SalinityG Harris, Lancaster University, UK

ã 2009 Elsevier Inc. All rights reserved.

The hydrological cycle in watersheds includes boththe ‘green’ water – rainfall, evaporation, soil moistureand ground waters – as well and the ‘blue’ water instreams, rivers, and lakes (Falkenmark, 1998). Fromhill slope to the sea, water falling as rain flows acrossand through the landscape carrying dissolved inor-ganic and organic matter and modifying both itsown composition and that of the landscape as itdoes so. Water is both a conveyor of materials in awatershed as well as a reactant in the weatheringcycle (Stumm and Morgan, 1996). The water inlakes, rivers, and streams is in intimate contact withthe rocks, vegetation, and soils of the watersheds inwhich they lie. The total dissolved matter in water istherefore a function of the geology of the watershedand the rate of water movement through surface run-off and groundwater flow. Waters flowing fromheavily weathered tropical watersheds, which arisein regions of high seasonal rainfall (and hence highrunoff; e.g., the Amazon river in South America) areusually quite dilute and may reflect the ionic compo-sition of the rainfall. On the other hand waters flow-ing in arid or semiarid watersheds (where the runoffis low because of low rainfall and high evaporationrates; e.g., the Colorado river in the USA or theMurray Darling river system in Australia) may bequite concentrated by evaporation and modified bythe geology of the watershed.Saline inland waters differ markedly from the fresh-

water systems that are the traditional domain of lim-nology and freshwater biology (Williams, 2000). Salinewaters are common in arid areas on all continents,even Antarctica (Burton, 1981; Laybourn-Parry et al.,2002). Dryland areas occupy about 50% of the con-tinents and are home to upwards of one billion people.Dry regions have some of the World’s largest lakesand reservoirs (Williams, 2000), some of which maybe highly saline: for example the salinity of the ‘Big Sea’of the Aral Sea is 48 g l�1 – about one and a halftimes that of seawater (Letolle and Cherterikoff,2000). Saline lakes and reservoirs are frequentlymono-mictic or meromictic and possess a characteristicdepauperate biota.Salinity is defined as the weight in grams of the

dissolved inorganic matter in one kilogram of water(Stumm and Morgan, 1996). It is therefore expressedas S% – in parts per thousand. Seawater has a remark-ably constant salinity between 33% and 37%. Salin-ity is also commonly measured by the electrical

conductivity of the water, or more correctly its specificconductance. The units commonly used are either Sie-mens.cm�1 or mhos.cm�1. Distilled water has a verylow conductivity – about 1mS cm�1 or 10�6Ohm�1

cm�1. (1mS cm�1 is equivalent to 1 electrical conduc-tivity unit [EC unit].) There is no precise conversionfactor from specific conductance to total dissolved salts(TDS), if the total dissolved salts are expressed as mgl�1 or ppm then the conversion factor from EC units toTDS lies between0.55 and0.9 depending on the preciseionic composition of the water in question. Oncethe ionic composition of the water is known then theconductivity is proportional to concentration.

Gibbs (1970) examined the major factorscontrolling world water chemistry. He identified threemajor factors: first, precipitation dominance in dilute,low salinity waters where Naþ and Cl� dominatedthe ionic composition. This tends to be found in tropi-cal regions in watersheds dominated by igneousrocks where the TDS composition was similar to thatof seawater and the concentration was of the orderof 10ppm (e.g., the Rio Negro). Second, rock domi-nance in medium salinity waters where the waterswere in equilibrium with the underlying geology andsoils and where Ca2þ and HCO3� dominated. HereTDS concentrations were of the order of 200ppm(e.g., the Columbia, Nile, Rhine and Indus Rivers).Last, high salinity waters with high total dissolvedsalts concentration (2000ppm to seawater concentra-tions of 35000ppm, or higher) where a processof evaporation and precipitation once again led toNaþ and Cl� dominance. Gibbs noted that there wereregional differences in salinity across the continents. Inthe high rainfall tropical regions of the old weatheredcontinents (e.g., South America, Africa, and Australia)Naþ and Cl� dominated the low salinity river andsurface waters. Similarly, Naþ and Cl� dominated thehigh salinity surface waters in arid regions of the sub-tropics, where evaporation rates are high. In regionswhere the surface rocks and soils were dominated bysedimentary rocks and limestones and evaporationrates were low (e.g., Europe and North America)Ca2þ and HCO3� dominated the ionic composition.

