Environmental Geoscience Notes

Environmental Geoscience

  • Subject coordinator: Prof. Ralf Haese (ralf.haese@unimelb.edu.au).

Preface

  • Environmental Geoscience studies physical-chemical processes at Earth’s surface caused or accelerated by human activity, covering terrestrial, marine, and energy resource systems.
  • The subject started in 2015, attracting students from geology, environmental science, geography, engineering, and chemistry.
  • It requires no prerequisites, explaining all underlying concepts.
  • Environmental science blends biology, chemistry, geography, geology, atmospheric, social, economic sciences, and environmental engineering.
  • Curriculum balances fundamental processes, quantitative treatments, case studies, and discussion of environmental issues.
  • The subject includes lectures, practicals, and a field trip to Anglesea (Victoria), focusing on water quality measurement and acid sulfate soils assessment.
  • Anglesea faces environmental management issues like estuarine acidification and mine rehabilitation.
  • Students will review existing data, acquire new data, and discuss options for Anglesea.

Contents

The notes cover Environmental Geoscience and the Anthropocene, Catchment Land Management, Estuarine Eutrophication, Acid Sulfate Soils and Arsenic Contamination in Coastal Lowlands.

Environmental Geoscience and the Anthropocene

  • Environmental Change:

    • Ubiquitous due to increasing human population and consumption.
    • Growing demands for resources lead to environmental deterioration.
    • Conservation of biodiversity and habitats is often legislated.
    • Stakeholder tensions lead to public debates and legal cases.

  • Environmental Science Role:

    • Informs public debate with scientific evidence.
    • Supports policy and regulation development.
    • Contributes to education and advances research.
    • Provides information to environmental management bodies.

  • Major Stakeholders:

    • Communities, industries, governments, and NGOs.

  • Four Areas of Environmental Science:

    1. Systems: Comprehensive assessment of areas including landscape, biodiversity, ecosystem functioning, and environmental services.
    2. Processes and Conditions: Focus on physical-chemical processes essential for ecosystem functioning, such as nutrient retention and pH buffer capacity.
    3. Change: Identifying human-caused trends as opposed to natural variability, and using understanding of past changes to predict future changes.
    4. Technologies: Utilizing technologies to analyze, monitor, mitigate, and remediate environmental damage.

  • Environmental Geoscience:

    • Focuses on the role of rocks and sediments in environmental processes, including water-rock reactions and contaminant mobilization.
    • Land clearance, coastal drainage, mining, and unconventional gas production are key topics.
    • Requires understanding of physical-chemical processes involving rocks.

  • Paleo-environmental Reconstruction:

    • Uses rock records as archives of environmental change.
    • Analyzes lithological, micropaleontological, and chemical variations in sediments.
    • Examples include sea level fluctuations and the breakup of Pangea.

  • The Anthropocene:

    • A proposed new epoch marked by significant human-induced global environmental change.
    • Markers include increased atmospheric CO2, engineered materials, and nutrient levels in coastal waters.

Catchment Land Management

  • Introduction:

    • Environmental degradation is often localized, but its causes may lie elsewhere.
    • Hydraulic connectivity within catchments links causes and effects.
    • Surface runoff and groundwater interactions are key pathways.
    • The catchment-to-coast continuum highlights these interconnections.

  • Coastal Catchments:

    • Have high population densities and industrial infrastructure.
    • Coastal soils are often fertile and productive.
    • Land management requires a system approach.
    • Catchment management authorities facilitate stakeholder consultation and develop management plans.

  • Catchment Definition:

    • Defined by topography with ridges forming boundaries.
    • Land management uses thematic digital maps (topographic, geological, soil, land use).
    • Attributes like water retention capacity are crucial.

  • Catchment Assessment Tool (CAT):

    • Upscales localized interactions to catchment management scales.

  • Calculating Catchment Loads:

    • Changes in land management impact water, sediment, and nutrient transport.
    • A mass balance approach assesses reservoir changes based on input and output.
    • Volume: volume[L,m3]volume [L, m^3]
    • Mass: mass[Kg,t]mass [Kg, t]
    • Flux: Flux,volume  or  mass  per  time,  for  example,  [m3yr−1]  or  [Kgyr−1]Flux, volume \; or \; mass \; per \; time, \; for \; example, \; [m^3 yr^{-1}] \; or \; [Kg yr^{-1}]
    • Non-Steady State: If Input≠OutputInput \ne Output, the reservoir changes volume or mass.
    • Steady State: If Input=OutputInput = Output, the reservoir maintains volume or mass.
    • Load/Flux Calculation: Load∗  or  Flux∗[mg  d−1]=Conc[mg  L−1]×Flow[L  d−1]Load^* \; or \; Flux^* [mg \; d^{-1}] = Conc [mg \; L^{-1}] \times Flow [L \; d^{-1}] (where * denotes sediment or nutrients).

