Enrichment Index Research Articles

Geochemical and ecotoxicological evaluation of sediments of a semiarid estuary on the northeast of Brazil (Natal / RN)

The Jundiaí-Potengi Estuary (JPE), northeast of Brazil, suffers from intense degradation due to anthropogenic pollution from different sources, including several punctual treated and untreated domestic sewage discharges. To evaluate the estuary surface sediment quality near the outlet of a wastewater treatment plant (WWTP), five sampling points were selected. Four campaigns were performed on dry and rainy seasons of the years 2015 and 2016. The sediment samples were submitted to chronic ecotoxicological tests with Nitocra sp., and to metals, granulometry, and total organic matter analysis. The geochemical data were analyzed through enrichment indexes and, multivariate analysis, was performed integrating the ecotoxicological data. The sediment did not display toxicity to Nitocra sp. however, some metals’ concentration (Mn, Pb, Cu, Ni, and Cd) exceeded the limits established by Brazilian legislation. In general, the concentration of the analyzed metals doubled from rainy season to dry season. Considering our findings, we suggest quantifying other classes of contaminants and conducting studies on the bioavailability of metals in JPE, as well as using other organisms of different trophic levels in ecotoxicity tests.

The transformation and enrichment of Cd in fine particulate matter during coal combustion: The key roles of Ti-bearing components

Fine particulate matter (PM) emitted from coal-fired power plants (CFPPs) has aroused widespread environmental and human health concerns. Cadmium (Cd), as one of the prime toxic air pollutants, which exists in fine PM intensifies its toxicity. In this research, three particle sizes of PM (PM1, PM2.5, and PM10) at the outlet of electrostatic precipitator (ESP), along with feed coal, bottom ash, and ESP ash, were collected from a 300-MW pulverized CFPP. Results showed that Cd was more enriched in the fly ash than in bottom ash. With the PM diameter decreasing, the relative enrichment index (REI) value of Cd increases from 2.30 to 7.84. The concentration of Cd was found to be intimately related to Ti in the PM. Abundant Ti-rich particles were identified in the PM1, having quite different chemical compositions as compared to particles larger than 2.5 μm. The major processes governing the formation of Ti-rich particles included melting of silicate-bound Ti and heterogeneous condensation of gaseous Ti from the decomposition of organic-associated Ti in coal. The transformation behavior of Cd to PM in a coal combustion process was discussed based on its occurrence mode in coal, thermodynamic property, and the possible interactions with ash particle compositions. The retention of Cd (g) by Ti-rich particle were probably dominated by chemisorption at high temperature; at lower temperature, physical adsorption or condensation may be the primary mechanisms for capturing CdCl2 (g).

Long-term nitrogen addition and precipitation reduction decrease soil nematode community diversity in a temperate forest

Terrestrial ecosystems are driven by different global change factors, such as atmospheric nitrogen deposition and precipitation reduction. Nitrogen deposition and precipitation reduction have a great impact on the above- and underground processes. Most previous studies mainly focused on the effects of nitrogen deposition and/or precipitation reduction on aboveground processes, while the effects on underground processes were relatively scarce. As an important part of the underground soil food web, soil nematode community occupies different nutritional niches and is sensitive to external disturbances, and it is often used as indicator for studying underground processes. However, we know little about the response of soil nematode community to nitrogen deposition and/or precipitation reduction. Here, we used a 10-year of factorial manipulation by applying nitrogen solution and reducing the amount of precipitation to the soil, and to investigate the responses of soil nematode community to nitrogen deposition and/or precipitation reduction in a temperate forest. We expected that nitrogen addition could promote while precipitation inhibited the activity of soil nematode community. Furthermore, we expected nitrogen addition and precipitation could have interactive effect on soil nematode community. Our results found that nitrogen addition and/or precipitation reduction treatment caused significant changes in the composition of soil nematode community. Nitrogen addition and nitrogen addition combined with precipitation reduction induced negative effects and significantly decreased the abundance and diversity of soil nematode community, while precipitation reduction only decreased the abundance of soil nematode community. Nitrogen addition and precipitation reduction had synergistic effect on soil nematode community with higher trophic levels. Compared with precipitation reduction treatment, the negative effect of nitrogen addition on soil nematode community was more severe. According to the structural equation model (SEM), we found that nitrogen addition and precipitation reduction could affect the abundance of soil nematode community by affecting the plant richness and soil pH. Since the decrease of enrichment index (EI) and the increase of structure index (SI), our research results revealed that nitrogen addition could lead to soil food web in a lower nutrients available condition.

