Novel brominated flame retardants relevant for European aquatic environments: ranking of analytes to monitor and focus on the French Eastern Mediterranean coastline.

Around a hundred of novel brominated flame retardants are currently being used to replace those regulated in the 2000s. However, data about their production, usage, and toxicity is still scarce, as well as their levels of contamination in the Mediterranean Sea and the subsequent risk. Our goal was to select the relevant novel brominated flame retardants to monitor and to apply it along the northeastern Mediterranean Sea. We proposed a ranking for novel brominated flame retardants based on their production or import, occurrence, and ecotoxicology, yielding to a selection of 21 priority molecules. From this list, 16 compounds were analyzed in ten coastal suspended matter samples, together with six related chemicals. To assess their occurrence in comparison to better documented flame retardants, eight legacy polybromodiphenyl ethers, seven polychlorobiphenyls, and short- and medium-chain chlorinated paraffins were also targeted. Novel brominated flame retardants and polychlorobiphenyls were detected in all the samples. Polybromodiphenyl ethers and chlorinated paraffins were detected in nine and seven samples, respectively. Out of the 22 novel brominated flame retardants analyzed, nine were detected, with total concentrations ranging from 0.4 to 18.5 ng.g-1 d.w., which was often higher than that of polybromodiphenyl ethers. A high risk for 2,4,6­tribromophenol and PCB 118 was assessed in two and six samples, respectively. To our knowledge, this is the first priority ranking and screening of most of the novel brominated flame retardants selected in the French Mediterranean Sea.

Solar-powered single-stage distillation and complex conductivity analysis for sustainable domestic wastewater treatment.

This study investigates the efficacy of a solar-powered single-stage distillation system for treating domestic wastewater, supplemented with complex conductivity analysis. Domestic wastewater samples were collected from a municipal manhole in El Jadida, Morocco, over a 24-h period. The single-stage distillation system, designed for domestic wastewater treatment, utilizes heat to vaporize the wastewater, followed by condensation to produce pure liquid water. The system demonstrated increased distilled water production with rising temperatures, with domestic wastewater outperforming seawater as a feed water source. Physical and chemical testing of the treated water revealed significant improvements in water quality, meeting, or exceeding Moroccan irrigation water standards. Reductions in parameters such as biological oxygen demand (BOD), chemical oxygen demand (COD), suspended matter, and heavy metals underscored the effectiveness of the distillation process. Complex conductivity analysis provided insights into the electrical properties of untreated wastewater and distilled water. Deconvolution of complex conductivity data using an equivalent electrical circuit model elucidated the electrochemical processes during treatment, highlighting the efficiency of the distillation process. The integration of solar energy addresses water scarcity while promoting environmental sustainability. Complex conductivity analysis enhances process understanding, offering avenues for monitoring and control in wastewater treatment.

Changes in coastal ecosystems affected by overburden dumping from amber open-cut mining on the Sambia Peninsula (Baltic Sea).

The Sambia Peninsula (Kaliningrad region) is historically well known for its amber mining. The 2019 year was the last year of direct overburden disposal into the Baltic Sea as a part of technological amber mining process. The extremely high-suspended particulate matter concentrations during that disposal were recorded immediately after the discharge of significant volumes of pulp and reached 200 mg/L. The impact of pulp discharge had sequentially suppressed plankton communities development due to the high content of suspended solids and afterwards stimulated plankton development due to the glauconite infusion. Cladocera were the most sensitive group to the effects of suspended matter. According to the preliminary forecast, when the pulp discharge stops, the restoration of plankton communities may take from 1 to 2 seasons to 1 year for different groups. This is due to the timing of the removal of fine suspended particulate matter from sediments and the possibility of secondary entry during resuspension.

Spatio-temporal distribution and source identification of antibiotics in suspended matter in the Fen River Basin.

