Agriculture provides food, fibre, energy and, last but not least, a living for many people around the world [1
]. A drawback of agricultural production is pollution of the terrestrial environment with nitrogen via atmospheric deposition [4
] and the aquatic environment by nutrients, pesticides and trace elements [5
]. Thus, growth of agricultural production, as has occurred in Europe and North America since the 1950s and more recently in many other parts of the world, threatens the quality of groundwater and surface waters or has already led to deterioration of the quality of these waters [10
]. Problematic hotspot areas are found in all countries around the world with typical examples in Denmark, the Netherlands, Germany, Belgium, United Kingdom, northern Italy, France, China, the United States and New Zealand.
Policies to abate the deterioration of water quality have been developed and programmes to improve water quality implemented around the world. For example, the European Union has adopted directives (the Nitrates Directive in 1991 [13
]; the Water Framework Directive in 2000 [14
]; the Groundwater Directive in 2006 [15
]) with the objective of obtaining good quality in all waters by 2027.
Experience from the last 15 to 25 years shows that it will be a great challenge to realise the objectives of these policies in the remaining years of this decade, not only because the easy, low-cost measures have already been implemented, but also because the need for food for a growing world population creates a pressure to increase agricultural production. Since the easy, low cost measures generally have already been introduced, there is a need for answers to questions like ‘Which measures are most effective and at the same time the most cost-effective for water quality improvement’? As most of the additional measures will have a larger effect on farm management, their implementation may be less straightforward. This raises the question ‘Should measures be enforced by law or implemented on a voluntary basis’?
Schoumans et al. [16
] developed a new system for implementing mitigation measures in agricultural systems to reduce phosphorus losses to water. Moreover, within the EU Cost-Action 869 programme, a wide range of mitigation measures for reducing nutrient emissions from agriculture was collected [17
]. Mitigation of nonpoint source nutrient pollution can be grouped into eight categories: (1) nutrient management; (2) crop management; (3) livestock management; (4) soil management; (5) water management within agricultural land; (6) land use change; (7) landscape management and (8) surface water management. These mitigation measures can be further divided into source and transport measures (Figure 1
Source measures typically belong to groups 1–4 and 6, whereas transport measures belong to groups 5, 7 and 8 (Figure 1
). Mitigation measures can be adapted as mandatory requirements for farmers as was the case during the period 1987–2015 in Denmark. This strategy was successful as demonstrated by a reduction of nitrogen and phosphorus concentrations and loadings in streams and rivers of nearly 50% and 70%, respectively, since 1990 [20
]. A new era of management has, however, evolved in Denmark involving the application of targeted mitigation measures in agriculture, including local N-retention in groundwater and surface waters [21
], as well as identification of phosphorus loss hotspots in agricultural catchments (P-risk mapping) [22
]. Currently, development, scientific testing and application of new mitigation measures are ongoing worldwide. Research into new and more engineered types of mitigation measures assisting in removing and capturing nutrients during the transport from source to recipient waters is in progress [18
Some of the above issues are touched upon in this Special Issue from the Land use and Water Quality (LUWQ) conference series, of which the most recent, LuWQ2019, was held at Aarhus University from 3 to 6 June 2019.
2. History and Themes of the LuWQ Conference Series 2013–2021
The Land use and Water Quality conferences have their origin in the series of so-called international MonNO3 workshops focusing on monitoring the effectiveness of the European Nitrates Directive action programmes. The first MoNO3 workshop was held in The Hague in 2003 and the second in Amsterdam in 2009. The workshops were limited to invited researchers and policy advisors from north-west and central European countries. At the latter workshop, the importance of the European Water Framework Directive for nutrients and other agriculture-related pollutants became clear. Furthermore, in countries outside the European Union, interesting developments in agri-environmental research, water management and policies have taken place. Therefore, we decided to broaden the scope of the meetings and to continue them in the form of conferences.
Thematically, LuWQ currently covers a wide range of topics covered by the nine themes. Three themes relate to more fundamental research:
to increase our knowledge about ‘system functions’, i.e., basic hydrogeological and biogeochemical processes and related tools and methodologies,
water quality monitoring which is about improving the effectiveness and increasing the added value of monitoring,
impact of weather variability and climate change on water quality.
Three themes deal with the impact of policy and measures on water quality on plot, field, catchment and national scales:
assessing national or regional policy, e.g., with regard to the effectiveness of programmes of measures on water quality,
improving water quality by farm management practices (monitoring and modelling) and changes in land use,
improving water quality by establishing eco-technological mitigation measures and discussing development, testing, implementation and operation to quantify the effects of such measures.
The last three themes cover management and social–economic aspects:
managing protected areas for water supply and nature conservation including risk assessment techniques, monitoring and modelling,
decision-making on Programmes of Measures with topics which look into the role of stakeholder input and science in policy decision-making, and
implementation of Programmes of Measures that focusses on social and economic incentives and regulatory mandates that drive implementation (carrots and sticks).
At the first LuWQ conference in The Hague in 2013, we had a total of 170 participants from 30 different countries from all continents. Since then, the number of participants rose to 175 at the conference in Vienna in 2015, to 195 at the conference in The Hague in 2017 and to 240 participants in Aarhus in 2019. Feedback of participants resulted in a separate theme about monitoring in 2017 and distinguishing explicitly separate themes on farm management and technical measure for improving water quality in 2019. Furthermore the setup of the conference developed, for example, by introducing special sessions and workshops giving more room for in-depth discussion. However, the key strength of the LuWQ conferences remained which is twofold: (1) LuWQ has a well-defined narrow focus on ‘agriculture and water quality’ and (2) the conference is broadly oriented with regard to the various professional disciplines related to the conference topics.