RIVERS: Major Components

1) water

2) suspended inorganic matter - major elements are Al, Fe, Si, Ca, K, Mg, Na and P

3) dissolved major spp. - HCO3-, Ca2+, SO4

2-, H4SiO4, Cl-, Na+, Mg2+,K+

a) no gaseous phase - Ca2+, Cl-, H4SiO4, Na+, Mg2+ ,K+

b) with gaseous phase - HCO3-, SO4

2-

4) dissolved nutrient elements - N, P - Si

5) suspended and dissolved organic matter

6) trace metals

• Runoff ratio - avg. river runoff / avg. rainfall

• World average - 0.46

• Thus, 50% of rainwater returned to atmosphere by evaporation

Major dissolved components:

• CHLORIDE in rocks very soluble - not reactive with other ions - good tracer of water mass

1) main source to river - sea salt - rain - dry fallout

2) dissolved during weathering of halite (NaCl) evaporites

3) thermal and mineral springs in volcanic areas

4) saline crusts in desert basins (not primary)

5) pollution - oil well brines, road salt, sewage

• SODIUM - seawater input to atmosphere; Na in halites - sedimentary rock - brine, road salts, etc.

• POTASSIUM

1) 90% weathering of silicate minerals - feldspar, orthoclase, mica (biotite)

2) 3/4 sedimentary rocks

3) 1/4 igneous and metamorphic (also fertilizer)

• CALCIUM & MAGNESIUM - rock weathering

1) Ca - carbonate rocks: calcite(CaCO3),

dolomite(CaMg(CO3)2)

2) 65% of Ca2+ in river water -- dolomite is main source of Mg

•HCO3- - rock weathering

1) soils: CO2 + H2O + CaCO3 ---> Ca2+ + 2HCO3-

2) soils: 2CO2 + 11H2O + 2NaAlSi3O8 ---> 2Na+ +

2HCO3- + Al2Si2O5(OH)4 + 4H4SiO4

3) some weathering by sulfuric acid formed by

oxidation of pyrite: H2SO4 + 2CaCO3 ---> 2Ca2+ +

2HCO3- + SO4

2-

H2SO4 + 9H2O + NaAlSi3O8---> 2Na+ + SO42- +

Al2Si2O5(OH)4 + 4H4SiO4

• SILICA - silicate weathering

1) 20% Si relative to HCO3- (carbonate

weathering dominant)

2) 8% chert in carbonate rocks

3) more dissolved silica in tropics --

4) Si minerals weather to kaolinite - 1.5 times dissolved Si versus smectite in temperate systems; gibbsite even more in tropics

5) biogenic source not important as in oceans

• SULFATE -

1) 2% from salt, 33% weathering, 54% pollution, 8% volcanic, 3% biological

2) pyrite FeS2, gypsum CuSO4· H2O, anhydrite CuSO4

3) FeS2 weathers to H2SO4 which then reacts with Si and Ca minerals

4) pyrite - derived SO42- in river water

Organic Carbon:

• Average river dissolved organic carbon (DOC) - 5.3 mg/l; global is 200Tg DOC/yr (avg. global DOC/total dissolved substances (TDS) - 1:19)

• POC - 172 Tg/yr; on average 1% of TSS is CARBON

• TOC = POC + DOC

•Black Water River - pH is 4.3 due to dissociation of humic carboxyl groups (R-COOH)--->(R-COO)- + H+

• DOC 24 mg/l -- DOC (humics and fulvics) / TDS -- 1:1

• HCO3- is low

• HCO3- + H+ ---> H2O + CO2

• (R-COOH) + HCO3- ---> (R-COO)- + H2O + CO2

• High DOC rivers also have high Fe and Al

• Using total concentration of dissolved ions in river water one can calculate the chemical denudation rate of a drainage basin, continent - even the whole world.

Nutrients

Atmospheric Nutrients:

• C, N, P, S, S, K, Mg, Na, Ca, Fe, Mn, Zn, Cu, Mo, Co, B

• macronutrients, micronutrients

• NITROGEN - oxid-states - NO3-, (+5 state) (of N) to

NH4+, (-3 state) (of N)

• organic N highly reduced; urea, amino acids

• PHOSPHORUS - PO43- (+5 state) (of P)

• 3 structural configurations - ortho, para, meta.

However, can occur in (+4 state) = PO42-

• SILICON

• detrital quartz - crystalline silica, aluminosilicate clays, dissolved silicon

• oceans > opal - biogenic silica - amorphous silica polymer

• silicic acid - H4SiO4

• SiO42- (+4 state)

• There is significant competition for nutrients between bacteria and algae

• Uptake kinetics - organisms with a half-saturation coefficient (ks) for a given nutrient will have greater affinity for that nutrient

• Organisms with large ks can take greater advantage of large pools

• Plant Redfield Ratio (1934) - C:N:P - 106:16:1

• Redfield 1963 - uptake of N, P - 16:1 ratio

• Phytoplankton organic matter

• 106 CO2 + 122 H2O + 16 HNO3 + H3PO4 ---> C(H2O)106 + (NH3)16 + H3PO4 + 138 O2

•Nutrient regeneration via decomposition will return

• N2 fixation - 78% of atmospheric N2

• bacteria and cyanobacteria “fixing” N2 into the inorganic salt ammonium

• N2 + 3H2 ---> 2NH3

• Nitrogenase inhibited by oxygen

• Heterocysts - maintain anoxic conditions

• Clostridium, Azobacter, Pseudomonas

• Heterocystic cyanobacteria - Trichodesmium, Oscillatoria, Calothrix

• P enhances N2 fixation, inhibited by NH4+

• can use acetylene reduction

• 15N - labelled N2

• Nitrogen fixation - high in lakes, not in estuaries

1) NH4+ inhibited, or:

2) SO4 may inhibit uptake of molybdate - needed to make nitrogenase

• Important in marshes, ~5% of NH4+ needed for

Spartina growth

Nitrification and Denitrification:

• Nitrification - oxidation of NH4+ to NO3

- under aerobic conditions

• Nitrifying bacteria use NH4+ as energy source

to fix CO2 into organic matter

Nitrification - 2 steps:

• Nitrosomonas, Nitrocystis

• NH4 + 3/2 O2 ---> HNO2 + H2O

• Nitrobacter - HNO2 + 1/2 O2 ---> HNO3

• can measure with 15N - labeled NH4+ substrate

• sewage outfalls - high nitrification rates -- due to NH4

+ concentrations

Denitrification - bacteria use NO3- as e- acceptor to

oxidize organic matter anaerobically, releasing N2 gas

5C6H12O6 + 24HNO3 ---> 30CO2 + 42H2O + 12N2

• Pseudomonas - also, N O produced in reaction

• C6H12O6 + 6HNO3 ---> 6CO2 + 9H2O + 3N2O

• denitrification - limited by NO3 -