Chlorophyll Concentrations in the Water Column

Chlorophyll concentrations in UK marine waters of the Greater North Sea and the Celtic Seas are generally below levels used in the diagnosis of eutrophication. Since 1990, there has been no significant change in chlorophyll concentration and this meets the target set. 

Background

UK Targets on chlorophyll concentrations

The UK targets for the direct effects of nutrient enrichment include the indicator for chlorophyll concentrations in the water column. The UK target for eutrophication ‘non-problem areas’ is that there should be no increase in the chlorophyll 90^th percentile in the growing season (linked to increasing anthropogenic input) based on periodic surveys. Percentiles describe statistical distribution.  The 90^th percentile value is the concentration greater than 90% of observations, or conversely less than 10% of observations.

Key pressures and impacts

In the UK Initial Assessment (HM Government, 2012) the key pressures associated with this indicator were the riverine and direct inputs of nutrients (nitrogen and phosphorus) from various industrial and diffuse sources and atmospheric deposition. These are still relevant, but, considering that eutrophication problem areas are generally limited to a small number of coastal waters, estuaries and embayments, the key pressures are likely to be related to local agriculture and wastewater treatment.

Measures taken to address the impacts

The UK Marine Strategy Part Three (HM Government, 2015) describes the robust UK legislative framework for controlling and reducing discharges, emissions and losses of nutrients from sources affecting specific eutrophication problem areas. Measures include the Water Framework Directive (European Commission, 2000) River Basin Management Plans which are particularly relevant for UK problem areas in estuarine and coastal waters. There are improvements in some of the places where measures are in place but, it can take many years for those measures to take effect.

Monitoring and assessment

Risk based monitoring of chlorophyll is carried out under the Clean Seas Environment Monitoring Programme and assessments follow OSPAR guidance and procedures (OSPAR Commission, 2013). Mann-Kendall tests are used to analyse trends.

Regional cooperation

The UK regularly reports information on chlorophyll concentrations to OSPAR and has contributed to the monitoring and assessment of the OSPAR chlorophyll common indicator. The UK results have been used in the OSPAR Intermediate Assessment 2017 (OSPAR Commission, 2017).

Further information

Phytoplankton (algae; Figure 1) contain chlorophyll and their concentration in seawater is related to the level of nutrients which are present in the water column. Eutrophication is the result of excessive enrichment of water with nutrients. This may cause accelerated growth of algae and/or higher forms of plant life and may result in an undesirable disturbance to the balance of organisms present and overall water quality. Undesirable disturbances include shifts in the composition and extent of flora and fauna and depletion of oxygen due to decomposition of accumulated biomass. Such disturbances can have other effects such as changes in habitats and biodiversity, blooms of nuisance algae or macroalgae, and behavioural changes or death of fish and other species. Low oxygen levels, for example, may result in increased abundances of species which are able to tolerate low oxygen conditions. Very low oxygen levels may result in death of marine organisms. Identifying causal links between disturbances and nutrient enrichment is often difficult and complicated by other pressures. Cumulative effects of global change, including climate change, may have similar effects on biological communities and dissolved oxygen, complicating efforts to demonstrate causal links. Although oxygen depletion can be an indirect effect of nutrient enrichment, other factors which influence oxygen concentrations include changes in water temperature and salinity. Additionally, some degree of seasonal oxygen depletion is a natural process, particularly where the water column stratifies seasonally.

Figure 1. Different types of phytoplankton found in UK waters (source: Richard Kirby; the Secchi disk study).

 

For the Marine Strategy Framework Directive Article 8 (European Commission, 2008) UK Assessment of Eutrophication (HM Government, 2012), four eutrophication criteria have been assessed: riverine inputs, nutrient concentrations and ratios, chlorophyll concentrations, and dissolved oxygen levels (see Figure 2). The individual assessment results of any one of these indicators do not diagnose eutrophication by themselves, however, the assessments provide useful information about trends and are important for informing management measures (Painting and others, 2016).

Figure 2. Three stages in the identification of eutrophication. The criteria marked ¹ are common indicators for the OSPAR Intermediate Assessment 2017. The criteria marked ² are not relevant in all Contracting Parties’ waters.

