Forests and surface water eutrophication and Forests and surface water eutrophication and sedimentationsedimentation

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

Dr Simon Harrison, Dr Stephen Dr Simon Harrison, Dr Stephen Hutton, Prof. John O’Halloran, Dr Hutton, Prof. John O’Halloran, Dr Guillaume Juhel, Mr Paul Phelan Mr Guillaume Juhel, Mr Paul Phelan Mr Tad KirakowskiTad Kirakowski

University College Cork University College Cork University College DublinUniversity College Dublin

IntroductionIntroductionConifer 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: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 (250-1000μm) and fine (50-250μm), 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/LGood status = ≥ 0.025 ≤ 0.035 mg P/lFailed status = >0.035 mg P/l

Mean Ammonia (mg N/L)High status = ≤ 0.040 mg N/LGood status = ≥ 0.065 ≤ 0.040 mg N/lFailed 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 IndexTD

I

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!