Seasonal variation in greenhouse gas concentrations and diffusive fluxes in three river-reservoir systems in the Seine Basin (France).

River and reservoir ecosystems have been considered as hot spots for GHG (greenhouse gas) emissions while their specific hydrological and biogeochemical processes affect GHG concentrations; however, few studies integrated river-reservoir systems to identify the dominant drivers of GHG concentrations and flux changes associated with these systems. In the present study, we examined the seasonal variations in GHG concentrations in the surface water of three river-reservoir systems in the Seine Basin. The levels and seasonal variations of GHG concentrations exhibited distinct patterns among reservoirs, upstream, and downstream rivers. The concentrations of CH4 (methane) in the reservoirs were notably higher than those observed in both upstream and downstream rivers and showed higher values in summer and autumn, which contrasted with CO2 (carbon dioxide) concentrations, while N2O (nitrous oxide) concentrations did not show an obvious seasonal pattern. A high mole ratio of CH4/CO2 was found in these reservoirs, with a value of 0.03 and was more than 30 and 10 times higher than that in the upstream and downstream rivers, respectively. The three river-reservoir systems were oversaturated with GHG during the study period, with the average diffusive fluxes (expressed as CO2eq: CO2 equivalent) of 810 ± 1098 mg CO2eq m-2 d-1, 9920 ± 2413 mg CO2eq m-2 d-1, and 7065 ± 2704 mg CO2eq m-2 d-1 in the reservoirs, upstream and downstream rivers, respectively. CO2 and CH4-CO2 were respectively the dominant contributors to GHG diffusive fluxes in river and reservoir sections, while N2O contributed negligibly to GHG diffusive fluxes in the three river-reservoir systems. Our results showed that GHG concentrations and gas transfer coefficient have varying importance in driving GHG diffusive fluxes among different sections of the river-reservoir systems. In addition, our results also show the combined effect of reservoirs and upstream rivers on the water quality variables and hydrological characteristics of downstream rivers, highlighting the future need for additional investigations of GHG processes in the river-reservoir systems.

Unravelling nutrient fate and CO2 concentrations in the reservoirs of the Seine Basin using a modelling approach.

Reservoirs are active reactors for the biogeochemical cycling of carbon (C) and nutrients (nitrogen: N, phosphorus: P, and silica: Si), however, our in-depth understanding of C and nutrient cycling in reservoirs is still limited by the fact that it involves a variety of closely linked and coupled biogeochemical and hydrological processes. In this study, the updated process-based Barman model was applied to three reservoirs of the Seine Basin during 2019-2020, considering the variations of carbon dioxide (CO2) concentrations and key water quality variables. The model simulations captured well the observed seasonal variations of water quality variables, although discrepancies remained for some variables. According to the model, we found that: (1) the three reservoirs are autotrophic ecosystems and showed high removal efficiency of dissolved inorganic carbon and nutrients during 2019-2020; (2) phytoplankton assimilation, benthic denitrification, precipitation and dissolution of calcium carbonate, and gas exchange at the water-air interface are the dominant processes for water quality variations in reservoirs; (3) based on scenarios results, trophic state and mean water depth of reservoir would impact the biogeochemical processes and the retention efficiency of nitrate and dissolved silicate. Finally, we expect that the successful application of Barman model in the reservoirs of the Seine Basin could provide a useful tool for simulating reservoir water quality changes and thus evaluating the impacts of reservoirs on downstream water quality.

Reservoirs change pCO2 and water quality of downstream rivers: Evidence from three reservoirs in the Seine Basin.