Assessment method

For this assessment, chlorophyll concentrations in marine waters (salinity ≥ 30) were analysed for the Greater North Sea and Celtic Seas, and for the sub-regions/regional seas within the Greater North Sea and Celtic Seas. For the Greater North Sea, sub-regions are the northern North Sea, the southern North Sea and the eastern English Channel. For the Celtic Seas, sub-regions are the western Channel and Celtic Sea, the Irish Sea, Minches and western Scotland, the Scottish Continental Shelf and the Atlantic North-West Approaches.

Data on chlorophyll concentrations, and all supporting information (for example, latitude, longitude, water column depth, sample depth, temperature, salinity) were obtained from 1990 until 2014 (Figure 3). Data were obtained from the International Council for the Exploration of the Sea database and from national (the UK Marine Environment Monitoring and Assessment National database (MERMAN), National Oceanographic Database) and institutional databases (Cefas Sapphire and SmartBuoy, Marine Scotland Science). All available data were used, collected using all sampling platforms (such as ships and submersible sensors), and analysed by all analytical methods (for example fluorometry, spectrophotometry and pigment analysis, see Baretta-Bekker and others, 2015; Walsham and others, 2015). Duplicates between databases were removed. Data were averaged over the whole water column for each cruise station and day, with the exception of the Marine Environment Monitoring and Assessment National database data where date and time were used instead of day as there were multiple records in different locations (along transects) for the same station and day. Continuous data from SmartBuoys were averaged over 7-day intervals to be equivalent to survey-based data (see Capuzzo and others, 2015). These averages were included in the final data set. Data were filtered by salinity, to assign to coastal waters (salinity 30 - <34.5 in all sub-regions, except in the Irish Sea, 30 - <34) or offshore waters (salinity >34.5 in all sub-regions, except in the Irish Sea, salinity >34), and by season for chlorophyll (growing season, March to October inclusive). Chlorophyll 90^th percentiles were calculated over the growing season.

Figure 3. Map showing where data on growing season chlorophyll concentrations were available, 1990 to 2014. X = sampling locations at coastal (red) and offshore (blue) sites. Locations of Cefas SmartBuoy moorings and benthic landers, and Scottish coastal monitoring sites are shown. Active moorings in the southern North Sea (West Gabbard, the Warp, Dowsing) and Liverpool Bay are indicated by red triangles; other moorings and landers are currently inactive.

The 90^th percentiles were plotted per year to identify trends in the data. Where fewer than five data points were available in any given year in an assessment area, these data points were excluded in order to improve the robustness of the analysis. Mann-Kendall non-parametric tests were used for trend analysis (Mann, 1945; Kendall, 1975; Barry and Maxwell, 2015). Where p-values are greater than 0.05, a trend cannot be detected statistically. Where p-values are less than 0.05, it is assumed that there is a significant trend. Where trends were significant, weighted least squares regression lines were calculated, using the 95% confidence intervals for the means.

For assessments of status (2006-2014), growing season chlorophyll 90^th percentiles were compared against assessment thresholds for coastal waters (15 µg l^-1) and offshore waters (10 µg l^-1. Determination of the reference values and thresholds used for chlorophyll in coastal and offshore waters is described in Foden and others (2011). For chlorophyll, 90^th percentiles during the growing season should be below the assessment thresholds.

Confidence ratings of chlorophyll 90^th percentiles being below area-specific thresholds were calculated (2006-2014) using the approach described in Annex 8 of the OSPAR guidance (OSPAR Commission, 2013). The representativeness of the available data in space and time was calculated by following an approach similar to that described in the OSPAR guidance (OSPAR Commission, 2013). Overall confidence in representativeness is provided by the worst score in either space or time.

Within each regional sea, estuarine and coastal water bodies within 1 nautical mile of baseline (3 nautical miles in Scotland) were assessed under the Nitrates Directive (European Commission, 1991b), Urban Waste Water Treatment Directive (European Commission, 1991a) and Water Framework Directive (European Commission, 2000). Assessment methods used are comparable with those used for OSPAR and Marine Strategy Framework Directive assessments. Assessment outcomes are used as the basis for reporting on eutrophication status.

Results

Findings from the 2012 UK Initial Assessment

The UK initial assessment (HM Government, 2012) did not provide specific information on chlorophyll but used the data to contribute to the assessment of eutrophication problems in marine, coastal and transitional waters in UK seas.

Latest findings

Status assessment

For marine waters, growing season 90^th percentiles for chlorophyll were below assessment levels during the assessment period (2006-2014, Figure 4) in marine waters of the Greater North Sea or Celtic Seas. This suggests that chlorophyll concentrations do not contribute to an assessment of eutrophication problems. Light availability is a significant limiting factor in some regions, particularly the southern North Sea. Confidence in the assessment methodology and in the data is high.

