JOINT POLICY BRIEF
30-09-2025
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JOINT POLICY BRIEF
In oduc ion
Eu ophica ion has eme ged as one o he mos pe sis en and widesp ead en i onmen al challenges a ec ing
aqua ic ecosys ems ac oss No hwes e n Eu ope o e he pas cen u y. D i en p ima ily by excessi e nu ien
inpu s—pa icula ly ni ogen and phospho us— om ag icul u e, was ewa e , and indus ial sou ces,
eu ophica ion has se e ely impac ed ma ine, coas al and eshwa e sys ems. These nu ien o e loads ha e led
o algal blooms, oxygen deple ion, biodi e si y loss, and he deg ada ion o wa e quali y, h ea ening bo h
ecological in eg i y and socio-economic ac i i ies such as ishe ies, ou ism, and d inking wa e supply. Despi e
decades o policy in e en ions and echnological
imp o emen s, he p oblem emains deeply en enched,
highligh ing he need o coo dina ed, c oss-sec o al
s a egies ha add ess bo h legacy pollu ion, cu en
nu ien managemen and eme ging p essu es, including
clima e change.
In suppo o i s Ze o Pollu ion Ac ion Plan, he EU
suppo ed h ee p ojec s (NAPSEA, NORDBALT-ECOSAFE
and NEW-HARMONICA) wi h he objec i es o de elop and
demons a e me hodologies o:
- Iden i y sa e ecological bounda ies o ni ogen and
phospho us and load educ ion a ge s.
- Quan i y sou ces and pa hways o ni ogen and
phospho us om sou ce o sea.
- Quan i y he impac o clima e change on hese
sou ces and pa hways om sou ce o sea.
- De elop mo e e ec i e go e nance app oaches.
These p ojec s di e ed in geog aphical scope (spa ial
domains shown in Figu e 1) and scien i ic app oach. This
policy b ie summa izes he esul s o he h ee p ojec s on
he objec i es abo e.
Key messages
1. Ha monise nu ien h eshold s anda ds ac oss No hwes Eu ope o uni y es o a ion goals.
2. In es in ha monized and enhanced nu ien and hyd ological moni o ing.
3. Use na ional Load Reduc ion Ta ge (LRT) models o quan i y sec o -speci ic con ibu ions, assign
esponsibili ies, and ensu e compliance.
4. In eg a e clima e change conside a ions in o nu ien managemen policies by add essing local-scale
app oaches.
5. Suppo he implemen a ion o si e-speci ic nu ien managemen s a egies o enhance e iciency,
educe en i onmen al impac , and ailo solu ions o local condi ions.
6. Enable inclusi e, mul i-s akeholde ca chmen go e nance pla o ms o lead local es o a ion e o s,
suppo ed by cohe en op-down amewo ks ha in eg a e egula ion, incen i es, and ad iso y se ices
o d i e beha iou al and sys emic change.
Figu e 1. The a ious ca chmen s ha he h ee sis e
p ojec s (de ined by colou ) wo ked on h oughou he
las h ee yea s.
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1. Ha monise nu ien h eshold s anda ds ac oss No hwes Eu ope o uni y
es o a ion goals
Main indings in p ojec s:
NAPSEA:
The analysis o nu ien h eshold s anda ds in Ri e Rhine and Elbe showed ha he e was a missing
link be ween ma ine and eshwa e nu ien s anda ds (Ense ink e al., 2024). The e is a need o
including nu ien s oichiome y as bo h phospho us and ni ogen (and silica) and hei a ios a e
ele an o ecological impac s ( an Beusekom e al., 2025a,b). In policies his is o en no ye ully
conside ed. Sepa a e s anda ds a e needed o achie e good ecological s a us locally and
downs eam. The la e should be exp essed as nu ien load a ge s and load educ ion a ge s.
