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In a commercial fishery, some fish are classified as low-value, but their classification varies in different countries. The aim of this study was to determine the abundance, contribution, and dominance of low-value fish species, such as Abramis brama < 1000 g, Alburnus alburnus, Blicca bjoerkna, Gymnocephalus cernua, Perca fluviatilis < 100 g, Rutilus rutilus < 200 g, and Scardinius erythrophthalmus < 200 g, in 145 Polish lakes of different areas, depths, and trophic statuses situated in the northern and central parts of Poland in 2021. Perca fluviatilis and R. rutilus were the most frequent low-value species (100% and 99%, respectively). The contribution of all low-value fish to the total biomass of caught fish was relatively high, ranging from 37% in the mesotrophic lake to 100% in the eutrophic lake (mean of 77 ± 14%). Lakes in which the contribution of low-value species exceeded 90% were relatively numerous (24 lakes, 17% of the studied lakes). Among a total of about 437.5 thousand low-value fish, 261 thousand specimens (60%) had a body weight of below 10 g. All low-value fish species, except for P. fluviatilis and S. erythrophthalmus, were related to the studied environmental variables. The relative biomass of these species increased with increasing lake productivity, while it decreased with the increasing maximum and mean depth of the studied lakes. The high contribution of low-value fish to the total biomass in many lakes indicates the need for the constant monitoring of the abundance and structure of fish communities and the use of appropriate actions (biomanipulation and stocking with piscivorous fish species) to improve the ecological condition of lakes. [ABSTRACT FROM AUTHOR]

This study was undertaken to elucidate the food web structure and interspecific interactions in the lakes and reservoirs undergoing eutrophication and to assess the efficacy of lake-wide non-traditional biomanipulation (direct predation of cyanobacteria by proliferating planktivorous fish) for bloom management. Analyses of aquatic organisms and stable isotopes of basic food sources and consumers were performed for Zhangze Reservoir in North-central China. Additionally, an improved scheme based on plankton changes and interspecific interactions is proposed on this basis. Compared with other widely-studied eutrophic reservoirs, the δ15N value of each component of the food web in Zhangze Reservoir was higher, the food chain was relatively long and the δ13C range of fish consumers was narrower. Planktivorous fish consumed phytoplankton as their primary food source. However, the phytoplankton biomass and the percentage of cyanobacteria increased, and eutrophication did not improve. The findings concerning the composition of consumers and their food sources in Zhangze Reservoir indicate the urgent need to change the fish structure to optimise the structure of plankton community and mitigate phytoplankton overgrowth. The study findings provide a basis for the implementation of effective eutrophication management strategies in lakes and reservoirs where planktivorous fish are prevalent. [ABSTRACT FROM AUTHOR]

The rising challenge of eutrophication in aquatic systems globally necessitates an understanding of phytoplankton community dynamics under diverse biomanipulation approaches. This study, conducted from June 2022 to July 2023 in the Yuqiao Reservoir's ponds in China, explored phytoplankton dynamics across ponds under different biomanipulation strategies. The study included a pond (BL) without fish stocking, a pond (CH) stocked with carnivorous and herbivorous fish, and another pond (CFD) incorporating a mix of carnivorous, filter-feeding, and detritus-feeding fish. Substantial seasonal variations in phytoplankton density and biomass were observed. In the BL pond, phytoplankton density ranged from 0.23 × 107 to 3.21 × 107 ind/L and biomass from 0.71 to 7.10 mg/L, with cyanobacteria predominantly in warmer seasons and a shift to cryptophytes and chrysophytes in winter. The CH pond exhibited a density range from 0.61 × 107 to 8.04 × 107 ind/L and biomass of 1.11 to 7.58 mg/L. Remarkably, the CFD pond demonstrated a significant reduction in both density (0.11 × 107 to 2.36 × 107 ind/L) and biomass (0.27 to 5.95 mg/L), indicating the effective implementation of its biomanipulation strategy. Key environmental factors including total nitrogen, water temperature, pH, chlorophyll-a, and total phosphorus played a significant role in shaping phytoplankton communities. The study highlights the importance of tailored biomanipulation strategies in aquatic ecosystem management, emphasizing long-term monitoring for sustainable management of eutrophication. [ABSTRACT FROM AUTHOR]

Harmful algal blooms (HABs) are a primary environmental concern, threatening freshwater ecosystems and public health and causing economic damages in the billions of dollars annually. These blooms, predominantly driven by phytoplankton species like cyanobacteria, thrive in nutrient-rich, warm, and low-wind environments. Because of the adverse impacts of HABs, this review examines various control methods, focusing on biological strategies as sustainable solutions. While effective in disrupting algal populations, traditional chemical and physical interventions carry ecological risks and can be resource-intensive. Biological control methods, including biomanipulation and using algicidal microorganisms such as Streptococcus thermophiles, Myxobacteria, and Lopharia spadicea, emerge as eco-friendly alternatives offering long-term benefits. Additionally, barley and rice straw application has demonstrated efficacy in curbing HAB growth. These biological approaches work by inhibiting algal proliferation, disrupting cellular structures, and fostering algal cell aggregation. Despite their advantages over conventional methods, biological controls face challenges, including intricate ecological interactions. This article delves into the latest biological techniques aimed at eradicating HABs, intending to diminish their frequency and reduce toxin levels in aquatic environments. While most research to date has been confined to laboratory settings, scaling these methods to field applications presents hurdles due to the variability and complexity of natural ecosystems. The review underscores the need for further research and development in this critical area of environmental science. [ABSTRACT FROM AUTHOR]

Bubble‐driven microsystems inspired by the therapeutic use of microbubbles under clinical ultrasound actuation offer innovative remote manipulation in biological settings. Ultrasound‐powered microrobots, benefiting from a distribution of vibrating microbubbles (1–100 μm in diameters), exhibit localized fluid flow for self‐propulsion. Microbubbles also contribute to the design of acoustic metamaterials, where distributed actuation of bubbles enables exotic material properties (e.g., negative refractive index). Herein, a metamaterial‐inspired microrobot design, which exploits the streaming induced by the collective oscillation of microbubble arrays (> 10), is reported. Such a large distribution of bubbles offers twofold advantages: a mesoscale microrobot allowing ease of handling and motion at a considerably low acoustic driving pressure of 50 kPa. In this work, the oscillatory amplitude of a single bubble that acts as a unit cell of the metamaterial‐based microrobot is first characterized. Thereon, this amplitude is related to the flow generated by the collective vibration of all the bubbles close to the theoretically predicted resonant frequency of the bubbles. Finally, the hovering motion of the microrobot induced by the streaming and flow‐assisted debris clearance is demonstrated. Such auxiliary functionalities of the microrobot can be useful for applications like contactless sample extraction in inaccessible biological environments. [ABSTRACT FROM AUTHOR]

Large reductions in fish biomass are common both as a method of managing lake ecosystems by fish removals (biomanipulation) and as naturally occurring fish kills. To further understand how fish reductions change feeding patterns of fish, we studied the diets of small‐ to medium‐sized roach (Rutilus rutilus) and European perch (Perca fluviatilis) on a monthly basis using gut‐content analysis during an 18‐month period before and after a whole‐lake fish removal in a eutrophic shallow lake. Further, we performed in‐depth analyses of zoobenthos communities of the profundal and littoral zones, as well as analysed the zooplankton community in the littoral and pelagic parts of the lake to estimate abundance and biomass of potential diet items. We found that, in general, there was a trend toward increased zoobenthivory in both species and among all‐sized fish after fish removal, regardless of prior diet preference. Reduced piscivory among larger perch (>150 mm) and reduced zooplanktivory among smaller perch and roach (<150 mm) were also observed. Moreover, during a short period of high zooplankton biomass after fish removal, both perch and roach (all sizes) shifted their diet toward daphnids, which likely caused a decrease in daphnid population. We suggest that such change toward periodical zooplanktivory across fish species and size groups may lead to unexpectedly high top‐down control by fish after lake restoration by fish removal. [ABSTRACT FROM AUTHOR]

