Output for a modelling system for Latvia
The component 1 of the project fiche stipulated that the twinning objective was to select
and/or develop the best suitable models for Latvian conditions which ensure assessment of
impact of different diffuse and point source load to surface water quality. The first step of this
project was to develop a framework for a modelling system for Latvia with the aim of
building a comprehensive framework to link data as a basis for modelling in the context of the
European Water Framework Directive. This first report outlines the rationale for the
framework we developed and which serves as a basis for project.
Several issues and challenges had to be taken into account:
1. From the WFD point of view
There are two main objectives: i) assessment of aquatic ecosystem functioning and ii)
protection and restoration of water quality. Several questions are still pending because
of the lack of sound scientific knowledge. Therefore they need to be addressed
carefully because there is not yet any scientific consensus on them.
Assessment of aquatic ecosystem functioning
o What is a healthy ecosystem?
Beside the WFD definition, there is a lot of controversy on how to define a
healthy ecosystem both in terms of pertinent indicators (see below) and the
timeframe of analysis.
o What is a reference site?
The challenge here is to find sites which are in a healthy status within an
ecoregion and socio-economic context because they should constitute the target
objective of restoration measures.
o What are the pertinent indicators of functioning?
Most of the indicators focus on rather descriptive (geochemistry) or integrative
(biodiversity) parameters, but none of them really addresses the ecosystem
functioning per se. Moreover, the monitoring time and space frames are not
easy to set up since most of these indicators naturally vary both in time and
space.
 Protection and restoration of water quality
o Resistance and resilience of the ecosystems
These fundamental concepts are crucial for our understanding of the reaction of
ecosystems to perturbation, both in term of resistance to disturbance and
trajectory of recovery after the disturbance has stopped.
River management plan
Implicitly this requires to understand or at least to be able to forecast both the
resistance and resilience of river ecosystems under the pressure of several types
of disturbances and under climate change.
2. From the modelling point of view
 No model can do it all
There is a need to find the most suitable model depending on the objective, the
expected output and the required/available data.
 Trade-off between complexity of model and data requirement
Deterministic models (process oriented) need a high level of data both in terms of
diversity and quantity but can tackle high level of complexity, while empirical or
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statistical models only provide trends out of a black box type of model; yet they do not
require the same level of data.
3. From the Latvian situation point of view
 Physical, biological and economic characteristics of Latvian aquatic ecosystems
Several natural features should be considered, including, high natural concentration of
organic carbon, sensitive water bodies to eutrophication (mires, shallow lakes and gulf
of Riga) and pick flood events driven by snowmelt. Moreover, there have been
significant land cover and land use changes since 1990.
 Availability of data
Analysis of data quality (type of measurements) and quantity (space and time) has to
be done (see report on assessment on data availability and quality).
The framework for the modelling system for Latvia has been considered and elaborated based
on the above-mentioned issues. Modelling, although not specifically stipulated in the WFD, is
often suggested as a powerful tool to fulfil these analyses. This is particularly relevant for
Article 5 of the WFD “Characteristics of the river basin district, review of the environmental
impact of human activity and economic analysis of water use”. It is clear that modelling
cannot replace monitoring since reliable data are necessary to adapt/test the model to
local conditions. However, models can help reduce the overall monitoring effort, or provide
knowledge on monitoring methodology. Spatially, models can forecast water quality and
fluxes in non-monitored sites under similar conditions. Temporally, models can forecast
trends at a more accurate time scale than the monitoring.
Figure 1: Framework of a modelling system for Latvia in the context of the European Water
Framework Directive. Texts in red refer to compulsory requirements of the WFD. Numbers
are explained in the text below. Arrows symbolise the flow of data. Blue lozenges represent
the required models.
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Assessment and restoration measures required by the European WFD can both benefit from
modelling tools (Figure 1). A combination of hydrological and coefficient export models
(Figure 1, n°1) can help designing the operational monitoring (Annex II of the WFD): These
models will provide an analytical tool for surveillance monitoring data (Annex II §1.3.1 &
§2.4.1 of the WFD). They will also contribute to the selection of operational monitoring sites
(Annex II §1.3.2 & §2.4.2 of the WFD). Ecosystem process models (Figure 1, n°2) will offer
a mechanistic understanding of the investigative monitoring sites (Annex II §1.3.3 of the
WFD). They can also help to determine the natural buffering capacity of aquatic ecosystems,
which is the underlying process of resistance of ecosystems to disturbance. Water quality
models (Figure 1, n°3) will analyse the spatial and temporal trends required in the Article 4
“Environmental Objectives” of the WFD. These models will also constitute a support for
public awareness required in Article 14 “Public information and consultation” and reporting
(Article 15). Finally, spatially-distributed processed based models (Figure 1, n°4) will propose
interactive modelling tools for management plan analysis and scenarios analysis under human
impact as stipulated in article 13 “River basin management plans” of the WFD.
The model selection and their implementation/customization have to be done in the context of
the existing and foreseen data, database and geographic information systems. These elements
are elaborated in the report on “Assessment of data availability and quality” and in the report
on “Applicable models and recommendations”.
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