The Hydrological (water) Cycle - The cyclic exchange of water between the atmosphere and biosphere.

• Water precipitates as rain which then falls to earth → returns to the air by evaporating

• As water flows through and on the ground, it carries nutrients both beneficial and harmful

  • Carbon runoff accelerates microbial respiration which causes O² becomes depleted

    • Example of Heterotrophy

A metric used to evaluate or gauge metabolic activity would be Biochemical oxygen demand (BOD). Microbial oxygen consumption creates a biochemical oxygen demand (BOD).

• Biochemical oxygen demand (BOD): amount of O₂ removed from the environment by aerobic respiration.

• You can see how active these microbes are being breaking down material through BOD.

When measuring O₂ with dissolved oxygen probe, the rate of decrease is proportional to the organic matter concentration.

• If there is more organic matter concentration, there would be more oxygen consumption and therefore a higher BOD.

• If there is less, there would be less organic oxygen consumption and therefore lower BOD.

High BOD levels can threaten viability of fish & other aquatic animals when O₂ levels are < 5 mg/L

• Air saturated water = 8 mg/L O₂ → that’s as much O₂ as is can hold

Eutrophication results in high levels of aerobic, bacterial decomposition of organic matter.

• Occurs from an influx of excess nutrients that trigger hypoxic zones in water

• Think of runoff water bringing fertilizer into a body of water which brings about a boom in growth. Once the nutrients brought from the runoff is depleted, the growth dies off and falls to the bottom. Heterotrophic bacteria then feeds off the dead mass. The aerobic respiration from the bacteria breaking down the dead mass depletes oxygen from the water which causes fish and other life to die.

The purpose of wastewater treatment plant is to produce a clear outgoing stream, possessing minimal levels of organic solutes

Wastewater treatment - decreases the BOD and the level of human pathogens before water is returned to local rivers.

• Water undergoes:

  • Preliminary treatment - removes solid debris

  • Primary treatment - fine screens & sedimentation tanks remove insoluble particles. EX: sediments

  • Secondary treatment - microbial decomposition of organic content.

  • Tertiary (advanced) treatment - chlorination or other chemical application to eliminate pathogens

• Water Treatment Process

  • About enhancing the growth of heterotrophic, aerobic respirers

  • Clarification - knock down high BOD along with removing the organic matter causing the high BOD (settle out) → those organic matter is recycled into the activated sludge which is then used to help lower high BOD

• Activated Sludge - a process for treating wastewater using air and a biological floc composed of bacteria and protozoa

• Healthy sludge - a brown floc, largely composed of saprotrophic bacteria (feed on decayed matter) but also an important protozoan flora

  • composed of amoebae, ciliated protozoan, stalked ciliates, and others

  • floc formation is critical in promoting settling of bacteria & associated microbes from treatment process.

    • yields abundant, clarified effluent

    • Filamentous bacteria important in floc formation; optimal ratio of filamentous to planktonic types

  • The microbes in flocculation will eat free floating microbes

  • We want microbes to settle so flocculation is what we want and is a good thing

The conversion of nitrate (NO₃^-) to N₂ is called denitrification

Ammonia/ammonium ion (NH₃/NH₄⁺) would be the end products of nitrogen fixation and ammonification

Nitrogen has more oxidation states than any other major biological elements

• Some forms of nitrogen is as a food source or a way to breath

• More reduced forms of nitrogen or those with more electrons are better used for food sources

• More oxidized is better for respiration

The nitrogen cycles also cannot exist without prokaryotes

Lithotrophy/nitrification (assimilation) → food sources

• ammonia is turned into nitrates

Denitrification (dissimilation) → ways to respire.

• Results in N₂ which is released to the air.

Nitrogen fixation - brings back the nitrogen lost from the denitrification and turns it into Ammonia

Ammonification - decomposing plants and animals turn into ammonia which is then inserted into nitrification

The major accessible nitrogen source is the atmosphere, of which N₂ constitutes 79%

Artificial nitrogen fixation is accomplished by the Haber process. → generates fertilizers for agriculture: N₂ + 3H₂ → 2NH₃

• How you fix in ammonia artificially

• Uses high pressure and catalysts. Very energy consuming

The nitrogen cycle can be viewed as a nitrogen triangle

In fixation, the symbiotic types do the most of the activity of bringing in the nitrogen in the air. → After the nitrogen from the air is converted into reduced oxygen (one of which is ammonia) → Nitrification turns them into oxidized nitrogen (NO2-;NO3-) → Denitrification uses oxidized nitrogen which turns them into atmospheric nitrogen

Nitrogen Fixation

• N₂ → NH₃ → NH₄⁺

• NH₄⁺ is assimilated into amino acids

Nitrogen fixation is catalyzed by nitrogenase

• Only functions anaerobically

• requires tremendous input of energy N₂ is three bonded and takes lots of energy to break those bonds down

Occurs in all ecosystems & widespread across many bacterial species → free living-types and symbiotic types (ones who have relationships with plants)

• Symbiotic - bacterial associations with certain plant types

• Cyanobacteria in oceans and freshwater; compartmentalizes N₂ fixation in heterocysts - strictly nitrogen fixation.

  • heterocysts are separated from other cells because of the photosynthetic cells. since oxygen would cause nitrogenase to become inactive and photosynthesis produces oxygen, they have to be kept seperated.

Nitrification

NH₄⁺ → NO₂^- → NO₃^-

• Lithotrophy - oxidation of NH₄⁺ provides electrons, energy

• In soil, Nitrosomonas oxides NH₄⁺ to NO₂^-

• Nitrobacter oxidizes NO₂^- to NO₃^-

• excessive fertilizer use causes nitrate runoff; eutrophication of streams, danger to water supplies

  • Can also change soil pH or water pH

Denitrification

NO₃^- → NO₂^- → NO → N₂O → N₂

• represents anaerobic respiration

• leads to loss of nitrogen

• reducing nitrogen