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1.
Water Res ; 208: 117866, 2022 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-34800853

RESUMO

Human activities and climate change are two major stressors affecting lake ecosystems as well as phytoplankton communities worldwide. However, how the temporal dynamics of phytoplankton are directly or indirectly linked to anthropogenic activities and climatic oscillation remains unclear. We assessed the annual trends (1988-2018) in phytoplankton abundance (PA) in Lake Dongting, China and related it to five groups of variables characterizing human activities, global climate oscillation, water nutrients, hydrology, and meteorology. We found a significant increase in PA, urbanization (Upop), total nitrogen (TN), fertilizer application (FA), number of summer days (SU), and the warm speed duration index (WSDI) and a significant decrease in the water discharge of three inlets (TIWD) and the sediment discharge of three inlets (TISD) and four tributaries (FTSD) and the net sediment deposition (NSD). However, no significant annual trends were observed for the number of rainstorm days (R50mm), the simple precipitation intensity index (SDII) and yearly anomalies of El Niño-Southern oscillation events (ENSOi). Cross-correlation Function analyses demonstrated that the operation of the Three George Dam (TGD) strengthened the effects of hydrology, rainfall patterns and ENSOi on phytoplankton, but strongly weakened the association between water nutrients, human activities and phytoplankton abundance. Path analysis revealed that TP, TN, FA, R50 mm as well as WSDI had a direct positive effect on PA, while a direct negative effect was found for ENSOi, NSD and TISD. Human activities (Upop and FA), warming (WSDI and SU), and rainfall patterns (SDII and R50 mm) exerted indirect controls on phytoplankton through changes in water nutrients and hydrology. Climate change (ENSOi) had a direct effect on PA, but also showed twelve indirect pathways via changes in hydrology and meteorology (both positive and negative effects were found). Overall, meteorology contributed most markedly to the variations of PA (29.3%), followed by hydrology (25.3%), human activities (24%), water nutrients (10.5%), and ENSOi (1.9%). Our results highlight a strongly causal connection between human activities as well as global climate change and phytoplankton and the benefits of considering multiple environmental drivers in determining the temporal dynamics of lake biotic communities.


Assuntos
Lagos , Fitoplâncton , China , Ecossistema , Monitoramento Ambiental , Atividades Humanas , Humanos
2.
Sci Total Environ ; 806(Pt 1): 150505, 2022 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-34844323

RESUMO

Climate-induced changes in precipitation and land-use intensification affect the discharge of streams worldwide, which, together with eutrophication and loss of riparian canopy, can affect periphyton biomass and composition, and therefore, ultimately the stream functioning. We investigated the responses of periphyton biomass and life-forms (i.e., high profile, low profile and motile) to these changes applying an experimental approach by modulating nutrients (nutrient diffusion substrates enriched with 0.5 M NH4NO3 + 0.031 M KH2PO4 and without nutrient enrichment) and light availability (50% shade and full light) along a gradient in discharge ranging from 0.46 to 3.89 L/s (0.7 to 6.5 cm/s) in twelve large-sized (12- m long) outdoor flumes resembling lowland streams. We also analysed the potential effects of other environmental variables including macroinvertebrates on the responses of periphyton to discharge, nutrients, and light. Light and nutrient availability drastically affected periphyton biomass and composition responses to discharge. Periphyton biomass decreased with increasing discharge when shaded but this did not happen when exposed to full light. Under full light conditions, nutrient enrichment mediated an increase in the periphyton biomass with increasing discharge, possibly reflecting an increased metabolism, but this did not happen under non-enriched conditions. Enrichment further affected the compositional responses of periphyton to discharge, with an increase in the biomass of motile, fast-growing, small-sized flagellated at low discharge conditions, and mitigating a loss of high profile periphyton under higher discharges. Light did not affect periphyton composition, and the abundance or feeding-group composition of the macroinvertebrates did not affect biomass or composition of the periphyton either. Our results suggest that nutrient enrichment and light play an important synergistic role in the responses of the periphyton biomass and composition to discharge and emphasize the relevance of riparian canopy conservation and eutrophication control to avoid periphyton growth under increased discharge scenarios in small lowland streams.


