3.1.2 Diffuse source pollution

3.1.2 Diffuse source pollution


In Europe, agriculture is the main diffuse source for water pollution with high emissions of nutrients, like nitrogen and phosphorus, as well as chemicals such as pesticides (EEA 2018b). Drivers for nutrient surpluses in soil and water pollution are excess use of fertilizer for crop production coming from mineral fertilizers and manure from livestock farming. Nutrients (as well as pesticides) enter the water cycle via erosion, surface run-off, leaching, or via inflow from polluted drainage and groundwater to surface waters with impacts to water quality, aquatic communities, and human health. In the second RBMPs, Member States identified that diffuse pollution from agriculture affects 22 % of surface water bodies and 30 % of the groundwater area leading to failure of good ecological and chemical status.

Nutrients are key for plant growth. In the EU, nitrogen surplus from agriculture is estimated to a total of approximately 27 million tons per year (Misselbrook et al., 2019), and since 2010, no improvement to reduce nitrogen surplus has been seen ([1]). Today, the highest total nitrogen surpluses occur generally, although not exclusively, in Western Europe.

Based on reported long-term data of nitrate in European waters, nitrate concentration in rivers showed a decreasing trend (Figure 3). The decline reflects the effects of improvements in waste water treatment, but also reductions of agricultural inputs. In contrast to rivers, nitrate concentration in groundwater does not show any trend during the last decades ([2]).

([1]) Source: https://www.eea.europa.eu/data-and-maps/indicators/agriculture-nitrogen-balance-1, download 16.04.2020

([2]) Source: https://www.eea.europa.eu/data-and-maps/indicators/nutrients-in-freshwater/nutrients-in-freshwater-assessment-published-9

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Pesticides are used to prevent or control any pest causing harm for agricultural products (FAO 2002). Pesticide sales data in Europe show, that in the time period 2011 to 2016, pesticide sales had an amount of 400 000 tonnes per year (EEA 2018c). Despite the high amount of pesticide sales, only 0.4 % of all surface water bodies and 6.5 % of groundwater area fail good chemical status based on exceedances of pesticide standards according to the status assessments in the 2nd RBMP (ETC/ICM 2020). Based on WISE – Waterbase reporting data for European surface water monitoring stations suggest that in the time period 2007 to 2017, 5–15 % showed exceedances by herbicides and 3–8 % by insecticides. For groundwater, the percentages were about 7 % for herbicides and below 1 % for insecticides. Exceedances of fungicides seemed to be less prevalent for both surface waters and groundwater (Mohaupt, et al., 2020). Atmospheric deposition plays a role as a diffuse source for water pollution with chemicals, such as mercury and polycyclic aromatic hydrocarbons (PAH). PAH emissions occur during all combustion processes involving organic materials such as wood, coal, or oil. Mercury is released into the atmosphere, mainly by coal combustion, spreading over great distances and wash-out with rain to soil and waters (BMU/UBA, 2016). It can lead to accumulation in biota, especially fish, which is a risk for fish-eating animals and a potential risk for human health, e.g. (Zupo, et al., 2019). In Europe, mercury is the main reason for failing good chemical status in more than 30 % of all surface water bodies (EEA 2018b)).

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Nutrients and pesticides releases as well as sediment run-off from agriculture have high impacts on surface waters and groundwater. The presence of too many nutrients leads to eutrophication with high levels of algae and aquatic plant growth in surface. Algae blooms also reduce transparency and lead to a lack of oxygen with a high risk for fish and other aquatic communities. In lakes, high nutrient concentrations can induce potentially toxic blue-green algae proliferation, that can be detrimental to human health. Coastal water bodies show similar reactions to excessive nutrient inputs (Ibisch et al., 2016).

Figure 4             Toxic blue-green algae bloom in a dam in Germany

Photo not included

Notes: Insert notes here

Source: © J. Völker

Elevated groundwater nitrate concentrations are affecting raw water for drinking water and thus create a risk to human health. Groundwater containing nitrates can also be emitted into surface water bodies that are fed by groundwater (BMU/UBA, 2016).

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Pesticides input from diffuse sources can have impacts to aquatic communities, if they are directly exposed to pesticides inflow from farmland via erosion or indirectly through trophic chain (Hasenbein, et al., 2016; Maksymiv, 2015). Pesticides can also threaten human health, if contaminated surface waters or groundwater are used for drinking water supply. Furthermore, aquatic communities are exposed to mixtures of different pesticide substances. The knowledge on their combined effects of these mixtures to the aquatic environment is rare ([3]). 

([3]) Mohaupt, V., Völker, J., Altenburger, R., Birk, S., Kirst, I., Kühnel, D., Küster, E., Semeradova, S., Šubelj, G., Whalley, C., 2020, Pesticides in European rivers, lakes and groundwaters – Data assessment. ETC/ICM Technical Report 1/2020: European Topic Centre on Inland, Coastal and Marine waters, 86 pp.

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Sediment run-off from agricultural fields can result in accumulation of fine sediments (see Box 2 in section 3.2), which overlay the natural riverbed resulting in the loss of habitats, e.g. spawning ground for trout and salmon ([4]). 