Zinc Enrichment in two Contrasting Genotypes of Triticum aestivum L. Grains: Interactions between Edaphic Conditions and Foliar Fertilizers.

This study aimed to assess the implications of Zn enrichment in wheat grains as a function of contrasting genotypes, edaphic conditions and foliar fertilizers. Triticum aestivum L. varieties Roxo and Paiva were grown in four production fields, and sprayed with ZnSO4 (0, 16.20 and 36.40 kg/ha) Zn-EDTA (0, 6.30 and 12.60 kg/ha) and Tecnifol Zinc (0, 3.90 and 7.80 kg/ha). The heterogeneous edaphic conditions of the wheat fields were chemically characterized, it being found that soil properties determine different Zn accumulation in the grains of both genotypes. Foliar spraying enhanced to different extents Zn content in the grains of both genotypes, but the average of enrichment indexes varied among the wheat fields. Zinc mostly accumulated in the embryo and vascular bundle and to a lesser extent in the endosperm. Grain yield and test weight sprayed by ZnSO4 gave the highest values in both genotypes, but the opposite was found for Zn-EDTA. Considering the color parameters, lightness and red–green transitions were found to be a conjunction of genotype characteristics, fertilization types and edaphic conditions prevailing in each field. It is concluded that the index of Zn enrichment in wheat grains is a docket of edaphic conditions, genotype and type of fertilization.

Microplastics as hubs enriching antibiotic-resistant bacteria and pathogens in municipal activated sludge

Microplastics can serve as carriers of antibiotic-resistant bacteria (ARB) and pathogens, representing a pressing concern to aquatic biota and human health. Activated sludge units at municipal wastewater treatment plants (WWTPs) are “hotspots” converging microplastics and antibiotics. In this batch study with activated sludge samples from three domestic WWTPs, we demonstrated both polyethylene (PE) and polystyrene (PS) microplastics can acclimate biofilms enriched with sulfonamide resistance genes (sul1 and sul2) and the associated mobile genetic element (intI1) in comparison with fine sands as control particles. Absolute abundances of these genes were further elevated by 1.2∼4.5 fold when sulfamethoxazole was initially spiked as a representative sulfonamide. The combination of 16S rRNA amplicon sequencing and differential ranking analysis revealed that microplastics selectively promoted antibiotic-resistant and pathogenic taxa (e.g., Raoultella ornithinolytica and Stenotrophomonas maltophilia) with enrichment indices ranging from 1.6 to 3.3. Furthermore, heterotrophic Novosphingobium and filamentous Flectobacillus accounted for 14.6 % and 3.3 % on average in microplastic biofilms, respectively, which were up to 2.8 and 11.1 times higher than those in sand biofilms. Dominance of these bacterial species may contribute to initial biofilm formation that facilitates subsequent colonization and proliferation of ARB and pathogens, thus amplifying their risks in the receiving environments and beyond.

Induced changes of pyrolysis temperature on the physicochemical traits of sewage sludge and on the potential ecological risks

Biochar from sewage sludge is a low-cost sorbent that may be used for several environmental functions. This study evaluates the induced effects of pyrolysis temperature on the physicochemical characteristics of sewage sludge (SS) biochar produced at 350 (SSB350), 450 (SSB450) and 600 (SSB600), based on the metal enrichment index, metal mobility index (MMI), and potential ecological risk index (PERI) of Cd, Cu, Pb, and Zn. Increased pyrolysis temperature reduced the biochar concentration of elements that are lost as volatile compounds (C, N, H, O, and S), while the concentration of stable aromatic carbon, ash, alkalinity, some macro (Ca, Mg, P2O5, and K2O) and micronutrients (Cu and Zn), and toxic elements such as Pb and Cd increased. Increasing the pyrolysis temperature is also important in the transformation of metals from toxic and available forms into more stable potentially available and non-available forms. Based on the individual potential ecological risk index, Cd in the SS and SSB450 were in the moderate and considerable contamination ranges, respectively. For all pyrolysis temperature biochar Cd was the highest metal contributor to the PERI. Despite this, the potential ecological risk index of the SS and SSBs was graded as low.

