Threshold Indicator Taxa Analysis Research Articles

Threshold responses and relationships between waterbird distribution and habitat factors at Shengjin Lake, China

The wintering period is an essential part of the annual life history of waterbirds. The environmental conditions of habitats in winter directly affect the abundance and physical condition of waterbirds. Therefore, it is important to study the relationship between waterbird abundance and habitat factors. In this study, we conducted significance and threshold analyses between habitat factors and the waterbird community at Shengjin Lake, a Ramsar Site in China, using Redundancy Analysis (RDA), Spearman Correlation Analysis, and Threshold Indicator Taxa Analysis (TITAN). The results indicate that seven environmental variables significantly affected the abundance of waterbird communities, that is, fractional vegetation cover, degree of receding water, grassland area, mudflat area, shallow water area, deep water area, and distance to reeds. Waterbird communities exhibited significant threshold responses to all seven factors. The number of species significantly responding to different habitat factors varied among waterbird communities, with the highest number of species (15) responding to distance to reeds. Except for the deep water area and distance to reeds, waterbirds showed higher positive than negative thresholds for the remaining five factors. Different groups of waterbirds influenced the threshold responses of waterbird communities to habitat factors, and there were variations in how each waterbird group responded to these factors. The results of this study highlight the importance of habitat type, water recession degree, and shelter conditions in waterbird habitat selection. Minor differences in habitat structure can influence waterbird habitat preferences. Therefore, wetland management at Shengjin Lake should consider the specific habitat needs of different waterbird species.

Salt Belt Index (SBI): A biotic index for streams within the North American “salt belt,” with proposed baseline chloride thresholds

Road salt (commonly NaCl, CaCl2, and MgCl2) is widely used in the northern United States as a deicing agent for roadways and other byways. Millions of tons of road salt are used annually in the United States, resulting in drastic increases in freshwater salinity. This study aims to determine the chloride optima and tolerance ranges of macroinvertebrates using publicly accessible stream monitoring data from the US EPA. We assigned taxa region-specific tolerance values, which we then used to calculate the Salt Belt Index (SBI). In addition to the SBI, we determined new, region-specific, chronic Cl− thresholds, determined using threshold indicator taxa analysis (TITAN). Using generalized linear models, we found the SBI was highly accurate at estimating chloride concentration (mg/L Cl−) across the salt belt states. Macroinvertebrate community richness exhibited a significant negative relationship with increasing chloride concentrations. Newly proposed chloride thresholds, based on the richness-chloride relationship, were far lower than current thresholds. The SBI was able to differentiate between Low-, Medium-, and High-Impact sites, grouped based on proposed chloride thresholds. Based on our findings, it is clear current salinity thresholds are too high, and management practices should factor in regional variability, taxon-specific physiology, and historical instream chemistry when implementing salinity thresholds.

Succession of medico-legal important flesh flies (Diptera: Sarcophagidae) in the temporal gradient of pig decomposition in the Brazilian Cerrado

Flies belonging to the Sarcophagidae family play a significant role in forensic investigations by aiding in the estimation of post-mortem interval through the assessment of the developmental time of their immature stages and/or the succession patterns of species on carcasses and cadavers. In this regard, this study aimed to investigate the ecological succession of these flies on pig carcasses within Cerrado of Brazil. The progression of fly succession was examined over a 10-day period using the Threshold Indicator Taxa Analysis (TITAN) approach. Six Z + species (Oxysarcodexia thornax (Walker), Peckia (Sarcodexia) lambens (Wiedemann), Peckia (Euboettcheria) collusor (Curran & Walley), Ravinia belforti (Prado & Fonseca), Tricharaea (Sarcophagula) canuta (Wulp) and Tricharaea (Sarcophagula) occidua (Fabricius)) were identified, with change points ranging from 2.5 to 3 days during the dry season and 2.5 to 5.5 days during the rainy season. Two Z− species (Dexosarcophaga carvalhoi (Lopes) and Peckia (Sarcodexia) tridentata (Hall)) were present, with a change point of 6.5 days during the rainy season. This study provides a continuous analysis of the temporal succession of flies, enabling an investigation into species progression based on their change points and directions (Z + and Z− ), thereby offering methodological advancements to avoid the arbitrary categorization of inherently continuous data.