NORDBALT-ECOSAFE:
An analysis o Ecological Quali y Ra io’s (EQRs) o se e al biological indica o s o lowland i e and
lake ypes in he No dic and Cen al Bal ic egion showed ha p esen nu ien h eshold s anda ds o
o al phospho us and o al ni ogen in some coun ies may no suppo Good Ecological S a us (GES)
(Solheim e al., 2024; Th ane e al., 2025). Unde s anding coupled elemen cycles is key o:
i) N:P:C - assessing ade-o s be ween nu ien e en ion and g eenhouse gas p oduc ion in
indi idual we lands;
ii) N:P:Si - a ge ed educ ions in e es ial nu ien loads o mi iga e ma ine eu ophica ion
New-Ha monica:
An analysis o he Ri e Meuse ca chmen o he Flemish and Du ch egions and compa ison o he
Neagh-Bann and Wye ca chmen s in he UK and I eland e ealed ha he e a e di e en nu ien
s anda d h esholds o c oss-bo de i e s and canals ac oss NW Eu ope. The objec i es o canals
a e also no well-coo dina ed wi h he nume ous s eams ha ake in la ge quan i ies o wa e om he
canals in summe s.
Policy ecommenda ions
• Suppo c oss-bo de coope a ion ini ia i es o es ablish a common science base o unde pin
ecologically sa e nu ien h esholds (N and P) ha guide consis en wa e body es o a ion
unde he Wa e F amewo k Di ec i e (WFD) as well as he Ma ine S a egy F amewo k
Di ec i e (MSFD).
• P omo e amewo ks and ca chmen -scale indica o s ha enable compa abili y o
en i onmen al pe o mance ac oss ju isdic ions and acili a e in eg a ion o egional nu ien
educ ion measu es.
• Suppo he inclusion o s oichiome y in p o ec ion o eshwa e and ma ine wa e s.
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2. In es in ha monized and enhanced nu ien and hyd ological moni o ing.
Main indings in p ojec s
NAPSEA:
Moni o ing obse a ions ( ime and space) o discha ge and concen a ions a e o en no measu ed a
he same ime/loca ion which is c ucial o achie ing eliable empo ally and spa ially dis ibu ed
nu ien load es ima es o he WFD and he MSFD (Ebeling e al., 2022).
NORDBALT-ECOSAFE:
In oduc ion o high- equency senso echnology o moni o ing o nu ien concen a ions can gi e
mo e p ecise and unbiased mean concen a ion and load es ima es and is be e sui ed o cap u e
ex emes ela ed o clima e change (Rozemeije e al., 2025; an’ Veen e al., 2025a,b; Ska bø ik e
al., 2023).
New-Ha monica:
The p ojec highligh ed he low equency, inconsis ency and gaps in he cu en moni o ing
p og ammes ac oss NW Eu ope o deli e and ack achie emen o sa e ecological bounda ies,
Chemical pa ame e s included in Ni a e Di ec i e (ND) and WFD moni o ing migh di e be ween
coun ies such as o phospho us specia ion in su ace wa e s.
Policy ecommenda ions
• Assu e ha nu ien concen a ions and discha ge is moni o ed a he same sampling s a ions
in i e basins, especially o moni o ing s a ions si ua ed nea he ou le s o he ca chmen s
and i e s.
• Alloca e unding o de elop high equency senso echnology o nu ien moni o ing a key
moni o ing si es in i e basins o achie e p ecise and unbiased mean concen a ions and
load es ima es.
• Ensu e moni o ing cap u es seasonal a iabili y o discha ges and concen a ions and
clima e-d i en ex emes o imp o e sou ce appo ionmen model calib a ion and alida ion o
Load Reduc ion Ta ge s (LRTs) ha a e de i ed om hese models.
• In oduce and suppo mo e widesp ead moni o ing o nu ien use by sec o s wi hin
ca chmen s o help de e mine hei ai -sha e esponsibili ies and ac ions o mi iga e he N
and P pollu ion h ea .
• Ha monise me hods used o wa e quali y moni o ing and manda e da a anspa ency and
open access o moni o ing esul s o suppo e idence-based decision-making.