Assuntos
Perifíton , Biomassa , Ecossistema , Eutrofização , Nutrientes , Rios
3.
J Environ Manage ; 301: 113898, 2022 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-34626943

RESUMO

In shallow eutrophic lakes, submersed macrophytes are essential for maintaining a clear water state, and they are affected markedly by fishes directly through herbivory and indirectly by fish-invertebrate-periphyton complexity, a pathway that presently is not well understood in subtropical lakes but probably vital to lake managements. We conducted a mesocosm study involving benthic fish (Misgurnus anguillicaudatus), snails (Radix swinhoei) and submersed macrophyte (Vallisneria natans), aiming to examine whether benthic fish is detrimental to reestablishment of clear-water macrophyte-dominated state in eutrophic degraded lakes. In addition, we aimed to investigate the cascading effect that benthic fish might have on periphyton and phytoplankton and to what extent snails can alleviate this effect. Our results showed that benthic fish promoted nutrient release from the sediment and thereby facilitated the growth of phytoplankton and periphyton, leading to reduced growth of submerged macrophytes due to shading. Snails consumed the periphyton attached on the leaves of macrophytes, thereby being beneficial to the plant growth, albeit it could not fully counteract the adverse effects from benthic fish. The water quality indicators in terms of nutrients concentrations, phytoplankton biomass and light extinction coefficient along the water column was affected primarily by benthic fish, followed by macrophytes and snails. To target a clear-water condition, the water quality was best at the presence of macrophytes alone or in combination with snails, and worst at the presence of benthic fish. Our results implied that the removal of benthic fish should be a useful ecological restoration method for rehabilitation of submersed macrophytes and water quality improvement in subtropic, eutrophic, shallow lakes following external nutrient loading reduction.


Assuntos
Hydrocharitaceae , Lagos , Animais , Biomassa , Peixes , Fósforo , Fitoplâncton
4.
Sci Total Environ ; 803: 150049, 2022 Jan 10.
Artigo em Inglês | MEDLINE | ID: mdl-34500271

RESUMO

A mesocosm experiment was conducted in a temperate eutrophic lake with the hypotheses: 1) the addition of a labile form of DOC would trigger a more pronounced response in phytoplankton biomass and composition compared with a non-labile form; 2) DOC addition would increase phytoplankton biomass by co-inserting organic nutrients for phytoplankton growth; 3) DOC addition would change phytoplankton composition, in particular towards mixotrophic taxa due to higher DOC availability; and that 4) there would be differences in phytoplankton responses to DOC addition, depending on whether sediment was included or not. We used two types of mesocosms: pelagic mesocosms with closed bottom, and benthic mesocosms open to the sediment. The experiment ran for 29 days in total. The DOC addition occurred once, at Day 1. Besides the control, there were two treatments: HuminFeed® (non-labile DOC) at a concentration of 2 mg L-1, and a combination of 2 mg L-1 HuminFeed® and 2 mg L-1 DOC from alder leaf leachate (labile). Responses were detected only in the treatment with alder leaf extract. Ecosystem processes responded immediately to DOC addition, with the fall in dissolved oxygen and pH indicating an increase in respiration, relative to primary production (Day 2). In contrast, there was a delay of a few days in structural responses in the phytoplankton community (Day 6). Phytoplankton biomass increased after DOC addition, probably boosted by the phosphorus released from alder leaf extract. Changes in phytoplankton composition towards mixotrophic taxa were not as strong as changes in biomass, and happened only in the pelagic mesocosms. With the DOC addition, diatoms prevailed in benthic mesocosms, while the contribution of colonial buoyant cyanobacteria increased in the pelagic ones. This study points towards the necessity to look in greater detail at specific responses of phytoplankton to DOC concentration increases considering lake-habitat and sediment influence.


