event 29 Apr 2020

Publication // Integrated modelling and management of water resources: the ecosystem perspective on the nexus approach

By Hülsmann, S., Sušnik, J., Rinke, K., Langan, S., van Wijk, D., Janssen, A. B., & Mooij, W. M. (2019). This publication was developed by the SIM4Nexus project (https://www.sim4nexus.eu) and has been re-published here with their friendly permission. It gives an introduction towards aquatic ecosystem modelling approaches, and the valuable role they can provide when assessing the water-energy-food Nexus.

Sim4nexus ecosystems

In order to address challenges of water, energy and food security, in recent years attention has been paid to truly integrated approaches to resources management across these sectors, and considering interrelated resources in a balanced and coherent way. The nexus concept (in particular addressing Water, Energy and Food: WEF nexus) is rooted in earlier integrated resources management concepts, e.g., Integrated Water Resources Management (IWRM). Considering the need to provide water for people, food, nature, industry and other users, IWRM conceptually captures some aspects of the nexus concept, but its scope of integration is clearly sectoral, thus missing many potential trade-offs as well as synergies. Given the integrative nature of the nexus approach, it was argued that ecosystem services (ES), including provisioning, regulating and maintenance as well as cultural services (categories following The Common International Classification of Ecosystem Services (CICES), see https://www.sciencedirect.comcices.eu/) have to be considered as central elements in nexus assessments. From a resources perspective, ES are obviously essential for any integrated management approach in order to consider all dimensions of sustainability as they provide the basic resource base on which society develops. This holds in particular for the WEF nexus, where the equitable allocation of water resources between these sectors has to integrate knowledge on ES provided by rivers, lakes, wetlands and aquifers, given that the provision of water both in terms of quantity and quality relies on them. Such services include:

Provisioning services:

  • Water provision at a distinct quality, depending on its use;
  • Biomass production, including fish production (with food and economic implications);

Regulating and maintenance services:

  • Self-purification by mineralisation of organic compounds;
  • Nutrient retention of N and P (i.e. lowering nutrient loading towards downstream rivers and coasts/estuaries;
  • Carbon sequestration;
  • Buffering capacity for extreme events (floods and droughts) Nutrient recycling, enabling biomass production;

Cultural services:

  • Touristic, recreational and religious services, implying sufficient water quantity and quality.

One common concern about earlier integrated resources management approaches was that the ecosystem dimen- sion was neglected with regard to IWRM) and this has similarly been concluded for the nexus. The need for including the ecosystem perspective in the nexus has been emphasised by several studies, but mostly on a rather general and conceptual level. In this paper, therefore, we explore the interrelations between the nexus approach and ecosystem management from both perspectives. Our basic hypothesis is that there is a division between scientific communities focusing on either a nexus approach or on aquatic ecosystem management – linking to and rooted in IWRM. After briefly reflecting on the need for appropriate modelling tools, we take a closer look at current examples of nexus-oriented and ecosystem-based modelling approaches to explore how close or separate both lines of research and the respective communities are. We then provide a perspec- tive on how to close this gap in order to proceed towards modelling tools which better reflect nexus-oriented and sustainable resources management with a focus on water – as related to food and energy security.

Aquatic ecosystem models (AEMs) originated from studies on eutrophication and were firstly developed in the 1970s. The major goal of AEMs during that time was to provide quantitative tools for predicting the responses of lakes and reservoirs to nutrient loading, the definition of critical loading levels, and the evaluation of alternative eutrophication control measures. While being kept rather simple initially, many AEMs are nowadays designed as complex system models with respect to their physical representation and the ecosystem architecture including detailed routines for representing trophic interactions, community dynamics, and biogeochemical cycling. Modern AEMs demand detailed input data for meteorological conditions as well as inflow volumes and nutrient loadings from the water bodies’ catchment and therefore can be linked to atmospheric or hydrological models. This enables the integration of AEMs into wider model systems at the landscape scale in order to assess the interaction between land use (including food produc- tion), energy production (which links strongly to water demand and quality) climate change, and aquatic ecosys- tem dynamics. Several examples of AEM integrations into larger scale models were provided recently. These examples link catchment models with AEMs and by that establish a model system that consistently simulates water and nutrient fluxes from the catchment into the lake, as well as the corresponding ecosystem and water quality dynamics within the receiving lake. Model results for Lake Beyşehir, the largest freshwater lake in Turkey, suggest thatlower nutrient loading will be anoption to at leastpartly offset the negative effects of warming, confirming conclusions from earlier studies.