The global increase in the construction of reservoirs has drawn attention given its documented hydrological and biogeochemical impacts on downstream rivers; however, the impact of reservoirs on downstream pCO2 (partial pressure of carbon dioxide) is still poorly understood. To evaluate these impacts, the interactions between reservoirs and their corresponding upstream and downstream rivers were analyzed for three reservoirs in the Seine Basin based on monthly measurement during two hydrological years. The seasonal variations of water quality in the reservoirs were mainly driven by the entering water and the biogeochemical processes occurring in the reservoirs. Our results unravel the crucial role of reservoir in downstream water quality, which significantly increased DOC (dissolved organic carbon) and BDOC (biodegradable DOC) concentrations, while lowered DSi (dissolved silica) concentrations during emptying period (p < 0.01). Furthermore, the impacts of reservoirs on the annual fluxes of DOC, BDOC, and DSi were quantified and suggested that the three reservoirs respectively increased 20% and 23% of annual fluxes of DOC and BDOC, while decreased 33% of annual DSi fluxes in their downstream rivers. Additionally, the reservoirs significantly decreased downstream riverine pCO2 (p < 0.01), and enhanced the gas transfer coefficient of CO2 in downstream rivers by 1.3 times during the emptying period, which highlights the necessity to consider the potential impact of reservoirs on riverine CO2 emissions. Overall, our results highlight the importance of combining biogeochemical and hydrological characteristics to understand the impacts of reservoirs on downstream rivers, and emphasize the need of similar studies under the current context of increasing reservoir constructions.

Long-term assessment of nutrient budgets for the four reservoirs of the Seine Basin (France).

Artificial reservoirs represent one of the most significant human disturbances of water flows and associated water quality, including nutrients and SM (suspended matter). However, most of the previous studies were only focused on few years or even single year, and the long-term dynamics of nutrient retention in reservoir are under explored. In this study, we present the long-term (1998-2018) hydrological characteristics and water quality in four reservoirs (Marne, Aube, Seine, and Pannecière reservoirs) and their related rivers (Marne, Aube, Seine, and Yonne rivers) of the Seine Basin, France. Based on the hydrology and water quality data, the long-term budgets of nutrients and SM were evaluated in these reservoirs according to mass balance calculation. The results indicated that the four reservoirs play important roles in the retention/elimination of nutrients and SM, and the retention/elimination rates may be affected by hydrophysical and biogeochemical processes. The mean annual retention rates accounted for 16-53% of the inputs of DIN (dissolved inorganic nitrogen), 26-48% of PO43--P (orthophosphates), 22-40% of Si (dissolved silicon), and 36-76% of SM in the four reservoirs during the 1998-2018 period. Further analysis suggested that the annual residence time and the percentage of water released from reservoirs during the filling period significantly correlated with DIN retention rates in the four reservoirs (p < 0.01), which highlights the importance of reservoir water management strategies for the DIN concentrations in the downstream rivers. Interestingly, the Wilcoxon test results also revealed that the three diverted reservoirs (Marne, Aube, and Seine reservoirs) indeed lowered the nutrient concentrations in their downstream rivers during the emptying period, thereby modifying the biogeochemical functioning in the downstream river networks. Finally, these results emphasized the importance of hydrological characteristics in better understanding nutrient retention in reservoirs.

Simultaneous inversion of concentrations of POC and its endmembers in lakes: A novel remote sensing strategy.

Data on the concentration of particulate organic carbon (POC) and its endmembers provide a basis for the characterisation of lake biogeochemical cycles. Here, a novel remote sensing strategy (the SCPOC algorithm) was developed to determine total POC concentrations, as well as terrestrial and endogenous POC concentrations in lakes. This strategy provides a successful example for the combination of isotope tracer and remote sensing technology. First, we obtained the terrestrial and endogenous POC concentration at the sampling point based on isotope tracing technology. Afterwards, we established a relationship between the phytoplankton absorption coefficient and the endogenous POC concentration (Cend), and applied a semi-analytical algorithm to invert the Cend value. Finally, the POC source ratio model and Cend value were combined to obtain the POC concentration (CPOC) and terrestrial POC (Cter). The results of synchronisation verification based on ocean and land colour instrument (OLCI) images show that the SCPOC algorithm has high Cend, Cter, and CPOC inversion accuracy, with MAPE values of 26.07%, 30.43%, and 42.28%, respectively. In fact, the SCPOC algorithm not only improved the accuracy of lake POC mapping, but also fills the gap of optical retrieval of POC endmember concentrations. Additionally, data from the OLCI images indicated that the studied lakes were dominated by external POC. However, because of the greater contribution of algal blooms to POC, this dominant advantage weakens in summer, although the terrestrial organic carbon carried by rainfall runoff also affects lake POC composition. Different POC sources have different ecological roles in lakes, and the superior POC end-element estimation capability of the SCPOC algorithm can not only be used as a supplement to traditional tracing methods, but also provides accurate spatial data for lake management.

