Restoration Ecology: Biogeochemical Thresholds

Today's Agenda

• Lecture 1 is about the course outline and an introduction to restoration ecology.
• Lecture 2 will discuss biogeochemical thresholds in restoration, focusing on acidification.
• A short lecture will introduce case study work.
• Groups A1-14 will meet in B3031+B3032 from 14:00-17:10 for a case introduction.
• Groups B15-28 will meet in B1032 from 14:00-17:10 for a case introduction.
• Self-study involves papers 1 & 2, with questions answered on Brightspace.

Main Biogeochemical Thresholds in Restoration

• Acidification involves a decrease in the acid-buffering capacity of soils.
• Eutrophication involves an increase in plant-available nutrients such as nitrogen (N), phosphorus (P), and potassium (K).
• Desiccation includes a deeper water table, decreased water availability, and a shift in water type from groundwater to rainwater.
• Other processes include invasive species, habitat loss, and fragmentation.
• Invasive species cause an increase in unwanted exotic dominant species.
• Habitat loss and fragmentation result in decreased area and increased isolation of nature.

Acidification in Detail

• Soil acidification results from the accumulation of unbound H+ ions in the soil.
• Soil pH decreases with acidification and can calculated as pH = -log10(H+).

Causes of Acidification

• It is a natural process due to weathering which involves the leaching of base cations.
• Weathering influences rainwater and carbon dioxide production from plants, roots, and soil microorganisms.
• Acid deposition accelerates Acidification because of nitrogen and sulfur emissions.
• The main sources of these emissions come from industry, traffic, agriculture, and coal burning.

Sources of Acid Deposition

• Nitrogen oxides (NOx) turn into nitric acid, and sulfur dioxide (SO2) transforms into sulfuric acid.
• These undergo photo-oxidation.
• Gases and particles can undergo both wet and dry deposition. Deposition increases with total leaf area.

Soil Acidification Sources

• Soil acidification occurs directly from H⁺ in deposition, specifically 2H+ from sulfur oxides (SOx) and 1H+ from nitrogen oxides (NOx).
• It is also a product from processes in the soil.
• Ammonium (NH4+) uptake by plants and microorganisms leads to the release of H+.
• This involves biota + NH4+ resulting in (-NH3 aminoacid/amides) + H+.
• Nitrification is a microbial, aerobic process occurring when pH is greater than 4.5 with the equation NH4+ + 2O2 → H2O + NO3- + 2H+.
• Pyrite (FeS2) oxidation, both chemical and microbial, produces 8H+. Desiccation and mining can cause pyrite oxidation.
• If the ratio of sulfur to calcium and magnesium (S:(Ca+Mg)) in the soil is less than 0.67, there is no acidification risk.

Emissions in the Netherlands

• The Netherlands produces a lot of manure.
• Emissions of air pollutants are regulated by the EU's National Emission Ceilings Directive (NECD).
• Air pollutants include nitrogen oxides (NOx), non-methane volatile organic compounds (NMVOS), ammonia (NH3), sulfur dioxide (SO2), and particulate matter (PM2.5).

Vegetation's Role in Acid Deposition

• As nitrogen(N) deposition increases pH decreases.
• Deposition is influenced by vegetation, dry deposition increases with total leaf area.

Understanding Buffer Capacity

• Buffer capacity is a soil's ability to neutralize acids.
• Without it, H+ accelerates weathering.
• Soil buffers pH when it contains soil + H+ which keeps the pH stable.
• If a soil contains Soil + H+ H+ H+ H+ H+ the pH changes.
• The dominant buffer mechanisms are carbonate, cation exchange, silicate, and aluminum.

Buffering Process in Soil

• Carbonate buffers soil pH in the alkaline range of 8.6-6.2.
• Exchange buffers the soil pH in the 6.2-5.0 range.
• Silicate buffers soil pH in the weakly acidic range of 5.5-4.2.
• Aluminum buffers soil pH in the acidic range of 4.2-3.8.
• Iron buffers soil pH in the acidic range < 3.8.