Figure 4. Chlorophyll 90^th percentiles over the assessment period (2006-2014).

For coastal and transitional water, the overall outcome from assessments under the Water Framework Directive and related Directives (Nitrates Directive, Urban Waste Water Treatment Directive) showed that 21 water bodies in estuarine and coastal water bodies within 1 nautical miles of baseline (3 nautical miles in Scotland) were problem areas in terms of OSPAR eutrophication status.

Trend assessment

Trend analysis (1990-2014) indicates no significant trends in chlorophyll concentrations in marine waters of the Greater North Sea and Celtic Seas, indicating that the target for trends has been met.

Confidence in the assessment methodology and in the data is high (Painting and others, 2016).

Further information

Greater North Sea and Celtic Seas

Assessment of trends

Time series of chlorophyll 90^th percentiles (Figure 5) were below the assessment thresholds in all years (1990-2014) in coastal (15 µg l^-1) and offshore waters (10 µg l^-1) in the Greater North Sea. In the Celtic Seas, chlorophyll 90^th percentiles in coastal waters were above the assessment level in four years (1996, 1997, 1999, 2004). This did not affect overall eutrophication status assessments during the assessment period, 2006-2014. Time series plots indicate considerable inter-annual variability in the data.

Results of trend assessments indicate downward trends in chlorophyll 90^th percentiles in the coastal and offshore waters of the Greater North Sea, and upward trends in the Celtic Seas (Table 1). None of the trends were shown to be significant, indicating that the trend targets have been met in both assessment regions.

Table 1. Results of Mann-Kendall analyses for growing season chlorophyll 90^th percentiles (µg l^-1) in coastal and offshore waters in the Greater North Sea and the Celtic Seas. The sign of the Mann-Kendall statistic gives the direction of the trend. Where p-values are greater than 0.05, it is assumed that there is no significant trend. n = number of years with data.

 

Region	Coastal waters			Offshore waters
	n	Mann-Kendall Statistic	p-value	n	Mann-Kendall Statistic	p-value
Greater North Sea	25	-1.1912	0.2336	24	-0.0248	0.9802
Celtic Seas	22	0.1692	0.8656	23	1.3208	0.1866

Figure 5. Growing season chlorophyll 90^th percentiles (µg l^-1) in the Greater North Sea and Celtic Seas, 1990 to 2014 in coastal (blue symbols) and offshore (orange symbols) water. No trendlines are shown as no significant trends are observed (using Mann-Kendall analysis, see Table a). Assessment thresholds (red lines) are 15 µg l^-1 in coastal water and 10 µg l^-1 in offshore waters. Results are shown for years with five or more data points. A 95% confidence interval is provided for every 90^th percentile value.

Assessment of Status

Growing season 90^th percentiles for chlorophyll over the assessment period 2006-2014 (Figure 6) did not exceed the assessment levels in coastal or offshore waters in either the Greater North Sea or Celtic Seas. This suggests that nutrient enrichment did not have direct effects on the phytoplankton biomass in these regions.

Figure 6. Growing season chlorophyll 90^th percentiles (µg l^-1) in marine waters in the Greater North Sea and Celtic Seas from 2006 to 2014. Results are shown for coastal and offshore waters, where 5 or more data points were available. Thresholds (red lines) are 15 µg l^-1 in coastal water and 10 µg l^-1 offshore.

Confidence levels in chlorophyll 90^th percentiles being below assessment thresholds are given in Table 2. These results show that confidence levels in chlorophyll assessments are high (100%) in coastal and offshore waters of the Greater North Sea and Celtic Seas.

Table 2. Confidence levels (%) for assessing whether growing season chlorophyll 90^th percentiles (µg l^-1, 2006-2014) were below the assessment threshold in coastal and offshore waters in the Greater North Sea and the Celtic Seas. n = number of available data points.

Assessment region	Coastal water		Offshore water
	%	n	%	n
Greater North Sea	100	1126	100	1401
Celtic Seas	100	1634	100	1063

Sub-regions of the Greater North Sea and Celtic Seas

The UK sub-regions/regional seas of the Greater North Sea are the northern North Sea (Region 1), southern North Sea (Region 2), and eastern English Channel (Region 3). The sub-regions/regional seas of the Celtic Seas include the western Channel and Celtic Sea (Region 4), the Irish Sea (Region 5), Minches and western Scotland (Region 6), the Scottish Continental Shelf (Region 7), and the Atlantic North-West Approaches (Region 8).

