Ch. 7.1-7.7: Soil Aeration and Temperature
wetland hydrology
(1) balance of in and outflows as well as quantity of water detemrine the water table (within or above soil). (2) The seasonal hydroperiod. (3) The anaerobic soil conditons. (4) Characteristic long residence time of water in the soil. (5) other indicators (i.e. hydric soils, above ground root masses, water stains) of flooding/saturation
reglation of oxygen availability
(1) soil macroporosity (2) soil water content (3) oxygen consumption
wetland fxns for ecosystems and society
(1) species habitat (2) water filtration (3) flooding reduction (4) shoreline protection (5) commercial/recreational acitivitie s(hunting) (6) natural products)
3 agreed upon characterisitics of wetland
(1) wetland hydrology (2) hydric soils (3) hydrophytic plants
redox window fo rGHG from wetladn (Eh)
-0.15 - 0.18 V
% composition of gasesous components in atmosphere
21% oxygn, 0.035% CO2, 78% N
Oxygen levels that inhibit plant and microbial activity
<20% of pore space or <10% of soil volume
greenhouse gases released by wetlands
CH4 (from CO2), NOx, CO2. Can be kept to reasonable levels by keeping moderately low Eh values
other elextron acceptors
Fe, C, N, Mn, S
constructed wetlands
WWTP. wetland mitigation to mediate destruction of wetlands by constructing more (ideally w/in same watershed), not super successful.
oxidizing agent/gets reduced
accepts electrons
hydrophytic vegetation
adapted to life in saturated, anaerobic soils
poor soil aeration
availabiiy of oxygen is insufficient to support upward growth of plants and animals (<0.1 L/L) (80-90% pore space filled with water). Can be caused by compaction
quick diffusion of O2
can allow subsoil to remain aerobic when the topsoil is waterlogged and anaerobic, OTherise, topsoil tends to be higher in O2
large pores
can be anaerobi cin the center if the pore has a great enoguh diameter and small enough intraaggregate pores
partial pressure gradient
concentration gradient for each gas
reducing agent/gets oxidized
donates electrons
factors affecting soil aeration and Eh
drainage (macropores, articial drainage), respiration rates (higher in warmer soil), soil heterogeneity
wetland loss
draining for farms, urban development, once encouraged by USDA and Army Corps of Engineers
hydric soil indicators
features associated with saturation and reduciton (1) accum OM (black) (2) gray, gleyed, redox depletions (<1 chroma, no >4) (3) redoximorphic features of orange/gray in upper layers (4) black nodules of reduced Mn
higher plants and flooding
flooding by stagnant water is worse than flooding by flowing water bc stagnant water does not replensih O2 at all ,but flowing water would a little bit
color of reduction
grays, blue
distribution of soil gases throughout profile
higher O2 and N2 at topsoil, higher CH4 and CO2 at subsoil
Hydric soils
histosols, aquic. Subject ti periods of saturation that inhibit O2 in soil. reduced conditions for extended periods of time (electron acceptors other than O2 useD). hydric soil indicators
adaptive features of hydrophtyic vegetation
hollow aerenchyma, buttress roots, pneumatophores, above ground roots, greater area of shallow roots
aerenchyma tissue
hollow structure in plant stems used to transport O2 to roots
wetland delineation
identifying the exact drier end of the wetand on the ground(for political, law)
tillage
increases heterogeneity and oxygen in the short run, reduces oxgen (via macroporodity) in long term
relationship between O2 and CO2 in soil air
inverse
% composition of gasesous components in soil air
less O2 than air (especially deeper soil w/o macropores), more CO2 than air about same N, higher H2O vapor than atm, more methand and H2S than atm 9especially when waterlogged)
reducing conditions
low Eh, low O2, acidic (protons are product of reduction rxns), less red oxide color and more gray/gleyed color
wetland chemistry
low redox potetnial (low Eh)! low oxygen, but sometimes a thin aerobic layers in top cm of soil if not saturated. N present in gases released to atm. Eh ow enough for visible Fe redox, rotten egg smell (H2S), methane, removal of metals like Cr and Se from water, neutralization of acids. OVerall, detox is helpful for society
ventilation mechanisms
mass flow, diffusion. bulk of gaseous interchange is by diffusion
mottled
mix of reduced and oxidized colors, not good sign for plant growth
oxygen vs. other requisites for plant growth
nutrients, water, etc. may be in supply but if there's no oxygen then the plant will stop functioning
primary oxidizing agent/electron acceptor
oxygen
gaseous components of soil air
oxygen, CO2,
order of most to lest favorable elecron accecptor (in an ideal soil)
oxygen, nitrogen, manganese, iron, sulfur, carbon, hydrogen (most soils are not ideal as not all protons and e- are completely available for rxns)
drier end of a wetland
plant-soil-animal community no longer predomnantly indfluenced by precense of anaerobic conditions
hydrophytes
plants adapted to life in waterlogged soils (rice). transport O2 to roots via arenchyma tissue
rate of decay and aeration
poor aeration slows down the rate of decay of OM (poorly aerated soils are hgih in OM)
partial oxidation
poorly aerated soils can partially oxidize intoethylene gas, alcohols, organic acids, which can be toxic
partial pressure
pressure a gas would exert if it were alone in the volume occupied by the mixture
soil aeration
rate of ventilation of toxic gases (methane, ethylene), proportion of pore space filled wit air, composition of soil air, resulting redox potential in soil envmnt
color of oxidation
red, yellow, reddich-brown
toxicants
reducd arsenic is much more toxic and soluble. oxidized chromium is much more souble and toxic.
reduced nutirents
reduced forms of Fe and Mn are much more soluble than the oxidized forms, so some reduction can improve soilfertility, but too much can cause toxicity
core cultivation
removing thousands of small cores fro the soil to faciliatate gas exhnage throgh soil. less effective than holes from spikes in soil bc area around the spike becomes compacted
planting trees
rough, large hole for tree to prevent drowning, breathign tubes to facillitate oxygen to roots, mulch for fine tree roots and compaction prevention. Don't pile soil around trunk. Use fence to protect rough circle around tree, size of circle dependent on root zone
wetland
soils that are water-saturated near the surface for prolonged periods when soil temperatures and other conditions are such that plants and microbes can grow and remove soil oxygen, thereby ensuring anaerobic conditions
potted plants
tall pots allow for best aeration bc allows for a lower water table. Best to add water whn BOTTOM of soil is dry, top is inaccurate indicator. More susceptible to extreme temps, waterlogging, drought, but easie to conrol than whole field
redox potentials (Eh)
tendency of electrons to be exchanged between substances. V or mV
hydroperiod
the temporal pattern of water table changes
ethylene
toxic in low proportion to plants
wetter end of a wetland
water is too deep for rooted vegeation to take hold
redox potential of variously aerated soil
well aerated: 0.4-0.7 V poor aerated: 0.3-0.35 V (range for use of other electron acceptors) waterlogged, high OM: -0.3 V
water saturated/waterlogged
when all or nearly all of the soil pores are flled with water
oxidized form of electron acceptors
when the element is bound to an oxygen, or for the case of Fe or Mn, when the charge is +3 or +4, respectivly