Short-Time Impact of Soil Amendments with Medicago Plant Materials on Soil Nematofauna.

Soil amendments with plant materials from Medicago species are widely acknowledged for a suppressive effect on plant-parasitic nematodes but their impact on beneficial components of soil nematofauna is still unknown. A study on potted tomato was carried out to investigate the short-time effects on the overall nematofauna of dry biomasses from six different Medicago species, i.e., M. sativa, M. heyniana, M. hybrida, M. lupulina, M. murex and M. truncatula, incorporated to natural soil at 10, 20, or 40 g kg−1 soil rates. All amendments resulted in a significant decrease of the total nematofauna biomass, whereas total abundance was significantly reduced only by M. heyniana, M. hybrida, and M. lupulina biomasses. Almost all the Medicago amendments significantly reduced the relative abundance of plant-parasites and root fungal feeders. All amendments significantly increased the abundance of bacterivores, whereas fungivores significantly increased only in soil amended with M. heyniana, M. lupulina and M. sativa plant materials. Mesorhabditis and Rhabditis were the most abundant genera of bacterivores, whereas Aphelenchoides and Aphelenchus prevailed among the fungivores. Predators were poorly influenced by all the tested Medicago biomasses, whereas the abundance of omnivores was negatively affected by M. heyniana and M. lupulina. Values of the Maturity Index and Sum Maturity Index were reduced by treatments with M. heyniana, M. hybrida, M. lupulina and M. sativa plant materials, whereas most of the tested amendments decreased values of the Channel Index while increasing those of the Enrichment Index. Enrichment and bacterivore footprints raised following soil addition with Medicago biomasses, whereas composite and fungivore footprints were significantly reduced. According to their overall positive effects on soil nematofauna, amendments with Medicago plant materials or their formulated derivatives could represent an additional tool for a sustainable management of plant-parasitic nematodes.

Identification of Candidate Biomarkers for EGFR-T790M Drug-resistant Gene Mutation in Advanced Lung Adenocarcinoma

背景与目的奥希替尼（Osimertinib）是美国食品和药物管理局（Food and Drug Administration, FDA）批准用于携带表皮生长因子受体（epidermal growth factor receptor, EGFR）-T790M突变的晚期非小细胞肺癌（non-small cell lung cancer, NSCLC）患者的药物，用药前需行EGFR-T790M检测。不少患者因进展病灶隐匿或体弱无法进行组织活检错过Osimertinib治疗，本研究希望能从血清中筛查出预测EGFR-T790M耐药突变相关蛋白，为临床用药提供帮助。本研究旨在探索EGFR-T790M耐药基因相关蛋白，为临床用药提供帮助。方法本研究纳入口服易瑞沙晚期肺腺癌患者36例，在疾病进展后行组织活检，使用ARMS方法检测出EGFR-T790M突变组患者18例，非EGFR-T790M突变组18例。收集耐药患者血清，采用同位素标记相对和绝对定量标记结合二维液相色谱串联质谱蛋白组学技术筛选与EGFR-T790M耐药相关蛋白。结果筛出17种差异性蛋白，与EGFR-T790M基因突变相关上调蛋白6种，下调蛋白11种，主要参与31种生物过程，7种细胞组分，26种分子功能；反应途径中共鉴定出12种富集途径，其中富集指数最高的是凝血级联途径。结论发现与EGFR-T790M耐药相关蛋白共17种，参与凝血级联途径蛋白有望成为预测EGFR-T790M耐药突变相关的生物标志物。

Vertical Distribution of Soil Free-living Nematode in a Playa Habitat in the North-Western Negev Desert, Israel.

