This document describes a regional assessment of the status and trends of metal concentrations in biota in Scottish marine waters. It builds on the 2020 assessment of data from the UK’s Clean Seas Environmental Monitoring Programme conducted by the Clean Safe Seas Evidence Group. In this, assessments of status and trends were made for a large number of metal time series, each of a single metal in a single species and tissue at a single monitoring station. The regional assessment synthesises the results of the individual time series to assess status and trends at the biogeographic regional level.
The regional assessment considers the following metals: Arsenic, Cadmium, Chromium, Cobalt, Copper, Lead, Mercury, Nickel, Selenium, Silver, Zinc.
The regional assessment synthesises data from monitoring stations that are in estuarine, coastal and offshore waters. The results might therefore differ from regional assessments for Marine Strategy purposes, which exclude estuarine stations.
The following sections:
A time series of metal concentrations is assessed for status if:
The conditions are more stringent for trends. Specifically, a time series is assessed for trends if:
Note that all trend assessments for individual time series and most status assessments are based on the fit of a parametric model. This is important because only the parametric results are passed into the regional assessments in the following sections. As it turns out, none of the metal time series were assessed for status using a non-parametric test.
The first tab below shows all the monitoring stations where there are individual time series assessments of trend or status for metals. The purple circles are stations where there is a trend assessment for at least one metal, and the light blue cirles are stations where there are only status assessments.
The next set of tabs show the trend and status assessments for each metal in turn. The colours have the following meaning:
And the shapes have the following meaning:
The final set of tabs give:
Note that:
Number of time series with upwards, downwards or no trend by biogeographic region
region | status | Cadmium | Lead | Mercury | total |
---|---|---|---|---|---|
Northern North Sea | upward trend | 6 | 3 | 8 | 17 |
no trend | 14 | 20 | 21 | 55 | |
downward trend | 8 | 5 | 7 | 20 | |
Scottish Continental Shelf | upward trend | 1 | 0 | 0 | 1 |
no trend | 3 | 5 | 5 | 13 | |
downward trend | 1 | 0 | 0 | 1 | |
Minches & W Scotland | upward trend | 1 | 1 | 2 | 4 |
no trend | 7 | 6 | 9 | 22 | |
downward trend | 0 | 1 | 0 | 1 | |
Irish Sea | upward trend | 2 | 1 | 3 | 6 |
no trend | 10 | 10 | 14 | 34 | |
downward trend | 1 | 3 | 0 | 4 | |
total | upward trend | 10 | 5 | 13 | 28 |
no trend | 34 | 41 | 49 | 124 | |
downward trend | 10 | 9 | 7 | 26 |
Proportion of time series with upwards, downwards or no trend by biogeographic region
region | status | Cadmium | Lead | Mercury | total |
---|---|---|---|---|---|
Northern North Sea | upward trend | 21 | 11 | 22 | 18 |
no trend | 50 | 71 | 58 | 60 | |
downward trend | 29 | 18 | 20 | 22 | |
Scottish Continental Shelf | upward trend | 20 | 0 | 0 | 7 |
no trend | 60 | 100 | 100 | 86 | |
downward trend | 20 | 0 | 0 | 7 | |
Minches & W Scotland | upward trend | 12 | 13 | 18 | 15 |
no trend | 88 | 75 | 82 | 81 | |
downward trend | 0 | 12 | 0 | 4 | |
Irish Sea | upward trend | 15 | 7 | 18 | 14 |
no trend | 77 | 72 | 82 | 77 | |
downward trend | 8 | 21 | 0 | 9 | |
total | upward trend | 18 | 9 | 19 | 16 |
no trend | 63 | 75 | 71 | 70 | |
downward trend | 19 | 16 | 10 | 14 |
Number of time series with each status by biogeographic region
region | status | Cadmium | Lead | Mercury | total |
---|---|---|---|---|---|
Northern North Sea | blue | 8 | 0 | 0 | 8 |
green | 0 | 0 | 0 | 0 | |
orange | 23 | 31 | 0 | 54 | |
red | 0 | 0 | 44 | 44 | |
Scottish Continental Shelf | blue | 1 | 0 | 0 | 1 |
green | 0 | 0 | 0 | 0 | |
orange | 4 | 5 | 0 | 9 | |
red | 0 | 0 | 5 | 5 | |
Minches & W Scotland | blue | 0 | 1 | 0 | 1 |