Assuntos
Lagos , Fitoplâncton , Biomassa , Ecossistema , Fósforo
5.
Sci Total Environ ; 804: 150050, 2022 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-34509851

RESUMO

Fish larvae play an important structuring role for their prey and show ontogenetic shifts in diet. Changes in diet differ between species and habitats and may also be affected by turbidity (eutrophication). We investigated the diet (stomach content) and the food selection (ratio of ingested prey and prey availability) of roach and perch larvae in a clear lake and of roach, perch and pikeperch larvae in a turbid lake multiple times during spring to autumn. The diet of the fish larvae changed with size, and for roach and perch larvae between the lakes. Coexisting species of fish larvae had different diets in the two lakes, pointing to resource partitioning; yet, in the clear lake, medium-sized larvae had a high diet overlap, suggesting a competitive relationship at this developmental stage. In the clear lake, roach larvae showed diel differentiation in diet, while perch demonstrated diet shifts between habitats, which probably aided in reducing competition and also evidenced an effect of light on the larval prey capture and/or predator-fish larvae interactions. In the turbid lake, roach and perch larvae did not reveal differences in diet between habitats or time of the day, owing to homogeneity of food items and poor light conditions. However, the diet of pikeperch larvae differed between day and night following daily variations in the abundance of its preferred prey. The roach larvae were highly selective for Bosmina, Daphnia and benthic cladocerans, perch larvae generally consumed what was available, while pikeperch primarily preyed on cyclopoid copepodites. We conclude that turbidity acted as a cover for fish larvae in the turbid lake. Under eutrophication-induced turbidity scenarios the effects of fish larvae on their prey are stronger (i.e., high selectivity for several resources) than that of larvae in clear waters, creating a negative feedback on the path to restore water clarity.


Assuntos
Lagos , Percas , Animais , Dieta , Preferências Alimentares , Larva , Água
6.
Sci Total Environ ; 803: 150063, 2022 Jan 10.
Artigo em Inglês | MEDLINE | ID: mdl-34525706

RESUMO

Coastal lagoon sediments provide continuous and high-resolution records of the activity of past typhoons. In this study, multiple proxies were analyzed with a core taken from Pinqing Lagoon located on the northeast margin of the South China Sea. Based on 210Pb dating, grain sizes and other geophysical/geochemical analyses, a total of seven typhoon-induced layers covering the past ~170 years were identified and compared with observational and historical records of typhoons. The layers were characterized by a higher sand fraction, lower loss-on-ignition, decreased magnetic susceptibility, and increased element ratios of Sr/Fe, Sr/Ba, Ca/Ti, and Ca/K. We found reduced sensitivity of the sedimentary response to typhoons due to the coastal geomorphological evolution, such as sand spit growth, which emphasizes the value of using a multiple-proxy approach. The typhoon activity revealed by both sedimentary proxies and observational/historical records in Shanwei was closely related to the variations of the El Niño/Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and to sunspot activity, providing useful clues for reconstructing the long-term typhoon history in the lagoon in order to decipher the patterns and mechanisms of typhoons in South China.


Assuntos
Tempestades Ciclônicas , China , El Niño Oscilação Sul
7.
Ecotoxicol Environ Saf ; 228: 113044, 2021 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-34863077

RESUMO

Urban lakes are important natural assets but are exposed to multiple stressors from human activities. Submersed macrophytes, a key plant group that helps to maintain clear-water conditions in lakes, tend to be scarce in urban lakes, particularly when they are eutrophic or hypertrophic, and their loss is linked, in part, to impaired underwater light climate. We tested if enhancing the underwater light conditions using light-emitting diodes (LEDs) could restore submersed macrophytes in urban lakes. Twelve mesocosms (1000 L each) were each planted with tape grass (Vallisneria natans) and monitored over three months (22 August-7 November), using a control and three artificial light intensity treatments (10, 50, and 100 µmol m-2 s-1). Compared with the control, the high light treatment (100 µmol m-2 s-1) had higher leaf number, maximum leaf length, and average leaf length (3.9, 5.8, and 2.8 times, respectively). Shoot number, leaf number, leaf dry mass, root dry mass, and photosynthetic photon flux density in the high-light treatment were significantly greater than the control, but root length and phytoplankton chlorophyll a were not related to plant growth variables and were low in all treatments. Periphyton chlorophyll a increased significantly with the plant growth variables (i.e., shoot number, leaf number, and maximum leaf length) and was high in the light treatments but did not hamper the growth of the macrophytes. These results indicate that LED light supplementation enables the growth of V. natans under eutrophic conditions, at least in the absence of fish as in our experiment, and that the method may have potential as a restoration method in urban lakes. Lake-scale studies are needed, however, to fully evaluate LED light supplementation under natural conditions where other stressors (e.g., fish grazing) may need to be controlled for successful restoration of urban lakes.

