Delta Sites Research Articles

High O3 pollution initiated by cold front passage over Pearl River Estuary

The influence of cold fronts on the formation of ozone (O3) pollution, particularly the contributions of physical and chemical processes to O3 abundance during the passage of cold fronts in winter over the Pearl River Estuary (PRE) region was still unclear. This study provided an in-depth analysis on the occurrence of high O3 pollution based on data from field measurements and simulation of a chemical transport model (i.e., WRF-Chem) over the PRE region during winter 2021 when cold fronts were frequently observed. Totally 7 high O3 episode days were observed during pre- and post-frontal stages at DWS (i.e., Da Wan Shan island), a downwind island site of the inland Pearl River Delta (PRD) region, which were accompanied with the prevailing northerly wind patterns with insignificant variations of wind speeds in a stable boundary layer over the whole PRE region. The quantitative analysis based on simulation results indicated that horizontal transport and chemical processes accounted for the buildup of O3 abundance at DWS, with the highest mean rates of 7.3 and 5.6 ppbv/h at pre- and post-frontal stages, respectively. The high contributions from horizontal transport to O3 levels at DWS were associated with the persistent northerly winds with small variations, while the contributions of chemical processes were varied with the abundance of precursors and meteorological conditions. However, vertical transport made negative contributions to O3 abundance, with the most significant mean diffusion rate of −2.6 ppbv/h at the frontal stage because of the control of high-pressure system, while the less influence of vertical transport at pre- and post-frontal stages was associated with the weak pressure gradient forces and wind patterns. The sensitivity analysis further demonstrated that the emissions of precursors from the inland PRD region contributed 50–76% to O3 abundance over PRE at different stages. Overall, the above results quantitatively confirmed the dominant role of transport from inland PRD to the O3 pollution over the downwind PRE region and were helpful for better understanding of O3 pollution in winter over PRE.

Small-strain site response of soft soils in the Sacramento-San Joaquin Delta region of California conditioned on VS30 and mHVSR

Sites located in the Sacramento-San Joaquin Delta region of California typically have peaty-organic soils near the ground surface, which are characteristically soft, with shear wave velocities as low as 30 m/s. These unusually soft geotechnical conditions, which are outside the range of applicability of existing ergodic site amplification models, can be anticipated to produce significant site effects during earthquake shaking. We evaluate site response for 36 seismic stations in the Delta region using non-ergodic methods with low-amplitude ground motion data. We model first-order site effects using a period-dependent relation conditioned on the 30 m time-averaged shear wave velocity ( VS30). Relative to extrapolations of global ergodic models, this Delta-specific model provides lower and higher levels of amplification for short and long periods, respectively. While the local model provides unbiased predictions for Delta sites as a whole, it smooths over site-specific effects such as resonant peaks. Microtremor-based horizontal-to-vertical spectral ratios (mHVSRs) were measured for 34 sites, from which additional site parameters such as peak frequency ( fp), peak amplitude ( ap), and average mHVSR amplitude over some frequency bandwidth ([Formula: see text]) are derived. Sites with prominent mHVSR peaks are found to often exhibit site resonance effects, while sites without prominent peak features generally do not. A modified Ricker wavelet pulse function conditioned on fp is used to model resonance effects, while a logistic function whose amplitude is correlated with [Formula: see text] is used to model general broadband amplification that transitions to zero at long periods. These mHVSR-informed models are implemented as additive components to the VS30-scaling model. Relative to a global ergodic model, the VS30-scaling model does not appreciably change the site-to-site aleatory variability ([Formula: see text]) for periods shorter than about 1.5 s but reduces [Formula: see text] by ~0.1 (natural log units) at long periods. When the mHVSR-informed model components are used, [Formula: see text] is reduced by ~0.05 to 0.1 for short-to-intermediate periods (up to ~2 s). A model for nonlinear effects, derived from nonlinear ground response analyses, will be presented in a separate paper.

