• Energy Research

Worldwide, anthropogenic activities threaten surface water quality by aggravating eutrophication and increasing total nitrogen to total phosphorus (TN:TP) ratios. In hydrologically connected systems, water quality management may benefit from in-ecosystem nutrient retention by preventing nutrient transport to downstream systems. However, nutrient retention may also alter TN:TP ratios with unforeseen consequences for downstream water quality. Here, we aim to increase understanding of how nutrient retention may influence nutrient transport to downstream systems to improve long-term water quality management. We analyzed lake ecosystem state, in-lake nutrient retention, and nutrient transport (ratios) for 3482 Chinese lakes using the lake process-based ecosystem model PCLake+. We compared a low climate change and sustainability-, and a high climate change and economy-focused scenario for 2050 against 2012. In both scenarios, the effect of nutrient input reduction outweighs that of temperature rise, resulting in more lakes with good ecological water quality (i.e., macrophyte-dominated) than in 2012. Generally, the sustainability-focused scenario shows a more promising future for water quality than the economy-focused scenario. Nevertheless, most lakes remain phytoplankton-dominated. The shift to more macrophyte-dominated lakes in 2050 is accompanied by higher nutrient retention fractions and less nutrient transport to downstream waterbodies. In-lake nutrient retention also alters the water's TN:TP ratio, depending on the inflow TN:TP ratio and the ecosystem state. In 2050 higher TN:TP ratios are expected in the outflows of lakes than in 2012, especially for the sustainability-focused scenario with strong TP loading reduction. However, the downstream impact of increased TN:TP ratios depends on actual nutrient loadings and the limiting nutrient in the receiving system. We conclude that nutrient input reductions, improved water quality, higher in-lake nutrient retention fractions, and lower nutrient transport to downstream waterbodies go hand in hand. Therefore, water quality management could benefit even more from nutrient pollution reduction than one would expect at first sight.

Phosphorus (P) precipitation is among the most effective treatments to mitigate lake eutrophication. However, after a period of high effectiveness, studies have shown possible re-eutrophication and the return of harmful algal blooms. While such abrupt ecological changes were attributed to the internal P loading, the role of lake warming and its potential synergistic effects with internal loading, thus far, has been understudied. Here, in a eutrophic lake in central Germany, we quantified the driving mechanisms of the abrupt re-eutrophication and cyanobacterial blooms in 2016 (30 years after the first P precipitation). A process-based lake ecosystem model (GOTM-WET) was established using a high-frequency monitoring data set covering contrasting trophic states. Model analyses suggested that the internal P release accounted for 68% of the cyanobacterial biomass proliferation, while lake warming contributed to 32%, including direct effects via promoting growth (18%) and synergistic effects via intensifying internal P loading (14%). The model further showed that the synergy was attributed to prolonged lake hypolimnion warming and oxygen depletion. Our study unravels the substantial role of lake warming in promoting cyanobacterial blooms in re-eutrophicated lakes. The warming effects on cyanobacteria via promoting internal loading need more attention in lake management, particularly for urban lakes.

This repository contains the dataset linked to the following publication: Article title: Synergistic effects of warming and internal nutrient loading interfere with the long-term stability of lake restoration and induce sudden re-eutrophication Journal: Environmental Science & Technology DOI: 10.1021/acs.est.2c07181 Abstract: Phosphorus (P) precipitation is among the most effective treatments to mitigate lake eutrophication. However, after a period of high effectiveness, studies have shown possible re-eutrophication and the return of harmful algal blooms. While such abrupt ecological changes were attributed to the internal P loading, the role of lake warming and its potential synergistic effects with internal loading, thus far, has been understudied. Here, in a eutrophic lake in central Germany, we quantified the driving mechanisms of the abrupt re-eutrophication and cyanobacterial blooms in 2016 (30 years after the first P precipitation). A process-based lake ecosystem model (GOTM-WET) was established using a high-frequency monitoring dataset covering contrasting trophic states. Model analyses suggested that the internal P release accounted for 68% of the cyanobacterial biomass proliferation, while lake warming contributed to 32%, including direct effects via promoting growth (18%) and synergistic effects via