CO2 dynamic of Lake Donghu highlights the need for long-term monitoring.

Inland freshwater lakes have been widely considered as significant sources of CO2 to the atmosphere. However, long-term measurements of CO2 dynamics in lakes are still lacking, but are necessary due to their large temporal variations. Herein, we present the long-term dynamics of water parameters in Lake Donghu from 2002 to 2016, and further calculate the partial pressure of CO2 (pCO2) based on the measurements of pH, water temperature, and alkalinity from 2008 to 2016. The results revealed that a significantly high pCO2 occurred during the winter in Lake Donghu (p < 0.01), whereas no significant spatial difference was observed (p = 0.37). Statistical analysis indicated that the pCO2 in the lake was only positively correlated with the total phosphorus (TP) concentration (p < 0.05). A multilinear regression model provided the best predictors for the pCO2; however, it only explained 16% of the observed pCO2 variability. This indicates the complex factors that influenced the pCO2 in Lake Donghu between 2008 and 2016. Our estimated CO2 flux revealed that Lake Donghu acted as a small CO2 source to the atmosphere during this period, with a mean CO2 flux of 10.8 ± 37.4 mg m-2 day-1 corresponding to a mean CO2 emission of 0.13 ± 0.43 Gg year-1. The CO2 emission fluxes in Lake Donghu were much lower than the mean CO2 fluxes reported for other lakes in China and globally. Furthermore, the long-term evolution of the CO2 flux indicated that Lake Donghu has shifted between acting as a CO2 source and sink, which highlights the need for long-term monitoring to accurately evaluate CO2 emissions from lakes.

Parallelism of Nutrients and CO2 Dynamics: Evidence Based on Long-Term Data in Taihu Lake.

Inland lakes are important ecosystems for the carbon cycle at both regional and global scales. However, a knowledge gap still exists about the correlations between the partial pressure of CO2 (pCO2) and nutrient dynamics in lakes. In this study, we analysed the long-term dynamics of nutrient and pCO2 in Taihu Lake. Strong spatial heterogeneity was observed with highest nutrient concentrations occurring in the River mouth and significant lower concentrations (p < 0.01) occurring in East Taihu and Other zone. For pCO2, the average values were 1136.81 ± 1240.16 µatm, 433.07 ± 305.45 µatm, and 487.05 ± 414.02 µatm in Rive mouth, East Taihu, and Other zone, respectively. Statistical analysis revealed that pCO2 was significantly and positively related to nutrient (TN: total nitrogen and NH4+: ammonium) concentrations (p < 0.01), but negatively related to Chla (Chlorophyll a) concentrations in River mouth and Other zone (p < 0.01). The parallelism of nutrient concentrations and pCO2 in Taihu Lake highlights the dual effects of external pollution inputs from the surrounding catchment. In addition, progressive mitigation was found for not only nutrients but also pCO2, which was attributed to the previous effort in the environmental protections in Taihu Lake basin. Our results also suggest the importance of long-term monitoring for the future assessment of anthropogenic impacts on nutrient and CO2 dynamics in freshwater lakes.

Cyanobacteria blooms: A neglected facilitator of CH4 production in eutrophic lakes.

Lakes are regarded as one of the important sources of atmospheric CH4. However, the role of cyanobacteria blooms (CBBs) play in the CH4 production in eutrophic lakes is not fully clear. In this study, the spatial distribution characteristics of CH4 concentrations in surface water and sediment columns were investigated in Zhushan Bay of Taihu lake, China. Results showed that CH4 concentrations in CBBs accumulated zones were much higher than that in the open lake areas, with the highest values of 3.79 µmol·L-1 and 2261.88 µmol·L-1 in surface water and sediment columns, respectively. CH4 concentrations were strongly influenced by various factors. In surface water, the occurrence of CBBs greatly contributed to CH4 productions, as evidenced by the well-predicting for CH4 concentrations using Chl-a and NH4+ concentrations. In the sediments, the Ignition Loss and C:N ratio values were two indicators of CH4 contents, suggesting that the methanogenesis processes were influenced by not only the quantities, but also the qualities of organic matter. The labile substrates produced during the CBBs decomposition processes promoted the CH4 production and migration from sediments to the water column, resulting in the coherence in CH4 concentrations between the sediments and the surface water. The high-resolution determinations of CH4 concentrations in surface water and sediments clarified that the CBBs were a neglected facilitator of CH4 productions, which should be considered in the future estimation of CH4 emissions in eutrophic lakes.

