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HYDROLOGY, DRAINAGE AND AFFORESTATION OF PEATLANDS -

THE BALQUHIDDER CATCHMENT

Erica Massey

Land-Use Hydrology EESc 305

University of British Columbia Okanagan

November 21, 2011

Email: rockymountainerica@shaw.ca Tel: (250) 307-0773

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ABSTRACT

Peatland ecosystems, including fens, bogs and mires, have been historically exploited in land-

use by extraction for fuel, afforestation and grazing. Ecosystem services of peatlands were not

initially recognized and appreciated, thus a significant loss of undisturbed habitat occurred. The

change in land-use of peatland has resulted in almost irreversible impacts on net carbon

exchange, runoff, erosion, loss of biodiversity, water quality and flooding. Hydrological

processes are crucially important to peatland; their drainage and afforestation has impacted

catchment stability. The analysis of research conducted in the Scottish Highlands at the

Balquhidder catchments were an important research study of the consequences of peatland

drainage and afforestion to a coniferous plantation. The rapid and significant loss of peatland in

Britain and Scotland began to concern conservation groups and the government of Scotland,

leading to a new appreciation for the ecosystem services of peatland and implementation to

enforce their protection.

Background

In the United Kingdom, peatlands have undergone anthropological disturbances primarily from

extraction for fuel-use, afforestation and agriculture. Since pre-historic times, peat and peatland

forests have been a useful fuel source. During the 17th century forests were cleared without

proper planning and left peat as the primary fuel source. When peat was dug, bog wood was

unearthed and utilized for construction of roofs, vessels and homes. In the 1800‟s and early

1900‟s peatlands were considered as wasted land (Parkyn 1997). By the 1920‟s afforestation

was considered as an option to grow timber rather than importing softwood (Calder et al 1989).

During the 1980‟s and 1990‟s, continued loss of peatland habitat occurred from continued

afforestation, fuel-use, open-cast mining, and agriculture.

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Afforestation was first considered to be an issue between the 1960‟s in northern Scotland‟s

blanket bogs by scientists, government and conservation groups such as the Royal Society for

the Protection of Birds (RSPB) and the Nature Conservancy Council (NCC) (Newson and

Calder 1989). Awareness increased for the peatland‟s unique ecosystem services and

dependent species such as birds (i.e. golden plover, dunlin and greenshank) (Parkyn 1997).

Scotland‟s peatland ecosystems cover 14% of the country‟s landscape and include mires, fens,

bogs and wetlands (Bragg 2001). In the UK, blanket mire loss is now 90% and raised mire loss

is 98% (Hughes 1995).

Sensitivity of Peat-forming Mires & Peatland

Raised mires, with their characteristic domed form, are hydrologically sensitive because rainfall

is its only influx of water and balances water loss through evaporation, runoff, transpiration,

lateral and downward seepage. It is especially prone to instability because it is unable to easily

replace loss of water resulting from land-use disturbance (Hughes 1995).

Undisturbed peat grows approx 1 mm per year whereas mechanical peat extraction can remove

500 mm per year, creating a completely unsustainable use of the resource (Hughes 1995).

Hydrology of Peatland and Mire

Mire and its active, organic decaying peat-forming ecosystems (i.e. fens, bogs or raised mires)

occur as waterlogged land that experiences greater inflow than outflow of water. Peatland

ecosystems are classified by their source of nutrients and water. Bogs are more acidic as they

receive water and nutrients by precipitation whereas fens are less acidic from receiving water

and nutrients from groundwater (Holden et al 2004). They serve an important role in helping to

delay storm run-off and soil erosion while retaining inorganic nutrients (Hughes 1995).

Drainage of Peatland

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Peats are most commonly drained by construction of plough furrows and deep ditches (Holden

et al 2004). Drained peatland favours deeply rooted plants which supports different vegetation

(Hughes 1995). Evapotranspiration decreases due to less open water and a lower water table.

Roots and plants pull water up from the deeper peat which increases evaporation, decreases

the water table and aerates/dries the peat so that decomposition occurs more rapidly (Hughes

1995).

In Finland, over 295,000 ha of forested peatlands were drained with reports of change in annual

runoff and low flows. During the first ten years, annual runoff increased (Rosbjerg 1997). When

the water table of the peat is lowered, it was previously thought to help prevent flooding

whereas more recently it has been associated with increased flooding (Holden 2006). Peat

catchments in the uplands commonly have flashy responses to storms (Holden et al 2004).