green | 0 | 0 | 0 | 0 | |
orange | 8 | 7 | 0 | 15 | |
red | 0 | 0 | 11 | 11 | |
Irish Sea | blue | 3 | 1 | 0 | 4 |
green | 0 | 0 | 1 | 1 | |
orange | 11 | 13 | 0 | 24 | |
red | 0 | 0 | 18 | 18 | |
total | blue | 12 | 2 | 0 | 14 |
green | 0 | 0 | 1 | 1 | |
orange | 46 | 56 | 0 | 102 | |
red | 0 | 0 | 78 | 78 |
Proportion of time series with each status by biogeographic region
region | status | Cadmium | Lead | Mercury | total |
---|---|---|---|---|---|
Northern North Sea | blue | 26 | 0 | 0 | 8 |
green | 0 | 0 | 0 | 0 | |
orange | 74 | 100 | 0 | 51 | |
red | 0 | 0 | 100 | 41 | |
Scottish Continental Shelf | blue | 20 | 0 | 0 | 7 |
green | 0 | 0 | 0 | 0 | |
orange | 80 | 100 | 0 | 60 | |
red | 0 | 0 | 100 | 33 | |
Minches & W Scotland | blue | 0 | 12 | 0 | 4 |
green | 0 | 0 | 0 | 0 | |
orange | 100 | 88 | 0 | 55 | |
red | 0 | 0 | 100 | 41 | |
Irish Sea | blue | 21 | 7 | 0 | 9 |
green | 0 | 0 | 5 | 2 | |
orange | 79 | 93 | 0 | 51 | |
red | 0 | 0 | 95 | 38 | |
total | blue | 21 | 3 | 0 | 7 |
green | 0 | 0 | 1 | 1 | |
orange | 79 | 97 | 0 | 52 | |
red | 0 | 0 | 99 | 40 |
Tabulating the number of time series with each status category by region provides a quick summary of the individual time series results. However, it does not provide an objective regional assessment of status. Similarly, tabulating the number of time series with an upward or downward trend does not provide an objective regional assessment of trend. This section describes how the individual time series results can by synthesised in a meta-analysis to assess both status and trend at the regional level.
For a regional trend assessment, the trend in each time series is summarised by the estimated change in log concentration over the last twenty years (or shorter if the time series doesn’t extend that far back). Regional trends are then estimated by fitting the following linear mixed model by restricted maximum likelihood:
The fixed model means that a separate regional trend is estimated for each metal. The random model has four terms:
The meta-analysis is restricted to time series from monitoring stations that are classified as ‘representative’ or ‘baseline’ (near pristine conditions or only subject to very diffuse inputs). ‘Impacted’ stations (those close to a point source) are omitted because trends there will likely reflect changes due to the point source and will be ‘unrepresentative’ at the regional level.
The meta-analysis is further restricted to region and metal combinations with at least three trend stations with good geographic spread. Three stations is considered the minimum required to provide some sort of evidence base at the regional level.
For a regional status assessment, the status of each time series is summarised by the difference between the estimated mean log concentration in the final monitoring year and the log assessment concentration. This ensures that status is always measured on the same scale, even though the assessment concentration might vary between metals and species. The regional status against the BAC is assessed by fitting essentially the same linear mixed model as for trends:
where status estimation variation is the variation in the status estimates from the individual time series analysis, assumed known and fixed.
The regional status assessment against the QSsp has only one metal (mercury) and incorporates a trophic adjustment in the fixed model. This is in the form of a two-level categorical variable, labelled class, that distinguishes bivalves from fish. The model is:
Essentially, the class effect adjusts mercury concentrations in bivalves to fish equivalents giving regional mean concentrations standardized to fish. These can be thought of as the mean concentrations that would have been observed had fish been monitored at every station. The model also includes a species random effect to allow for variation between bivalve species and between fish species. The development of this model was based on the data in the 2021 OSPAR CEMP assessment and is described here.