Radke et al. (2002) have explained the sequence ofevents that occurs in the evaporation of inland watersin terms of the Eugster–Jones–Hardie model of evap-oration and precipitation (Drever, 1982) so that ini-tial waters dominated by divalent cations (e.g., Ca2þ)may, through a stepwise process of concentration and

79

80 Inorganic Chemicals _ Salinity

precipitation, become to be monovalent cation (Naþ

and Cl�) dominated. Branch points occur dependingon the stoichiometeric ratios of major ions whencalcite/aragonite, gypsum and dolomite/Mg-silicateare precipitated.

Ecological Responses

Although it is a simple matter to measure the EC of awater sample, interpretingwhat itmeans ecologically isa more complex task. The interactions of changingsalinity with the biota are quite complex. The salinityof seawater is quite constant and most marine organ-isms are termed stenohaline – they have a narrow toler-ance range for variability in salinity around 35%.Similarly freshwater organisms are also stenohaline –they have a narrow tolerance range at low salinitylevels. Estuarine organisms, and some of those thatlive in saline inland waters, are what is termed euryha-line and can tolerate quite large and rapid changes insalinity. Freshwaters are usually defined as waters withsalinity below 3% (3000ppm) although as a result ofevaporation and saline inflows values as high as60–100% (60 000 to 100000ppm) may be found ininland waters in arid regions; up to three times moresaline than seawater. Stenohaline freshwater organismsare adapted to salinities in the region from 0–3%(Nielsen et al., 2003). A survey of the biota of 230wetlands of varying salinity by Pinder et al. (2005)showed little effect of salinity below 4.1% followedby a rapid decline in biodiversity at higher concen-trations. If the euryhaline halophytic species (whichoccurred in the salinity range from 3–10%) wereremoved from the analysis then biodiversity of thestenohaline freshwater invertebrates began to declineat 2.6 %. The biodiversity of highly saline inlandwaters is quite low and is usually dominated by asmall number of stenohaline salt tolerant species,most notably species of cyanobacteria (e.g.,Arthrospira(Spirulina) sp., Nodularia sp.), algae (e.g., Dunalliellasp.), small crustacea (e.g.,Artemia sp.) and a few higherplants (e.g., Ruppia sp.). Radke et al. (2003) showedthat as the salinity of inland waters rose owing toevaporation and precipitation (following the Eugster–Jones–Hardie model) then the occurrence of ostracodsfollowed specific pathways of the model. Pathways ofconcentration and precipitation follow the ratios ofNaþ/Hþ, Naþ/Ca2þ and alkalinity/Cl� and dividedthe ostracods into freshwater, transitional, halophile,and halobiont (stenohaline) groupings.Hammer et al. (1990) found a steep decline in the

biodiversity of benthic organisms as salinity increasedin prairie lakes in Canada (see also Hammer, 1986).Williams et al. (1990) examined the response of

organisms to increasing salinity in 79 lakes in westernVictoria, Australia, and showed that the number ofspecies declined less steeply than in Canada, particu-larly at higher salinities >10%. While stenohalinefreshwater organisms declined sharply at low sali-nities, there was a group of euryhaline speciesthat spanned a wide range of habitats and salinities(Williams et al., 1990). Clearly for euryhaline speciessalinity is not the primary determinant of success. Inaccord with this conclusion, Wood and Talling (1988)found that salinity was not the primary determinantof occurrence for a group of phytoplankton species ina series of Ethiopian inland waters varying in salinity.