In this study, 26 typical antibiotics in the suspended matter of the Fen River basin were analyzed during the wet and dry seasons, and the main sources of antibiotic contamination were further identified. The results showed that the concentrations of antibiotics in the suspended matter varied seasonally. Sixteen antibiotics were detected in the suspended matter during the wet season with an average concentration of 463.56 ng/L. However, a total of 21 antibiotics were detected in the dry season, with an average concentration of 106.00 ng/L. The concentration of chloramphenicol antibiotics was outstanding in the wet season and dry season. The spatial distribution of the antibiotics in suspended matter showed little spatial discrepancy during the wet season. During the dry season, nevertheless, the concentration was higher upstream than midstream and downstream. The main sources of antibiotics in the Fen River Basin were livestock and poultry breeding, wastewater from wastewater treatment plants (WWTPs), agricultural drainage, domestic sewage, and pharmaceutical wastewater. Wastewater from WWTPs and domestic sewage were identified as two primary sources in the suspended matter during the wet season, with wastewater from WWTPs contributing the most accounting for 37%. While the most significant source of antibiotics in the suspended matter in the dry season was pharmaceutical wastewater, accounting for 36%. In addition, the contribution proportion of sources for antibiotics exhibited discrepant spatial distribution characteristics. In the wet season, wastewater from WWTPs dominated in the upstream and midstream, and livestock and poultry breeding was prominent in the midstream and downstream. Pharmaceutical wastewater was the main source in the midstream and downstream regions during the dry season.

Effects of microplastics mixed with natural particles on Daphnia magna populations.

The toxicity of microplastics on Daphnia magna as a key model for freshwater zooplankton is well described. While several studies predict population-level effects based on short-term, individual-level responses, only very few have validated these predictions experimentally. Thus, we exposed D. magna populations to irregular polystyrene microplastics and diatomite as natural particle (both ≤63 µm) over 50 days. We used mixtures of both particle types at fixed particle concentrations (50,000 particles mL-1) and recorded the effects on overall population size and structure, the size of the individual animals, and resting egg production. Particle exposure adversely affected the population size and structure and induced resting egg production. The terminal population size was 28-42 % lower in exposed compared to control populations. Interestingly, mixtures containing diatomite induced stronger effects than microplastics alone, highlighting that natural particles are not per se less toxic than microplastics. Our results demonstrate that an exposure to synthetic and natural particles has negative population-level effects on zooplankton. Understanding the mixture toxicity of microplastics and natural particles is important given that aquatic organisms will experience exposure to both. Just as for chemical pollutants, better knowledge of such joint effects is essential to fully understand the environmental impacts of complex particle mixtures. ENVIRONMENTAL IMPLICATIONS: While microplastics are commonly considered hazardous based on individual-level effects, there is a dearth of information on how they affect populations. Since the latter is key for understanding the environmental impacts of microplastics, we investigated how particle exposures affect the population size and structure of Daphnia magna. In addition, we used mixtures of microplastics and natural particles because neither occurs alone in nature and joint effects can be expected in an environmentally realistic scenario. We show that such mixtures adversely affect daphnid populations and highlight that population-level and mixture-toxicity designs are one important step towards more environmental realism in microplastics research.

Phthalate esters delivery to the largest European lagoon: Sources, partitioning and seasonal variations.

Phthalate esters (PAEs) due to their ability to leach from plastics, widely used in our daily life, are intensely accumulating in wastewater water treatment plants (WWTP) and rivers, before being exported to downstream situated estuarine systems. This study aimed to investigate the external sources of eight plasticizers to the largest European lagoon (the Curonian Lagoon, south-east Baltic Sea), focusing on their seasonal variation and transport behaviour through the partitioning between dissolved and particulate phases. The obtained results were later combined with hydrological inputs at the inlet and outlet of the lagoon to estimate system role in regulating the transport of pollutants to the sea. Plasticizers were detected during all sampling events with a total concentration ranging from 0.01 to 6.17 µg L-1. Di(2-ethylhexyl) phthalate (DEHP) was the most abundant PAEs and was mainly found attached to particulate matter, highlighting the importance of this matrix in the transport of such contaminant. Dibutyl phthalate (DnBP) and diisobutyl phthalate (DiBP) were the other two dominant PAEs found in the area, mainly detected in dissolved phase. Meteorological conditions appeared to be an important factor regulating the distribution of PAEs in environment. During the river ice-covered season, PAEs concentration showed the highest value suggesting the importance of ice in the retention of PAEs. While heavy rainfall impacts the amount of water delivered to WWTP, there is an increase of PAEs concentration supporting the hypothesis of their transport via soil leaching and infiltration into wastewater networks. Rainfall could also be a direct source of PAEs to the lagoon resulting in net surplus export of PAEs to the Baltic Sea.

