Nutrients in transitional, coastal and marine waters

Indicator Specification
Indicator codes: CSI 021 , MAR 005
Created 04 Nov 2014 Published 03 Mar 2015 Last modified 04 Sep 2015, 07:00 PM
Topics: , ,
This indicator illustrates the levels and trends in winter means of dissolved inorganic nitrogen (nitrate + nitrite + ammonium), oxidised nitrogen (nitrate + nitrite) and phosphate concentrations (micromol/l) in the regional seas of Europe.

Assessment versions

Published (reviewed and quality assured)

Rationale

Justification for indicator selection

The water quality in transitional, coastal and marine regions could be adversely affected by anthropogenic activities, such as the application of agricultural fertilisers and manure, the discharge of wastewater and airborne emissions from shipping and combustion processes. These activities may result in elevated nutrient (nitrogen and phosphorus) concentrations leading to eutrophication and causing a chain of undesirable effects.

Usually a distinction is made between the direct and indirect effects of nutrient enrichment. The direct effects include high chlorophyll concentration in the water column as a result of increased phytoplankton primary production and changes in species composition and functioning (such as diatom to flagellate ratio, benthic to pelagic shifts, as well as bloom events of nuisance/toxic algal blooms). The increase in the risk of algal blooms (e.g. cyanobacteria) may cause the death of benthic fauna, wild and caged fish, or shellfish poisoning of humans. In addition to the effects on the aquatic ecosystem, discoloration of water may be a disturbance to bathers, thus impairing recreational activities.

The indirect effects of nutrient enrichment include increased abundance of perennial seaweeds and seagrasses (e.g. fucoids, eelgrass and neptunegrass), reduced water transparency related to an increase in suspended algae and oxygen depletion. Increased growth and dominance of fast-growing filamentous macroalgae in shallow sheltered areas may change the coastal ecosystem, increase the risk of local oxygen depletion and reduce biodiversity and nurseries for fish. Increased consumption of oxygen due to increased organic matter decomposition can lead to oxygen depletion particularly in areas with stratified water masses, changes in community structure and hypoxia with bottom fauna mortality. Even a short-time hypoxia event will kill most invertebrates living on or within the seabed, creating 'dead zones'. Dead zones in marine ecosystems due to hypoxic conditions have doubled in size globally every decade since the 1960s.  

The main nutrients causing eutrophication are nitrogen (in the form of nitrate, nitrite or ammonium) and phosphorus (in the form of orthophosphate). Silicate is essential for diatom growth, but it is assumed that its input is not significantly influenced by human activity. Europe´s regional seas have different sensitivities to eutrophication, determined by their physical characteristics. The Baltic and Black Seas have a high sensitivity to eutrophication due to limited water exchange with connecting seas. 

Scientific references

Indicator definition

This indicator illustrates the levels and trends in winter means of dissolved inorganic nitrogen (nitrate + nitrite + ammonium), oxidised nitrogen (nitrate + nitrite) and phosphate concentrations (micromol/l) in the regional seas of Europe.

Units

Concentrations in micromol/l

Policy context and targets

Context description

Measures to reduce the adverse effects of excess anthropogenic inputs of nutrients and to protect the coastal and marine environment are being taken as a result of various initiatives at all levels - global, European, regional (i.e. through Regional Sea Conventions and/or regional Ministerial Conferences) and national.

There are a number of EU Directives aimed at reducing the loads and impacts of nutrients, including the Nitrates Directive (91/676/EEC) - aimed at the protection of waters against pollution caused by nitrates from agricultural sources; the Urban Waste Water Treatment Directive (91/271/EEC) - aimed at reducing pollution from sewage treatment works and from certain industries; the Integrated Pollution Prevention and Control Directive (96/61/EEC)  - aimed at controlling and preventing pollution of water from industry; the Water Framework Directive (2000/60/EC) - which requires the achievement of good ecological status or good ecological potential of transitional and coastal waters across the EU by 2015; and the Marine Strategy Framework Directive (2008/56/EC) which  requires the achievement or maintenance of good environmental status in European seas by 2020 at the latest, through the adoption of national marine strategies based on 11 qualitative descriptors. The Ecological Descriptor 5 is on Eutrophication.

