Water Cycle| Carbon Cycle| Nitrogen Cycle| Oxygen Cycle etc.

Water Cycle| Carbon Cycle| Nitrogen Cycle| Oxygen Cycle etc.

• The term biogeochemical is a contraction / abbreviation that refers to the consideration of the biological geological and chemical aspects of each cycle.
• Any of the natural cycles by which essential elements of living matter are circulated called Bio-geo-chemical Cycle. For example: Water-cycle, Carbon-cycle, Nitrogen cycle, Oxygen-cycle, Phosphorous cycle etc. Biogeochemistry: it is a branch of science that was founded by Russian geochemist and mineralogist Vladimir Ivanovich (V.I) vernadsky (1863-1945) in 1926.

Water Cycle

The water cycle, also known as the hydrologic cycle, describes the continuous movement of water within the earth and atmosphere. It is a complex global process involving water evaporation, transportation, condensation, precipitation, and accumulation. The water cycle is powered by the sun’s energy.

Evaporation and Transportation

About 90% of the moisture in the atmosphere is contributed by oceans, seas, lakes, and rivers through evaporation, with the sun’s heat energy providing the evaporative force. As water evaporates, water vapor rises into the air. Plants also lose considerable amounts of water vapor through transpiration from their leaves. This evapotranspiration contributes massive volumes of water into the atmosphere to be circulated globally.

Water vapor is also released into air through sublimation, the direct phase change of water from solid ice to gaseous vapor state, without entering the liquid phase. Sublimation often occurs from frozen surfaces such as glaciers and snowfields.

The water vapor circulates through the atmosphere, transported around the globe by wind currents in cloud formations.

Condensation and Precipitation

As gaseous water vapor cools, it condenses into tiny liquid water droplets that group together around condensation nuclei to form clouds. When these water droplets combine and grow in size, they eventually fall out of the sky as precipitation.

Precipitation falls in various forms like rain, snow, hail, or sleet depending on atmospheric conditions and temperatures. On average, about 505,000 cubic kilometers of water fall as precipitation across global land and ocean surfaces annually.

Collection (Accumulation and Groundwater Recharge)

The precipitation that falls on land collects in lakes, rivers, streams, as ice and snow, or infiltrates underground as soil moisture and groundwater. Snow and ice accumulations form glaciers, ice caps, and ice sheets, which store frozen water over long periods. Precipitation over oceans collects as surface water.

Of precipitation over land, 67% recharges fresh groundwater stores while the rest evaporates or discharges via surface flows into lakes, wetlands, and oceans. Infiltrating precipitation replenishes subterranean aquifers – a process called ‘groundwater recharge’. This soil moisture and groundwater keeps landscapes from becoming dry and inhospitable. Groundwater also sustains river baseflows and wetlands during droughts.

Through the above mechanisms, water cycles continuously via evaporation, condensation, and precipitation processes across the world’s oceans, ice masses, atmosphere, landmasses, and underground stores.

Why It Matters

The water cycle is a fundamental Earth system supporting all life on the planet. It regulates global water distribution and drives weather patterns influencing local climates and ecosystems. Evapotranspiration from forests creates clouds and rainfall vital for habitats. Condensing water also releases heat that powers storm systems which redistribute moisture. Losing moisture and precipitation patterns would make many places inhabitable.

Any changes to the water cycle such as land-use changes, pollution, climate shifts can degrade essential resources. Monitoring water fluxes helps predict water availability, floods, or droughts through seasons. Managing usage, conservation and land-use patterns also helps moderate water cycle changes. Due to its immense significance, maintaining the integrity of Earth’s water cycle remains a global priority.

Carbon-Cycle:

An Example of Bio-geo-chemical Cycle

• Carbon dioxide constitutes just 0.03% by volume of the atmosphere, but yet it is vital to life (Note: The percentage of carbon dioxide in the dissolved gaseous state/form present in the water is 0.3%). Plants take carbon from carbon dioxide in the air and they use chlorophyll to gather energy from the Sun. From these inputs and water, plants make glucose. In this processof photosynthesis, plants release oxygen. Animals breathe in this oxygen, digest their food that’s comes from plants. This is called carbon-cycle- In the words of mathematics:  Photosynthesis process + Respiration process of organism + Combustion process of coal, oil etc. = Carbon-cycle.
• When we bum fossil fuels like coil, oil etc., the carbon in the fuel combines with atmospheric oxygen to form carbon dioxide. This is called combustion process.
• Since we burn a lot of fuel, there is a huge emmission of carbon dioxide. This increase in carbon dioxide concentration upsets the carbon balance in the atmosphere.
• There are not enough growing plants to absorb all the excess carbon dioxide.
• Things become worse when we cut down forests and burn more trees.
• The current excessive level of carbon dioxide however, leads to a higher temperature, global warming and climate change.