Real-time breath analysis towards a healthy human breath profile.

The direct analysis of molecules contained within human breath has had significant implications for clinical and diagnostic applications in recent decades. However, attempts to compare one study to another or to reproduce previous work are hampered by: variability between sampling methodologies, human phenotypic variability, complex interactions between compounds within breath, and confounding signals from comorbidities. Towards this end, we have endeavored to create an averaged healthy human 'profile' against which follow-on studies might be compared. Through the use of direct secondary electrospray ionization combined with a high-resolution mass spectrometry and in-house bioinformatics pipeline, we seek to curate an average healthy human profile for breath and use this model to distinguish differences inter- and intra-day for human volunteers. Breath samples were significantly different in PERMANOVA analysis and ANOSIM analysis based on Time of Day, Participant ID, Date of Sample, Sex of Participant, and Age of Participant (p< 0.001). Optimal binning analysis identify strong associations between specific features and variables. These include 227 breath features identified as unique identifiers for 28 of the 31 participants. Four signals were identified to be strongly associated with female participants and one with male participants. A total of 37 signals were identified to be strongly associated with the time-of-day samples were taken. Threshold indicator taxa analysis indicated a shift in significant breath features across the age gradient of participants with peak disruption of breath metabolites occurring at around age 32. Forty-eight features were identified after filtering from which a healthy human breath profile for all participants was created.

Spatial variability of edaphic attributes on Coleoptera (Insecta) in land use systems

The alteration of the natural landscape structure affects abiotic conditions and promotes a biological response in the local community. The diversity of edaphic organisms is related to the diversity of other taxa and abiotic characteristics, which represent potential bioindicators of the ecosystem. The objective of this study was to identify which soil attributes explain the beetle community and explore their effects through spatial modeling. The study was conducted in three landscapes in western Santa Catarina (Brazil), located in Chapecó, Pinhalzinho, and São Miguel do Oeste. The land use and cover systems identified were: no-till farming, native forest, pasture, eucalyptus planting, crop-livestock integration, and shrub vegetation. Soil, plant litter, and Coleoptera samples were collected. The variables were selected through the Threshold Indicator Taxa Analysis and spatial modeling by Geostatistics. Higher values of soil penetration resistance, associated with the no-till system, resulted in a lower abundance of Staphylinidae beetles, conditioned by total soil porosity. Lower volumetric moisture values, identified in the no-till system near native vegetation fragments, led to increased abundance of Nitidulidae family beetles, due to the family's adaptability to dry environments. The trend of higher microbial carbon concentration in native vegetation areas explained the greater abundance of Chrysomelidae family beetles in these areas, due to the phytophagous habits of the species in this family. Thus, the Coleoptera community has the potential to serve as bioindicators of soil quality, and their relationships with soil physics, chemical, and microbial attributes can be spatially modeled through Geostatistics.

Assessment of chemical integrity based on ecological thresholds in one of the largest basins in China

Chemical integrity plays a crucial role in maintaining the ecological integrity of aquatic ecosystems. Despite its significance, assessments of ecological integrity often prioritize biological evaluations, leading to infrequent and inadequate scrutiny of chemical integrity. Additionally, a comprehensive framework for separately assessing chemical integrity has not been established. To address this issue, we established a new index for evaluating chemical integrity, achieved through indicator screening, normalization, and weight assignment. Combined with the threshold indicator taxa analysis (TITAN) and Pearson correlation analysis, main evaluation indicators and their indicator species were identified and the corresponding response threshold was determined. These thresholds were then applied to improve the normalization method, with weights determined by indicator species proportions. This index was applied to evaluate the chemical integrity of the Huai River Basin, which is one of the largest basins in China. The results indicated that ammonia nitrogen (NH3-N), nitrate nitrogen (NO2-N), pH, and turbidity (Turb) were identified as the core parameters for evaluating chemical integrity. The conventional normalization method (max–min normalization) led to overestimation of the assessment results, whereas improved normalization method based on ecological threshold yielded better and more reasonable results. This study provided a reference for the selection of appropriate indicators and improvement of normalization method to better assess chemical integrity. And it would become a useful tool for monitoring and rehabilitating the chemical integrity in such basins.

