Restoration Of Aquatic Vegetation Research Articles

Temporal variations in dissolved organic matter properties in a eutrophic lake under water dilution and aquatic plant litter decomposition: A simulated microcosm study revealing the environmental and microbial driving factors

Dilution by importing external clean water and restoration of aquatic vegetation are widely applied strategies for improving water quality of eutrophic lakes, while the influence of dilution or aquatic plant litter decomposition on dissolved organic matter (DOM) properties, which is closely associated with the health of aquatic ecosystems, is rarely known. In this study, the temporal variations of DOM properties in the overlying water of a eutrophic lake (Yilong lake in Yunnan, southwest China) under water dilution and aquatic plant litter decomposition were comparatively investigated via a simulated microcosm study using in situ samples. The results showed that water dilution reduced DOM concentration and bioavailability in the overlying water in a short term (about 45 d), and increased DOM humification, but such effect diminished over time. DOM concentration increased substantially during aquatic plant litter decomposition, and reed litter released much more amounts of DOM than that of cattail litter, which dominated by protein-like substances and characterized by high bioavailability and low humification degree. Nutrient (available phosphorus (AP), NH4+-N and TN) contents in the sediment indirectly affected DOM properties by remarkably influencing microbial community compositions and enzyme activities. The strong correlations between the relative abundances of dominant genera Bacillus and Clostridium and concentrations of DOM components implied the important roles of these taxa in DOM transformations. Our findings highlighted the effects and potential mechanisms of dilution and aquatic plant litter decomposition on DOM properties in eutrophic water bodies, and the necessity of proper water diversion and plant litter harvest to reduce endogenous organic pollution in lakes.

The native submerged plant, Hydrilla verticillata outperforms its exotic confamilial with exposure to polyamide microplastic pollution: Implication for wetland revegetation and potential driving mechanism

Microplastic pollution and biological invasion, as two by-products of human civilization, interfere the ecological function of aquatic ecosystem. The restoration of aquatic vegetation has been considered a practical approach to offset the deterioration of aquatic ecosystem. However, a lack of knowledge still lies in the species selection in the revegetation when confronting the interference from microplastic pollution and exotic counterpart. The present study subjected the native submerged species, Hydrilla verticillata and its exotic confamilial, Elodea nuttallii to the current and future scenarios of polyamide microplastic pollution. The plant performance proxies including biomass and ramet number were measured. We found that the native H. verticillata maintained its performance while the exotic E. nuttallii showed decreases in biomass and ramet number under severest pollution conditions. The restoration of native submerged plant such as H. verticillata appeared to be more effective in stabilizing aquatic vegetation in the scenario of accelerating microplastic pollution. In order to explore the underlying driving mechanism of performance differentiation, stress tolerance indicators for plants, sediment enzymatic activity and sediment fungal microbiome were investigated. We found that polyamide microplastic had weak effects on stress tolerance indicators for plants, sediment enzymatic activity and sediment fungal diversity, reflecting the decoupling between these indicators and plant performance. However, the relative abundance of sediment arbuscular mycorrhizal fungi for H. verticillata significantly increased while E. nuttallii gathered “useless” ectomycorrhizal fungi at the presence of severest polyamide microplastic pollution. We speculate that the arbuscular mycorrhizal fungi assisted the stabilization of plant performance for H. verticillata with exposure to the severest polyamide microplastic pollution.

Water Level Fluctuation Rather than Eutrophication Induced the Extinction of Submerged Plants in Guizhou’s Caohai Lake: Implications for Lake Management

The intensifying global decline in submerged aquatic lake plants is commonly attributed to lake eutrophication, while other drivers such as water levels are seldom considered. This study focused on the sudden extinction of the submerged plants in Caohai Lake, Guizhou, and employed long-term data and a whole-lake water level manipulation experiment to explore the impacts of nutrients and water level changes on the decline in submerged plants. The results indicated that over the past 40 years, the total nitrogen and ammonia nitrogen in the water did not change significantly, while the total phosphorus showed a significant decreasing trend. In recent years, however, the water level rose. The biomass of submerged plants continuously increased until a sudden large-scale extinction occurred in 2021; chlorophyll a also significantly increased. It is speculated that the large-scale extinction of the submerged plants was caused by water level fluctuations rather than eutrophication. After the restoration of the natural hydrological regime of low water levels in winter and spring and high levels in summer and autumn, the submerged plants gradually recovered, with the biomass increasing to 922.6 g/m2 in 2023. The structural equation modeling indicated that the water depth and bottom light availability were the main drivers for the changes in the submerged plants. However, in lake protection and management, more attention is often paid to controlling nutrients, while other influencing factors are neglected. These findings confirm the importance of water levels in the decline in and restoration of submerged plants in shallow lakes, suggesting a focus on water level management in lake protection and aquatic vegetation restoration.