The drainage of peatlands is unsustainable and related to the following issues (Holden et al

2004):

1. Lowering and instability of water tables;

2. Increased aeration above water table, resulting in increased decomposition;

3. Change in runoff generation, depending on steepness of slopes and soil composition;

4. Increased flooding in rivers;

5. Increase in low flows, due to catchment „dewatering‟;

6. Increase of N and P, and decrease in K, due to bulk density increasing;

7. Decreased water quality, from increased nutrient leaching, (i.e. NH4) and release of

sediments;

8. Loss of nutrients, such as Ca, Mg, K, Mn and Al (these are short-term results. No study

confirmed results 5 years following afforestation);

9. pH studies have not reached one conclusion;

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10. Higher and earlier peak flows can occur;

11. Increased erosion; and

12. Increased ecosystem destruction.

Afforestation of Peatland

First, the peatland is drained which lowers its water table and increases decomposition rates

because of less saturation of the peat (Hughes 1995). The peat continues to dry, shrink and

crack, becoming more aerated. Methane and carbon dioxide transfer from the peat to the

atmosphere. Instability due to change in flux of water pathways can occur (Hughes 1995). Soil

composition, slope gradient and the catchment‟s drainage system have different responses,

thus analysis of drainage and afforestation of peatland must be site-specific (Holden et al 2004:

table 1).

Depending on how nutrient-rich the peat was prior to afforestion impacts how well the planted

forests flourish. Experiments with fertilizers rich in nitrogen, potassium and phosphorous were

conducted in some afforested peatlands. The native North American, south-coast Lodgepole

Pine was unsuccessful in Northern Scotland - the trees did not grow straight for timber-use or

survive heavy snowfall. Raised bogs were found to be the most degraded and vulnerable

habitats (Parkyn 1997).

Archival of Deposition Data

The importance of peatland preservation is that it contains accurate data back to the Holocene,

by using measurements of various metals and depositions such as lead and pollutants. This

chronological tool is an invaluable tool that is irreversible when a peatland is drained for another

land-use purpose (Holden 2006:479).

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Carbon Balance

Peatlands normally accumulate carbon from the atmosphere and release methane (Hargreaves

et al 2003). Carbon is fixated increasingly by the trees, vegetation and soil once peatland is

afforested. Studies seem to have not determined whether the CO2 taken up by the trees during

photosynthesis balances the CO2 loss to the atmosphere from peat disturbance (Parkyn 1997).

Utilizing a carbon accounting model, the annual net CO2 exchange of undisturbed deep

peatland was measured over a period of 22 months (Hargreaves et al 2003). Comparatively,

peatlands in Scotland that had been drained, ploughed and afforested were measured for

annual CO2 exchange by collecting solar radiation, night-time and day-time fluxes and air

temperature data.

Illustrated below in fig. 1, night time fluxes responding to temperature of afforested peatland

measured losses of CO2 whereas daytime fluxes responding to light and solar radiation showed

a gain of CO2 (Hargreaves et al 2003).

Figure 1: Afforested peatland carbon exchange (Hargreaves et al 2003)

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As the forest canopy closes, increased interception and evaporation occurs, which has been

found to dry, shrink and crack the peat (Holden et al 2004). Research studies have found

interesting results showing an increase in carbon storage in a drained and afforested peatland

over an undisturbed peatland. This increase in carbon depends on the age and type of

peatland and is possibly due to the ability of trees to increase movement of carbon towards the

soil (Holden et al 2004).

Figure 2: net fluxes of carbon during afforestation (Hargreaves et al 2003)

In summary, an undisturbed peatland is a carbon sink; a newly drained, plowed peatland is a

carbon source; a 4-8 yr old forest is a carbon sink, and finally, a growing, more mature forest

has the greatest uptake of carbon, as illustrated in fig. 2 (Hargreaves et al 2003).

