Bioturbation effects on bioaccumulation of cadmium in the wetland plant Typha latifolia: A nature-based experiment

Spatiotemporal profile and ecological impacts of major and trace elements in surface sediments of marginal seas of the Arctic and Northern Pacific Oceans

The status and ecological impacts of sedimentary elements of the marginal seas of Arctic and Northern Pacific Oceans was investigated during 2016 to 2018 by using inductively coupled plasma mass spectrometry. Industrial (0.006 mg kg-1-64.6 g kg-1), precious (0.003-43.8 mg kg-1), rare earth (0.006-112.9 mg kg-1), and heavy metal (0.009-398.9 mg kg-1) elements showed spatial variation, and temporal uniformity. The results indicated ΣREEs and light REEs enrichment compared to chondrite and heavy REEs, respectively, while nonsignificant positive and negative δCe and δEu anomalies existed, respectively. High contamination and extreme enrichment of priority control, industrial (As, Mo, Re, Sb), precious (Au, Ir, Pd, Pt, and Ru) and RE elements indicated potential moderate to high ecological and biological risks. The study highlighted the ecological importance and fragile nature of these ecosystems and calls for an urgent action to ensure sustainability of these ecosystems.

Cadmium stress interacts with nutrient availability and light condition to affect the growth of Hydrocotyle vulgaris

Heavy metal pollution is becoming a serious problem in wetland and often co-occurs with nutrient availability and light conditions variation. We hypothesized that nutrient availability and light condition can affect the growth of wetland plants under heavy metal stress. To test this hypothesis, single ramets of a common, clonal wetland plant Hydrocotyle vulgaris were grown for four weeks at three levels of cadmium with three levels of nutrient availability under 30% or 100% light conditions. High level of nutrient availability and high light condition overall promoted growth of H. vulgaris under Cd stress. Under the two light conditions, responses of H. vulgaris to Cd treatments differed among three nutrient levels. Under 30% light condition, 2 mg L-1 Cd2+ treatment decreased total mass at the low nutrient level and decreased ramet number at the medium nutrient level; 0.5 and 2 mg L-1 Cd2+ treatments decreased leaf mass ratio at the low and the medium nutrient levels. Under 100% light condition, 2 mg L-1 Cd2+ treatments significantly decreased total mass at the high level of nutrients; 2 mg L-1 Cd2+ treatment decreased ramet number at the medium and the high nutrient levels and decreased leaf mass ratio at the medium nutrient levels. Our results suggested that Cd stress can interact with nutrient availability and light condition to affect the performance of wetland plants such as H. vulgaris.

Effects of fiddler crab bioturbation on the geochemical migration and bioavailability of heavy metals in coastal wetlands

Fiddler crabs, found in coastal wetlands worldwide, function as ecosystem engineers. Their burrowing activity can significantly alter biogeochemistry at the local scale, however, the mobility of heavy metals (HMs) in burrow sediments remains unclear. Here, we used diffusive gradients in thin-film probes to obtain bioavailable Fe and HMs (Cu, Zn, Ni, Cd, Pb, Co, and Mo) in crab burrows from coastal wetlands (mudflats, salt marshes, and mangroves). The depth-profile results showed that most HMs were enriched at shallow and deep depths but deficient at middle depths. We highlighted that bioturbation improved oxic conditions, enhanced HM concentrations, and favored dissolved HM retention in burrow sediments, which served as a sink for overlying water HMs via burrow flushing but a potential source of particle HMs via enhanced resuspension. In deep anoxic layers, Fe(III) reduction drove the remobilization of HMs, except Cu and Mo, leading to the co-release of HMs with Fe. This Fe-HM coupling/decoupling was verified using enhanced two-dimensional high-resolution imaging, which revealed highly spatial heterogeneity of multiple HMs. Moreover, the hydrological conditions regulating bioturbation effects on HM behavior varied across different coastal wetlands. With coastal environmental changes, the key role of ubiquitous bioturbation in HM migration and bioavailability should be reconsidered.