Does littoral substrate affect macroinvertebrate assemblages in Mediterranean lakes?

The objective of this study was to investigate the effects of substrate type in macroinvertebrate assemblages in Mediterranean lakes. Samplings have taken place in the littoral zone of 21 lakes in Greece, between 2015 and 2018. We compared benthic macroinvertebrate assemblages among three substrate types of their littoral zones; sandy, covered with macrophytes and stony substrate. Benthic macroinvertebrate assemblages at sites with extended macrophyte cover differed only slightly in composition and abundance from the ones found in stony and sandy substrates. Coenagrionidae were indicative of sites covered with macrophytes and Oligochaeta and Erpobdellidae were representative of stony substrates. The type of substrate proved to be a statistically significant factor influencing the number of benthic macroinvertebrate taxa, the relative abundance of Oligochaeta and the relative abundance of Odonata. In the context of designing site-adapted management measures, priority could be given to the conservation and restoration of aquatic vegetation in lake littoral zones, which host rich macroinvertebrate assemblages with abundant taxa of Odonata.

Effect of Aquatic Vegetation Restoration after Removal of Culture Purse Seine on Phytoplankton Community Structure in Caizi Lakes

Many reports have demonstrated that the removal of aquaculture purse seine is conducive to the restoration of aquatic vegetation and the improvement in water quality, but less attention has been paid to the effects on phytoplankton. This paper addressed the response of phytoplankton community structure to aquatic vegetation restoration after purse seine removal in Caizi Lakes. The results showed that the average dissolved oxygen (from 7.43 ± 0.25 mg/L to 9.12 ± 0.49 mg/L) and Secchi depth (from 28.40 ± 6.20 cm to 47.61 ± 14.62 cm) in the water column of the Caizi Lakes increased after the restoration of aquatic vegetation, while the average concentrations of total nitrogen (from 2.00 ± 0.16 mg/L to 1.34 ± 0.18 mg/L) and total phosphorus (from 0.15 ± 0.02 mg/L to 0.06 ± 0.01 mg/L) decreased. After the restoration of the aquatic vegetation, the cell density of phytoplankton declined from 21.04 ± 4.57 × 106 cells/L to 12.74 ± 3.63 × 106 cells/L, and the biomass fell from 18.13 ± 3.57 mg/L to 9.72 ± 2.55 mg/L. We also observed that Shannon–Wiener diversity, Margalef and Pielou indices of phytoplankton surged by 66.50%, 46.20% and 84.68%, respectively. Because this study demonstrated that aquatic vegetation could alleviate the eutrophication, it can provide guidance for the restoration and protection of the aquatic ecosystem.

Eutrophication evolution trajectory influenced by human activities and climate in the shallow Lake Gehu, China

Lake eutrophication has become a global environmental pollution problem. Analysis of the eutrophication recovery trajectory of lakes can help to accurately implement regulations and reduce the cost of management. The degradation and recovery trajectories of Lake Gehu were firstly analyzed based on 34-years monitoring data of water quality. A dynamic correlation analysis of the relationship between chlorophyll-a (Chla) and the total phosphorus (TP) (total nitrogen [TN]) at an annual scale was conducted using the filtering trajectory method (FTM). The result showed that the recovery trajectory of Lake Gehu was nonlinear, and showed a short lag time in Chla decrease. The regime shift from a clear-water state to a turbid-water state occurred in Lake Gehu when the TP threshold was 120 μg/L. Combined the filtering trajectory diagram with a principal component analysis, the results revealed that the adverse climate change did not completely offset the positive effect of nutrient load reduction, which required further attention and had significance for eutrophication control. According to the dynamic changes in the algae production efficiency of total phosphorus (ETP), the result showed that the sensitivity of lake eutrophication increased and the TP carrying concentration reduced by 40%-60%. The water quality goal for controlling algae was determined as TP = 40 μg/L (Chla = 10 μg/L), which was 20% stricter than the national standard (TP = 50 μg/L). In conclusion, aquatic vegetation restoration and biological manipulation can be effective alternatives for controlling eutrophication in addition to nutrient load reduction. The eutrophication control target and adaptive strategies were determined according to the recovery trajectory of Lake Gehu in this study. The ETP has reference significance for the management of shallow lakes.