A new diatom-based multimetric index to assess lake ecological status

Eutrophication impairs lake ecosystems at a global scale. In this context, as benthic microalgae are well-established warnings for a large range of stressors, particularly nutrient enrichment, the Water Framework Directive required the development of diatom-based methods to monitor lake eutrophication. Here, we present the diatom-based index we developed for French lakes, named IBDL (Indice Biologique Diatomées en Lacs). Data were collected in 93 lakes from 2015 to 2020. A challenge arose from the discontinuous pressure gradient of our dataset, especially the low number of nutrient-impacted lakes. To analyze the data we opted for the so-called “Threshold Indicator Taxa ANalysis” method, which makes it possible to determine a list of “alert taxa.” We obtained a multimetric index based on specific pressure gradients (Kjeldahl nitrogen, suspended matter, biological oxygen demand, and total phosphorous). Considering the European intercalibration process, the very good correlation between IBDL and the common metric (R2 from 0.52 to 0.87 according to the lake alkalinity type) makes us very confident in our ability to match future IBDL quality thresholds with European standards. The IBDL proved at last to be particularly relevant as it has a twofold interest: an excellent relationship with total phosphorus (R2 from 0.63 to 0.83 according to the lake alkalinity type) and a possible application to any lake metatype. Its complementarity with macrophyte-based indices moreover justifies the use of at least two primary producer components for lake ecological status classification.

Protecting the invisible: Establishing guideline values for copper toxicity to marine microbiomes

Understanding the rapid responses of marine microbiomes to environmental disturbances is paramount for supporting early assessments of harm to high-value ecosystems, such as coral reefs. Yet, management guidelines aimed at protecting aquatic life from environmental pollution remain exclusively defined for organisms at higher trophic levels. In this study, 16S rRNA gene amplicon sequencing was applied in conjunction with propidium monoazide for cell-viability assessment as a sensitive tool to determine taxon- and community-level changes in a seawater microbial community under copper (Cu) exposure. Bayesian model averaging was used to establish concentration-response relationships to evaluate the effects of copper on microbial composition, diversity, and richness for the purpose of estimating microbiome Hazard Concentration (mHCx) values. Predicted mHC5 values at which a 5 % change in microbial composition, diversity, and richness occurred were 1.05, 0.72, and 0.38 μg Cu L−1, respectively. Threshold indicator taxa analysis was applied across the copper concentrations to identify taxon-specific change points for decreasing taxa. These change points were then used to generate a Prokaryotic Sensitivity Distribution (PSD), from which mHCxdec values were derived for copper, suitable for the protection of 99, 95, 90, and 80 % of the marine microbiome. The mHC5dec guideline value of 0.61 μg Cu L−1, protective of 95 % of the marine microbial community, was lower than the equivalent Australian water quality guideline value based on eukaryotic organisms at higher trophic levels. This suggests that marine microbial communities might be more vulnerable, highlighting potential insufficiencies in their protection against copper pollution. The mHCx values proposed here provide approaches to quantitatively assess the effects of contaminants on microbial communities towards the inclusion of prokaryotes in future water quality guidelines.

Conservation tillage and moderate nitrogen application changed the composition, assembly pattern and interaction network of abundant and rare microbial community on straw surface

Microbial-driven straw decomposition is important for soil organic carbon accumulation, nutrient uptake, and crop utilization. However, the mechanism by which tillage and fertilization interactions form the abundant and rare microbial communities that mediate straw degradation in dry farmland remains unclear. Based on an interaction experiment between three tillage practices (zero-till, chisel-till, and conventional plow-till) and three levels of nitrogen fertilizer (180, 240, and 300 kg·N·ha−1), we aimed to understand the community assembly process of abundant and rare microbe in the decomposition of maize straw. We found that the abundant bacterial and fungal communities were governed by stochastic processes, whereas the rare bacterial communities were dominated by deterministic processes. Furthermore, the relative importance of deterministic assembly of all microbial communities was higher in conservation tillage; in addition, the deterministic assembly process of the abundant bacterial and fungal communities was significantly increased by the medium level of nitrogen fertilizer (240 kg·N·ha−1), but the rare microbial community was not significantly affected. Redundancy analysis (RDA) and threshold indicator taxa analysis (TITAN) indicated that soil temperature, pH, and NO3− are the key influencing factors for the abundant and rare microbial communities. Overall, conservation tillage and a medium level of nitrogen fertilizer (240 kg·ha−1) in dry farmland promoted straw decomposition by regulating the development and turnover of straw-decomposing communities, in which they regulated bacterial community succession rather than fungi within a short decomposition time. These findings highlight the distinct responses to conservation tillage and N fertilization in the community assembly of abundant and rare biospheres in maize straw decomposition, and provide additional evidence for the development of conservation tillage applications in drylands.