8.
Environ Pollut ; : 118593, 2021 Dec 02.
Artigo em Inglês | MEDLINE | ID: mdl-34864100

RESUMO

Periphyton is considered important for removal of organic pollutants from water bodies, but knowledge of the impacts of antibiotics on the community structure and ecological function of waterbodies remains limited. In this study, the effects of oxytetracycline hydrochloride (OTC) on the communities of photoautotrophic epilithon and epipelon and its effect on nitrogen and phosphorus concentrations in the water column were studied in a 12-day mesocosm experiment. The dynamics of nitrogen and phosphorus concentrations in the epipelon and epilithon experiment showed similar patterns. The concentrations of total nitrogen, dissolved total nitrogen, ammonium nitrogen, total phosphorus and dissolved total phosphorus in the water column increased rapidly during the initial days of exposure, after which a downward trend occurred. In the epilithon experiment, we found that the photosynthesis (Fv/Fm) and biomass of epilithon were significantly (P < 0.05) stimulated in the low concentration group. Contrarily, growth and photosynthesis (Fv/Fm) were significantly (P < 0.05) reduced in the medium and high concentration group. We further found that the photosynthetic efficiency of photoautotrophic epilithon was negatively correlated with the concentrations of nitrogen and phosphorus in the water column (P < 0.05). Principal coordinate analysis (PCoA) analysis showed that the communities of epilithic algae in the control group and in the low concentration group were significantly (P < 0.05) different from that of the high concentration group during the initial 4 days. After 8 days' exposure, all groups tended to be similar, indicating that epilithon showed rapid adaptability and/or resilience. Similar results were found for the relative abundance of some epilithic algae. Our findings indicate that the biofilm system has strong tolerance and adaptability to OTC as it recovered fast after an initial suppression, thus showing the important role of periphyton in maintaining the dynamic balance of nutrients with other processes in aquatic ecosystems.

9.
Mar Pollut Bull ; 174: 113203, 2021 Dec 09.
Artigo em Inglês | MEDLINE | ID: mdl-34896755

RESUMO

Increased urea is one of the common nitrogen forms polluting coastal waters and affecting nutrient dynamics. To investigate the effects of urea on sediment phosphorus (P) release, we carried out a 2-month mesocosm experiment with six targeted loadings of urea (0-0.6 mg N L-1 d-1). Results showed that: i) urea was rapidly transformed into ammonium and then nitrate (NO3-). ii) When nitrogen occurred as urea or ammonium, minor P release was observed. iii) After urea were mostly converted to NO3-, P release became clearer. iv) NO3- had a dual effect by promoting P release through decreasing sediment pH and increasing alkaline phosphatase activity or by inhibiting P release through improving sediment oxidation. v) The overall effects of urea on P release depended on the ultimate NO3- concentrations, being prominent when NO3- ≥ 11 mg N L-1. Our findings are of relevance when determining nitrogen reduction targets needed for combating eutrophication.

10.
J Anim Ecol ; 2021 Dec 25.
Artigo em Inglês | MEDLINE | ID: mdl-34954827

RESUMO

Under increasing nutrient loading, shallow lakes may shift from a state of clear water dominated by submerged macrophytes to a turbid state dominated by phytoplankton or a shaded state dominated by floating macrophytes. How such regime shifts mediate the relationship between taxonomic and functional diversities (FD) and lake multifunctionality is poorly understood. We employed a detailed database describing a shallow lake over a 12-year period during which the lake has displayed all the three states (clear, turbid and shaded) to investigate how species richness, FD of fish and zooplankton, ecosystem multifunctionality and five individual ecosystem functions (nitrogen and phosphorus concentrations, standing fish biomass, algae production and light availability) differ among states. We also evaluated how the relationship between biodiversity (species richness and FD) and multifunctionality is affected by regime shifts. We showed that species richness and the FD of fish and zooplankton were highest during the clear state. The clear state also maintained the highest values of multifunctionality as well as standing fish biomass production, algae biomass and light availability, whereas the turbid and shaded states had higher nutrient concentrations. Functional diversity was the best predictor of multifunctionality. The relationship between FD and multifunctionality was strongly positive during the clear state, but such relationship became flatter after the shift to the turbid or shaded state. Our findings illustrate that focusing on functional traits may provide a more mechanistic understanding of how regime shifts affect biodiversity and the consequences for ecosystem functioning. Regime shifts towards a turbid or shaded state negatively affect the taxonomic diversity and FD of fish and zooplankton, which in turn impairs the multifunctionality of shallow lakes.