High-light inhibition of two submerged macrophytes in a shallow water experiment

The negative effects, caused by high light, on algae, terrestrial and marine aquatic plants are well documented; those negative effects on freshwater submerged plants are, however, not well known. We determined the negative effects of two common submerged species, Myriophyllum spicatum and Vallisneria natans, on their growth and reproduction in a shallow water experiment along an irradiance gradient. Our results highlighted that the plant mass, relative growth rate and shoot height of V. natans and M. spicatum, and root mass and root length:root mass of M. spicatum and leaf mass and shoot height:shoot mass of V. natans were significantly negatively affected in shallow water with high-light regime (>50 % of full light). While the ramet number of the two species was stimulated by from 20.0 to 36.4 %, and root length, root:shoot, chlorophyll (a:b), chlorophyll (a + b), leaf carbon, nitrogen and phosphorus contents of the two studied macrophytes were not significantly impacted by light. Our results indicated that the high-light inhibition of plant growth was greater on the shoots than on the roots of the plants, although these effects were significantly different between the two studied submerged species and among the measured traits. Accordingly, we should avoid negative effects caused by high light to improve the performance of submerged species when we conduct submerged aquatic vegetation restoration programmes in eutrophic lakes.

Community structure and behavioral characteristics of wintering dabbling ducks (<i>Anas</i>) at Lake Shengjin, the middle and lower reaches of the Yangtze River floodplain

升金湖是长江中下游地区典型的浅水通江湖泊，是东亚-澳大利西亚候鸟迁徙路线上水鸟重要的越冬地. 2017年11月-2018年3月，以该湖泊越冬鸭属(Anas)鸟类为研究对象，对其在芦苇湿地、芡实塘、退耕还湿和水生植被恢复湿地4种湿地生境中的群落结构、行为特征及其环境影响因素进行了研究. 结果表明，升金湖分布有10种越冬鸭属鸟类，斑嘴鸭(Anas poecilorhyncha)、绿翅鸭(A. crecca)和绿头鸭(A. platyrhynchos)为该属鸟类群落的优势种. 鸭属鸟类群落在越冬前期种类和数量最多，在整个越冬期，鸭属鸟类在芦苇湿地中种数、数量、密度和多样性指数最高. 在水生植物盖度高、人为活动弱的芦苇湿地，鸭类的主要行为是休息；在食物资源丰富、人为活动强的芡实塘和退耕还湿湿地，其主要行为是觅食和警戒. 鸭属鸟类群落种数、数量、密度和多样性指数与湿地的面积、水域面积、水生植物盖度呈正相关，与干扰度和水深呈负相关. 觅食时间与气温和沉水植物的盖度呈正相关，与水深和干扰度呈负相关，警戒时间与干扰度呈正相关，与挺水植物的盖度呈负相关. 各种恢复类型的湿地生境成为越冬鸭属鸟类的重要栖息地，因此恢复多种湿地栖息地对于越冬水鸟的保护具有重要意义.;Lake Shengjin, a typical shallow lake connecting Yangtze River in the middle and lower Yangtze floodplain, is an important wintering habitat for waterbirds on the East Asian-Australasian Flyway. From November 2017 to March of 2018, ccommunity structure, behavioral characteristics of wintering dabbling duck (Anas) and the dominant environmental factors in reed wetland, foxnut ponds, farmland-returning wetland and aquatic vegetation restoration wetland at Lake Shengjin were studied. The results show that there were 10 species of dabbling duck at Lake Shengjin, in which spot-billed duck (Anas poecilorhyncha), common teal (A. crecca) and mallard (A. platyrhynchos) were dominant species in the community. In early winter the species and numbers of dabbling duck reached maximum. During the whole overwintering period, the species, number, density and diversity of dabbling ducks reached the peak in reed wetland. The main behavior of dabbing ducks was taking rest in reed wetlands with large-coverage aquatic plants and weak human activity, and was foraging and vigilance in foxnut ponds and farmland-returning dampness with abundant food and strong human activities. The number, flock size, density, diversity and foraging behaviors of dabbling duck community were positively correlated with the wetland area, water area, aquatic plant coverage, while negatively correlated with disturbance degree and water depth. The foraging time of dabbling duck has positive relationship with temperature and coverage degree of submerged plants, and negative relationship with water depth and disturbance. The vigilance time of dabbling ducks was positively related with disturbance and negatively related with the coverage degree of water plants. Various types of restored wetlands have become important habitats for wintering dabbling ducks, therefore, restoring a variety of wetland habitats is of great importance to the protection of wintering waterbirds.