EDNA of zooplankton reveals the ecological community thresholds for key environmental factors in the Baiyangdian Lake aquatic ecosystem

BackgroundThe drastic change in an ecosystem as a threshold phenomenon caused by abrupt changes in environmental conditions is a focus of current ecological research. However, the study of ecological thresholds has generally been limited to estimating the threshold values of single factors. Using eDNA metabarcoding technology, we collected zooplankton data from Baiyangdian Lake, the largest freshwater lake in the North China Plain, to explore the zooplankton community distribution characteristics and the relevant environmental factors. We used Threshold Indicator Taxa Analysis (TITAN) to determine the thresholds of key environmental factors and to identify the factors influencing biological diversity.ResultsBy comparing previous studies, we found that the zooplankton community composition based on eDNA metabarcoding was similar to that based on morphological methods, and that the data could be used to estimate ecological thresholds and assess risk conditions. Temperature (T), electrical conductivity (EC), and turbidity were the major environmental factors affecting the zooplankton community structure. The composition and structure of zooplankton communities in rivers and lakes were significantly different due to the influence of specific environmental factors. The results of TITAN analysis showed that there were different indicator species for T and EC in rivers and lakes. The protection thresholds of zooplankton in rivers were T = 19.0 °C and EC = 795 μS/cm, whereas the protection thresholds of zooplankton in lakes were T = 14.3 °C and EC = 1920 μS/cm. The overall values for the Baiyangdian watershed were T = 15.5 °C and EC = 1073 μS/cm. Compared with the field monitoring results, approximately 50% of the water quality index values at the sampling points in the Baiyangdian watershed exceeded the negative response threshold, indicating that Baiyangdian Lake was disturbed.ConclusionsThe validity of eDNA technology in biodiversity analysis was confirmed by the zooplankton community data from Baiyangdian Lake. The ecological thresholds derived by combining eDNA technology with Threshold Indicator Taxa Analysis (TITAN) are beneficial to the biological conservation of the region.

Molecular and Dual-Isotopic Profiling of the Microbial Controls on Nitrogen Leaching in Agricultural Soils under Managed Aquifer Recharge.

Nitrate (NO3-) leaching is a serious health and ecological concern in global agroecosystems, particularly those under the application of agricultural-managed aquifer recharge (Ag-MAR); however, there is an absence of information on microbial controls affecting NO3- leaching outcomes. We combine natural dual isotopes of NO3- (15N/14N and 18O/16O) with metagenomics, quantitative polymerase chain reaction (PCR), and a threshold indicator taxa analysis (TITAN) to investigate the activities, taxon profiles, and environmental controls of soil microbiome associated with NO3- leaching at different depths from Californian vineyards under Ag-MAR application. The isotopic signatures demonstrated a significant priming effect (P < 0.01) of Ag-MAR on denitrification activities in the topsoil (0-10 cm), with a 12-25-fold increase of 15N-NO3- and 18O-NO3- after the first 24 h of flooding, followed by a sharp decrease in the enrichment of both isotopes with ∼80% decline in denitrification activities thereafter. In contrast, deeper soils (60-100 cm) showed minimal or no denitrification activities over the course of Ag-MAR application, thus resulting in 10-20-fold of residual NO3- being leached. Metagenomic profiling and laboratory microcosm demonstrated that both nitrifying and denitrifying groups, responsible for controlling NO3- leaching, decreased in abundance and potential activity rates with soil depth. TITAN suggested that Nitrosocosmicus and Bradyrhizobium, as the major nitrifier and denitrifier, had the highest and lowest tipping points with regard to the NO3- changes (P < 0.05), respectively. Overall, our study provides new insight into specific depth limitations of microbial controls on soil NO3- leaching in agroecosystems.

