EARTH 444: Wetlands

core indicators of a wetland

hydrology - water at or near surface long enough to shape environment

hydric soils - lox oxygen, gleying, or mottling

hydrophytes - plants adapted to saturated oxygen-poor conditions

UN wetland definition

marsh, fen, peatland, water, natural or artificial, permanent or temporary with water that is static or flowing, fresh, brackish, or salt including areas of marine water, the depth of which at low tide does not exceed 6 metres

made 2000 RAMSAR sites

canadian wetland definition

Land that is saturated with water long enough to promote wetland or aquatic processes as indicated by poorly drained soils, hydrophytic vegetation and various kinds of biological activity which are adapted to a wet environment

why definitions matter

what gets counted, where are boundaries, which get protected?

Ontario Wetland Evaluation System changes

evaluated separately as opposed to in a complex, not protected

plus less SAR importance and MNR no longer has final say so overall less provincially significant wetlands :(

wetland class diagram

category, class, form (surface, soil and water), type (dominant vegetation)

mineral wetlands

<40cm organic material, mineral soils w low O, Fe, and Mn. Grey-blue gleyed soils

marsh, swamp

organic wetlands (peatlands)

>40cm organic material

dead partially decomposed plant material

bog and fen

bog

raised above surrounding terrain w water at or just below surface. Ombrogenous (water only from precipitation falling on top (not runoff either)), old, mossy and shrubby, low productivity and diversity. More acidic and less minerals. pH 3-5

Fen

Minerogenous (groundwater and SW w minerals), graminoids grasses/sedges and shrubs. pH 5-7. More nutrients and diversity.

where are bogs and fens in Canada

boreal areas, interspersed w forest. South central Canada

swamp

mineral or organic, minerogenous, water table below surface w dry hummocks, seasonally flooded, high P, trees! (cedar, maple, black ash)

marsh

mineral soils w some peat, minerogenous, shallow surface water, herbaceous vegetation, floating plants, lots of nutrients and P and biodiversity! v commin in SO

shallow water wetland

open water >75%, mineral soil. ponds, potholes, estuaries. may dry up. not including our reservoirs

canadian wetland classes diagram

wetland continuum

between lake and upland can be marsh and swamp, boundaries v gradual

why is class a CLUE of function

presence DNE function. hydrology, soils, and vegetation, chemistry, and disturbance determine what it actually does

core 4 ecosystem services

provisioning (food, peat harvesting)

regulating (flood mitigation, aquifer recharge, filtration)

cultural (aesthetic, recreation)

supporting (nutrient cycling, photosynthesis)

how wetlands matter differently

theoretical potential (type, size) leads to actual performance (depending on hydrology and soil) leads to social value (what does it actually do and for who)

main drivers of wetland loss

agriculture, pollution, development, alteration, roads, channelization, mining, and climate change

mostly small upland ones than large riverine

functions of a wetland

biological condition informs hydrologic (like storage) and water-quality (like nutrient retention) function

4 types of wetland intervention

restoration, creation, enhancement, treatment

artificial vs human-induced wetland

only if persistent and continuous human activity vs

one time action by humans lead to persistent, functioning wetland

what is no net loss policy?

developers can get rid of wetlands as long as they make new ones in the same proportion. 2:1 mitigation ratio means 2ha created for every 1 lost

we can compare restoration success against

baseline (what was lost)

reference (similar ecology or function)

good success criteria

specific

measurable

linked to goals

sensitive to time scale

compared to appropriate benchmark

steps for site selection

easier to restore

look at land use, check hydrology, go where inundation frequent, characterize soil, and chemistry of water sources

local seed banks, materials, ownership, corridor for animals, access, and size

tile drains

need to make sure water won’t just leave wetland if constructing. these are tubes in agricultural soil to drain in spring, may need to be blocked if making wetland and good to be in depressional area

riparian wetlands

can be dried out if concrete channel, need to let river reconnect to floodplain and meander

get lots of runoff and snowmelt and interact w gw

can’t be a bog

top 2 drainers of peatland

agriculture and forestry

steps of peatland drainage

also more vulnerable to drought, change run-off & chemistry, loss of vegetation, and decline of peat surface