Effect of fast restoration of aquatic vegetation on phytoplankton community after removal of purse seine culture in Huayanghe Lakes

The disappearance of submerged aquatic vegetation caused by the use of purse seine in productive fishery has aroused the attention of the national government. In order to restore aquatic vegetation, the government has removed the seine nets on the Huayanghe Lake's surface. Here, fourteen cruises were conducted in the Huayanghe Lakes from 2016 to 2019 to study the response of water quality and phytoplankton communities to rapidly recovering aquatic vegetation. The results showed that the restoration of aquatic vegetation increased the Secchi depth (from 65.36 to 105.52 cm) and dissolved oxygen (from 8.98 to 12.17 mg/L), while the concentration of total nitrogen (from 0.98 to 0.53 mg/L), and total phosphorus (from 0.04 to 0.02 mg/L) decreased, resulting in a 35.3% and 11.6% reduction in the total phytoplankton density and chlorophyll ɑ, respectively. In addition, the restoration of aquatic vegetation significantly increased Shannon–Wiener diversity, Margalef richness indices by 51.6% and 40.1%. We also observed that phytoplankton density exhibited significant changes based on nonmetric multidimensional scaling analysis (NMDS). In Lake Huangda, the coverage of aquatic vegetation was as high as 80%. We also observed that after the restoration of aquatic vegetation, the proportion of cyanobacteria decreased significantly by 21%. Our study emphasizes that aquatic plants can alleviate eutrophication and increase the diversity of phytoplankton, thus providing guidance for the restoration and protection of water ecosystems in the lakes connected to the Yangtze River.

Hatchling short-necked turtles (Emydura macquarii) select aquatic vegetation habitats, but not after one month in captivity

Knowledge of turtle hatchling ecology is fundamental for managing wild populations. Information on habitat selection by turtle hatchlings is particularly important to ensure that conservation programmes that release hatchlings into the wild give them the best chances of surviving to adulthood. Currently, knowledge of the ecology of turtle hatchlings worldwide is limited, which restricts evidence-based management for threatened species. Here, we used laboratory and field experiments to test for effects of captivity on habitat selection, movement, and short-term survival of Murray River turtle hatchlings (Emydura macquarii). This species has declined > 60% since the 1970s, and a conservation plan is urgently needed to manage their recovery. In both the laboratory and field, we found that hatchlings select aquatic vegetation when it is available. Hatchlings raised in captivity for a month, however, were radio-tracked in habitats significantly further from vegetation after release, and over three times as many of these hatchlings were attacked by predators, compared to those released immediately after hatching. Aquatic vegetation is clearly an important habitat for hatchling E. macquarii, and therefore, (i) hatchling conservation should prioritise areas with appropriate aquatic vegetation, and (ii) aquatic vegetation restoration should be prioritised to ensure E. macquarii hatchling survival in the wild. Moreover, since captivity affects hatchling habitat selection, E. macquarii hatchlings should be released immediately upon hatching. Further research on soft release techniques and longer-term captivity is required to determine whether the impact of captivity can be reduced.

