Response of microbial communities to nutrient removal in coastal sediment by using ecological concrete.

Ecological concrete (eco-concrete) is a kind of environment-friendly material with porous characteristics. In this study, the eco-concrete was used to remove the total nitrogen (TN), total phosphorus (TP), and total organic carbon (TOC) in marine coastal sediment. The bacterial communities in sediment and on eco-concrete surface were also investigated by using high-throughput sequencing and quantitative PCR of 16S rRNA gene. We found that the mean removal efficiencies of TN, TP, and TOC in treatment group were 8.3%, 8.4%, and 12.3% after 28 days. The bacterial community composition in the treatment group was significantly different from that in the control group on day 28. In addition, the bacterial community composition on eco-concrete surface was slightly different from that in sediment, and the copy numbers of 16S rRNA gene were higher on eco-concrete surface than in sediment. The types of eco-concrete aggregates (gravel, pebble, and zeolite) also had effects on the bacterial community composition and 16S rRNA gene copy numbers. Furthermore, we found the abundant genus Sulfurovum increased significantly on eco-concrete surface in the treatment group after 28 days. Bacteria belonging to this genus were found having denitrification ability and were commonly detected in bioreactors for nitrate removal. Overall, our study expands the application scopes of eco-concrete and suggests that the bacterial communities in eco-concrete can potentially enhance the removal efficiency of nutrients in coastal sediment.

Nutrient Removal in Eutrophic Water Promotes Stability of Planktonic Bacterial and Protist Communities.

Nutrient (nitrogen and phosphorus) removal by using bioremediation technologies in eutrophic water alters bacterial and protist community structure and function, but how it changes the stability of community remains unclear. To fill this gap, in this study, bacterial and protist communities were investigated using 16S and 18S rRNA gene high-throughput sequencing during the nutrient removal by using ecological floating beds of Canna indica L. Our results showed that both bacterial and protist community compositions in the treatment group were similar to those in the control group at the beginning of the experiment (day 1 to day 11), but then bacterial and protist community compositions became more stable with the removal of nutrients in the treatment group than those in the control group (day 12 to day 18). We further explored the mechanisms for this increased stability and found that the contribution of the stochastic process to bacterial and protist community variations was higher in the control group than that in the treatment group. This suggests that the high nutrient concentration in the control group might increase the random colonization or extinction, and therefore resulted in the high temporal variability (i.e., unstable) of bacterial and protist communities. Our findings suggest that bioremediation for eutrophication can promote the stability of aquatic communities, and therefore potentially maintain aquatic ecosystem functions and services to humanity.

Transformations from specialists to generalists cause bacterial communities are more stable than micro-eukaryotic communities under anthropogenic activity disturbance.

Different microbial components have different responses to environmental disturbances. Here, we found that the planktonic bacterial and micro-eukaryotic communities had different responses to anthropogenic activity disturbance in a subtropical river, because they had different survival strategies (generalist and specialist). We used nutrients (nitrogen and phosphorus) as indicators of anthropogenic activities. We found that river stretch 1 showed low nutrient concentrations from October 2018 to September 2019. However, a nutrient disturbance was observed in river stretch 2. The nutrient concentrations increased largely in December and January but recovered to low values in June. Bacterial communities had higher resilience under this disturbance than micro-eukaryotic communities in river stretch 2. The bacterial community composition were quite different between the two river stretches in December and January but were similar in June and July. However, the differences of micro-eukaryotic community composition between the two river stretches were always high during the study period. The bacterial communities in river stretch 2 contained more generalists and nutrient tolerant specialists. The bacterial nutrient tolerant specialists rapidly decreased in the low nutrient months and were replaced by the generalists. Bacteria which were involved in this shifts accounted for 29.3% of the total abundance. However, the micro-eukaryotic communities in river stretch 2 contained more moderate generalists. These moderate generalists were insensitive to the variation of nutrients and only 19.56% of the micro-eukaryotes had significant responses to the disturbance. The survival strategies caused bacterial communities had higher adaptability than eukaryotes to environmental fluctuation.