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3. Use na ional Load Reduc ion Ta ge (LRT) models o quan i y sec o -
speci ic con ibu ions, assign esponsibili ies, and ensu e compliance
Main indings in p ojec s
NAPSEA:
In he NAPSEA p ojec , he e ec i eness o cu en ly planned measu es om di e en sec o s we e
e alua ed wi h ca chmen models (example o ni ogen in he Rhine in Figu e 2; Musol e al., 2025;
an Beusekom e al., 2025a,b). I was es ima ed ha he educ ion o nu ien loads due o cu en ly
planned measu es would be la gely insu icien o achie e nu ien concen a ions wi hin sa e
ecological bounda ies in he whole ca chmen o he Wadden Sea. Di e en app oaches o mo e
e ec i e measu es we e e alua ed and only he mos d as ic se o measu es was able o comply wi h
he sa e ecological bounda ies de ined in he p ojec .
Figu e 2. Ni ogen loads om he Rhine a Lobi h o all model scena ios. The dashed ho izon al lines show he
educ ion a ge s o : seag ass eco e y in he Wadden Sea (g een) na u al ni ogen o silica e a ios p e en ing
blooms o non-silici ying phy oplank on in he Wadden Sea (pu ple) and WFD h eshold o which modelled
discha ges whe e used o he e e ence (dashed pink) yea as well as 2030 and 2050 (do ed pink; o e laps wi h
dashed line). Re : e e ence pe iod 2010–2020, ligh e colou s in scena ios: a e age 2028–2032, da ke colou s:
a e age 2046–2050, whiske s: 5–95% con idence in e al (100 model ealiza ions). Mo e de ails in an
Beusekom e al., 2025b.
NORDBALT-ECOSAFE:
In he NORDBALT-ECOSAFE p ojec he applica ion o SWAT+ on six i e basins wi h one in each o
he pa icipa ing coun ies was es ed and compa ed o na ional models and me hods. The SWAT+
calib a ion and alida ion o he six i e basins which ep esen ed huge di e ences in clima e,
geology, soil ype and land use showed gene ally a good pe o mance o wa e and ni ogen wi h
less good pe o mance in gene al o phospho us. Fu u e scena ios simula ions o iden i y sui able
measu es o close he gap be ween cu en condi ions and nu ien h eshold s anda ds o achie ing
good ecological condi ions in i e s we e un a e discussion wi h local s akeholde s. The ou come is
sha ed as p ojec deli e ables and scien i ic a icles a e cu en ly in p epa a ion (Ma ila e al., 2025;
Biege e al., 2025 a,b).
New-Ha monica:
The po en ial impac o Bes -Managemen P ac ice (BMP) scena ios on mee ing nu ien LRT’s in
each New Ha monica ca chmen was assessed using a sui e o models (MFA, CRAFT, SLAM,
NEMO, INITIATOR-SWAP-ANIMO). Scena ios we e modelled unde he assump ion o bo h cu en
and u u e clima e condi ions, whe e possible. LRT’s ha e been calcula ed acco ding o he me hod
as de ined by he policy make s in each pa ne coun y. The di e ences be ween he me hods ha e
been iden i ied and e alua ed. O e all, modelling indica es ha combina ions o many measu es will
be needed o achie e a ge s now and in u u e and mus add ess sou ces and pa hways in unison
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and ac oss sec o s. Bo h egula ions and olun a y measu es o e ed o s akeholde s mus acili a e a
mul i-s anded app oach. S akeholde s consis en ly a ed inpu educ ion BMPs o con ol nu ien
s ocks in soil as he mos e ec i e measu es (bu mos di icul o implemen ) ac oss all a eas.
Was ewa e ea men measu es and he expansion o he sewe ne wo k in u al a eas we e also
highly a ed.
Resul s ha e been discussed wi h egional s akeholde s and wi hin he Policy Science Wo king G oup
nu ien s o NW-Eu ope. I ’s impo an o no ice ha LRT is no ensh ined in cu en policy legisla ion
o p o ec ing wa e bodies.
