Loire Research Articles

Exploring possible controlling factors of spatial distribution of microplastics in sediments of a river segment (Loire River, France)

Microplastics (MP) have been reported in many rivers across the globe but their depositional and archiving mechanisms in sediments are not fully understood yet. The aim of this study was to identify potential controlling factors of MP spatial distribution in surface sediment after a characterisation (sediment composition, hydrological conditions, sedimentary environment) of 14 sampling sites in an 8 km2 segment of the Loire river. Samples were collected from 3 sedimentary environments (sandbars, riverbanks and semi-active channels) with diverse flooding frequencies, grain size distributions and total organic carbon (TOC) contents. After treatment of sediment samples, MP concentrations and sizes were determined and polymer types identified by μFTIR (micro Fourier transform infrared) spectroscopy. After checking the influence of sample-scaled variability over river segment-scaled variability, MP concentrations were evaluated to 867–10635 MP/kg of sediment dry weight (sed dw, size range 25–5000 μm) in the river segment. No environmental parameters were individually correlated with MP contamination in our study, possibly due to complex depositional environments in this river segment. A systemic approach however allowed to exhibit that sediment composition reflecting hydro-morpho-sedimentary conditions can help to understand MP distribution in a river segment. A higher MP contamination observed in semi-active channel samples (median contamination value of 4797 MP/kg sed dw) could indicate that MP deposition is favoured in fine-grained (FGS) and TOC-rich sediment, reflecting less energetic hydrological conditions. Moreover, increasing flooding frequency seems to favor accumulation of MP only in the case of semi-active channels. On the contrary, less MP were detected in sandbars and riverbanks (median contamination of 1296 MP/kg sed dw), formed in higher hydrodynamical energy conditions. As a 10-fold variability of MP concentration exists in the study area, the importance of multiplying replicates even at the scale of a small river segment is underlined to access representativity of MP contamination.

Human genetic structure in Northwest France provides new insights into West European historical demography

The demographical history of France remains largely understudied despite its central role toward understanding modern population structure across Western Europe. Here, by exploring publicly available Europe-wide genotype datasets together with the genomes of 3234 present-day and six newly sequenced medieval individuals from Northern France, we found extensive fine-scale population structure across Brittany and the downstream Loire basin and increased population differentiation between the northern and southern sides of the river Loire, associated with higher proportions of steppe vs. Neolithic-related ancestry. We also found increased allele sharing between individuals from Western Brittany and those associated with the Bell Beaker complex. Our results emphasise the need for investigating local populations to better understand the distribution of rare (putatively deleterious) variants across space and the importance of common genetic legacy in understanding the sharing of disease-related alleles between Brittany and people from western Britain and Ireland.

Untargeted metabolomic insights into plastisphere communities in European rivers.

Every year, rivers introduce a staggering amount of hundred kilotons of plastic into the Oceans. This plastic is inhabited by microorganisms known as the plastisphere, which can be transferred between different ecosystems through the transport of microplastics. Here, we simulated the microbial colonization of polyethylene-based plastic pellets that are classically used to manufacture large-scale plastic products. The pellets were immersed for 1month in four to five sampling stations along the river-to-sea continuum of nine of the major European rivers. This study presents the first untargeted metabolomics analysis of the plastisphere, by using ultra high-performance liquid chromatography coupled to high-resolution mass spectrometry (UHPLC-HRMS). The plastisphere metabolomes were similar in the Rhine and Rhone rivers, while being different from the Tiber and Loire rivers, which showed greater similarity to the Thames and Seine rivers. Interestingly, we found a clear distinction between plastisphere metabolomes from freshwater and marine water in most of the river-to-sea continuum, thus suggesting a complete segregation in plastisphere metabolites that is not consistent with a major transfer of microorganisms between the two contrasted ecosystems. Putative annotations of 189 discriminating metabolites suggested that lipid metabolism was significantly modulated. These results enlightened the relevance of using environmental metabolomic as complementary analysis to the current OMICs analysis.