Use of ecological concrete for nutrient removal in coastal sediment and its effects on sediment microbial communities.

Ecological concrete (eco-concrete) can reduce excess nutrients (nitrogen and phosphorus) in water, but its effectiveness in removing nutrients in marine coastal sediments and the response of sediment microbial communities to its use are largely unknown. In this study, eco-concrete planted with Bruguiera gymnorrhiza was used to remove nutrients in marine coastal sediment. We found that the mean removal efficiencies of sediment total nitrogen and total phosphorus by using planted eco-concrete were 11.50% and 30.31% on day 60, and were higher than those obtained by only using B. gymnorrhiza (7.14% and 7.36%). the Diatoms and bacterial genera Fusibacter and Anoxynatronum (which belong to Firmicutes) increased and became the abundant microbes by day 60 when using planted eco-concrete, indicating their potential roles in nutrient removal. Moreover, the eco-concrete did not endanger the core microbes in sediment suggesting its environment-friendly character. Our results suggest a potential method to control marine coastal eutrophication.

Characteristics of microbial eukaryotic community recovery in eutrophic water by using ecological floating beds.

Ecological floating beds can rapidly remove nutrients (nitrogen and phosphorus) from eutrophic water, but we still know little about whether this process can simultaneously recover microbial eukaryotic communities. To fill this gap, planktonic microbial eukaryotic communities were investigated using 18S rRNA high-throughput gene sequencing during nutrient removal by floating beds of Canna indica L. We found that nutrient concentrations were high in both the control and treatment groups during period 1 (days 0-5) but rapidly decreased in the treatment group during period 2 (days 6-9) and period 3 (days 10-18). However, the microbial eukaryotic species richness and community compositions were similar between the control and treatment groups during periods 1 and 2 but showed small differences during period 3. The microbial eukaryotic co-occurrence networks between the control and treatment groups also showed similar degree centrality and interconnected eukaryotic members. We found that some abundant fungi species significantly responded to nutrient variations, but a large number of abundant ciliates were insensitive to nutrient removal. Our findings suggest that ecological floating beds can rapidly remove nutrients in eutrophic waters but that it is difficult to quickly and simultaneously improve microbial eukaryotic communities. This result reveals the critical influence of nutrient pollution on aquatic ecosystems and therefore on long-term and comprehensive aquatic habitat restoration, as aquatic macrophyte recoveries should be conducted after nutrient controls have been implemented.

Hysteretic response of Microbial Eukaryotic Communities to Gradually Decreased Nutrient Concentrations in Eutrophic Water.

External environments to microbial eukaryotic communities often change gradually with time. However, whether the responses of microbial eukaryotic communities to these gradually changed environments are continuous or hysteretic and the mechanisms underlying these responses are largely unknown. Here, we used a microcosm to investigate the temporal variation of microbial eukaryotic communities with the gradually decreased nutrient concentrations (nitrogen and phosphorus). We found the differences of microbial eukaryotic community composition and species richness between the control and treatment groups were low during the days 0 to 12, although the nutrient concentrations decreased rapidly during this period in treatment group. However, these differences were clear during the days 14 to 18, although the nutrient concentrations decreased slowly during this period in treatment group. The mechanisms for these results are that the strong homogenous selection (perhaps due to the biotic factors) during the days 8 to 10 in treatment group might enhance the stability of microbial eukaryotic communities. However, the continuously decreased nutrient concentrations weakened the homogenous selection and promoted the strength of environmental filtering, and therefore resulted in the distinct change of microbial eukaryotic communities during the days 14 to 18 in treatment group. Fungi, Chlorophyta and Chrysophyta which associated with the nutrient removal played important roles in this hysteretic change of microbial eukaryotic communities. Overall, our findings suggest that disentangling the non-linear response of communities to gradual environmental changes is essential for understanding ecosystem restoration and degradation in future.

Decline in water level boosts cyanobacteria dominance in subtropical reservoirs.

