Protection of Water Resources from Nitrate Pollution of Agricultural Origin: Administrative and Methodological Aspects of Significant Interest of the Nitrates Directive 91/676/EEC

1. Introduction

The Directive concerning the protection of waters against pollution caused by nitrates from agricultural sources (91/676/EEC) so-called Nitrates Directive [1] is a European Union (EU) measure adopted in 1991 to reduce and prevent pollution of surface and groundwater and soil by nitrates from agricultural sources (mainly fertilizers and manure) [2, 3].

EU Member States, in order to protect waters from pollution caused by nitrates of agricultural origin, are required to implement water monitoring programs, with precise deadlines and timetables, on their respective national territories.

These monitoring programs shall include the analysis of parameters such as nitrate concentrations of surface and groundwater. Impairment of the water resource and, where appropriate, its level of pollution shall be assessed based on nitrate concentrations greater than 50 mg/l, evaluated both as point data and an annual average and as a significant trend that identifies the short-term overshoot [4].

In these EU areas, the Directive provides for:

1. Identifing the Vulnerable Zones from Nitrates of agricultural origin (NVZs), where the spreading of wastewater over 170 kg of nitrogen per hectare per year is prohibited. The designation shall be reviewed and, where appropriate, reviewed at least every 4 years to take account of any changes that may have occurred.

2. Regulating and monitoring the agronomic use of livestock waste through action programs, a series of measures that farmers are obliged to take in farm management in order to improve the quality of water, such as periods when the application of certain types of fertilizer to soil or the limitation of the application of fertilizers to soil following good agricultural practices and which according to the characteristics of the vulnerable zone concerned is prohibited.

3. Developing a Code of Good Agricultural Practice (COGAP), which farmers apply voluntarily and which establishes a set of good practices, for example by indicating when fertilizer use is not appropriate. Examples of GAP are slurry storage and management to reduce the impact of nutrient losses in the riskiest time of the year and low emission slurry spreading, chemical fertilizer controls and others [5].

2. What are NVZs?

Nitrate Vulnerable Zones (NVZs), regulated by the Nitrate Directive, are designed to protect groundwater and surface water from pollution caused by agricultural nitrates. The Directive requires States and Regions to limit the use of nitrates in predetermined areas. These areas show compromises in water quality or have a higher sensitivity to contamination from chemical substances mainly derived from agricultural fertilizers and other sources of pollution. Vulnerable zones are periodically reevaluated and updated based on changes in environmental conditions, agricultural practices, regulations, and other relevant factors. The zones are established by institutions responsible for managing water resources at the regional level. Decisions are made involving environmental authorities responsible for monitoring water quality in various supply sources, such as rivers, lakes, and wells, to determine nitrate levels. Monitoring data are analyzed by a pool of experts identifying areas where nitrate levels exceed safety limits set by current legislation. The data provide the basis for assessing the potential risk of nitrate impacts on human health and the environment. Based on the results of the analysis and risk assessment, authorities define zones that are considered vulnerable to nitrate pollution. The identified NVZs are included in Plans and Programs aimed at reducing pollution through regulations, sustainable agricultural practices, continuous monitoring, and integrated management strategies involving farmers, local authorities, and other interested parties.

Effectively addressing this issue requires a coordinated effort at the local, national, and international levels to promote sustainable practices and reduce the impact of human activities on the environment. The current trend is exploring new methods to monitor and manage NVZs using advanced technologies such as drones or satellites for aerial monitoring. These technologies can help identify risk areas more accurately and promptly. In addition, artificial intelligence (AI) and machine learning (ML) can be powerful tools in identifying zones and managing nitrate pollution [6, 7, 8, 9]. They can be used to analyze large amounts of heterogeneous data concerning water quality, agricultural practices, weather data, and other factors that influence the presence of nitrates in the environment. It is possible to develop predictive models that estimate future nitrate levels based on historical and current data, helping to make proactive decisions. AI and ML can be used to optimize management strategies, making them more efficient and less subject to human error, and with continuous learning, they can exploit the ability to learn and adapt to new data.

A further trend envisages an integrated approach based on chemical and biomolecular methodologies for the identification and quantification of potential sources of nitrate pollution and site-specific pressures, implementation of the control register, implementation of precision livestock farming practices, enhancement of the use of biochar as an amendment in agriculture, and improvement of environmental communication [10, 11, 12, 13, 14].

3. Description of the action programme with principles and objectives

The Action Program is drafted at the regional level under the Nitrate Directive. The Program regulates the agronomic use of livestock effluents, wastewater, reclaimed wastewater for irrigation uses, digestates, other nitrogen fertilizers, vegetation waters from olive mills, and sewage sludge within Nitrate Vulnerable Zones (NVZs) of agricultural origin [15].