SummaryIn order to investigate the vertical distribution of soil nematode community under a playa area in the Nizzana inter-sand dune area in the north-western Negev Desert of Israel, soil samples were collected from 0 – 10, 10 – 20, 20 – 30, 30 – 40, and 40 – 50 cm depths in the playa and loessial plain area (as control) during the dry and wet seasons. Each of soil samples was determined for soil moisture, organic matter concentration, electrical conductivity, and nematode community structure and biodiversity. The results revealed that soil moisture, organic matter, electrical conductivity, total nematode abundance and trophic groups were significantly influenced by sampling positions (P < 0.0001) and depths (P < 0.05) and significant interaction effect of position and depth (P < 0.05) was also found. Total number of nematodes in the playa area ranged from 1 to 15 individuals per 100 g dry soil, whereas they ranged from 60 to 631 individuals per 100 g dry soil in the loessial plain area. The greatest nematode number was found in 0 – 10 cm soil depth and the lowest nematode number was found in 40 – 50 cm soil depth. Total number of nematodes, bacterivores, fungivores, plant parasites and omnivores-predators were significantly (P < 0.05) greater in the loessial plain area than that in the playa area in all sampling depths under the dry and wet seasons. Total thirteen genera were found in the playa area, with Acrobeloides as the dominant genus, whereas there were fifty-five genera, with Acrobeles as the dominant genus in the loessial plain area. Nematode ecological indices, such as fungivores/bacterivores ratio (F/B), nematode channel ratio (NCR), trophic diversity (T), Shannon Index (H’), genus dominance (λ), species richness (SR), maturity index (MI), modified maturity index (MMI), Enrichment Index (EI) and Structure Index (SI) were significantly (P < 0.01) differentiated between sampling locations. As conclusion, soil free-living nematode inhabited mostly the upper soil layers (0 – 20 cm) and the number of nematode had gradually decreasing trend with soil depths increasing in the playa area. Moreover, each soil layer had a little nematode abundance and community diversity in the playa area in contrast to loessial plain area during the dry and wet seasons. Sampling sites and depths significantly effected on soil properties, nematode abundance and trophic groups, but nematode ecological indices were affected only by sampling sites.

Status, source, human health risk assessment of potential toxic elements (PTEs), and Pb isotope characteristics in urban surface soil, case study: Arak city, Iran.

The current study was conducted to assess the level of potentially toxic elements (PTEs) contamination (Cu, Pb, Zn, Cr, As, Cd, and Ni) in surface soils from Arak city. Arak, which is an industrial city, is a prominent center of chemicals, metal/electric, manufacturing factories, and other industries. Forty-three surface soil samples were collected from 0-20cm after removing the visible surface contamination in the dry season in June 2017. Metal concentrations were found highly variable, ranging from 174-3950mg/kg for Cu, 181-3740mg/kg for Pb, 48-186mg/kg for Zn, 105-1721mg/kg for Ni, 0.8-0.9mg/kg for As, 114-1624mg/kg for Cr, and 3.45-12.36mg/kg for Cd. The results of geochemical fraction indicated that the main components of Pb, Cr, and Zn at most of the sampling sites are Fe-Mn bound/reducible. Meanwhile, the residual fraction is the dominant fraction of sequence extraction for Ni, Cu, and Cd. Higher values of reducible bound for Pb, Cr, and Zn, as well as a considerable percentage of Ni, Cu, and Cd, imply that the main source of the studied PTEs (except As) in the study area is both anthropogenic and geogenic inputs. The results of principal component analysis (PCA), correlation analysis, enrichment factor (EF), enrichment index (EI), and top enrichment factor (TEF) confirm that Pb, Ni, Cu, Cr, Cd, and Zn had a similar anthropogenic source which is confirmed by geochemical fractionation analysis. Carcinogenic risks (CR) of studied PTEs were estimated to be higher than the target limit of 1.0E-06, for adults and children except for Cr with values of 5.91E-04, and 3.81E-04 for children and adults, respectively. Higher CR values of Cr compared to other PTEs in Arak surface soil demonstrate that living target populations, including children and adults, particularly children, are more at risk of carcinogenic risks of PTEs. 206Pb/207Pb ratios of the collected samples indicated that Pb in Arak surface sample was derived from industrial inputs and deposition, as well as re-suspension vehicle exhaust emission from previously leaded gasoline. The findings concerning the applied end-member contribution of geogenic and industrial and vehicle emission represented that the contribution could vary from 68.0% to 15% (mean: 39.3) for industrial emission, 65% to 19% for vehicle exhaust (mean: 39), and 46% to 10% (mean: 21.6) for geogenic sources.