Estimating sedimentary organic matter sources by multi-combined proxies for spatial heterogeneity in a large and shallow eutrophic lake.

The multiple proxies involving elemental and stable isotope ratios (C/N, δ15N and δ13C) and biomarkers are powerful tools for estimating sedimentary organic matter (SOM) sources. However, the systematic and reasonable evaluation of organic matter sources existing with serious spatial heterogeneity in large, shallow and eutrophic lakes is still far from clear. Samples of sediments, aquatic plants and particulate organic matter (POM) collected from different ecotype regions of Taihu Lake, China, including algae-type lakeshore, grass-type lakeshore, algae-grass-type lakeshore, inflow rivers and estuary, groove reed zone, offshore and central regions, were analyzed for their SOM sources via elemental and stable isotope ratios (C/N, δ15N and δ13C), n-alkanes and fatty acids (FA). More depleted δ13CTOC values (-26.3‰ to -25.4‰) and higher relative percentages of odd n-alkanes (C26 to C35) and long-chain FA (C24:0 to C32:0) clarified the influence of inflow rivers carrying terrestrial inputs on SOM. The higher relative percentages of n-alkanes from C14 to C20, FA (C16:0), and polyunsaturated FA (C18:2 and C18:3) in the reed belt of the groove demonstrated that some special terrain was important for the accumulation of algae-derived OM in sediments. Short-chain and middle-chain biomarker compounds revealed a large contribution from macrophytes in the grass-type region and an obvious algae-derived organic matter accumulation in the algae-type region, respectively. However, some overlapping ranges of C/N, δ15N and δ13C among aquatic plants, the ubiquity of lipid biomarkers compounds, anthropogenic influences, meteorological factors and lake topography caused some biased identification results for partial samples using different indicators. These biased identifications were mainly embodied in the source category and contribution difference based on principal component analysis and an end-member mixing model. Therefore, the estimation of SOM sources by multiple proxies cannot be uniformly applied in large freshwater lakes. The systematic investigation and comprehensive understanding of the different ecotypes and their surrounding environments are the important links in the identification of SOM sources via multiple indicators.

Climate warming and cyanobacteria blooms: Looks at their relationships from a new perspective.

Climate warming and eutrophication are regarded as two important contributors to the occurrence of cyanobacteria blooms in aquatic ecosystems. However, the feedback of cyanobacteria blooms to climate warming and eutrophication is not fully clear. In this study, a microcosm system was established to simulate the decomposition processes of cyanobacteria blooms. It was observed that a large amount of nitrogen and phosphorus was released into the overlying water, and the concentrations of nitrogen and phosphorus were increased with the amount of added cyanobacteria bloom biomass addition. Subsequently, these released nutrients became available for primary production and intensified the eutrophic state of freshwater lakes. During the decomposition of cyanobacteria blooms, the microenvironment acquired low DO, low pH, and reductive conditions. Together with abundant organic matter in the water column and sediment, a large amount of CH4 and CO2 produced through organic matter mineralization, in which CH4 was the dominant fraction, occupied 50%-92% in mass of emitted carbon. Furthermore, a certain amount of N2O, probably underestimated, was produced with a strong greenhouse effect, even though its magnitude was small. These observations clarify that the feedbacks among cyanobacteria blooms formation and climate warming as well as the eutrophication of freshwater lakes are not unidirectional, but bidirectional. Given that climate warming enhanced the occurrence of cyanobacteria blooms, it was proposed that there are two vicious loops between cyanobacteria blooms, lake eutrophication and climate warming, which should be considered in the future management of aquatic ecosystems.

Transcriptomic analysis of neuropeptides and peptide hormones in the barnacle Balanus amphitrite: evidence of roles in larval settlement.