Assessment of trends

Time series of growing season chlorophyll 90^th percentiles (Figure 7) were generally below the assessment levels for coastal and offshore waters in all sub-regions assessed. There was one exception (1999) in the southern North Sea when the chlorophyll 90^th percentile in coastal waters was approximately 34 µg l^-1. In the Irish Sea, chlorophyll 90^th percentiles in coastal waters exceeded the assessment level in five years from 1996 to 2007. This did not have an impact on overall eutrophication status assessments during the assessment period, 2006-2014.

Figure 7. Trends in growing season chlorophyll 90^th percentiles (µg l^-1) in Regional Seas 1 to 8, 1990 to 2014, in coastal (blue symbols) and offshore (orange symbols) water. A 95% confidence interval is provided for every 90^th percentile value. Results are shown for years with five or more data points. Trendlines are shown only where trends are significant using Mann-Kendall analysis. Obs = observations. Assessment thresholds are 15 µg l^-1 in coastal water and 10 µg l^-1 in offshore waters. See Table 3 for names of each regional sea/sub-region.

Results of Mann-Kendall trend assessments (Table 3, Table 4 and Table 5) show significant trends (increasing) in chlorophyll 90^th percentiles in the coastal and offshore waters of the northern North Sea. Chlorophyll levels in this region were well below the assessment thresholds and the increasing trends do not appear to be linked to nutrient concentrations, which did not show significant trends. Chlorophyll trend assessments show no significant trends in other sub-regions.

Table 3. Summary of the trends obtained by applying the Mann-Kendall analyses (1990-2014) to growing season chlorophyll 90^th percentiles.    ↘ = decreasing trend, ↗ = increasing trend, - = no trend. nan = no data. N/A = not applicable. Symbols in bold indicate that the trend is statistically significant at the 95% level (α=0.05).

 

Regional Sea		Growing season Chl
	Coast		Offshore
Northern North Sea	↗		↗
Southern North Sea	-		-
English Channel	nan		-
Western Channel & Celtic Sea	-		-
Irish Sea	-		-
Minches & West Scotland	-		-
Scottish Continental shelf	-		-
Atlantic North West Approaches	N/A		-

Table 4. Results of Mann-Kendall analyses for growing season chlorophyll 90^th percentiles (µg l^-1) in coastal areas. The sign of the Mann-Kendall statistic gives the direction of the trend. Where p-values are less than 0.05, it is assumed that there is a significant trend. n = number of years with data. nan = no data. N/A = not applicable. See Table 3 for names of each regional sea/sub-region.

Regional Sea	n	Mann-Kendall Statistic	p-value
1	23	2.4303	0.0151
2	24	-1.3148	0.1886
3	1	nan	nan
4	4	0	1
5	16	-1.1259	0.2602
6	18	1.5909	0.1116
7	3	-1.1547	0.2482
8	0	N/A	nan

Table 5. Results of Mann-Kendall analyses for growing season chlorophyll 90^th percentiles (µg l^-1) in offshore areas. The sign of the Mann-Kendall statistic gives the direction of the trend. Where p-values are less than 0.05, it is assumed that there is a significant trend. n = number of years with data. See Table 3 for names of each regional sea/sub-region.

Regional Sea	n	Mann-Kendall Statistic	p-value
1	24	2.952	0.0032
2	22	-1.5231	0.1277
3	5	-0.25	0.8026
4	12	-1.1676	0.2430
5	12	-1.4423	0.1492
6	12	1.0302	0.3029
7	18	0.606	0.5445
8	17	1.607	0.1081

Assessment of Status

Growing season 90^th percentiles for chlorophyll over the assessment period (2006-2014, Figure 8) were below the assessment levels in coastal or offshore waters in all of the regional seas assessed. This suggests that nutrient enrichment did not have direct effects on the phytoplankton biomass in these regions. Light availability is considered to be a significant limiting factor in the southern North Sea (Region 2).

Figure 8. Growing season chlorophyll 90^th percentiles (µg l^-1) in marine waters in each of the regional seas (2006-2014). Results and thresholds are shown for coastal (15 µg l^-1) and offshore waters (10 µg l^-1). Results are shown where 5 or more data points were available.