This paper examines the zooplankton abundance and composition along with various environmental factors in Lake Arekit – a shallow freshwater habitat in Ethiopia's rift valley system. Zooplankton samples and specific environmental data were collected by a seasonal campaign (rainy season: June to August) and dry season: March to May 2023) from three sites: inlet area (IA), pelagic area (PA), and macrophyte area (MA). In total, 11 zooplankton taxa from four different groups – rotifera (7 taxa), cladocera (2 taxa), copepod (1 taxa), and ostracoda (1 taxa) – were identified in Lake Arekit. Large-bodied copepoda and cladocera comprised 90% of the zooplankton density in the lake, but small-bodied rotifers dominated the zooplankton diversity. The most noticeable zooplankton in the lake were Mesocyclops aequatorialis, Daphnia barbata, and Cypridopsis vidua. Seasonal difference in the total zooplankton abundance was evident (p < 0.01): being high during the rainy season which was accompanied by an increase in the lake's water temperature and nutrient levels. At MA, where D. barbata predominated, chlorophyll a was relatively low. Chlorophyll a had a strong negative correlation with the abundance of grazing zooplankton, especially with D. barbata (r = −0.563) and C. vidua (r = −0.518). The zooplankton composition and abundance of Lake Arekit reveal a low Shannon diversity index (H') (1.03) and a predominance of a few species, indicating heavy contamination of the lake's water. Moreover, Lake Arekit was determined to be hypertrophic (TSI > 70) using Carlson's trophic index (TSI), which took into account the lake's water transparency, total phosphorus, and chlorophyll a. Our results indicated that high densities of Daphnia should be the goal of biomanipulation since they can achieve filtration potentials high enough to enhance the water's clarity in hypereutrophic lake. Even though high D. barbata concentrations cannot address the underlying cause of eutrophication, grazing can assist by lengthening the clear-water stages in a hypertrophic lake – Lake Arekit. The sources of pollution for the lake are the discharge of wastewater from nearby water bottling companies and possibly high nutrient levels from the lake's geological history. Stopping the discharge of wastewater from the nearby commercial industries (the major source of contaminant) into heavily washed open areas and establishing a buffer zone may help manage the water quality of Lake Arekit. [ABSTRACT FROM AUTHOR]

A project to mechanically remove an over-abundant population of cyprinids (Gila bicolor) was tested in a hydropower impoundment, Lemolo Lake (USA). The netting program removed 29.7 tons of fish (163 kg/ha) over a seven-year period that resulted in a reduction in the intensity and duration of cyanobacteria blooms. However, the suppression of the tui chub population apparently allowed for a residual population of kokanee (Oncorhynchus nerka) to proliferate. The resurgence of the kokanee, combined with the initiation of a rainbow trout stocking program, offset some of the gains in water quality achieved with the reduction of tui chub biomass. The dominant cyanobacterium present in Lemolo Lake transitioned to Gloeotrichia echinulata in 2013, but the majority of these colonies were apparently derived from an upstream lake. The changes in water quality from 2005–2013 were simulated for Lemolo Lake using the two-dimensional, hydrodynamic model, CE-QUAL-W2. The model reproduced many aspects of the water quality in Lemolo Lake and was used, in combination with a simple Bayesian model, to evaluate a number of potential scenarios for further improving water quality in the impoundment. Promoting a deeper drawdown of the hydroelectric impoundment during the winter to selectively increase entrainment of tui chub and kokanee, combined with continued netting targeted at tui chub, was judged to offer the greatest opportunity to manage the facility for water quality, fisheries and hydropower objectives.

Bubble‐driven microsystems inspired by the therapeutic use of microbubbles under clinical ultrasound actuation offer innovative remote manipulation in biological settings. Ultrasound‐powered microrobots, benefiting from a distribution of vibrating microbubbles (1–100 μm in diameters), exhibit localized fluid flow for self‐propulsion. Microbubbles also contribute to the design of acoustic metamaterials, where distributed actuation of bubbles enables exotic material properties (e.g., negative refractive index). Herein, a metamaterial‐inspired microrobot design, which exploits the streaming induced by the collective oscillation of microbubble arrays (> 10), is reported. Such a large distribution of bubbles offers twofold advantages: a mesoscale microrobot allowing ease of handling and motion at a considerably low acoustic driving pressure of 50 kPa. In this work, the oscillatory amplitude of a single bubble that acts as a unit cell of the metamaterial‐based microrobot is first characterized. Thereon, this amplitude is related to the flow generated by the collective vibration of all the bubbles close to the theoretically predicted resonant frequency of the bubbles. Finally, the hovering motion of the microrobot induced by the streaming and flow‐assisted debris clearance is demonstrated. Such auxiliary functionalities of the microrobot can be useful for applications like contactless sample extraction in inaccessible biological environments.

With increasing anthropogenic activities, freshwater ecosystems around the world are becoming increasingly affected by various pressures, including eutrophication, overfishing, and irrational stocking, which may have a negative impact on the food web structure. Despite the extensive research and proposed management measures for eutrophic lakes, there are only few analysis on long-term monitoring data regarding fishery resources. Additionally, there is a lack of evaluation and prediction of the effectiveness of current fish management policies. To remedy this, we analyzed long-term monitoring data from Lake Taihu, China, a severely eutrophicated lake with a skewed fish size structure exhibiting dominance of small individuals. We first constructed 14 Ecopath models to investigate how trophic interactions and biomass fluxes changed from 2007 to 2020. Subsequently, the Ecosim model was used to predict how the biomass of fish and the ecosystem network respond to the initiated 10-years fishing ban. Our results demonstrate long-term changes in fish biomass and ecosystem stability. The analyses revealed that 1) the biomass development in different feeding types of fish is controlled by human activities (mainly catches and stocking) and trophic interactions and 2) the rate of decline in ecosystem network stability slows down during the fishing ban. The primary focus of this study was to fill the gap in long-term serial studies of fish monitoring data and ecosystem stability in the lake and, for the first time, to predict the outcome of the fishing ban from an ecosystem perspective using the Ecosim model. Overall, our results emphasize the importance of rational stocking and fishing policies and provide a better understanding of the changes in the ecological dynamics in Lake Taihu of relevance for the management and restoration of the lake.

Urban ponds provide the most important public contact with surface waters, implying that good water quality is crucial to the quality of urban life. Three eutrophic urban ponds in the south of The Netherlands with a long history of eutrophication-related nuisance were studied and subjected to mitigating measures. The external nutrient load from a mixed sewer overflow to one of the ponds had already been dismantled prior to the study, in a second pond it was dismantled during, while in the third pond the major nutrient source (stormwater run-off from impervious surfaces) was left untouched. In order to rehabilitate the ponds, all were dredged to reduce the internal loading, the fish biomass was reduced, the banks were softened, macrophytes were planted, users were advised to minimize the feeding of the fish and waterfowl, and the external nutrient load was reduced in two of the ponds. The two ponds in which the major external load was reduced showed strongly improved water quality after the additional in-pond measures. In contrast, the pond with ongoing external loading from stormwater run-off showed only marginally improved water quality. This study underpins that stormwater run-off can be polluting and that mitigating measures should only be implemented when the system analysis has revealed their feasibility. [ABSTRACT FROM AUTHOR]

Biomanipulation has been widely used in the ecological restoration of eutrophic lakes for decades. However, biomanipulation is prone to failure if external nutrient loads are not reduced. In order to explore the importance of filter‐feeding fish and bivalves on algal control, an outdoor mesocosm experiment was conducted using different nutrient concentrations. Four treatments simulating daily loads of nutrients in Lake Taihu were studied: current, two times, and three times average daily loads of nutrients with both fish (Aristichthys nobilis) and Asian clam (Corbicula fluminea) and as a control current daily loads without fish or bivalves. Results showed that stocking of filter‐feeding fish and bivalves (80 g m−3 bighead carp; 200 g cm−2 clams) at two times daily nutrient loads could effectively control water column Chl a concentrations and phytoplankton biomass. At higher nutrient concentrations (TN ≥ 260 μg L−1 d−1; TP ≥ 10 μg L−1 d−1), top‐down control of filter‐feeding fish and bivalves was less effective and bottom‐up effects resulted in significant increases of Chl a concentration. Thus, as phytoplankton biomass in freshwater ecosystems is determined by both the top‐down effects of predators and the bottom‐up effects of nutrients, external loadings should be controlled when filter‐feeding fish and bivalves are used for algal control to ensure the efficacy of biomanipulation. [ABSTRACT FROM AUTHOR]

