Forests and surface water eutrophication and sedimentation

choppedspleenMécanique

21 févr. 2014 (il y a 3 années et 1 mois)

81 vue(s)

Forests and surface water eutrophication and
sedimentation

Dr Mary Kelly
-
Quinn, Dr Michael
Bruen, Dr Ted Farrell, Dr
Jan
-
Robert Baars, Dr Robert
Cruikshanks, Dr Ronan Matson, Mr
James Johnson

Dr

Simon Harrison,
Dr

Stephen
Hutton, Prof. John O’Halloran,
Dr

Guillaume
Juhel
,
Mr

Paul Phelan
Mr

Tad
Kirakowski

University College Cork

University College Dublin

Introduction

Conifer afforestation of catchments is known to pose a risk to
the chemical and biological integrity of receiving waters:


-

Low pH
(mid and mature phase)

-

High sediment loading
(planting and harvesting)

-

High concentrations of plant nutrients and other dissolved
and particulate substances
(planting and harvesting)

-

Low light and temperature
(mature phase)


Although all these effects have been documented at local scales,
there has been few attempts to assess the wider scale risk of
commercial conifer afforestation to stream water quality.

The impact of a particular plantation will depend on many
factors including:

-

Geology, geomorphology and soil type.

-

Small scale ‘random’ factors such as the nature of a
particular planting or felling operation, rainfall patterns, water
drainage from a site.

Research question:

What is the risk posed by afforestation to receiving waters?

-

Assess the relative impact of forestry on water quality, in
relation to other land uses.

-

Effective mitigation measures for current and future plantations

Sampling

200+ streams draining upland catchments across the Republic
were sampled three times in 2007
-
8:





Sampling was restricted to 1st & 2nd order upland streams



‘Forest’ sites were streams that flowed through conifer
plantations



‘Control’ sites were streams that flowed through
neighbouring unforested moorland




Forested catchments were either mature plantations
without felling or mature plantations with felling




Catchments were chosen in peat and podsol/lithosol
(poorly drained mineral soil) catchments

Chemical parameters:
Water samples taken 3x from each stream.
Comprehensive range of parameters analysed, including plant
nutrients, heavy metals, DOC, suspended solids, pH, alkalinity.

Sediments
Sediment collected using a modified Surber sampler
.

Sample sieved at two fractions; coarse (250
-
1000
μ
m) and fine
(50
-
250
μ
m), dried and weighed.

Macroinvertebrates
:

3

multi
-
habitat

kick

samples

taken

from

each

stream

on

one

occasion
.


Diatoms
: Diatoms scraped from stone surfaces taken from each
stream in summer.

Sampling Locations

101
Peat catchment streams


88
Podsolic

lithosolic

streams

Results


water chemistry

Mean water chemistry parameters (1)

Peat catchments

Podsol lithosol catchments

Peat catchments

Podsol lithosol catchments

Mean water chemistry parameters (2)

Mean DOC concentration in streams vs percentage
catchment felled within last 5 years

% catchment felled

Mean total ammonia concentration in streams vs
percentage catchment felled within last 5 years

% catchment felled

Mean total phosphorus in streams vs percentage
catchment felled within last 5 years

% catchment felled

Draft European Communities Environmental Objectives
(Surface Waters) Regulations 2008:
these define ‘high’ and
‘good’ water quality status according to a suite of chemical
and biological parameters:


Mean MRP (mg P/l)


High status = ≤ 0.025 mg P/L


Good status = ≥ 0.025 ≤ 0.035 mg P/l


Failed status = >0.035 mg P/l

Mean Ammonia (mg N/L)


High status = ≤ 0.040 mg N/L


Good status = ≥ 0.065 ≤ 0.040 mg N/l


Failed status = > 0.065 mg P/l

Criteria for impact assessment:

Phosphorus water quality status of streams in data set

Impact assessment Phosphorus (SRP)

Peat catchments
Podsol lithosol catchments
Control
Mature
Clearfelling
Control
Mature
Clearfelling
>0.035 mgP/l
Failed status
0.0
0.0
14.0
0.0
0.0
0.0
0.025-0.035 mgP/l
Good status
0.0
0.0
9.3
0.0
0.0
0.0
<0.025 mgP/l
High status
100.0
100.0
76.7
100.0
100.0
100.0
SRP concentration
Status
Total Ammonia water quality status of streams for the
different catchment soil types

Impact assessment Total Ammonia

Peat catchments
Podsol lithosol catchments
Control
Mature
Clearfelling
Control
Mature
Clearfelling
>0.065 mgN/l
Failed status
0.0
4.0
18.6
0.0
0.0
2.6
0.04-0.065 mgN/l
Good status
3.0
20.0
32.6
3.2
16.7
5.1
<0.04 mgN/l
High status
97.0
76.0
48.8
96.8
83.3
92.3
Total Ammonia
concentration
Status
Results
-

Macroinvertebrates

Small Stream Risk Scores

Peat catchments

Podsol lithosol catchments

Invertebrate metrics

Peat catchments

Podsol lithosol catchments

Trophic Diatom Index

TDI

Conclusions



Clear impacts of forestry operations on stream water chemistry
and sediment bedload.



Elevated levels of key eutrophication and sedimentation
parameters seen in streams draining
peat

catchments, but not
mineral
-
soil
podsol lithosol
catchments.



High percentage of streams draining peat catchments subject
to clearfelling fail water chemistry standards.



Benthic macroinvertebrate and diatom metrics reflect reduced
water quality in streams draining forests planted in peatsoil
catchments.

..Don’t plant or re
-
plant conifer trees on peat!