Work due 01 Jan 2013
Medium term work: 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) description of nitrogen compounds, b) units, c) classification, d) geographical aggregation, e) temporal scale and f) salinity correction.
a) Description of nitrogen compounds:
The description of nitrogen is limited to oxidized nitrogen (nitrite + nitrate) and does not include ammonium (NH4) which is another important inorganic nitrogen compound. This approach deviates from the common practice in OSPAR and HELCOM, where all dissolved inorganic nitrogen compounds (described as DIN=nitrite+nitrate+ammonium) are taken into consideration. It also differs from the approach in the WFD where generally also DIN concentrations are reported. In many cases, ammonium is a substantial fraction of winter average DIN and a description of oxidized nitrogen (nitrite+nitrate) alone may therefore significantly underestimate eutrophication status.
The concentrations of nitrogen and phosphorus are reported after classification in three classes (low, moderate, high). The classification uses class boundary values for each regional sea. The classification 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 mixing of river water with oceanic water, resulting in a negative relation between nutrient concentrations and salinity. Therefore, salinity-correction based on salinity data is needed for a more consistent comparison. 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 between good and moderate ecological status as in the WFD. 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.
c) 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.
d) 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 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).
f) Salinity correction:
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. Salinity gradients cause conditions in the surface water bodies to vary greatly. Therefore, the use of a simple mixing model to calculate individual surface water body reference conditions corrected for background nutrient concentrations according to salinity will be investigated.
- Access to more data in terms of spatial coverage and time series
- Data associated with unique station identifiers
- Methods developed for comparing data from the same region over different years, visualisation techniques investigated
- Salinity-correction based on salinity data
- Streamlining class boundaries with boundaries defined as part of European water policies