11.
Ecotoxicol Environ Saf ; 227: 112933, 2021 Dec 20.
Artigo em Inglês | MEDLINE | ID: mdl-34700166

RESUMO

Along with a steady increasing use of artificial nitrogen fertilizer, concerns have been raised about the effects that high nitrogen loading may have on ecosystems. Due to the toxicity of unionized ammonia (NH3), tolerance criteria have been proposed for ambient water management in many countries; however, these are mainly based on acute or chronic tests carried out under lab conditions run with purified water. Aiming at understanding the responses of organisms to natural exposure to high ammonia concentrations, a Viviparidae gastropod, Bellamya aeruginosa, was tested at three experimental scales: standard 96-h lab test, one-month cage test in 6 experimental ponds with continuous nitrogen inputs, and intensive investigation of the B. aeruginosa from these ponds in spring and winter. The results were: 1) 96-h LC50 in the standard lab test was 0.56 mg NH3-N/L and 343.3 mg TAN/L (total ammonia expressed as N, standardized at pH 7 and 20 â„ƒ). 2) In the one-month cage test, the survival rate was 97% when NH3-N was 0.61 mg/L (i.e., a higher concentration than the lab 96-h LC50) and the body size of the gastropods actually increased with increasing NH3-N concentrations. 3) In the winter-spring investigation, little effect of ammonia on the standing crops of gastropods was found, and the body size of the gastropods tended to increase with increasing ammonia concentrations (NH3-N concentration range of 0.05 ~ 2.06 mg/L). Thus, B. aeruginosa showed higher tolerance to ammonia exposure (NH3-N concentration < 0.81 mg/L) in the field than under laboratory conditions. Our study points to the necessity of considering the relevant scale when determining criteria for ammonia toxicity in water management.


Assuntos
Amônia , Gastrópodes , Amônia/toxicidade , Animais , Ecossistema , Laboratórios , Pseudomonas aeruginosa
12.
Innovation (N Y) ; 2(2): 100092, 2021 May 28.
Artigo em Inglês | MEDLINE | ID: mdl-34557746

RESUMO

The recent mass mortality event of more than 330 African elephants in Botswana has been attributed to biotoxins produced by cyanobacteria; however, scientific evidence for this is lacking. Here, by synthesizing multiple sources of data, we show that, during the past decades, the widespread hypertrophic waters in Southern Africa have entailed an extremely high risk and frequent exposure of cyanotoxins to the wildlife within this area, which functions as a hotspot of mammal species richness. The hot and dry climatic extremes have most likely acted as the primary trigger of the recent and perhaps also of prehistoric mass mortality events. As such climate extremes are projected to become more frequent in Southern Africa in the near future, there is a risk that similar tragedies may take place, rendering African megafauna species, especially those that are already endangered, in risk of extinction. Moreover, cyanotoxin poisoning amplified by climate change may have unexpected cascading effects on human societies. Seen within this perspective, the tragic mass death of the world's largest terrestrial mammal species serves as an alarming early warning signal of future environmental catastrophes in Southern Africa. We suggest that systematic, quantitative cyanotoxin risk assessments are made and precautionary actions to mitigate the risks are taken without hesitation to ensure the health and sustainability of the megafauna and human societies within the region.