The program aims to ensure the protection of the soil and subsoil from potential nitrate pollution. It also seeks to protect water bodies and achieve surface and groundwater quality objectives [16]. Furthermore, the program aims to maximize the efficiency of fertilizing action for crops and soil amendment. Additionally, it aims to ensure the balance between the potential needs of crops and the inputs of exogenous and/or natural nitrogen and phosphorus. Moreover, the program aims to protect the Natura 2000 network, consisting of Sites of Community Importance (SCI) and Special Conservation Zones (SCZ) under the Habitat Directive [17], as well as sites designated as Special Protection Zones (SPZ). It also prioritizes the protection of air quality and the reduction of greenhouse gas emissions in line with the specific regional strategy contained in the current regional air quality plan [18, 19].

The purposes of the program are to ensure that distribution techniques limit as much as possible the diffusion of nutrients in surface and groundwater, ammonia losses due to volatilization, the dispersion of aerosols towards areas not affected by agricultural activities, and the emission of unpleasant odors. These must guarantee a uniform and rational distribution of fertilizers on a company scale, the adoption of good practices that favor the optimal absorption of nutrients by crops, such as the administration of nitrogen fertilizers as close as possible to the time of their use by plants, the fractionation of applications to cover the entire useful period, the use of distribution techniques and tools aimed at minimizing dispersions in the atmosphere. It is also necessary to provide recourse, whenever possible, to crop rotation practices, integrated management strategies of livestock effluents for the rebalancing of the agriculture-environment relationship, including the adoption of animal rearing and feeding methods aimed at containing, already in the production phase, nitrogen excretions [13, 20, 21, 22].

Manure, sewage and similar materials may contain high concentrations of nitrogen and other nutrients, which could contribute to water pollution. Digestate, produced by anaerobic digestion of organic waste, may contain high amounts of nitrogen and other nutrients. Reducing the use of nitrogen fertilizers and/or phosphatic fertilizers is essential to limit nitrogen and phosphorus pollution. In the various action programmes, in addition to the constraints on quantities, there are spatial and temporal prohibitions according to the type of manure or fertilizer used. In Italy, as a general rule, agronomic use is prohibited in the vicinity of watercourses, sea and lake waters, in sloping land, in forests and on frozen land, snowy, with landslides in place or saturated with water and in all situations where the competent authority provides for specific prohibition measures for the protection of man and the environment. The temporal prohibition indicates no use of manure or fertilizers during the period from November to February, except in specific cases that must be specified in the action plan itself. For example, in Austria, it is forbidden to spread fertilizers on arable land in autumn after the harvest of the main crop, except for winter oilseed rape, winter barley and catch crops. The temporal prohibition prevents the use of manure and fertilizers in the period between November and February of the subsequent year [23].

In addition, in the Italian regulations [24, 25] there are prohibitions on space use related to slopes. The use of manure and similar materials, as well as nitrogen, is prohibited in case of significant risks of nutrient losses due to surface flow or depth percolation. In NVZs the use of sewage and similar materials is prohibited, as a rule, on soils with an average slope, referring to a homogeneous business area, of more than 10%. This slope can be increased by not more than 20% in the presence of hydraulic-agrarian arrangements if the best available spreading techniques are adopted (e.g. direct injection into soil or low-pressure surface distribution by plowing within 12 hours for arable land; direct injection, if technically possible, or low-pressure surface distribution on grassland and pasture; low pressure spreading in bands, or low-pressure surface spreading on cereals or second harvest).

4. Methodology for slope calculation

The methodology used for the calculation of the slope of the Territory at Resolution 100 meters is reported in order to comply with the provisions of current legislation.

The calculation of the slope of the land at 100 m resolution represents an important step of topographic analysis that provides valuable information for a wide range of applications, from urban planning to land management, from civil engineering to the prediction of natural events. In this context, the use of precise methodologies and accurate methods is essential to obtain reliable and meaningful results.

The procedure is divided into several processing phases, each aimed at ensuring the accuracy and reliability of the results obtained.

Step 1: Calculate the slope of each cell in the elevation raster file.

Initially, the slope of each cell of the territory under examination is calculated. This calculation is based on the method proposed by [26]. It is recognized for its effectiveness in topographic analysis. Through this preliminary phase, a detailed assessment of the local slope is obtained, providing a solid basis for subsequent processing. The elaborations are carried out on the raster of the digital elevation model (DEM).

Step 2: Calculation of the accumulation based on the length of the slope at the downstream point.

Subsequently, the downstream calculated slope length values are evaluated using a deterministic flow direction algorithm. This algorithm makes it possible to determine the preferential direction of water flow in each cell of the territory, which is essential for soil erosion assessment and hydrological modeling.

