|Main authors:||Oene Oenema, Meindert Commelin, Piet Groenendijk, John Williams, Susanne Klages, Isobel Wright, Morten Graversgaard, Irina Calciu, António Ferreira, Tommy Dalgaard, Nicolas Surdyk, Marina Pintar, Christophoros Christophoridis, Peter Schipper, Donnacha Doody|
|FAIRWAYiS Editor:||Jane Brandt|
|Source document:||»Oenema, O. et al. 2018. Review of measures to decrease nitrate pollution of drinking water sources. FAIRWAY Project Deliverable 4.1, 125 pp
In this article we presenta brief overview of the process and procedures related to the execution of the review. A total of 16 institutions across EU-28 (including those running the FAIRWAY case studies) have been involved in the review process, including, Aarhus University, ADAS, Agri-Food & Biosciences Institute, Aristotle University of Thessaloniki, BGRM, CLM, Coimbra Polytechnic Agri. School, GEUS, ICPA, Kmetijsko gozdarski zavod Maribor, LWK (Chamber of Agriculture), SEGES, Thünen Institute, University of Ljubljani, University of Lincoln, Wageningen Research, and Wageningen University.
|1. Literature review procedures|
|2. Quantitative analysis of the effect size of measures|
1. Literature review procedures
Measures to prevent and reduce the risk of surface runoff and leaching can be categorized according to the source-pathway-receptor concept, i.e. there are
- source-based measures,
- pathway-based measures, and
- receptor or effects-based measures.
Examples of source-based measures are appropriated storage of animal manures and fertilizers, balanced fertilization, and prohibition periods for and restrictions on the application of manures and fertilizers. Examples of pathway-based measures are irrigation measures, drainage, buffer strips, green covers, terracing. Examples of receptor or effects-based measures are dredging and, creation of riparian zones, etc.
The review presented in this section of FAIRWAYiS focusses mainly on source-based measures and pathway-based measures. At the start, a protocol was written and discussed by all partners involved in the review. The purpose of the protocol was ‘to provide guidance for a uniform, effective and efficient literature review and assessment of measures aimed at decreasing pollution of drinking water resources by nitrates’. Two types of reviews were made
- a qualitative review of measures, practices and factors that affect nitrate pollution of groundwater and surface waters, and
- a quantitative review of the effectiveness and efficiency of measures, based on experimental studies in the field.
The qualitative review focussed on the processes and factors that control the pollution of groundwater and surface waters with nitrates from agricultural sources. The results of this review are presented in
»The nitrogen cycle and nitrogen transformation processes
»Agriculture in EU-28 and the use of nitrogen
»Processes and factors that transfer nitrates to drinking water resources
»Overview of measures and practices that decrease nitrate losses
This review yielded also a so called ‘longlist’ of possible measures to reduce nitrate pollution of groundwater and surface waters. The measures of the longlist were characterized using a common format (Table 2). The longlist of measures are derived from literature review and are presented in Annexes 1 and 2 of »Review of measures to decrease nitrate pollution of drinking water souces
Next, a systematic search was performed through online databases, and a local/expert based search was done throughout Europe. The aim of the local search was to find high quality studies which are not easily accessible through online databases, but which contain valuable data. The criteria used for this search were;
- well documented (peer reviewed or reports),
- the article/report should provide the results of one or more experiments to decrease nitrate leaching to groundwater/surface waters,
- the article/report should present quantitative data of results and statistics to enable a meta-analysis.
For the online systematic search online databases were used; CAB-Abstract/Ovid and Web of Science. Query criteria used:
(nitrate and (leaching or drain* or "surface water" or groundwater or "ground water" or runof*) and (mitigat* or measure) and (effect* or reduct* or decreas*) and(treatment or "field trial" or experiment))
Other options involved excluding of the key “model*” and including the key word “agricult*”. The final search yielded 496 results
(nitrate and (leaching or drain* or "surface water" or groundwater or "ground water" or runof*) and (mitigat* or measure) and (agricult* or farm* or crop* or field*) and (effect* or reduct* or decreas*) and(treatment or "field trial" or experiment) not (model*))
CAB-Abstract/Ovid: 121 records
Web of Science: 496 records
In addition, University and Institute libraries were examined in Member States of the European Union, also because a significant fraction of the research on measures to reduce nitrate leaching and surface runoff has been conducted before the 1990s and 2000s when it was still common to publish the results in reports and documents. These reports and documents quite often have not been digitalized and made available to the international scientific audience and as such are not traced by the search machines of Google Scholar and Scopus.
Data and results of reviewed reports and articles were collected in Excel spreadsheets in a uniform manner. The Excel spreadsheets were subsequently transferred to a database for statistical analyses . Annex 3 in »Review of measures to decrease nitrate pollution of drinking water souces presents the list of references of the studies that have been examined.
The flowchart in Figure 1 shows the general lay-out of the protocol of the review. Each block represents a set of questions, as described in the Excel spreadsheet and here further below:
- Contributor: information on person(s) who did the data collection
- Reference: Two option available, 1) peer reviewed articles, and 2) book or report. This last category includes so-called ‘grey literature’.
- Number of measures: the number of measures described in the literature source.
- Pollution type: Nitrate or pesticides or both.
- General information: Data about the location, land use, soil type etc. This information is used to categorize and specify the results (and effectiveness of the measure).