Nitrogen Cycle:

The nitrogen cycle comprises biogeochemical transformations of various nitrogen compounds across different environmental systems. Nitrogen availability often limits biological productivity. But microbial conversions and human interventions now accelerate nitrogen flows creating environmental issues like eutrophication.

Nitrogen Forms and their Cycling

Nitrogen exists in multiple oxidized and reduced chemical forms throughout ecosystems. Key forms include:

Atmospheric dinitrogen gas (N2):

Constitutes 78% volume of air. Highly stable and unavailable directly to most organisms except some bacteria.

Ammonia (NH3) and ammonium (NH4+):

Usable nitrogen compound for organisms produced from nitrogen fixation or ammonification processes. Ammonia strongly associates with water as ammonium ion (NH4+).

Nitrites (NO2-) and nitrates (NO3-):

Oxidized inorganic nitrogen compounds denoting productivity but can pollute water at high levels causing eutrophication. Common nutrient components.

Organic nitrogen:

Diverse compounds containing nitrogen get incorporated into living biomass like amino acids and proteins necessary for growth. Decomposing organic matter releases organic nitrogen.

Nitrogen Cycle Processes

Nitrogen Fixation:

Specialized prokaryotes like Rhizobium bacteria associated with plant root nodules perform nitrogen fixation – energetically converting inert N2 from air into ammonia (NH3) usable for growth. Certain bacteria also fix nitrogen in aquatic systems. Lightning provides minor fixation.

Ammonification and Assimilation:

Decomposers convert organic nitrogen within dead matter back into ammonium (NH4+) which plants directly absorb for protein building. Grazers like animals directly take up organic nitrogen by eating plants and microbes.

Nitrification:

Two types of autotrophic bacteria - Nitrosomonas and Nitrobacter genera oxidize ammonia progressively into nitrites (NO2-) and nitrates (NO3-). Nitrification occurs in most soils and all aerobic environments.

Denitrification:

In oxygen-limited environments like wetlands or estuaries, specialized heterotrophs anaerobically respire nitrates into nitrogen gases like N2O, NO and N2 which releases back into the atmosphere.

Anammox process:

The anammox biochemical reaction also converts nitrites and ammonia directly into dinitrogen gas under anaerobic conditions like ocean oxygen minimum zones. This shortcuts lengthy nitrification and denitrification steps.

Assimilatory nitrate reduction:

Plants and microbes take up nitrates and nitrites and incorporate them into organic compounds through assimilatory pathways different from denitrification.

Why It Matters

The nitrogen cycle regulates bioavailable nitrogen for ecosystems. Nitrogen often limits net primary productivity in soils and water which this microbial-driven cycle ameliorates via natural ammonia generation.

Oxygen Cycle

The oxygen cycle describes the movement of oxygen atoms between the atmosphere, biosphere, lithosphere, and hydrosphere. Oxygen constitutes 21% of atmospheric gases and exists in many inorganic forms across Earth's surface. But nearly half Earth’s oxygen is locked within the lithosphere bound to rocks and minerals.

Oxygen gains entry into the atmosphere via photosynthesis and gets utilized during aerobic respiration and combustion processes. Global oxygen budgets depend on the balance between oxygen-producing and oxygen-consuming reactions.

Main Oxygen Reservoirs

Atmosphere –

Molecular oxygen (O2) gas amounts to 21% of air. Atmospheric oxygen levels fluctuate across geological timeframes based on production and consumption fluxes. Oceans and soils also exchange oxygen with the atmosphere.

Hydrosphere –

Dissolved oxygen enters water bodies from air and photosynthesis. It sustains aquatic lifeforms and leaves via respiration. Modest amounts get contributions from chemical weathering of rocks by surface water flows.

Biosphere –

Oxygen incorporated into plant biomass during photosynthesis and consumed during plant and animal respiration using organic compounds to release energy along with carbon dioxide and water vapor.

