Nutrient Cycling

Nutrient Cycling

  • Definition: Nutrient cycling refers to the movement of materials through ecosystems, emphasizing the unintended consequences of human efforts to improve quality of life. This involves recycling elements necessary for life.

Movement of Materials Through Ecosystems

  • Key Elements Needed for Life:

    • Carbon (C)

    • Hydrogen (H)

    • Oxygen (O)

    • Nitrogen (N)

    • Phosphorus (P)

    • Sulfur (S)

  • Biogeochemical Cycle: The cycling of these elements through biotic (living) and abiotic (non-living) components of ecosystems.

Specific Elements and Their Roles

Hydrogen (H)

  • Most Abundant Element: Hydrogen is the most abundant element in the universe.

Oxygen (O)

  • Abundance:

    • Third most abundant element (after Helium)

    • Constitutes 49.2% of Earth's crust mass.

    • 89% of the mass of oceans.

    • 21% of the atmosphere is O2.

  • Photosynthesis: All waste products from noncyclic electron flow in photosynthesis are gases, primarily oxygen.

  • Electron Source: Water serves as a source of electrons and protons during photosynthesis.

Carbon (C)

  • Role in Organisms: All important macromolecules contain carbon, including proteins, nucleic acids, carbohydrates, and lipids.

  • Atmospheric Carbon:

    • Primarily sourced from volcanic activity, CO2 is absorbed by autotrophs via photosynthesis.

    • Heterotrophs acquire carbon by consuming autotrophs or other heterotrophs, including their remains and waste.

  • Carbon Reservoirs:

    • The majority of carbon is found in soils, rocks, marine sediments, and dissolved in ocean water.

  • Evolution of Land Plants: Early land plants captured carbon through photosynthesis, producing sugars for metabolism and cellulose for cell walls.

  • Vascular Plant Evolution: The evolution of vascular tissue allowed plants to synthesize lignin around 420 million years ago, enhancing strength and resistance to decay.

  • Carboniferous Period: During this period:

    • Vascular plants decomposed poorly as no decomposers could digest lignin.

Lignin

  • Composition and Structure: Lignin strengthens cell walls and is almost indigestible.

Lignin Decomposition

  • Fungi: Only white rot fungi can decompose lignin, while brown rot fungi digest cellulose while avoiding lignin.

  • Historical Context: The ability to digest lignin emerged at the end of the Carboniferous period, coinciding with significant CO2 absorption by plants for 120 million years.

Carbon Dioxide (CO₂) and Climate

  • Greenhouse Gas: CO₂ significantly affects climate and is primarily released by burning fossil fuels.

  • Historical CO₂ Levels:

    • Low CO₂ levels at the end of the Carboniferous led to high glaciation.

    • Increased CO₂ reduces global ice cover.

Volcanism, CO₂, and Extinctions

  • Correlation with Extinctions:

    • Volcanic activity often aligns with mass extinction events, creating basalt rock formations like the Palisades.

Periodic Mass Extinctions in Geologic History

  • Mass Extinctions: Many geologic periods conclude with large-scale species disappearances, potentially linked to high CO₂ concentrations:

    • Greenhouse gas emissions warm Earth, interrupting nutrient distribution and causing die-offs, especially in oceans.

    • Decomposition can release toxic H2S gas, harmful to flora and fauna.

Fossil Fuels and CO₂ Emission

  • Energy Sources:

    • Fossilized remains include coal, oil, natural gas, and peat, which are carbon-rich energy sources.

  • Combustion Reaction:
    2 C8H{18} + 25 O2 ightarrow 16 CO2 + 18 H_2O + ext{energy}

  • Historical Emissions:

    • CO₂ levels rose from 265 ppm in the 1850s to 403 ppm in November 2016 and 429.64 ppm projected by April 2025.

Historical CO₂ Levels Over Time

  • Graphical Data:

    • CO₂ levels measurements indicate highest concentrations in recent history, surpassing previous centuries' averages.

Photosynthesis Rates

  • Recent Increases:

    • Plant growth has accelerated, converting 31% more CO₂ into organic compounds compared to pre-industrial times.