- Control treatment: Describe the characteristics of the reference or control situation. This information is essential for estimating the effectiveness and efficiency of the measure(s).
- Measure: Describe briefly the characteristics of the tested measure.
- Effectiveness: Describe the test results, in terms of reduced leaching and/or loading of the pollutant.
- Economic cost: Describe the operational (running) economic cost of the tested measure, in euro per ha per year, compared to the control (reference) treatment.
In the review, common definitions were used, as follows:
Measure: an agro-management technique, or a change in an agro-management technique, applied at field, farm, landscape and/or water basin levels. A measure often involves a plan or action to achieve a particular purpose. Measures may relate to (changes in) crop types, rotations, cover crops, soil tillage and cultivation, fertilization, irrigation, drainage, pest and disease management, weed management, harvesting, machines and trafficking, landscape management, etc.
Effectiveness: The extent to which the objectives have been achieved, i.e., the extent to which the pollution of drinking water resources by nitrates and pesticides have decreased. The effectiveness can be expressed in different units; here we propose to use the decrease in pollutant concentration (mg/l, or µg/l) or pollutant load (kg/ha/year or g/ha/yr), depending on the results available in the literature source.
Efficiency: The extent to which the desired effects are achieved per unit of cost. The term refers also to “cost effectiveness”, which is expressed as ratio of the effect achieved and the costs required (e.g. mg nitrate per litre per euro or µg pesticides per litre per euro).
Applicability: Applicability is the extent to which a measure can be implemented in practice (without the special provisions that can be made during a research or experiment). Applicability is expressed in the percentage of the area where the measure can be implemented in practice without much difficulty.
Willingness (or adaptability): the extent to which stakeholders implement the measures without additional incentives and, if necessary, maintain the extra facilities that have to be taken. Willingness is expressed in the percentage of stakeholders who implemented the measure(s) without external incentives.
The literature review was divided among the FAIRWAY partners involved, according to regions. Five regions have been distinguished, as follows:
- Central EU: Czech, Slovakia, Hungary, Romania, Bulgaria, Slovenia, Croatia, Bosnia, Serbia
- Central – northern EU: Poland, Germany, Austria, Switzerland, Baltic States
- Mediterranean: Andorra, Portugal, Spain, Italy, Greece,
- Scandinavia: Denmark, Norway, Sweden, Finland, Iceland
- Western Europe: Ireland, United Kingdom, Netherlands, Belgium, France
- The world outside EU: America, Australia, Asia
2. Quantitative analysis of the effect size of measures
The results discussed in this report are based on literature study and statistical analyses. There are roughly three approaches to express the effects of measures.
The first approach applied in this report through simple response ratios, which is the nitrate leaching loss from a treatment measure divided by the nitrate leaching loss of the reference treatment (control treatment), according to
RR = YT/YC
where RR is the response ratio (dimensionless; or percentage), YT is the measured result (expressed in terms of nitrate concentration in groundwater or surface waters, or in terms of soil mineral N, or N surplus) of the treatment measure, and YC is the measured result of the reference treatment or control treatment. The latter is usually current practice or conventional practice. The ratio may vary from 0 to more than 1; a value smaller than 1 indicates that the treatment measure decreases the nitrate leaching loss relative to the reference treatment. A ratio of 1 means no effect.
Instead of a relative comparison of nitrate leaching loss, the response ratio was sometimes derived from a comparison of nitrate concentration in waterbodies or from the amounts of soil mineral N in the soil between treatments, depending on the availability of the data in the reviewed publications.
A second approach is to express the effectiveness in terms of relative effects, i.e., the ratio of the treatment measures, corrected for the reference treatment, and the reference treatment according to
where ES is the effect size (dimensionless; or percentage). In case a treatment measure does not result in a (significant) different outcome than the reference treatment, then ES = 0. For YT > YC this results in ES > 0, and vice-versa.
A third approach is the one used in most meta-analyses studies; the means and standard deviations of the effects are determined based on ln-transformed ratio’s (following the protocol of Hedges et al (1999) as given by
Once the ln-transformed average ratio (and standard deviation) are known, it can be back-transformed to obtain the average effect size according to
Similarly the confidence interval for ES can be determined by back-transforming the confidence interval limits for L. The reported average ES is significant when the available confidence interval (based on standard deviation) does not include the value zero. Formal meta-analysis studies often are based on the ln-transformed approach, whereas single studies and some reviews mostly consider the effect size or the response ratio RR=YT/YC.
In this review, we estimated and used RR (see »Quantitative analysis of measures and practices), because it is the most straightforward expression of the response of a measure. The data as collected through the structured data review from the Excel sheets was processed in the statistical software programme R, following a careful check of all data manually, so as to obtain a good quality and uniform database. Main focus during the processing was on homogenizing units of measurement and setting the right reference treatment. This was done to optimize the calculation of the response ratio for each treatment in each study.
The collected data was divided in categories based on the already identified measures in the shortlist. For each category of measures the reference was defined and this was applied to all individual treatments, in this way the uniformity between studies was optimized.
As general analysis the response ratios for each study within a category were combined and a summery effect ratio was calculated for each measure. In the case of input control there was a clear relation between effectiveness and amount of reduction, so a linear regression was applied to study the relation. However further analysis of co variables and the fitting of a random effect model will be done as next step in this research to identify the most promising measure included in the database.
Note: For full references to papers quoted in this article see