13.
Sci Total Environ ; 797: 148998, 2021 Nov 25.
Artigo em Inglês | MEDLINE | ID: mdl-34346382

RESUMO

Warming, eutrophication, and increased omnivory by small-sized fish are global change processes that induce major effects on the food web structure and primary producers of shallow lakes. Despite the key relevance of phytoplankton and periphyton in freshwaters, the combined and potential synergistic effects of fish omnivory, warming and eutrophication, especially on periphyton, remains little addressed, particularly for subtropical shallow lakes. We experimentally tested the food web effects on phytoplankton and periphyton induced by small visually feeding omnivorous fish (Rhodeus ocellatus), high nutrient enrichment and warming (+4.5 °C) in thirty-two 1000 L-mesocosms simulating littoral conditions of subtropical shallow lakes. We aimed at analysing the mechanisms and responses of periphyton and phytoplankton to these experimental factors. All mesocosms included the submerged macrophytes Vallisneria denseserrulata and Potamogeton lucens and artificial plants at 50% plant volume inhabited, plankton and macroinvertebrates. Small-sized visually feeding omnivorous fish enhanced phytoplankton dominance and periphyton loss. These changes coincided with a decrease in zooplankton biomass and a diversity loss of both zooplankton and macroinvertebrates as well as an increase in snail abundance. Fish presence led to a collapse of cladocerans, thereby releasing the grazing pressure on phytoplankton, and predator and collector macroinvertebrates were replaced with small snails (Radix peregra < 0.5 cm) resulting in enhanced grazing on periphyton. Eutrophication reinforced the fish effects, while warming had weak or no effects. Our results indicate that omnivory by small-sized visually feeding fish may induce stronger effects on the food webs of shallow lakes, towards phytoplankton-dominated states, than the combined effect of nutrient enrichment and warming under the present experimental conditions.


Assuntos
Cadeia Alimentar , Lagos , Animais , Biomassa , Eutrofização , Fitoplâncton , Zooplâncton
14.
Water Res ; 202: 117460, 2021 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-34343871

RESUMO

Understanding microbial metacommunity assembly and the underlying methanisms are fundamental objectives of aquatic ecology. However, little is known about how eutrophication, the primary water quality issue of aquatic ecosystems, regulates bacterioplankton metacommunity assembly at a regional scale in reservoirs. In this study, we applied a metacommunity framework to study bacterioplankton communities in 210 samples collected from 42 tropical coastal reservoirs in the wet summer season. We found that the spatial pattern of bacterioplankton community compositions (BCCs) at a regional scale was shaped mainly by species sorting. The reservoir trophic state index (TSI) was the key determinant of bacterioplankton metacommunity assembly. BCC turnover increased significantly with the TSI differences between sites (∆TSI) when ∆TSI was < 20, but remained at a level of about 80% when ∆TSI was > 20. Compared to oligo-mesotrophic and mesotrophic reservoirs, increased heterogeneity of co-occurrence bacterioplankton networks and bacterioplankton ß-diversity were observed across eutrophic reservoirs. We propose that larger variation in phytoplankton community assembly may play directly or indirectly deterministic processes in controlling the bacterioplankton metacommunity assembly and became the potential mechanisms behind the observed higher BCC heterogeneity across the eutrophic reservoirs. Our research contributes to a broader understanding of the ecological effects of eutrophication on reservoir ecosystems and provides clues to the management of the tropical coastal reservoirs.


Assuntos
Ecossistema , Eutrofização , Organismos Aquáticos , China , Fitoplâncton , Qualidade da Água
15.
J Environ Sci (China) ; 107: 205-217, 2021 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-34412783

RESUMO

Interactions between dissolved organic matter (DOM) and bacteria are central in the biogeochemical cycles of aquatic ecosystems; however, the relative importance of biodegradable dissolved organic carbon (BDOC) compared with other environmental variables in structuring the bacterial communities needs further investigation. Here, we investigated bacterial communities, chromophoric DOM (CDOM) characteristics and physico-chemical parameters as well as examined BDOC via bioassay incubations in large eutrophic Lake Taihu, China, to explore the importance of BDOC for shaping bacterial community structures and co-occurrence patterns. We found that the proportion of BDOC (%BDOC) correlated significantly and positively with the DOC concentration and the index of the contribution of recent produced autochthonous CDOM (BIX). %BDOC, further correlated positively with the relative abundance of the tryptophan-like component and negatively with CDOM aromaticity, indicating that autochthonous production of protein-like CDOM was an important source of BDOC. The richness of the bacterial communities correlated negatively with %BDOC, indicating an enhanced number of species in the refractory DOC environments. %BDOC was identified as a significant stronger factor than DOC in shaping bacterial community composition and the co-occurrence network, suggesting that substrate biodegradability is more significant than DOC quantity determining the bacterial communities in a eutrophic lake. Environmental factors explained a larger proportion of the variation in the conditionally rare and abundant subcommunity than for the abundant and the rare bacterial subcommunities. Our findings emphasize the importance of considering bacteria with different abundance patterns and DOC biodegradability when studying the interactions between DOM and bacteria in eutrophic lakes.