Globally aquatic ecosystems are likely to become more vulnerable to extreme water fluctuation rates due to the combined effects of climate change and human activity. However, relatively little is known about the importance of water level fluctuations (WLF) as a predictor of phytoplankton community shifts in subtropical reservoirs. In this study, we used one year of data (2010-2011) from four subtropical reservoirs of southeast China to quantify the effects of WLF and other environmental variables on phytoplankton and cyanobacteria dynamics. The reservoirs showed an apparent switch between a turbid state dominated by cyanobacteria and a clear state dominated by other non-cyanobacterial taxa (e.g., diatoms, green algae). Cyanobacterial dominance decreased, or increased, following marked changes in water level. Multiple regression analysis demonstrated that pH, euphotic depth, WLF, and total phosphorus provided the best model and explained 30.8% of the variance in cyanobacteria biomass. Path analysis showed that positive WLF (i.e. an increase in water level) can reduce the cyanobacteria biomass either directly by a dilution effect or indirectly by modifying the limnological conditions of the reservoirs in complex pathways. To control the risk of cyanobacterial dominance or blooms, WLF should be targeted to be above +2m/month; that is an increase in water level of 2m or more. Given that WLF is likely to be of more frequent occurrence under future predicted conditions of climate variability and human activity, water level management can be widely used in small and medium-sized reservoirs to prevent the toxic cyanobacterial blooms and to protect the ecosystem integrity or functions.

Phytoplankton Communities Exhibit a Stronger Response to Environmental Changes than Bacterioplankton in Three Subtropical Reservoirs.

The simultaneous analysis of multiple components of ecosystems is crucial for comprehensive studies of environmental changes in aquatic ecosystems, but such studies are rare. In this study, we analyzed simultaneously the bacterioplankton and phytoplankton communities in three Chinese subtropical reservoirs and compared the response of these two components to seasonal environmental changes. Time-lag analysis indicated that the temporal community dynamics of both bacterioplankton and phytoplankton showed significant directional changes, and variance partitioning suggested that the major reason was the gradual improvement of reservoir water quality from middle eutrophic to oligo-mesotrophic levels during the course of our study. In addition, we found a higher level of temporal stability or stochasticity in the bacterioplankton community than in the phytoplankton community. Potential explanations are that traits associated with bacteria, such as high abundance, widespread dispersal, potential for rapid growth rates, and rapid evolutionary adaptation, may underlie the different stability or stochasticity of bacterioplankton and phytoplankton communities to the environmental changes. In addition, the indirect response of bacterioplankton to nitrogen and phosphorus may result in the fact that environmental deterministic selection was stronger for the phytoplankton than for the bacterioplankton communities.

Quantifying the effects of geographical and environmental factors on distribution of stream bacterioplankton within nature reserves of Fujian, China.

Bacterioplankton are important components of freshwater ecosystems and play essential roles in ecological functions and processes; however, little is known about their geographical distribution and the factors influencing their ecology, especially in stream ecosystems. To examine how geographical and environmental factors affect the composition of bacterioplankton communities, we used denaturing gradient gel electrophoresis and clone sequencing to survey bacterioplankton communities in 31 samples of streamwater from seven nature reserves in Fujian province, southeast China. Our results revealed that dominant bacterioplankton communities exhibited a distinct geographical pattern. Further, we provided evidence for distance decay relationships in bacterioplankton community similarity and found similar community gradients in response to elevation and latitude. Both redundancy analyses and Mantel tests showed that bacterioplankton community composition was significantly correlated with both environmental (electrical conductivity, total phosphorus, and PO4-P) and geographical factors (latitude, longitude, and elevation). Variance partitioning further showed that the joint effect of geographical and environmental factors explained the largest proportion of the variation in distribution of bacterioplankton communities (13.6 %), followed by purely geographical factors (11.2 %), and purely environmental factors (0.6 %). The Betaproteobacteria were the most common taxa in the streams, followed by Firmicutes and Gammaproteobacteria. Therefore, our results suggest that the biogeographical patterns of stream bacterioplankton communities across the Fujian nature reserves are more influenced by geographical factors than by local physicochemical properties.

Effects of Spartina alterniflora invasion on biogenic elements in a subtropical coastal mangrove wetland.