Measures also arise from international initiatives and policies including: the UN Global Programme of Action for the Protection of the Marine environment against Land-Based Activities; the Mediterranean Action Plan (MAP) 1975; the Helsinki Convention 1992 (HELCOM); the OSPAR Convention 1998; and the Black Sea Environmental Programme (BSEP).

Targets

The most relevant EU policy target with regard to chlorophyll concentrations is from the Water Framework Directive (WFD), which aims to reach good ecological status of all EU surface waters by 2015. Member States have defined water-type specific environmental standards to support the achievement of good ecological status. As natural and background concentrations of nutrients vary between and within the regional seas, and between types of coastal water bodies, nutrient targets or thresholds for achieving good ecological status have to be determined while taking into account local conditions.

Within the scope of the Marine Strategy Framework Directive, nutrient levels (nutrient concentrations in the water column and nutrient ratios for nitrogen, phosphorus and silica, where appropriate) are the relevant criteria and indicators in marine waters under the Goof Environmental Status (GES) Descriptor 5: Human-induced eutrophication. The aim of the MSFD is to reach or maintain GES of the marine environment by 2020. The assessment of eutrophication in marine waters needs to combine information on nutrient levels as well as a range of ecologically relevant primary and secondary effects, taking into account relevant temporal scales. The nutrient targets and thresholds for achieving good environmental status have not been defined yet.

Related policy documents

Key policy question

Are nutrient concentrations in European transitional, coastal and marine waters decreasing?

Methodology

Methodology for indicator calculation

The data used in this indicator is part of the WISE - State of the Environment (SoE) data, available in Waterbase - TCM (Transitional, Coastal and Marine) waters. Waterbase is the generic name given to the EEA´s database on the status, quality and quantity of Europe´s water resources. Waterbase – TCM waters contains data collected from both EEA member countries (i.e. belonging to the EIONET) and from the Regional Seas Conventions through the WISE-SoE TCM data collection process. The resulting WISE SoE TCM dataset is therefore made of sub-samples of national data assembled for the purpose of providing comparable indicators of state, pressures and impacts of transitional, coastal and marine waters (TCM-data) on a Europe-wide scale.

Consistent time series are used as the basis for assessment of the development over time. The trend analyses are based on time series from 1985 onwards. Stations with  data in, at least, the last six years (2007 or later), and five or more years in the period since 1985 are selected. For nitrogen, dissolved inorganic nitrogen (DIN – nitrate + nitrite + ammonium) and oxidised nitrogen (OxN - nitrate + nitrite) are both used. In the case of gaps in nitrite data, only ammonium and nitrate were used to complete the time series.

In previous assessments, the description of nitrogen was limited to oxidised nitrogen (nitrite + nitrate) and did not include ammonium (NH4+), which is another important inorganic nitrogen compound. This approach deviated from the common practice in most Regional Sea Conventions and that described in the WFD and MSFD, where all dissolved inorganic nitrogen compounds (described as DIN=nitrite + nitrate + ammonium) should be taken into consideration. In many cases, ammonium is a substantial fraction of winter average DIN and a description of oxidised nitrogen (nitrite + nitrate) alone may therefore lead to a biased assessment result. For the sake of comparison with previous assessments, both DIN and OxN are considered in this assessment.

 The winter period is defined as follows:

  • January, February and March for stations east of longitude 15 degrees (Bornholm) in the Baltic Sea
  • January and February for all other stations

 

Primary aggregation

The primary aggregation consists of:

  • Identifying stations and assigning them to countries and sea regions.
  • Creating statistical estimates for each combination of station and year.