Leaf litter decomposition and detrital communities following the removal of two large dams on the Elwha River (Washington, USA)

Large-scale dam removals provide opportunities to restore river function in the long-term and are massive disturbances to riverine ecosystems in the short-term. The removal of two dams on the Elwha River (WA, USA) between 2011 and 2014 was the largest dam removal project to be completed by that time and has since resulted in major changes to channel dynamics, river substrates, in-stream communities, and the size and shape of the river delta. To assess ecosystem function across the restored Elwha watershed, we compared leaf litter decomposition at twenty sites: 1) four tributary sites not influenced by restoration activities; 2) four river sites downstream of the upper dam (Glines Canyon Dam); 3) four river sites within the footprint of the former Aldwell Reservoir upstream of the lower dam (Elwha Dam); 4) four river sites downstream of the lower dam; and 5) four lentic sites in the newly developing Elwha delta. Three major findings emerged: 1) decomposition rates differed among sections of the Elwha watershed, with slowest decomposition rates at the delta sites and fastest decomposition rates just downstream of the upper dam; 2) aquatic macroinvertebrate communities establishing in leaf litterbags differed significantly among sections of the Elwha watershed; and 3) aquatic fungal communities growing on leaf litter differed significantly among sections. Aquatic macroinvertebrate and fungal diversity were sensitive to differences in canopy cover, water chemistry, and river bottom sediments across sites, with a stronger relationship to elevation for aquatic macroinvertebrates. As the Elwha River undergoes recovery following the massive sediment flows associated with dam removal, we expect to see changes in leaf litter processing dynamics and shifts in litter-dependent decomposer communities (both fungal and invertebrate) involved in this key ecosystem process.

Double gains: Boosting crop productivity and reducing carbon footprints through maize-legume intercropping in the Yellow River Delta, China

The increasing demand for environmentally friendly agricultural practices has driven the need for diversified crop cultivation to optimize crop productivity while minimizing carbon footprints (CFs). However, the impacts of crop diversification on crop production and environmental benefits are still poorly understood. In this study, conducted at two sites in the Yellow River Delta, China, we investigated the effects of legume intercropping, specifically maize/soybean (M/S) and maize/peanut (M/P) systems, on crop productivity, economic return, ecosystem economic budget (NEEB), CF, and carbon sustainability index (CSI) in comparison to conventional monocrops. Crops were grown in replicated field plots and fertilized in their strips according to common practice for monocrops. Compared to the expected averages of monocrops, maize/legume intercropping demonstrated higher crop yields, with M/S achieving a 37% and 43% increase at the two sites, respectively, and M/P achieving an 11% and 20% increase. The higher overyielding in M/S was attributed to stronger selection effects, i.e., interspecific facilitation. However, the complementarity effects induced by the competitive dominance of maize were similar in both intercropping systems. Additionally, M/S exhibited greater potential for improving net revenues compared to M/P. Life cycle assessments revealed lower CFs in the intercropping systems compared to monocultures. M/S reduced CFs per unit of area by 26.8% at both sites, CFs per unit of maize equivalent energy yield by 25% and 33%, and CFs per unit of revenue by 20% and 25% at the two sites, respectively. M/P also resulted in reduced CFs, albeit to a lesser extent. Intercropping enhanced the CSI, with the highest values observed in the M/S system. However, both intercropping systems showed limited effects on soil C sequestration. Overall, our results highlight that maize/legume intercropping is a feasible approach to enhance crop productivity while reducing CFs. The M/S system outperformed the M/P system in terms of crop yields, economic benefits, and CF reduction. However, the intercropping systems showed limited effects on SOC storage. This study provides important implications for sustainable agriculture by appropriate crop diversification.

Exploring cultural values of African wetlands for sustainable conservation: Okavango Delta World Heritage Site, Botswana

