Drought Induced Degeneration of Drought Induced Degeneration of DicranumDicranummoss and Implications for Carbon Budgets in moss and Implications for Carbon Budgets in the Hudson Bay Lowlandthe Hudson Bay Lowland

Richard BelloElizabeth MillerAnna Abnizova

York University Geography Department

Toronto, On. Canada

Tim Papakyriakou* Mario TenutaS

University of Manitoba Department of Environment and Geography* Department of Soil ScienceS

Winnipeg, Mb. Canada

ContextContext

Earth presently has the lowest concentrations of atmospheric CO2 on a geologic timescale but it is increasing rapidly.The global carbon budget doesn’t balance. Present day atmospheric CO2 increases:

0.7% per year when modeled; 0.4% per year when measured.Polar regions will undergo the most severe and rapid environmental changes, primarily because of the positive ice-albedo feedback mechanism.

Weakened capacity to act as an energy sink for remainder of planet Earth.Weakened oceanic thermohaline circulation system for redistributing global energy.Ice sheet instability and sea level rise.Newly exposed carbon reservoirs due to melting permafrost.

ContextContext

The carbon presently stored in peatlands represents one-third of the global soil reservoir and will increase global atmospheric CO2 by two-thirds if released, independent of fossil fuel emissions.Peatland carbon is converted to atmospheric carbon when decomposition exceeds photosynthetic uptake.Both photosynthesis and decomposition are sensitive to temperature, moisture and nutrients so climate change has the potential to upset the carbon budget in the near term.

COCO22 exchange from the terrestrial environment changes interexchange from the terrestrial environment changes inter--annually.annually.

Rouse, Wayne R., Richard L. Bello, Alberta D’Souza, Timothy J. Griffis and Peter LaFleur, 2002: The Annual Carbon Budget for Fen and Forest in a Wetland at Arctic Treeline, Arctic Vol 55, No. 3, p229-237.

24.024.028.728.751.651.6--8.348.34

TreeTree--lineline

10.710.710.410.411.011.010.810.810.810.810.710.7

T T ((00C)C)

--5858--4242--3131--3636--6464--116116

Soil Soil Moisture Moisture

Deficit Deficit (mm)(mm)

MeanMean1999199919981998199719971996199619941994

COCO2 2 Flux Flux ((gCgC mm--22yy--11))

52.552.5--7.2(7.2(--4.6)4.6)81.881.8--24.524.573.173.130302.72.7--19.419.4

31.431.4--53.553.5

ForestForestFenFen

Range=59.9Range=59.9ΔΔC=57.1C=57.1

Plant communities may adjust to climate and soil changes, so thePlant communities may adjust to climate and soil changes, so the longlong--termtermcarbon budget will depend on the character of the new plant commcarbon budget will depend on the character of the new plant community.unity.

Major Peatland Types in the Hudson Bay Lowland in Major Peatland Types in the Hudson Bay Lowland in Northern ManitobaNorthern Manitoba

Vary with distance from coast and peatland age due to isostatic uplift of 8-10 mm y-1.

Polygonized peat plateauPolygonized peat plateau(zone B) 12,000 km2 is inaccessible and poorly understood.Peat deposits up to 4 m thick represent the largest potential greenhouse gas sources.

DredgeandNixon(1990)

Ice rich peat has already melted in some ice-wedge polygons to form collapse scar (thermokarst) ponds. 4000 yr old peat profile is Sphagnum dominated and interlaced with charcoal needle layers indicating past forest environments. Lake banks are collapsing into lakes as permafrost melts.

Dominated by lichens, heaths and mosses which all Dominated by lichens, heaths and mosses which all have adaptations to the dry polar environment.have adaptations to the dry polar environment.

0%

20%

40%

60%

80%

100%

Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7 Site 8 Site 9 Site 10 Site 11 Site 12 Mean

Peat Plateau Vegetation

Bare Peat Vascular plantsMossesLichens

ArcticNet study site (peat plateau) in coastal Hudson Bay.

DicranumDicranum elongatumelongatum covers 26% of the plateau and is 25% dead. covers 26% of the plateau and is 25% dead. Degenerating zones are partially covered with the microDegenerating zones are partially covered with the micro--lichen, lichen, OchrolechiaOchrolechia..

What triggered the mortality and when? Why did some individualsWhat triggered the mortality and when? Why did some individuals completely die while completely die while others survived? What were the impacts on carbon exchange?others survived? What were the impacts on carbon exchange?

Field Season 2003Field Season 2003-- one seventeen day drought but slightly wetter than normal.

12- 5x5 m sites selected bracketing the habitat, elevation and slope range for the plateau.100 grid cells measure:

Relative elevationLength, width and height of each moss cushion (n=2893)% cover as living, dead, otherDepth of dimples

Continuous meteorological data and moss moisture and temperature.

Spatial patterns of mortalitySpatial patterns of mortalityPeat Plateau Dicranum

y = -3030x + 306.14R2 = 0.7627

020406080

100120

0.05 0.06 0.07 0.08 0.09 0.1

Dicranum Cushion Height (m)

Mor

talit

y %

Mortality increases as cushions decrease in size both on an individual site and plateau wide basis.