Response of total suspended matter to natural and anthropogenic factors since 1990 in China's large lakes.

Total suspended matter (TSM) as a critical water quality parameter is closely linked with nutrients, micropollutants, and heavy metals threatening the ecological health of aquatic ecosystems. However, the long-term spatiotemporal dynamics of lake TSM in China and their response to natural and anthropogenic factors are rarely explored. In this study, based on Landsat top-of-atmosphere (TOA) reflectance embedded in GEE and in-situ TSM data collecting in the periods 2014-2020, we developed a unified empirical model (R2 = 0.87, RMSE = 10.16 mg/L, and MAPE = 38.37 %) to retrieve the autumn TSM of lakes at national scale. This model exhibited stable and reliable performances through transferability validation and comparative analysis with published TSM models, and was implemented to generate autumn TSM maps for large lakes (≥50 km2) across China during 1990-2020.We found that 78.03 % of large lakes with TSM < 20 mg/L were dominant in 2020 across China, and these lakes were mainly located in the plateau and mountain regions. In the first gradient terrain (FGT) and second gradient terrain (SGT), the number of lakes showing significant (p < 0.05) decreasing TSM trends increased from 1990-2004 to 2004-2020, while those with opposite directions in TSM decreased. Lakes in the third gradient terrain (TGT) exhibited the inverse quantitative change in these two TSM trends compared with the FGT and SGT. A relative contribution analysis at the watershed level indicated that the first two leading factors that control TSM significant change in the FGT were lake area and wind speed, in the SGT were lake area and NDVI, and in the TGT were population and NDVI, respectively. The impacts of anthropogenic factors on lakes are continuing, particularly in eastern China, and more efforts are needed to improve and protect the water environment in the future. Our findings might help water resource managers better grasp the current state of water quality.

An improved hyperspectral sensing approach for the rapid determination of copper ion concentrations in water environment using short-wavelength infrared spectroscopy.

Copper ion is one of the hazardous pollutants often present in industrial wastewater or acid mine drainage that is regarded as a primary environmental challenge. Hyperspectral remote sensing has a long tradition in water quality monitoring. However, its application in heavy metal detection is relatively similar, and the detection is highly influenced by water turbidity or total suspended matter (TSM), requiring research efforts to improve accuracy and generalize the applicability of this technique. In this study, the use of simple filtration (pore size of 0.7 µm) for sample pretreatment to improve hyperspectral remote sensing of copper ion concentrations (Cu, 100-1000 mg/L) in water samples is proposed. A wide variety of water samples, including as-prepared and field (fish pond and river water) samples, were investigated to validate the developed method. Spectral data containing sensitive bands characterized in the range of 900-1100 nm were first preprocessed with logarithm transformation, followed by quantitative prediction model development using stepwise multivariate linear regression (SMLR) with the most sensitive wavebands at around 900 nm and 1080 nm. Satisfactory prediction performance for Cu ions was found for turbid water samples (TSM greater than approximately 200 mg/L) after simple filtration pretreatment, suggesting that pretreatment removed suspended solids in the mixtures and enhanced the spectral features of Cu ions in the model. Moreover, good agreement between the laboratory results and the field samples (adjusted R2 > 0.95 and NRMSE <0.15) highlights the suitability of the developed model and filtration pretreatment for obtaining relevant information for the rapid determination of Cu ion concentrations in complex water samples.

Quantification of Poly(vinyl chloride) Microplastics via Pressurized Liquid Extraction and Combustion Ion Chromatography.