Geographical classification: Sea region, coastal/offshore

All geographical positions defined in the data (i.e. in stations) are assigned to Europe´s regional seas by coordinates and used in the aggregation process for different determinants. The stations are then further classified as coastal or open water (>20 km from coast) by checking them against the coastal contour. Open waters stations – off-shore - are distinguished per regional sea, whereas coastal stations are further attributed to country. These classifications are done in ArcGIS.

Eionet stations

TCM data reported directly from countries are assigned to station identifiers that are listed with coordinates.

Marine convention data from ICES

For the data reported through ICES, there are no consistent station identifiers available in the reported data but only geographical positions (latitude/longitude). The reported coordinates for what is intended to be the same station may vary between sampling visits because the exact sampling position is recorded, not the target position. Identifying a station from its real sampling position may fragment time series too much. Therefore, for open waters (>20 km from land), coordinates are rounded to two decimal points. This is used to create stations (i.e. time series) with station names derived from rounded coordinates. The station coordinates are the average in the sampling visits to the station rather then the rounded coordinates. This ensures that, in cases where most observations are in a tight cluster within the rounding area, a position within the cluster is used. For the coastal ICES stations, there may be some overlap with Eionet stations. In coastal stations rounding coordinates to two decimal points may be too much (about 500m to 1km). However, the rounding is also done for coastal stations but the grouping of observations to rounded coordinates is done separately only within observations from each country and the originator country is listed. Note that these stations are not necessarily close to the coast of the originator country.

Many countries have made measurements over large areas, including some observations fairly close to the coast of other countries, although probably not normally within territorial waters of other countries. This means that, at least for open waters, assigning data to originating country may not necessarily reflect geographical location. Duplicates between data reported through ICES or from the Eionet directly may occur. A visual inspection of coastal data (< 20 km from shoreline) is performed to identify those issues and correct them where possible (namely through feedback with the originator country(ies).

Statistical aggregation per station and year

The aggregation is done in two- or three-stage query sequences, which include:

  • Selecting season (month) and depth;
  • If needed, building a cross-table with determinants in columns, and water samples in rows, and deriving composite determinants from that;
  • Aggregating over depth for each combination of station and date; and
  • Aggregating over dates within each combination of station and year. 

The basic data consists of two tables:

Measurement values table
WaterbaseID (Country and Station)
Date (Year, Month and Day)
SampleDepth
SampleID
Determinant, with Determinant codes "Ammonium", "Nitrate", "Nitrite", "DIN", "Total oxidised nitrogen" and "Orthophosphate".

 

Stations table
Unique identifier: data provider, Country and Station ID
Position
Sea region (Atlantic, North Sea, Baltic, Mediterranean and the Black Sea)

The two tables are combined in a query which joins data to stations, linked by WaterbaseID, and including Country Code and Sea Region (used in Selection Criteria below). This query (or a table made from it) is used in the Aggregate queries.

Description of specific aggregation query sequencesNitrate and Phosphate
Step 1

Crosstable query, with determinands "Ammonium", "Nitrate", "Nitrite", "DIN", "Total oxidised nitrogen" and "Orthophosphate" as columns, and row heading Sea Region, WaterbaseID, Year, Month, and SampleDepth.
Include data for:
SampleDepth <=10 m and 
Month = 1,2,3 (Jan. - Mar.) for stations east of longitude 15 degrees (Bornholm) in the Baltic Sea
Month = 1,2 (Jan.- Feb.) for all other stations.

Step 2

For each combination of WaterbaseID*Year*Month*Day, calculate [Total Oxidised Nitrogen] and [DIN]: Calculate best possible estimate of nitrate including nitrite 

Aggregate arithmetic mean of Oxidised Nitrogen and Orthophosphate over depths.