PurposeThis study applied the Heritage Place Lab (HPL) research-practice teams methodology to identify missing cultural values and/or oversubscribed natural values and assess impacts on sustainable conservation of the Okavango Delta World Heritage Site. The authors found that cultural elements are often overlooked owing to limited inputs from trans-disciplinary and cross-stakeholder perspectives to conservation. This may explain why the majority of African sites on the List of World Heritage in Danger are of “natural” designations, as an absence of cultural values is linked to the exclusion of people and, therefore, gives rise to conflicts of access and use.Design/methodology/approachWorld Heritage Site statistics, published and non-published documents/literature, site maps, site registers, consultancy reports and archival materials were used to assess whether existing as well as potential natural and cultural site values were considered for the contemporary management of the Okavango Delta site in a way that leads to a sustainable conservation approach. The composition of the research-practice team as suggested by the HPL methodology constituted a ready-made diverse team of academics, policy makers and community members that could apply its diverse expertise to fully assess whether all values necessary for a sustainable conservation approach are accounted for.FindingsUsing expertise of trans-disciplinary team populated during the HPL, the authors found that cultural values of the OD-WHS are not highlighted in the OUVs dossier but are significantly expressed on site by locals, leading to potential conflicts of conservation. The research alerts conservationists to embrace an approach that includes all values on the site in order move towards sustainable conservation.Research limitations/implicationsMore research that require funding is needed to cover a wider area of the site, as well as enable work in adjoining countries to compare experiences per country - The Okavango waterbody starts in Angola and go through Namibia, and finally to Botswana.Practical implicationsConservation indicators of African nature world heritage sites constitute of, and border on, diverse stakeholders. An all-encompassing approach such as the Heritage Place Lab (HPL) methodology approach always needs to be factored in.Social implicationsIncluding cultural aspects of world heritage sites designated as ‘natural' is important to allow for socio-cultural inclusion in conservation management. This allows for local communities to become visible and active participants in the management of the site as they contribute their socio-cultural qualities to landscape conservation and management, a process that has potential to enhance sustainable conservation of the Okavango Delta site landscape, as well as other wetlands across the world.Originality/value The adopted approach to values assessment has somehow not conformed to the OUVs emphasis or other dichotomies of the World Heritage criteria but instead assessed on-the-ground management practice against key sustainable conservation indicators. Using the ICCROM HPL trans-disciplinary research-practice team approach, the focus was on a holistic values assessment of the site. The authors found that cultural values are currently under recognised, under-acknowledged and less expressed; creating potential conflicts that may hinder achievement of sustainable conservation and management of the site towards 2030 SDG agenda.

Identifying Strategies to Reduce Low-Value Preoperative Testing for Low-Risk Procedures: a Qualitative Study of Facilities with High or Recently Improved Levels of Testing.

Healthcare agencies and perioperative professional organizations recommend avoiding preoperative screening tests for low-risk surgical procedures. However, low-value preoperative tests are still commonly ordered even for generally healthy patients and active strategies to reduce this testing have not been adequately described. We sought to learn from hospitals with either high levels of testing or that had recently reduced use of low-value screening tests (aka "delta sites") about reasons for testing and active deimplementation strategies they used to effectively improve practice. Qualitative study of semi-structured telephone interviews. We identified facilities in the US Veterans Health Administration (VHA) with high or recently improved burden of potentially low-value preoperative testing for carpal tunnel release and cataract surgery. We recruited perioperative clinicians to participate. Questions focused on reasons to order preoperative screening tests for patients undergoing low-risk surgery and, more importantly, what strategies had been successfully used to reduce testing. A framework method was used to identify common improvement strategies and specific care delivery innovations. Thirty-five perioperative clinicians (e.g., hand surgeons, ophthalmologists, anesthesiologists, primary care providers, directors of preoperative clinics, nurses) from 29 VHA facilities participated. Facilities that successfully reduced the burden of low-value testing shared many improvement strategies (e.g., building consensus among stakeholders; using evidence/norm-based education and persuasion; clarifying responsibility for ordering tests) to implement different care delivery innovations (e.g., pre-screening to decide if a preop clinic evaluation is necessary; establishing a dedicated preop clinic for low-risk procedures). We identified a menu of common improvement strategies and specific care delivery innovations that might be helpful for institutions trying to design their own quality improvement programs to reduce low-value preoperative testing given their unique structure, resources, and constraints.