steps of peatland restoration

REWET PEAT - raise wt and block drainage and erosion

STABILIZE PEAT - reprofile, protect surface

RESTART FORMATION - spread mulch and introduce plants

salt marsh

mid-high latitude, equal sediment accumulation and subsidence, medium waves

tidal flooding, salinity, permeability and N-limited

salt-tolerant grasses and rushes

INTERTIDAL, SALINE, SEDIMENT- AND TIDE-DRIVEN

freshwater tidal marsh

TIDAL BUT FRESH, CONNECTED TO ESTUARIES

inland along tidal rivers

salt and inland mixy

more plant diversity and bird use bc less salt

near human centres :(

mangrove swamp

WARM-CLIMATE INTERTIDAL FOREST SHAPED BY TIDES AND GEOMORPHOLOGY

tropical and subtropical

replace salt marshes where it’s warm

mangroves love salt

depend strongly on hydrology and geomorphology

ecosystem services of mangrove swamps

tropical coasts! roots stabilize sediment and exchange gas (pneumatophores)

supports fisheries

COASTAL PROTECTION, HABITAT, CARBON, WATER/SEDIMENT REGULATION, PEOPLE AND LIVELIHOODS

why mangrove planting can fail (4 reasons)

wrong place - have mangroves been there historically?

wrong conditions - too much flooding or salt or erosion

wrong ecology - wrong species, monocultre

wrong social setting - people don’t gaf

controls on mangrove establishment

hydrology (flooding and drainage)

geomorphology (elevation, slope, sediment)

disturbance (waves, grazing, erosion)

propagule (can seeds get there?)

why mangroves were bad in hawaii

not supposed to be there! altered mudflats and bird habitat

trapped sediment and obstructed waterways

invaded fishponds

issues with Prime Hook salt-marsh

lots of storms, altered hydrology w construction, saltwater came in by accident, marsh becoming open water, vegetation lost

prime hook restoration

tidal channels - reopened exchange and dredged where drainage would usually be

marsh platform - raised elevation w sediment, rebuilt shoreline, helped vegetation return

recovery support - grass plugs, monitoring, adaptive management

three restoration responses

two conditions for wetland formation

water source and retention mechanism (low permeability, depression, poor drainage)

NEEDS BOTH! so good in N bc less evap, glacial melt, fine glacial till, and glacial depressions

rule of thumb for wetland location in a drainage basin

form at the lowest-energy positions in a drainage basin — where water moves slowest and has time to accumulate

slope sleep (geomorphological control along w depression)

gw reaches surface at break in slope

kettle wetland “prairie pothole”

NA prairies from glaciers, many lost to agriculture

sww or marshes, may dry in summer

how biota alter hydrology (beaver, sphagnum, marsh, trees, geese)

beaver - blocks outflow → raises hydroperiod → creates shallow water/marsh

Sphagnum / peat builds peat → raises surface → isolates from mineral water

Marsh vegetation slows flow → traps sediment → shallower basin

Trees increase transpiration → lower summer water levels

Muskrat / geese remove vegetation → open water and altered flow paths

4 key hydrologic characters of a wetland

water levels (table and h), hydroperiod & pattern, water residence time, water budget

water table

surface where pore water pressure equals atmospheric pressure. It may lie below the soil surface or rise above
it during inundation.

hydroperiod vs pattern

period is how long and when inundated, strongly influences vegetation

pattern is complete change over time

capillary zone

saturated zone immediately above the water table. Capillary forces hold water under slightly negative pressure.

hydropatterns can be used to infer

1) Permanence and duration of inundation (flooding)

• 2) Predictability (variability)

• 3) Seasonal timing of inundation

• 4) Harshness, extremes in inundation or drought

• All of these will influence the ecosystem that develops in the wetland

• And wetland’s ability to perform flood control, sediment capture

• Sometimes infers water source but not always!

E.g. tides, seasonal river flooding...

subsidy-stress model

seasonal flooding brings nutrients and sediments in a little boost for higher P

aggressive flooding can remove these things and be a stress

recharge vs discharge wetland

have contribution to gw (output>input)

recieve gw annually (input>output)

rain and runoff can change wetland head quickly and reverse roles where gw reacts slowly because percolation takes time

change in storage deltaV=

water entering (precipitation, gw, runoff) - water leaving (et, surface outflow, gw outflow)

water budget eqn

where T = tidal

why is total precipitation (P) not net (Pn)

because I = interception where some sits on surfaces and evaporates

TF = throughfall sf = stemflow

Vro = surface runoff =

C (coefficient, unitless) x A (watershed area, m2) x P (precip depth, m) = m3 (not mm)

C (runoff coefficient)

depends on watershed! higher for paved or roofed

higher = rapid runoff, less interception, infiltration, and storage

water budget worked example

direct precipitation (Vp)

