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Graphical abstract Highlights • Water level management is important for rehabilitation of wetland plants. • Field investigations and simulation experiments were combined. • WLRs of Carex regarding to each life history stage were considered. • We established an WLRs model of Carex cinerascens in Yangtze floodplain lakes. • A methodology for assessment of WLRs of hygrophytes was presented. Abstract Water level management is of great importance regarding conservation and rehabilitation of wetland plants. However, water level requirements (WLRs) of these plants are not well studied. In the present study, we conducted a systematic assessment of WLRs of Carex cinerascens regarding to each life history stage, based on field investigations and a series of simulation experiments in the Yangtze River floodplain. Results showed that C. cinerascens was well developed in lakes with intermittent water level fluctuations. Its rhizomes could not emerge underwater or in water-saturated conditions, and the optimum soil moisture for emergence was 15–30% with air temperature above 6 °C. Its growth was prohibited when the whole plant was inundated (i.e. inundation depth > plant height), and when rate of water level change exceeded 1.2 cm/d. Although summer inundation was not essential for C. cinerascens development, it was beneficial to the plant for excluding competitive species. The timing of habitat inundation was suggested to be after May when the plant matured. The timing of rhizome emergence in the second growing season was determined by when the habitat was exposed. With inclusion of temperature limits, the optimum timing of habitat exposure in autumn was October, and the duration of summer inundation was therefore 0–150 days. We finally combined WLRs of each life history stage and established an integrated WLRs model of C. cinerascens in Yangtze floodplain lakes. It is the first time that such a WLRs model was proposed for hygrophytes in lakes. Moreover, we presented a methodology for assessment of WLRs of hygrophytes which can be widely used in riverine lakes as well as other wetlands. Our results provide important implications for water level management regarding the conservation and rehabilitation of wetland plants. [ABSTRACT FROM AUTHOR]

The increasing concern for environmental remediation has led to a search for effective methods to remove eutrophic nutrients. In this study, Methylobacterium gregans DC-1 was utilized to improve nitrogen removal in a sequencing batch biofilm reactor (SBBR) via aerobic denitrification. This bacterium has the extraordinary characteristics of strong auto-aggregation and a high ability to remove nitrogen efficiently, making it an ideal candidate for enhanced treatment of nitrogen-rich wastewater. This strain was used for the bioassessment of a test reactor (SBBRbio), which showed a shorter biofilm formation time compared to a control reactor (SBBRcon) without this strain inoculation. Moreover, the enhanced biofilm was enriched in TB-EPS and had a wider variety of protein secondary structures than SBBRcon. During the stabilization phase of SBBRbio, the EPS molecules showed the highest proportion of intermolecular hydrogen bonding. It is possible that bioaugmentation with this strain positively affects the structural stability of biofilm. At influent ammonia loadings of 100 and 150 mg. L−1, the average reduction of ammonia and nitrate-nitrogen was higher in the experimental system compared to the control system. Additionally, nitrite-N accumulation was lower and N 2 O production decreased compared to the control. Analysis of the microbial community structure demonstrated successful colonization in the bioreactor by a highly nitrogen-tolerant strain that efficiently removed inorganic nitrogen. These results illustrate the great potential of this type of denitrifying bacteria in the application of bioaugmentation systems. [Display omitted] • Bioaugmentation with strain DC-1 resulted in faster biofilm formation compared to non-inoculated controls. • Bioaugmentation with strain DC-1 improves ammonia and nitrate-N removal, reduces nitrite-N accumulation, and decreases N 2 O production. • Bioaugmentation with strain DC-1 enhances biofilm structural stability. • Strain DC-1 was able to effectively colonize the bioreactor for an extended period of time. [ABSTRACT FROM AUTHOR]

Managing water level from an ecological perspective has become an urgent issue in recent years in efforts to conserve and restore lake ecosystems. Here we provide a novel methodology to assess water level requirements (WLRs) of shallow lakes, combining geomorphological, hydrological and biological characters. The approach involves five calculation steps, and was applied in a shallow lake of the Yangtze River basin. Whole-lake aquatic vegetation coverage was regarded as a surrogate of ecosystem health. Water level and light availability, two major factors limiting the distribution of aquatic plants, were considered and quantitative relationships were established between water level during germination and vegetation coverage. The germination water level was then treated as a benchmark in determining WLRs of life history stages of aquatic plants. In the model, water levels during the early life history stages were held low and constant to enable germination, and the overall regime was matched with historical natural conditions. The case study showed that vegetation coverage decreased with increasing water level during germination, and a higher Secchi depth (greater water clarity) was associated with a larger coverage. The observed vs. estimated regression line was not significantly different from unity, indicating a high predictive power of the model. The methodology established a quantitative linkage between hydrological variables and ecosystem health. It could be widely used in WLRs assessments in Yangtze shallow lakes as well as other similar waterbodies, providing a useful tool to manage lake ecosystems for conservation and restoration. [ABSTRACT FROM AUTHOR]

Twenty-four lakes associated with the Yangtze floodplain and Huaihe basin, China, with different degrees of disconnection from the river systems, exhibited managed hydrologies ranging from minimally fluctuating reservoir-like lakes, through intermittently fluctuating lakes to those with large, quasi-natural fluctuations in level. We hypothesized that annual water-level fluctuations limit growth and survival of the emergent macrophyte Zizania latifolia. We investigated adaptations to submergence and sought to define the tolerances of Z. latifolia to the amplitude and timing of water-level fluctuations in these types of lake, at different stages in its phenology and life cycle. Shoots from rhizome buds emerged in early spring and reached maximum extension with high water levels in summer. Z. latifolia did not occur in lakes with the highest amplitude (>5 m) of fluctuation. Height growth in lakes with low amplitude (reservoir-like) was smaller than in lakes with greater amplitude (intermittent to quasi-natural fluctuations), giving the appearance of 'short' and 'tall' phenotypes. Across all lakes, however, maximum height was linearly related to water depth in June and to annual amplitude of water level, indicating a continuous phenotypic response. Peak biomass was weakly affected by these environmental drivers. Field experiments showed that seedlings tolerated water depths of c. twice their height (0.6 m), and submergence rates similar to their maximum extension growth rate (2 cm.d−1). Sprouting of rhizome buds was unaffected by submergence to a depth of 0.4 m, but then declined with depth. This study reveals the effects of large-scale hydrological engineering on an emergent macrophyte of economic and conservation importance and informs the management of its populations under seasonally fluctuating water-level regimes. Unlabelled Image • 24 lakes with varied disconnections to a river had different annual hydrologies. • Zizania latifolia tolerated a wide range and pattern of water-level fluctuations. • Tolerances and requirements at different life-history stages were identified. • Adaptation to amplitude in water level involved considerable phenotypic plasticity. • Knowing tolerances facilitates ecohydrological management for multiple-purposes. [ABSTRACT FROM AUTHOR]