Salinity of Lakes, Rivers, and
Reservoirs
Saline vs. Marine
• Marine water mainly sodium chloride 35%o
• Saline waters vary in dominant ions
• Surface waters range from almost pure water
to several times the ionic strength of sea
water
Saline lake Classification
Name
Concentration range
Subsaline
0.5-3‰
Hyposaline
3-20‰
Mesosaline
20-50‰
Hypersaline
>50‰
Some Saline Inland Waters
Name
Location
Salinity
Other
Don Juan Pond
Antarctica
>400‰
Never freezes
Lake Vanda
Antarctica
<400‰
Meromictic
Lake Assal
Djibouti (Affar)
348‰
-155m
Dead Sea
Jordan/Israel
337‰
-378m
Great Salt Lake
Utah, USA
50-270‰
Remnant of Lake
Bonneville
Mono Lake
California, USA
50-99‰
Highly productive
• Don Juan
Pond
(~400‰)
• Lake Vanda
–deep
meromictic
lake
Lake Assal -Djibouti
• Crater lake 155m
below sea level.
• Salinity 348 ‰
Dead Sea
337‰ and
378m below
sea level
Great Salt Lake
Mono Lake
Major Cations of Surface Waters
Hard Water
• Calcium
• Magnesium
• Sodium
• Potassium
Soft Water
• Calcium
• Sodium
• Magnesium
• Potassium
Major Anions of Surface Waters
comment on Tables 10-1, 10-3, & 10-4
Hard Water
• Bicarbonate
• Carbonate
• Sulfate
• Chloride
Soft Water
• Chloride
• Sulfate
• Carbonate
Salinity due to:
• Substrate (soil, geology)
• Total precipitation
• Ratio of precipitation to evaporation
Comment on Table 10-2
Aral Sea
Saline lakes form when
• Outflow is restricted
• Evaporation rate exceeds inflow or outflow
• Inflow equals evaporation plus outflow
Saline Lakes are different from hard
water lakes
• Mainly sodium chloride
• Conductivity
• Specific conductance
Sources of ions
• Direct weathering of rock (e.g. sodium
chloride)
• ReDox reactions involving iron, manganese,
sulfur, nitrogen, phosphorus, and carbon
• H+ from carbonic acid, acid rain, humic acids
• Influence of groundwater
Precipitation as a source of ions
• Wind-borne salt
• Dust
• Acid rain
Calcium
• Essential element for most living things
• Soft-water: low Ca
• Hard-water: high Ca
• Photosynthesis causes decline of Ca
• Metabolism causes increase of Ca
Interpret Figures 10-3, 10-4, & 10-5
Ca & conductivity in Lawrence Lake
Ca in Wintergreen Lake
Magnesium
• Necessary for chlorophyll
• Unlike Ca, very soluble and does not easily
precipitate
Interpret Figure 10-6 and compare with Figure
10-3
Magnesium in Lawrence Lake
• Sodium, potassium and other minor cations
also very soluble
Sodium concentrations
Monovalent: Divalent Cation Ratios
• M:D < 1.5 favors diatoms
• M:D > 1.5 favors desmids
Anions, especially halides in surface
waters
• Examine Figure 10-8, chloride concentrations
in Little Crooked Lake
Chloride in Little Crooked Lake
Origins of freshwater biota
• Bacteria: homiosmotic
• Protists: variable, most from marine forms
• Plants: from terrestrial groups, few saline
plants (e.g. Spartina). Some like Nymphaea
primitive freshwater aquatic forms
• Animals: Many from marine environments;
however, insects from terrestrial groups