P x Awetland

Vet

ET x Awetland

change in stored volume (deltaV)

Awetland x (hend-hstart)

average storage-change rate (dV/dt)

dV/days

net GW exchange (Gnet)

dV-Vro-Vp+Vet

impact of more upland trees

more ET, less inundation, less methane (methanogens need anaerobic water), less amphibians

residence time (TR)

avg time a H2O spends in wetland, only easy if in steady state though ☹

Tr = V/Qt

if v is avg volume of storage and Qt is total in or outflow (volume/time)

JUST AN AVERAGE

surface water inflow depth Si

depth that annual volume would create if spread uniformly over the wetland

=annual inflow volume / wetland area

most common outflow by wetland type

bog = ET

fen = ET and runoff

marsh = gw, et, runoff

swamp = et bc trees

wetland soil importance

record hydrologic history, control plants via chemistry, store C and nutrients to cycle, change more slowly than other abiotic factors

can totally change O supply based on saturation

what does organic soil look like?

input>decomp

brown-black, plant fragments, waterlogged, slow decomp

peat formation feedback loop

wet → low O → slow decay → accumulation of peat → more water storage

organic soils can be saturated lots or a little, this changes…

organic carbon content. saturation means <20% OC and not saturation means >20%

also always have more OC than mineral

porosity =

Vv/Vt

higher in organic, super wet in peatlands bc more S

bulk density =

dry weight/total soil volume

higher in mineral soils bc dry is closer to total

porosity and bulk density relationship

behaviour of less decomposed peat

visible plant fibres (fibric), low bulk density (p_b), high n, high K, lighter colour

cation exchange capacity (CEC)

how many exchangeable cations soil can hold. H+ gets released and Ca2+ or something binds to neg surface

clay and organic v negative, higher CEC

helpful for plant uptake of ammonium

organic soil has low nutrient availability despite high CEC because…

they’re in organic forms and having so much water stops them from mineralizing. dissolved inorganic (mineral) would be better

why do organic soils have lower pH (more acidic)?

in mineral, carbonates and silicates consume H+ and make things basic

in organic, CO2 from decomp makes things acidic

gw tends to be higher pH than rain

organic matter is usually the electron…

donor. O2 is a good acceptor (gets reduced). more Eo (reduction potential) means more energy yield

what gets reduced in soil in what order!

O2, then nitrate (NO3-), then Mn and Fe, then Sulfate, then Methanogenesis under v reducing conditions

more donor (oxidation) than acceptor (reduction) as O2 runs out quick

why do soils go grey? (gleying)

fe3+ oxide is red, when reduced it goes to Fe2+ and leaves soil matrix

prolonged reducing conditions, where iron was reduced and mobilized long enough ago that soil chemistry has been altered a lot

oxidized rhizospheres

just root holes where a little o gets in causing mottled rust colour in soil

regulators of soil redox conditions

wt fluctuation, e- acceptors and donors, microbial populations, temp, pH

grey and mottled (red) soil means

repeated wetting/drying, wt fluctuation, or root-channel O

soil colour by wetland type

example of open and closed systems

tidal marsh vs dome bog

transformers

no net change of nutrients but change in speciation

top 3 geochemical parameters

pH, redox potential, EC

specific conductivity

dissolved ions carry electrical current through water

uS/cm. carbonate rich gw probably higher than rain-fed bog

redox metabolism

organisms harness e- energy to do work. commonly done by microbes in flooded environments

oxidation state

O very EN, H much less EN (gives e-)

Eo and Eh

More positive E⁰ means a greater tendency to accept electrons under standard conditions. Every half reaction has a corresponding value With the same electron donor, a higher E⁰ of the electron acceptor generally offers a greater energy yield

Gibbs free energy

energy payoff in kJ/mol

dEo = Eaccept-Edonor

dGo = -nDdEo

pos E = -G (releases energy)

n = electrons, F = faraday constant

Eo doesn’t change in this class!

Eh

measures redox potential. higher for oxidized species and oxidized conditions

Eh after flooding

falls bc o eaten up and things become reducing

but other acceptors can keep doing decomp so don’t worry

soil pH after flooding

CO2 lowers pH but reduction can consume H+ so buffering capacity ofen leaves itt at 6-7

impacts on nutrient budgets

seasonal (flood/growth), us/ds connection, soil and sediment storage, humans

P cycling

often as phosphates (dissolved reactive P)

organic, dissolved or particulate

limits p

released from organic in decomp, adsorbs to minerals, sedimented into soils, released in anoxic conditions