A project to mechanically remove an over-abundant population of cyprinids (Gila bicolor) was tested in a hydropower impoundment, Lemolo Lake (USA). The netting program removed 29.7 tons of fish (163 kg/ha) over a seven-year period that resulted in a reduction in the intensity and duration of cyanobacteria blooms. However, the suppression of the tui chub population apparently allowed for a residual population of kokanee (Oncorhynchus nerka) to proliferate. The resurgence of the kokanee, combined with the initiation of a rainbow trout stocking program, offset some of the gains in water quality achieved with the reduction of tui chub biomass. The dominant cyanobacterium present in Lemolo Lake transitioned to Gloeotrichia echinulata in 2013, but the majority of these colonies were apparently derived from an upstream lake. The changes in water quality from 2005–2013 were simulated for Lemolo Lake using the two-dimensional, hydrodynamic model, CE-QUAL-W2. The model reproduced many aspects of the water quality in Lemolo Lake and was used, in combination with a simple Bayesian model, to evaluate a number of potential scenarios for further improving water quality in the impoundment. Promoting a deeper drawdown of the hydroelectric impoundment during the winter to selectively increase entrainment of tui chub and kokanee, combined with continued netting targeted at tui chub, was judged to offer the greatest opportunity to manage the facility for water quality, fisheries and hydropower objectives. [ABSTRACT FROM AUTHOR]

Abstract Biomanipulation has been widely used in the ecological restoration of eutrophic lakes for decades. However, biomanipulation is prone to failure if external nutrient loads are not reduced. In order to explore the importance of filter‐feeding fish and bivalves on algal control, an outdoor mesocosm experiment was conducted using different nutrient concentrations. Four treatments simulating daily loads of nutrients in Lake Taihu were studied: current, two times, and three times average daily loads of nutrients with both fish (Aristichthys nobilis) and Asian clam (Corbicula fluminea) and as a control current daily loads without fish or bivalves. Results showed that stocking of filter‐feeding fish and bivalves (80 g m−3 bighead carp; 200 g cm−2 clams) at two times daily nutrient loads could effectively control water column Chl a concentrations and phytoplankton biomass. At higher nutrient concentrations (TN ≥ 260 μg L−1 d−1; TP ≥ 10 μg L−1 d−1), top‐down control of filter‐feeding fish and bivalves was less effective and bottom‐up effects resulted in significant increases of Chl a concentration. Thus, as phytoplankton biomass in freshwater ecosystems is determined by both the top‐down effects of predators and the bottom‐up effects of nutrients, external loadings should be controlled when filter‐feeding fish and bivalves are used for algal control to ensure the efficacy of biomanipulation.

The research was carried out on Lake Długie, which, from the mid-1950s was transformed into a receiver for domestic and storm water sewage. Together with the sewage, 51 tons of phosphates, 51 tons of ammonia, 2.6 tons of nitrates, 243 tons of calcium, and 294 tons of chlorides were introduced into the lake. The lake was completely degraded (P > 4 mg/L, N > 30 mg/L, Cl > 70 mg/L). Cutting off the sewage inflow did not improve the environmental conditions in the water body, which indicated that it was necessary to carry out further protection and restoration treatments: artificial aeration with destratification (1987–2000), a phosphorus inactivation method with the use of PAX 18 liquid coagulant (2001, 2002, 2003), cutting off the inflow of storm water (2015), and biomanipulation via the removal of macrophytes (2020). Research has shown that the protective measures carried out in the lake's catchment area, in combination with appropriately selected restoration methods, are an example of good practices that enable the improvement of water quality. The phosphate concentrations in the bottom layers of water do not exceed 0.2 mg P/L, and the ammoniacal nitrogen does not exceed 1.2 mg N/L. The chloride content in the lake water is kept at the level of 20 mg Cl/L, and the calcium in the range from 28 to 40 mg Ca/L. [ABSTRACT FROM AUTHOR]

Submerged macrophytes have attracted increasing attention in lake restoration due to the importance of their structuring communities and stabilizing functions in lake ecosystems. However, there is still a lack of systematic reviews on lake restoration with submerged macrophytes. Thus, we performed a systematic review based on a bibliometric analysis via analyzing and visualizing 934 published works from 1996 to 2023 from the Web of Science core collection. Publication characteristics were summarized, and keyword co-occurrence networks, reference co-citation analysis, and keyword burst tests were conducted. Our results suggest that the increasing attention in this field has partly resulted from the many water treatments and scientific schemes in Europe, China, and the USA and extensive international cooperation. The development of this field was divided into three stages based on keyword bursts (e.g., early, turning, and recent stages). Alternative stable states and biomanipulation laid the foundations of this field in the early stage. Progress in the field was discussed based on four aspects, the influence of environmental factors on submerged macrophytes, theory and mechanisms, targets, and evaluation and methods. Therefore, our results provide a new and comprehensive understanding of lake restoration with submerged macrophytes. [ABSTRACT FROM AUTHOR]

The biomanipulation technique has been developed and implemented for decades, yielding favorable results in various lakes both domestically and globally. This technology uses fish to reduce algae biomass, giving a natural and environmentally friendly solution to improve water quality. The effectiveness of biomanipulation technology in large-scale artificial water canals, on the other hand, has been unclear. To address this, from 15 December 2019 to 30 April 2020, an in situ experimental study on the biomanipulation of periphytic algae was conducted in the Lushan section of the main canal of the Middle Route of the South-to-North Water Diversion Project (MSNWDP). The study aimed to verify the control effect of fish on periphytic algae. Various combinations of Megalobrama terminalis and Xenocypris davidi were fixed on the canal with a triangular cylindrical cage, and their feeding effects on periphytic algae were observed. The results showed that the density of periphytic algae at the bottom of the cages was substantially lower than before the experiment, with a 68.75% average reduction. We graded the food-filling results based on the amount of digestive tract content, which was represented using Arabic numerals ranging from 0 to 5. The study discovered that M. terminalis had the best adaptability to the environment, with full intestines primarily composed of periphytic algae and a food-filling degree between grades 4 and 5. X. davidi, on the other hand, had a food-filling degree of 0. Furthermore, the weight of each M. terminalis increased significantly following the experiment, whereas the weight of each X. davidi decreased to varying degrees. Additionally, the study highlights the importance of selecting the appropriate fish species for biomanipulation, as different species may have varying levels of effectiveness in controlling periphytic algae. Overall, this study provides valuable insights into the potential of biomanipulation technology in large-scale artificial water canals and other water conservancy projects. [ABSTRACT FROM AUTHOR]

Eilers J, Miller R, Loomis D, Vogel A. 2023. Effects of cyprinid removal and reintroduction: Diamond Lake, Oregon. Lake Reserv Manage. 39:156–173. Diamond Lake, located in the Oregon Cascade Range, was treated with rotenone in 2006 to remove invasive populations of cyprinids, Gila bicolor and Notemigonus crysoleucas. The treatment successfully removed all fish, and the lake was restocked in 2007 with rainbow trout (Oncorhynchus mykiss). The treatment resulted in large increases in transparency, large cladocerans (Daphnia pulicaria), and benthic invertebrates. The previous cyanobacterial blooms were comprised almost exclusively of Anabaena [Dolichospermum], whereas the current populations of cyanophytes include Gloeotrichia. Cyprinids were reintroduced into the lake and documented in 2008 (Notemigonus crysoleucas) and 2015 (Gila bicolor), likely contributing to a decline of several metrics of water quality. Piscivorous trout (Salmo trutta and Salmo trutta x Salvelinus fontinalis) were introduced into the lake starting in 2016 to control the introduced cyprinids. The cyprinid populations have stabilized, and most metrics of lake status (Secchi disk transparency, phytoplankton biovolume, abundance of large cladocerans, zoobenthic biomass, trout condition factor) indicate that the lake has improved substantially since the treatment and introduction of piscivorous trout. It is unclear whether the cyprinid populations are constrained by behavioral mechanisms associated with the introduction of the piscivorous trout or whether other factors currently keep the cyprinids in check. The success of this biomanipulation project requires continued monitoring and use of adaptive management strategies to respond to changes in fish composition. [ABSTRACT FROM AUTHOR]

