Content
Natural Small Water Retention Measures (NSWRM) aim to strengthen the natural regulation of water and nutrient cycles within agricultural catchments. In intensively managed landscapes, hydrological processes are often accelerated: runoff increases, infiltration decreases, and nutrients are transported rapidly toward surface waters. This leads to reduced water availability during dry periods, higher flood peaks during extreme rainfall events, and elevated nitrogen and phosphorus loads in rivers and downstream water bodies.
Within OPTAIN, the goals of NSWRM are analysed through process-based modelling frameworks, which simulate how different measures influence water and nutrient fluxes under current and projected climatic conditions. Rather than focusing on physical implementation, the project evaluates how NSWRM portfolios perform in a structured modelling environment at both field and catchment scales.
The core goals can be structured into four interrelated dimensions:
1. Increasing Water Retention Efficiency
A central objective of NSWRM is to improve the capacity of soils and landscapes to retain water. This includes:
- Enhancing soil water storage through improved infiltration
- Reducing rapid surface runoff
- Moderating peak discharge during high-flow events
- Supporting water availability during dry periods
Model simulations in OPTAIN assess how individual measures and combinations of measures influence catchment-scale water balance components, including evapotranspiration, percolation, groundwater recharge, and river discharge dynamics.
Water retention efficiency is particularly important under climate change scenarios, where more frequent droughts and intensified rainfall events are projected. By simulating alternative climate conditions (Deliverable D3.1), OPTAIN evaluates the robustness of NSWRM portfolios under altered hydrological regimes.
2. Reducing Nutrient Losses and Improving Retention Efficiency
Agricultural landscapes are major sources of diffuse nutrient emissions, especially nitrogen and phosphorus. Excess nutrient export contributes to eutrophication in downstream water bodies and deteriorates water quality.
NSWRM aim to:
- Reduce surface and subsurface nutrient transport
- Enhance nutrient uptake and retention within soils
- Decrease sediment-bound phosphorus export
- Lower nitrate leaching to groundwater
Within OPTAIN, nutrient retention efficiency is quantified using model-based indicators derived from hydrological and nutrient transport simulations (D4.3 and D4.4). The modelling framework allows comparison of how different spatial allocations of measures influence nutrient fluxes across heterogeneous landscapes.
Importantly, results vary significantly across case studies due to differences in soil properties, land use, climate, and hydrological connectivity. This highlights that NSWRM performance is context-dependent and must be analysed within each catchment-specific modelling environment.
3. Maintaining Agricultural Productivity
NSWRM must function within productive agricultural systems. A key goal is therefore to explore how water and nutrient retention strategies interact with crop performance.
OPTAIN explicitly integrates agricultural productivity into its multi-objective optimisation framework. Crop yields are simulated within the modelling systems (e.g., SWAT+ and SWAP) to assess:
- Effects of improved soil moisture availability
- Impacts of reduced nutrient losses on crop growth
- Trade-offs between retention efficiency and production
This is crucial because some measures that strongly reduce nutrient losses may also influence land availability or management intensity. The optimisation framework therefore seeks Pareto-optimal portfolios that balance environmental performance with productive viability.
4. Enhancing Cost-Effectiveness and Economic Attractiveness
In addition to hydrological and agronomic indicators, OPTAIN integrates economic considerations into its evaluation framework (see D4.5 and D6.3). Measures are assessed not only in terms of environmental effectiveness but also in relation to:
- Investment costs
- Maintenance requirements
- Cost-performance ratios
- Farmer preferences and stakeholder acceptance
By combining environmental and socio-economic performance indicators (D2.2), the project ensures that NSWRM portfolios are analysed within a realistic decision-making context.
5. Supporting Climate Adaptation and System Resilience
Although OPTAIN does not implement measures in the field, it explicitly explores how NSWRM portfolios perform under projected future climate conditions. Through climate scenario simulations, the modelling framework assesses:
- Sensitivity of performance indicators to increased rainfall intensity
- Effects of prolonged drought periods
- Robustness of measure portfolios across different climate projections
This scenario-based analysis supports understanding of how agricultural catchments might adapt to climate variability and long-term change.
Integrated Multi-Objective Perspective
A defining feature of OPTAIN is that these goals are not evaluated independently. Instead, the project applies multi-objective optimisation algorithms (D5.1 and D5.2) to explore trade-offs between:
- Water retention efficiency
- Nutrient retention efficiency
- Agricultural productivity
- Cost-related indicators
Rather than identifying a single “best” measure, the optimisation process produces sets of Pareto-optimal NSWRM portfolios, allowing stakeholders to examine alternative trade-offs within a transparent modelling framework.
Summary
In the OPTAIN project, the goals of NSWRM are analysed through a harmonised, model-based framework that integrates hydrological, nutrient, agronomic, and economic dimensions.
NSWRM are therefore not presented as universally effective solutions, but as context-specific planning options whose performance depends on climate, soils, land use, spatial allocation, and stakeholder priorities.
Through simulation and optimisation, OPTAIN provides structured evidence on how different NSWRM portfolios may influence water and nutrient management across European agricultural catchments.