Number of time series available showing increasing, decreasing or no trends in dissolved inorganic nitrogen and orthophosphate concentrations for each regional sea for two time periods; Pre 2000 (1980-1999) and Post 2000 (2000-2023)
Chart (interactive)
The different sea regions are presented by one bar each. The numbers corresponds to the number of grid cells (time series) with statistically significant (p<0.05) decreasing trends (green), increasing trends (orange) and no trends (grey) for two time periods; Pre 2000 (1980-1999) and Post 2000 (2000-2023). P is a statistical term describing the probability that the trend is significant.
European Environment AgencyNIVA Denmark water reaserch
Units
Number of time series
Additional information
* The trends for the barcharts have been calculated using the 10x10 EEA grid to provide a more accurate representation of time series availability. * The temporal range specified is the maximum range of dates for raw observations but this range varies upon the availability of observations at each location. * The different sea regions are presented by one bar each; additional bar is added to show European results.
Methodology
* Trends in concentrations of the nutrients, nitrogen (dissolved inorganic nitrogen - DIN) and dissolved inorganic phosphorus (DIP, as orthophosphate, in the upper 10m of the water column in European seas during the season of low phytoplankton growth (SLPG) are shown for two time periods; Pre 2000 (1980-1999) and Post 2000 (2000-2023). * DIN refers to the sum of ammonium, nitrite and nitrate concentrations, although in many samples not all three forms of nitrogen were measured. During the winter period the nitrate concentration can be used to represent DIN as the contribution form ammonium and nitrite are very low. If nitrate was missing the DIN was not estimated for that observatuion. * Data were aggregated into squares with sides of squares with sides of 1.375km for coastal stations within 20km from the coastline (m=80) and 5.5 km for open water station more than 20km away from the coastline (m=20). A masking of 5km inwards from the coast was also applied. The aggregated data were transffered to the offcial EEA assessment grid of 10km. * The trends were calculated based on yearly averages for each grid cell.The averages were calculated using a combination of estimated marginal means (EMM) and arithmetic means, where the EMM were used for time series containing data from both different years and months and the arithmetic means were used for time-series with yearly observations. * Temporal trends were estimated with the non-parametric Mann-Kendall test. Only stations having data of at least 5 years were considered. A p-value <0.05 was used to consider a statistically significant trend. * Green bars indicate time-series in grid cells with significant (p<0.05) decreasing trends; orange bars show time-series in grid cells with significant (p<0.05) increasing trends; and grey bars show time-series in grid cells with no significant trends. * SLPG was considered for the winter months: January - March for stations within Baltic Sea and east of 15E and January - February was used for all other stations.