Soil enzymes are crucial in mediating ecosystems' responses to environmental drivers, so that the comprehension of their sensitivity to drivers of global change can help make predictions of future scenarios and design tailored interventions of biomanipulation. Drivers of global change usually act in combination of two or more, and indirect effects of one driver acting through modification of another one often occur, yet most of both manipulative and meta‐analysis studies available tend to focus on the direct effect of one single driver on the activity of specific soil enzymes. One of the biggest challenges is, therefore, represented by the difficulty in assessing the interactions between different drivers, due to the complexity of disentangling the single direct effects from the indirect and combined ones. In this review, after elucidating the general mechanisms of soil enzyme production and activity regulation, we display the state‐of‐the‐art knowledge on direct, indirect and combined effects of the main drivers of global change on soil enzyme activities, identify gaps in knowledge and challenges from research, plus we analyse how this can reverberate in the future of biomanipulation techniques for the improvement of ecosystem services. We conclude that qualitative but not quantitative outcomes can be predicted for some interactions such as warming + drought or warming + CO2, while for other ones, the results are controversial: future basic research will have to center on this holistic approach. A general trend toward the overall increase of soil enzyme activities and acceleration of biogeochemical cycles will persist, until an inflection will be caused by factors such as future shifts in microbial communities and changes in carbon use efficiency. Applied research will develop toward the refinement of "in situ" analytical systems for the study of soil enzyme activities and the support of bioengineering for the better tailoring of interventions of biomanipulation. [ABSTRACT FROM AUTHOR]

Degradation of lake ecosystem is a common problem existing in many countries. Remediation of degraded lake is urgently needed in order to maintain water safety and lake ecosystem health. Restoration of submerged macrophyte is considered as an important measure of ecological remediation of shallow lakes after pollution loading get effectively controlled. Nowadays, enclosures resembling those used in aquaculture historically are widely used for submerged macrophyte restoration. Although submerged macrophyte can be successfully restored in enclosure, it's contribution to the whole lake ecological remediation is limited. Fish manipulation, which reduces fish stock and adjusts fish community structure, was found able to improve water quality and promote submerged macrophyte restoration in many lakes. However, the role of fish in ecological restoration do not receive enough attention in many ecological remediation projects. Future studies are required to better understand the role of fish in lake nutrient cycle and the influence on submerged macrophyte to help develop theory that better guide the fish manipulation for the ecological remediation in shallow lakes. In the end, we want to point out that manipulation of fish community structure following by natural restoration and/or artificial planting of submerged macrophyte could be an effective strategy for whole lake ecological remediation of shallow lakes, and suggest that fish manipulation measure should be tested in more ecological remediation projects of shallow lakes worldwide. [ABSTRACT FROM AUTHOR]

Benthic primary production (BPP) plays an important functional role in lakes, improving water quality by stabilizing clear-water regimes. Shallow, eutrophic lakes lacking BPP communities can be difficult to restore because self-stabilizing feedbacks of phytoplankton dominance can impede the establishment of BPP. BPP in lakes is light limited, and ecosystem models can provide guidance for determining the water clarity necessary to re-establish BPP dominance. We developed a multi-tiered framework for the restoration of shallow, eutrophic lakes that incorporates multiple turbidity sources, lake morphometry, and water-level fluctuations to determine water-clarity thresholds above which BPP dominance may be established. We present a case study applying this restoration target framework to a large, shallow lake (Utah Lake, Utah, USA), where water clarity was greatly impeded by sediment resuspension and high algal biomass. Our analysis, which used commonly available lake-monitoring data, indicated that a return to BPP dominance is possible in Utah Lake, particularly if external nutrient loading to its shallow, wind-protected bays is reduced. Our novel framework incorporates regime shift theory to improve shallow, eutrophic lake restoration efforts. By incorporating ecological feedbacks when identifying the restoration targets necessary for returning a lake to a self-stabilizing, clear-water regime, this restoration target framework offers economical and logistical advantages over strategies that focus solely on phytoplankton management or fish biomanipulation. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate microbubble ozonation for the removal of toxic cyanobacteria, Microcystis aeruginosa. The microbubble ozonation (30 min) at 3.47 mg O3 L−1 decreased the M. aeruginosa concentration from 1.5 × 107 to 0.8 × 107 cell mL−1. However, the acute toxicity (48 h) to Daphnia magna (<24 h old) was considerably increased after the microbubble ozonation, possibly owing to the release of intracellular microcystins (MCs). Considering the release of toxic MCs, the microbubble ozonation was optimized at an environmentally relevant concentration (1.74 × 106 cell mL−1) of M. aeruginosa. Microbubble ozonation at 0.26–1.92 mg O3 L−1 for 30 min removed M. aeruginosa by 26 to 83% without any acute toxicity on D. magna. Moreover, D. magna feeding enhanced the removal rate from 85 to 100% for 48 h. These findings suggest that microbubble ozonation, possibly combined with D. magna biomanipulation, can be a promising tool to control toxic cyanobacteria in ambient water. [ABSTRACT FROM AUTHOR]

AbstractThis paper examines the zooplankton abundance and composition along with various environmental factors in Lake Arekit – a shallow freshwater habitat in Ethiopia’s rift valley system. Zooplankton samples and specific environmental data were collected by a seasonal campaign (rainy season: June to August) and dry season: March to May 2023) from three sites: inlet area (IA), pelagic area (PA), and macrophyte area (MA). In total, 11 zooplankton taxa from four different groups – rotifera (7 taxa), cladocera (2 taxa), copepod (1 taxa), and ostracoda (1 taxa) – were identified in Lake Arekit. Large-bodied copepoda and cladocera comprised 90% of the zooplankton density in the lake, but small-bodied rotifers dominated the zooplankton diversity. The most noticeable zooplankton in the lake were Mesocyclops aequatorialis, Daphnia barbata, and Cypridopsis vidua. Seasonal difference in the total zooplankton abundance was evident (p 70) using Carlson’s trophic index (TSI), which took into account the lake’s water transparency, total phosphorus, and chlorophyll a. Our results indicated that high densities of Daphnia should be the goal of biomanipulation since they can achieve filtration potentials high enough to enhance the water’s clarity in hypereutrophic lake. Even though high D. barbata concentrations cannot address the underlying cause of eutrophication, grazing can assist by lengthening the clear-water stages in a hypertrophic lake – Lake Arekit. The sources of pollution for the lake are the discharge of wastewater from nearby water bottling companies and possibly high nutrient levels from the lake’s geological history. Stopping the discharge of wastewater from the nearby commercial industries (the major source of contaminant) into heavily washed open areas and establishing a buffer zone may help manage the water quality of Lake Arekit.

Harmful algal blooms (HABs) are a primary environmental concern, threatening freshwater ecosystems and public health and causing economic damages in the billions of dollars annually. These blooms, predominantly driven by phytoplankton species like cyanobacteria, thrive in nutrient-rich, warm, and low-wind environments. Because of the adverse impacts of HABs, this review examines various control methods, focusing on biological strategies as sustainable solutions. While effective in disrupting algal populations, traditional chemical and physical interventions carry ecological risks and can be resource-intensive. Biological control methods, including biomanipulation and using algicidal microorganisms such as Streptococcus thermophiles, Myxobacteria, and Lopharia spadicea, emerge as eco-friendly alternatives offering long-term benefits. Additionally, barley and rice straw application has demonstrated efficacy in curbing HAB growth. These biological approaches work by inhibiting algal proliferation, disrupting cellular structures, and fostering algal cell aggregation. Despite their advantages over conventional methods, biological controls face challenges, including intricate ecological interactions. This article delves into the latest biological techniques aimed at eradicating HABs, intending to diminish their frequency and reduce toxin levels in aquatic environments. While most research to date has been confined to laboratory settings, scaling these methods to field applications presents hurdles due to the variability and complexity of natural ecosystems. The review underscores the need for further research and development in this critical area of environmental science.