Assuntos
Carbono , Lagos , Bactérias , Carbono/análise , China , Ecossistema
16.
PeerJ ; 9: e11605, 2021.
Artigo em Inglês | MEDLINE | ID: mdl-34239778

RESUMO

Farming operation and amino acid profiles of pond-reared Chinese mitten crabs, Eriocheir sinensis (Milne Edwards, 1853), collected from different areas in Jiangsu Province, China were investigated and compared with the aim to elucidate how farming practices affected the nutritional values of three edible tissues (muscle, hepatopancreas and gonad) of crab. The crab pond aquaculture practices including snail input, macrophytes coverage, total commercial feed, the ratio of trash fish to total feed, were much higher in Gaochun and Jintan than that in other sites (having larger pond size), which leads to higher average individual body weight and commercial yields. Further, the mean body weight, muscle weight, carapace length and width, and the ratio of gonad to hepatopancreas were significantly higher in Jintan, Suzhou and Gaochun areas than in other regions. Amino acid assessment showed that all crabs collected delivered high-quality protein (Amino acid score >1 except Valine), the main amino acids being glutamic acid, aspartic acid, and alanine. Significant differences in amino acid profiles were observed between sites, tissues and sexes. Muscles were rich in total amino acids, essential amino acids, and delicious amino acids, followed by gonads and hepatopancreas. The contents of essential amino acids in crab muscles from Gaochun, Jintan, Suzhou and Guannan were significantly higher than those from Suqian, Sihong and Xinghua. All the amino acids except Serine and Glycine were significantly higher in gonads from males than from females. The redundancy analysis revealed that the snail input, trash fish ratio to the total feed, macrophytes coverage and total trash fish supply explained 84.3% of the variation in the amino acid content and structure in crabs from Gaochun, Jintan and Suzhou. Overall, our results show that mitten crabs collected in Jiangsu province had good nutritional quality suitable for human dietary needs, and that farming practices, especially degree of fish-source protein feeding, influence the amino acids composition of crabs.

17.
Nat Commun ; 12(1): 4475, 2021 07 22.
Artigo em Inglês | MEDLINE | ID: mdl-34294719

RESUMO

High Arctic ecosystems and Indigenous livelihoods are tightly linked and exposed to climate change, yet assessing their sensitivity requires a long-term perspective. Here, we assess the vulnerability of the North Water polynya, a unique seaice ecosystem that sustains the world's northernmost Inuit communities and several keystone Arctic species. We reconstruct mid-to-late Holocene changes in sea ice, marine primary production, and little auk colony dynamics through multi-proxy analysis of marine and lake sediment cores. Our results suggest a productive ecosystem by 4400-4200 cal yrs b2k coincident with the arrival of the first humans in Greenland. Climate forcing during the late Holocene, leading to periods of polynya instability and marine productivity decline, is strikingly coeval with the human abandonment of Greenland from c. 2200-1200 cal yrs b2k. Our long-term perspective highlights the future decline of the North Water ecosystem, due to climate warming and changing sea-ice conditions, as an important climate change risk.