New index of organic mass enrichment in sea spray aerosols linked with senescent status in marine phytoplankton

Linking the amount of organic matter (OM) in sea spray aerosols (SSAs) to biological processes in ocean surface is essential for understanding marine aerosol formation and their potential to affect cloud formation. To date, chlorophyll (Chl) a concentration has been widely used as a surrogate for surface phytoplankton biomass or productivity to predict the relative abundance of OM in SSAs (OMSSA). Here we show a new index to present OMSSA using concentrations of Chl a and chlorophyllide (Chllide) a, which is a breakdown product of Chl a and has been used as a biomarker of senescent algal cells. The index was compared with submicrometer OMSSA, based on surface seawater and aerosol samples obtained during the pre-bloom in the western subarctic Pacific. Our results showed that the OMSSA was highly correlated with this unique index, suggesting that the OMSSA was closely linked with senescent algal cells and/or cell lysis. Furthermore, the hygroscopicity parameters κ derived from water-extracted SSA samples implied a reduction in the SSA hygroscopicity with increasing senescent status of phytoplankton. The index can represent OMSSA on a timescale of a day during the pre-bloom period, which should be further examined over different oceanic regions.

Impacts of litter addition and root presence on soil nematode community structure in a young Eucalyptus plantation in southern China

Eucalyptus plantations are widely established in degraded ecosystem as a fast-growing species for restoration. However, the impact of Eucalyptus aboveground litter and living root on soil nematode community structure is poorly understood. We conducted a field manipulative experiment to investigate the impact of litter addition and root presence on soil nematode community composition in a young Eucalyptus plantation in southern China. Our results showed that both litter addition and root presence significantly increased soil nematode abundance. Litter addition altered nematode community composition by decreasing relative fungivore abundance, and increasing relative omnivore-predator abundance and the nematode channel ratio. However, no obvious effect of root presence on nematode community was detected. There were interactions between litter addition and root presence on nematode ecological indices. Litter addition increased maturity index and structure index, and reduced enrichment index in the absence of root, but did not change these indices under root presence. Our findings highlight the critical role of aboveground litter resources in shaping nematode community structure and function. Meanwhile, the influence of litter resources on soil nematode community structure and function are regulated by root input. The study provides theoretical support for plantation management in southern China.

Effects of straw mulching practices on soil nematode communities under walnut plantation

Agricultural management techniques such as mulching with crop straw can impact soil properties and may in turn change the structure and function of the soil food web. We investigated different straw mulching types and straw mulching coverage levels on soil nematodes community structure in walnut orchards. We set up a randomized experimental design with three straw mulch types, and three straw mulch distance treatments in a walnut plantation. The results indicated that the number of soil nematodes after straw mulching was lower than that found in the control (CK). However, the metabolic and structure footprints of the omnivore-predator nematodes showed higher values as compared to CK. The abundances of plant parasite and omnivore-predator nematodes were negatively correlated with ammonium nitrogen (NH4+–N) and dissolved organic nitrogen (DON), whereas soil moisture content (SM) had a negative correlation with the abundance of total nematodes. High structure index (SI), maturity index (MI) and low enrichment index (EI) values revealed a structured soil food web, medium soil enrichment, and fungal decomposition channel under the mix straw mulching treatments. Soil nematodes should be used as an indicator of soil functional changes resulting from straw mulching.

Pollution assessment and land use land cover influence on trace metal distribution in sediments from five aquatic systems in southern USA

Trace elements and heavy metals concentrate in aquatic sediments, potentially endangering benthic organisms. Comparing the concentration of metals in different aquatic bodies will help evaluate their accumulation and distribution characteristics within these systems. Metal pollution and enrichment indices in sediments from diverse aquatic systems in Southern USA, including agricultural ponds, man-made reservoir, river, swamp, and coastal environment were investigated. Following total digestion of the sediments, the concentrations of chromium (Cr), cobalt (Co), copper (Cu), zinc (Zn), arsenic (As), selenium (Se), cadmium (Cd), antimony (Sb), lead (Pb), and uranium (U) were measured using inductively coupled plasma-mass spectrometry (ICP-MS). Pb was found to be highly enriched in the sediment samples from all five environments. The samples from coastal and agricultural ponds showed highest degree of anthropogenic modification (enrichment factor >10), especially with Se, U, and Pb. Agricultural ponds, previously unknown as a metal hotspot, had the most deteriorated sediment quality as determined by high pollution load index (>1) and contamination factor (>6) for Cd and U. Principal component analysis comparing land use land cover distribution surrounding the aquatic systems to metal concentrations confirmed that agriculture-related land activities correlated well with majority of the metals. Overall, compared to agricultural ponds and coastal regions, sediments in river, swamp and man-made reservoir systems contained relatively fewer metal pollutants, the former two serving as collection points for metal-laden fertilizers and chemicals. The research provides key insights into simultaneously comparing metal accumulation in multiple water bodies and is useful to test and develop effective sediment quality guidelines.