Wastewaters discharged to Lake Vesijärvi ruined its recreational value and demanded mitigation measures. In the mid-1970s, the diversion of wastewaters elsewhere reduced epilimnetic total phosphorus concentration by ~ 40% from > 100 mg P m−3 in 5 years, but this was not enough to eliminate cyanobacterial blooms. In 1979–1984, hypolimnetic oxygenation was applied to decrease internal nutrient loading, but pumping warm surface water to the hypolimnion probably intensified gas ebullition from the sediment, carrying nutrients to the epilimnion and intensifying cyanobacterial blooms. Intensive fish removal in 1989–1994 was more successful. Five years of summer trawling removed over three-quarters of roach and smelt stock, and after the two most intensive fishing years, TP and chlorophyll concentrations abruptly decreased by ~ 35%. During subsequent years fish removal continued at ~ 30% intensity and maintained chlorophyll and total nutrient concentrations at a lower level until the end of the study. At the same time, the frequency of cyanobacterial blooms decreased from annual to twice per decade. Larger-scale oxygenation after 2010 no longer resulted in ebullition, and its effect on phytoplankton was indistinguishable from natural variability. Consequently, it was abandoned. The intensity of fish removal needed to maintain the present status of the lake is still awaiting evaluation. [ABSTRACT FROM AUTHOR]

Freshwater ecosystems are threatened by eutrophication, which causes persistent and harmful algal blooms. Filter-feeding bivalve mollusks and submerged macrophytes (SMs) alleviate the eutrophication effects by inhibiting phytoplankton biomass blooms. However, very little is known about whether and how the combined manipulation of filter-feeding bivalves and SMs control eutrophication and influence phytoplankton assemblages. Here, we performed a nutrient-enriched freshwater mesocosm experiment to assess the combined effects of the filter-feeding bivalve Cristaria plicata, a cockscomb pearl mussel, and the macrophyte Hydrilla verticillate on the biomass and composition of phytoplankton assemblages. We found that addition of C. plicata and H. verticillate decreased the water nutrient concentrations and suppressed overall phytoplankton biomass. Further, distinct differences in taxa between restoration and control treatments were observed and noticeably competitive exclusion of cyanobacteria in the restoration treatments occurred. An antagonistic interaction between filter-feeding bivalves and SMs was only detected for total cyanobacteria biomass demonstrating that a larger magnitude of SM restoration may override the effect of filter-feeding bivalves. Our results suggest that manipulation, through the addition of bivalves as grazers, associated with the restoration of SMs, is an efficient approach for reducing cyanobacterial blooms and alleviating eutrophication. [ABSTRACT FROM AUTHOR]

In this paper we describe a 25-year (1986-2010) dataset of phytoplankton cell density abundance and biovolume in Lake Candia, a eutrophic, natural, small, and shallow lake located in north-western Italy, with data that are made available through the GBIF repository. The lake belongs to the national (LTER-Italy), European (LTER-Europe) and International (ILTER) long-term ecological research (LTER) networks. Phytoplankton samples were collected approximately monthly at the maximum depth station of the lake (7.7 m) and analysed with the inverted microscope, estimating both the cell density abundance and biovolume of each taxon. The dataset includes 10,120 georeferenced occurrences related to 545 taxa. During this 25-year period, the lake underwent profound modifications mainly related to the lake biomanipulation activities addressed to the management of aquatic macrophyte and to the evolution of the trophic condition. Making this dataset available represents a contribution to the current activities of the LTER networks for defining and reconstructing spatial and temporal dynamics and to identify and compare reliable trends. [ABSTRACT FROM AUTHOR]

Invasive species are a global concern. After an invasive species establishes, they often disrupt ecosystems leading to new dynamics and species interactions, making management efforts difficult. Panarchy theory is a conceptual framework to account for the dual and seemingly contradictory characteristics (stability and change) of all complex systems across distinct spatial and temporal scales. Panarchy theory has the potential to be applied to gain better insight into invaded system dynamics by creating a framework to characterize complex natural systems. This framework allows for management actions (e.g., whole-lake biomanipulations, invasive species control, native species restoration) to be leveraged against natural and induced ecosystem processes, providing a greater probability of desired outcomes. In this review, panarchy theory is applied to invasive species management using rainbow smelt Osmerus mordax as a case study. First, panarchy theory and the invasion history and subsequent ecological effects of rainbow smelt in inland lakes were reviewed. Second, rainbow smelt eradication and control efforts were reviewed to better understand mechanisms that led to long-term success or failure. Last, panarchy theory was applied to discuss future control and(or) native species restoration efforts in invaded lakes. This review found that invasive rainbow smelt cause negative effects on some native ecosystems. The success of invasive rainbow smelt control and(or) eradication efforts depended on whether: 1) enough rainbow smelt were removed to devoid their niche space; and 2) devoid niche space was filled with desired native species from remnant populations or through stocking. This review suggested that the probability of successful invasive species control and(or) native species restoration may be dependent on the four phases of the nested adaptive cycle (i.e., growth, conservation, release, and reorganization) through management intervention during the release phase. The application of panarchy theory should be viewed as a conceptual extension of efforts to restore ecosystems and(or) manage fisheries using a food web and ecosystem context (i.e., "food web thinking", ecosystem-based fisheries management). [ABSTRACT FROM AUTHOR]

Introduction of planktivorous fish or eutrophication can alter lake food webs, especially the zooplankton communities are susceptible to changes in top–down and bottom-up controls, and eventually lead to the dominance of harmful cyanobacteria. Hence, for the recovery of large-size zooplankton abundance that graze on cyanobacteria, there is an urgency to understand the relative roles of top–down and bottom-up effects. Although much is known about these two effects in temperate lakes, little knowledge about their relative importance in subtropical highland lakes exists, where eutrophication and stocked planktivorous fish are of particular concern. Thus, we conducted research in Lake Erhai in Yunnan plateau, China, to examine the drivers affecting the dynamics of crustacean zooplankton. Redundancy analysis (RDA) was used to analyze the effects of environmental variables, phytoplankton biomass, and planktivorous fish on the biomass and body weight of zooplankton taxa in the lake, and variance decomposition analysis was applied to examine the relative roles of the bottom–up and top–down controlling factors on zooplankton biomass. The results of RDA and Pearson correction analysis showed that total nitrogen (TN) in the water column affected phytoplankton and altered the biomass of cladocerans, while water temperature directly affects the biomass of cladocerans. These findings indicate a pronounced bottom–up control link exists from nutrients to phytoplankton, and then to zooplankton. The abundance of Japanese smelt was negatively correlated both with the biomass and body weight of cladocerans. This finding suggests the pronounced top–down control link exists from fish to zooplankton. The results of variance decomposition analysis showed that TN and zooplanktivorous predation were more important in driving total zooplankton biomass, while TN, water temperature and fish predation were more essential in the variation of zooplankton biomass. Our study provides a reference for the recovery of large-size zooplankton populations in eutrophicated lakes. [ABSTRACT FROM AUTHOR]

This brief review describes the major causes of lake cultural eutrophication and assesses different strategies applied to control or reduce the negative consequences of this eutrophication. Excessive nutrient inputs, particularly from agricultural lands through non‐point source runoff, are among the main causes of cultural eutrophication on a global scale. Reducing nutrient inputs from agricultural lands through management of lake catchment areas, therefore, is an integral part of any effort to control lake eutrophication. Nutrient enrichment results in algal blooms and creates favourable condition for the invasion of a lake by alien aquatic weeds, making this invaluable freshwater resource unsuitable for many purposes, including drinking, agricultural and industrial water resources, fishing, transportation and recreational purposes. A major part of this review addresses attempts made to address the negative impacts of eutrophication by restoring water quality. Several research outputs discussing bottom‐up and top‐down control mechanisms were utilized for the present review. Much emphasis has been given in the literature regarding the use of biomanipulation as a promising and sustainable solution for controlling eutrophication. Biomanipulation tools used to control cyanobacteria and algal bloom have involved zooplanktivorous fish removal, piscivorous fish stocking, daphnia stocking, benthivorous fish removal, planktivorous fish stocking and mussel stocking. Further, some insect and fungal species have been used as biological control agents in an effort to control invasive aquatic weeds in tropical lakes. Although this review is limited in its analysis and explanation of the drawbacks associated with each described biomanipulation method, it can be deduced that biomanipulation generally exhibits considerable potential for controlling or reducing phytoplankton overgrowth and aquatic weed invasions, assuming it is also integrated with strategies to control external nutrient loadings to lakes. [ABSTRACT FROM AUTHOR]