Frequency Analysis of the Loire River water Total Suspended Solid and Electrical Conductivity (Orléans, France)

Frequency Analysis of the Loire River water Total Suspended Solid and Electrical Conductivity (Orléans, France)

Quantifying particulate organic matter: source composition and fluxes at the river-estuary interface

Particulate organic matter (POM) characteristics and variability have been widely studied along the land-ocean aquatic continuum, yet, gaps remain in quantifying its source composition, fluxes, and dynamics at the river-estuary interface. POM in rivers consists of a complex mixture of sources, derived both from locally produced (i.e. phytoplankton) and from adjacent ecosystems (e.g. terrestrial POM). Each source differ in its trophic and biogeochemical characteristics, hence impacting its integration into local food webs, its transfer to estuaries and sea, and its contribution to biogeochemical processes. In this study, we use a robust approach based on in situ POM to characterize river POM end-members, to quantify POM composition and dynamics, and to identify the related key drivers. This study was performed at the River-Estuary interface of one of the main rivers in Western Europe (the Loire River, France). For 3 years, we conducted bimonthly measurements of carbon and nitrogen isotopic (δ13C, δ15N) and elemental (C/N) ratios to quantify the contribution of two sources (phytoplankton and terrestrial POM) to the POM mixture and calculated annual fluxes of particulate organic carbon (POC) and nitrogen (PN) sources. Throughout the year, POM consisted of ~65% phytoplankton and 35% terrestrial POM. The mean annual export fluxes were 40.6 tPOC/year and 2.45 tPN/year over the studied period, with half of it originating from phytoplankton (53 and 55% for POC and PN, respectively). We observed a clear seasonal pattern in POM composition: phytoplankton predominated from March to October, in relation to high primary production, while terrestrial contributions were the highest from November to February, driven by greater autumn-winter hydrodynamics. Our study illustrate the interest of such an approach to quantify POM composition in aquatic system and estimate source fluxes, and provide fundamental results for estimating seasonal baselines in food webs, establishing biogeochemical budgets, and quantifying POM exports to estuarine and marine environments. Applying this methodology across a broad spectrum of aquatic systems should enhance our understanding of biogeochemical processes and organic matter transformation along the land-ocean continuum and illustrates the contribution of these ecosystems to global biogeochemical cycles.

Earliest evidence of human occupations and technological complexity above the 45th North parallel in Western Europe. The site of Lunery-Rosieres la-Terre-des-Sablons (France, 1.1 Ma)

The site of LuneryRosieres la-Terre-des-Sablons (Lunery, Cher, France) comprises early evidence of human occupation in mid-latitudes in Western Europe. It demonstrates hominin presence in the Loire River Basin during the Early Pleistocene at the transition between an interglacial stage and the beginning of the following glacial stage. Three archaeological levels sandwiched and associated with two diamicton levels deposited on the downcutting river floor indicate repeated temporary occupations. Lithic material yields evidence of simple and more complex core technologies on local Jurassic siliceous rocks and Oligocene millstone. Hominins availed of natural stone morphologies to produce flakes with limited preparation. Some cores show centripetal management and a partially prepared striking platform. The mean ESR age of 1175 ka ± 98 ka obtained on fluvial sediments overlying the archaeological levels could correspond to the transition between marine isotopic stages (MIS) 37 and 36, during the normal Cobb Mountain subchron, and in particular at the beginning of MIS 36. The Lunery site shows that hominins were capable of adapting to early glacial environmental conditions and adopting appropriate strategies for settling in mid-latitude zones. These areas cannot be considered as inhospitable at that time as Lunery lies at some distance from the forming ice cap.

