Nadeem W. Shah

The wid and the watter: Trees, diffuse pollution and WFD objectives

The Past

Negative impacts of forests on the water environment

• Large-scale conifer afforestation following first and second world wars –creation of a strategic timber reserve with little consideration of environmental damage

• Non-native trees, uplands, close to the water’s edge, on peat and lots of drainage

Upland plantation

Peatlands

Close to the water’s edge

Sitka Road

Water Resources

• Forestry could impact upon water resources – high water use

• Frank Law showed that conifer afforestation reduced water resource at Stocks reservoir

• Catchment studies – Institute of Hydrology

Water use of trees

Two major processes:

Transpiration - water is taken up by tree roots from the soil and evaporated through the pores or stomata on the surface of leaves; a physiological process responding to soil and atmospheric factors.

Interception - the interception, and subsequent evaporation, of water by the surfaces of leaves, branches and trunks during rainfall.

Water quality

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• Forestry could adversely impact water quality - acidification, eutrophication and siltation.

• Drinking water quality

• Biological impacts – damage spawning areas, clog gills; algal blooms.

Acidification

Acidification was (and still is) a major environmental issue

Acidification

Nitrogen oxides (NOx) and sulfur dioxide (SO2) released into the atmosphere (mainly from burning of fossil fuels) reach the ground as dry deposition, or are deposited in precipitation, snow or sleet as wet deposition. Occult deposition is the direct transfer from clouds - occurs at high altitude (image from ‘Acid Rain Revisited, Hubbard Brook Research Foundation’)

Acidification

• Acid deposition and subsequent acidification of soil and water can trigger a number of interrelated environmental changes

• Research showed that forested areas, although not a source of acidification, could increase deposition on to soil and water through enhanced capture of acidifying chemicals - the forest scavenging effect.

• Chemical impacts

• Biological impacts

• Killer conifers

Killer conifers

Negative Impacts

EARLY RESEARCH WAS MAINLY ON NEGATIVE IMPACTS

The efficiency of the forest scavenging effect varies between pollutants and is greater for nitrogen compared to sulphur due to the more reactive nature of nitrogen gases.

The Present

Hydrological benefits from forests – Natural Flood Management and Diffuse Pollution Mitigation

• Woodland NFM techniques that can help to mitigate downstream flooding

• Targeted woodland planting to mitigate against diffuse pollution.

Diffuse Pollution

Woodland and Diffuse Pollution Mitigation

• Diffuse pollution is pollution arising from land-use activities (urban and rural) that are dispersed across a catchment or sub-catchment.

• The main diffuse pollutants are phosphorus, nitrogen, pesticides, sediment, ammonia and faecal microorganisms

• Agriculture is the primary source and thought to be responsible for nearly half of water bodies across Scotland failing due to diffuse pollution, a total of 495 water bodies (SEPA, 2007).

• Commercial forestry can also act as a pressure on the water environment if poorly designed and managed. It is thought to contribute to 75 failing water bodies, mainly due to conifer crops having been planted too close to watercourses.

Fertiliser use

• Huge increase in fertiliser use since the 1960s

• Significant reductions in recent years but legacy remains

• SEPA estimates that some 45,000 tonnes of nitrate are lost from agriculture to surface waters and groundwater every year, as well as some 2,800 tonnes of phosphate - manure/slurry spreading, poaching, silage and manure heaps.

Use of inorganic N fertilisers in the UK (Environment Agency (2005). Attenuation of nitrate in the sub-surface environment.)

Nutrients applied (kg/ha) to crops and grass, 1986-2012 (British survey of fertiliser practice)

Sediment/silt

• An important diffuse pollutant and a carrier of pollutants – ecological effects

• Flooding – increase flood risk

• Pontbren – bedload yield 12x greater and suspended sediment 5x greater from agricultural intensification than undisturbed moorland (Henshaw)

• Soil erosion - carbon losses of almost 50% can occur in upland soils with a peaty surface horizon when the protective vegetation cover is lost (Grieve (2000)

Soil erosion off the coast of Burma (left) and in the Ganges delta

Soil erosion is a natural process but it is accelerated due to removal of protective vegetation and land use practices – forestry and farming.

WFD

• The WFD was introduced in 2000 to establish systems to manage the water environment - it was transposed into Scots Law in 2003.

• Provides a framework for the protection of all water bodies including rivers, canals, lochs, estuaries, wetlands, groundwaters and coastal waters.

• Key aims are to prevent the deterioration of water quality and resources, promote the sustainable use of water, mitigate the effects of floods and droughts, and achieve good chemical and/or ecological status in all surface and ground waters.

• Implementation is facilitated by River Basin Management Plans (RBMP), supported by programmes of measures to tackle pressures.