There are no restrictions on the time series used in the status meta-analysis based on the classification of the monitoring station; time series from baseline, representative and impacted stations are all included.
Again, the meta-analysis is restricted to regions and metal combinations with at least three status stations with good geographic spread.
The results of both the trend and status regional assessments are back-transformed for presentation. The estimated regional trend is then interpreted as the percentage yearly change in concentration and the estimated regional status as the ratio of the mean regional concentration to the assessment concentration. To illustrate the latter, a value of 1 indicates that the mean regional concentration is equal to the assessment concentration; a value of 0.5 indicates that it is half the assessment concentration, and a value of 2 indicates that it is twice the assessment concentration.
This section provides more detail on the number and geographic spread of the time series available for the meta-analyses. The map shows the stations with parametric trend and status assessments having excluded trend assessments at baseline and impacted stations. The purple circles are stations where there is a trend assessment for at least one metal, and the light blue cirles are stations where there are only status assessments.
The following regions have an insufficient number or time series or spread of stations and are excluded from the regional assessment:
The first 3 tabs show:
The symbols in all these plots have the following interpretation:
The final tab shows the estimates of the regional trend by metal.
This table shows the estimates of the regional trend by determinand:
region | metal | trend | se | lower | upper | % yearly change | %yc lower | %yc upper |
---|---|---|---|---|---|---|---|---|
Northern North Sea | Arsenic | -0.79 | 0.59 | -1.95 | 0.36 | -0.79 | -1.93 | 0.36 |
Cadmium | -0.23 | 0.64 | -1.49 | 1.03 | -0.23 | -1.48 | 1.03 | |
Chromium | 2.27 | 0.98 | 0.36 | 4.19 | 2.30 | 0.36 | 4.28 | |
Cobalt | -0.25 | 1.60 | -3.38 | 2.88 | -0.25 | -3.32 | 2.92 | |
Copper | -0.90 | 0.60 | -2.08 | 0.29 | -0.89 | -2.06 | 0.29 | |
Lead | -0.26 | 0.69 | -1.60 | 1.09 | -0.26 | -1.59 | 1.10 | |
Mercury | 0.64 | 0.60 | -0.54 | 1.81 | 0.64 | -0.53 | 1.83 | |
Nickel | 0.75 | 0.74 | -0.71 | 2.20 | 0.75 | -0.71 | 2.23 | |
Selenium | -0.20 | 0.82 | -1.81 | 1.41 | -0.20 | -1.79 | 1.42 | |
Silver | 4.61 | 3.38 | -2.02 | 11.24 | 4.72 | -2.00 | 11.90 | |
Zinc | -0.81 | 0.56 | -1.91 | 0.30 | -0.80 | -1.89 | 0.30 | |
Minches & W Scotland | Arsenic | 0.99 | 1.19 | -1.34 | 3.31 | 0.99 | -1.33 | 3.37 |
Cadmium | 2.00 | 1.44 | -0.82 | 4.82 | 2.02 | -0.81 | 4.94 | |
Chromium | 0.95 | 1.75 | -2.47 | 4.38 | 0.96 | -2.44 | 4.48 | |
Cobalt | -0.26 | 2.51 | -5.17 | 4.65 | -0.26 | -5.04 | 4.76 | |
Copper | -0.42 | 1.18 | -2.73 | 1.90 | -0.41 | -2.69 | 1.91 | |