The Balquhidder Catchments

The Balquhidder catchments of Kirkton and Monachyle, located 60 km north of Glasgow in the

Grampian Mountains of the Scotland Highlands were studied for research on land-use change

in peatland reservoirs. Back in the mid-1950‟s, “Frank Law, engineer to the Fylde Water Board,

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found that forests reduce water yield” (Calder 1993). Since the Balquhidder catchment provided

a source of water for industry and power, the afforestation of its peatland and predictions of

diminished water yield were understandably met with resistance (Calder 1993).

The water industry in collaboration with the Institute of Hydrology established a hydrological

research unit to study the effect of land-use change on hydrological processes. Eventually,

experimental research at Balquhidder was approved and commenced operation in 1981

(Johnson and Whitehead 1993).

Annual precipitation is 2500 mm with slightly more precipitation in Monachyle than Kirkton, and

higher drainage density and steeper slopes in Kirkton (Johnson and Whitehead 1993). Between

1932 and 1944, Sitka and Norway spruce had been planted in 40% of the Kirkton catchment,

with clear-felling taking place from 1986 to 1990. The Monachyle catchments‟ vegetation was

primarily heather, bilberry and bracken at higher altitude and grassland in the lower areas with

rocky outcrops. In 1986, it was drained and 6% (111 ha) was afforested in the catchment

(Johnson and Whitehead 1993). Kirkton and Monachyle catchments are illustrated in fig. 3

(Roberts et al 1993):

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Figure 3: (Roberts et al 1993)

Techniques utilized in the Balquhidder catchment research study for measuring data seasonally

and annually (Calder 1993):

1. Plastic-sheet net-rainfall gauges

2. Gamma-ray attenuation methods

3. „Wet lysimeter‟ studies, on grasses

4. Whole tree weighing studies

5. Drainage lysimeters

6. Weighing lysimeters

7. Neutron probe measurements of soil moisture

8. Plant physiological studies of stomatal response

Ground cover in the catchments were classified as 1) forested area; 2) upright vegetation

(bilberry, heather, bracken); and 3) flat vegetation (hill grass, mesomires) (Eeles and Blackie

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1993). Rain gauges were used to calculate the mean precipitation and monthly Penman

potential evapotranspiration (ET) values were calculated from local weather station data.

Snowmelt contributed to surface runoff and groundwater yet the 600m altitude difference,

complexity of topography and varied wind speeds resulted in inaccurate data for snowmelt

contribution to streamflow. Until the end of 1988, the mean observed flow increased by 12% in

Monachyle and 9% in Kirkton (Eeles and Blackie 1993).

Neutron soil moisture metres were used to measure soil moisture content at various locations.

A metre was placed under the forest area at a point of interception in Kirkton (1981-1987), in the

grasslands of the lower Monachyle (1984-1989) and under the heather vegetation in the upper

Monachyle (1982-1989). Moisture content was highest in the grassland during the winter and

lowest soil moisture in the forest, as noted in fig. 4 (Eeles and Blackie 1993).

Figure 4: Kirkton soil moisture (Eeles and Blackie 1993)

Experimental results have commonly found that mature trees demand more water than the prior

vegetation type (heather, sphagnum moss) resulting in decreased low flows during dry weather

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(Newson and Calder 1989). The deeper root systems of trees result in increased interception

during rainy periods and increased transpiration rates during dry weather which also usually

reduces low flows. Gradients can shift during the peatland drainage process and effect low

flows. During the drainage process a short-term increase in low flow was followed by a

decrease in low flows (Newson and Calder 1989). Results from the effects of afforestation on

low flows in the Balquhidder catchment were not absolute and, therefore, considered unknown

(Calder 1993).

Simulated decrease in runoff from afforestation in Kirkton, illustrated in fig. 5:

Figure 5: Kirkton afforestation effect on runoff (Source: Eeles and Black 1993)

As a forest matures the canopy progressively fills in, resulting in a closed canopy with higher

leaf area index (LAI), higher interception and evaporation rates and decreasing levels of runoff

and low flow (Calder 1993). From 1986-1989, Kirkton‟s land-use change from felling trees

suggested a reduction in water use (Blackie 1993).

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At higher altitudes, wind speed and solar radiation increased evaporation while decreasing in

the lower altitude grassland, which was determined by Penman potential evaporation (ET)

calculations (Calder 1993).