Soil salinity determines the assembly of endophytic bacterial communities in the roots but not leaves of halophytes in a river delta ecosystem

Although soil and rhizosphere microbiomes in highly saline environments have been well-studied, the role of soil salinity in the ecological processes affecting endophyte colonization and persistence remain largely unclear in halophytic plants. The present study sampled young and mature plants of the halophyte Suaeda salsa from 42 sites in the Yellow River Delta, China that varied in soil salinity. Soil physicochemical properties, root and leaf microbiomes, phylogenetic variation among plant ecotypes, and leaf metabolites were analysed. In the roots of both young and mature plants, soil salinity significantly influenced the composition of the endophytic microbiota (r = 0.29 ∼ 0.45, P < 0.001), and negatively correlated with endophyte alpha-diversity (r = -0.75 ∼ -0.78, P < 0.001). Leaf microbiome dissimilarity increased with geographic distance (r = 0.17 ∼ 0.26, P < 0.001), based on a distance-decay model, and was associated with plant phylogenetic variation (r = 0.15, P = 0.015 for young plants only). Additionally, leaf microbiome diversity and composition were correlated with soil age, pH, P content, and certain leaf metabolite compounds, but not with soil salinity. The dominant genera observed in young roots were Mesorhizobium spp. and Rhodomicrobium spp., while Pelagibius spp. was dominant in mature roots, and Pseudomonas spp. and Kushneria spp. were dominant in leaves. Soil salinity exerted a strong deterministic effect on the diversity and composition of the root endophyte community, while the acquisition and assembly of the leaf microbiome was affected by the dispersal effects, and the leaf metabolism of the host halophyte.

Theoretical Study of Hydroxylation of α- and β-Pinene by a Cytochrome P450 Monooxygenase Model

Previous studies on biocatalytic transformations of pinenes by cytochrome P450 (CYP) enzymes reveal the formation of different oxygenated products from a single substrate due to the multistate reactivity of CYP and the many reactive sites in the pinene scaffold. Up until now, the detailed mechanism of these biocatalytic transformations of pinenes have not been reported. Hereby, we report a systematic theoretical study of the plausible hydrogen abstraction and hydroxylation reactions of α- and β-pinenes by CYP using the density functional theory (DFT) method. All DFT calculations in this study were based on B3LYP/LAN computational methodology using the Gaussian09 software. We used the B3LYP functional with corrections for dispersive forces, BSSE, and anharmonicity to study the mechanism and thermodynamic properties of these reactions using a bare model (without CYP) and a pinene-CYP model. According to the potential energy surface and Boltzmann distribution for radical conformers, the major reaction products of CYP-catalyzed hydrogen abstraction from β-pinene are the doublet trans (53.4%) and doublet cis (46.1%) radical conformer at delta site. The formation of doublet cis/trans hydroxylated products released a total Gibbs free energy of about 48 kcal/mol. As for alpha pinene, the most stable radicals were trans-doublet (86.4%) and cis-doublet (13.6%) at epsilon sites, and their hydroxylation products released a total of ~50 kcal/mol Gibbs free energy. Our results highlight the likely C-H abstraction and oxygen rebounding sites accounting for the multi-state of CYP (doublet, quartet, and sextet spin states) and the formation of different conformers due to the presence of cis/trans allylic hydrogen in α-pinene and β-pinene molecules.

White-tailed deer (Odocoileus virginianus) nutritional carrying capacity over two decades after exclusion

Studies on the impacts of white-tailed deer (Odocoileus virginianus; hereafter deer) herbivory on vegetation biomass and nutritional availability are limited. Considering deer can shift plant species composition and abundance through selective browsing, we sought to investigate whether deer could influence their own nutritional carrying capacity. Using paired control and exclosure experimental units constructed in 2000 on three Wildlife Management Areas in the Upper Coastal Plain, Lower Coastal Plain, and Mississippi Alluvial Valley (hereafter Delta) ecoregions of Mississippi, we collected biomass samples following methods initially used on the sites in 2005. Biomass data were collected during July – August of 2021 at 15 random sampling points per experimental unit. Additionally, representative samples of each plant species were collected and analyzed for crude protein content to determine nutritional carrying capacity. By analyzing biomass data from 2005 and 2021, we found between-year differences, but no differences by treatment (exclosure vs. control). Notably, there was a simultaneous increase in shade tolerant species and decrease in shade intolerant species from 2005 to 2021, and a decrease in preferred forage species. Nutritional carrying capacity was only determined using 2021 data and revealed a lack of treatment effects. The differences between ecoregions demonstrated abundant low quality forage on both Coastal Plain sites (Upper and Lower) and a comparatively low amount of forage that was higher in quality in the Delta. Results suggest changing understory light conditions and a need for additional management if increasing available forage for deer is a desired management outcome. Specifically, regional differences in nutritional availability between the Coastal Plain sites and the Delta site illustrate the potential for active management to aid in the promotion of herbaceous understory forage species.

