Sulfur and Silica

Background

  • Nutrient: any element that an organism must take in to live, grow, and reproduce

  • Macronutrients: C, H, N, O, P, S

    • Hydrologic = C and H (water)

    • Gaseous = C and N (main nutrients in atmosphere)

    • Sedimentary = P and S (mostly in rocks and soil)

Liebig’s Law of Minimum

  • Composition of Silica (Si)

    • Biosphere = ~0

    • Lithosphere = 20.5

    • Hydrosphere = ~0

    • Atmosphere = ~0

    • Demand/Supply (in water) = 2000

  • Composition of Sulfur (S)

    • Biosphere = ~0.03

    • Lithosphere = ~0.06

    • Hydrosphere = ~0.01

    • Atmosphere = ~0

Forms of Sulfur

  • SO42- (sulfate) = most oxidized form

    • is 2nd only to carbonate as the principle anion in lakes

  • H2S (hydrogen sulfide)

    • during decomposition, S is reduced to H2S

    • oxidized rapidly in oxygenated waters

    • toxic to all eukaryotes (only some bacteria can survive)

Chemosynthetic bacteria

  • Chemosynthetic bacteria: get their energy from breaking down chemical bonds

Sulfur Cycle

Bacteria in Lake

  • Bacteria can be important producers in lakes, as well as food sources

    • e.g. foor for zooplankton

Silica Cycle

  • Silica mainly important for one dominant algal group: the DIATOMS

    • silica is a major component of their cell walls (= frustules)

  • Chrysophyte algae also have some silica requirements

    • all chrysophytes form siliceous resting stages call stomatocytes

    • some chrysophyte genera are characterized by external siliceous scales

  • Silica utilization (or uptake) - Si that disappears from the water column as the result of production of biogenic Si

  • Silica limitation - [Si] where growth becomes limiting (<0.4 mg/L)

  • Silica depletion - long-term biogechemical decrease in [Si]

  • Oligotrophic lakes use a lot of silica and phosphorus is limiting

  • Eutrophic lakes use a lot of phosphorus which use up the very limiting silica

  • Heterograde lakes have algae blooms that photosynthesize and diatom blooms leading to an increase in both silica and phosphorus

  • Diatom changes in a lake can often be linked to SiO2 levels

Coupling of Silica and Phosphorus Cycles

  • Why are [Si] so low in lake Ontario and so high in lake Superior?

    • Lake Superior is an oligotrophic lake, so diatoms don’t get to high of a biomass, meaning they can’t and won’t use up all the silica because they don’t have enough phosphorus

    • Lake Ontario is a mesotrophic lake, so diatoms will use up more silica due to the higher availability of phosphorus because they have a greater biomass

Nutrients

  • Some nutrients can move “uphill” or against gravity in the water column

    • 1) Aquatic insects (e.g. larval stages in water, remove nutrients, emerge as flying insects)

    • 2) Aquatic invertebrates and some fish migrate up and down the water column (e.g. feed in hypolimnion, excrete in epilimnion)

    • 3) Macrophytes (can take up nutrients from sediments, and then release them to water coloum)

    • 4) Birds (e.g., Arctic seabirds) feed in the ocean, but return to land to nest

      • nutrient transport (via guano), as well as other sources (e.g., dead bodies)

    • 5) Anadromous fish (like sockeye salmon), hatch in lakes (nursery lakes), then migrate to ocean and accumulate over 95% of biomass in sea, then return to nursery lakes to spawn and die

      • decaying carcasses are a major source of N and P and other nutrients to nursery lakes

    • 6) Large animals such as grizzly bears or moose, who may feed in water, but excrete on land