A multi-scale framework for strategic management of diffuse pollution

Abstract

A multi-scale framework for decision support is presented that uses a combination of experiments, models, communication, education and decision support tools to arrive at a realistic strategy to minimise diffuse pollution. Effective partnerships between researchers and stakeholders play a key part in successful implementation of this strategy. The Decision Support Matrix (DSM) is introduced as a set of visualisations that can be used at all scales, both to inform decision making and as a communication tool in stakeholder workshops. A demonstration farm is presented and one of its fields is taken as a case study. Hydrological and nutrient flow path models are used for event based simulation (TOPCAT), catchment scale modelling (INCA) and field scale flow visualisation (TopManage). One of the DSMs; The Phosphorus Export Risk Matrix (PERM) is discussed in detail. The PERM was developed iteratively as a point of discussion in stakeholder workshops, as a decision support and education tool. The resulting interactive PERM contains a set of questions and proposed remediation measures that reflect both expert and local knowledge. Education and visualisation tools such as GIS, risk indicators, TopManage and the PERM are found to be invaluable in communicating improved farming practice to stakeholders.

Introduction

The use of nutrients is central to modern farming because of the requirement for high yields. This often results in nutrient-rich runoff into waterways especially during storm events. Dealing with this issue is difficult because the pathways by which phosphorus and nitrates enter the water vary widely as a complex function of soil type, climate, topography, hydrology, land use and land management. Consequently widespread, intermittent, and poorly defined diffuse sources degrade water quality in ways that are difficult to control. Recent major investment has focused on reducing point source discharges of pollution, and this has resulted in significant improvements in water quality. Conversely, this has in turn highlighted the contribution of diffuse agricultural pollution to the degradation of water quality generally.

Recent European legislation in the form of the Water Framework Directive has brought the issue of diffuse pollution into sharp focus (2000/60/EC). Its principal theme is integrated water management at the river basin scale and its main objectives are to prevent deterioration, restore and enhance bodies of surface water to achieve and maintain ‘good ecological status.’ This status is defined and assessed according to chemical, biological and physical measures. The consequences of human activities, for example the effects of nutrients from farming on rivers, must be identified and characterized and a programme of measures established to address such impacts.

Understanding the way in which nutrients are retained within complex landscapes and released to adjacent streams via surface and subsurface flow paths is crucial to land management in the context of the Water Framework Directive and this represents a major research challenge. There are multiple loss-pathways for nutrients from fields, and unpredictable reactions and attenuation of these nutrients (and eroded soil) can occur beyond the application zone of, for example, inorganic fertilisers and manures. To meet this challenge it is necessary to identify the key landscape and land management factors driving nutrient mobilization (e.g. bare soil, fresh applications of manures and fertilisers, high rainfall and vulnerable slopes). Integrating these factors with a methodology for field characterization allows the primary flow paths of nutrient transport to be identified. For example, in surface water driven systems, field characterization should focus on surface runoff, flow in tramlines and tyre tracks, and flow along roads or other impermeable features; in subsurface systems, land drains, near surface interflow, deeper subsurface storm flow and groundwater flow are the most important characteristics. Through field characterization it is possible to identify Critical Source Areas (CSA) within the landscape whereby any zone, from a small area by a gate trampled by cattle to a whole field that is underdrained, may be classed as a CSA if there is a significant source of nutrient input and flow from that land is in direct connection with the receiving waters (Gburek et al., 2000).

This paper introduces a multi-scale water management framework to help integrate research and decision making. The framework is a conceptualisation of an ongoing iterative procedure aimed at improving land management at all scales utilising demonstration farms, scale appropriate dynamic simulation models, decision support tools, visualisation tools and stakeholder workshops. The objective of the framework is to reflect our belief that

• hydrological processes,

• land and water management issues,

• measurements monitoring and data,

• models and decision support tools

are all scale related. The role of the framework is to allow knowledge and expertise arising from specific scales and from both research and practice to be used in a complimentary way. Hence we argue for a suite of scale-appropriate tools (Quinn, 2004, Quinn et al., 2004).

There is already a great deal in the literature on good practice in applying models and knowledge in appropriate ways. For example, the “ten iterative steps in development and evaluation of environmental models” proposed by Jakeman et al. (2006) is extremely useful from a modelling point of view. Texts such as Beven's rainfall-runoff modelling primer (Beven, 2004) and Maidment and Djokic's Hydrologic and Hydraulic Modeling Support with Geographic Information Systems (Maidment and Djokic, 2000) also provide excellent guidance on modelling and uncertainty which can be capitalized on to help the framework work. However, they do not provide solutions to specific environmental problems and in reality we have to recognise that we can only address certain aspects of their work at certain scales. Gaining knowledge from the state of the art helps the framework but does not delay the need for intervention in the landscape now, despite many gaps in our knowledge. While some practitioners have successfully brought together information technology, data and models to facilitate dialogue with stakeholders and carry out transformative projects (see, for example, Thorkilsen and Dynesen, 2001) this type of approach is still far from becoming day to day practice. We argue that the framework proposed in this paper, which is a conceptualization of work already taking place, provides a means to addressing real problems in situ.

The tools which constitute the framework are used to communicate to farmers, agronomists, land use managers and decision makers how to better manage flow on, through and from farm land. The approach, which we describe as integrated runoff management (www.ncl.ac.uk/iq), is truly interdisciplinary, applying skills in mathematical modelling, hydrology, soil science, engineering and sociology. The models and communication tools described focus on scale-appropriate land management measures, particularly the introduction of features and structures in the landscape which provide multiple benefits: reducing nutrient and pesticide export and reducing the risk of flooding at all scales from a single field to a whole catchment. An application of this framework based on a UK research project is presented.