Iron Age sites in northern Botswana’s Okavango Delta 1: the southern Delta sites Mat82 and Matlapaneng plus Qogana on the region’s eastern margin

ABSTRACT This paper, one of three focused on Early Iron Age (EIA) sites of the Okavango Delta in northern Botswana, provides descriptions and analyses of two sites, Mat82 and Matlapaneng, on the southern margin of the Delta and of a small contemporary hunting-fishing camp at Qogana in its eastern middle reaches. The relationship of these sites to others, particularly in the areas of the confluence of the Chobe and Zambezi Rivers and Victoria Falls, is examined in detail. Pottery recovered from the Delta sites is shown to be a western expression of the eastern Kalundu Tradition. Optical petrographic analyses of 26 sherds from Mat82, Matlapaneng and Qogana compared with 60 sherds from Chobe-Victoria Falls sites, plus clays from most lithological exposures in these regions, confirms that most of the Mat82 and Matlapaneng sherds can be associated with local southern Delta clays, while five have fabrics comparable with Chobe-Victoria Falls clays and sherds, documenting that these Matlapaneng sherds are from vessels made in, and imported from, that region. While the distribution of finds at Matlapaneng displayed a higher concentration of lithic artefacts on the site’s outer margins with a corresponding higher pottery concentration in the centre, all areas have the same representation of lithic tools, débitage, pottery fabrics and décor motifs and proportions of wild game to domestic animals, thus providing no evidence for a herder/hunter or inner/outer space dichotomy in residence or subsistence activities. This trio of sites, then, provides a further lesson regarding the archaeological erasure of mistaken isolationist tenets in southern African archaeology in which peoples have been automatically segregated according to the material inventory of the sites at which they lived.

CRISPR-Based Multi-Gene Integration Strategies to Create Saccharomyces cerevisiae Strains for Consolidated Bioprocessing

Significant engineering of Saccharomyces cerevisiae is required to enable consolidated bioprocessing (CBP) of lignocellulose to ethanol. Genome modification in S. cerevisiae has been successful partly due to its efficient homology-directed DNA repair machinery, and CRISPR technology has made multi-gene editing even more accessible. Here, we tested the integration of cellulase encoding genes to various sites on the yeast genome to inform the best strategy for creating cellulolytic strains for CBP. We targeted endoglucanase (EG) or cellobiohydrolase (CBH) encoding genes to discreet chromosomal sites for single-copy integration or to the repeated delta sites for multi-copy integration. CBH1 activity was significantly higher when the gene was targeted to the delta sequences compared to single gene integration loci. EG production was comparable, though lower when the gene was targeted to a chromosome 10 site. We subsequently used the information to construct a strain containing three cellulase encoding genes. While individual cellulase activities could be assayed and cellulose conversion demonstrated, it was shown that targeting specific genes to specific loci had dramatic effects on strain efficiency. Since marker-containing plasmids could be cured from these strains, additional genetic changes can subsequently be made to optimize strains for CBP conversion of lignocellulose.

Distribution, risk assessment, and source identification of trace metal pollution along the Babolsar coastal area, Caspian Sea.