Using taxa-based approaches to delineate stream macroinvertebrate assemblage responses to stressor gradients in modified alluvial agroecosystems

Alluvial plain landscapes are some of the most agriculturally productive lands in the world but often have modified stream ecosystems due to cultivation history. This context requires consideration when establishing water quality management goals. We analyzed state water quality databases to demonstrate that Mississippi Alluvial Plain (MAP) ecoregion streams have elevated specific conductivity (SC) and nutrients and lower macroinvertebrate local and regional taxa pools compared to streams in other ecoregions, potentially reducing the efficacy of traditional biomonitoring approaches within the region. To overcome these challenges, we used threshold indicator taxa analysis (TITAN) to compare macroinvertebrate assemblage responses to water quality gradients among ecoregions in Mississippi. We identified individual taxa and assemblage-level responses to increasing water quality degradation in MAP streams. Observed responses occurred at higher concentrations for SC, total organic carbon (TOC) and total phosphorus (TP), but not total nitrogen (TN) relative to other ecoregions. These responses appeared to be driven by a large proportion of indicator taxa considered tolerant or unresponsive in other ecoregions, responding negatively to increasing water quality stressors in MAP streams. Our observed assemblage-level stressor responses to WQ gradients in MAP streams demonstrate shifting tolerance in highly altered ecosystems may require adjustments to recovery expectations but also provide useful measures for monitoring improvements in regional water quality. For example, our observed macroinvertebrate assemblage response to increasing TP identified a management goal similar to guidance based on distributional analysis of water quality data within the MAP ecoregion (0.11 vs 0.128 mg L−1) and thus provide some biological basis for previously identified nutrient goals for the region. Our approach can guide and monitor success of nutrient reduction efforts in MAP watersheds and other alluvial plain agroecosystems where reference conditions do not exist, and local and regional taxa pools are less diverse and may not support full recovery of ecological assemblages. While our results are promising, they should also be compared with more sensitive and less habitat-limited biological assemblages (e.g., algae or bacteria) to better understand complex ecological responses to best management practices designed to increase sustainability of high production agricultural regions.

Diatom–salinity thresholds in experimental outdoor streams reinforce the need for stricter water quality guidelines in South Australia

Water quality guidelines are an important tool for managing environmental pressures on freshwater streams, but guidelines are frequently set using conditions from reference sites that are assumed to be unimpacted. Using biological thresholds potentially provides a better foundation for guidelines. However, guidelines based on field observations alone may be compromised by confounding influences. This study used an outdoor stream mesocosm, an artificial substrate (rope), and six salinity concentrations to assess the veracity of a diatom–salinity threshold determined previously in natural temperate South Australian streams. In addition, shaded treatments assessed the synergistic influences of salinity and reduced sunlight. Salinity had the strongest effect on diatoms, influencing both species and functional compositions. Species diversity and richness, and functional diversity had negative correlations with salinity. Shade strongly reduced diatom concentrations and altered species composition, with no observed interaction between salinity and light. Threshold Indicator Taxa ANalysis indicated a salinity threshold of 1610 μS cm−1 for both shade treatments, lower than the upper limit of the range used in current freshwater guidelines. This study recommends a new candidate guideline of 1600 μS cm−1 for regional freshwater streams and suggests that contemporary methods for deriving water quality guidelines may not adequately protect aquatic health.

Increasing depth reduces macrophyte coverage but increasing transparency promotes composition turnover through environmental thresholds

Context Environmental filters modify the coverage and frequency patterns of macrophyte communities. Aims We characterised the thresholds in depth and transparency at which the macrophyte distribution shifted in an Atlantic Forested wetland. Methods Macrophyte communities were characterised in 150 plots divided into 6 transects. Key results Threshold indicator taxa analysis (TITAN) indicated that free-floating life forms respond negatively to depth and transparency increase. Rooted-floating species responded negatively to an increase in depth and transparency; by contrast, submerged species responded positively to increased transparency. Conclusion TITAN also highlighted that the entire macrophyte community responded negatively to increased depth but exhibited a synchronous turnover among species responding positively and negatively to transparency. Implications Our results demonstrated that macrophyte responses to increasing depth and transparency are non-linear and depend on species life forms.