Mortality and Drainange

y = 961.47x + 17.983R2 = 0.713

0

20

40

60

80

100

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07

Elevation Variance

Mor

talit

y (%

)Sites with highest variation in topography and steepest slopes have the highest mortality.

Spatial patterns of mortalitySpatial patterns of mortality

Distinct asymmetry with dead zones predominantly on south facing aspects of cushions.

Asymmetry in Degeneration on Moss

-60-40-20

0204060

1 3 5 7 9 11 13 15 17 19S a mpl e Cushi on

microlichen

new vegetation

active vegetation

initialdegeneration maturedegeneration advanceddegeneration advancedd ti

Spatial patterns of growthSpatial patterns of growth

Tallest cushions grow at lowest elevations in proximity to water table

Elevation and Cushion Height Site 3

y = -0.1705x + 0.0856R2 = 0.7975

0.02

0.04

0.06

0.08

0.1

0.12

-0.15 -0.1 -0.05 0 0.05 0.1 0.15

Relative Elevation (m)

Mea

n Cu

shio

n H

eigh

t (m

)

InterpretationInterpretation

Mortality is related to severe moisture stress

Large scale patterns related to elevationSmall scale patterns related to aspect

Growth is related to moisture stress

Taller cushions found in wetter zonesMoisture is limiting to moss growth on the plateauSmall mounds spend greater time under sub-optimal moisture conditions

Small Cushions are subject to extremes in moisture content becauSmall Cushions are subject to extremes in moisture content because of se of small volume:surface area ratio and due to their large distance small volume:surface area ratio and due to their large distance from from water table.water table.

Seasonal Variation in Moisture Storage of Three D. elongatum Specimens

Dry Weights

0

1

2

3

4

5

6

7

21 24 281-J

ul 5 8 12 15 19 22 26 292-A

ug 5 9

Date

Gra

vim

etric

Moi

stur

e C

onte

nt (g

H2O

/g)

26.5 g 172 g 380.5 g threshold

How old are theHow old are the D. elongatumD. elongatum cushions on the cushions on the plateau? How long ago did mortality set in?plateau? How long ago did mortality set in?

D. elongatum grows slowly from 0-5 mm/y.No distinguishing morphological features for dating.Deepest dimples occur on fastest growing moundsAssume growth rates pre-and post-drought are comparable.Mounds established in 1949 (53 y B.P.) and degeneration triggered in 1994 (9 y B.P).

Cushion Height: Dimple Depth Relationship

y = 2.0925x + 5.8654R2 = 0.8214

67

89

10

1112

0 0.5 1 1.5 2 2.5 3

Maximun Dimple Depth (cm)

Med

ian

Cus

hion

Hei

ght

(cm

)

Modelled Cushion HeightE=1949:D=1994

y = 0.99xR2 = 0.78

6789

101112

6 7 8 9 10 11 12

Measured Height (cm)

Estim

ated

Hei

ght

(cm

)

D. elongatum green photosynthesizing tissue turns brown after three years. Varying canopy depths were used to estimate growth rates and age in three different micro-habitats. (shade=tall, open-moist=medium, open-dry=small)

Bulk Density Variations (2 mm) in Three Micro-Habitats

0

10

20

30

40

50

60

0 0.05 0.1 0.15 0.2

Bulk Density (g cm-3)

Year

s BP

ShadeOpen-moist

Open-dry

Moss growing in three very different habitats all established 52-53 years ago in agreement with dimple analysis.Shade (rare) is not limiting for growth.Ample moisture closer to water table produces consistent low-density annual growth.Exposed sites (majority) experience highly variable high-density annual growth.

Drought severity is dependent on duration. Laboratory experimentDrought severity is dependent on duration. Laboratory experiments s indicate drought duration is critical to moss mortality and indicate drought duration is critical to moss mortality and metabolism recovery.metabolism recovery.

Cumulative Daily Summertime (May-Aug.) Precipitation Excess (+) and Deficit (-) from 1943 to 2004 at Churchill, Manitoba.

-125

-100

-75

-50

-25

0

25

50

75

100

125

150

1943

1943

1944

1945

1946

1947

1948

1949

1950

1951

1952

1953

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2003

2004

Date

Prec

ipita

tion

(mm

)

19941994

1949

How do the long term apparent rates of carbon How do the long term apparent rates of carbon accumulation compare to present day fluxes? accumulation compare to present day fluxes?

Insert 10 cm diameter collars approx. 25 cm deep into three healthy living D. elongatumcushions.Insert three collars into dead D. elongatum with Ochrolechiagrowing on surface.Sample CO2 exchange from mid-June to October.Ancillary measurements of temperature and moisture in the air and soil as well as photosynthetically active radiation (PAR) are collected.

2004 growing season: 2004 growing season: normal precipitationnormal precipitation

Dark chamber CODark chamber CO22 concentrations increase over time in response to autotrophic anconcentrations increase over time in response to autotrophic and d heterotrophic respiration.heterotrophic respiration.

