Environmental Science Biogeochemical Cycles and Eutrophication

Water Cycle Top Sinks / Reservoirs

1. Oceans, 2. Glaciers and Permanent Ice.

Evaporation

The process of changing from a liquid or solid state into vapor.

Transpiration

The evaporation of water specifically from plant leaves.

Infiltration and Percolation

The absorption and/or filtration of water gradually through a porous surface or substance into the soil and aquifers.

Runoff

The draining away of water (or substances carried in it) from the surface of land.

Human Impacts on Water Cycle

Clearing vegetation and creating impervious surfaces (concrete) reduces infiltration and dramatically increases surface runoff and flooding.

Carbon Cycle Top Sinks / Reservoirs

1. Marine sediments, rocks, and shells, 2. Oceans (dissolved $CO_2$), 3. Fossil fuels, 4. Soil, 5. Forests.

Photosynthesis

Producers pull carbon dioxide from the atmosphere or water to convert it into sugars.

Respiration

Producers and consumers release carbon dioxide back into the atmosphere as a product of cellular respiration.

Exchange

Carbon dioxide in the atmosphere and dissolved in water constantly interchange because there is no barrier between them.

Combustion

The burning of fossil fuels and plant material which converts them into $CO_2$.

Human Impacts on Carbon Cycle

Extracting and burning fossil fuels and clear-cutting carbon-absorbing forests release massive amounts of $CO_2$ into the atmosphere.

Nitrogen Cycle Top Sink / Reservoir

The Atmosphere (mostly $N_2$ dinitrogen gas).

Why Nitrogen is a Limiting Factor

Although abundant in the atmosphere, organisms cannot use $N_2$ directly because it requires breaking a very strong triple bond; it must be fixed first.

Nitrogen Fixation

Converting nitrogen gas ($N_2$) into ammonia ($NH_3$) and ammonium ($NH_4^+$) via bacteria in legume root nodules, lightning, or industrial fertilizers.

Nitrification

Nitrifying bacteria convert ammonium ($NH_4^+$) into nitrites ($NO_2^-$) and then into Nitrates ($NO_3^-$), which is the preferred form for plants.

Assimilation

Plants take up nitrates/ammonium and consumers eat the plants to produce proteins, vitamins, and nucleic acids (DNA/RNA).

Ammonification

Decomposers convert dead and decaying organic matter (detritus) back into ammonia ($NH_3$) and ammonium ($NH_4^+$).

Denitrification

Specialized denitrifying bacteria in waterlogged soils and water bottoms convert nitrates ($NO_3^-$) back into nitrogen gas ($N_2$).

FNAAD ANPAN Memory Trick

Fixation $ ightarrow$ Ammonia; Nitrification $ ightarrow$ Nitrates/Nitrites; Assimilation $ ightarrow$ Proteins; Ammonification $ ightarrow$ Ammonia; Denitrification $ ightarrow$ Nitrogen Gas.

Phosphorus Cycle Top Sinks / Reservoirs

Rocks and Ocean Sediments.

Unique Feature of Phosphorus Cycle

There is no atmospheric component; it is very slow to cycle compared to water, carbon, and nitrogen.

Importance of Phosphorus

Phosphate ions ($PO_4^{3-}$) are incorporated into nucleic acids (DNA/RNA), ADP, ATP, bones, and teeth.

Weathering and Erosion

Water erodes away inorganic compounds containing phosphates from rocks, releasing them into soil and water.

Human Impacts on Phosphorus Cycle

Mining massive amounts of rock to make fertilizers and runoff from animal waste add excess phosphorus into aquatic ecosystems.

Oligotrophic Conditions

Water bodies that are relatively low in plant nutrients and contain abundant oxygen in deeper parts.

Eutrophic Conditions

Water bodies with too many plant nutrients (Nitrogen and Phosphorus) that cause dense algae growth and subsequent oxygen depletion.

Step 1 of Eutrophication

Excess plant nutrients (nitrates and phosphates) enter water via runoff from farms and gardens.

Step 2 of Eutrophication

Nutrients are no longer a limiting factor, causing a massive algae growth explosion called an algal bloom.

Step 3 of Eutrophication

Algae blocks sunlight from reaching underwater plants, halting photosynthesis and lowering oxygen.

Step 4 of Eutrophication

Algae dies and sinks; aerobic bacteria decompose it and consume massive amounts of dissolved oxygen, leading to fish kills and destroyed ecosystems.

Solutions to Eutrophication

Switch to organic fertilizers, avoid fertilizing before rain, test soil first, plant riparian buffers, and reduce meat/food waste.