Lead | -1.85 | 1.58 | -4.95 | 1.24 | -1.84 | -4.83 | 1.25 | |
Mercury | 0.29 | 1.34 | -2.34 | 2.91 | 0.29 | -2.31 | 2.95 | |
Nickel | -0.03 | 1.74 | -3.44 | 3.38 | -0.03 | -3.38 | 3.44 | |
Zinc | -0.66 | 1.12 | -2.86 | 1.54 | -0.66 | -2.82 | 1.55 | |
Irish Sea | Arsenic | -0.48 | 0.98 | -2.39 | 1.43 | -0.48 | -2.36 | 1.44 |
Cadmium | -1.85 | 1.12 | -4.04 | 0.33 | -1.84 | -3.96 | 0.33 | |
Chromium | -5.92 | 1.51 | -8.89 | -2.95 | -5.75 | -8.50 | -2.91 | |
Copper | -0.47 | 0.98 | -2.39 | 1.45 | -0.47 | -2.36 | 1.46 | |
Lead | -1.95 | 1.22 | -4.35 | 0.44 | -1.94 | -4.26 | 0.44 | |
Mercury | 0.40 | 1.01 | -1.59 | 2.39 | 0.40 | -1.57 | 2.42 | |
Nickel | -3.65 | 1.44 | -6.47 | -0.83 | -3.59 | -6.27 | -0.83 | |
Zinc | -0.69 | 1.00 | -2.65 | 1.27 | -0.69 | -2.61 | 1.28 |
The first 3 tabs show:
The symbols in all the plots have the following interpretation:
Note that to see why some points might be coloured blue, it is necessary to look ahead to the next section, where status is compared to the BAC. Unfortunately, it isn’t easy to present the assessment of status relative to the QSsp with the assessment of status relative to the BAC because the ratio of the BAC to the QSsp can vary between metals and species.
The final tab shows the estimates of the regional status by metal.
This table shows the estimates of the regional trend by determinand:
region | metal | status | se | upper | concentration | conc upper |
---|---|---|---|---|---|---|
Northern North Sea | Cadmium | |||||
Copper | ||||||
Lead | ||||||
Mercury | 1.80 | 0.12 | 2.00 | 6.04 | 7.36 | |
Zinc | ||||||
Minches & W Scotland | Cadmium | |||||
Copper | ||||||
Lead | ||||||
Mercury | 1.35 | 0.19 | 1.67 | 3.85 | 5.30 | |
Zinc | ||||||
Irish Sea | Cadmium | |||||
Copper | ||||||
Lead | ||||||
Mercury | 1.40 | 0.15 | 1.65 | 4.07 | 5.22 | |
Zinc |
The first 3 tabs show:
The symbols in all the plots have the following interpretation:
The final tab shows the estimates of the regional status by metal.
This table shows the estimates of the regional trend by determinand:
region | metal | status | se | upper | concentration | conc upper |
---|---|---|---|---|---|---|
Northern North Sea | Cadmium | 0.89 | 0.21 | 1.24 | 2.43 | 3.46 |
Copper | 0.57 | 0.23 | 0.95 | 1.77 | 2.59 | |
Lead | 0.82 | 0.21 | 1.17 | 2.27 | 3.23 | |
Mercury | 1.51 | 0.23 | 1.89 | 4.54 | 6.64 | |
Zinc | 0.96 | 0.23 | 1.33 | 2.60 | 3.80 | |
Minches & W Scotland | Cadmium | 0.88 | 0.42 | 1.57 | 2.41 | 4.83 |
Copper | 0.42 | 0.45 | 1.16 | 1.52 | 3.18 | |
Lead | 0.38 | 0.43 | 1.08 | 1.46 | 2.95 | |
Mercury | 0.95 | 0.45 | 1.69 | 2.58 | 5.43 | |
Zinc | 0.66 | 0.45 | 1.41 | 1.94 | 4.10 | |
Irish Sea | Cadmium | 0.41 | 0.31 | 0.92 | 1.50 | 2.51 |
Copper | 0.39 | 0.33 | 0.93 | 1.47 | 2.55 | |
Lead | 0.72 | 0.31 | 1.23 | 2.05 | 3.44 | |
Mercury | 0.91 | 0.33 | 1.46 | 2.48 | 4.30 | |
Zinc | 0.52 | 0.34 | 1.08 | 1.68 | 2.94 |