The Caspian Sea is exposed to numerous anthropogenic activities such as untreated wastewater discharge and agricultural activities which increased trace metals contamination. The current study was employed to assess the distribution, ecological risk assessment, and source identification of some trace metals in 125 samples of surface sediments and soil from 6 distinctive sections of Babolsar in the coastal line of the Caspian Sea. The sediment quality guidelines (SQGs) and individual risk assessment indices including enrichment factor (EF), geo-accumulation index (Igeo), contamination factor (Cf), and potential risk factor (Er) suggested a hazardous level of Cd and Cr contamination. There was a relatively high level of Pb contamination while other studied trace metals were at a low contamination level. Cumulative risk indices such as modified degree of contamination (mCD), pollution load index (PLI), and the potential ecological risk index (RI) identified that the river, wetland, and farmland sites were more contaminated compared to the Caspian Sea samples which exhibited a moderate level of contamination. The lowest level of contamination was recorded in the coastline and river delta sites. Two analytical methods including Pearson's correlation coefficient and multivariate clustering dendrogram were also applied to identify the potential sources of contamination. The results suggested that wastewaters, nitrogen, and phosphate fertilizers were the main anthropogenic source of Cd, Co, Pb, and Ni while fossil fuels and transportation activities were the predominant sources of anthropogenic Cu, V, and Zn contamination. Further studies about trace metals risk assessment and fractionation could contribute to more effective decisions for reducing the anthropogenic trace metal pollution in the Caspian Sea.

Spatial Distribution and Eco-stoichiometric Characteristics of Soil Nutrient Elements Under Different Vegetation Types in the Yellow River Delta Wetland

To clarify the distribution characteristics and the ecological stoichiometric characteristics of nutrient elements in soils under different vegetation types, four typical natural wetlands, i.e., Phragmites australis wetland, Tamarix chinensis wetland, Suaeda salsa wetland, and Tidal flat wetland, as well as Gossypium spp. fields that were reclaimed from natural wetlands, were selected as study sites in the Yellow River Delta, and comparisons between the agricultural reclamation land and natural wetlands were conducted. The results showed that the soil total organic carbon (TOC) and total nitrogen (TN) contents in the natural wetlands were as follows:P. australis wetland and T. chinensis wetland>S. salsa wetland>Tidal flat, and the contents of TOC and TN were significantly negatively related to electrical conductivity (EC) and pH values (P<0.05). The contents of TOC, TN, and total phosphorus (TP) in Gossypium spp. fields were significantly higher than those in natural wetlands (P<0.05), especially the contents of nitrate nitrogen (NO3--N) in Gossypium spp. fields, which were 9.4-11.4 times that of natural wetlands. However, no significant correlations between TOC, TN, and TP and EC and pH values (P>0.05) were observed in Gossypium spp. fields. The results of correlation analysis showed that the C/N of natural wetlands were mainly controlled by the contents of TN (P<0.05), and the C/N of the Gossypium spp. fields were significantly lower than those of natural wetlands (P<0.05). The soil C/P and N/P of natural wetlands and Gossypium spp. fields in the Yellow River Delta were low, and the variation trends were consistent with those of soil TOC and TN. Comparative analysis revealed, on the whole, that there were significantly different soil nutrient element contents, C/N, C/P, and N/P in Gossypium spp. fields compared to those of natural wetlands (P<0.05). The process of reclamation could significantly change the spatial distribution of nutrient elements in wetlands. Our results should be of importance in revealing the biogeochemical process of soil nutrient elements in coastal wetland and the influence of agricultural reclamation activities on the differentiation of soil nutrient elements.

Herding then farming in the Nile Delta

The Nile Delta in Egypt represents a valuable location to study the history of human societal development and agricultural advancement. However, the livelihood patterns of the earliest settlers – whether they were farmers or herders – remains poorly understood. Here we use non-pollen palynomorphs and pollen grains from a sediment core taken at Sais, one of the earliest archaeological sites in the west-central Nile Delta, to investigate the livelihood patterns and transition of early settlers there. We find that animal microfossils (dung and hair) occur in substantial quantities from around 7,000 years ago in our high-resolution-dated non-pollen palynomorphs spectrum, while domesticated cereals emerge in the spectrum around 300 years later. We also identify evidence of fire-enhanced land exploitation after this time. We interpret our microfossil evidence to indicate that the earliest settlers in the Nile Delta were herders and that this then developed into a combination of herding and farming.