Spatial distribution of soil iron across different plant communities along a hydrological gradient in the Yellow River Estuary wetland

Iron is an important element and its biogeochemical processes are vital to the matter and energy cycles of wetland ecosystems. Hydrology greatly controls characteristics of soil property and plant community in wetlands, which can regulate the behavior of iron and its oxides. However, it remains unclear how the spatial distribution of iron and its forms in estuarine wetlands responses to hydrological conditions. Five typical plant communities along a naturally hydrological gradient in the Yellow River Estuary wetland, including Phragmites australis in freshwater marsh (FPA), Phragmites australis in salt marsh (SPA), Tamarix chinensis in salt marsh (TC), Suaeda salsa in salt marsh (SS) and Spartina alterniflora in salt marsh (SA), as sites to collect soil samples. The total iron (FeT) and three iron oxides (complexed iron, Fep; amorphous iron, Feo; free iron, Fed) in samples were determined to clarify the spatial distribution of iron and explore its impact factors. The mean contents of FeT, Fep, Feo and Fed were 28079.4, 152.0, 617.2 and 8285.3 mg⋅kg–1 of soil at 0–40 cm depth in the different sites, respectively. The means were significantly different across communities along the hydrological gradient, with the higher values for SA on the upper intertidal zone and for SPA on the lower intertidal zone, respectively. Iron and its forms were positively correlated with the total organic carbon (TOC), dissolved organic carbon (DOC), total nitrogen (TN) and clay, and negatively correlated with electrical conductivity (EC). The indexes of iron oxides (Fep/Fed, Feo/Fed and Fed/FeT) were also different across communities, with a higher value for SA, which were positively correlated with soil water content (WC) and TOC. The results indicate that a variety of plant community and soil property derived from the difference of hydrology might result in a spatial heterogeneity of iron in estuarine wetlands.

Density Effect of Eisenia sp. Epigeic Earthworms on the Hydraulic Conductivity of Sand Filters for Wastewater Treatment

Inside sand filters, as inside other microporous substrates, several invertebrates create temporary burrows that impact on water movement through the filter. Lumbricids Eisenia fetida and Eisenia andrei live under a wide range of environmental conditions and have a high reproduction rate so they are good candidates for ecological engineering tests. We assessed the impact of these species at different densities (0, 100, 500, 1000 g m−2) on the hydraulic conductivity of small-sized experimental filters made of columns filled with filter sand classically used for sanitation mixed with 5% organic matter. The hydraulic conductivity was recorded every 7 days over 37 days in non-saturated conditions. On day 23, 40 g of peat bedding was added at the column surfaces to simulate a surface clogging organic matter pulse input. Columns with an earthworm density equal or superior to 500 g m−2 revealed the highest hydraulic conductivities during the first 21 days. At these densities, the hydraulic conductivity was also restored in less than 7 days after the addition of the surface organic matter, showing the influence of the earthworm species on the resilience capacity of the hydraulic conductivity. It was also highlighted that the hydraulic flow was dependent on the lumbricid densities with an optimal density/effect around 500 g m−2 in this specific substrate composition. This study showed that the feeding habits and burrowing activity of both Eisenia species significantly enhanced the hydraulic flow in a sandy substrate, providing a sustainable solution to limit the clogging of the substrate similar to the one used in filters to treat wastewater.

Efficacy of Lemna minor and Typha latifolia for the treatment of textile industry wastewater in a constructed wetland under citric acid amendment: A lab scale study