Carbonate Buffer Range

• Limestone, young sand, clay, and loam use carbonate as buffers.
• The main chemical equation is CaCO3 + H+ → Ca2+ + HCO3-.
• HCO3- + H+ which results in CO2 and H2O.

Cat-Ion Exchange

• Cat-ions are exchanged with (Mg2+, Ca2+) with H+.
• This takes place on Clay or organic matter.

Silicate Weathering

• Many different silicates are used but the process is very slow. For example, Mg2SiO4 + 4H+ -> 2Mg2+ + H4SiO4 (olivine)

Effects of Acidifying Deposition on Plants

• Increased weathering dissolves limestone & marble.
• Acid deposition can create direct leaf damage, especially from occult (fog or cloud water) and dry deposition.
• Acidification leaches cat-ions such as calcium (Ca2+), potassium (K+), magnesium (Mg2+), and manganese (Mn2+), which declines plant growth rate.
• There is increased mobility of heavy metals like aluminum (Al3+) that causes root damage.
• It reduces overall soil pH, causing germination problems and affecting soil organisms.
• It affects decomposition and nitrification.
• It is correlated with decreased plant growth and reproduction.
• It is correlated with an increase in sensitivity to pests and diseases.

Aluminum Toxicity

• The Al:Ca ratio should be kept below 1.
• If there is still enough calcium in the soil, the aluminum is not damaging.

Ammonium Toxicity

• The NH4:NO3 ratio should be kept below 5, pH 4.6-5.9.

Buffer Capacity and Soil

• Leaching of cat-ions correlates to decline plant growth.
• Increased mobility of heavy metals such as Al3+ causes root damage.
• It reduces soil pH.
• There is a shift in dominant nitrogen (N) form.

High vs. Low Buffer Capacity

• High buffer capacity requires a high amount of acid to change the soil pH.
• Soils that are low in silicates, rich in carbonates like CaCO3 and MgCO3.
• Soils rich in clay and organic matter -> CEC.
• Low buffer capacity requires a low amount of acid to change soil pH.
• Soils are rich in silicates, like Si. Dutch mineral sandy soils are an example because they consist of 80-90% of SiO2.

Recognizing Acidification in Geology

• Acidification is related to old geological deposits.
• Related to old (sandy) soils (Pleistocene > Holocene), deposits low in lime and high in silicon (Si like granite).
• Acidification is impacted by desiccation.
• Pyrite (FeS2)- or iron sulfide (FeS), in rich sediments exposed to O₂ can cause acidification.
• It can be caused by water table fluctuation. It can be caused by sludge from dredging and mine spills.

Soil Chemistry and Acidification

• Base saturation correlates to pH and vegetation health.
• Greater than 80% correlates to a pH of ~ 6.5.
• Less than 60% correlates to degradation of base-rich vegetation types.
• 40 % or less means there is no longer any cat-ion exchange buffering.
• Less than 15 % means the pH could drop below 4.2
• pH below 4.2 poses a risk of aluminum (Al) toxicity because it is the aluminum buffering range.
• An aluminum to calcium (Al : Ca) ratio in soil extract that is greater than 1 indicates a risk of aluminum toxicity.
• An ammonium to nitrate (NH4 : NO3) ratio in soil extract that is greater than 5 indicates a risk of ammonium toxicity.

Vegetation Changes

• Plant communities in weakly buffered soils (4.2 > pH < 5.5) are the most sensitive to acidity.
• Shifts in plant species composition can happen over time.
• Base-loving species decline while acid-tolerant species increase..
• It is important to check indicator species and plant communities.
• The Ellenberg indicator value can be used for acidity levels.

Effects on Fauna

• Acidification on certain environments is proven to cause broken legs in animals due to loss of calcium