Effects of codon optimization, N-terminal truncation and gene dose on the heterologous expression of berberine bridge enzyme

Morphine, sanguinarine and chelerythrine are benzylisoquinoline alkaloids (BIAs), and these compounds possess strong biological activities. (S)-scoulerine is a commonly shared precursor of these compounds, and berberine bridge enzyme (BBE) is a key rate-limiting enzyme in the synthesis of (S)-scoulerine. We isolated the BBE gene from Macleaya cordata (McBBE) and used CEN.PK2-1C as a chassis strain. We compared the catalytic efficiency of five codon-optimized McBBE genes in Saccharomyces cerevisiae and finally obtained a yeast strain (YH03) that exhibited a 58-fold increase in yield (1.12mg/L). Then, we truncated the N-terminus of McBBE by 8 and 22 amino acids and found that with the increase in the number of N-terminal truncated amino acids, the production of (S)-scoulerine gradually decreased. Additionally, we used CRISPR-Cas9 to integrate the McBBE gene at the delta site of the S. cerevisiae genome to achieve stable genetic inheritance and found that the yield of (S)-scoulerine was not significantly increased in the integrated strain. In conclusion, our work achieved high-efficiency expression of McBBE in S. cerevisiae, explored the influence of N-terminal truncation on the yield of (S)-scoulerine, and obtained a genetically stable S. cerevisiae strain with high McBBE expression. This study provides a reference for further complex metabolic engineering optimization and lays a foundation for the efficient biosynthesis of BIAs.

Mangrove sediment organic carbon storage and sources in relation to forest age and position along a deltaic salinity gradient

Abstract. Mangroves are widely recognised as key ecosystems for climate change mitigation as they capture and store significant amounts of sediment organic carbon (SOC). Yet, there is incomplete knowledge on how sources of SOC and their differential preservation vary between mangrove sites in relation to environmental gradients. To address this, sediment depth profiles were sampled from mangrove sites ranging from river-dominated to marine-dominated sites and including old and young mangrove sites in the Guayas delta (Ecuador). The stable carbon isotope ratios (δ13C) and the elemental composition (OC %, C : N) of sediment profiles, local vegetation (i.e. autochthonous carbon) and externally supplied suspended particulate matter (i.e. allochthonous carbon) were obtained to assess variations in the amount and sources of SOC at different locations throughout the delta. In general, across all sites, we found that increasing SOC contents and stocks are associated with decreasing δ13C and increasing C : N ratios, indicating that SOC stocks and sources are intrinsically related. The SOC stocks (down to 0.64 m depth profiles) are significantly lower in young mangrove sites (46–55 Mg C ha−1) than in old sites (78–92 Mg C ha−1). The SOC in the young mangrove sites is mainly of allochthonous origin (estimated on average at 79 %), whereas in the old sites there is a slight dominance of autochthonous OC (on average 59 %). Moreover, from river- to marine-dominated sites, a pattern was found of increasing SOC stocks and increasing autochthonous SOC contribution. These observed differences along the two studied gradients are hypothesised to be mainly driven by (1) expected higher sedimentation rates in the river-dominated and lower-elevation younger sites, thereby `diluting' the SOC content and decreasing the relative autochthonous contribution, and (2) potential differences in preservation of the different SOC sources. Our finding of high contributions of allochthonous SOC, especially in young mangroves, implies that this carbon is not originating from CO2 sequestration by the mangrove ecosystem itself but is externally supplied from other terrestrial, marine or estuarine ecosystems. We argue that accounting for lower SOC stocks and higher contribution of allochthonous SOC in young and river-dominated mangrove sites, as compared to old and marine-dominated sites, is particularly relevant for designing and valuing nature-based climate mitigation programmes based on mangrove reforestation.

Seasonal and interannual variation in high-latitude estuarine fish community structure along a glacial to non-glacial watershed gradient in Southeast Alaska

Along the Gulf ofAlaska, rapid glacier retreat has driven changes in transport of freshwater, sediments, and nutrients to estuary habitats. Over the coming decades, deglaciation will lead to a temporary increase, followed by a long-term decline of glacial influence on estuaries. Therefore, quantifying the current variability in estuarine fish community structure in regions predicted to be most affected by glacier loss is necessary to anticipate future impacts. We analyzed fish community data collected monthly (April through September) over 7 years (2013–2019) from glacially influenced estuaries along the southeastern Gulf of Alaska. River delta sites within estuaries were sampled along a natural gradient of glacial to non-glacial watersheds to characterize variation in fish communities exposed to varying degrees of glacial influence. Differences in seasonal patterns of taxa richness and abundance between the most and least glacially influenced sites suggest that hydrological drivers influence the structure of delta fish communities. The most glacially influenced sites had lower richness but higher abundance overall compared to those with least glacial influence; however, differences among sites were small compared to differences across months. Two dominant species—Pacific staghorn sculpin and starry flounder—contributed most to spatial and temporal variation in community composition; however, given only small interannual differences in richness and abundance over the period of the study, we conclude that year-to-year variation at these sites is relatively low at present. Our study provides an important benchmark against which to compare shifts in fish communities as watersheds and downstream estuaries continue to transform in the coming decades.