Drainage‐induced browning causes both loss and change of benthic biodiversity in headwater streams

AbstractConcentrations of dissolved organic carbon (DOC) have increased over the past few decades, causing freshwater browning. Impacts of browning on biodiversity have been little studied, despite many of the individual stressors associated with browning being known to control freshwater communities. We explored the responses of benthic invertebrates along a wide gradient of DOC concentrations (3.6–27 mg L−1) in 63 boreal streams variously impacted by peatland drainage or peat production. DOC was a prime determinant of macroinvertebrate diversity and abundance, with the strongest negative response in algal scrapers. Threshold indicator taxa analysis indicated an abrupt community change at 12–13 mg DOC L−1, with only four taxa increasing, while 13 taxa decreased along the gradient. Our findings of both a gradual loss and abrupt change of biodiversity along a browning gradient provide a benchmark against which changes to stream biodiversity relative to the predicted browning trend can be gauged.

Ecological thresholds in Brazilian savanna: Environmental conditions modulating the composition of woody species in different substrates

Neotropical savannas are complex ecosystems whose species compositions are determined by different environmental factors, acting at regional (altitude, geomorphology, and climate) and local scales (substrate deep, soil properties, relief, and fire). We investigated the ecological thresholds, at the large (regional) and small scale (local), at the community levels of woody plants in two adjacent savanna environments. These savannas occur on distinct substrates with deep soils and flat relief (DS) and shallow soils with rocky outcrops and steep relief (RS). We compiled abundance data of the woody species and regional and local variables in 32 sites, with 1 ha each (16 DS and 16 RS). All sites are in protected areas with no recent sign of fire. We applied the Threshold Indicator Taxa Analysis (TITAN) to detect changes in species distribution in response to environmental predictors. The communities of the two environments differed in their responses to the local (soil properties) and regional (altitude), but climate had little influence on the vegetation of these environments. The woody communities of DS and RS present differences in response to predictors. We conclude that the distribution of species in both environments is determined by multiple and distinct factors, which depend on the scale analyzed.

Developing Ecological Thresholds for Nitrogen and Phosphorus in the Haihe River Basin in China.

Many aquatic ecosystems are eutrophicated due to human inputs of nitrogen and phosphorus. Therefore, it is now considered important to establish nutrient criteria to prevent eutrophication. In this study, the water quality and biological data for 26 stations in the lower reaches of the Haihe River Basin were collected. The total nitrogen (TN) and total phosphorus (TP) ecological thresholds were derived from the threshold indicator taxa analysis (TITAN) and frequency distribution approach. The results showed that the TN threshold was 1.8 mg/L based on the TITAN and the TP threshold was 0.039 mg/L based on the frequency distribution approach. The TITAN also identified 29 indicator species of TN and 28 indicator species of TP. Based on these criteria, we found 73% sites with TN concentrations higher than the 1.8 mg/L. As for TP, 58% sites exceeded 0.039 mg/L. This study showed that most of the downstream areas of the Haihe River are subject to relatively serious disturbances. This finding could provide implications for identifying the water quality traits of and generating protection strategies for the Haihe River in Tianjin.

Environmental filtering of macroinvertebrate traits influences ecosystem functioning in a large river floodplain