intensifying internal P loading (14%). The model further showed that the synergy was attributed to prolonged lake hypolimnion warming and oxygen depletion. Our study unravels the substantial role of lake warming in promoting cyanobacterial blooms in re-eutrophicated lakes. The warming effects on cyanobacteria via promoting internal loading need more attention in lake management, particularly for urban lakes. SYNOPSIS: Warming synergistically promotes re-eutrophication with internal nutrient loading and exacerbates cyanobacterial blooms in urban lakes 30 years after phosphorus mitigation. Data description by Xiangzhen Kong (xzkong@niglas.ac.cn), 2023-02-20 ---Wet chemical analysis on water samples taken at five depths (0.5, 2.5, 5.0, 7.0 and 9.0 m) from the deepest point in the lake (BA1) at biweekly intervals from 2018.5-2021.8. File name: BAB_BA1_TN_mgL.obs (total nitrogen concentration) BAB_BA1_NH4_mgL.obs (ammonium nitrogen concentration) BAB_BA1_NO3_mgL.obs (nitrate nitrogen concentration) BAB_BA1_TP_mgL.obs (total phosphorus concentration) BAB_BA1_SRP_mgL.obs (Soluble reactive phosphorus concentration) BAB_BA1_DP_mgL.obs (dissolved P concentration) BAB_BA1_DOC_mgL.obs (Dissolved organic carbon concentration) BAB_BA1_Si_mgL.obs (dissolved silicon concentration) BAB_BA1_Chla_HPLC_DIN_mgL.obs (Chl-a concentration) ---CTD probe profile data from the deepest point in the lake (BA1) from 2017.8 to 2021.8 at biweekly basis with approximately 0.1 m vertical resolution File name: t_prof_file_barleber_ctm644.obs (water temperature) oxy_prof_file_barleber_ctm644 (Dissolved oxygen) turb_prof_file_barleber_ctm644.obs (Turbidity) chla_prof_file_barleber_ctm644.obs (Chl-a concentration) ---BBE probe profile data from the deepest point in the lake (BA1) from 2017.8 to 2021.8 at biweekly basis with approximately 0.1 m vertical resolution File name: totalChla_prof_file_barleber_FP2101.obs (Chl-a concentration) bluegreen_prof_file_barleber_FP2101.obs (Blue-green algae Chl-a concentration) green_prof_file_barleber_FP2101.obs (Green algae Chl-a concentration) diatom_prof_file_barleber_FP2101.obs (Diatom Chl-a concentration)

Lakes are fundamental to society and nature, yet they are currently exposed to excessive nutrients and climate change, resulting in algal blooms. In the future, this may change, but how and where still needs more scientific attention. Here, we explore future trends in algal blooms in lakes globally for >3500 'representative lakes' for the year 2050, considering the attribution of both nutrient and climate factors. We soft-coupled a process-based lake ecosystem model (PCLake+) with a watershed nutrient model (MARINA-Multi) to assess trends in algal blooms in terms of the Trophic State Index for chlorophyll-a (TSI-Chla). Globally between 2010 and 2050, we show a rising trend in algal blooms under fossil-fuelled development (TSI-Chla increase in 91 % of lakes) and a declining trend under sustainable development (TSI-Chla decrease in 63 % of lakes). These changes are significantly attributed to nutrients. While not always significant, climate change attributions point to being unfavourable for lakes in 2050, exacerbating lake water quality. Our study stresses prioritising responsible nutrient and climate management on policy agendas. This implies that the future of algal blooms in lakes is in our hands.

Submerged macrophytes play an important role in maintaining good water quality in shallow lakes. Yet extensive stands easily interfere with various services provided by these lakes, and harvesting is increasingly applied as a management measure. Because shallow lakes may possess alternative stable states over a wide range of environmental conditions, designing a successful mowing strategy is challenging, given the important role of macrophytes in stabilizing the clear water state. In this study, the integrated ecosystem model PCLake is used to explore the consequences of mowing, in terms of reducing nuisance and ecosystem stability, for a wide range of external nutrient loadings, mowing intensities and timings. Elodea is used as a model species. Additionally, we use PCLake to estimate how much phosphorus is removed with the harvested biomass, and evaluate the long-term effect of harvesting. Our model indicates that mowing can temporarily reduce nuisance caused by submerged plants in the first weeks after cutting, particularly when external nutrient loading is fairly low. The risk of instigating a regime shift can be tempered by mowing halfway the growing season when the resilience of the system is highest, as our model showed. Up to half of the phosphorus entering the system can potentially be removed along with the harvested biomass. As a result, prolonged mowing can prevent an oligo-to mesotrophic lake from becoming eutrophic to a certain extent, as our model shows that the critical nutrient loading, where the lake shifts to the turbid phytoplankton-dominated state, can be slightly increased.