A reliable analytical method has been developed to quantify poly(vinyl chloride) (PVC) in environmental samples. Quantification was conducted via combustion ion chromatography (C-IC). Hydrogen chloride (HCl) was quantitatively released from PVC during thermal decomposition and trapped in an absorption solution. Selectivity of the marker HCl in complex environmental samples was ensured using cleanup via pressurized liquid extraction (PLE) with methanol at 100 °C (discarded) and tetrahydrofuran at 185 °C (collected). Using this method, recoveries of 85.5 ± 11.5% and a limit of quantification down to 8.3 µg/g were achieved. A variety of hard and soft PVC products could be successfully analyzed via C-IC with recoveries exceeding >95%. Furthermore, no measurable overdetermination was found for various organic and inorganic matrix ingredients, such as sodium chloride, sucralose, hydroxychloroquine, diclofenac, chloramphenicol, triclosan, or polychlorinated biphenyls. In addition, sediments and suspended particular matter showed PVC concentrations ranging up to 16.0 and 220 µg/g, respectively. However, the gap between determined polymer mass and particle masses could be significant since soft PVC products contain plasticizers up to 50 wt %. Hence, the results of the described method represent a sum of all chlorine-containing polymers, which are extractable under the chosen conditions.

Does suspended sediment affect the phytoplankton community composition and diversity in an Arctic fjord? A comparative study during summer.

The Arctic regions experience strong seasonality and are largely affected by increasing temperature. This is particularly evident in the Kongsfjorden, which is surrounded by glaciers and is affected by seasonal and annual changes in temperature. It is largely influenced by glacial meltwater bringing in fluvial inputs such as total suspended matter (TSM) and warm Atlantic waters, which could alter the phytoplankton community. Seven stations in the Kongsfjorden representing glacier-influenced head (KF7, KF6, KF5), mid (KF4, KF3), and open region of the fjord (KF2 and KF1) were considered to evaluate the effect of TSM on phytoplankton community structure, abundance, chlorophyll a (Chl a), diversity index, evenness, and richness during summer 2011 (June) and 2018 (August) and related with atmospheric and hydrological parameters. The annual average atmospheric temperature (AAAT) over Ny-Ålesund showed an increase in temperature by a degree from -3.52 °C in 2011 to -2.44 °C in 2018, while the summer average atmospheric temperature (SAAT) over the same period increased from 5.80 to 6.16 °C. Increased freshening of the fjord led to an increase in TSM during 2018 which coincided with a decrease in Chl a by an order of magnitude. Although sea surface temperature (SST) was warmer in 2011, TSM was higher in 2018. The number of phytoplankton groups identified decreased from 11 in 2011 to 4 in 2018. A distinct alteration in phytoplankton community structure was observed from head fjord to open fjord with higher diversity observed during 2011 compared to 2018. This work highlights the effect of TSM on the phytoplankton community in the Kongsfjorden.

Suspended matter filtration causes a counterintuitive increase in UV-absorption.

In water treatment, filtration is often a first step to avoid interference of chemical or UV-disinfection with suspended matter (SPM). Surprisingly, in testing a ballast water filter with 25 and 40 µm mesh screens, UV-absorption (A, 254 nm) of filtered water increased with the largest increase in the finest screen. The hypothesis that filtration partly removes large particles and partly replaces them with small unfiltered ones, leading to an overall increase in absorption, was tested by measuring particle counts, particle-size distributions (PSD) and by modeling the Mass Normalized Beam Attenuation Coefficient (A/SPM) before and after filtration. An independent model verification was made by measuring and modeling A/SPM of three differently sized Arizona test dust suspensions. It is concluded that filtration is a good pretreatment for chemical disinfection systems because it removes the suspended matter mass, but that the production of smaller particles increases UV-absorption and hence may reduce disinfection performance.

Variation of satellite-derived total suspended matter in large lakes with four types of water storage across the Tibetan Plateau, China.