Step 3: Apply a threshold value.

A key element of this phase is the identification of a criterion for the application of a threshold value aimed at optimizing the accumulation values along the slope. In particular, accumulation occurs only if the slope of the receiving cell is steeper than half of the slope of the contributing cell. This criterion makes it possible to avoid insignificant accumulations in the presence of slope profiles that are not very pronounced, ensuring an accurate assessment of areas with significant slopes.

Step 4: Manage multiple contributions.

If multiple cells contribute to the value of a receiving cell, a multiple contribution management approach is adopted that consists of assigning the maximum length values of the different slopes calculated in the contributing cells to the receiving cell.

Final result: identification of agricultural areas with a slope greater than 10% (Figure 1).

5. Case studies on livestock manure management technologies: a comprehensive analysis

Livestock manure management poses a significant challenge for the livestock industry, with direct implications for the environment and public health. These effluents, primarily consisting of animal excreta and liquid waste, contain a wide range of nutrients and contaminants that require proper treatment to reduce environmental impact and valorize them as a sustainable resource. In this analysis, we will explore livestock manure management technologies, dividing them into conservative and reductive treatments and evaluating their applications, benefits, and limitations.

6. Discussion

Water pollution by nitrates of agricultural origin is an increasingly critical environmental challenge, with direct consequences on public health and the aquatic ecosystem. The European Union’s Nitrates Directive aims to reduce and prevent such pollution through concrete measures and water monitoring programmes, with particular emphasis on vulnerable territories and risk areas. The water monitoring programs required by the Nitrates Directive are a fundamental tool for assessing the quality of water resources and identifying any critical situations related to nitrate levels. Exceeding nitrate concentration limits of 50 mg/l is a warning sign of potential contamination of surface and groundwater. It is therefore necessary to implement timely and targeted actions to counter this phenomenon and protect water resources. One of these actions is the delimitation of Nitrate Vulnerable Zones (NVZs), identified according to the provisions of the Nitrates Directive, which play a key role in protecting water from agricultural pollution. Such areas, characterized by compromises in water quality or increased sensitivity to chemical contamination, are subject to restrictions on the use of nitrates to reduce the risk of pollution. NVZs must be regularly monitored and updated according to evolving environmental conditions and agricultural practices.

The elaboration of Action Programmes at the regional level, as required by the Nitrates Directive, is also a crucial step in the fight against nitrate pollution of agricultural origin. Such programmes must include restrictions on the use of manure, wastewater and other nitrogen fertilizers in NVZs while ensuring sustainable agricultural practices and adequate nutrient management. It is important to provide for temporal and spatial bans on the use of materials with a high nitrogen content, to minimize the risk of water pollution.

Another very important aspect is the promotion and adoption of innovative technologies and practices for the management of livestock waste, to reduce the environmental impact of breeding activities. The use of conservative and reductive treatments, such as liquid/solid separation and anaerobic digestion, can contribute significantly to the reduction of nitrate pollution. However, a joint effort by farmers, local authorities and control bodies is needed to ensure the effectiveness and sustainability of these interventions.

To overcome these challenges and improve the protection of waters from nitrate pollution, the following strategies can be considered:

• Integrated monitoring: implement an integrated monitoring system that includes the evaluation of chemical, microbiological and isotope parameters of the water. This would allow for a more comprehensive understanding of the sources of pollution and the health risks.

• Vulnerability models: to develop hydrogeological models that consider the intrinsic vulnerability of aquifers and the presence of nitrate precursor compounds. This would allow for a more precise delimitation of NVZs and a more targeted allocation of resources.

• Specific Action Plans: draw up national and regional Action Plans taking into account the cultural and territorial specificities. Promote the adoption of sustainable agricultural practices such as precision fertilization, the use of cover crops, and crop rotation.

• Economic instruments: evaluate the use of economic instruments such as incentives for the application of sustainable practices and penalties for excessive use of fertilizers.

• Research and development: invest in the research and development of new technologies for the sustainable management of livestock manure, such as anaerobic digestion and nutrient separation.

• Training and technical assistance: provide farmers with training and technical assistance to facilitate the adoption of sustainable farming practices and to optimize nutrient management.

• Communication and involvement: promoting effective communication between authorities, researchers, farmers and citizens to raise awareness of the importance of water resources protection and encourage the active participation of all stakeholders.

7. Conclusions

What is reported in this chapter aims to contribute to the promotion of greater sustainability in companies through specific actions to reduce pollution caused by nitrates of agricultural origin.

Technologies to reduce impacts and data processing methodologies are proposed to obtain a more rigorous knowledge framework in the context of the application of community legislation on pollution from nitrates of agricultural origin.