Assessing diffuse pollution and land management impacts on water quality in the Lunan Water, using event-based monitoring
Published on 16 February 2011 in Ecosystems and biodiversity , Food, health and wellbeing
Introduction
Diffuse pollution is the most significant pressure leading to failure of lochs and rivers to achieve objectives set out in the Water Framework Directive. The Scottish River Basin Plan sets out programmes of measures to achieve improved compliance, including the General Binding Rules (GBRs), whereby activities posing a risk, such as cultivation of land, need to follow rules to protect the water environment. These rules are based on good practice and provide a level playing field for land managers. Examples include the establishment and maintenance of a 2m buffer between watercourses and cultivated land (part of GBR20-cultivation of land), avoidance of poaching within 5m of a watercourse (GBR19-keeping of livestock) and maintaining a minimum distance of 10m from watercourses for storage of manures (GBR 18 - management of fertilisers and manures). More details are available on SEPA's Diffuse Pollution page. As part of this process, a group of 14 Priority Catchments (PCs) for catchment wide implementation of pollution control measures have been identified using a risk-based approach by SEPA and partner organisations.
To support this strategy, evidence is needed of policy effectiveness and efficiency, and Diffuse Pollution Monitored Catchments (DPMCs) have been established to assess these measures at catchment scales, using a level of monitoring that would not be possible across the 14 priority catchments. One of these DPMCs is the Lunan Water, a 134 km2 catchment in Angus, Eastern Scotland. It is a typical mixed arable farmland catchment, containing water bodies currently at less than GES. Within the catchment are two Lochs, Rescobie and Balgavies, which have been designated as an SSSI covering 1.78 km2. These lochs suffer from over-enrichment with P leading to serious eutrophication in summer, which also affects the Lunan Water downstream. In addition, much of the catchment is underlain by porous groundwater bodies, vulnerable to nitrate pollution, the river drains to a designated bathing water, and a previously healthy population of salmon and sea trout is now in serious decline.
Evidence of the impacts of diffuse pollution mitigation is difficult and expensive to obtain, because of the event-based nature of many water pollution episodes, and the site-specific nature of diffuse pollution hotspots, which depend on factors such as landscape topography, cropping and cultivation practices etc. Our approach is to use automated turbidity and water level/stage-discharge measurements (see picture) to provide multiple event datasets, which can be used as a proxy for chemical sampling, to cost-efficiently assess catchment responses to implementation of Water Framework Directive programmes of measures. This is supplemented by much less frequent event based sampling and chemical analysis.
Key Points
- In a paired catchment design, we are measuring stream turbidity during storm events to assess efficacy of diffuse pollution mitigation intervention. To demonstrate an overall 33% reduction in event-based pollution, with acceptable statistical power, requires capture of around 130 events both pre-and post intervention.
- This approach has estimated costs of < 10% of the figure for event based chemical analysis, making it attractive for wide scale assessment of impacts of diffuse pollution mitigation measures, eg in SEPA’s Priority Catchments.
Research Undertaken
In order to assess the impact of land management on water quality, we are measuring stream turbidity and discharge, in first order streams draining into the Lunan Water, pre- (2007-2009) and post- (2009 onwards) intervention to mitigate difuse pollution using a paired catchment approach (Bishop et al., 2005). We can assess the statistical “power” to detect changes due to future pollution mitigation intervention in one sub-catchment, whilst the other remains as a control. Technically this “power” can be defined as the probability that a statistical test (such as a t-test with p=0.05) will reject a false null hypothesis. A “power” of 0.80 is a common standard for for adequacy. Intervention in the treated catchments consists of awareness raising, farm audits for compliance with the General Binding Rules (part of the 2008 Scottish Government Controlled Activities Regulations), as well as specific measures such as buffer strips.
The Lunan project is using a participative approach to catchment research, in which farmers and other land users and stakeholders are engaged as active players in catchment management. For this to be successful, a knowledge of the P loads to receiving standing waters (Rescobie and Balgavies Lochs), which we are estimating using turbidity and event chemistry data, is desirable. P loading has a direct impact on standing waters, enabling farmers and others in the catchment to identify the impact of their activities on loch quality, and to be appraised of catchment loads. Calibration of turbidity against water chemistry allows estimated of these loads to be made.