The Industrial Pollution History Inferred by Stable Pb Isotope in the Chronological Sedimentary Record of a Plateau Lake, Yunnan Province, Southwestern of China

Zhang, Y.; Chang, F.Q.; Duan, L.Z.; Wu, H., Zhang, H.C., 2020. The industrial pollution history inferred by stable Pb isotope in the chronological sedimentary record of a plateau lake, Yunnan Province, Southwestern of China. In: Bai, X. and Zhou, H. (eds.), Advances in Water Resources, Environmental Protection, and Sustainable Development. Journal of Coastal Research, Special Issue No. 115, pp. 641-647. Coconut Creek (Florida), ISSN 0749-0208.Lake Yangzong, a plateau deep water lake, located in the in Yunnan Province where was the one of the most industrialized regions in China, was suffered seriously mining pollution threat in recent decades. In the present research, based on the 210Pb and 137Cs methods, the chronological sequence of the sediment record collected from the lake basin was established. Combined with the stable isotopic compositions, Pb content and geochemical enrichment index (Igeo), the background of industrial activities and anthropogenic lead (Pb) pollution history were investigated. These results revealed that pollution history could divided into four stages. The contribution of Pb was primarily affected by regional emissions since the open reforming period, and local metal production industries was more involved in the late 1990s. Furthermore, the regional pollution pathways of anthropogenic Pb were mainly affected by atmospheric precipitation and transportation, which were predominately related to mining consumption and smelting industry.

Crop tree release increased the density of soil nematodes and improved the food web structure

As a special thinning method, crop tree release (CTR) has a beneficial effect on forest environments and structures by changing forest light, heat, and water. However, the impact of CTR on underground biodiversity remains unclear. Therefore, we analyzed the composition, diversity, and metabolic footprints of soil nematode communities under three CTR (100, 150, and 200 trees·ha–1) treatments, as well as a no CTR treatment, in Pinus massoniana Lamb. plantations. The results showed that CTR increased the density of soil nematodes (P &lt; 0.05), the number of omnivore–predator nematodes (P &lt; 0.05), and the diversity (H′) of nematodes (P &lt; 0.05) and enriched the food web structure of soil nematodes. In the medium CTR density treatment (150 trees·ha–1), the nematode density and diversity (H′) were the highest (P &lt; 0.05), the number of omnivore–predator nematodes was also the highest (P &lt; 0.05), and the enrichment index and structure index values of the soil nematodes reached the maximum at the depth of 0–10 cm (P &lt; 0.05). Our results indicated that the community structure of soil nematodes became more stable and mature after CTR, which may be attributed to the changes of soil condition, especially soil organic matter, and plant diversity indirectly.

Efficiency of Pinus nigra J.F. Arnold in removing pollutants from urban environment (Plovdiv, Bulgaria).

The aim of this study was to assess the efficiency of urban vegetation in removing pollutants from the environment using Pinus nigra J.F. Arnold as a model tree. For this purpose, the concentrations of some heavy metal and potentially toxic elements (Al, As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, U, and Zn) in needles, branches, and roots of P. nigra, as well as in the surrounding soil, have been analyzed and the removal capacity has been estimated on the basis of element translocation. The relationship between ecosystem services provisioning and plant well-being was also analyzed through physiological (photosynthetic pigment content and ratio) and anatomical (leaf injuries appearance) indicators. Enrichment factor, translocation factor, bioaccumulation factor, and index of translocation were calculated in order to assess the urban impact and removal efficiency of sampled trees, as well as the general transport of trace elements between the studied plant's organs as results of wet and dry atmospheric deposition. Anthropogenic pollution with As, Cd, and Pb was proven in whole urban environment, so these high values of translocation through pine trees have given an added value to the regulating ecosystem services of urban vegetation. Searching and planting of trees with higher removal efficiency could be crucial for improving quality of urban environment.