  • Measurement Techniques:

    • Determined through studying carbonyl sulfide (COS) levels in Antarctic ice bubbles, indicating direct links to photosynthetic rates.

Oceanic Carbon Storage

  • Dissolved CO₂:

    • CO₂ from the atmosphere diffuses into oceans, with oceans storing 20-25 million tons of CO₂ per day.

  • Historical Context: This is more than any time in the last 20 million years.

Ocean Acidification

  • Impact of Fossil Fuels:

    • CO₂ returned to the atmosphere from burning fossil fuels leads to significant oceanic absorption.

  • Marine Photosynthetic Utilization: Phytoplankton utilize some of this CO₂, creating a feedback loop in carbon cycling.

Effects of pH on Marine Life

  • Shell Formation:

    • Shell development relies on calcium carbonate, which is present due to limestone erosion and remains from shellfish.

  • Reaction with CO₂:

    • Reaction of CO₂ with water yields carbonic acid:
      CO2 + H2O
      ightleftharpoons H2CO3

  • Acidic Consequences: Carbonic acid forms bicarbonate and hydrogen ions, leading to ocean acidification, which affects marine life.

  • Neutralization Reaction:

    • Carbonate ions act to cover H+ ions forming more bicarbonate:
      CO2 + H2O + CO3^{-2} ightarrow 2 HCO3^{-}

Examples of Affected Species

  • Pteropod (Sea Butterfly): Illustrates the negative effects from acidification as conditions project for 2100 show deteriorating shell structures.

The Nitrogen Cycle

  • Nitrogen Requirements:

    • All organisms need nitrogen, primarily usable only by certain prokaryotes (requires substantial energy: 16 ATPs per molecule of N2 fixed).

  • Plant Utilization: Plants convert ammonium (NH₄), nitrates (NO₃), and nitrites (NO₂) into amino acids, making nitrogen a limiting mineral element for primary production.

  • Industrial Process: The Haber-Bosch process enables nitrogen fixation under extreme conditions, surpassing biological processes today.

  • Environmental Impact:

    • Nitrogen in fertilizers is highly water-soluble, leading to runoff into waterways, contributing to eutrophication (an excess of nutrients in aquatic systems).

  • Nitrous Oxide Emissions: Fertilizer contributes to atmospheric N2O, a potent greenhouse gas, with agricultural levels exceeding naturally occurring nitrogen levels by 2.5 times as of 2020.

Eutrophication Explained

  • Algal Blooms:

    • Fertilizer runoff stimulates excessive algal growth in fresh and marine waters. Once nutrients are depleted, algae die leading to decomposition processes that deplete oxygen.

Land Use in Iowa

  • Land Allocation:

    • Various land uses documented, with total land use in Iowa amounting to 36,002,874 acres.

  • Nitrogen Runoff Statistics: Annually, 660 million pounds of nitrogen runoff from Iowa into the Mississippi River.

Sulfur

  • Biological Role: Sulfur is essential in amino acids such as cysteine (cys) and methionine (met), and thus in protein synthesis.

  • Natural Sources: Most sulfur is stored in rocks and released through erosion into soil and seawater, taken up by primary producers.

  • Atmospheric Sulfur: Sulfur exists in particulate forms in the atmosphere, contributing to cloud formation, with implications for photosynthetic rates.

  • Pollution from Combustion: Burning fossil fuels releases sulfur compounds (SO2) that react with water to form sulfuric acid, contributing to acid rain, which damages plant life and affects sensitive aquatic species negatively.

Phosphorus

  • Biological Importance: Required for nucleic acids and generally found in phosphate salts or deep sediments with a much slower geological cycling compared to nitrogen.

  • Soil Dynamics: Phosphorus is less soluble than nitrogen, adhering closely to soil and thus can play a role in aquatic eutrophication when eroded into lakes.

  • Historical Examples: The use of STPP (sodium tripolyphosphate) in detergents during the 1960s contributed significantly to pollution in the Great Lakes, rendering them unswimmable.