Step 3

For each combination of WaterbaseID *Year,

calculate the arithmetic mean over the depth averages from Step 2.
Export result to Aggregate database as table 't_Base_Metadata_N_and_P'

 

Classification

Concentrations from the most recent year available (2012) are presented on a map, where concentrations are classified as low, moderate or high. Low concentrations are defined as concentrations smaller than the 20-percentile value of concentrations within the specific regional sea in the last six years (i.e. 2007-2012). High concentrations are concentrations higher than the 80-percentile value of concentrations within the regional sea in the last six years (i.e. 2007-2012). All other concentrations are classified as moderate. This classification helps to identify areas of low and high concentrations and is based on six-year percentiles, unlike previous assessments, which only considered the percentile values within a regional sea based on data from that specific year.

 

Trend analysis

Trend analysis was carried out for each station in a region having data in, at least, the last six years (2007 or later), and at least five or more years in the period since 1985. Trend detection for each time series was done with the Mann-Kendall Statistics using a two-sided test with a significance level of 5% (Sokal & Rohlf 1995).

In the presentation of the results, a distinction is made between trends based on relatively short time series (≤ 10 years) and longer time series (> 10 years).

A nutrient-salinity gradient is commonly observed along the freshwater-seawater continuum in transitional, coastal and marine water bodies. The variation of nutrient concentration with salinity is commonly represented in “mixing curves”, with elevated nutrient concentrations at the freshwater end decreasing towards marine waters. At some stations in this salinity gradient, year-to-year variations in salinity may result in large variations in nutrient concentrations. For stations where interannual variations in nutrient concentrations were correlated with changes in salinity, data were corrected for the salinity effect before carrying out a trend analysis.

The Mann-Kendall method is a non-parametric test suggested by Mann (1945) and has been extensively used for environmental time series (Helsel and Hirsch, 2002; Hipel and McLeod, 2005). Mann-Kendall is a test for monotonic trends in a time series y(x), which in this analysis is nutrient concentration (y) as a function of year (x). The test is based on Kendall's rank correlation, which measures the strength of monotonic association between the vectors x and y. In the case of no ties in the x and y variables, Kendall's rank correlation coefficient, tau, may be expressed as tau=S/D where S = sum {i<j} (sign(x[j]-x[i])*sign(y[j]-y[i])) and D = n(n-1)/2. S is called the score and D, the denominator, is the maximum possible value of S. The p-value of tau is computed by an algorithm given by Best and Gipps (1974). The tests reported here are two-sided (testing for both increasing and decreasing trends). Data series with p-value < 0.05 are reported as significantly increasing or decreasing. The test analyses only the direction and significance of the change, not the size of the change.

The Mann-Kendall test is a robust and accepted approach. Due to the multiple trend analyses, approximately 5% of the conducted tests will turn out significant (identify a trend) if in fact there is no trend. The accuracy at the regional level is largely influenced by the number of stations for which data is available.

Methodology for gap filling

For nitrogen, dissolved inorganic nitrogen (DIN – nitrate + nitrite + ammonium) and oxidised nitrogen (OxN - nitrate + nitrite) are both used. In the case of gaps in nitrite data, only ammonium and nitrate were used to complete the time series assuming the nitrite fraction was negligible.

Methodology references

Data specifications

EEA data references

  • No datasets have been specified here.

Data sources in latest figures

Uncertainties

Methodology uncertainty

The Mann-Kendall test for the detection of trends is a robust and accepted approach. However, due to the multiple trend analyses, approximately 5% of the tests conducted will turn out significant if, in fact, there is no trend. Also, the accuracy at the regional level is largely influenced by the number of stations for which data is available.

There are also a number of uncertainties related to temporal and spatial use of the data. Currently, the winter period is defined as January and February for all stations except for stations east of longitude 15 degrees (Bornholm) in the Baltic Sea. However, this definition may be too broad to reflect the climatic differences across the European sea regions. For example, for the Black Sea, it is suggested to also consider spring concentrations due to the nutrient enrichment of coastal waters as a result of increased riverine inputs (BSC, 2010). 