Aquatic Macrophytes in Morphological and Physiological Responses to the Nanobubble Technology Application for Water Restoration

Nanobubble technology, as an emerging and sustainable approach, has been used for remediation of eutrophication. However, the influence of nanobubbles on the restoration of aquatic vegetation and the mechanisms are unclear. In this study, the effect of nanobubbles at different concentrations on the growth of Iris pseudacorus (Iris) and Echinodorus amazonicus (Echinodorus) was investigated. The results demonstrated that nanobubbles can enhance the delivery of oxygen to plants, while appropriate nanobubble levels will promote plant growth, excess nanobubbles could inhibit plant growth and photosynthesis. The nanobubble concentration thresholds for this switch from growth promotion to growth inhibition were 3.45 × 107 and 1.23 × 107 particles/mL for Iris and Echinodorus, respectively. Below the threshold, an increase in nanobubble concentration enhanced plant aerobic respiration and ROS generations in plants, resulting in superior plant growth. However, above the threshold, high nanobubble concentrations induced hyperoxia stress, particularly in submergent plants, which result in collapse of the antioxidant system and the inhibition of plant physiological activity. The expression of genes involved in modulating redox potential and the oxidative stress response, as well as the generation of relevant hormones, were also altered. Overall, this study provides an evidence-based strategy to guide the future application of nanobubble technology for sustainable management of natural waters.

Submerged macrophytes successfully restored a subtropical aquacultural lake by controlling its internal phosphorus loading.

Intensive aquaculture has largely changed the global phosphorus (P) flow and become one of the main reasons for the eutrophication of global aquatic ecosystem. Artificial planting submerged macrophytes has attracted enormous interest regarding the restoration of eutrophic lakes. However, few large-scale (>80km2) studies have focused on the restoration of aquatic vegetation in the subtropical lakes, and the mechanism underlying the restrain of sediment P release by macrophytes remains unknown. In this study, field surveys and the diffusive gradients in thin films (DGT) technique were used to elucidate the effects of macrophytes on internal P loading control in a typical eutrophic aquacultural lake. Results showed that half of the P content in overlying water and sediments, particularly dissolved P in overlying water and calcium bound P (Ca-P) in sediment, were removed after restoration. Temperature, as well as dissolved oxygen (DO) and P concentration gradients near the sediment-water interface (SWI) jointly controlled the release of labile P from surface sediments. Submerged macrophytes can effectively inhibit the release of sediment P into the overlying water, which depended on DO concentration in the bottom water. Future restoration projects should focus on the temperature response of submerged macrophytes of different growth forms (especially canopy-forming species) to avoid undesirable restoration effects. Our results complement existing knowledge about submerged macrophytes repairing subtropical P-contaminated lakes and have positive significance for lake restoration by in situ phytoremediation.

Diversity of wintering waterbirds enhanced by restoring aquatic vegetation at Shengjin Lake, China

The restoration of planted vegetation contributes towards improving the habitat quality of waterbirds and enhancing the diversity of their communities. Thus, the success of projects attempting to restore aquatic vegetation could, in part, be quantified by evaluating the community structure of wintering waterbirds. Here, we evaluated the effect of wetland restoration (through planting aquatic vegetation) by comparing waterbird communities in restored versus unrestored areas over two wintering periods (2017–2018 and 2018–2019). Specifically, the use of aquatic vegetation by waterbirds was evaluated following restoration, and was compared against three control (unrestored) areas; namely, a Euryale ferox planting area, freshwater aquaculture area, and rice planting area. Twenty-nine species belonging to eleven families of waterbirds were recorded across the four habitats. Species richness and density of waterbirds in the restored aquatic vegetation area were significantly higher than those in the three control areas. The restored aquatic vegetation area had the highest absolute value of Temporal Beta-diversity Index (TBI), while species gains (C) were significantly greater than species losses (B). Additionally, there was a significant increase in the number of wintering waterbird species from three foraging guilds in the restored aquatic vegetation area during the wintering period of 2018–2019 compared to 2017–2018 (Granivore guild; Invertivore guild; Piscivore guild). The restoration of aquatic vegetation mainly caused the number of Anatidae species to increase, including ruddy shelduck (Tadorna ferruginea), common teal (Anas crecca), common mallard (Anas platyrhynchos), spot-billed duck (Anas poecilorhyncha), and common pochard (Aythya ferina). Submerged vegetation provides ducks with important food resources, such as seeds. And emerging vegetation facilitating the concealment of waterbirds. In conclusion, the artificial promotion of aquatic vegetation restoration at Shengjin Lake has contributed towards maintaining the structure of wintering waterbird communities.

