01), "Chloride", in Likens, Gene E. (ed.), Encyclopedia of Inland Waters, Oxford: Academic Press, pp.23–29, ISBN978-0-12-370626-3, retrieved 2020-10-13
1 2 Timpano, Anthony J.; Schoenholtz, Stephen H.; Soucek, David J.; Zipper, Carl E. (2018). "Benthic macroinvertebrate community response to salinization in headwater streams in Appalachia USA over multiple years". Ecological Indicators. 91: 645–656. doi:10.1016/j.ecolind.2018.04.031. ISSN1470-160X. S2CID90410472.
↑ Hoagstrom, Christopher (2009). "Causes and impacts of salinization in the lower pesos river". Great Planes Research. 19: 27–44.
Salinity is the saltiness or amount of salt dissolved in a body of water, called saline water. It is usually measured in g/L or g/kg.
Halotolerance is the adaptation of living organisms to conditions of high salinity. Halotolerant species tend to live in areas such as hypersaline lakes, coastal dunes, saline deserts, salt marshes, and inland salt seas and springs. Halophiles are organisms that live in highly saline environments, and require the salinity to survive, while halotolerant organisms can grow under saline conditions, but do not require elevated concentrations of salt for growth. Halophytes are salt-tolerant higher plants. Halotolerant microorganisms are of considerable biotechnological interest.
A halophyte is a salt-tolerant plant that grows in soil or waters of high salinity, coming into contact with saline water through its roots or by salt spray, such as in saline semi-deserts, mangrove swamps, marshes and sloughs, and seashores. The word derives from Ancient Greek ἅλας (halas) 'salt' and φυτόν (phyton) 'plant'. Halophytes have different anatomy, physiology and biochemistry than glycophytes. An example of a halophyte is the salt marsh grass Spartina alterniflora. Relatively few plant species are halophytes—perhaps only 2% of all plant species. Information about many of the earth's halophytes can be found in the ehaloph database.
The term chloride refers either to a chloride ion, which is a negatively charged chlorine atom, or a non-charged chlorine atom covalently bonded to the rest of the molecule by a single bond. Many inorganic chlorides are salts. Many organic compounds are chlorides. The pronunciation of the word "chloride" is.
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 environments and are an example of an ecotone. Estuaries are subject both to marine influences such as tides, waves, and the influx of saline water, and to fluvial influences such as flows of freshwater and sediment. The mixing of seawater and freshwater provides high levels of nutrients both in the water column and in sediment, making estuaries among the most productive natural habitats in the world.
Seawater, or sea water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5%. This means that every kilogram of seawater has approximately 35 grams (1.2 oz) of dissolved salts. The average density at the surface is 1.025 kg/L. Seawater is denser than both fresh water and pure water because the dissolved salts increase the mass by a larger proportion than the volume. The freezing point of seawater decreases as salt concentration increases. At typical salinity, it freezes at about −2 °C (28 °F). The coldest seawater still in the liquid state ever recorded was found in 2010, in a stream under an Antarctic glacier: the measured temperature was −2.6 °C (27.3 °F).
A salt marsh, saltmarsh or salting, also known as a coastal salt marsh or a tidal marsh, is a coastal ecosystem in the upper coastal intertidal zone between land and open saltwater or brackish water that is regularly flooded by the tides. It is dominated by dense stands of salt-tolerant plants such as herbs, grasses, or low shrubs. These plants are terrestrial in origin and are essential to the stability of the salt marsh in trapping and binding sediments. Salt marshes play a large role in the aquatic food web and the delivery of nutrients to coastal waters. They also support terrestrial animals and provide coastal protection.
Water pollution is the contamination of water bodies, usually as a result of human activities, so that it negatively affects its uses. Water bodies include lakes, rivers, oceans, aquifers, reservoirs and groundwater. Water pollution results when contaminants mix with these water bodies. Contaminants can come from one of four main sources: sewage discharges, industrial activities, agricultural activities, and urban runoff including stormwater. Water pollution is either surface water pollution or groundwater pollution. This form of pollution can lead to many problems, such as the degradation of aquatic ecosystems or spreading water-borne diseases when people use polluted water for drinking or irrigation. Another problem is that water pollution reduces the ecosystem services that the water resource would otherwise provide.
Freshwater ecosystems are a subset of Earth's aquatic ecosystems. They include lakes, ponds, rivers, streams, springs, bogs, and wetlands. They can be contrasted with marine ecosystems, which have a larger salt content. Freshwater habitats can be classified by different factors, including temperature, light penetration, nutrients, and vegetation. There are three basic types of freshwater ecosystems: Lentic, lotic and wetlands. Freshwater ecosystems contain 41% of the world's known fish species.
An aquatic ecosystem is an ecosystem found in and around a body of water, in contrast to land-based terrestrial ecosystems. Aquatic ecosystems contain communities of organisms—aquatic life—that are dependent on each other and on their environment. The two main types of aquatic ecosystems are marine ecosystems and freshwater ecosystems. Freshwater ecosystems may be lentic ; lotic ; and wetlands.
