Trends in dissolved inorganic nitrogen and orthophosphate concentrations in transitional, coastal and marine waters in Europe, for two periods; Pre 2000 (1980-1999) and Post 2000 (2000-2023)

Additional information

• Data with bad quality flags (bad value, probably bad value), uncertain (value in excess, uncertain value, missing value) or duplicates were discarded and the 99.9% percentile of the highest values were sorted out.
• 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 first aggregated into squares with sides of 1.375km for coastal stations within 20km from the coastline (m=80) and 5.5km 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 hybrid grid of 20km in coastal areas and 100km for open sea areas. 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.
• SLPG was considered for the winter months: January - March for stations within Baltic Sea and east of 15 E and January – February was used for all other stations.

Temporal coverage
1980-2023 (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).