Policy ecommenda ions
• Recognize needs o de elop imp o ed wa e quali y modelling in EU o close he gap
be ween cu en condi ions and nu ien h eshold s anda ds
• Con inue o imp o e modelling and managemen collabo a ion wi hin EU
• Key policy ac ions a e needed o e ec i ely implemen ca chmen modelling as a ool o
s akeholde engagemen and o in eg a e land use and wa e quali y planning mo e
holis ically
• To imp o e suppo o LRT, ha monize sou ce appo ionmen me hods o dis inguish he
na u al pa o nu ien loadings o wa e Adop an in eg a ed sou ce- o-sea app oach o
selec ing and implemen ing nu ien educ ion measu es ac oss he en i e ca chmen s a eas,
including all coun ies o he ansbounda y i e basins in ol ed. Suppo imp o ed access
o and exchange o da a (moni o ing and model ou pu s) be ween he neighbou ing coun ies
o his.
• Apply LRT o e alua e policy scena ios o he implemen a ion o he Ni a e Di ec i e and
WFD. I also gi es use ul insigh in ups eam-downs eam issues, o example consequences
o con lic ing h esholds in c oss-bo de wa e bodies.
• Elabo a e guidelines o apply LRT me hods using he Pollu e Pays P inciple (PPP) o achie e
WFD- a ge s o wa e quali y, and o s eng hen he in eg a ion o he PPP in o he
implemen a ion o he WFD.
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4. In eg a e clima e change conside a ions in o nu ien managemen policies
by add essing local-scale app oaches, p epa ing o ex eme wea he e en s
(e.g. d ough s, hea wa es, hea y ain all), and suppo ing adap i e ag icul u al
p ac ices such as c op di e si ica ion and o a ion
Main indings in p ojec s
NAPSEA:
Loads a e calcula ed as concen a ion imes discha ges. I p ecipi a ion pa e ns change due o
clima e change his is bound o a ec he dilu ion, esidence imes and o al loads o nu ien s om
ca chmen s ( an Beusekom e al., 2025a,b).
In he NAPSEA p ojec , he impac o clima e change on nu ien loads om he Elbe and Rhine was
e alua ed wi h models o a mode a e clima e scena io RCP4.5 (Musol e al., 2025). The modelled
ou come cla i ied ha he nu ien loads in he Elbe and Rhine eac di e en ly owa ds 2050 o
clima e change (see clima e scena io (Sc. 6) in
Figu e 3), wi h loads inc easing la gely in he Elbe
compa ed o he Rhine (be ween 2030 and 2050).
Figu e 3. Ni ogen loads om he Rhine a Lobi h (le ) and he Elbe ou le ( igh ) o all model scena ios. Re –
e e ence pe iod 2010–2020, ligh e colou s in scena ios – a e age 2028–2032, da ke colou s – a e age 2046–
2050, whiske s – 5–95% con idence in e al o he bes pe o ming 100 model ealiza ions.
NORDBALT-ECOSAFE:
The p ojec has analysed he impo ance o clima e change ( empe a u e and p ecipi a ion) o he
ecological bounda y condi ions o nu ien s (ni ogen and phospho us) o suppo achie ing good
ecological quali y o di e en biological indica o s in s eam, i e and lake ypes in he No dic-Bal ic
egion (Lyche Solheim e al., 2024). The main esul s show ha he nu ien h eshold bounda ies
seem o be adequa e in s eams bu need o be mo e s ingen in many lake ypes in a u u e wa me
clima e (Th ane e al., 2025).
New-Ha monica:
The p ojec simula ed he po en ial impac s o clima e change on sou ce and pa hway con ol
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measu es o imp o ing wa e quali y in he ca chmen s. Fo phospho us, we e win e s will inc ease
isk o losses in uno and limi he e ec i eness o bu e ing/in e cep ion measu es so his should be
conside ed in hei design going o wa d. Sou ce con ol measu es in he ca chmen s we e only
minimally impac ed and emained e ec i e. Fo ni ogen, d ie summe s may inc ease esidual ni a e
in au umn/win e h ough educ ion in bo h plan up ake and deni i ica ion. Reduced base lows a e
likely o lowe he ca ying capaci y o i e s o con aminan s.
