The CSTT model underpinning the UK defence in European Court of Justice
Submitting InstitutionUniversity of the Highlands & Islands
Unit of AssessmentEarth Systems and Environmental Sciences
Summary Impact TypeEnvironmental
Research Subject Area(s)
Chemical Sciences: Other Chemical Sciences
Biological Sciences: Ecology
Engineering: Environmental Engineering
Summary of the impact
Eutrophication results from excessive nutrient discharge to a water-body,
quality. Eutrophication status must comply with the Urban Waste Water
(UWWTD). As part of a consortium, UHI developed, validated and researched
a model (CSTT)
capable of screening a water-body for eutrophication. The model was used
to defend the UK
in the European Court of Justice (2009), against proceedings brought by
Commission alleging infraction of UK obligations under the UWWTD. The
model proved that
British waters were not harmfully impacted by eutrophication, sparing the
UK government ~£6
billion to implement tertiary sewage treatment across England and Wales.
Eutrophication is the process by which a body of water acquires a high
nutrients, especially Nitrate and Phosphate, promoting excessive growth of
algae resulting in
severe reduction in water quality. UHI research1,2,3 shows that
growth of algae may not occur
where there is a lack of sunlight or where energy levels in the water are
high enough to cause
dispersion of the algae. The European Urban Waste-Water Treatment
(1991) specifies that the amount of treatment required for discharge of
depends, among other things, on the actual or potential level of
eutrophication of the receiving
In response to the UWWTD, the UK government set up the Comprehensive
Team (CSTT) to produce guidelines for studies to check that British waters
were not becoming
eutrophic. To understand the potential of a water body become eutrophic,
several factors have
to be taken into consideration: water exchange and mixing relationships
within the water-body,
chlorophyll content and nutrient effects and light intensity.
Prof Tett proposed to the CSTT (1993) to develop a model which could
accommodate all of
these parameters to enable an effective means to screen a water body for
conditions. Model development and refinement took place from 1994-1997
during a number of
collaborative research projects2,3,4,5,6,7 of UHI, Napier
University and University of Bangor.
The UHI component built on over 30 years of research into water exchange
characteristics in sea-lochs and estuaries (Inall), phytoplankton growth
theory (Droop) and
nutrient effects on water quality (Gowen). This work was brought together
with work on the
other crucial parameters relating to photosynthetic efficiency and
growth-related respiration in
response to underwater light carried out at Napier University and
University of Bangor, to
develop the CSTT Model for Eutrophication.
The model uses the rate of exchange between water-bodies, the rate of
addition of nutrients,
and light levels to predict whether or not there will be eutrophication in
a body of water under
specified conditions and was published in the CSTT guidelines (1997).
From 1997-2003, the model was validated by UHI and Napier University
during a joint PhD
Studentship, against observations from the Mediterranean to the Arctic in
European project OAERRE4. Further tests were also carried out
in Loch Creran by Napier-SAMS
PhD student Celine Laurent5 (2002-2006). During this study, the
CSTT model was
applied to Loch Creran to assess the capacity of the loch to assimilate
nutrients from fish-farms.
Model simulations were found to retain a significant correlation with
demonstrating the model's ability to replicate actual conditions of the
water-body, in this case
The model continues to be developed and adapted for wider use and with
funding from the
Scottish Aquacultural Research Forum (SARF, 2005-2011), UHI researchers
led by Prof's
Tett & Inall have been developing a new version of the model for
predicting the environmental
impacts of aquaculture in sea lochs6 and has been developed
further to the ACExR model for
seasonal exchange and mixing in enclosed sea lochs.
References to the research
1. CSTT (1997). Comprehensive studies for the purposes of Article 6 &
8.5 of DIR 91/271
EEC, the Urban Waste Water Treatment Directive, second edition. Report,
Published for the Comprehensive Studies Task Team of Group Coordinating
Monitoring by the Department of the Environment for Northern Ireland, the
Agency, the Scottish Environment Protection Agency and the Water Services
2. Gowen, R. J., P. Tett and K. J. Jones. 1992.
Predicting marine eutrophication: the yield of
chlorophyll from nitrogen in Scottish coastal phytoplankton. Marine
Ecology — Progress
Series, 85: 153-161.
3. Edwards, V. R., P. Tett and K. J. Jones. 2003. Changes
in the yield of chlorophyll a from
dissolved available inorganic nitrogen after an enrichment event
-applications for predicting
eutrophication in coastal waters. Continental Shelf Research, 23:
4. Tett, P., L. Gilpin, H. Svendsen, C. P. Erlandsson, U.
Larsson, S. Kratzer, E. Fouilland, C.
Janzen, J.-Y. Lee, C. Grenz, A. Newton, J. G. Ferreira, T. Fernandes and
S. Scory (2003).
Eutrophication and some European waters of restricted exchange. Continental
Research, 23, 1635-1671.
5. Laurent, C., P. Tett, T. Fernandes, L. Gilpin and K. J.
Jones. 2006. A dynamic CSTT
model for the effects of added nutrients in Loch Creran, a shallow fjord.
Journal of Marine
Systems, 61: 149-164.
6. Tett, P., E. Portilla, P. A. Gillibrand and M. Inall
(2011). Carrying and assimilative
capacities: the ACExR-LESV model for sea-loch aquaculture. Aquaculture
7. Gillibrand, P. A., M. E. Inall, E. Portilla and P. Tett
(2013). A Box Model of the Seasonal
Exchange and Mixing in Regions of Restricted Exchange: Application to Two
Scottish Inlets. Environmental Modelling & Software, 43, 144-159.
