Peatlands and Sphagnum ecology

Notetaking Guide

Introduction

What you'll learn

What bogs are and where they're formed

Characteristics of sphagnum moss, effect on water

Several physical gradients affect bog formation

Plant communities respond to these gradients, other gradients as well

Chemistry of sphagnum bogs

Unique plant communities inhabit bogs

Sphagnum specialist beetles often occur in bogs

King County bogs

Protection strategies

Definition:

Bog: a generic term applied to wetlands in which the rate of accumulation of organic matter exceeds the rate of decomposition (equivalent to the term "mire" in European literature).

Bog can also be used specifically to mean a wetland dominated by a dense growth of sphagnum moss, underlain by peat rather than mineral soils and having acid water. I will use the term "sphagnum bog" when I wish to refer to this specific definition.

Characteristics of a sphagnum bog.

Sphagnum moss can form mats which are at least somewhat buoyant

bacterial communities are severely depressed in acidic water

lack of bacteria means low decomposition rates. Moss accumulates

sphagnum mats often form hummocks with hollows in between. Unique plant communities grow on the hummocks which are better drained.

The term "fen" refers to wetlands that also accumulate organic material in the form of peat, but are not dominated by moss, but by sedges and grasses. The pH is less acidic (circumneutral). Plant communities may also be of infrequent occurrence (ex. Dulichium )

Bogs form in specific environmental situations

precipitation exceeds evaporation

drainage is poor (plateaus, drainage divides)

poor soils, usually glaciated

often form in kettle holes left by melted glacial ice

cool temperatures

often seems to be an oceanic influence-- rainfall higher in Na and Cl

Types of mires

blanket, raised, flat basin, flat valley, string or "aapa" bogs

Characteristics of sphagnum moss

indeterminate growth

only the upper portion actively grows

dead portion sloughs away & sinks to bottom

dozens of species, each have different tolerances for light, wetness, and pH

cells have thin walls, only 2 cells thick

high concentration of polyuronic acid, an active cation exchanger

Typical profile through a sphagnum hummock

Zone 1. interstitial spaces in hummock aerated, above water table. Roots of shrubs grow in this zone.

Zone 2. interstitial spaces saturated, water is oxygenated = acrotelm

Zone 3. interstitial spaces saturated, water anaerobic = catotelm

Gradients in peatland development & classification

Source of water: ombrotrophic (rain) vs. Minerotrophic (groundwater or runoff) poor-rich gradient
water mobility: ombrogenic vs. rheogenic - fluctuation
water chemistry-- pH, cations, anions, nutrients
water level-seasonal high water level-stable or fluctuating
sphagnum bog to fen gradient
summer to winter gradient
hummock to hollow gradient
mat to lagg (marginal ditch) gradient

Some observations... Sphagnum bogs are isolated from the influences of groundwater / surface water in some way:

1. Topography itself (small watershed, flat area),

2. raised character of hummocks can isolate upper mat from mineral-rich water below,

3. moat can channelize water around and away from the mat proper.

Terms ombrotrophic and minerotrophic seem most widely used to describe bog to fen gradient, but see recent paper by ____

(Review: pH of 7 is neutral. Large lakes, like Lake Washington are about pH 8.3, smaller lakes are about 7, northwest streams are around 6, and rain is about 4.5 )

(Review CO2 --- bicarbonate --- carbonate equilibrium at different pH values

Also review cation dissociation and salt formation at different pH values)

                   Sphagnum bog        Fen                           

Source             rain                groundwater, runoff           

Mobility           stagnant            flowing                       

Chemistry                                                            

     pH            3.5 ---             5.5 ---                       

     cations       Na +                Ca++  K+                      

     anions        SO4-                Cl-, HCO3-                    

     nutrients     low                 higher                        

Water level        stable              high, fluctuating

Cation/anion content of waters represented in Mauncha diagrams (octagon, each with an axis radiating from the center)

Plant community gradients

sphagnum bog --- poor fen --- rich fen

sphagnum moss --- brown mosses --- emergents

margin --- interior position
coastal BC sphagnum peatlands - 6 species groups related to degree of shading, height above water table and surface water chemistry

Conclusions

Many gradients are important and interact to provide a specific microhabitat that is fairly reliably indicated by vegetation
- source of water
- water movement
- water chemistry
- water level characteristics
- plant communities
It makes sense to use a "weight of evidence" approach is referring to peatlands as either bogs or fens rather than a single indicator. Vegetation should probably be one of them, but vegetation also responds to latitudinal and altitudinal influences.

Water chemistry of various northwest waters

alkalinity

hardness

total phosphorus

nitrate

Case study of water chemistry characteristics of a small sphagnum bog near Beaver Lake, ELS 21

Urbanization changes the character of the runoff

higher pH, more cations, especially Ca, more anions, especially carbonate, more nutrients (phosphates and nitrates), more dissolved oxygen D.O.), more bacteria

Probable bog responses to urban runoff

binding of cations by sphagnum moss
buffering system impact, change from organic acids to bicarbonate
increase D.O., lower depth of acrotelm
increase bacteria, decomposition rates in acrotelm
more water level fluctuation, higher winter water level in some systems
higher nutrients-favor more typical emergents

Sphagnum bog protection in King County

Treat urban runoff before it enters bog. Treatment goal--

reduce total phosphorus by 50%
reduce nitrogen by 40%
maintain alkalinity below 10 mg/L
pH below 6

Passive treatment facilities include wetponds, sand filters, constructed wetlands, compost filters, usually in some combination

Unique plant communities

Labrador tea (Ledum sp.)

Bog laurel (Kalmia occidentalis)

Bog rosemary (Andromeda polifolia)

Bog cranberry (Vaccinium oxycoccos)

Sundew (Drosera rotundifolia)

Unique beetles

Beller's ground beetle (Agonum belleri)

Hatch's click beetle (Eanus hatchi)

Long-horned leaf beetle (Donacia idola)

Cultural aspects

historical mid-European culture "bog men"

peat cutting (fuel, garden supplement, bandages in WW1)

cranberry crops

conversion to truck gardens