As a key link between top‐down regulators and bottom‐up factors, zooplankton responds sensitively to environmental variations and provides information on the ecological state of freshwater systems. Although the response of zooplankton to anthropogenic pressures and fluctuating natural conditions, such as nutrient loading and climate change, has been extensively examined, findings have varied markedly. The mechanistic basis for the correlation between environmental variability and the zooplankton community is still debated, particularly for subtropical eutrophic lakes. We used two methods to analyze physicochemical and selected biological variables derived from long‐term monitoring of Lake Taihu, a subtropical shallow lake in China. We first applied random forest regression to examine how changes in zooplankton were related to a set of environmental variables on interannual time scales. Then we used the results to guide the construction of a conceptual model for piecewise structural equation modeling (pSEM) to quantify more precisely the zooplankton–environment relationship. Zooplanktivorous fish and nutrient concentrations were the most important predictors of long‐term trends in zooplankton in RF regression. Intensification of planktivorous fish predation led to a lower zooplankton biomass and smaller individuals through the removal of larger crustaceans. Moreover, suppression of zooplankton can in part be explained by increases in inedible algae, triggered by a combination of reduced nutrient concentrations and weakened grazer control. These results were also confirmed in the pSEM, which further indicated that top‐down regulators might be more important than bottom‐up factors for the zooplankton community in Lake Taihu. Our results suggest that stocking of filter‐feeding fish in the lake did not meet the expectation that they would control algae, but that the use of biomanipulation measures considering both water quality and fishery management seems promising. This study offers insights into how indicator metrics of zooplankton can improve our understanding of the associations between plankton communities and ecosystem alterations. [ABSTRACT FROM AUTHOR]

Subtropical lakes are often dominated by benthi-omnivorous fish (e.g., crucian carp) that may substantially disturb sediments and thereby increase water turbidity and nutrient concentrations. Piscivores stocking is sometimes used to control these benthi-omnivores in the expectation that they will reduce their adverse effects on the water quality. However, in shallow subtropical lakes the benthic foraging activities of piscivorous fish may also disturb sediments, a topic that has not yet been well elucidated. Here, we conducted a 6-day mesocosm experiment to explore the bioturbation effects of two native subtropical piscivorous fish (i.e., snakehead, Channa argus and mandarin fish, Siniperca chuatsi) in prey fish (crucian carp, Carassius carassius) present and absent scenarios. Our results showed that in mesocosms without prey, both snakehead and mandarin fish greatly increased the concentrations of suspended solids. However, the concentrations of total, organic and inorganic suspended solids were significantly higher in the mesocosms with snakehead than in those with mandarin fish, suggesting that snakehead has higher bioturbation effects than mandarin fish. When crucian carp were present, we found that both snakehead and mandarin fish significantly reduced prey abundance, whereas piscivore stocking did not significantly decrease the suspended solids and nutrient concentrations. Our study revealed differential effects of two subtropical piscivorous fish species on sediment disturbance and water quality, and we suggest that for lake restoration with piscivores stocking, mandarin fish are a better option than snakehead fish as their predation effect was equal but the strength of sediment disturbance by mandarin fish was lower than that of snakehead. [ABSTRACT FROM AUTHOR]

• System analysis guided to a set of measures to revert lake eutrophication. • Coordinated measures were implemented instead of a single intervention. • Five years pre-intervention water quality was compared with five years after. • Water quality strongly improved and no cyanobacteria blooms after intervention. • A combination of measures is powerful in controlling eutrophication in lakes. Controlling lake eutrophication is a challenge. A case-specific diagnostics driven approach is recommended that will guide to a suite of measures most promising in restoration of eutrophic lakes as exemplified by the case of the shallow lake Groote Melanen, The Netherlands. A lake system analysis identified external and internal nutrient load as main reasons for poor water quality and reoccurring cyanobacterial blooms in the lake. Based on this analysis, a package of restoration measures was implemented between January 2015 and May 2016. These measures included fish removal, dredging, capping of peat rich sediment with sand and an active barrier (lanthanum-modified bentonite), diversion of two inlet streams, reconstruction of banks, and planting macrophytes. Dredging and sand capping caused temporarily elevated turbidity and suspended solids concentrations, while addition of the lanthanum-modified clay caused a temporary exceedance of the Dutch La standard for freshwaters. Diversion of inflow streams caused 35 % less water inflow and larger water level fluctuations, but the lake remained water transporting with strongly improved water quality as was revealed by comparing five years pre-intervention water quality data with five years' post-intervention data. Total phosphorus concentration in the water column was reduced by 93 % from 0.47 mg P l -1 before the intervention to 0.03 mg P l -1 after the intervention, total nitrogen by 66 % from 1.27 to 0.21 mg N l -1, total chlorophyll- a by 75 % from 68 to 16 µg l -1, cyanobacteria chlorophyll- a by 88 % from 32 to 4 µg l -1. Turbidity had declined by 58 % from 23.5 FTU to on average 9.9 FTU. No cyanobacteria blooms were recorded over the entire post-intervention monitoring period (2016–2021). Submerged macrophytes increased from complete absence before intervention to around 10 %–15 % coverage after intervention. Repeated fish removal lowered the fish stock to below 100 kg ha-1 with 12 % of bream and carp remaining. Hence, the package of cohesive measures that was based on a thorough diagnosis resulted in rapidly, strongly and enduringly improved water quality. This case provides evidence for the power of combining measures in restoring eutrophic lakes. [Display omitted] [ABSTRACT FROM AUTHOR]

Urban ponds provide the most important public contact with surface waters, implying that good water quality is crucial to the quality of urban life. Three eutrophic urban ponds in the south of The Netherlands with a long history of eutrophication-related nuisance were studied and subjected to mitigating measures. The external nutrient load from a mixed sewer overflow to one of the ponds had already been dismantled prior to the study, in a second pond it was dismantled during, while in the third pond the major nutrient source (stormwater run-off from impervious surfaces) was left untouched. In order to rehabilitate the ponds, all were dredged to reduce the internal loading, the fish biomass was reduced, the banks were softened, macrophytes were planted, users were advised to minimize the feeding of the fish and waterfowl, and the external nutrient load was reduced in two of the ponds. The two ponds in which the major external load was reduced showed strongly improved water quality after the additional in-pond measures. In contrast, the pond with ongoing external loading from stormwater run-off showed only marginally improved water quality. This study underpins that stormwater run-off can be polluting and that mitigating measures should only be implemented when the system analysis has revealed their feasibility.

Freshwater ecosystems are threatened by eutrophication, which causes persistent and harmful algal blooms. Filter-feeding bivalve mollusks and submerged macrophytes (SMs) alleviate the eutrophication effects by inhibiting phytoplankton biomass blooms. However, very little is known about whether and how the combined manipulation of filter-feeding bivalves and SMs control eutrophication and influence phytoplankton assemblages. Here, we performed a nutrient-enriched freshwater mesocosm experiment to assess the combined effects of the filter-feeding bivalve Cristaria plicata, a cockscomb pearl mussel, and the macrophyte Hydrilla verticillate on the biomass and composition of phytoplankton assemblages. We found that addition of C. plicata and H. verticillate decreased the water nutrient concentrations and suppressed overall phytoplankton biomass. Further, distinct differences in taxa between restoration and control treatments were observed and noticeably competitive exclusion of cyanobacteria in the restoration treatments occurred. An antagonistic interaction between filter-feeding bivalves and SMs was only detected for total cyanobacteria biomass demonstrating that a larger magnitude of SM restoration may override the effect of filter-feeding bivalves. Our results suggest that manipulation, through the addition of bivalves as grazers, associated with the restoration of SMs, is an efficient approach for reducing cyanobacterial blooms and alleviating eutrophication.

