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 ClassificationName Concentration range

Subsaline 0.5-3‰

Hyposaline 3-20‰

Mesosaline 20-50‰

Hypersaline >50‰

Some Saline Inland WatersName 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 Waterscomment 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 CaInterpret 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

precipitateInterpret 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