Lead (Pb), copper (Cu) and chromium (Cr) are one of the most harmful heavy metals (HMs), entering into the food chain through the irrigation of crops with an industrial effluent. The present study was performed to evaluate the toxic effects of textile effluents and performance of citric acid (CA) on phytoextraction potential of Lemna minor L. and Typha latifolia L. in an artificially designed wetland. Different doses of textile wastewater (0, 25, 50, 75, and 100%) and CA (10 mM) were applied alone and in combination. Plants were harvested and the data was collected regarding agronomic traits, photosynthetic pigments, antioxidant enzymes, reactive oxygen species (ROS), electrolytic leakage (EL) and HMs uptake and accumulation. The results depicted that the concentration and accumulation of Cu, Pb and Cr in different parts of T. latifolia plant was increased with and without CA addition. The maximum concentration of Pb, Cu and Cr increased in leaves by 279, 240 & 171%, in stem by 192, 172 & 154%, and in roots by 224, 183 & 168%, respectively. Similarly, the accumulation of Pb, Cu and Cr increased in leaves by 91, 71 & 36%, in stem by 57, 46 & 36% and in roots by 76, 53 & 45%, respectively in plants treated with 100% textile effluent as compared to the 25% textile effluent treated plants under CA amendment. In L. minor, the concentration of Pb, Cu & Cr increased by 542, 411 and 397% while accumulation increased by 101, 59 & 55% respectively in overall plant biomass.

Effects of tubificid bioturbation on bioaccumulation of Cu and Zn released from sediment by aquatic organisms

To investigate the effects of bioturbation on absorption and enrichment of pollutants from sediments by aquatic organisms, microcosm systems similar to natural aquatic environment were established, and the release of Cu and Zn from the sediment, and their accumulation in some typical aquatic organisms, including submerged plants, floating plants and fish, with the presence of tubificids of different densities were measured. The results of this pilot study showed that the presence of tubificids promoted the migration of the trace metals from sediment to overlying water, especially when there were more worms and especially for Cu which is not easily released from the sediment. During the experiment, Cu in overlying water was mainly in particulate fraction. While for Zn, it was mainly in dissolved form in the early stage of the experiment, and then the dominant fraction gradually changed to particulate fraction. The bioturbation of tubificids also promoted the accumulation of both Cu and Zn in the aquatic organisms. In one system, different types of aquatic organisms showed different features for the accumulation of Cu and Zn. Meanwhile, with the presence of different intensity of bioturbation, the concentration of Cu or Zn in the same kind of organism was different. After a 30-day experiment, trace metal concentration in the aquatic organisms generally decreased in the order of floating plants (lesser duckweed) > submerged plants (Amazon sword) > small fish (zebrafish), and the concentration of Zn in the organisms was usually significantly higher than that of Cu in the same organism, especially in duckweed and zebrafish. However, the presence of tubificids and the density of them had more considerable effects on the uptake of Cu by the organisms, than on the uptake of Zn.

Spatial distribution, source identification, and risk assessment of heavy metals in seawater and sediments from Meishan Bay, Zhejiang coast, China

The aim of this study is to determine the spatial distribution, potential sources, and ecological risks of 8 heavy metals (Zn, Cu, Cr, Ni, As, Cd, Hg, and Pb) in Meishan Bay, Zhejiang coast, China. Surface water (n = 31), bottom water (n = 31), and surface sediments (n = 31) were collected. Water physicochemical properties and sediment resuspension were important factors affecting spatial distributions of heavy metals. The spatial distributions of Cr, Ni, Pb, As, Cu, and Zn were consistent with the clay distribution. Atmospheric deposition was the main source of Cd and Pb, mainly from industrial and transportation exhausts, while Zn was mainly from ship transportation. Agriculture pesticides and sewage wastewater were considered as the main sources for Hg. The geo-accumulation index results indicated that there was limited pollution of Cu, Zn, Cr, Pb, and As, and mild to moderate pollution of Cd and Hg. The potential ecological risk assessment suggested a high ecological risk of Hg in Meishan Bay.

Elemental Contaminants in Surface Sediments from Jiulong River Estuary, China: Pollution Level and Ecotoxicological Risk Assessment

Estuaries, being the transitional zones between freshwater and marine environments, are important for protecting and rehabilitating the aquatic environments. Sediments from freshwater and marine environments were studied in Jiulong River Estuary (JRE) in different years for rare earth elements (REEs) and some environmentally important metal and metalloid elements (MMEs). The concentration of REEs ranged from 0.11 (Tm) to 296.20 mg kg−1 (Ce), while that of MMEs ranged from 0.40 (Cd) to 86,000 mg kg−1 (Al). The temporal analysis indicated an increase of both REEs and MMEs contaminants from 2012 to 2018. Fractionation of REEs and Ce and Eu anomalies indicated natural weathering, erosion processes and changes in redox chemistry at the sampling sites. Spatial structure analysis showed relatively higher levels of both REEs and MMEs in the freshwater sediments. These variations among the sampling sites indicated different land use and anthropogenic activities. The values of enrichment factor (EF) and geoaccumulation index (Igeo) indicated anthropogenic sources of accumulation, while, ecological risk assessment (Eix) and potential ecological risk index (PERI) indicated potential hazards for biota due to the accumulation of Pb, Zn and As elements.