Total suspended matter (TSM), as an indicator of the concentration of fine materials in the water column including particulate nutrients, pollutants, and heavy metals, is widely used to monitor aquatic ecosystems. However, the long-term spatiotemporal variations of TSM in lakes across the Tibetan Plateau (TP) and their response to environmental factors are rarely explored. Accordingly, taking advantage of the Landsat top-of-atmosphere reflectance and in-situ data, an empirical model (R2 = 0.83, RMSE = 1.08 mg/L, and MAPE = 19.49 %) was developed to estimate the average autumnal TSM in large TP lakes (≥50 km2) during the 1990-2020 period. For analyzing the spatiotemporal variability in TP lakes TSM, the examined lakes were classified into four types (Type A-D) based on their water storage changing in different periods. The results showed that the lakes in the southern and some northeastern parts of the TP exhibited lower TSM values than those situated in other regions. The assessment of TSM in each of these four lake types showed that more than half of them had a TSM value of <20 mg/L. Apart from Type D, the lakes with the TSM showing significantly decreasing trends were dominantly Types A-C. A relative contribution analysis involving five driving factors indicated that they contributed by >50 % to lake TSM interannual variation in 73 out of 114 watersheds, and the lakes area change demonstrated the greatest contribution (82.2 %), followed by wind speed (11.0 %). Further comparison between the entire lake and the non-expansive regions suggested that the expansive region played an indispensable role in determining the TSM value of the whole lake. This study can help to better understand the water quality condition and provide valuable information for policy-makers to maintain sustainable development in the TP region.

Spatiotemporal partition dynamics of typical herbicides at a turbid river estuary.

Organic pollutants are ubiquitous in estuarine areas, nonetheless, the transport mechanisms of herbicides in such areas are limited. Atrazine and acetochlor were analyzed in suspended particle matter (SPM), surface sediment, and surface water from the Yellow River estuary and the surrounding rivers and sea. Among these rivers, the Yellow River contributes the most herbicide flux to the sea annually. The herbicide concentrations in water and sediment decreased from the estuarine areas to the deep sea. The fugacity fraction values of atrazine exceeded 0.5 in the Yellow River estuary, which supported that the herbicides in sediment desorbed at the estuarine areas. The herbicide in the SPM showed high concentration in the outer sea and increased as a power function with decreasing SPM content. The increasing partition capacity indicated that the herbicides tended to sink into sediment, increasing the ecological risk posed by herbicides. The ecological risk of acetochlor deserves continuous attention.

Development of total suspended matter prediction in waters using fractional-order derivative spectra.

More and more hyper-spectral satellites will be used to estimate total suspended matter (TSM) in waters instead of multi-spectral satellites, such as China's Gaofen-5 and Zhuhai-1. Although they have not been widely used because of the consistency of sampling and image time. Hence, the study based on measured hyper-spectroscopy is important for applying to hyper-spectral satellites. Fractional-order derivatives (FODs) considers more detailed spectral information, and it is a better spectral preprocessing method than conventional integer-order derivatives. The application and analysis of FODs for spectra in waters is rare. If FOD is successfully applied to estimate TSM, the TSM mapping with FOD using hyper-spectral satellites will be meaningful. Based on these points, this study aimed to apply FOD to predict TSM and to prove the prediction feasibility of FOD in waters. Different prediction models and eight FOD transformation processes with increment of 0.25 per step for 392 spectral reflectance data from China were used and compared. The prediction models include the optimum models of the single wavelength, ratio index, difference index and TSM index at each FOD order, and the random forest (RF) model with all wavelengths was also used. Discrete wavelet transform (DWT) was used to reduce noise and improve the model accuracy after using FOD. Our results achieved the followings First, FOD enhanced spectral characteristics at 500-600 nm and 800 nm that were affected by TSM. Second, the correlation between TSM and FOD spectra was enhanced (e.g., the correlation coefficients of 19 wavelengths (789-807 nm) of 0.75-order were higher than 0.8 but the original spectra were not). Third, FOD improved the performance of different prediction models, and the RF model from 0.5-order to 1.25-order derivative spectra all led good results (). Fourth, DWT can reduce the noise and improve the performance, and FOD-DWT model of 1.25-order led the R2 of 0.84, RMSE of 16.30 and MAPE of 78.62 in validation. Overall, our results suggest that FOD can improve the prediction performance for most models, and the optimum order of some models is not integer. Our results also provide a reference for predicting other water quality parameters and mapping these parameters using hyper-spectral satellites. The accurate estimation of TSM is helpful for protecting ecological and social environments.

Floating particles with high copper concentration in the sea-surface microlayer.