Details of the impact
Eutrophication is a process involving the excessive build-up of nutrients
in a water body
leading to the deterioration of the water quality. Whilst eutrophication
can happen naturally,
human impacts such as sewage discharge can greatly enhance the process. As
eutrophication status is controlled by The European Urban Waste Water
(UWWTD) of 1991. The UK set up the Comprehensive Studies Task Team (CSTT)
guidelines for studies to check that British waters were not becoming
despite these guidelines, in 1999 the European Commission (EC) accused the
UK of infracting
the UWWTD, by failing to identify certain coastal waters in England and
Wales as eutrophic.
This accusation led to a court case in the European Court of Justice,
which was finally decided
in the UK's favour in 20097. The CSTT model, developed by UHI,
Napier University and
University of Bangor was key to the UK's successful defence1.
The UK was brought before the Court in 2007, and presented its defence in
writing over the
next two years, culminating in a hearing in Luxembourg in April 2009.
Prof. Tett contributed
written and oral evidence during this period and attended the hearing in
person as an expert
advisor, supporting the UK government solicitors and Defra officers.
The defence included data showing lack of undesirable disturbance due to
of UK waters, and made the argument, based quantitatively on the CSTT
model, that many of
our coastal waters and estuaries were light-limited, and therefore not
As part of the judgement, the Court ruled that eutrophication comprises
four linked steps: (1)
enrichment with nutrients; (2) accelerated growth of algae, etc.; (3) an
to the balance of organisms; (4) an undesirable disturbance to water
quality; and that, for
eutrophication to be proven, a causal relationship between each step must
It was agreed that the relevant waters in question were nutrient-enriched
(step 1), but the UK
claimed that accelerated algal growth (step 2), was often prevented by
turbidity. Results from
the CSTT model were put forward to show that this was the case1.
In December 2009 it was announced that the UK had won the relevant part
of its case1. The
CSTT model provided the scientific evidence which helped to uphold the
reputation of British
scientific research and save the British government and taxpayers a hefty
bill for additional
water treatment. A similar case was lost by the French government in 20042,
resulting in heavy
fines and the expensive obligation to build extra sewage treatment plants.
Enforcement of the
directive, if the UK had lost the case, would have required the
installation of nutrient-stripping
treatment systems to all waste water discharges identified as being
eutrophic — affecting every
major city and town from the east of England up to Liverpool, an area with
population of around 20 million. This tertiary level of sewage treatment
would have cost on the
order of £6 billion to implement, accounting for initial capital costs of
installation, running costs
and maintenance over a 20-year period1. It is assumed these
extra water treatment costs
would have been passed down to consumers.
Other impacts of the research include:
- The Centre for Environment, Fisheries and Aquaculture Science (Cefas)
from the Environment Agency) continues research to combine the CSTT
their `combined macroalgae and phytoplankton model' (CPM), for
use in evaluating the
trophic status of shallow coastal water bodies such as Poole harbour.
on this evaluation project3.
- In 2011, Prof. Tett was invited to serve on a European Task Group set
International Council for the Exploration of the Sea and the EC Joint
Committee, chaired by Dr. João Ferreira, to provide guidance to the
Commission on implementing 'Qualitative Descriptor' 5, Eutrophication,
of the Marine
Strategy Framework Directive. Prof. Tett led clarification of the
eutrophication (Ferreira et al., 2011)4.
- Further developments of the model by UHI for use in aquaculture by
Profs. Tett & Inall
(2005-2011 SARF (Scottish Aquacultural Research Forum) funded research)
been transferred to Marine Science Scotland and Scotland's Environment
Agency (SEPA) and reported to the industry at the Association of
Growers Conference in 2011. A report on the Development of Assimilative
and Carrying Capacity Models for Water Bodies utilized for Marine
Bivalve and Caged
Fish-farming, was prepared by Prof. Tett on behalf of SARF and published
SARF website to provide a guide to the model system and advice on model
for businesses and regulators5.
Sources to corroborate the impact
- ECJ (2009). Commission of the European Communities v United Kingdom
by Portuguese Republic. Judgement of the European Court of Justice (3rd
10 December 2009, In Case C-390/07, under Article 226 EC for failure to
obligations, pursuant to Articles 3(1) and (2) and 5(1) to (3) and (5)
of, and Annex II to,
Council Directive 91/271/EEC of 21 May 1991 concerning urban waste water
(OJ 1991 L 135, p. 40).
- ECJ (2004). Commission of the European Communities v French Republic.
of the European Court of Justice (2nd chamber) on 23 September 2004, in
concerning: Failure of a Member State to fulfil obligations — Directive
91/271/EEC — Urban waste water treatment — Article 5(1) and (2) and
Annex II — Failure
to identify sensitive areas — Meaning of 'eutrophication' — Failure to
stringent treatment of discharges into sensitive areas.
- The Centre for Environment, Fisheries and Aquaculture Science (Cefas)
use the CSTT model in collaboration with UHI. For more information
individual from Cefas as reported to the REF submission Team, or details
from the UHI REF audit contact.
- Ferreira, J. G., J. H. Andersen, A. Borja, S. B. Bricker, J. Camp, M.
Cardosa da Silva,
E. Garces, A. S. Heiskanen, C. Humborg, L. Ignatiades, C. Lancelot, A.
Tett, N. Hoepffner and U. Clausen (2011). Overview of eutrophication
assess environmental status within the European Marine Strategy
Estuarine, Coastal and Shelf Science, 93, 117-131.
- SARF commissioned report http://www.sarf.org.uk/cms-assets/documents/48900-379750.sarf012a.pdf