Phytoremediation of polluted soils and waters by native Qatari plants: Future perspectives

Because pollution is predicted to worsen and sources of quality water for agriculture and other human activities are limited, many countries have been motivated to seek novel water sources. Qatar relies on groundwater and water desalinization to meet its water needs, and additional water resources will be needed to avoid unexpected crises in the future. Industrial wastewater (IWW) is an alternative water source, and much research activities should be focused on developing innovative and contemporary approaches to removing pollutants from IWW. Phytoremediation methods, shown to be efficient methods of removing and degrading contaminants of various kinds from polluted waters and soils, require knowledge of the native plants and associated microorganisms. In Qatar, many native plants (monocot and dicot, indigenous or introduced) have been shown to be greatly effective in remediating polluted areas. This article is a guide for Qatari scientists aiming to identify promising native plants and associated microbes for IWW phytoremediation. In it, we review the basic components of bioremediation and summarize the principle phytoremediation approaches and preferred recycling options. The multiple mechanisms and methods of phytoremediation for cleansing polluted soils and waters are also discussed as are details of the metabolic reactions degrading the organic components of oil and gas. Finally, heavy metal accumulation is addressed. Wastewater from industrial and domestic activities is currently being used to create green areas around Doha, Qatar, and such areas could be at risk of contamination. Many native Qatari plants and soil-dwelling microbes are efficient at removing organic and inorganic contaminants from polluted soils and waters, and some are promising candidates for achieving a clean environment free of contaminants.

The application of bioturbators for aquatic bioremediation: Review and meta-analysis

Human activities introduce significant contamination into aquatic systems that impact biodiversity and ecosystem function. Many contaminants accumulate, and remediation options are now required worldwide. One method for bioremediation involves the application of macrofauna to stimulate microbial ecosystem processes including contaminant removal. However, if we are to confidently apply such a technique, we need clarity on the effect of bioturbators on different contaminants and how these vary under different environmental scenarios. Here we used a systematic review and meta-analysis to analyse current knowledge on the activities of bioturbating macrofauna in contaminated sediments and quantify how bioturbation-bioremediation changes depend on the taxonomic group, the aquatic ecosystem and important environmental variables. Three common contaminant classes were reviewed and analysed: metals, nutrients (i.e. ammonia and phosphorous) and polycyclic aromatic hydrocarbons (PAH). In addition, meta-regressions were calculated to estimate the effect of environmental and experimental design variables on effect sizes. Meta-analytic results revealed that deeper burrowing and more active sediment surface animals (e.g. polychaetes) increased metal release from sediments, nutrients and oxygen uptake by microbial fractions in comparison to bioturbators that inhabit shallower depths in sediments. In addition, there was a different effect of bioturbators on response variables in different aquatic systems. Finally, bioturbator effects on nutrient and metal release appeared modulated by context-specific variables such as temperature, pH, sediment grain size, animal density and experimental duration. Our findings highlight critical knowledge gaps such as field applications, less studied macrobenthic fauna and the incorporation of molecular approaches. Our results provide the first quantitative synthesis of the effects of bioturbators on contaminant fate and the variables that need to be considered for the optimization of this method as a viable approach for sediment remediation and contaminant management in aquatic systems.