This study sought to clarify whether suspended particles containing high Cu concentrations are present in the sea-surface microlayer (S-SML). For this reason, suspended particles (10-2000 µm) in the S-SML were collected periodically from a ship mooring pond during 2018-2020, and the acid-soluble Cu concentration in the suspended particles was measured as particulate Cu (P-Cu). The highest concentration of P-Cu in the S-SML of the pond was 75 µg L-1 with a 90th percentile value of 2.5 µg L-1. This is below P-Cu values reported for the S-SML in North American ports, but 140 times higher than this found in bulk seawater in the Atlantic Ocean. The highest P-Cu concentration in the S-SML of non-organism (abiotic) origin was 17 µg L-1, and the abiotic P-Cu to P-Cu ratio varied from 0.2 to 100%, likely depending on the quality and quantity of biogenic material in the S-SML samples. It is assumed that the S-SML particles examined here contain high Cu concentrations originating from ship antifouling paints.

Water quality assessment of the Ganges River during COVID-19 lockdown.

Ganges River water quality was assessed to record the changes due to the nation-wide pandemic lockdown. Satellite-based (Sentinel-2) water quality analysis before and during lockdown was performed for seven selected locations spread across the entire stretch of the Ganges (Rishikesh-Dimond Harbour). Results revealed that due to the lockdown, the water quality of the Ganges improved with reference to specific water quality parameters, but the improvements were region specific. Along the entire stretch of Ganges, only the Haridwar site showed improvement to an extent of being potable as per the threshold set by the Central Pollution Control Board, New Delhi, India. A 55% decline in turbidity at that site during the lockdown was attributed to the abrupt halt in pilgrimage activities. Absorption by chromophoric dissolved organic matter which is an indicator of organic pollution declined all along the Ganges stretch with a maximum decline at the downstream location of Diamond Harbour. Restricted discharge of industrial effluent, urban pollution, sewage from hotels, lodges, and spiritual dwellings along the Ganges are some of the reasons behind such declines. No significant change in the geographic trend of chlorophyll-a was observed. The findings of this study highlight the importance of regular monitoring of the changes in the Ganges water quality using Sentinel-2 data to further isolate the anthropogenic impact, as India continues the phase-wise opening amidst the pandemic.

Mercury in the world's largest hypersaline lagoon Bay Sivash, the Sea of Azov.

There are few studies on mercury content in hypersaline waters. Mercury content was studied in Bay Sivash (the Sea of Azov), the world's largest hypersaline lagoon with a strong salinity gradient from 36 to 90 g l-1. The dissolved mercury compounds ranged from 120 to 250 ng l-1, Hg varied from 60 to 450 ng l-1 in the suspended matter, and total mercury in the water ranged from 200 to 600 ng l-1. Salinity and the total suspended matter had practically no effect on the amount of dissolved and suspended forms of mercury separately, but their growth significantly increased total mercury content in water. Only the concentration of dissolved forms of mercury in water significantly correlated with dissolved organic matter. The Hg concentration in the bottom sediments averaged 13.8 ng g-1 wet weight. Both high salinity and human activities on the Sivash drainage area are responsible for high Hg content in lagoon water.

Event-driven dynamics of the total mobile inventory in undisturbed soil account for significant fluxes of particulate organic carbon.

Considerable portions of the total mobile inventory of soil seepage are the diverse colloidal and larger suspended materials that essentially contribute to pedogenesis, soil functioning, and nutritional supply of subsurface ecosystems. However, the size- and material-spectra of the total mobile inventory, and field-scale factors controlling its long-term seasonal and episodic dynamics in undisturbed soil, are scarcely investigated so far. In a 4.5-year field-scale study, we utilized automated tension-controlled lysimeters optimized for in situ-sampling of total mobile inventory. Covering different land uses in a low-mountain groundwater recharge area in central Germany, seepage of top- and subsoil was collected at least biweekly and analyzed by hydrochemical and spectromicroscopic techniques (SEM/EDX, nanoparticle tracking analysis). In undisturbed soil, diverse mineral-, mineral-organic, organic, and bioparticles (microbial cells, biotic detritus) up to 75 µm was mobile. Atmospheric forcing was the major factor that governed transport of the total mobile inventory, causing considerable seasonality in seepage pH and certain solutes (e.g. sulphate), as well as episodic fluctuation of particulates. Especially episodic high-flow events, like those following snow melts and lasting rainstorms, primarily contributed to the export of inorganic/organic matter beyond the subsoil-regolith boundary. Individual infiltration events during winter accounted for up to 80% of annual fluxes of particulate organic carbon. On average, a significant proportion of 21% of the mobile organic carbon belonged to the >0.45 µm fraction. The pedological setting and land use mostly impacted the solute signature but were of minor importance for the particle load. Our ongoing monitoring provides evidence of significant episodic nutrient fluxes and unveiled pronounced temporal patterns of field-scale pH fluctuations. We conclude that dynamics of the total mobile inventory, including particulates >0.45 µm must be considered in approaches that budget carbon and elemental fluxes, but also in concepts and models on nutrient cycles and subsurface ecosystem functioning.