More recent work at the high salinity end of thespectrum (from 10% to >35%) has uncovered arange of specialized salt tolerant species that maybe regionally diversified so that biodiversity in salinelakes is a matter of scale and evolutionary history(Williams et al., 1990, Timms, 2007). Biodiversitymay fall sharply with salinity in a subset of lakes –and in some casesmany speciesmay be absent (Seamanet al., 1991) – but if biodiversity is studied in a widegeographical range of lakes then biogeographical fac-tors and the evolutionary history ensures that thedecline in species number is slower and regionally spe-cific. In this way the history of isolation and evolutionhas a significant role to play in the ecological responseof inland waters.

So deep time plays a role in what we see today.Nielsen et al. (2003) and Timms (2007) reviewed theeffects of changing salinity on organisms in inlandwaters in Australia and concluded that the responseof major groups depended on their evolutionary his-tory. Many stenohaline freshwater phytoplankton,higher plants, andmicro-invertebrates were quite sen-sitive to increased salinity because of a long evolu-tionary history in freshwaters. Biodiversity wasreduced at salinities above 2–3%. Australian macro-invertebrate and fish populations on the other hand,many of which have a more recent marine evolution-ary history, are euryhaline, tolerant of increased salin-ity and regionally diversified. Macro-invertebratesand fish species have the ability to tolerate salinitiesin the 9–10% range or even higher, although Nielsenet al. (2003) note that some species have particularlysensitive life history stages. Adult fish may toleratesalinities up to 30%while their eggs fail to develop atsalinities over 4%. Desiccation is also a key factor inarid regions: while some species may tolerate highsalinities they are unable to tolerate drying outcompletely (Timms, 2007). In arid inland regionssurvival of many euryhaline species may be verydependent on the persistence of small refuges duringdry periods and may also reflect biogeographical dis-tributions that arose during wetter periods in the

Inorganic Chemicals _ Salinity 81

distant past (Timms, 2007). Water birds, because oftheir migratory abilities are not so regionally differ-entiated, but they do show continental scale bio-geographical patterns of distribution. Water birdsmigrate very long distances to find water dependingon rainfall patterns in any particular year and salinelakes and wetlands may be important refigures onmigratory flyways (Andrei et al., 2006).As noted earlier, increased TDS in waters in arid

subtropical regions may be associated with domi-nance by monovalent cations (Naþ and Kþ) togetherwith a preponderance of Cl� resulting from long per-iods of rainfall, evaporation, and salt deposition.Early work by Pearsall (1932) on the effects on phyto-plankton of changing the monovalent to divalent cat-ion ratios in inland waters showed that this ratioinfluenced the major groups of plankton present. Dia-toms appear to be most common in waters dominatedby divalent ions, whereas desmids seem to occur mostcommonly in waters dominated by monovalent ions.Zooplankton appear to be equally sensitive to fluctua-tions in the ratio of (NaþþKþ)/(Ca2þþMg2þ) ininland waters (see e.g., Radke et al., 2002).In addition to the physiological effects of the chang-

ing ratio of (NaþþKþ)/(Ca2þþMg2þ) there are alsoeffects on the coagulation of clays in thewater. In diluteNaþ dominatedwaters clay particles are slow to coagu-late and settle, thus leaving very turbid waters inwhich there are sufficient particles in suspension tosignificantly influence light penetration and the avail-ability of phosphorus and other elements (Nielsenet al., 2003). The salinity of inland waters is rarelyconstant; levels may decrease during periods of highflows when salinity is diluted by runoff and increaseduring low flow periods as a result of evaporation andgroundwater intrusions. Saline groundwater intrusionsmay be sufficiently concentrated as to induce densitystratification in the water column, restricting the mix-ing depth and tending to lead to anoxic bottomwaters in eutrophic situations. Organisms must there-fore cope with fluctuations in salinity over spaceand time.The salinity of inland waters, and particularly the

salinity of saline groundwater inflows into bottomwaters, strongly influences the exchange of minorelements and nutrients between the sediments andthe water column. Not only do microbial popula-tions change along salinity gradients (Bouvier and delGiorgio, 2002, Del Giorgio and Bouvier, 2002) but theexchange of key nutrients such as phosphorus is criti-cally determined by the concentrations of Fe and SO4

