Dam reoperation to reconcile agricultural sustainability with native fish habitat and competition with invasive fish species in semi-arid areas

Global change impacts are likely to compromise agricultural benefits and the ecological status of rivers. The latter would be caused by modifications in fish population dynamics as fish species react in different ways against hydrological changes, and the establishment of alien and invasive fish species. To guarantee native fish sustainability, impact assessment studies should encompass habitat evaluations and competition assessment under future scenarios (i.e., including future hydrological scenarios and land use, and changes in agricultural demands). Moreover, their interplay with economic uses should also be considered, designing adaptation measures that take advantage of synergies and minimize trade-offs between them. Dam reoperation is a promising alternative to this end, given its direct and immediate impact on downstream streamflows and its absence of building costs. However, it requires consensus between water users, including native fish; thus, it should be carefully evaluated taking into account stakeholders’ views.

This contribution presents a framework to develop dam reoperation strategies that simultaneously address global change impacts on agricultural benefits, native fish habitat and competition with invasive fish species in a water resource system. The developed methodological framework has been tested in the Serpis River Basin (Spain). The global change scenarios combined CMIP6 climate change projections with three land use scenarios: current crop surface and technology (reference), drip irrigation implementation and drip irrigation with changes in crop types and areas. Hydrological discharges associated with climate change scenarios were derived using the Témez conceptual hydrological model. Future crop water needs were estimated, for each climate scenario, using the AQUACROP model. The changes in the agricultural benefits related to these scenarios were obtained with a hydroeconomic model developed with the GAMS software. The effects in the availability of suitable habitat for native fish species (Eastern Iberian chub, Squalius valentinus and European eel, Anguilla anguilla) and its competition with invasive species (Bleak, Alburnus alburnus and Pumpkinseed, Lepomis gibbosus) were assessed by combining a 2D hydraulic model with the corresponding fuzzy logic-based habitat suitability models by species. The Pareto-optimal strategies for dam reoperation were obtained with the BORG-MOEA algorithm implemented using the Platypus Python library. The goals were the maximisation of the agricultural benefits and of native fish habitat, and the minimisation of the competition between the two groups of species.

Our results suggest a trade-off between economic and ecological objectives and a positive relation between native fish habitat and native-invasive competition. They also indicate that economic and ecological sustainability could not be achieved by dam reoperation in the most pessimistic scenarios. However, dam reoperation shows a significant potential to contribute to climate change adaptation, entirely reverting its impacts in the most optimistic scenarios. It also shows synergies with land use scenarios, suggesting that dam reoperation could boost the positive impacts after the implementation of drip irrigation.

Acknowledgements: This study has received funding from the European Union’s Horizon 2020 research and innovation programme under the GoNEXUS project (grant agreement No 101003722); as well as from the SOS-WATER project, under the European Union’s Horizon Europe research and innovation programme (GA No. 101059264).