WFD

• WFD - Significant progress has been made towards improving the condition of affected water bodies across Scotland

• 40% continue to fail the environmental standards required to support good ecology, with diffuse pollution identified as one of the most important water management issues (SEPA, 2012).

• Scotland’s approach to addressing diffuse pollution is described in the Rural Diffuse Pollution Plan - identifies over one hundred catchments with failing waters that require catchment-based solutions.

• Fourteen of these have been prioritised for attention in the first RBMP due to risks posed to human health (by impacting on drinking and bathing waters) and designated sites.

Priority catchments - first cycle

River Ayr Eye Water

River Doon River Tay

River Irvine River South Esk

River Garnock River Dee (Grampian)

North Ayrshire Coast River Ugie

Galloway Coastal River Deveron

Stewartry Coastal Buchan Coastal

Priority catchments

• The primary aim of the Priority Catchment approach is to implement a range of land-based measures to reduce diffuse pollution, either by tackling pollutant sources or interrupting delivery pathways.

• A key measure recommended by the Scotland RBMP is to install buffer zones, including of woodland, to intercept and treat nutrient and pesticide pollutants from adjacent agricultural land (SEPA, 2009)

• SEPA’s pilot catchment project - Scoping opportunities for measures delivery (Phase 1)

• River Dee, River South Esk, River Nith, Glazert Water (part of the River Kelvin catchment)

• Woodland creation opportunities are identified in all reports

• Opportunity to work with SEPA at implementation phase to identify suitable catchments for woodland planting and monitoring

River Lyon

River Lyon

Approx. 30m buffer width - <10m have been shown to completely prevent P entry to watercourse (Borin et al, 2004)

River Tay

Approx buffer widths: East - 100m; West - 290m; South - 30m

River Beaulieu

Approx 100m buffer on west side

Beaulieu Buffer

Approx 100m buffer width on West side

Beaulieu

Approx. buffer on East side = 2.16 km! Habitat connectivity

Riparian mechanisms

Image taken from USDA forest service: http://www.na.fs.fed.us/spfo/pubs/n_resource/buffer/part7.htm

Woodland can help prevent or reduce diffuse pollution by a number of mechanisms, including:

• Interception: woodland canopies can provide a barrier to airborne pollutants such as ammonia, while the well-structured nature of woodland soils help to receive and retain dissolved or suspended pollutants in runoff (e.g.pesticides, nitrate, phosphate and sediment), reducing delivery to watercourses.

• Nitrate-reduction - nitrate removal by microbially-mediated nitrate reduction (using organic carbon as the electron donor)

Riparian mechanisms

• Biodegradation: biodegradation of contaminants (e.g. pesticides) can occur, with potential for simultaneous nitrate-reduction

• Substitution: woodland is a much less intensive land use compared to agriculture, with very infrequent and small inputs of fertiliser and pesticides, and low levels of site disturbance.

Multiple benefits

• Targeted woodland buffers along mid-slope or downslope field edges, or on infiltration basins appear effective for slowing down runoff and intercepting sediment and nutrients, but the evidence base is limited.

Other water related benefits provided by woodland creation include:

• Habitat connectivity: fragmented habitats can increase species isolation and extinction leading to reduced biodiversity; woodland can provide effective corridors along which species can move from the watercourse throughout the wider catchment.

• Societal benefits - recreation and health

• River morphology: a multi-layered canopy of native riparian woodland and associated inputs of dead wood and leaf litter can improve channel form and river function. Riparian woodland can also help to protect river banks through tree rooting and by excluding livestock.

• Temperature regulation: the provision of riparian shade can reduce thermal stress to sensitive freshwater life (e.g. salmonid fish), and thereby help to reduce the threat posed by climate warming.

Thermal regulation

Riparian woodland can provide shade and promote survival of fish and other aquatic species such as the freshwater pearl

mussel.

Measured data from New Forest comparing stream water temperatures between shaded and open reaches.(Broadmeadow, et al., 2010)

Mussels

Relationship between amount of shaded channel and the percentage of mussels occurring in shaded areas on individual cross-sections. [From: Gittings et al. (1998): Longitudinal variation in abundance of a freshwater pearl mussel population in relation to riverine habitat]

Nitrate removal

Nitrate concentrations (mg/l) in 75-90 cm depth in new forests after afforestation on former arable land. Average

of nine afforestation sites in Denmark. Shading indicates the standard deviation.

From Hansen, K. & Vesterdal, L. (eds.) (2004): Guidelines for planning afforestation on previously managed

arable land. Forest & Landscape, Hørsholm.

Opportunity mapping

Tay priority catchment

Taking account of constraints and opportunities

Identifying opportunities for targeted planting –the right tree in the right place.

Woodland and WFD

Woodland for Water