A Case Study of Nematode Communities’ Dynamics along Successional Paths in the Reclaimed Landfill

We assessed the abundance and composition of nematode communities in soil under herbaceous vegetation in reclaimed landfill sites at different ages after closure (3, 10 and 14 years) compared to those in neighboring semi-natural grazed grasslands (reference sites). We further applied network analysis based on the co-occurrence patterns of nematodes. Nematode abundance decreased between 3 and10 years of regeneration, but significantly increased from 10 to 14 years of regeneration. The number and identity of genera were comparable along the succession; however, there were dissimilarities in community composition during early- and mid-succession. The diversity, community composition and abundance at the sites after 14 years of regeneration converged with those at the reference sites. Moreover, changes during succession were not accompanied by the maturation of the soil food web, as demonstrated by Enrichment and Channel indices. In all the networks, centrality and modularity metrics differed significantly from those for random networks, whereas cohesion metrics showed no difference. All the networks exhibited Small-worldness indices higher than one, demonstrating that the networks of the interactions among genera at all the sites shared features that matched both random and non-random networks. The succession trajectory in reclaimed landfills was represented by a sequence of changes that differed in relation to the variable under consideration; network parameters tended to converge with those of a relatively resistant reference community, while the Enrichment and Channel indices did not. Additionally, the succession trajectory was not linear or steady; only the Channel index and Worldness index showed linear responses to succession time. However, across all the successional stages, the resource status remained basal or degraded while the nematode communities had an enhanced ability to cope with sudden changes.

Satellite observations of phytoplankton enrichments around seamounts in the South West Indian Ocean with a special focus on the Walters Shoal

Spatial anomalies associated with seamounts and islands have been detected in the South West Indian Ocean using a new surface chlorophyll-a based enrichment index (EI). Calculated from daily L3 4-km MODIS chl-a data from 2003 to 2018, the EI was used to quantify recurrent (seasonal) surface enrichment associated with these features. Most notable were the shallow Walters Shoal (18 m) and nearby deeper WS-2 seamount (480 m), both located on the southern Madagascar Ridge, which showed high EI values of 40% and 15% local enhancement. Tromelin Island, east of Madagascar, exhibited more moderate values of 15% local increase. Other shallower seamounts including La Pérouse (60 m) and MAD-Ridge (240 m) exhibited sporadic or no measurable surface maxima. Regions of strong mesoscale activity such as south of Madagascar where the South East Madagascar Current detaches from the continent also revealed high EI values. A marked seasonality of the EI was observed over the Walters Shoal, with higher values during the oligotrophic season than in the austral winter. The seasonal variability of the MLD in combination with the seamount bathymetry appears to induce the thermal and biological anomalies observed there, possibly favoured by the presence of a Taylor cap at the summit. Ship-collected in situ measurements showed the satellite observed enrichment to be associated with shallowing of the deep chlorophyll maximum, as well as a shift of phytoplankton groups towards diatoms and small flagellates. No net increase of integrated chl-a was measured but a potential doubling in primary productivity is expected. The EI developed in this study, designed to reveal sporadic, small localised chl-a maxima, is likely applicable to other areas in the ocean where there is local enrichments.

Short-term Effects of Cadmium and Mercury on Soil Nematode Communities in a Pot Experiment.

SummaryAnalysis of soil nematode feeding groups and functional guilds were used as a valuable tool to detect heavy metal pollution. Effects of cadmium (Cd) at 5 mg/kg, mercury (Hg) at 20mg/kg, combined Cd and Hg at 5+20mg/kg on the nematode communities were studied after three months application. Nematodes were collected from soil in rhizosphere of Morning glories (Pharhiris nil) which were applied as heavy metal accumulators and were grown in the experimental pots. Both single and combined heavy metals had marked effects on the nematode abundance, life-history strategies and feeding type composition. Bacteriovores and c-p 2 group were found to be the most abundant trophic group and functional guild, respectively. Acrobeloides and Pratylenchus were the most two abundant genera, decreasing number of them was responsible for the significant difference between control and polluted treatments. Cd-5 and Cd-Hg 5+20 presented lower values of nematode diversity index (H’) and evenness index (J’) than Hg-20. The combination of Cd and Hg showed lower nematode trophic diversity (TD), in comparison with single Cd or Hg. Conversely, heavy metals addition exhibited no pronounced effect on Maturity index (MI), structural index (SI) and enrichment index (EI). Our results demonstrate that genera composition is a better indicator to short-term heavy metal effects than some common indicator indices and emphasize that deeper assemblage analyses are needed for a correct interpretation of short-term disturbance on soil nematodes.