Lithosphere –

About 47% of Earth's oxygen is trapped within the crust and upper mantle bound with silicate and oxide minerals of the rocks and sediments. This mineral-combined oxygen entered from atmosphere over billions of years.

Oxygen Cycle Processes

Photosynthesis –

Plants, algae and cyanobacteria take water, carbon dioxide and sunlight to synthesize carbohydrates and release oxygen gas as byproduct. This biological photosynthesis produces all free atmospheric oxygen vital for aerobic life.

Respiration and Decay –

All aerobic organisms uptake atmospheric oxygen to metabolize organic carbon compounds and foods to derive energy for cellular processes. Byproduct includes carbon dioxide and water. Cellular respiration dominates oxygen consumption. Microbial decay also utilizes oxygen.

Combustion –

High temperature exothermic burning of carbon-based fossil fuels like coal, wood etc rapidly consumes and removes oxygen from air converting organic matter mainly into carbon dioxide and water vapor.

Geologic Oxidation –

Gradual chemical weathering of surface rocks and volcanic outputs through reaction with atmospheric oxygen over geological timescales. These reactions transfer oxygen atoms into mineral oxides and silicates within lithosphere.

Why It Matters

The oxygen cycle helped bootstrap complex life through oxygenating earth’s atmosphere over time. The advent of photosynthesis and atmospheric oxygen buildup allowed evolution of multicellular organisms reliant on aerobic respiration.

Today’s higher plants and phytoplankton sustain adequate oxygen regeneration to match utilization rates. But accelerated oxidation from excess fossil fuel burning without replenishment and deforestation now threatens oxygen budgets for marine and terrestrial life through atmospheric carbon loading and habitat impacts. Quantifying fluxes helps moderate global oxygen levels amidst climate change.

Phosphorus Cycle

The phosphorus cycle entails steady phosphorus element movement through rocks, water, soil and living organisms. Phosphorus denotes a scarce nutrient limiting growth in ecosystems. Runoff drainage from farmlands now causes excess phosphorus flows into waterways triggering algal blooms upon eutrophication.

Main Phosphorus Forms and their Cycling

Inorganic Phosphorus

Phosphorus mostly cycles in nature as the negatively charged phosphate ion (PO43-). Phosphate compounds like apatite constitute inorganic phosphorus within mineral deposits and fossils. Rock weathering slowly makes some sedimentary phosphorus bioavailable. But small fractions enter the biotic cycle annually relative to global reserves locked away for millions of years.

Organic Phosphorus

Phosphates dissolve rapidly in water flows unlike nitrogen. Absorbed by plants, phosphates get incorporated into vital organic molecules like sugar phosphates, ATP and DNA/RNA controlling metabolism and genetic functions. Phosphorus lodged in biomass passes through the food chain from producers to consumers.

Key Phosphorus Cycle Processes

Tectonic Uplifting and Exposure –

Gradual tectonic movements and mountain formation unveil subsurface phosphate-rich igneous and metamorphic rocks. Erosion then makes inorganic phosphates bioaccessible.

Rock Weathering and Runoff –

Rainfall wears down exposed rock surfaces. Chemical dissolution releases phosphates into soils to be absorbed by plants. Excess gets drained off via surface runoff into lakes and coastal ecosystems as soluble reactive phosphorus.

Organic Matter Decay –

Decomposers mineralize deceased biomass and waste organic matter of dead plants, algae, animals etc to release phosphates back into the soil pool for reuse. Decay also yields some soluble phosphates lost through runoff.

Sedimentation –

Transport of eroded particles by river drainage and diffusion of dissolved phosphates from lake zones collectively causes phosphorus accumulation onto lake and sea beds as sediments. This storage can reconstitute back into circulation over thousands of years via tectonic movements.

Why It Matters

Unlike nitrogen fixation replenishing soil nitrogen levels, the phosphorus cycle lacks atmospheric inputs. Phosphates instead stem from mineral liberation from ancient fossils. This makes phosphorus availability finite. Intensified cropping and fertilizer drainage now causes abnormal phosphorus loading in water bodies harming ecosystems. Quantifying phosphorus fluxes is vital for moderating fertilizer loads and preventing algal blooms. Conserving phosphates through ecological sanitation systems can also make human habitats more sustainable.