Policy ecommenda ions
• Take clima e change impac s in o accoun when designing nu ien educ ion measu es.
• Es ima e he combined impac s o nu ien s and clima e on biological quali y elemen s in
i e s, lakes and coas al wa e s.
• Gain mo e suppo o nu ien educ ion measu es by collabo a ing wi h o he policies aiming
a clima e adap a ion and e es ial biodi e si y
5. Suppo he implemen a ion o si e-speci ic nu ien managemen s a egies
o enhance e iciency, educe en i onmen al impac , and ailo solu ions o
local condi ions.
Main indings in p ojec s
NAPSEA:
In he Hunze ca chmen , a de ailed SWAT model enabled he e alua ion o 13 locally ailo ed
scena ios— anging om land use changes o na u e-based solu ions—de eloped in collabo a ion
wi h he Wa e Boa d Hunze and Aa’s (Musol e al., 2025). These scena ios assessed he
e ec i eness o planned and po en ial in e en ions unde bo h mode a e and ex eme clima e
p ojec ions. No ably, measu es such as imp o ed was ewa e ea men , educed ag icul u al uno ,
and we land expansion demons a ed p omising esul s in mee ing ecological a ge s. This case
highligh s he alue o si e-speci ic nu ien managemen s a egies ha enhance e iciency, educe
en i onmen al impac , and a e esponsi e o local condi ions and s akeholde inpu .
NORDBALT-ECOSAFE:
The p ojec has de eloped a classi ica ion amewo k o he implemen a ion o mi iga ion measu es
and na u e-based solu ions in ca chmen s (Biege e al., 2024). The aim o he classi ica ion
amewo k is o suppo ca chmen manage s in choosing he mos sui able op ions when ying o
educe nu ien pollu ion om mainly di use sou ces. Simila ly, he p ojec has de eloped a
Ca chmen Managemen Suppo Sys em (Ca chManSS) wi h he aim o suppo ing SWAT+
modelle s o conduc scena ios o s akeholde s and ca chmen manage s o educing nu ien
emissions and anspo in ca chmen s.
New-Ha monica:
S akeholde opinions wi hin he p ojec highligh ed he need o egion- and ca chmen -speci ic
measu es, and he need o ensu e sou ce and pa hway mi iga ions we e cohesi ely implemen ed.
Speci ic impac s will a y in esponse o a mul i ude o an agonis ic and syne gis ic p ocesses and be
dependen on local condi ions, including he physical landscape, land use and d ainage. S ong policy
and inancial suppo o a me s will be needed o o e come ba ie s o implemen sou ce educ ion
measu es such as slu y expo o des ocking. Scep icism abou Clima e change and/o models ha
a e used o e alua e en i onmen al policy may cause di icul ies in ge ing up ake o olun a y
measu es in some egions. Upg ades o sewe sys ems can also make signi ican s ides owa ds
educing nu ien loading in some NW Eu opean coun ies.
Policy ecommenda ions
• Suppo locally ailo ed, model-in o med s a egies ha combine s akeholde inpu wi h model
scena io analysis o educe nu ien pollu ion.
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• P omo e na u e-based solu ions such as we land expansion and imp o ed was ewa e
ea men as e ec i e, clima e- esilien in e en ions.
• Adop decision-suppo ools (e.g. Ca chManSS) and classi ica ion amewo ks o guide
ca chmen manage s in selec ing and e alua ing mi iga ion measu es.
• Embed hese ools and app oaches in o egional and na ional wa e policies o ensu e
consis en , e idence-based nu ien managemen ac oss di e se ca chmen s.
• The selec ion o measu es should be mo e aligned wi h a me s mo i a ion o pick up
measu es, such as planning secu i y and low bu eauc a ic bu den.