Controls on carbon dioxide and methane fluxes from a low-center polygonal peatland in the Mackenzie River Delta, Northwest Territories

Growing season surface–atmosphere exchange of carbon dioxide and methane were quantified at Fish Island, a wetland site in the lower northeast Mackenzie River Delta, Northwest Territories, Canada. The terrain consists of low-center polygonal tundra and is subject to infrequent flooding in high water years. Carbon dioxide and methane fluxes were continuously measured using eddy covariance and the relevance of different environmental controls were identified using neural networks. Net daily carbon dioxide uptake peaked in mid-July before gradually decreasing and transitioning to net daily emissions by September. Variations in light level and temperature were the main controls over diurnal net carbon dioxide uptake, whereas thaw depth and phenology were the main seasonal controls. Methane emissions measured at Fish Island were higher than comparable studies on river delta sites in the Arctic and were influenced by the interaction of a large number of factors including thaw and water table depth, soil temperatures, and net radiation. Spikes in methane emissions were associated with strong winds and turbulence. The Fish Island tundra was a net sink for carbon during the growing season and methane emissions only slightly reduced the overall sink strength.

Construction of yeast cell factories for production of azadirachtin precursor tirucalla-7,24-dien-3β-ol

Azadirachtin, as a botanical insecticide, is a highly oxidized limonoid triterpenoid existing in the seeds of Azadirachta indica. However, due to the low content in the seeds, the production of azadirachtin by seed extraction has low yield. Chemical synthesis of azadirachtin is characterized by complex process and low yield. Synthetic biology provides an alternative for the supply of azadirach-tin. In this study, two oxidosqualene cyclases AiOSC1 and MaOSC1 respectively derived from A. indica and Melia azedarach were identified in yeast. A yeast strain producing tirucalla-7,24-dien-3β-ol was constructed by integration of AiOSC1, Arabidopsis thaliana-derived squalene synthase gene(AtAQS2), and Saccharomyces cerevisiae-derived truncated 3-hydroxy-3-methyl-glutaryl coenzyme A reductase gene(PgtHMGR) into the delta site of yeast. Then, the function of MaCYP71BQ5 was successfully verified in yeast after this gene was introduced into the constructed yeast strain. This study not only laid a foundation for the biosynthesis of tirucalla-7,24-dien-3β-ol, but also provided a chassis cell for the functional identification of cytochrome oxidases(CYP450 s) in azadirachtin biosynthesis pathway.

Empirical correlations of soil parameters based on piezocone penetration tests (CPTU) for Hong Kong-Zhuhai-Macau Bridge (HZMB) project

The site investigation is a key part of the foundation analysis and design in the Hong Kong-Zhuhai-Macao Bridge (HZMB) mega project, as it provides accurate geotechnical parameters. This paper discusses about the collection of undisturbed soil samples, laboratory tests, and extensive piezocone penetration tests (CPTU) performed at the Pearl River Delta sites. First, soils were classified based on CPTU data and statistical analyses were conducted to determine the correlation between the physical parameters and CPTU data. Current interpretation methods were used to evaluate the physical, state, strength, and deformation characteristics of soil and develop new site-specific correlations. The analysis of a large amount of available data not only illustrated the significant potential of CPTU for obtaining soil stratification details and in-situ soil properties, but also revealed some limitations of widely used empirical correlations for characterizing the physical, state, strength, and deformation properties of soil. In this study, region-specific correlations between piezocone penetration resistance and soil properties, with special reference to physical, strength, and deformation characteristics, are established and verified with the existing recommendations.