AbstractThe biodiversity–ecosystem function hypothesis postulates that higher biodiversity is correlated with faster ecosystem process rates and increased ecosystem stability in fluctuating environments. Exhibiting high spatiotemporal habitat diversity, floodplains are highly productive ecosystems, supporting communities that are naturally resilient and highly diverse.We examined linkages among floodplain wetland habitats, invertebrate communities and their associated traits, and ecosystem function across 60 sites within the floodplain wetlands of the lower Wolastoq | Saint John River, New Brunswick, using structural equation modelling and Threshold Indicator Taxa ANalysis.We identified key environmental filters structuring invertebrate communities, by linking increased niche differentiation through shoreline change, flood pulse dynamics, and macrophyte bed complexity with increased taxa and functional diversity.Examination of traits linked to ecosystem functions revealed that more resilient wetlands with balance between primary productivity and decomposition as carbon sources were associated with greater functional evenness and richness, while habitat patches with elevated decomposition rates had lower functional richness, reflecting a simplified, more disturbed habitat.While our more complex overarching SEM model was ultimately compromised by an overspecified number of pathways, our results nevertheless are indicative of a divergence between wetland and riverine ecosystems in their relationships linking biodiversity and ecosystem function, illustrating how to define ecosystem health in wetland habitats, and demonstrating how critical functions support healthy wetland habitats by providing increased resilience to disturbance.Read the freePlain Language Summaryfor this article on the Journal blog.

Environmental Drivers and Aquatic Ecosystem Assessment of Periphytic Algae at Inflow Rivers in Six Lakes over the Yangtze River Basin

Periphytic algae is frequently utilized as a health indicator for ecosystems. Many research studies have been conducted in China on the periphytic algae community, but none has compared the periphytic algae community structure at inflow rivers among different lakes in the Yangtze river basin. The periphytic algae were investigated at 94 sites in inflow rivers of Dianchi Lake, Danjiangkou Reservoir, Dongtinghu Lake, Poyanghu Lake, Chaohu Lake, and Taihu Lake. Based on microscopic research, eight phyla and 126 genera of periphytic algae were found in the inflow river of six lakes, with Cyanobacteria and Bacillariophyta dominating. The CCA (Canonical Correspondence Analysis) was used to analyze the association between the periphytic algae community and environmental factors in the inflow river of six lakes, and the LefSe (Linear discriminant analysis effect size) analysis was used to find enriched species in the inflow river of six lakes. We discovered that TN (total nitrogen) and TP (total phosphorus) were the driving environment variables at the basin scale based on the combined results of the CCA and the Mantel Test. The TITAN (Threshold Indicator Taxa Analysis) analysis also revealed the indicator species and their TN and TP concentration thresholds. Finally, we assessed the ecosystem health of the inflow river at six lakes; biotic and abiotic indices yielded conflicting results, but utilizing both indices to assess ecosystem health using the Random Forest algorithm will yield objective and comprehensive results.

Using eDNA to Identify the Dynamic Evolution of Multi-Trophic Communities Under the Eco-Hydrological Changes in River

As significant players in material cycling and energy flow, bacteria and eukaryotes play a vital role in the ecosystem. Nevertheless, the community dynamics of bacteria and eukaryotes in rivers and their responses to changes in ecological hydrology have not been studied thoroughly. Based on eDNA technology, this study investigated the bacterial and eukaryotic communities in the upper, middle and lower reaches of the Weihe River in different seasons. The seasonal variation and geographical distribution of bacterial and eukaryotic community structures showed significant heterogeneity. The selective theory well explained the response of microbial community assembly to seasonal changes. Deterministic processes dominate microbial community assembly in the middle and lower reaches. The composition and metabolic potential of key functional genes of nitrogen and phosphorus cycling (nosZ, pqqB, pqqD, and pqqE) exhibited strong seasonal patterns and were significantly correlated with the physical and chemical properties of water. There were significant differences in molecular ecological networks in different periods (p &amp;lt; 0.05), with a gradually increasing trend in the complexity of the network from winter to summer. The keystone species (Hub) of the microbial food web in each season included microorganisms (Malikia), algae (Stephanodiscus), and invertebrates (Polyarthra). Structural equation modeling (SEM) results indicated that invertebrate was an important driving factor affecting the changes in community structures. In micro-food webs, both “bottom-up” (resources) and “top-down” (predation) forces strictly controlled the relationship between taxa. Nitrogen and phosphorus concentrations affected microbial networks, and there was a significant correlation between bacterial and eukaryotic groups and eco-hydrological variables (p &amp;lt; 0.05). Furthermore, we identified the taxon’s change point using threshold indicator taxa analysis (TITAN), quantitatively revealing the response thresholds of taxa to eco-hydrological changes.