  • Cumulative Nitrogen Load Calculation:

    • Represents the sum of nitrogen loads from different land uses in a sub-catchment.

  • Soils:

    • Integral part of the ecosystem, providing growth substrate, nutrients, and water.
    • Formed over geological times but can be diminished through erosion or degradation.

  • Soil Formation Factors:

    1. Parent material (host rock).
    2. Climate.
    3. Organisms (fauna, flora, bacteria).
    4. Topography.
    5. Time.

  • Major Soil Processes:

    1. Decomposition and humification of organic matter.
    2. Physical weathering.
    3. Chemical weathering.
    4. Leaching.
    5. Translocation.
    6. Capillary transport.

  • Soil Horizons:

    • O horizon: Accumulation of organic matter.
    • A horizon: Mixture of rock fragments and organic material.
    • E horizon: Eluviation zone with leaching and translocation; porous and rich in resistant minerals.
    • B horizon: Illuviation zone with accumulation of clay, Fe-, and Al-oxides; dense and often colored.
    • C horizon: Weathered parent material (regolith).
    • R horizon: Unweathered parent material.

  • Soil Types:

    • Podzol: Formed in temperate to boreal climates, characterized by distinct O, E, and B horizons; well-drained.
    • Latosols: Formed in wet and hot climates with intense chemical weathering; deep with no distinct horizons.
    • Laterites: Formed in hot, seasonally dry and wet climates; exhibit a leached zone between Fe/Al-rich layers; can form minable deposits.

  • Soil Erosion Types:

    1. Rill erosion: Small channels (<30 cm deep) formed during heavy rain.
    2. Sheet erosion: Mobilization of large soil patches during heavy rain.
    3. Gully erosion: Development of entrenched channels (>0.5 m deep) from concentrated water flows.
    4. Tunnel erosion: Removal of subsoil beneath intact surface soil, forming cavities.
    5. Wind erosion: Particle transport via rolling, saltation, or dust clouds.

  • Soil Salinization:

    • A severe form of soil degradation, often associated with land clearance.
    • Land clearance leads to shallower groundwater levels, increased runoff, and reduced evapotranspiration, resulting in salt precipitation.

  • Mitigation Options for Soil Erosion:

    1. Terracing.
    2. Contour farming.
    3. Shelter belts.
    4. Riparian wetlands and flood plains.

Estuarine Eutrophication

  • Introduction:

    • Estuaries are critical mixing zones between freshwater and seawater with high ecological and economic importance.
    • They provide habitats and breeding grounds for various species.
    • Vulnerable to nutrient enrichment (eutrophication), leading to boom-and-bust cycles, anoxia, and toxic algae blooms.

  • Estuarine Shapes and Hydrodynamics:

    • Vary widely, affecting nutrient cycling and retention.
    • Classified by the relative influence of river, tide, and wave energy.
    1. Wave- and tide-dominated deltas: Strongly influenced by river flow.
    2. Wave- and tide-dominated estuaries: Intermediate influence from river and wave/tide.
    3. Coastal lagoons: Largely wave-dominated with inverse flow in hot climates.
    4. Strandplains and tidal flats/creeks: Wave- and tide-dominated endmembers.

  • Estuary Types and Hydrodynamic Conditions:

    • Wave-dominated estuaries: South of ~30°S, low tidal range, internal circulation, limited water exchange, episodic freshwater inflow, sandbar formation.
    • Tide-dominated estuaries: Northern Australia, higher tidal range and river inflow, tidal flats, creeks, channels, months-long water residence time.

  • Estuarine Nutrient Dynamics:

    • Nitrogen is often a limiting nutrient.
    • Three groups of primary producers are distinguished:
      1. Phytoplankton (PP).
      2. Microbenthic algae (MBA).
      3. Submerged aquatic vegetation (SAV).