Analysis on the changes of zooplankton in the restoration of urban lake water

The combination of aquatic vegetation restoration and biological manipulation had become one of the important ways of ecological restoration of lake water. Zooplankton was closely related to aquatic plants, which affected the species composition, density and diversity index of zooplankton. Zooplankton was also a part of biological manipulation, which helped to control phytoplankton and improved the transparency of water body. Through the analysis of the role of zooplankton in ecological restoration and the response of zooplankton to the ecological restoration of water body fully reflected the complementary relationship between biological manipulation and aquatic vegetation restoration. Combined with the practice of zooplankton changes in the ecological restoration of typical tropical shallow city lake, it was expected to provide basis and support for the restoration of urban lake.

Study on the relationship of ecological effect in the ecological restoration of urban lakes

the combination of biological manipulation and aquatic vegetation restoration had become an important way of ecological restoration of lake water. The research on the relationship among fish, zooplankton and aquatic vegetation was helpful to lake ecological restoration. By investigating the distribution of fish, aquatic vegetation and zooplankton in some urban lakes in the South of the five ridges, the abundance and relative abundance of Cladocera and Copepoda were generally lower in the lakes where fish was farmed, while the abundance of Cladocera and crustacea was relatively higher in lakes with hydrophytes. The ecological restoration of typical tropical shallow urban lake showed that the combination of aquatic vegetation restoration and fish regulation was an effective measure for the control of tropical shallow eutrophication urban lake. It provided a reference for how to take biological control measures to restore the water body and how to maintain the stability of the ecosystem after the ecological restoration.

Effects of Increased Carbon Supply on the Growth, Nitrogen Metabolism and Photosynthesis of Vallisneria natans Grown at Different Temperatures

Vallisneria natans is often used for the ecological restoration of aquatic vegetation. V. natans thalli were cultured under ambient (400 ppm) and increased carbon supply, with low (18 °C) and high temperature (25 °C). The thalli were used to examine the effects of increased carbon and high temperature on the growth, nitrogen metabolism and photosynthetic characteristics of this plant. At 18 °C, the relative growth rate (RGR), N uptake rate and nitrate reductase (NR) activity of V. natans thalli grown under ambient carbon supply were lower than those under increased carbon supply. The increased carbon supply decreased the RGR, N uptake rate, NR activity and maximum inorganic carbon (Ci) -saturated photosynthetic rate (Vmax) of V. natans when it was cultured at 25 °C. Regardless of the carbon supply levels, the growth, nitrogen uptake capacity and photosynthesis of V. natans thalli grown at 25 °C decreased compared with those of V. natans thalli grown at 18 °C. The RGR and photosynthetic rate of V. natans grown in the presence of increased carbon supply and high temperature were the lowest amongst the four different conditions. Therefore, the negative effects caused by a high temperature were pronounced under the condition of a global atmospheric CO2 increase.

Unnatural hypoxic regimes

AbstractCoastal hypoxia is increasing worldwide in response to human‐caused changes in global climate and biogeochemical cycles. In this paper, we view anthropogenic trends in coastal hypoxia through the lens of disturbance ecology and complexity theory. Complexity theory provides a framework for describing how estuaries and other coastal aquatic ecosystems respond to hypoxia by understanding feedback loops. Can it also be valuable in understanding how these ecosystems behave under shifting (i.e., unnatural) disturbance regimes? When viewed as a disturbance regime, shifts in the spatial (areal extent and fragmentation) and temporal (frequency and duration of events) characteristics of coastal hypoxia can be used to track changes into a non‐stationary future. Here, we consider options for increasing the resilience of coastal aquatic ecosystems to future, unnatural hypoxic regimes. To start, we define desirable states as ecosystems with long trophic chains and slow nutrient and carbon dynamics that produce many ecosystem services. We then work backward to describe circumstances dominated by positive feedbacks that can lead ecosystems toward an undesirable state (i.e., depauperate communities and chemically reduced sediments). Processes of degradation and recovery can be understood in the context of island biogeography whereby species diversity in habitats fragmented by hypoxia is determined by the balance between rapid local extinction, slow recolonization from the edges of hypoxic patches, and opportunities for ecological succession during between disturbance events. We review potential future changes associated with changing global climate and highlight ways to enhance coastal resilience. In addition to efforts to slow climate change, potential interventions include reduced nutrient and carbon loadings from rivers, restoration of aquatic vegetation, and managing for key species, including those that promote sediment oxygenation, that enhance water clarity, or that promote grazing on epiphytic algae through top‐down control.