The invasion by exotic cordgrass (Spartina alterniflora) has become one of the most serious and challenging environmental and ecological problems in coastal China because it can have adverse effects on local native species, thereby changing ecosystem processes, functions, and services. In this study, 300 surface sediments were collected from 15 stations in the Jiulong River Estuary, southeast China, across four different seasons, in order to reveal the spatiotemporal variability of biogenic elements and their influencing factors in the subtropical coastal mangrove wetland. The biogenic elements including carbon, nitrogen, and sulfur (C, N, and S) were determined by an element analyzer, while the phosphorus (P) was determined by a flow injection analyzer. The concentrations of biogenic elements showed no significant differences among four seasons except total phosphorus (TP); however, our ANOVA analyses revealed a distinct spatial pattern which was closely related with the vegetation type and tidal level. Values of total carbon (TC) and total nitrogen (TN) in the surface sediment of mangrove vegetation zones were higher than those in the cordgrass and mudflat zones. The concentrations of TC, TN, TP, and total sulfur (TS) in the high tidal zones were higher than those in the middle and low tidal zones. Redundancy analysis (RDA) revealed that tidal level, vegetation type, and season had some significant influence on the distribution of biogenic elements in the Jiulong River Estuary, by explaining 18.2, 7.7, and 4.9 % of total variation in the four biogenic elements, respectively. In conclusion, S. alterniflora invasion had substantial effects on the distributions of biogenic elements in the subtropical coastal wetland. If regional changes in the Jiulong River Estuary are to persist and much of the mangrove vegetation was to be replaced by cordgrass, there would be significant decreases on the overall storage of C and N in this coastal zone. Therefore, the native mangrove reforestation and exotic cordgrass elimination should be a priority in mangrove sustainable management for coastal ecosystem health.

Temperature and nutrients are significant drivers of seasonal shift in phytoplankton community from a drinking water reservoir, subtropical China.

Reservoirs are an important source of water supply in many densely populated areas in southeast China. Phytoplankton plays an important role in maintaining the structure and function of these reservoir ecosystems. Understanding of seasonal succession in phytoplankton communities and its driving factors is essential for effective water quality management in drinking-water reservoirs. In this study, water samples were collected monthly at the surface layers of riverine, transitional, and lacustrine zones from May 2010 to April 2011 in Tingxi Reservoir, southeast China. The phytoplankton showed distinct seasonal shifts in community structure at both taxonomic and functional levels. Cyanophyta was the dominant group in summer, especially species of Raphidiopsis in May and Aphanizomenon in June, and cyanobacterial dominance was promoted by both warmer conditions and excessive nutrients loading. Cyanophyta was gradually replaced by Cryptophyta (e.g., Chroomonas caudata) in abundance and by Bacillariophyta (Fragilaria sp. or Synedra sp. and Melosira sp.) in biomass with decreasing temperature. It appeared that seasonal shifts in phytoplankton composition were closely related to climate, nutrient status, and hydrology in this reservoir. Our partial RDA results clearly showed that water temperature and nutrients (TN and TP) were the most critical factors driving phytoplankton community shift in the abundance and biomass data, respectively. Further, with the global warming, cyanobacterial blooms may increase in distribution, duration, and intensity. In our study, the abundance and biomass of cyanobacteria had significant and positive correlations with temperature and phosphorus. Therefore, a stricter limit on nutrient input should be a priority in watershed management to protect drinking water from the effects of cyanobacterial blooms, especially in high-temperature period.

Algae community and trophic state of subtropical reservoirs in southeast Fujian, China.