Confidence levels in the assessments of chlorophyll 90^th percentiles are given in Table 6 (coastal water) and Table 7 (offshore water). These results show that confidence levels in chlorophyll 90^th percentiles being below the assessment threshold were high (87 - 100 %) in all waters assessed, except in coastal waters of English Channel (47 %) and western Channel and Celtic Sea. In coastal waters of the English Channel, these results may have been partly due to the low number of data points available (n = 6, Table 6). No data were available for coastal waters of the western Channel and Celtic Sea (Region 4).

The representativeness of chlorophyll 90^th percentiles data in time and space is given in Table 8. Representativeness was lowest (< 30 %) in the English Channel and western Channel and Celtic Seas, and highest in the Irish Sea and Minches and western Scotland.

Table 6. Coastal areas - confidence levels (%, 2006-2014) for assessing whether growing season chlorophyll 90^th percentiles (µg l^-1) were below the assessment threshold. n = number of available data points. X = no data. Shading indicates where confidence levels were <50 %. Region 8 (Atlantic North-West Approaches) is an offshore region. N/A = not applicable.

Assessment region	Chlorophyll
	%	n
1. Northern North sea	100	660
2. Southern North Sea	100	460
3. English Channel	46.86	6
4. Western Channel & Celtic Sea	x	x
5. Irish Sea	100	952
6. Minches & W Scotland	100	580
7. Scottish Continental Shelf	97.75	36
8. Atlantic North West Approaches	N/A

Table 7. Offshore areas - confidence levels (%, 2006-2014) for assessing whether growing season chlorophyll 90^th percentiles (µg l^-1) were below the assessment threshold. n = number of available data points. X = no data.

Assessment region	Chlorophyll
	%	n
1. Northern North sea	100	827
2. Southern North Sea	100	555
3. English Channel	86.49	19
4. Western Channel & Celtic Sea	100	98
5. Irish Sea	99.94	70
6. Minches & West Scotland	100	236
7. Scottish Cont Shelf	100	585
8. Atlantic North West Approaches	100	111

Table 8. Spatial and temporal representativeness of available data (as a %) for growing season chlorophyll 90^th percentiles (µg l^-1) in each of the assessment regions. Note: these analyses use all data in an assessment region, and do not consider coastal and offshore waters separately.

Assessment region	Chlorophyll
1	71.23
2	70.41
3	19.21
4	12.52
5	72.81
6	78.41
7	59.04
8	30.29

In coastal and marine systems, direct relationships between nutrient inputs and concentrations and chlorophyll concentrations cannot be easily observed. This is due to time lags and other factors which influence the growth and loss of phytoplankton biomass (such as light conditions, grazing, shifts in species composition, and transport processes), and spatial and inter-annual variability in growth conditions within the areas assessed.

Conclusions

Chlorophyll concentrations in marine waters of the Greater North Sea and the Celtic Seas met the assessment thresholds in all years in the Greater North Sea, and in most years in the Celtic Seas. No significant trends were observed, indicating that the targets have been met. This is confirmed by fact that no eutrophication problems are found in 99.97% of UK waters. Eutrophication problems remain restricted to a small number of estuaries, embayments and coastal waters which represent a small proportion (0.03%) of the total area of UK waters. Measures are in place to reduce nutrient inputs.

Assessments of chlorophyll concentrations confirm the findings of the nutrient indicators which show no significant increases in nutrient inputs and decreasing trends in nutrient concentrations in coastal waters.

Knowledge gaps

Relationships between chlorophyll and nutrients are complex due to spatial and inter-annual variability in conditions which influence the growth and loss of phytoplankton. Although there are no major knowledge gaps, and the indicator is well developed, there is a need for further development given the advancements being made in satellite remote sensing of chlorophyll concentrations, and in measurement of chlorophyll.