When improving the water quality of natural bodies such as lakes, the explosive growth of filamentous green alga Cladophora can limit the growth of submerged macrophytes and prevent the water from shifting to a clear state. During the decay of Cladophora, it can cause various water quality issues such as reduced dissolved oxygen, increased nutrient levels and water odor. Biomanipulation, involving the introduction of a suitable density of aquatic animals into the water, can reduce the biomass of filamentous algae. We hypothesized that stocking appropriate densities of aquatic animals could reduce filamentous algal biomass and at the same time reduce the concentration of odorants in the water. Our study investigated the impact of stocking swamp shrimp (Macrobrachium nipponense), rosy bitterling (Rhodeus ocellatus), and silver carp (Hypophthalmichthys molitrix) at low (30 g/m 3 ), medium (60 g/m 3 ) and high (120 g/m 3 ) densities on water quality, biomass of primary producers (such as Cladophora, submerged macrophyte and algae) and malodorous volatile organic sulfur compound dimethyl sulfide (DMS) in the water, respectively. It was found that the swamp shrimp treatment groups and the rosy bitterling high-density groups effectively inhibited the growth of filamentous green algae cover, in which the rosy bitterling high-density group reduced the filamentous green algae mat coverage by 29.65 % compared with the control group. Additionally, the high-density swamp shrimp and rosy bitterling groups notably promoted the growth of submerged macrophytes (Vallisneria denseserrulata), and significantly reduced the concentration of the malodorous DMS in the water. Overall, stocking swamp shrimp and rosy bitterling can benefit the restoration of aquatic ecology and the maintenance of clear water. However, it is essential to consider potential changes in water quality resulting from excessive stocking density. Therefore, the appropriate density and proportion of stocking should be determined in conjunction with the specific scale of the aquatic ecological restoration project., Competing Interests: Declaration of competing interest All authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Rebuilding a clear-water state dominated by submerged macrophytes is essential for addressing eutrophication, yet the impact of benthic fish on water quality is complex. We conducted two experiments to explore the interaction of submerged plants and benthic fish on the water quality. Experiment I investigated the water clearing effects of submerged macrophytes with varying coverage (from 0% to 40%) before and after the removal of benthic fish. Experiment II explored the impacts of benthic fish at different densities on aquatic ecosystems with and without submerged macrophytes. The results showed that an increase in submerged macrophytes coverage significantly enhanced the reduction of some major water quality parameters. We assert that the coverage of submerged macrophytes should not be lower than 40% to establish and sustain a clear-water state in shallow lakes. However, benthic fish significantly weaken the ability of submerged macrophytes to improve water quality. Surprisingly, the presence or absence of macrophytes may reverse the role of benthic fish in freshwater ecosystems. When macrophytes are present, benthic fish can cause water quality to deteriorate. Conversely, when macrophytes are absent, benthic fish with a density of ≤ 10 g/m 3 can restrict the growth of phytoplankton by directly consuming algae or by disturbing sediments to increase turbidity, thereby potentially improving water quality. But the detrimental effects of benthic fish with higher densities may gradually outweigh their benefits to water clarity. Therefore, the percentage of submerged macrophyte cover in combination with the density of benthic fish play crucial roles in shaping the ecological effects of benthic fish and overall ecosystem dynamics. These findings underscore the importance of understanding ecosystem interactions and have practical implications for the management of shallow lakes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Ltd.)

Once introduced to shallow aquatic ecosystems common carp (Cyprinus carpio) often degrade habitat, negatively impacting the native organisms that rely on these systems. Detrimental effects often observed following the introduction of carp include a reduction in water clarity as bottom sediments become disturbed and resuspended and phytoplankton blooms become more severe and frequent. This results in a reduction of submersed aquatic vegetation (SAV), the effects of which are felt across multiple trophic levels. We sought to limit large carp (>70 mm maximum body width) access to a culturally and biologically significant 18,500 ha freshwater coastal wetland located in Manitoba, Canada to restore pre-carp conditions which were characterized by clear water and abundant SAV. In winter 2012–2013, exclusion structures were built to limit access by large carp to Delta Marsh during the spring and summer. A monitoring program (2009–2018) compared marsh conditions before and after carp exclusion. Water clarity improved following carp exclusion, largely driven by a reduction of inorganic suspended solids (ISS) rather than phytoplankton biomass, indicating that maintaining clear water conditions might be supplemented by reductions in nutrient export from agricultural areas adjacent to the marsh. The decrease in ISS and phytoplankton varied spatially, with the greatest change observed in the westernmost area of the marsh which is more sheltered compared to the large open bays characterizing eastern areas of the marsh. SAV doubled in percent cover through the 6 years of monitoring post-carp exclusion and SAV cover and species richness in the marsh was comparable to what was present in the early 1970s when there was also partial carp exclusion. Similar to water clarity, the increase in SAV cover was most significant in sheltered areas of the marsh. Our results suggest that excluding large carp can improve water clarity, SAV cover, and SAV species richness in large freshwater wetlands, benefiting waterfowl and other species.

Submerged macrophytes have attracted increasing attention in lake restoration due to the importance of their structuring communities and stabilizing functions in lake ecosystems. However, there is still a lack of systematic reviews on lake restoration with submerged macrophytes. Thus, we performed a systematic review based on a bibliometric analysis via analyzing and visualizing 934 published works from 1996 to 2023 from the Web of Science core collection. Publication characteristics were summarized, and keyword co-occurrence networks, reference co-citation analysis, and keyword burst tests were conducted. Our results suggest that the increasing attention in this field has partly resulted from the many water treatments and scientific schemes in Europe, China, and the USA and extensive international cooperation. The development of this field was divided into three stages based on keyword bursts (e.g., early, turning, and recent stages). Alternative stable states and biomanipulation laid the foundations of this field in the early stage. Progress in the field was discussed based on four aspects, the influence of environmental factors on submerged macrophytes, theory and mechanisms, targets, and evaluation and methods. Therefore, our results provide a new and comprehensive understanding of lake restoration with submerged macrophytes.

The biomanipulation technique has been developed and implemented for decades, yielding favorable results in various lakes both domestically and globally. This technology uses fish to reduce algae biomass, giving a natural and environmentally friendly solution to improve water quality. The effectiveness of biomanipulation technology in large-scale artificial water canals, on the other hand, has been unclear. To address this, from 15 December 2019 to 30 April 2020, an in situ experimental study on the biomanipulation of periphytic algae was conducted in the Lushan section of the main canal of the Middle Route of the South-to-North Water Diversion Project (MSNWDP). The study aimed to verify the control effect of fish on periphytic algae. Various combinations of Megalobrama terminalis and Xenocypris davidi were fixed on the canal with a triangular cylindrical cage, and their feeding effects on periphytic algae were observed. The results showed that the density of periphytic algae at the bottom of the cages was substantially lower than before the experiment, with a 68.75% average reduction. We graded the food-filling results based on the amount of digestive tract content, which was represented using Arabic numerals ranging from 0 to 5. The study discovered that M. terminalis had the best adaptability to the environment, with full intestines primarily composed of periphytic algae and a food-filling degree between grades 4 and 5. X. davidi, on the other hand, had a food-filling degree of 0. Furthermore, the weight of each M. terminalis increased significantly following the experiment, whereas the weight of each X. davidi decreased to varying degrees. Additionally, the study highlights the importance of selecting the appropriate fish species for biomanipulation, as different species may have varying levels of effectiveness in controlling periphytic algae. Overall, this study provides valuable insights into the potential of biomanipulation technology in large-scale artificial water canals and other water conservancy projects.

Dielectrophoretic manipulations are deft techniques for soft-matter processes. To actuate the target biomolecules more spatiotemporally, the manipulator which can maneuver the adjustable electric field at high speed is required. We have designed a virtual cathode (VC) tool drawn with an electron beam (EB), which is a deformable and maneuverable electrode. In this report, we investigated the electrochemical response of YOYO-1-labeled DNAs by applying the VC tool and evaluated dependency of its dielectric characteristics on pattern frequency. The specific fluorescent bleaching responses we obtained suggested that work lengths and strength of the VC-induced electric field were enhanced as the applied VC pattern has a high pattern frequency. Moreover, we validated the form of the EB-drawing pattern can also affect dielectric characteristics of the VC tool. These results therefore indicate that the VC tool can control the dielectric phenomenon by a well-tuned tool design, which will lead to more flexible manipulations. [ABSTRACT FROM AUTHOR]

Abstract Understanding the relative importance of multiple stressors is valuable to prioritize conservation and restoration measures. Yet, the effects of multiple stressors on ecosystem functioning remain largely unknown in many fresh waters. Here, we provided a methodology combining ecosystem modeling with linear regression to disentangle the effects of multiple stressors on matter flow, an important ecosystem function. Treating a shallow lake as the model ecosystem, we simulated matter flow dynamics during 1950s–2010s with different combinations of stressors by Ecopath with Ecosim (EwE) modeling and determined the relative importance of each stressor by generalized linear mixed models. We found that matter flow of the lake food web was highly dynamic, attributing to effects of multiple anthropogenic stressors. Biological invasion played the strongest role in driving the matter flow dynamics, followed by eutrophication, while biomanipulation (i.e., phytoplankton control by planktivorous fish stocking) was of little importance. Eutrophication had a stronger role on primary producers, pelagic food chain, and top predators, while biological invasion on consumers in the middle of food chains. The former was more important in driving the quantity of matter flow, while the latter on trophic transfer efficiencies. Scenario forecasting showed that reducing nutrients contents could largely shape the matter flow pattern, while biomanipulation had little effect. Our findings provided new insights into understanding the mechanistic links between anthropogenic stressors and ecosystem functioning by combining ecosystem modeling with linear regression.

