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<p>This study assesses epilimnion water quality in the Joumine Reservoir, Tunisia, by combining the PEGASE water quality model, the DEOLE-J thermal stratification model, and in situ measurements. Scenario analysis was developed to evaluate how future climate change and watershed management strategies may jointly influence water quality dynamics in semi-arid reservoirs. This multidisciplinary approach highlights the key drivers of nitrate, chlorophyll-a, dissolved oxygen, and water temperature, emphasizing the influence of thermocline variability on seasonal ecosystem dynamics. Among these variables, chlorophyll-a (Chl-a) shows the highest uncertainty, with noticeable under- and overestimation depending on the season, reflecting limitations in simulating phytoplankton dynamics. PEGASE reliably simulates hydrological variability at both the catchment (river network) and reservoir scales, as well as nutrient inflows, while reservoir-specific dynamics linked to stratification and phytoplankton required other parameterization. Best Management Practices (BMPs), including agricultural measures such as cover crops, mulching, and reduced nitrogen and phosphorus inputs, were implemented in the scenarios. Scenario analysis revealed strong contrasts between management strategies. Without best management practices (BMPs) (SC1), wet-season nitrate rose by ~ 65% compared to reinforced management (SC3), with peaks above 22&#xa0;mg/L and episodic eutrophication. Dissolved oxygen generally remained above thresholds but showed localized summer depletion. SC2, representing moderate climate change with partial adaptation (25% BMP adoption and partial wastewater treatment), produced intermediate nitrate and phytoplankton levels, showing partial mitigation and persistent oxygen stress. SC3, combining 75% BMP adoption with 90% advanced wastewater treatment, reduced nitrate loads by 63–66% and limited phytoplankton growth; however, oxygen stress persisted under extreme warming (+ 3.9&#xa0;°C by 2100), with summer epilimnion temperatures rising ~ 2&#xa0;°C and intensifying stratification. Climate change will likely worsen eutrophication and oxygen depletion without integrated measures. While BMPs and wastewater treatment reduce nutrient inputs, they cannot fully mitigate oxygen deficits caused by prolonged stratification. Overall, this study demonstrates the applicability of the coupled DEOLE-J and PEGASE models for simulating epilimnion water quality in semi-arid, data-limited contexts, and highlights the importance of implementing stricter nutrient regulations, enhancing wastewater treatment, and increasing monitoring frequency.</p>

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Thermal stratification and epilimnion water quality under climate and management scenarios: the Joumine reservoir (Tunisia)

  • 期刊论文

  • 发表日期：

    2026年5月26日

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  • Haifa Madyouni,
  • Viviana Almanza,
  • Mohamed Salah Romdhane,
  • Hamadi Habaieb,
  • Jean-François Deliège

摘要

This study assesses epilimnion water quality in the Joumine Reservoir, Tunisia, by combining the PEGASE water quality model, the DEOLE-J thermal stratification model, and in situ measurements. Scenario analysis was developed to evaluate how future climate change and watershed management strategies may jointly influence water quality dynamics in semi-arid reservoirs. This multidisciplinary approach highlights the key drivers of nitrate, chlorophyll-a, dissolved oxygen, and water temperature, emphasizing the influence of thermocline variability on seasonal ecosystem dynamics. Among these variables, chlorophyll-a (Chl-a) shows the highest uncertainty, with noticeable under- and overestimation depending on the season, reflecting limitations in simulating phytoplankton dynamics. PEGASE reliably simulates hydrological variability at both the catchment (river network) and reservoir scales, as well as nutrient inflows, while reservoir-specific dynamics linked to stratification and phytoplankton required other parameterization. Best Management Practices (BMPs), including agricultural measures such as cover crops, mulching, and reduced nitrogen and phosphorus inputs, were implemented in the scenarios. Scenario analysis revealed strong contrasts between management strategies. Without best management practices (BMPs) (SC1), wet-season nitrate rose by ~ 65% compared to reinforced management (SC3), with peaks above 22 mg/L and episodic eutrophication. Dissolved oxygen generally remained above thresholds but showed localized summer depletion. SC2, representing moderate climate change with partial adaptation (25% BMP adoption and partial wastewater treatment), produced intermediate nitrate and phytoplankton levels, showing partial mitigation and persistent oxygen stress. SC3, combining 75% BMP adoption with 90% advanced wastewater treatment, reduced nitrate loads by 63–66% and limited phytoplankton growth; however, oxygen stress persisted under extreme warming (+ 3.9 °C by 2100), with summer epilimnion temperatures rising ~ 2 °C and intensifying stratification. Climate change will likely worsen eutrophication and oxygen depletion without integrated measures. While BMPs and wastewater treatment reduce nutrient inputs, they cannot fully mitigate oxygen deficits caused by prolonged stratification. Overall, this study demonstrates the applicability of the coupled DEOLE-J and PEGASE models for simulating epilimnion water quality in semi-arid, data-limited contexts, and highlights the importance of implementing stricter nutrient regulations, enhancing wastewater treatment, and increasing monitoring frequency.