Evaporation was found to be higher in the Monachyle vegetation compared to the Kirkton forest,

which is contrary to most studies that have shown higher interception and evaporation from a

forest canopy (Roberts et al 1993). The measurements or the actual model may have had

errors, or there may be evaporation of hydrological processes not considered or accounted for

in the experiment (i.e. groundwater flows, cloud deposition, wind, rain-gauge location/accuracy

and systematic error) (Calder 1993).

Increased sediment yields were highest during low flows when yields were found to be 121%

higher in Monachyle and 595% higher in Kirkton following the land-use change (Johnson 1993).

A stream in the Monachyle catchment was found almost to the point of acidification, which

requires future research to confirm water quality issues (Calder 1993).

Summarized effects of afforestation to peatland in the Balquhidder catchments (Calder 1993):

1. Increased interception;

2. Less water yield probable, but not confirmed;

3. Reduced water quality;

4. Catchment acidification;

5. Increased sediment yields;

6. Increased evaporation rates, data requires further study;

7. Higher deposition rates of pollutants in the dry form as reactive gases and particles;

8. Higher deposition rates of pollutants in the wet form, contained within cloud and mist

droplets; and

9. Effects on low flows a plausible concern, yet not determined.

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Balquhidder Catchment Photos

Fig. 6-11 Photos of Kirkton area of the Balquhidder catchment (Source: Geolocation 2011)

Fig. 6 Kirkton: Blooming gorse in forefront of afforested peatland

Fig. 7 Kirkton looking SW - the

hill on the horizon is the SE end

of the Braes of Balquhidder.

Fig. 8 Kirkton gauging station for

measuring streamflow (1981-1991) on

water balance of upland catchment.

Fig. 9 Kirkton track; most of forest

clear-felled and recently replanted

Fig. 8 Kirkton: pine and spruce

Fig. 9 Kirkton: upstream is gauging station to measure water balance in catchment

Fig. 10 Kirkton Glen Fig. 11 Kirkton afforested peatland

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Land-use Management

Management practices are so crucial that, in fact, it could be more important than which

vegetation is planted. Sustainable land-use recommends staggered planting of plantations over

multiple years rather than planting the entire plantation at once. In addition, harvesting trees in

shorter intervals helps to limit the negative effect of mature forests on the catchment. Smaller

afforested areas may be preferable as a technique to have a less dominating effect on the

hydrology of peatland and downward streams (Newson Calder 1989).

Improved fertilizer knowledge and new tractors with less ground pressure were used for

ploughing (Parkyn 1997). Revegetation of peat with N, P, K and lime has been attempted

(Parkyn 1997).

Management of the design of ditches and recognition of the properties of soil in the catchment

must be recognized to lessen or eliminate the negative aspects of drainage on water tables and

runoff (Holden et al 2004). Afforestation of shallow peat rather than deep peet (>1m) is

considered more acceptable land management (Holden et al 2004).

The Scottish Raised Bog Conservation Project is an active program in which the Scottish

government officially recognizes that 94% of Scotland‟s lowland raised bogs have disappeared,

diminishing from 94,000 ha to 6000 ha (Scotland Government 2011). An important shift in land-

use management presently supports clearing (not planting or sustaining) tree plantations,

seedlings and the monitoring of overgrazing. Government inspectors facilitate land-use practice

of no planting of trees or peat extraction and enforcing the absence of fertilizers, pesticides and

herbicides. Peat dams were introduced and are currently promoted with federally-funded

financial incentives to help prevent erosion and slowed water flow rates. Control and

enforcement against ditch-digging, vehicle/machinery tracks and burning of muirs helps to

protect against the negative aspects of land-use change (Scotland Government 2011).

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Conclusions

The historic hydrological and biogeochemical importance of peatland habitats to local and global

systems have been overlooked and misunderstood. The drainage of peatlands change carbon

and chemical balance, runoff, low flow, interception, evaporation, transpiration, biodiversity,

sedimentation, erosion, soil infiltration and composition within the watershed catchment. The

drainage and afforestation of the Balquhidder catchments in northern Scotland have contributed

to the understanding and awareness of land-use change from quantifying and analysis of data.

Restoration of peatlands seems to be a complex, sensitive matter because the catchments are

not entirely understood and the ecosystem took hundreds of years to accumulate peat as a

saturated land area (i.e. 1 mm peat/year). It cannot be simply „fixed‟, as the adverse issues

require a long, gradual process to restore and regenerate.

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