2�

in sediment pore waters and in bottom waters (Rodenand Edmonds, 1997). The biogeochemistry of freshwaters and high SO4

2� marine and saline waters isquite different because of stoichiometric influences on

the major groups of organisms and on nutrient cycling(Harris, 1999; Sterner and Elser, 2002). A further fea-ture of saline inland waters is the widespread occur-rence of benthic bacterial and cyanobacterial mats(Bauld, 1981), which may be present because of arelative paucity of herbivores in these saline environ-ments. These are the inland water equivalents of thestromatolites known from hypersaline coastal watersand from the fossil record. Hepatotoxins and neuro-toxins produced by these cyanobacterial mats havebeen implicated in the deaths of Flamingos feeding inthe saline lakes of East Africa (Krienitz et al., 2003).

Recent work on the microbiology of saline inlandwaters has revealed a highly unusual group of bacteriaand archaea that are polyextremophiles. Species ofNatranaerobius and Halonatronum are able to growin high temperature, alkaline pH, high NaCl concen-tration, and anoxic environments. Genomic and pro-teomic studies will reveal how these unusual organismsevolved to cope with the stresses of living in multipleextreme conditions (Mesbah and Wiegel, 2008).

Salt as a Conservative Tracer inWatersheds

Of all the major ions in inland waters chloride showsthe most conservative behavior, so cyclical salts –derived from seawater carried inland and depositedas rainfall – may be used as a tracer of watershedfunction and to study the links between ‘green’ and‘blue’ water flows (Simpson andHerczeg, 1994). Nealand his co-workers have long studied themovement ofsea salt in the Plynlimon catchment inWales using Cl�

as a conservative tracer of water movement. Theresults are a series of paradoxical conclusions thatare set to revolutionize our understanding of water-shed hydrology (Neal, 1997). Kirchner’s analysis ofNeal’s data (Kirchner et al., 2000) showed that thetravel times of ‘green’ water exhibited fractal proper-ties and turned the essentially ‘white’ noise spectrumof the Cl� signal in the rainfall (equal amounts ofvariability across all input frequencies) into a ‘pink’spectrum in the ‘blue’ water with variability inverselyproportional to the frequency in the streams drainingthe watershed. There were delayed pathways of waterflow in the groundwaters of the watershed and, onoccasion, rainfall displaced ‘old’ water from thewatershed through the interaction of rainfall, pastwetting histories and groundwater discharges. Thesignal of Cl� in the stream draining the watershedshowed very complex variability over a range of fre-quencies resulting from mixtures of delayed ‘old’water and fresh ‘new’ water draining from the water-shed by flow paths that varied in time and space

82 Inorganic Chemicals _ Salinity

(Kirchner, 2003; Feng et al., 2004; Bishop et al.,2004). The ecological significance of this is that theorganisms in the streams and rivers see a spectrumof variability in salinity and water quality over time(Nielsen et al., 2003), transformed from the rainfallinput spectrum by watershed properties (Harris andHeathwaite, 2005).New techniques of collecting high frequency data

(e.g., 10min sampling intervals) using water qualityelectrodes, wireless connectivity and web based dataanalysis systems are set to revolutionize our knowl-edge of the behavior of ‘green’ and ‘blue’ water inwatersheds. We face a future high frequency datawave as new technologies for monitoring water qual-ity come on line (Kirchner et al., 2004). These datareveal hitherto unexpected aspects of pattern andprocess in watersheds – aspects certainly not resolvedby the usual method of collecting data weekly or atless frequent intervals (Harris, 2007).