Key messages

Acknowledging the earlier studies that stress the need to integrate ES in nexus assessments, we found that thus far such integration is only rudimentarily implemented in existing nexus modelling tools. We, therefore, see many opportunities to make use of AEMs in the nexus context using the following approaches:

  • Addition of AEMs to a nexus modelling framework to contribute to the incorporation of specific ES;
  • Integrating modules or the core of AEMs – quantifying specific ES – into existing or newly developed nexus models;
  • Linking AEMs to process models addressing, for example, land-use, crop production, soil erosion, water yield and so on in a watershed, to contribute to a comprehensive analysis of the nexus of water, soil/land, biomass production (food, bioenergy).

We have not been able to find examples of the first approach, but ongoing initiatives to improve AEMs in terms of applicability, user-friendliness, openness, and new implementations in commonly used programming languages such as R (https://www.r-project.org) or facilitating conversions by using a database approach will increase opportunities for such developments and reduce obstacles related to model complexity. Conversely, new nexus tools and modelling frameworks currently under development will also increase the potential for linking with AEMs or core parts thereof. For the second option, there are first examples available as discussed above, as well as ongoing initiatives, for example, the approach in SIM4NEXUS could be adopted and/or extended to include ecosystems by linking the water, agricultural and land sectors to aquatic ecosystem models in order to assess impacts arising from changes in land use patterns in a more explicit and robust manner. Policy targets related to ecosystems and biodiversity could be accounted for in a similar manner, again allowing one to explore the potential impact of such policy decisions on (aquatic) ecosystems using relevant indicators, which themselves can link to SDG goals. Not necessarily requiring the full complexity of AEMs, just considering specific processes or outputs related to specific ES can be sufficient for a well-defined nexus case. The third option also seems promising since some examples mentioned in the section on AEMs already point into this direction, being highly relevant for the WEF nexus, although originally not conceptually framed as nexus projects. This points to a non-technical issue needed to advance the inclusion of ES into the nexus approach: enhanced inter-action between the scientific disciplines and communities working on nexus issues or on ecosystem management.

While we refrain from claiming that ES have to be considered in all nexus assessments, we are convinced that, given the strong role of the nexus approach for the 2030 agenda, ES have to be given more attention and visibility in the nexus. This holds in particular for the development of transition pathways and scenarios towards achieving SDGs including those emphasising supply by resource sectors, SDG 2 (zero hunger), SDG 6 (clean water and sanitation) and SDG 7 (affordable and clean energy), but also those emphasising the preservaton of earth systems, SDG 13 (climate action), SDG 14 (life below water) and SDG 15 (life on land). This highlights the urgent need to have ES represented in models. When focusing on water resources management, we envision a strong future role for AEMs to include ES in the nexus approach. The required bridging between respective scientific communities would be one step towards the interdisciplinarity needed to achieve integrative nexus tools as proposed by Albrecht et al. Ultimately, nexus assessments might draw from model libraries within environmental observatories to predict systems resilience and the role of ES therein.


August 2019


© The authors.


Hülsmann, S., Sušnik, J., Rinke, K., Langan, S., van Wijk, D., Janssen, A. B., & Mooij, W. M. (2019). Integrated modelling and management of water resources: the ecosystem perspective on the nexus approach.

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