Macronutrients & Organic Carbon

Micronutrients

Silicon

Nitrogen

Phosphorous

Organic Carbon

Iron Cycling

• Ferrous is most bioavailable for assimilation.

• Chemoautotrophic oxidation by acidophilic or neutrophilic iron bacteria.

• Precipitation under oxic and phosphorous rich conditions.

• Organic carbon chelators prevent precipitation; bioavailability may increase with microbial siderophores yet high humic acids may cause limitations.

• Ferric can be used for anaerobic respiration by iron reducing bacteria.

Silicon

• Source is weathering of aluminosilicates!

• Extremely low solubility, yet everywhere.

• Silica and silicic acid as dissolved forms.

• Diatom need it for frustrules; supply limits growth.

Nitrogen• Macronutrient; Uptake and Assimilation to Organic-N:

– May limit freshwater 1º Production;– Algal autotrophs prefer inorganic-N (NH4

+ preferred to NO3-)

– Bacteria heterotrophs prefer organic-N (esp. amino acids)– Glutamine Synthetase expressed when N-starved.

• Major microbial processes that transform N:– N2-Fixation: N2 to NH4

+; needs absence of O2; only bacteria.– Regeneration (remineralization; decomposition):

• Organic-N to ammonium (NH4+) and excreted;

• N-replete bacteria ≥ protists > zooplankton >> others

– Nitrification: 2 different bacterial steps; NH4+ to NO2

- to NO3-

– Anaerobic NO3- Respiration: NO3

- as e- acceptor to NO2-.

– Denitrification: NO3- to NO2

- to N2O gas to N2 gas; gas to atm.

N2O

Nitrogen Analysis• Total N: Kjeldahl digestion of all N-forms to NO3

-, which gets analyzed (see below).

• Particulate N: Filter harvest particles; Dumas combustion followed by GC separation of N2 and thermocoupler detection.

• Total Dissolved N (TDN): Filtrate subject to Kjeldahl digestion to NO3

-.

• Dissolved Inorganic N (DIN) forms:– Ammonium: colorimetric; phenol or salicylate rxn.– Nitrate: Cd/Zn reduction to NO2

- (see next).– Nitrite: colorimetric; azo-dye rxn.

• Dissolved Organic Nitrogen (DON): = TDN – DIN

Phosphorous• Macronutrient; Uptake and Assimilation to Organic-P:

– Often limits freshwater 1º Production;– Algal autotrophs and bacterial heterotrophs prefer o-

phosphate (PO4-3) over organic-P forms.

– Bacteria can be superior competitors for PO4-3.

– Alkaline Phosphatase expressed when P-starved.

• Sources and Fates:– Weathering of P-containing minerals from soil and rocks.– Ultimately, stores in sediments of lakes and ocean.– Cycling very rapid and often in low concentration.– Total phosphorous is the best measure of available P.

Phosphorous Analysis• Particulate and dissolved forms separated by filtration.

• Total Phosphorous: heated acid persulfate (ox.) digestion to o-PO4

-3. Filtrate yields total dissolved P (TDP).

• Acid Hydrolysable P (AHP): o-PO4-3 and condensed

(polymerized) phosphates by heated acid hydrolysis to PO4

-3.

• Ortho-phosphate (o-PO4-3): soluble reactive phophorous

(SRP); assay is colorimetric by the ascorbate-molybdate complex rxn.

• Dissolved Organic P: DOP = TDP – AHP – SRP

Organic Carbon• Measured to approximate system energy flow and biomass.

• Sources:– Allochthonous (mostly from the terrestrial environment; plants and soil)– Autochthonous (made within system by autotrophs)

• Particulate Forms:– Biomass: living cells and organisms– Detritus: dead fragments of organisms; precipitates of organics

• FPOM; CPOM; Large Woody Debris

• Dissolved Forms: majority of organic matter!– Labile: reduced; simple; preferred and used rapidly by microbes.

• (e.g. carbohydrates, amino acids, lipids, peptides, nucleotides)– Refractory: oxidized; complex; polymeric; degrades slowly.

• (e.g. lignin, tannins, humics, other polyphenolics of terrestrial plant origin).– Effects: weak acidic buffer; toxicity (direct indirect); and color.

Carbon Cycling

Organic Carbon Analysis

• Again, dissolved and particulate forms separated by filtration.

• Acidification is used to remove carbonates so that analysis is only of organic carbon.

• Particulate organic C (POC): Dumas combustion followed by GS separation of CO2 and thermocoupler detection.

• Dissolved organic C (DOC): most common now is high temperature platinum catalyst oxidation and IR detection of evolved CO2.

Water Color

• Apparent Color (unfiltered):– True Color plus ….– Particles

• Clay and silt• Phytoplankton

– Bottom reflected color (in situ)

• True Color (filtered sample)- Pale yellow to dark coffee color of DOM- Pale blue of soda lakes (very high carbonate content)- Platinum Cobalt salts as standards

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UV light and O* free radicals →