τPAR=0.92

Clear chamber CO2 concentrations decrease over time during the dClear chamber CO2 concentrations decrease over time during the day as photosynthesis ay as photosynthesis exceeds respiration.exceeds respiration.

Photosynthetic response of Photosynthetic response of D. D. elongatumelongatum to sunlight and to sunlight and temperature behaves in predictable temperature behaves in predictable manner. manner.

PAR vs. Photosynthesis for Dicranum elongatum

y = -1.0432Ln(x) + 5.2636R2 = 0.751

-4

-3

-2

-1

0

1

2

3

0 500 1000 1500 2000

PPFD (μmol/m2/s)

Phot

osyn

thes

is

( μm

ol/m

2 /s)

Temperature vs. Photosynthesis for Dicranum elongatum

y = -0.0886x + 0.026R2 = 0.2527

-4

-3

-2

-1

0

1

Canopy Temperature (˚C)

Phot

osyn

thes

is

(um

ol/m

2/s)

Negative values indicate decrease in atmospheric CO2 and uptake by moss.

Respiration is three times more sensitive to a temperature increRespiration is three times more sensitive to a temperature increase ase when the moss is wet compared to dry.when the moss is wet compared to dry.

Respiration vs. Soil Temperture 5 Hour lag

y = 0.0304x + 0.4931R2 = 0.39060

0.2

0.4

0.6

0.8

1

1.2

1.4

0 2 4 6 8 10 12 14 16 18 20

Temperature (C)

Res

pira

tion

( μm

ol/m

2/se

c)

Increasing temperatures lead to increasing respiratory losses. Large time lags suggest deep decomposition driving CO2 release. When considering respiration alone, warm and moist future climates are most conductive to peat degeneration.

Wet: y=0.12x+0.39

r2=0.86

Dry: y=0.039x+0.32 r2=0.89

Living Moss NEELiving Moss NEE: Over the growing season, net ecosystem exchange of living mossremoves CO2 from the atmosphere during the day. This is offset by CO2 release to the atmosphere at night. The net effect is an overall uptake of CO2 from the atmosphere of 164 mg C m-2 d-1.

Seasonal Net Ecosystem ExchangeD. elongatum, 2004, n=599

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

3

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Solar Time

NE

E (

mol

m-2

s-1

)

0

2

4

6

8

10

12

14

16

18

6 cm

Pea

t Tem

pera

ture

(C)

Chamber NEE Ambient NEE* 6 cm Peat Temperature

Positive daytime fluxes represent plant uptake.

OchrolechiaOchrolechia sppspp. growing on dead moss NEE. growing on dead moss NEE: Over the growing season, net ecosystem exchange of dead moss continually releases CO2 to the atmosphere. The flux is stronger at night than during the day indicating Ochrolechia photosynthesis is present, but weak. The net effect is an overall release of CO2 to the atmosphere of 642 mg C m-2 d-1….a difference of 806mg C m-2 d-1 compared to living moss.

Seasonal Net Ecosystem Exchange Ochrolechia spp. on D. elongatum, 2004, n=143

-1.5

-1.3

-1.1

-0.9

-0.7

-0.5

-0.3

-0.1 0 2 4 6 8 10 12 14 16 18 20 22

Solar Time

NEE

( μm

ol m

-2 s

-1)

Net growing season impacts of moss mortality on peat Net growing season impacts of moss mortality on peat plateau carbon balance.plateau carbon balance.

-1.13 g C m-2 y-14.92 g C m-2 y-119.7 g C m-2 y-1-77.1 g C m-2 y-1flux

19.23 g C m-2 y-176.78 g C m-2 y-1survey

Plateau post-1994

Plateau pre-1994

Living Moss

Dead Moss

120 day growing season. Peat plateau losses are negative!

DiscussionDiscussionThe drought of 1994 reduced the coverage of peat accumulating D. elongatum. This shifted the moss contribution to the carbon budget of the plateau to net losses to the atmosphere compared to gains by the plateau that existed prior to 1994. This year also represented the largest losses of carbon from the fen.Mortality of the remaining living moss requires a drought of a magnitude not yet recorded. Severe droughts should be treated as disturbances, rather than stresses.Decomposition of the underlying peat exceeds the capacity of the moss community to uptake CO2.

Healthy moss takes up carbon at a rate comparable to the maximum rate for fens and 40% of the average for forests.Decomposition is sensitive to peat

temperature and moisture content indicating warmer and wetter future climates could enhance carbon losses.

What proportion of the decomposition is finding its way to Hudson Bay?

AcknowledgementsAcknowledgementsArcticNet III.2NSERCDepartment of Indian and Northern AffairsChurchill Northern Studies Centre-Dr. LeeAnne FishbackManitoba HydroFaculty of Arts, York UniversityDr. Peter Kershaw, U. of AlbertaDr. Michele Piercey-Normore, Botany, U. of ManitobaRaissa Abnizova

Questions?