Zooplankton is a good indicator of water quality state. Analysing the species composition and abundance, it is possible to assess the condition of the water body and predict the direction of changes. The aim of the study was to analyse the zooplankton in a shallow urban lake, in which restoration was limited to one method, i.e. wind-aeration. The results were compared with the earlier data obtained during sustainable restoration (three methods: wind-aeration, phosphorus inactivation, biomanipulation) and before the restoration period. The zooplankton was sampled monthly in 2015 and 2016 in the deepest place of the lake from the surface to the bottom. The trophic state was determined based on rotifer trophic state index for lakes (TSIROT). Although the species composition of zooplankton communities varied very little among the restoration periods (Keratella cochlearis f. tecta mainly dominated), significant changes in the abundance of zooplankton were found in the analysed lake. The maximum of total abundance was noted in 2015, almost 5500 ind. L−1, and in the next year its decrease was almost 3-fold, to ca. 1800 ind. L-1. Based on TSIROT, the water was still eutrophic. Leaving only one method of restoration (namely, oxygenation of the bottom waters) proved insufficient to support the development of crucial organisms as cladocerans. The changes in the abundance could have resulted more from seasonal changes than from the effects of aeration. A reduction in species number and maintaining a high proportion of rotifers typical for a high trophic state indicated a return of the ecosystem to its pre-restoration state. High variability in the rotifer abundance indicated a continuous imbalance of the ecosystem. Previous restoration treatments using several methods simultaneously showed better effectiveness. The change of strategy of restoration before obtaining a stable improvement of water quality destroyed previously achieved effects.

Eutrophication in freshwater has become increasingly severe around the world, resulting in phytoplankton overgrowth and benthic algae reduction. Bivalves can change the density, dominant species and community structure of phytoplankton, increase available light levels, and provide physical habitats and growth conditions for benthic algae. The nutritional composition, density, community structure, and toxin of algae affect the growth, feeding, digestion, metabolism, immunity of bivalves in return. Interactions of bivalves and algae and effects of environmental factors on these interactions need a synthesis of studies, when using bivalves as a biomanipulation tool to control eutrophication. Whether bivalves can effectively suppress phytoplankton and promote benthic algae is related to the collective filtration and excretion capacity determined by size, species, population densities of bivalves, the quantity and quality of algae, and environmental factors such as temperature, dissolved oxygen, pH, and hydrodynamic. Small scale bivalve biomanipulation experiments are mostly conducted in lakes, urban ponds, and reservoirs with some success, applying in the whole ecosystem should consider more questions such as natural conditions, selection and death or reproduction of bivalves, and ecological disturbances. This review provides new considerations for technical issues such as the sustainable cultivation of bivalves and the implementation of biomanipulation in eutrophic waters.

Eutrophication and cyanobacteria blooms are considered major problems for the biodiversity and water quality of urban ponds. While biomanipulation techniques such as drawdown with fish removal have great potential to restore turbid ponds to a clearwater status, it remains difficult to predict if and how macrophytes will recover naturally. Here, we used individual genotyping and population genetics based on 20 nuclear microsatellite loci to investigate the recruitment and recolonization strategies of the submerged macrophyte Stuckenia pectinata (L.) Börner. More specifically, we compared the founder genetic diversity of recovering populations just after biomanipulation to the genetic diversity of spontaneous, contiguous populations that settled over an extended period of time and were within the same catchment. Our results showed that turbid ponds may contain a persistent propagule bank that allows for an immediate re-establishment of genetically diverse populations of S. pectinata once a desired clearwater state is restored. Therefore, biomanipulation without sediment removal proved to be successful for founding populations to become immediately integrated with their established populations, thus maintaining the overall diversity of this species within local areas. Additionally, our results demonstrated an excess of heterozygotes in established populations that may be caused by substantial drift in albeit small effective population sizes of this predominantly outbreeding species. • Persistent seed banks accumulated past-generation diversity. • Seed banks acted as a source for spontaneous population re-establishment. • Spontaneous establishment was sufficient for maintaining genetic diversity. [ABSTRACT FROM AUTHOR]

Infochemicals refer to chemicals responsible for information exchange between organisms. We evaluated the effects of Daphnia magna and Daphnia galeata infochemicals on Microcystis aeruginosa for 15d. The Daphnia infochemicals were obtained from spent medium after culturing Daphnia in Elendt M4 medium for 48 h. Both Daphnia infochemicals significantly increased (p < 0.05) the intracellular reactive oxygen species level and microcystin-LR concentration in M. aeruginosa. This cellular effect increased colony formation of M. aeruginosa , thereby inhibiting the growth of M. aeruginosa. D. galeata infochemicals provoked significantly greater (p < 0.05) adverse effects on M. aeruginosa than those of D. magna infochemicals, which were further exaggerated by pre-exposure of Daphnia to M. aeruginosa. This result seems to be related to the different compositions and concentrations of Daphnia infochemicals. Several Daphnia infochemicals, such as methyl ferulate, cyclohexanone, 3, 5-dimethyl, hexanedioic acid, and bis(2-ethylhexyl) ester, showed a high correlation with M. aeruginosa cell concentration (| r | >0.6), suggesting that they may play a key role in controlling harmful cyanobacteria. Additionally, pre-exposure of D. magna and D. galeata to M. aeruginosa produced oleic acid, methyl ester, and n-hexadecanoic acid, with a highly correlation with M. aeruginosa cell concentration (| r | >0.6). p-tolyl acetate and linoleic acid were detected only in the pre-exposed D. galeata infochemicals. These findings suggest that some of Daphnia infochemicals identified in this study can be a promising tool to control M. aeruginosa growth. However, further studies are required to verify the specific actions of these infochemicals against cyanobacteria. [Display omitted] • Daphnia infochemicals inhibited the growth of Microcystis aeruginosa. • Daphnia galeata showed higher growth inhibition compared with Daphnia magna. • Pre-exposure of Daphnia to M. aeruginosa increased growth inhibition. • Some Daphnia infochemicals were well related to growth inhibition of M. aeruginosa. [ABSTRACT FROM AUTHOR]

Degradation of lake ecosystem is a common problem existing in many countries. Remediation of degraded lake is urgently needed in order to maintain water safety and lake ecosystem health. Restoration of submerged macrophyte is considered as an important measure of ecological remediation of shallow lakes after pollution loading get effectively controlled. Nowadays, enclosures resembling those used in aquaculture historically are widely used for submerged macrophyte restoration. Although submerged macrophyte can be successfully restored in enclosure, it’s contribution to the whole lake ecological remediation is limited. Fish manipulation, which reduces fish stock and adjusts fish community structure, was found able to improve water quality and promote submerged macrophyte restoration in many lakes. However, the role of fish in ecological restoration do not receive enough attention in many ecological remediation projects. Future studies are required to better understand the role of fish in lake nutrient cycle and the influence on submerged macrophyte to help develop theory that better guide the fish manipulation for the ecological remediation in shallow lakes. In the end, we want to point out that manipulation of fish community structure following by natural restoration and/or artificial planting of submerged macrophyte could be an effective strategy for whole lake ecological remediation of shallow lakes, and suggest that fish manipulation measure should be tested in more ecological remediation projects of shallow lakes worldwide.