BACKGROUND, AIM, AND SCOPE: Fujian reservoirs in southeast China are important water resources for economic and social sustainable development, although few have been studied previously. In recent years, growing population and increasing demands for water shifted the focus of many reservoirs from flood control and irrigation water to drinking water. However, most of them showed a rapid increase in the level of eutrophication, which is one of the most serious and challenging environmental problems. In this study, we investigated the algae community characteristics, trophic state, and eutrophication control strategies for typical subtropical reservoirs in southeast Fujian. MATERIALS AND METHODS: Surface water samples were collected using polyvinyl chloride (PVC) plastic bottles from 11 Fujian reservoirs in summer 2010. Planktonic algae were investigated by optical microscopy. Water properties were determined according to the national standard methods. RESULTS AND DISCUSSION: Shallow reservoirs generally have higher values of trophic state index (TSI) and appear to be more susceptible to anthropogenic disturbance than deeper reservoirs. A total of 129 taxa belonging to eight phyla (i.e., Bacillariophyta, Chlorophyta, Chrysophyta, Cryptophyta, Cyanophyta, Euglenophyta, Pyrrophyta, Xanthophyta) were observed and the most diverse groups were Chlorophyta (52 taxa), Cyanophyta (20 taxa), Euglenophyta (17 taxa), Chrysophyta (14 taxa). The dominant groups were Chlorophyta (40.58%), Cyanophyta (22.91%), Bacillariophyta (21.61%), Chrysophyta (6.91%). The species richness, abundance, diversity, and evenness of algae varied significantly between reservoirs. TSI results indicated that all 11 reservoirs were eutrophic, three of them were hypereutrophic, six were middle eutrophic, and two were light eutrophic. There was a strong positive correlation between algal diversity and TSI at P < 0.05. Our canonical correspondence analysis (CCA) results illustrated that temperature, transparency, conductivity, DO, TC, NH(4)-N, NO(x)-N, TP, and chlorophyll a were significant environmental variables affecting the distribution of algae communities. The transparency and chlorophyll a were the strongest environmental factors in explaining the community data. Furthermore, the degradation of water quality associated with excess levels of nitrogen and phosphorus in Fujian reservoirs may be impacted by interactions among agriculture and urban factors. A watershed-based management strategy, especially phosphorus control, should be developed for drinking water source protection and sustainable reservoirs in the future. CONCLUSION AND RECOMMENDATIONS: All investigated reservoirs were eutrophicated based on the comprehensive TSI values; thus, our results provided an early warning of water degradation in Fujian reservoirs. Furthermore, the trophic state plays an important role in shaping community structure and in determining species diversity of algae. Therefore, long-term and regular monitoring of Euglenophyta, Cyanophyta, TN, TP and chlorophyll a in reservoirs is urgently needed to further understand the future trend of eutrophication and to develop a watershed-based strategy to manage the Cyanophyta bloom hazards.

[Spatial variations of biogenic elements in coastal wetland sediments of the Jiulong River Estuary].

To reveal the spatial distribution of biogenic elements and their influencing factors in the typical subtropical coastal wetland, both surface and core sediment samples were collected from the Jiulong River Estuary, southeast China in summer 2009. The biogenic elements including carbon, nitrogen, phosphorus, sulfur (C, N, P, S) were determined by Element Analyzer and Flow Injection Analyzer. The concentrations of TC, TN, TP, and TS were (12.64 +/- 2.66) g x kg(-1), (1.57 +/- 0.29) g x kg(-1), (0.48 +/- 0.06) g x kg(-1), and (2.61 +/- 1.37) g x kg(-1), respectively. Further, these biogenic elements showed a distinct spatial pattern which closely related with the vegetation type and tide level. Values of TC, TN, TP in the surface sediment of mangrove vegetation zones were higher than those in the cord-grass and mudflat zones, while TC, TN, TP concentrations in the high tide level regions were higher than those in the middle and low tide level regions. The TS concentration was the highest in cord-grass vegetation and middle tidal level zones. The TC and TN values in sedimentary core decreased gradually with depth, and they were the highest in the mangrove sites, followed by cord-grass and mudflat sites at the same depth. In mudflat sedimentary core, the average content of TP was the lowest, whereas TS was the highest. Redundancy analysis revealed that vegetation type, pH and tide level were the main factors influencing the distribution of biogenic elements in surface sediments of the Jiulong River Estuary, by explaining 24.0%, 19.0% and 11.6% of total variation in the four biogenic elements (C, N, P and S), respectively.