([4]) Source: https://www.eea.europa.eu/archived/archived-content-water-topic/water-pollution/diffuse-sources

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Measures and management challenges  

Member States are implementing different kinds of measures to reduce nutrient pollution from agriculture. Those measures include for example imposing restrictions on organic fertilizer application (e.g. in compliance with the Nitrates Directive to 170 kg N/ha at farm level), or restrictions in the application conditions for mineral and organic fertilizer and the amount of application of certain types of fertilizer during specific periods (e.g. no spreading of manure during winter). For this, some Member States have limited the total applicable nitrogen for all crops, to inform farmers about their obligation and to facilitate progress in the implementation of the Nitrates Directive (EC 2019e). To further improve efficient nutrient use, the EU Farm to Fork Strategy includes integrated nutrient management action plans to tackle nutrient pollution at source, and to reduce pollution from fertilizer by 50% and their use by 20 % (EC, 2020b).

Further strategies to reduce diffuse nutrient pollution are extensification and expanding the scope of organic farming, the use of precision farming with new digital technologies and innovative monitoring concepts (e.g. remote sensing) as well as the reduction of livestock density. Technical measures include catch cropping, the use of ground coverings and of tillage methods, establishing buffer strips with strict use restrictions, or increase manure storage capacity at farm level. Manure storage can improve the timing of application to minimise the risk of excessive leaching into the water environment. Advisory services should lead to better informed farmers with concrete and relevant information and increase the acceptance to implement measures.  

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To reduce pesticide pollution, relevant measures include for example minimising the risk of off- site pollution caused by spray drift, drain-flow and run-off, or reducing or eliminating applications along infrastructure close to surface water or groundwater. Other measures comprise the preference to use pesticides that are not classified as dangerous for the aquatic environment, the establishment of untreated buffer zones, or ban, or restriction in the use of pesticides. Some European countries (Denmark, France, the UK and Sweden) use reduction targets and timelines within National Pesticide Action Plans for a stepwise reduction of pesticides (EC and Directorate-General for Health and Food Safety, 2017).

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Even though water quality has improved over the last decades, pollution from diffuse sources in particular agriculture still remains a severe water management problem in Europe and a major cause for failing good ecological and chemical status of surface waters and groundwater under the WFD. To protect water ecosystems, there will be a need to strengthen the implementation of agricultural measures (both basic and supplementary) and a need for further efforts to adapt measures to regional pressures (EC 2019e). Specific implementation challenges also remain in addressing water quality issues in 'hotspots' with high nutrient loads as a result of farming, via better coordination of national/regional sectoral administrations (e.g. agriculture, water), and balanced fertilizers application (EC, 2017b). Simultaneously, adaption of financing instruments is necessary within the reform of the CAP. Still, basic measures need to be more strictly implemented to fully comply with the Nitrates Directive (EEA 2018b,  2019b).

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Box 1 Non-connected dwelling

Non-connected dwellings is a diffuse source pollution pressure caused by discharge from households not connected to urban waste water treatment plants or other collection systems ([1]).

In 2017, 11 % of the European population (approximately 50 million people), were not connected to waste water collection systems with the highest shares located in the Eastern part of Europe ([2]). Based on the 2nd RBMP, 21 WFD countries reported significant diffuse source pollution pressures caused by discharges not connected to sewage systems in 10 % of all surface water bodies. Furthermore, about 7.5 % of all groundwater area is affected by this pressure ([3]).

If the waste water is not properly treated by the installation and maintenance of individual appropriate systems, discharges of untreated waste water to waters can lead to nutrient input, or load of pathogens with potentially human health risks in e.g. bathing waters ([4]).

Measures to reduce water pollution are mainly technical and include inter alia waste water package plants, sand filters, drain fields, seepage pits or constructed wetlands with varying purification efficiencies (Vorne, Virpi et al., 2019). Furthermore, national regulatory frameworks have been elaborated to require the installation of appropriate treatment systems, e.g. in Bulgaria, which requires that the water is collected and treated within watertight cesspools (Grebot, et al., 2019). However, the installation of treatment systems, monitoring and maintenance are mainly in responsibility of the homeowners, and technical or financial support by local, regional, or national authorities is rather rare. This makes it difficult to enforce those treatment techniques in single houses or very small agglomerations.

There is still a huge knowledge gap on the impacts of discharges from non-connected dwellings, because neither the UWWTD nor the WFD directly regulate mitigation measures, and reporting obligations solely address connected dwellings with more than 2 000 population equivalents. This hinder information and conclusions on the implementation and use on the effectiveness of individual technical treatment systems. There is a need to further improve the knowledge on this issue, the adaption and harmonization of both WFD and UWWTD measures and reporting, further financial support for homeowners, and control of implemented techniques (EC 2019a; Grebot, et al., 2019).    

([1]) Source: https://www.eea.europa.eu/archived/archived-content-water-topic/wise-help-centre/glossary-definitions/scattered-dwellings, modified.

([2]) Source: https://ec.europa.eu/eurostat/tgm/table.do?tab=table&init=1&language=en&pcode=ten00020&plugin=1

([3]) Source: https://www.eea.europa.eu/data-and-maps/dashboards/wise-wfd, 30.03.2020

([4]) Source: https://www.eea.europa.eu/themes/water/european-waters/water-use-and-environmental-pressures/uwwtd/urban-waste-water-treatment

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