Deep Gaussian processes for biogeophysical parameter retrieval and model inversion.

Parameter retrieval and model inversion are key problems in remote sensing and Earth observation. Currently, different approximations exist: a direct, yet costly, inversion of radiative transfer models (RTMs); the statistical inversion with in situ data that often results in problems with extrapolation outside the study area; and the most widely adopted hybrid modeling by which statistical models, mostly nonlinear and non-parametric machine learning algorithms, are applied to invert RTM simulations. We will focus on the latter. Among the different existing algorithms, in the last decade kernel based methods, and Gaussian Processes (GPs) in particular, have provided useful and informative solutions to such RTM inversion problems. This is in large part due to the confidence intervals they provide, and their predictive accuracy. However, RTMs are very complex, highly nonlinear, and typically hierarchical models, so that very often a single (shallow) GP model cannot capture complex feature relations for inversion. This motivates the use of deeper hierarchical architectures, while still preserving the desirable properties of GPs. This paper introduces the use of deep Gaussian Processes (DGPs) for bio-geo-physical model inversion. Unlike shallow GP models, DGPs account for complicated (modular, hierarchical) processes, provide an efficient solution that scales well to big datasets, and improve prediction accuracy over their single layer counterpart. In the experimental section, we provide empirical evidence of performance for the estimation of surface temperature and dew point temperature from infrared sounding data, as well as for the prediction of chlorophyll content, inorganic suspended matter, and coloured dissolved matter from multispectral data acquired by the Sentinel-3 OLCI sensor. The presented methodology allows for more expressive forms of GPs in big remote sensing model inversion problems.

Soils in lakes: the impact of inundation and storage on surface water quality.

The large-scale storage and inundation of contaminated soils and sediments in deep waterlogged former sand pits or in lakes have become a fairly common practice in recent years. Decreasing water depth potentially promotes aquatic biodiversity, but it also poses a risk to water quality as was shown in a previous study on the impact on groundwater. To provide in the urgent need for practical and robust risk indicators for the storage of terrestrial soils in surface waters, the redistribution of metals and nutrients was studied in long-term mesocosm experiments. For a range of surface water turbidity (suspended matter concentrations ranging from 0 to 3000 mg/L), both chemical partitioning and toxicity of pollutants were tested for five distinctly different soils. Increasing turbidity in surface water showed only marginal response on concentrations of heavy metals, phosphorus (P) and nitrogen (N). Toxicity testing with bioluminescent bacteria, and biotic ligand modelling (BLM), indicated no or only minor risk of metals in the aerobic surface water during aerobic mixing under turbid conditions. Subsequent sedimentation of the suspended matter revealed the chemical speciation and transport of heavy metals and nutrients over the aerobic and anaerobic interface. Although negative fluxes occur for Cd and Cu, most soils show release of pollutants from sediment to surface waters. Large differences in fluxes occur for PO4, SO4, B, Cr, Fe, Li, Mn and Mo between soils. For an indicator of aerobic chemical availability, dilute nitric acid extraction (0.43 M HNO3; Aqua nitrosa) performed better than the conventional Aqua regia destruction. Both the equilibrium concentrations in surface waters, and fluxes from sediment, were adequately (r2 = 0.81) estimated by a 1 mM CaCl2 soil extraction procedure. This study has shown that the combination of 0.43 M HNO3 and 1 mM CaCl2 extraction procedures can be used to adequately estimate emissions from sediment to surface waters, and assess potential water quality changes, when former sand pits are being filled with soil materials.