Dryland Salinity and Salinization ofInland Waters

Salinity in inland waters may be defined either asprimary salinity – where the salinity is natural dueeither to sources of salt in watersheds or to high evap-oration rates, or both – or secondary salinity wherethe salinity has arisen or increased due to humanactivity in the watershed (Williams, 1999). One sim-ple mechanism which causes the salinity of inlandwaters to rise is diversion of inflowing streams andrivers for urban and irrigation water supplies. Classicexamples of increased salinity due to river diversioninclude the Dead Sea (Middle East), Aral Sea (Asia),Pyramid Lake (Nevada, USA) and Mono Lake(California, USA). In all cases salinity rose markedlyover a period of decades due to water extraction andthe disturbance of the hydrological regime (Williams,1999). The only remedy is to cease or reduce waterextraction so as to (partially) restore the originalhydrological balance. Many naturally saline waterbodies occur in endorheic watersheds – where thereis no outflow and evaporation is the primarymeans ofwater loss (e.g., Lake Eyre, Australia). In these lakesand streams salinity is reduced by dilution duringperiods of rainfall and inflow followed by increasedsalinity as the water evaporates.Perhaps the most pressing applied issue concerning

the secondary salinity of inland waters is that arisingfrom human modification of the vegetation in water-sheds in arid zones (Williams, 1999). Many aridregions – where the potential evaporation rate exceedsthe rainfall – have, over long time periods, amassedlarge stores of salt in their soils. These salts, dominated

by NaCl, are what are called cyclical salts because theyarise from the deposition of marine salts by rainwater(Herczeg et al., 2001). Over millennia the water eva-porates and leaves the salt stored in the soil profiles.There is good evidence that over evolutionary time anequilibrium is established between rainfall and theevapotranspiration of the natural perennial vegetationleading to highly efficient ‘green’ water use and lowinfiltration (Harris, 2007). Naturally diverse perennialvegetation consists of many species with differing andcomplementary growth and rooting strategies whichcombine to make the most effective use of the scarcewater (see e.g., Pate and Bell, 1999). Human action toclear vegetation for agriculture replaces the nativeperennial vegetation with annual or perennial cropswith lower water use efficiencies which causes anincrease in water infiltration. Irrigation of these annualor perennial crops (e.g., fruit and citrus trees) alsofurther increases the infiltration of water into the soilprofile. The result is mobilization of the salt in thesoil profile, the salinization of groundwaters andincreasing salinity in streams, rivers and lakes (SimpsonandHerczeg, 1994). This is now awidespread problemin arid regions of Asia, southern Africa, the Americasand Australia. Rivers such as the Colorado and theMurray Darling, and lakes such as the Aral Sea nowshow increasing salinity as cyclical salts are fed into therivers by groundwatermovement. The salinity of riversfeeding the Aral Sea has risen seven-fold in the lastcentury since agriculture was developed in the water-shed (Letolle and Chesterikoff, 1999). Infiltration andgroundwater recharge is sporadic in timewhen rainfalloccurs and, as noted above, the travel times of ground-waters in the watershed modify the output of salt.The effects of saline groundwaters are often most pro-nounced during low flow periods when surfacerunoff ceases and the rivers are largely fed by salinegroundwaters.

Over time the salt is slowly moved out of the soilprofile and returned to the sea from whence it came(hence the term cyclical salts) and a new equilibrium isreached. Times to equilibrium can be long however:300–400years at least in watersheds with low reliefand low rainfall to as little as 50 years in steeper water-sheds. Thus, many watersheds which have been colon-ized by western agriculture in the last 200 years arestill salinizing and the rivers are slowly respondingto the new hydrological balance (Jolly et al., 2001).

Increasing salinity in these rivers leads to the slowelimination of freshwater biodiversity, including thedeath of trees and wetland plants, the elimination offish, and stimulation of toxic cyanobacterial blooms.One good sign of a dying wetland is the occurrence ofdead or dying trees and wetland plants at the margins(Williams, 1999). In the lower reaches of the Murray

Inorganic Chemicals _ Salinity 83

Darling system in Australia an entire cohort of 250-year-old River Red Gum trees has been killed in thelast decade by a combination of excessive waterextraction and prolonged drought.In many arid parts of the world the river systems