Proposing priorities of intervention for the recovery of native fish populations using hierarchical ranking of environmental and exotic species impact

The freshwater populations of native fish species (Ns) have reached critical levels in many parts of the world due to combined habitat deterioration by human interventions and exotic fish species (Es) invasions. These alarming conditions require combined and well-designed interventions for restoring environmental quality and restricting Es invasion. The aim of the study is to propose a method to design spatially explicit priorities of intervention for the recovery of Ns populations in highly impacted freshwater systems by exotic multi-species invasion and water quality (WQ) degradation. WQ and Es are used as Ns descriptors, which require intervention. The method uses gradient analysis (ordination method of Canonical Correspondence Analysis) for assessing the weights of Ns descriptors' effects, which are further used to develop weighted severity indices; the severity index of WQ (Swq) and Es invasion (Se), respectively. Swq and Se are further merged to one combined total severity index St. The proposed method provides a) a ranking of the sites, based on the values of St, which denotes the priority for combined intervention in space and can be visualized in maps, b) a ranking of the most important Ns descriptors for each site to perform site-specific interventions, and c) Es rankings based on their potential threat on Ns for species-specific interventions. WQ, Es and Ns data from 208 sampling sites located in the Emilia-Romagna Region (Northern Italy) were used as a case study for the presentation of the proposed method. The application of the method showed that the north and northwestern lowland areas of Emilia-Romagna region presented the higher priority for intervention since the Ns of these areas are the most impacted from combined Es invasions and WQ degradation. Specific Es belonging to cyprinids, which are mostly responsible for the decline of aquatic vegetation and the increase of water turbidity, and a top Es predator (Wels catfish) were mostly present in these areas. Additionally, the most important WQ stressors of Ns were found to be COD, BOD and temperature that are all connected to oxygen depletion. The aforementioned conditions in the areas described by high priority for intervention can be used as a basis for the development of specific Ns conservation practices targeting the containment of the most harmful Es, the restoration of aquatic vegetation and the improvement of oxygen conditions.

Submerged Aquatic Vegetation Restoration in Brackish Ecosystems Subject to Strong Winds and Coastal Jets

The bottom shear stress (BSS) in a windy Mediterranean lagoon has been carefully investigated through numerical modelling. BSS maps have been obtained for the entire lagoon. The aim is to compare BSS with its critical value in the near shoreareas selected for SAV replanting which are subject to downwind coastal jets.

The distribution of aquatic vegetation in Gonghu Bay, Lake Taihu, 2012

Gonghu Bay is an important drinking water resource area for Wuxi City and Suzhou City. With the rapid deterioration of water quality,cyanobacteria bloom has become progressively worse,which might endanger human healthy through water utilization.In order to provide a theoretical basis for managing water resources of Gonghu Bay,an aquatic vegetation survey was undertaken.Eight transects were set,and boat-based survey was performed. The results indicated: 1) There were 34 species,belonging to 27 genus and 20 families,distributed in Gonghu Bay. Monocotyledons and submerged plants were the dominant taxa and ecotypes,respectively. 2) Grass-dominated state and algal-dominated state were coexisted in Gonghu Bay,as the results of the percentage of aquatic vegetation distribution area to total area was 45. 35%,while the percentage of bare water area to total area was 54. 65%.3) The aquatic vegetation in Gonghu Bay could be divided into 8 community types,and the Potamogeton malaianus community was the biggest in terms of distribution area and biomass. 4) Overall,the distribution pattern of aquatic vegetation in Gonghu Bay illustrated that north area was associated with bare water,east area was dominated by macrophytes,and other areas were taken by macrophytes with low coverage and biomass. The distributions of aquatic macrophytes in Gonghu Bay might have responded to the deterioration of water quality and fishing practice by trap nets. Furthermore,we also speculated that over-excavated dredging wasthe reason that aquatic macrophytes disappeared in north area. The current research suggested that,in order to improve the vegetation growth,aquatic vegetation restoration projects should be carried out in the north and the bay mouth of Gonghu Bay. Meanwhile,water quality monitoring of Yangtze River-Lake Taihu water transfer project should be further strengthened. What's more,invasive plants,especially Cabomba caroliniana,should be effectively monitored.