The barnacle Balanus amphitrite is a globally distributed marine crustacean and has been used as a model species for intertidal ecology and biofouling studies. Its life cycle consists of seven planktonic larval stages followed by a sessile juvenile/adult stage. The transitional processes between larval stages and juveniles are crucial for barnacle development and recruitment. Although some studies have been conducted on the neuroanatomy and neuroactive substances of the barnacle, a comprehensive understanding of neuropeptides and peptide hormones remains lacking. To better characterize barnacle neuropeptidome and its potential roles in larval settlement, an in silico identification of putative transcripts encoding neuropeptides/peptide hormones was performed, based on transcriptome of the barnacle B. amphitrite that has been recently sequenced. Potential cleavage sites andstructure of mature peptides were predicted through homology search of known arthropod peptides. In total, 16 neuropeptide families/subfamilies were predicted from the barnacle transcriptome, and 14 of them were confirmed as genuine neuropeptides by Rapid Amplification of cDNA Ends. Analysis of peptide precursor structures and mature sequences showed that some neuropeptides of B. amphitrite are novel isoforms and shared similar characteristics with their homologs from insects. The expression profiling of predicted neuropeptide genes revealed that pigment dispersing hormone, SIFamide, calcitonin, and B-type allatostatin had the highest expression level in cypris stage, while tachykinin-related peptide was down regulated in both cyprids and juveniles. Furthermore, an inhibitor of proprotein convertase related to peptide maturation effectively delayed larval metamorphosis. Combination of real-time PCR results and bioassay indicated that certain neuropeptides may play an important role in cypris settlement. Overall, new insight into neuropeptides/peptide hormones characterized in this study shall provide a platform for unraveling peptidergic control of barnacle larval behavior and settlement process.

Toward an understanding of the molecular mechanisms of barnacle larval settlement: a comparative transcriptomic approach.

BACKGROUND: The barnacle Balanus amphitrite is a globally distributed biofouler and a model species in intertidal ecology and larval settlement studies. However, a lack of genomic information has hindered the comprehensive elucidation of the molecular mechanisms coordinating its larval settlement. The pyrosequencing-based transcriptomic approach is thought to be useful to identify key molecular changes during larval settlement. METHODOLOGY AND PRINCIPAL FINDINGS: Using 454 pyrosequencing, we collected totally 630,845 reads including 215,308 from the larval stages and 415,537 from the adults; 23,451 contigs were generated while 77,785 remained as singletons. We annotated 31,720 of the 92,322 predicted open reading frames, which matched hits in the NCBI NR database, and identified 7,954 putative genes that were differentially expressed between the larval and adult stages. Of these, several genes were further characterized with quantitative real-time PCR and in situ hybridization, revealing some key findings: 1) vitellogenin was uniquely expressed in late nauplius stage, suggesting it may be an energy source for the subsequent non-feeding cyprid stage; 2) the locations of mannose receptors suggested they may be involved in the sensory system of cyprids; 3) 20 kDa-cement protein homologues were expressed in the cyprid cement gland and probably function during attachment; and 4) receptor tyrosine kinases were expressed higher in cyprid stage and may be involved in signal perception during larval settlement. CONCLUSIONS: Our results provide not only the basis of several new hypotheses about gene functions during larval settlement, but also the availability of this large transcriptome dataset in B. amphitrite for further exploration of larval settlement and developmental pathways in this important marine species.

Bacterial expression and cellular localization of Helicoverpa armigera nucleopolyhedrovirus Orf33 in infected host cells.

Helicoverpa armigera single nucleocapsid nucleopolyhedrovirus (HearSNPV) is a selective, highly infectious pathogen to H. armigera and has been extensively used for the control of this pest. This study presents the bacterial expression and localization of ha33 in infected host cells. The ha33 protein expressed in Escherichia coli had protein size of 17kDa. Western blot analysis using polyclonal antibody showed that the product of ha33 in infected Helicoverpa zea cells (HzAM1) was a 31kDa protein, larger than the theoretically predicted size of 28.4kDa. The confocal laser scanning microscope observation demonstrated that ha33 gene product was localized in the cytoplasm of infected HzAM1 cells beginning at 6 h p. i. and remained throughout the infection.