18.
Sci Total Environ ; 796: 148916, 2021 Nov 20.
Artigo em Inglês | MEDLINE | ID: mdl-34328890

RESUMO

Water clarity (generally quantified as the Secchi disk depth: SDD) is a key variable for assessing environmental changes in lakes. Using remote sensing we calculated and elucidated the SDD dynamics in lakes in the Inner Mongolia-Xinjiang Lake Zone (IMXL) from 1986 to 2018 in response to variations in temperature, rainfall, lake area, normalized difference vegetation index (NDVI) and Palmer's drought severity index (PDSI). The results showed that the lakes with high SDD values are primarily located in the Xinjiang region at longitudes of 75°-93° E. In contrast, the lakes in Inner Mongolia at longitudes of 93°-118° E generally have low SDD values. In total, 205 lakes show significant increasing SDD trends (P < 0.05), with a mean rate of 0.15 m per decade. In contrast, 75 lakes, most of which are located in Inner Mongolia, exhibited significant decreasing trends with a mean rate of 0.08 m per decade (P < 0.05). Pooled together, an overall increase is found with a mean rate of 0.14 m per decade. Multiple linear regression reveals that among the five variables selected to explain the variations in SDD, lake area accounts for the highest proportion of variance (25%), while temperature and rainfall account for 12% and 10%, respectively. In addition, rainfall accounts for 52% of the variation in humidity, 8% of the variation in lake area and 7% of the variation in NDVI. Temperature accounts for 27% of the variation in NDVI, 39% of the variation in lake area and 22% of the variation in PDSI. Warming and wetting conditions in IMXL thus promote the growth of vegetation and cause melting of glaciers and expansion of lake area, which eventually leads to improved water quality in the lakes in terms of higher SDD. In contrast, lakes facing more severe drought conditions, became more turbid.


Assuntos
Tecnologia de Sensoriamento Remoto , Água , China , Clima , Lagos
19.
Microbiome ; 9(1): 128, 2021 06 03.
Artigo em Inglês | MEDLINE | ID: mdl-34082826

RESUMO

BACKGROUND: Freshwater salinization may result in significant changes of microbial community composition and diversity, with implications for ecosystem processes and function. Earlier research has revealed the importance of large shifts in salinity on microbial physiology and ecology, whereas studies on the effects of smaller or narrower shifts in salinity on the microeukaryotic community in inland waters are scarce. Our aim was to unveil community assembly mechanisms and the stability of microeukaryotic plankton networks at low shifts in salinity. RESULTS: Here, we analyzed a high-resolution time series of plankton data from an urban reservoir in subtropical China over 13 consecutive months following one periodic salinity change ranging from 0 to 6.1‰. We found that (1) salinity increase altered the community composition and led to a significant decrease of plankton diversity, (2) salinity change influenced microeukaryotic plankton community assembly primarily by regulating the deterministic-stochastic balance, with deterministic processes becoming more important with increased salinity, and (3) core plankton subnetwork robustness was higher at low-salinity levels, while the satellite subnetworks had greater robustness at the medium-/high-salinity levels. Our results suggest that the influence of salinity, rather than successional time, is an important driving force for shaping microeukaryotic plankton community dynamics. CONCLUSIONS: Our findings demonstrate that at low salinities, even small increases in salinity are sufficient to exert a selective pressure to reduce the microeukaryotic plankton diversity and alter community assembly mechanism and network stability. Our results provide new insights into plankton ecology of inland urban waters and the impacts of salinity change in the assembly of microbiotas and network architecture. Video abstract.


Assuntos
Ecossistema , Plâncton , China , Ecologia , Salinidade
20.
Sci Rep ; 11(1): 9377, 2021 04 30.
Artigo em Inglês | MEDLINE | ID: mdl-33931681

RESUMO

A machine learning approach was employed to detect and quantify Microcystis colonial morphospecies using FlowCAM-based imaging flow cytometry. The system was trained and tested using samples from a long-term mesocosm experiment (LMWE, Central Jutland, Denmark). The statistical validation of the classification approaches was performed using Hellinger distances, Bray-Curtis dissimilarity, and Kullback-Leibler divergence. The semi-automatic classification based on well-balanced training sets from Microcystis seasonal bloom provided a high level of intergeneric accuracy (96-100%) but relatively low intrageneric accuracy (67-78%). Our results provide a proof-of-concept of how machine learning approaches can be applied to analyze the colonial microalgae. This approach allowed to evaluate Microcystis seasonal bloom in individual mesocosms with high level of temporal and spatial resolution. The observation that some Microcystis morphotypes completely disappeared and re-appeared along the mesocosm experiment timeline supports the hypothesis of the main transition pathways of colonial Microcystis morphoforms. We demonstrated that significant changes in the training sets with colonial images required for accurate classification of Microcystis spp. from time points differed by only two weeks due to Microcystis high phenotypic heterogeneity during the bloom. We conclude that automatic methods not only allow a performance level of human taxonomist, and thus be a valuable time-saving tool in the routine-like identification of colonial phytoplankton taxa, but also can be applied to increase temporal and spatial resolution of the study.

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