River ecosystems are flowing waters that drain the landscape, and include the biotic (living) interactions amongst plants, animals and micro-organisms, as well as abiotic (nonliving) physical and chemical interactions of its many parts. River ecosystems are part of larger watershed networks or catchments, where smaller headwater streams drain into mid-size streams, which progressively drain into larger river networks. The major zones in river ecosystems are determined by the river bed's gradient or by the velocity of the current. Faster moving turbulent water typically contains greater concentrations of dissolved oxygen, which supports greater biodiversity than the slow-moving water of pools. These distinctions form the basis for the division of rivers into upland and lowland rivers.
Total dissolved solids (TDS) is a measure of the dissolved combined content of all inorganic and organic substances present in a liquid in molecular, ionized, or micro-granular suspended form. TDS are often measured in parts per million (ppm). TDS in water can be measured using a digital meter.
Freshwater fish are those that spend some or all of their lives in fresh water, such as rivers and lakes, with a salinity of less than 1.05%. These environments differ from marine conditions in many ways, especially the difference in levels of salinity. To survive fresh water, the fish need a range of physiological adaptations.
Soil biodiversity refers to the relationship of soil to biodiversity and to aspects of the soil that can be managed in relative to biodiversity. Soil biodiversity relates to some catchment management considerations.
Osmoregulation is the active regulation of the osmotic pressure of an organism's body fluids, detected by osmoreceptors, to maintain the homeostasis of the organism's water content; that is, it maintains the fluid balance and the concentration of electrolytes to keep the body fluids from becoming too diluted or concentrated. Osmotic pressure is a measure of the tendency of water to move into one solution from another by osmosis. The higher the osmotic pressure of a solution, the more water tends to move into it. Pressure must be exerted on the hypertonic side of a selectively permeable membrane to prevent diffusion of water by osmosis from the side containing pure water.
Freshwater biology is the scientific biological study of freshwater ecosystems and is a branch of limnology. This field seeks to understand the relationships between living organisms in their physical environment. These physical environments may include rivers, lakes, streams, ponds, lakes, reservoirs, or wetlands. Knowledge from this discipline is also widely used in industrial processes to make use of biological processes involved with sewage treatment and water purification. Water presence and flow is an essential aspect to species distribution and influences when and where species interact in freshwater environments.
Brackish marshes develop from salt marshes where a significant freshwater influx dilutes the seawater to brackish levels of salinity. This commonly happens upstream from salt marshes by estuaries of coastal rivers or near the mouths of coastal rivers with heavy freshwater discharges in the conditions of low tidal ranges.
Energy, nutrients, and contaminants derived from aquatic ecosystems and transferred to terrestrial ecosystems are termed aquatic-terrestrial subsidies or, more simply, aquatic subsidies. Common examples of aquatic subsidies include organisms that move across habitat boundaries and deposit their nutrients as they decompose in terrestrial habitats or are consumed by terrestrial predators, such as spiders, lizards, birds, and bats. Aquatic insects that develop within streams and lakes before emerging as winged adults and moving to terrestrial habitats contribute to aquatic subsidies. Fish removed from aquatic ecosystems by terrestrial predators are another important example. Conversely, the flow of energy and nutrients from terrestrial ecosystems to aquatic ecosystems are considered terrestrial subsidies; both aquatic subsidies and terrestrial subsidies are types of cross-boundary subsidies. Energy and nutrients are derived from outside the ecosystem where they are ultimately consumed.
Freshwater acidification occurs when acidic inputs enter a body of fresh water through the weathering of rocks, invasion of acidifying gas, or by the reduction of acid anions, like sulfate and nitrate within a lake. Freshwater acidification is primarily caused by sulfur oxides (SOx) and nitrogen oxides (NOx) entering the water from atmospheric depositions and soil leaching. Carbonic acid and dissolved carbon dioxide can also enter freshwaters, in a similar manner associated with runoff, through carbon dioxide-rich soils. Runoff that contains these compounds may incorporate acidifying hydrogen ions and inorganic aluminum, which can be toxic to marine organisms. Acid rain is also a contributor to freshwater acidification. It is created when SOx and NOx react with water, oxygen, and other oxidants within the clouds.
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 term specifically excludes seawater and brackish water, it does include non-salty mineral-rich waters such as chalybeate springs. Fresh water may encompass frozen and meltwater in ice sheets, ice caps, glaciers, snowfields and icebergs, natural precipitations such as rainfall, snowfall, hail/sleet and graupel, and surface runoffs that form inland bodies of water such as wetlands, ponds, lakes, rivers, streams, as well as groundwater contained in aquifers, subterranean rivers and lakes. Fresh water is the water resource that is of the most and immediate use to humans.
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