Heterologous expression of TuCAX1a and TuCAX1b enhances Ca2+ and Zn2+ translocation in Arabidopsis

TuCAX1a and TuCAX1b improved Ca²⁺ and Zn²⁺ translocation and TuCAX1b enhanced Ca²⁺, Zn²⁺, Mn²⁺ and Fe²⁺ content when exposed to Cd²⁺; Cd²⁺ translocation was inhibited under Ca²⁺ and Zn²⁺. Cation/H⁺ antiporters (CAXs) are involved in the translocation of Ca²⁺ and various metal ions in higher plants. In the present study, TuCAX1a and TuCAX1b, two cation/H⁺ antiporters, were isolated from the diploid wheat Triticum urartu, and their metal cation translocation functions investigated. TuCAX1a and TuCAX1b showed abundant tissue-specific expression in the internode and beard, respectively, and their expression levels were increased in shoots exposed to Cd²⁺, Zn²⁺ and Ca²⁺. Plant phenotype analysis showed that overexpression of TuCAX1a and TuCAX1b could improve the tolerance of Arabidopsis to exogenous Ca²⁺ and Zn²⁺. In the plant shoots and roots, the contents of Ca²⁺ and Zn²⁺ were higher than wild-type plants under Ca²⁺ and Zn²⁺ treatments, indicating that TuCAX1a and TuCAX1b can enhance Ca²⁺ and Zn²⁺ translocation. Ca²⁺, Zn²⁺, Mn²⁺ and Fe²⁺ contents showed higher accumulation in TuCAX1b-transgenic Arabidopsis shoots than in wild-type plants exposed to Cd²⁺, and the translocation of Cd²⁺ was inhibited under Ca²⁺ and Zn²⁺. Overall, the present study provides a novel genetic resource for improving the uptake of microelements and reducing accumulation of toxic heavy metals in wheat.

Spatial variation of heavy metals and uptake potential by Typha domingensis in a tropical reservoir in the midlands region, Zimbabwe

Pollution of aquatic ecosystems with heavy metals is now of global concern due to their dangers to human health and persistence in the environment. An investigation on the spatial distribution of heavy metals in water and sediments and the bioaccumulation potential of heavy metals by plant parts (i.e. roots, stems and leaves) of aquatic macrophyte Typha domingensis (Pers.) Steud in a tropical reservoir was carried out. The results showed no difference in spatial distribution of heavy metals (Fe, Cu, Cd, Cr, Pb, Zn, Mn) in water and sediments from the riverine to the dam wall. The concentration of heavy metals Fe, Cu, Cr and Zn in T. domingensis was of the order root > stem > leaves, but for Pb, Cd and Mn, it followed the order root > leaf > stem. The metal transfer between roots and shoots of T. domingensis followed the order Zn > Pb > Fe > Cu > Cd > Cr. The bio-concentration factor (BCF) was low (BCF < 1) for all the selected metals while the transfer factor (TF) varied among metals suggesting that T. domingensis is not an accumulator of the studied metals. The high concentration of heavy metals found in the water (0.7-16.14 mg L^-1) and sediments (43.6-569.18 mg kg^-1) present a potential risk to both ecological health and human health for the population living in the area. The results of metal concentration in water and sediments from this study are important as a baseline for future monitoring studies. Further studies on bioavailability of metals to other macrophytes and aquatic organisms are recommended.

Remobilization and bioavailability of polycyclic aromatic hydrocarbons from estuarine sediments under the effects of Nereis diversicolor bioturbation

The effects of Nereis diversicolor bioturbation on the remobilization and bioavailability of polycyclic aromatic hydrocarbons from estuarine sediment were determined after 60 d in a laboratory experiment. The release fluxes and mass transfer coefficients showed that bioturbation by N. diversicolor can lead to a significant remobilization of polycyclic aromatic hydrocarbons (PAHs) from estuarine sediments. Bioturbation enhanced the release of PAHs from sediment to water by accelerating the transport of sediment particles to the sediment-water interface followed by PAHs desorption to the water. The bioavailability of PAHs was described by SPMD-sediment accumulation factors (SSAF). The SSAF of low molecular weight PAHs with bioturbation was significantly higher than that of PAHs without bioturbation, and there were no significant variations in high-molecular-weight PAHs. Our results revealed that N. diversicolor bioturbation significantly increased PAHs release from sediment to water but only increased the bioavailability of low-molecular-weight PAHs.