are flood plain rivers where flow variability is largeand the entire system of river channels, wetlands andfloodplains depends on irregular flooding events tomaintain the health and biodiversity of the system.River regulation and water extraction for stock,domestic, and irrigation water supplies reduces boththe natural flow variability of the river systems andthe number of over bank floods. Floodplain ecosys-tems that are not frequently inundated and flushedwith fresh water tend to become salinized and thehealth of the vegetation declines over time. Remedia-tion of these inlandwaters is either through reductionsin water extractions – thus restoring a more naturalflow regime – or by artificial environmental wateringregimes where engineering structures employ smalleramounts of water to ensure flooding of flood plainecosystems (see, for example, http://thelivingmurray.mdbc.gov.au/). Also, large-scale catchment revegeta-tion programs are underway to replace perennial veg-etation (trees and crops such as Lucerne) in an effort toreduce groundwater recharge and salt movement.Such programs are supported by computer modelingin an effort to optimize plantings and achieve themaximum return on investment (see e.g., Tutejaet al., 2003).

Further Reading

Andrei AE, Smith LM, Haukos DA, and Surles JG (2006) Commu-

nity composition and migration chronology of shorebirds using

the saline lakes of the Great Plains, USA. Journal of FieldOrnithology 77: 372–383.

Bauld J (1981) Occurrence of benthic microbial mats in saline

lakes. Hydrobiologia 81: 87–111.

Bishop K, Seibert J, Kohler S, and Laudon H (2004) Resolving

the double paradox of rapidly mobilized old water with highlyvariable responses in runoff chemistry. Hydrological Processes18: 185–189.

Bouvier TC and del Giorgio P (2002) Compositional changes in

free-living bacterial communities along a salinity gradientin two temperate estuaries. Limnology and Oceanography 47:

453–470.

Burton HR (1981) Chemistry, physics and evolution of Antarcticsaline lakes. Hydrobiologia 82: 339–362.

Del Giorgio P and Bouvier TC (2002) Linking the physiologic and

phylogenetic successions in free-living bacterial communities

along an estuarine salinity gradient. Limnology and Oceanogra-phy 47: 471–486.

Drever JJ (1982) The Geochemistry of Natural Waters. 2nd edn.

New Jersey: Prentice Hall.

Falkenmark M (1998) Dilemma when entering the 21st century:Rapid change but lack of sense of urgency. Water Policy 1:

421–426.

Feng X, Kirchner JW, and Neal C (2004) Measuring catchment-

scale retardation using spectral analysis of reactive and passivetracer time series. Journal of Hydrology 292: 296–307.

Gibbs RJ (1970) Mechanisms controlling world water chemistry.

Science 170: 1088–1090.Hammer UT (1986) Saline Lake Ecosystems of the World.

Dordrecht: Junk.

Hammer UT, Sheard JS, and Kranabetter J (1990) Distribution and

abundance of littoral benthic fauna in Canadian Prairie saline

lakes. Hydrobiologia 197: 173–192.Harris GP (1999) Comparison of the biogeochemistry of lakes and

estuaries: Ecosystem processes, functional groups, hysteresis

effects and interactions between macro- and microbiology.

Marine and Freshwater Research 50: 791–811.Harris GP (2007) Seeking Sustainability in an Age of Complexity.

Cambridge, UK: Cambridge University Press.

Harris GP and Heathwaite AL (2005) Inadmissible evidence:Knowledge and prediction in land and waterscapes. Journal ofHydrology 304: 3–19.

Herczeg AL, Dogramaci SS, and Leaney FWJ (2001) Origin of

dissolved salts in a large, semi-arid groundwater system: MurrayBasin, Australia. Marine and Freshwater Research 52: 41–52.

Jolly ID, Williamson DR, Gilfedder M, et al. (2001) Historical

stream salinity trends and catchment salt balances in the

Murray-Darling basin, Australia. Marine and FreshwaterResearch 52: 53–64.

Kirchner JW (2003) A double paradox in catchment hydrology and

geochemistry. Hydrological Processes 17: 871–874.Kirchner JW, Feng X, and Neal C (2000) Fractal stream chemistry

and its implications for contaminant transport in catchments.

Nature 403: 524–527.Kirchner JW, Feng X, Neal C, and Robson AJ (2004) The fine

structure of water quality dynamics: the (high frequency) wave

of the future. Hydrological Processes 18: 1353–1360.Krienitz L, Ballot A, Kotut K, Wiegand C, Putz S, Metcalf JS,

Codd GA, and Pflugmacher S (2003) Contribution of hot springcyanobacteria to the mysterious deaths of Lesser Flamingos at

Lake Bogoria, Kenya. FEMS Microbiology Ecology 43:

141–148.

