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