Results
We have assessed the mean turbidity loads for 130 events in two monitored sub-catchments over 3 years, prior to intervention in 2009-10 (farm audits and awareness raising for compliance with the General Binding Rules for diffuse pollution mitigation). Paired catchment studies may be analysed either by testing the effect of period on the differences between the control and treated sites, or by regressing measurements from the treated site on those from the control site and testing for a shift in the regression line between the two periods. Because of the relately weak correlation in event loads across sites, information on the effectiveness of the intervention will only accrue slowly. We expect that, after monitoring for three years post-intervention, we will observe a further 130 paired events , giving an 80% power for detecting mean reduction in turbidity of 33% as being significant at the 5% level.
With chemical analysis at £10/sample and 10 samples/event, the chemical analysis costs alone for a chemical event based method would be ca. £50k/pair of sites. Add to this the costs of maintaining autosamplers and triggering them prior to events, and it is clear that a turbidity-based method (cost of turbidity probes plus loggers around £4,000/pair of sites) is attractive for generating evidence of change in stream quality.
Policy Implications
There is is a need to demonstrate efficacy of programmes of measures from the River Basin Management Plan (SEPA, 2009). This approach has attracted interest from SEPA diffuse pollution management advisory group (DPMAG), who consult with us on approaches to monitoring the 14 priority catchments for implementation of the Water framework Directive in Scotland.
If monitoring to achieve the above levels of uncertainty were required across the 14 Priority Catchments, with 5 pairs of monitoring sites in each catchment, the “pollutant analysis” budgets for the two approaches are £3.6m for chemical analysis as against £280k for the turbidimetric approach.
Further Research
A methodology to assess specific pollutant loads using event based calibration of turbidity against specific pollutants, is under development. This will extend the scope of this method to cost-effective and real time estimation of total P loads, which have a direct impact on standing waters enabling farmers and others in the catchment to identify the impact of their activities on loch quality. The work needs to continue for a 2-3 year period post-implementation of mitigation measures, in order to assess their impact.
For more information, see the Programme3 website.
References
Bishop, P.L., WD Hively, W.D., Stedinger, J.R., Rafferty, M.R., Lojpersberger, J.L. and Bloomfield, J.A. (2005). Multivariate Analysis of Paired Watershed Data to Evaluate Agricultural Best Management Practice Effects on Stream Water Phosphorus J Envt. Qual. 34:1087-1101.
SEPA (2006). Pressures and Impacts on the Scottish water environment.
SEPA (2009). Scotland River Basin Management Plan.
Vinten, A.J.A., M. Stutter, M., Sample,J., Dunn, S., Birkel,C. Potts,J., MacDonald,J. Napier, F. Jeffrey, W. and Christian,C.(2010). How effective is the implementation of controls on diffuse pollution under the Water Framework Directive in Scotland? Answers and questions from the Lunan Diffuse Pollution Monitored Catchment project. (2010).IN: DIPCON 2010, 14th International Conference of the IWA Diffuse Pollution Specialist Group, Diffuse Pollution and Eutrophication. September 12-17, 2010, Quebec, Canada. E. van Bochove, P.A. Vanrolleghem, P.A. Chambers, B. Novotna and G. Thériault (eds).
Vinten, A.J.A., Stutter, M., Potts, J., Watson, H., Abel, C., Taylor, C. and Cook, Y. (2010). Assessment of catchment scale efficacy of diffuse pollution mitigation using turbidity probes: a cost-efffective approach to monitoring in priority catchments? In: Climate, Water and soil: Science, Policy and Practice. In: proceeding of Agriculture and the Environment VIII, SAC and SEPA biennial conference. Crighton, K. and Audsley, R. (eds).
Author
Andy Vinten, Marc Stutter (MLURI) Jackie Potts (BioSS). a.vinten@macaulay.ac.uk
Topics
Ecosystems and biodiversity , Food, health and wellbeing