Laybourn-Parry J, Quayle W, and Henshaw T (2002) The biologyand evolution of Antarctic saline lakes in relation to salinity and

trophy. Polar Biology 25: 542–552.

Letolle R and Chesterikoff A (1999) Salinity of surface waters inthe Aral Sea region. International Journal of Salt Lake Research8: 293–306.

Mesbah NM andWiegel J (2008) Life at extreme limits. The anaero-

bic halophilic alkalithermophiles. Annals of the New York Acad-emy of Sciences 1125: 44–57, doi: 10.1196/annals.1419.028.

Neal C (1997) A view of water quality from the Plynlimon water-

shed. Hydrology and Earth System Sciences 1: 743–753.Nielsen DL, Brock MA, Rees GN, and Baldwin DS (2003) Effects

of increasing salinity on freshwater ecosystems in Australia.

Australian Journal of Botany 51: 655–665.

Pate JS and Bell TL (1999) Application of the ecosystem mimicconcept to species-rich Banksia woodlands of Western Australia.

Agroforestry Systems 45: 303–341.Pearsall WH (1932) Phytoplankton in the English Lakes. II.

The composition of the phytoplankton in relation to dissolvedsubstances. Journal of Ecology 20: 241–262.

Pinder AM, Halse SA, McRae JM, and Shiel RJ (2005) Occurrence

of aquatic invertebrates of the wheatbelt region of Western

Australia in relation to salinity. Hydrobiologia 543: 1–24.Radke LC, Howard KWF, and Gell PA (2002) Chemical diversity

in south-eastern Australian saline lakes I: geochemical causes.

Marine and Freshwater Research 53: 941–959.

84 Inorganic Chemicals _ Salinity

Radke LC, Juggins S, Halse SA, De Dekker P, and Finston T (2003)

Chemical diversity in south-eastern Australian saline lakes II:Biotic implications. Marine and Freshwater Research 54:

895–912.

Roden EE and Edmonds JW (1997) Phosphate mobilisation in iron-

rich anaerobic sediments: microbial Fe(III) oxide reduction ver-sus iron-sulphide formation. Archiv fur Hydrobiologie 139:

347–378.

Seaman MT, Ashton PJ, and Williams WD (1991) Inland salt

waters of southern Africa. Hydrobiologia 210: 75–91.Simpson HJ and Herczeg AL (1994) Delivery of marine chloride in

precipitation and removal by rivers in theMurray-Darling Basin,

Australia. Journal of Hydrology 154: 323–350.

Sterner RW and Elser JJ (2002) Ecological Stoichiometry: TheBiology of Elements fromMolecules to the Biosphere. Princeton,NJ: Princeton University Press.

Stumm W and Morgan JJ (1996) Aquatic Chemistry: ChemicalEquilibria and Rates in Natural Waters. New York: Wiley.

Timms BV (2007) The biology of saline lakes of central and eastern

Australia: A review with special reference to their biogeographi-cal affinities. Hydrobiologia 576: 27–37.

Tuteja NK, Beale G, Dawes W, et al. (2003) Predicting the effects

of land use change on water and salt balance – a case study of

a catchment affected by dryland salinity in NSW, Australia.Journal of Hydrology 283: 67–90.

WilliamsWD (1999) Salinisation: a major threat to water resources

in the arid and semi-arid regions of the world. Lakes and Reser-voirs: Research and Management 4: 85–91.

Williams WD (2000) Dryland lakes. Lakes and Reservoirs:Research and Management 5: 207–212.

Williams WD, Boulton AJ, and Taaffe RG (1990) Salinity as a

determinant of salt lake fauna: A question of scale. Hydrobiolo-gia 197: 257–266.

Wood RB and Talling JF (1988) Chemical and algal relationships

is a salinity series of Ethiopian inland waters. Hydrobiologia158: 29–67.