NUI Galway – UL Alliance First Annual ENGINEERING AND - ARAN ...

Assessment of Impacts of Forest Operations on the Environment
J. Finnegan, J.T. Regan and M.G. Healy*
Civil Engineering, National University of Ireland, Galway.
Email: mark.healy@nuigalway.ie
Abstract
The aim of this project was to assess experimentally the
impact of clearfelling of forests and the effectiveness of
buffer strips following clearfelling on sediment and
nutrient release, acidification and greenhouse gas
(GHG) emissions. Pre- and post-clearfelling data of
surface and subsurface flow, soil testing and gas
concentrations are now being collected. To date, results
obtained show there is an increase in dissolved reactive
phosphorus (DRP) concentrations moving from the
forest edge to under a brash mat, which is located in a
riparian area between the forest and a nearby river.
This reduces closer to the river. Greenhouse gas
emissions are highest in the riperian area and a virgin
peat site, while the lowest emissions are measured in a
standing and mature coniferous forest.
1. Introduction
Elevated levels of phosphorus (P) and suspended
sediment (SS) in surface waters are becoming a major
environmental issue both nationally and internationally.
(Mainstone et al., 2008). During clearfelling of forests,
there is the opportunity for a high runoff of P and SS to
nearby water courses. Riparian buffers may have the
ability to slow down and reduce the nutrient and
sediment release from forests. In this project, which is
being conducted in the Burishoole catchment in Co.
Mayo, two types of riparian buffer are studied: (1) a
naturally regenerated peatland buffer and (2) a standing
mature coniferous forest. The forest area upslope of the
study site is currently being clearfelled, allowing 4
years of regeneration on the riparian buffer zone.
2. Materials and Methods
Pre- and post-clearfelling data is being collected at
the study site. The following parameters are studied:
surface and subsurface water, various soil parameters
and greenhouse gas (GHG) emissions. Piezometers and
sampling tubes are installed across the site so that depth
to water table can be monitored and subsurface water
sampled. Sampling locations are at 1, 5, 10, 20, 30 and
40 m upslope of the river edge, before and after brash
mats, and in the forest. Each set of 3 sampling tubes are
positioned at 20 cm, 50 cm, and 100 cm depths below
the soil surface. Surface water samples are also
collected at these points. Surface and subsurface waters
are sampled across the site regularly and during storm
events, and chemically analysed for SS, dissolved
reactive phosphorus (DRP), total phosphorus (TP),
ammonium-N (NH4-N) and nitrate-N (NO3-N).
Greenhouse gas emissions are being studied in four
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areas: (1) the naturally regenerated peatland buffer (2)
the standing mature coniferous forest (3) a recently
clearfelled coniferous forest and (4) a virgin peatland
site. These are sampled using dark, static, manually
sampled, stainless steel chambers (height 9–18 cm)
equipped with butyl rubber septa for gas sampling, and
are tested with a gas chromatographer. This data will be
supplemented by a meso-scale study, comprising 3
hydraulically isolated plots each measuring 25 m-long
by 3.5 m-wide. This will allow us to fully examine the
flow, nutrients and sediment in and out of a
hydraulically isolated area in a controlled manner. All
samples were tested in accordance with the Standard
Methods.
3. Results and Discussion
Initial results obtained on site show there is an
increase in DRP concentration in the subsurface flow
moving from the forest edge to under the brash mat.
This reduces again closer to the river. This may be due
to a sand layer located close to the river.
Greenhouse gas emissions are highest in the
regenerated peatland buffer and the virgin peat site,
while the lowest emissions are measured in the standing
and mature coniferous forest.
4. Conclusions
Initial indications show that a revegetated buffer is
successful in reducing P concentrations from the forest
to the river bank. Greenhouse gas emissions are higher
before planting and after clearfelling than when the peat
is under forest cover. Further data will be collected
post-clearfelling to assess the impact of forest
operations, the effectiveness of two types of buffers,
and GHG emissions.
5. Acknowledgements
The authors acknowledge the support from the EPA for
funding this research under the STRIVE program.
6. References
[1] Mainstone, C. P., R. M. Dils, et al. (2008). "Controlling
sediment and phosphorus transfer to receiving waters - A
strategic management perspective for England and Wales."
Journal of Hydrology 350(3), 2008, pp. 131-143.