El lago Victoria de África oriental proporciona recursos y servicios a millones de personas en las orillas del lago y en el extranjero. En particular, las pesquerías del lago son una fuente importante de proteínas, empleo y conexiones económicas internacionales para toda la región. Sin embargo, la dinámica de las poblaciones es poco conocida y actualmente impredecible. Además, la dinámica pesquera está intrincadamente conectada con otros servicios de apoyo del lago, así como con las sociedades y economías de la orilla del lago. Se han realizado muchas investigaciones poco a poco sobre diferentes aspectos del sistema del lago Victoria; por ejemplo, las sociedades, biodiversidad, pesca y eutrofización. Sin embargo, para desentrañar los impulsores y la dinámica del cambio en este complejo sistema, debemos unir estas piezas y analizar el sistema en su conjunto. Lo hicimos primero construyendo un modelo cualitativo del sistema socioecológico del lago. Luego investigamos el sistema modelo a través de un análisis de bucle cualitativo y, finalmente, examinamos los efectos de los cambios en el estado y la estructura del sistema. El modelo y su análisis contextual nos permitieron investigar las reacciones en cadena de todo el sistema resultantes de las perturbaciones. Es importante destacar que construimos una herramienta que puede ser utilizado para analizar los efectos en cascada de las opciones de gestión y establecer los requisitos para su éxito. Encontramos que una alta conectividad del sistema a nivel de explotación, a través de pesquerías que tienen múltiples poblaciones objetivo, puede aumentar la vulnerabilidad de las poblaciones a la explotación, pero reducir la vulnerabilidad de la sociedad a la variabilidad en las poblaciones individuales. Describimos cómo existen múltiples vías para cualquier cambio en el sistema, lo que dificulta la identificación de la causa raíz de los cambios, pero también amplía el conjunto de herramientas de gestión. También, ilustramos cómo el enriquecimiento de nutrientes no es un proceso de autorregulación, y que la gestión explícita es necesaria para detener o revertir la eutrofización. Este modelo es simple y utilizable para evaluar los efectos de las políticas de gestión en todo el sistema, y puede servir como piedra angular para futuros análisis cuantitativos de la dinámica del sistema a escalas locales. Le lac Victoria en Afrique de l'Est fournit des ressources et des services à des millions de personnes sur les rives du lac et à l'étranger. En particulier, les pêches du lac sont une source importante de protéines, d'emplois et de liens économiques internationaux pour l'ensemble de la région. Néanmoins, la dynamique des stocks est mal comprise et actuellement imprévisible. En outre, la dynamique des pêches est étroitement liée à d'autres services de soutien du lac ainsi qu'aux sociétés et économies riveraines du lac. De nombreuses recherches ont été menées au coup par coup sur différents aspects du système du lac Victoria ; par exemple, les sociétés, biodiversité, pêcheries et eutrophisation.Toutefois, pour démêler les facteurs et les dynamiques de changement dans ce système complexe, nous devons rassembler ces éléments et analyser le système dans son ensemble.Nous l'avons fait en construisant d'abord un modèle qualitatif du système socio-écologique du lac.Nous avons ensuite étudié le système modèle à travers une analyse qualitative en boucle, et enfin examiné les effets des changements sur l'état et la structure du système.Le modèle et son analyse contextuelle nous ont permis d'étudier les réactions en chaîne à l'échelle du système résultant des perturbations.Important, nous avons construit un outil qui peut être utilisé pour analyser les effets en cascade des options de gestion et établir les conditions de leur succès. Nous avons constaté qu'une connectivité élevée du système au niveau de l'exploitation, grâce à des pêcheries ayant plusieurs stocks cibles, peut augmenter la vulnérabilité des stocks à l'exploitation mais réduire la vulnérabilité de la société à la variabilité des stocks individuels. Nous décrivons comment il existe de multiples voies vers tout changement dans le système, ce qui rend difficile l'identification de la cause profonde des