References

Baretta-Bekker H, Sell A, Marco-Rius F, Wischnewski J, Walsham P, Webster L, Mohlin M, Wesslander K, Ruiter H, Gohin F, Enserink L (2015) ‘The chlorophyll case study in the JMP NS/CS project’ Document produced as part of the EU project: “Towards joint Monitoring for the North Sea and Celtic Sea” (Reference: ENV/PP 2012/SEA) 72 pages (viewed 10 October 2018)

Barry J, Maxwell D (2015) ‘Tools for environmental and ecological survey design and analysis’ (viewed on 31 October 2018)

Capuzzo E, Stephens D, Silva T, Barry J, Forster RM (2015) ‘Decrease in water clarity of the southern and central North Sea during the 20th century’ Global Change Biology 21: 2206–2214 (viewed 10 October 2018)

European Commission (1991a) ‘Council Directive 91/271/EEC of 21 May 1991 concerning urban waste-water treatment’ Official Journal of the European Union L 135, 30.5.1991, pages 40–52 (viewed on 8 October 2018)

European Commission (1991b) ‘Council Directive 91/676/EEC of 12 December 1991 concerning the protection of waters against pollution caused by nitrates from agricultural sources’ Official Journal of the European Union L 375, 31.12.1991, pages 1–8 (viewed on 8 October 2018)

European Commission (2000) ‘Directive 2000/60/EC of the European Parliament and of the Council of 23 October 2000 establishing a framework for Community action in the field of water policy’ Official Journal of the European Union L 327, 22.12.2000, pages 1–73 (viewed on 8 October 2018)

European Commission (2008) ‘Directive 2008/56/EC of the European Parliament and of the Council of 17 June 2008 establishing a framework for community action in the field of marine environmental policy (Marine Strategy Framework Directive)’ Official Journal of the European Union L 164, 25.6.2008, pages 19-40 (viewed 21 September 2018)

Foden J, Devlin MJ, Mills DK, Malcolm SJ (2011) ‘Searching for undesirable disturbance: an application of the OSPAR eutrophication assessment method to marine waters of England and Wales’ Biogeochemistry 106: 157–175 (viewed 12 October 2018)

HM Government (2012) ‘Marine Strategy Part One: UK initial assessment and Good Environmental Status’ (viewed 10 October 2018)

HM Government (2015) ‘Marine Strategy Part Three: UK Programme of Measures’ (viewed on 5 July 2018)

Kendall M (1975) ‘Rank correlation methods’ 4th ed. Charles Griffith: London.

Mann, HB (1945) ‘Non-parametric tests against trend’ Econometrica 13: 245-259 (viewed 9 October 2018)

OSPAR Commission (2013) ‘Common Procedure for the Identification of the Eutrophication Status of the OSPAR Maritime Area’ OSPAR Agreement 2013-8, supersedes Agreements 1997-11, 2002-20 and 2005-3 (viewed 12 October 2018)

Painting S and others (2016) ‘Common Procedure for the Identification of the Eutrophication Status of the UK Maritime Area’ (viewed 12 October 2018)

Walsham P, Webster L, Mohlin M and others (2015) ‘Differences in methodologies for chlorophyll analysis and implications for data reporting and assessments under the Marine Strategy Framework Directive’ Annex II In Baretta-Bekker and others, 2015 (viewed 10 October 2018)

