Elsevier

Ecological Modelling

Volume 312, 24 September 2015, Pages 222-238
Ecological Modelling

Bayesian belief network models to analyse and predict ecological water quality in rivers

https://doi.org/10.1016/j.ecolmodel.2015.05.025Get rights and content

Highlights

  • We developed BBNs for analysing ecological water quality in a tropical river basin.

  • Model evaluation was based on technical criteria and practical simulations.

  • Relevant restoration options were simulated to determine ecological effects.

  • Model sensitivity analysis and simulations revealed the importance of flow velocity.

  • Hydropower dams and water abstraction decrease ecological water quality.

Abstract

Economic growth is often based on the intensification of crop production, energy consumption and urbanization. In many cases, this leads to the degradation of aquatic ecosystems. Modelling water resources and the related identification of key drivers of change are essential to improve and protect water quality in river basins. This study evaluates the potential of Bayesian belief network models to predict the ecological water quality in a typical multifunctional and tropical river basin. Field data, expert knowledge and literature data were used to develop a set of Bayesian belief network models. The developed models were evaluated based on weighted Cohen's Kappa (κw), percentage of correctly classified instances (CCI) and spherical payoff. On top, a sensitivity analysis and practical simulation tests of the two most reliable models were performed. Cross-validation based on κw (Model 1: 0.44 ± 0.08; Model 2: 0.44 ± 0.11) and CCI (Model 1: 36.3 ± 2.3; Model 2: 41.6 ± 2.3) indicated that the performance was reliable and stable. Model 1 comprised of input variables main land use, elevation, sediment type, chlorophyll, flow velocity, dissolved oxygen, and chemical oxygen demand; whereas Model 2 did not include dissolved oxygen and chemical oxygen demand. Although the predictive performance of Model 2 was slightly higher than that of Model 1, simulation outcomes of Model 1 were more coherent. Additionally, more management options could be evaluated with Model 1. As the model's ability to simulate management outcomes is of utmost importance in model selection, Model 1 is recommended as a tool to support decision-making in river management. Model predictions and sensitivity analysis indicated that flow velocity is the major variable determining ecological water quality and suggested that construction of additional dams and water abstraction within the basin would have an adverse effect on water quality. Although a case study in a single river basin is presented, the modelling approach can be of general use on any other river basin.

Introduction

Increasing human activity in countries often leads to water quality deterioration (Holguin-Gonzalez et al., 2013, Kibena et al., 2014, Mereta et al., 2012, Yillia et al., 2008). Water resources are essential to support biodiversity and to provide social and economic benefits to humans (Bérenger and Verdier-Chouchane, 2007, Hajkowicz, 2006). Monitoring, modelling and forecasting water quality is essential to support management in maintaining a good water quality status while responding to current anthropogenic stressors (Schnoor, 2014).

Various water quality models have been developed in the past. These models range from empirical models quantifying physicochemical water quality (Burchard-Levine et al., 2014, Cuesta Cordoba et al., 2014, Lessels and Bishop, 2013, Xu and Liu, 2013), models integrating hydraulic, physicochemical and ecological water quality (Chan et al., 2013, Clarke et al., 2003, Holguin-Gonzalez et al., 2013), to complex system dynamics models (Ramin et al., 2012, Zhao et al., 2014). However, limited availability of field data frequently restricts the use of these data-driven or complex modelling techniques to support water resource management in countries.

As a result, knowledge-based models, such as, Bayesian belief networks (BBN) are increasingly being used as decision support tool to support river basin management (Adriaenssens et al., 2004, Kragt et al., 2011). Due to their graphical nature, BBNs can be easily understood by non-technical users (Ames et al., 2005, Chen and Pollino, 2012, Uusitalo, 2007). Other advantages of BBNs include the ability to deal with small and incomplete datasets, the ability to include expert knowledge during model training and the ability to take into account uncertainties without increasing calculation time. These aspects and, especially, the capability of combining knowledge-based (expert) and evidence-based (empirical) information make BBNs attractive for environmental modelling (Aguilera et al., 2011, Chen and Pollino, 2012, Landuyt et al., 2013, Pollino et al., 2007, Varis, 1997). Major limitations of BBNs include mandatory discretization of continuous variables and the inability to support feedback loops (Uusitalo, 2007).

Within the Ecuadorian Guayas River basin, various human activities (i.e. hydroelectric dams, agriculture, industrial plants) threaten the quality of the water. Poor management of the basin has resulted in biodiversity loss, unsafe potable water, eutrophication and reduced water availability (Alvarez-Mieles et al., 2013, Andres, 2009). Therefore, water quality models are needed to guide current management. In this study, we developed several BBN models to predict the water quality in the Guayas River basin as a tool to support decision-making. The developed models were evaluated based on their predictive accuracy and their ability to simulate a variety of restoration scenarios. On top, consistency of model predictions was compared. The influence of several environmental variables on the ecological water quality was explored. The paper concludes with some potential restoration opportunities to improve the ecological water quality and discusses potential application of the modelling approach on other river basins.

Section snippets

Study area

The Guayas River basin is located in central-western Ecuador and is the largest watershed in the Guayas province (Fig. 1). It occupies a land surface area of 34,000 km2, 13% of the country's territory and hosts approximately 40% of the Ecuadorian population (Andres, 2009, Nguyen et al., 2015). The Guayas River, with a total length of 60 km, discharges in the Pacific Ocean. Annual rainfall and daily mean temperature vary between 300 and 4000 mm and 22 to 27 °C. The dry season falls between May and

Current water quality status

13% of the sampled sites have a good water quality status. 21%, 32%, 19% and 15% of the sampled sites are characterised by moderate, poor, bad, and very bad water quality, respectively (Fig. 3). Table 5 summarises the chemical, physical and hydromorphological water quality characteristics for which continuous data were gathered in the field.

Model performance

The model development process described in Section 2.4 resulted in two graphical layouts (Fig. 4, Fig. 5). Among all developed models (>30), the two

Model development

BBN models offer a lot of advantages. First of all, BBNs are able to deal with missing data, a frequently recurring issue in environmental research, while most classical statistical techniques are not (Gupta and Chen, 2010, Pollino et al., 2007). Also in the present dataset, missing values occurred. For instance, there were 20 missing values for the COD variable. Yet, COD could be included in the model using the other 100 measurements that were available. An additional strength of BBNs, as

Conclusion

Bayesian belief networks (BBN) were developed to model the ecological water quality based on macroinvertebrates in the Guayas River basin. Out of the developed models, two best-performing models were selected. While the predictive performance of the second model was slightly higher than that of the first, simulation outcomes of the first model were more coherent. Also more management options could be evaluated with the first model. Model performance is important to have confidence in the model.

Acknowledgements

This research was performed in the context of the VLIR Ecuador Biodiversity Network project. This project was funded by the Vlaamse Interuniversitaire Raad—Universitaire Ontwikkelingssamenwerking (VLIR-UOS), which supports partnerships between universities and university colleges in Flanders and the South. The authors would also like to thank the assistance of the Department of Chemical and Environmental Sciences (CADS-ESPOL) staff during the sampling campaign in Ecuador, Dr. Christine Vander

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