changements, mais élargit également la boîte à outils de gestion. Nous illustrons également comment l'enrichissement en nutriments n'est pas un processus d'autorégulation, et qu'une gestion explicite est nécessaire pour arrêter ou inverser l'eutrophisation. Ce modèle est simple et utilisable pour évaluer les effets des politiques de gestion à l'échelle du système, et peut servir de pavé pour les futures analyses quantitatives de la dynamique du système à l'échelle locale. East Africa's Lake Victoria provides resources and services to millions of people on the lake's shores and abroad.In particular, the lake's fisheries are an important source of protein, employment, and international economic connections for the whole region.Nonetheless, stock dynamics are poorly understood and currently unpredictable.Furthermore, fishery dynamics are intricately connected to other supporting services of the lake as well as to lakeshore societies and economies.Much research has been carried out piecemeal on different aspects of Lake Victoria's system; e.g., societies, biodiversity, fisheries, and eutrophication.However, to disentangle drivers and dynamics of change in this complex system, we need to put these pieces together and analyze the system as a whole.We did so by first building a qualitative model of the lake's social-ecological system.We then investigated the model system through a qualitative loop analysis, and finally examined effects of changes on the system state and structure.The model and its contextual analysis allowed us to investigate system-wide chain reactions resulting from disturbances.Importantly, we built a tool that can be used to analyze the cascading effects of management options and establish the requirements for their success.We found that high connectedness of the system at the exploitation level, through fisheries having multiple target stocks, can increase the stocks' vulnerability to exploitation but reduce society's vulnerability to variability in individual stocks.We describe how there are multiple pathways to any change in the system, which makes it difficult to identify the root cause of changes but also broadens the management toolkit.Also, we illustrate how nutrient enrichment is not a self-regulating process, and that explicit management is necessary to halt or reverse eutrophication.This model is simple and usable to assess system-wide effects of management policies, and can serve as a paving stone for future quantitative analyses of system dynamics at local scales. توفر بحيرة فيكتوريا في شرق إفريقيا الموارد والخدمات لملايين الأشخاص على شواطئ البحيرة وخارجها. على وجه الخصوص، تعد مصايد أسماك البحيرة مصدرًا مهمًا للبروتين والعمالة والروابط الاقتصادية الدولية للمنطقة بأكملها. ومع ذلك، فإن ديناميكيات الأرصدة غير مفهومة جيدًا ولا يمكن التنبؤ بها حاليًا. علاوة على ذلك، ترتبط ديناميكيات مصايد الأسماك ارتباطًا وثيقًا بالخدمات الداعمة الأخرى للبحيرة وكذلك بالمجتمعات والاقتصادات الشاطئية للبحيرة. تم إجراء الكثير من الأبحاث بشكل تدريجي على جوانب مختلفة من نظام بحيرة فيكتوريا ؛ على سبيل المثال، المجتمعات، التنوع البيولوجي ومصائد الأسماك والمغذيات. ومع ذلك، لفك تشابك محركات وديناميكيات التغيير في هذا النظام المعقد، نحتاج إلى تجميع هذه القطع معًا وتحليل النظام ككل. لقد فعلنا ذلك أولاً من خلال بناء نموذج نوعي للنظام الاجتماعي البيئي للبحيرة. ثم قمنا بالتحقيق في النظام النموذجي من خلال تحليل حلقة نوعي، وأخيرًا فحصنا آثار التغييرات على حالة النظام وهيكله. سمح لنا النموذج وتحليله السياقي بالتحقيق في تفاعلات السلسلة على مستوى النظام الناتجة عن الاضطرابات. والأهم من ذلك، قمنا ببناء أداة يمكن أن تكون تستخدم لتحليل الآثار المتتالية لخيارات الإدارة وتحديد متطلبات نجاحها. وجدنا أن الترابط العالي للنظام على مستوى الاستغلال، من خلال مصايد الأسماك التي لديها مخزونات مستهدفة متعددة، يمكن أن يزيد من تعرض المخزونات للاستغلال ولكنه يقلل من تعرض المجتمع للتقلبات في المخزونات الفردية. نصف كيف توجد مسارات متعددة لأي تغيير في النظام، مما يجعل من الصعب تحديد السبب الجذري للتغييرات ولكن أيضًا يوسع مجموعة أدوات الإدارة. أيضًا، نوضح كيف أن إثراء المغذيات ليس عملية ذاتية التنظيم، وأن الإدارة الصريحة ضرورية لوقف أو عكس المغذيات. هذا النموذج بسيط وقابل للاستخدام لتقييم الآثار على مستوى النظام لسياسات الإدارة، ويمكن أن يكون بمثابة حجر رصف للتحليلات الكمية المستقبلية لديناميكيات النظام على المستويات المحلية.