Acknowledgements

Assessment metadata

Assessment Type	UK Marine Strategy Framework Directive Indicator Assessment
	D5
	Eutrophication
	In addition to links provided in ‘References’ section above: European Court of Justice (2009) ‘Judgment of the Court (Third Chamber) of 10 December 2009, European Commission v United Kingdom of Great Britain and Northern Ireland’ Failure of a Member State to fulfil obligations - Environment - Directive 91/271/EEC - Urban waste water treatment - Article 3(1) and (2), Article 5(1) to (3) and (5) and Annexes I and II - Initial failure to identify sensitive areas - Concept of ‘eutrophication’ - Criteria - Burden of proof - Relevant date when considering the evidence - Implementation of collection obligations - Implementation of more stringent treatment of discharges into sensitive areas. Case C-390/07, European Court Reports 2009 I-00214*, ECLI identifier: ECLI:EU:C:2009:765 (viewed on 12 January 2019) OSPAR Commission (2003) ‘OSPAR integrated report 2003 on the eutrophication status of the OSPAR maritime area based upon the first application of the Comprehensive Procedure’ OSPAR Eutrophication Series, publication 189/2003. OSPAR Commission, London (viewed on 12 January 2019) OSPAR Commission (2008) ‘Second OSPAR integrated report on the eutrophication status of the OSPAR maritime area’ OSPAR Eutrophication Series, publication 372/2008. OSPAR Commission, London (viewed on 12 January 2019) OSPAR Commission (2010) ‘The North-East Atlantic Environment Strategy: Strategy of the OSPAR Commission for the Protection of the Marine Environment of the North-East Atlantic 2010-2020’ 27 pages (viewed on 12 January 2019) Painting S and others (2016) UK National Report. Common Procedure for the Identification of the Eutrophication Status of the UK Maritime Area (viewed 12 October 2018)
Point of contact email	marinestrategy@defra.gov.uk
Metadata date	Monday, October 1, 2018
Title	Nutrient levels; chlorophyll concentrations; concentrations of dissolved oxygen near the seafloor
Resource abstract	Data on primary indicators for eutrophication status (nutrients, chlorophyll and dissolved oxygen) were assessed for the UK sector of the Greater North Sea and the Celtic Seas. Targets have been met for nutrients, chlorophyll and dissolved oxygen concentrations. Problem areas are limited to 21 areas in estuarine and inshore coastal waters.
Linkage	Painting S and others (2016) UK National Report. Common Procedure for the Identification of the Eutrophication Status of the UK Maritime Area (viewed 12 October 2018)
Conditions applying to access and use	© Crown 2018 copyright Defra, licenced under the Open Government Licence (OGL). and OSPAR Data terms and conditions.
Assessment Lineage	Data were obtained for both OSPAR and Marine Strategy Framework Directive assessments. Data on chlorophyll concentrations, and all supporting information (e.g. latitude, longitude, water column depth, sample depth, temperature, salinity) were obtained from 1990 until 2014. Data were obtained from the ICES database and from national (MERMAN, NODB) and institutional databases (Cefas Sapphire and SmartBuoy databases, Marine Scotland Science). All available data were used, collected using all sampling platforms (e.g. ships and submersible sensors), and analysed by all analytical methods (e.g. fluorometry, spectrophotometry and pigment analysis). Duplicates between databases were removed. Data were averaged over the whole water column for each cruise station and day, with the exception of MERMAN data where datetime was used instead of day as there were multiple records in different locations (along transects) for the same station and day. Continuous data from SmartBuoys were averaged over 7-day intervals to be equivalent to survey based data; these averages were included in the final data set. Data were filtered by salinity, to assign to coastal waters (salinity 30 - <34.5) or offshore waters (salinity >34.5). For the OSPAR Common Procedure, salinity filters for the Irish Sea were 30 - <34 for coastal waters and >34 for offshore waters), and by season for chlorophyll (growing season, March to October inclusive). Chlorophyll 90th percentiles were calculated over the growing season. The 90th percentiles were plotted per year to identify trends in the data. Where fewer than five data points were available in any given year in an assessment area, these data points were excluded, in order to improve the robustness of the analysis. Mann-Kendall non-parametric tests were used for trend analysis (Mann 1945; Kendall 1975; Barry and Maxwell 2015). Where p-values are greater than 0.05, a trend cannot be detected statistically. Where p-values are less than 0.05, it is assumed that there is a significant trend. Where trends were significant, weighted least squares (WLS) regression lines (see http://statsmodels.sourceforge.net/) were calculated, using the 95% confidence intervals for the means. For assessments of status (2006-2014), growing season chlorophyll 90th percentiles were compared against assessment thresholds for coastal waters (15 µg l-1) and offshore waters (10 µg l-1, see Foden et al 2011). Determination of the reference values and thresholds used for chlorophyll in coastal and offshore waters is described in Foden et al (2011). For chlorophyll, 90th percentiles during the growing season should be below the assessment thresholds.
Indicator assessment results
Dataset metadata
Dataset DOI	Contact marinestrategy@defra.gov.uk

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Recommended reference for this indicator assessment

Suzanne Painting¹, Kate Collingridge¹, Luz Garcia¹, Jon Barry¹, Simon Leaf², Mike Best², Alison Miles², Michael McAliskey³, Mark Charlesworth⁴, Lucie Haines⁴, Rob Fryer⁵, Pamela Walsham⁵, Lynda Webster⁵, Eileen Bresnan⁵, Ashley Roberts⁶, Clare Scanlan⁶ and Clemens Engelke⁶ 2018. Chlorophyll concentration. UK Marine Online Assessment Tool, available at: https://moat.cefas.co.uk/pressures-from-human-activities/eutrophication/chlorophyll/

¹Centre for Environment, Fisheries and Aquaculture Science

²Environment Agency

³Department of Environment, Agriculture & Rural Affairs, Northern Ireland

⁴Natural Resources Wales

⁵Marine Scotland

⁶Scottish Environment Protection Agency