Skip to main content

Full text: Deriving pre-eutrophic conditions from an ensemblemodel approach for the North-West European seas

van Leeuwen et al. 
rivers. For P loads, E-HYPE percentage results were used for most 
vers, but for some rivers alternative estimates were used. Due to 
‚arge differences between E-HYPE and the finer scale catchment 
models, and uncertainty in the E-HYPE P load estimation 
‚Donnelly et al., 2013; Stegert et al., 2021), its historic P load 
percentages were replaced for rivers where alternative, more 
detailed information was available, as follows. The Danish 
authorities, basing their estimates on Timmermann et al. (2021) 
set their pre-eutrophic P loads at 36% of current day loads for all 
Danish rivers. The German authorities opted to use the MONERIS 
results for P loads in German rivers. In bilateral negotiations with 
‚he Netherlands, Dutch riverine P loads of rivers arriving through 
German territory (or severely interlaced with such rivers) were 
adjusted to reflect the MONERIS results (Rhine, Meuse, Lake 
IJssel). Note that E-HYPE historical nutrient levels were not used, 
only the E-HYPE estimate of the percentage change in riverine 
nutrients compared to current day loads. E-HYPE coastal areas 
were then linked to actual rivers, and the CS and HS riverine loads 
were derived from the observation-based ICG-EMO riverine 
database for 2006-2014, using 100% and the reduction percentage 
estimates, respectively. The reduction percentages are shown in 
Figure 4, while Appendix A provides the same information as a 
table. No change was applied to rivers with pre-eutrophic loads 
higher than current loads (mainly Scottish rivers north of Inverness 
where populations have declined), in order to preserve reduction 
effects from other rivers. River freshwater discharges were kept at 
current day levels and therefore are equal to those of the simulated 
period: this choice was made to allow for easier definition of 
(achievable) nutrient reductions in the current situation. 
Estimates of atmospheric nitrogen deposition rates around 1900 
were calculated based on the trends in TOxN and NH; emissions 
Historic Scenario N levels 
Historic level 
3$ „urrent day 
100 
Y 
10.3389/fmars.2023.1129951 
estimated by Schöpp et al. (2003) over Europe, including its 
marginal seas. These trends were then used to estimate the 
spatially resolved nitrogen deposition rate estimates by EMEP 
\2020) for the years 1890-1900 following the method of Große 
et al. (2016). Table 2 shows the current and pre-eutrophic 
atmospheric deposition rates estimated by Schöpp et al. (2003), 
and their ratio. These historic/current ratios are applied to current 
deposition fields from EMEP to estimate historic atmospheric 
deposition rates. Atmospheric phosphorous deposition rates were 
deemed negligible, both in the current state and historical scenario. 
For the nutrient inputs across model open boundaries, we 
assumed that boundaries to the open sea were sufficiently far 
away from riverine sources to not be affected by nutrient 
reductions, and these were kept the same for CS and HS. For the 
Baltic boundary a different approach was taken, as the Baltic is 
highly eutrophic. As such, the pre-eutrophic boundary should 
reflect the historic nutrient status at the Darss sill and Drogden 
sill. Reduction percentages for nutrients at these locations were 
derived from a long model simulation (1850 - 2008) with the 
ERGOM model provided by Thomas Neumann (IOW, Germany). 
The resulting historic percentages (compared to current-day loads) 
are given in Table 3. 
2.7 Weighted ensemble method 
As models have varying skills in different areas, and variables, 
we applied the weighted ensemble approach of Almroth and Skogen 
2010) to calculate ensemble averages. This method uses 
observations to determine a model’s skill in representing a certain 
variable in a certain area, and assigns appropriate weights to the 
. . . Historic level 
Historic Scenario P levels % of current day 
65 
ar 
5} 
E 
a 
1 
50 
rh 
Pe 
u 
3 
U 
Longitude [deg. LE 
1Ur 
P 
k 
vv 
Longitude [deg. 
FIGURE 4 
?re-eutrophic riverine loads as percentages of current day loads. Left: pre-eutrophic N loads, right: pre-eutrophic P loads. 
"rontiers in Marine 1cience 
frontiersin.org
	        
Waiting...

Note to user

Dear user,

In response to current developments in the web technology used by the Goobi viewer, the software no longer supports your browser.

Please use one of the following browsers to display this page correctly.

Thank you.