Moreover, two types of geographical aggregation are performed in the current methodology, based on the Country Code and Sea Region. In both cases, differences in physical, chemical and biological characteristics between sampling stations are not taken into account. Measured nutrient concentrations should be related to natural background values that reflect spatial/geographical differences. Furthermore, data collected over the different years is obtained from different laboratories, possibly following different methodologies and it is combined in the same trend analysis. This might also influence the results.

Data sets uncertainty

Data for this assessment is still scarce, considering the large spatial and temporal variations inherent in European transitional, coastal and marine waters. Long stretches of European coastal waters are not covered in the analysis due to lack of data or sufficiently long and recent time series. 

Rationale uncertainty

Due to variations in freshwater discharges, the hydro-geographic variability of the coastal zone and internal cycling processes, trends in nutrient concentrations, as such, cannot be directly related to measures taken in nearby river basins. However, overall trends reflect the effects of measures to reduce nutrient pollution.

 

 

Further work

Short term work

Work specified here requires to be completed within 1 year from now.

Work description

It is necessary to get access to more data, in terms of better spatial coverage and longer time series, in order to improve the assessment. In order to obtain longer time series it is also important that data is associated with unique station identifiers such that observations within a specific area can be merged. Ongoing work includes the improvement of methodologies used to calculate CSI 021 and streamlining with indicators developed under the MSFD. Methodological aspects that require revision include: a) classification, b) geographical aggregation, c) temporal scale

Resource needs

No resource needs have been specified

Status

In progress

Deadline

2016/06/01 00:00:00 GMT+2

Work description

a) Classification The concentrations of nitrogen and phosphorus are reported after classification in three classes (low, medium, high). The classification uses class boundary values for each regional sea; for the NE Atlantic region, separate boundary values were calculated for the Greater North Sea and for the other seas. The classification distinguishes areas with low and high concentrations, but does not take into account that there may be large differences in natural background concentrations within regional seas. These differences are, for example, due to the riverine inputs into coastal waters. What is considered a “low” concentration in coastal waters might be considered “high” in offshore waters. One way of streamlining CSI 021 with nutrient indicators developed under regional seas conventions or European policy objectives, is to apply the same class boundaries, for instance as those used by RSCs or those applied in the WFD for transitional and coastal waters. As the implementation of the MSFD is still in progress, a future option will be to apply the environmental targets that are being developed under the MSFD. The threshold/targets established by the RSCs are already being evaluated and will be taken in consideration in future improvements of the indicator methodology. b) Geographical aggregation In the current methodology, two types of geographical aggregation are performed based on the Country Code and Sea Region. In both cases, differences in physical, chemical and biological characteristics between sampling stations are not taken into account. Measured nutrient concentrations should be related to natural background values that reflect spatial/geographical differences. c) Temporal scale Currently, the winter period is defined as January and February for all stations except for stations east of longitude 15 degrees (Bornholm) in theBaltic Sea. However, this definition may be too broad to reflect the climatic differences across the European sea regions. For example, for the Black Sea, it is suggested to also consider spring concentrations due to the nutrient enrichment of coastal waters as a result of increased riverine inputs (BSC, 2010) whereas annual means are deemed more suitable for the Mediterranean Sea. Adjustments of the definition of seasons per subregion are currently being evaluated and will be taken into consideration in the future revision of the indicator methodology.

Resource needs

No resource needs have been specified

Status

In progress

Deadline

2016/06/01 00:00:00 GMT+2

Long term work

Work specified here will require more than 1 year (from now) to be completed.

General metadata

Responsibility and ownership

EEA Contact Info

Constança De Carvalho Belchior

Ownership

European Environment Agency (EEA)

Identification

Indicator code
CSI 021
MAR 005
Specification
Version id: 2
Primary theme: Marine Marine

Frequency of updates

Updates are scheduled every 2 years

Classification

DPSIR: State
Typology: Descriptive indicator (Type A - What is happening to the environment and to humans?)

Related content

Data used

Latest figures and vizualizations

Relevant policy documents

European Environment Agency (EEA)
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1050 Copenhagen K
Denmark
Phone: +45 3336 7100