  • Nutrient Cycling:

    • Primary producers take up nutrients during photosynthesis.
    • Organic matter is decomposed, recycling nutrients.
    • Bacteria use oxidants, leading to a depth zonation.
    • Denitrification converts usable nitrogen into N2 gas.
    • Phosphorous adsorption onto iron oxides limits P recycling.

  • Wave-Dominated Estuary Nutrient Cycling Summary:

    • Light penetration drives photosynthesis.
    • Organic matter decomposes in the water column and sediments.
    • Benthic nutrient fluxes occur.
    • Denitrification and phosphorus trapping occur in sediments.
    • Nutrient residence times are long.

  • Case Studies illustrate estuarine bathymetry, light penetration, dominant plant groups and water quality indicators.

    • St. Georges Basin (NSW):
      • Deep, phytoplankton-dominated with little seagrass.
      • Anoxia can develop in deep basins.
      • Monitor: Phytoplankton and dissolved O2 and nutrients.
    • Wilson Inlet (WA):
      • Intermediate depth, phytoplankton-dominated in winter, MBA in summer, substantial seagrass.
      • Monitor: Seagrass cover, light penetration, nutrients.
    • Lake Wollumboola (NSW):
      • Shallow, clear water, often macrophyte-covered.
      • Prone to boom-and-bust cycles.
      • Monitor: Macrophyte cover, O2, nutrients.
    • Torbay Inlet (WA):
      • Very shallow, tannin-rich water limits light penetration, low macrophyte cover, surface phytoplankton observed.
      • Prone to toxic blue-green algae blooms.
      • Monitor: Light penetration, nutrients, phytoplankton community.

Acid Sulfate Soils and Arsenic Contamination in Coastal Lowlands

  • The rise and fall of sea levels over thousands of years significantly impacts coastal zone environments by alternately flooding and exposing sediments, affecting erosion and sediment composition.

  • Pyrite (iron sulfide) forms through iron and sulfur inputs in estuaries where fresh and sea water mix.

  • Terrestrial runoff supplies iron, while seawater provides sulfate.

  • Dissolved iron from rivers reacts in saline conditions to form iron oxides, which aggregate and settle.

  • Sulfate from seawater is reduced to sulfide (H2S) by bacteria, which then reacts with iron minerals to form monosulfidic black ooze then pyrite.

  • Multiple oxidation states of sulfur (-2 to +6) exist, making sulfur chemistry complex.

  • Determining the Oxidation State of Sulfur in Sulfate ((SO_4^{2-})):

    1. Calculate the charge for oxygen within the molecule, assuming oxygen has a charge of -2. In (SO_4^{2-}), the total charge is -8 (4×−2=−84 \times -2 = -8).
    2. Subtract this total oxygen charge from the overall molecule charge. Since, (SO_4^{2-}) has an overall charge of -2, subtract -2 from -8, giving -6 (−8−(−2)=−6-8 - (-2) = -6).
    3. Balance the resulting charge from the remaining ions in the molecule with sulfur.S+(−8)=−2S + (-8) = -2, so,S=+6so, S = +6.
    • Therefore, the oxidation state of sulfur in (SO_4^{2-}) is +6.

  • During interglacial periods, high sea levels lead to deposition of iron oxides and sulfate, resulting in extensive pyrite formation.

  • In glacial phases, pyrite ((FeS_2)) is exposed to oxygen, leading to pyrite oxidation, forming iron oxides and releasing protons, which leads to acid formation.

  • Iron oxides formed bind heavy metals, acting like a sponge.

  • During reflooding after a glacial period, iron oxides are reduced by overlying sulfidic sediments, releasing heavy metals into groundwater, making the areas prone to this exposure to heavy metals such as Bangladesh.

  • Arsenic Contamination in Bangladesh:

    • Caused by arsenic absorption to iron oxides.
    • As iron oxides dissolve, arsenic is released, contaminating groundwater.
    • Local communities fully oxygenate water to precipitate iron oxide and absorb arsenic.

  • Pyrite oxidation leads to the formation of iron oxides, sulphate and the net formation of protons in the system. It can be summarized by the following generalized reaction: FeS<em>2+O</em>2+H<em>2O→Fe−oxides+SO</em>42−+H+FeS<em>2 + O</em>2 + H<em>2O \rightarrow Fe-oxides + SO</em>4^{2-} + H^+

  • These reactions contribute to the acidification of the environment. Acidification is associated with a range of problems, including the dissolution of toxic heavy metals.
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