Middle Loire Valley settlement: First chronology using ESR on quartz grains

Over the past two decades, stepped-terrace systems within the Loire River basin's tributaries have undergone comprehensive multidisciplinary studies, encompassing Quaternary geology, prehistory and geochronology. Surprisingly, the geochronological exploration of the Loire River itself, the longest river in France, and its fossil stepped terraces system has been relatively limited, especially in the middle section near Orléans. However, for about fifty years, this region has been pivotal in providing evidence of the historical confluence of two ancient rivers, shaping the current Loire Valley. Researchers have suggested the existence of a Plio-Pleistocene Loire paleo-river, flowing northward from the Massif Central to the Seine valley and eventually reaching the English Channel. Subsequently, this Loire River would have underwent a reorientation of its flow westward, from the Blois area to the Atlantic Ocean, after being disconnected from its previous course.The absence of alluvial deposits in the area between the current Loire valley and the Seine valley, attributed to substantial erosion, prevents direct exploration of evidence related to the south-north paleo-river. To address this challenge, the hypothesis suggests that the preserved alluvial terraces in the intermediate sector were established post-capture, offering an opportunity to determine when this significant geological event occurred. Through the application of Electron Spin Resonance (ESR) quartz dating, a chronological model for the Middle Loire has been then constructed. This model identifies five distinct phases in the evolution of the Middle Loire system, spanning from 800 ka to the present day. These phases indicate a gradual capture process, initiating between 900 and 800 ka, resulting in alterations to fluvial dynamics and ultimately leading to the establishment of the current course approximately 250 ka.

A multi-tissue de novo transcriptome assembly and relative gene expression of the vulnerable freshwater salmonid Thymallus ligericus

Freshwater ecosystems are among the most endangered ecosystems worldwide. While numerous taxa are on the verge of extinction as a result of global changes and direct or indirect anthropogenic activity, genomic and transcriptomic resources represent a key tool for comprehending species' adaptability and serve as the foundation for conservation initiatives. The Loire grayling, Thymallus ligericus, is a freshwater European salmonid endemic to the upper Loire River basin. The species is comprised of fragmented populations that are dispersed over a small area and it has been identified as a vulnerable species. Here, we provide a multi-tissue de novo transcriptome assembly of T. ligericus. The completeness and integrity of the transcriptome were assessed before and after redundancy removal with lineage-specific libraries from Eukaryota, Metazoa, Vertebrata, and Actinopterygii. Relative gene expression was assessed for each of the analyzed tissues, using the de novo assembled transcriptome and a genome-based analysis using the available T. thymallus genome as a reference. The final assembly, with a contig N50 of 1221 and Benchmarking Universal Single-Copy Orthologs (BUSCO) scores above 94%, is made accessible along with structural and functional annotations and relative gene expression of the five tissues (NCBI SRA and FigShare databases). This is the first transcriptomic resource for this species, which provides a foundation for future research on this and other salmonid species that are increasingly exposed to environmental stressors.

Updating the alluvial mapping of the middle Loire catchment: Predictive geomorphology approach and mineralogical characterization of the deposits

This study aims to provide a full synthesis of recent work on the fluvial terraces of the middle section of the Loire River, between its exit from the “Massif Central” montane area and its entry into the Touraine region, with the aim of better understanding of the evolution of the river during the Pleistocene period.New fieldwork and topographic analyses (including a predictive geomorphology approach) permit updating the spatial extent and geometry of the different Quaternary alluvial sedimentary formations in this area. In addition, new analytical data were acquired both by X-ray diffraction (XRD) on heavy minerals and by gamma spectrometry measurements on alluvial sandy sediments. These analyses allow us to characterize and distinguish the alluvial formations.This work has identified three distinct periods in the history of the Loire: the oldest, corresponding to the deposition of sediments characterised by an abundance of metamorphic minerals, originating from the Massif Central; an intermediate period, corresponding to the deposition of the high terraces of the Loire system, not characterised by mineralogical analyses but by the approach of the predicted geomorphology showing different terrace geometries; lastly, a recent period comprising the low and medium altitude terraces, characterised by an abundance of volcanic minerals also originating from the Massif Central.

Contrasting platinum trajectories in three major French rivers using dated sediment cores (1910–2021): From geochemical baseline to emerging source signals

Platinum (Pt) is a Technology Critical Element (TCE) which, since the 1990s, has been mainly used in the industry in catalytic converters for automobile emission control. Previous studies have shown Pt contamination of road-side sediments and surface sediments in urban rivers and lakes but few of them have addressed temporal variations. The present work presents historical Pt concentration trends in 137Cs-dated sediment cores from floodplains or secondary channels at the outlets of three major French watersheds (Loire, Rhone, and Seine Rivers) covering the past ∼110 years, i.e., from the 1910s to 2021. Platinum baseline levels in the sediment were estimated for the Loire River (0.76 ± 0.22 μg kg−1 for the period ∼1910-∼1955) and the Rhone River (1.64 ± 0.41 μg kg−1), and historical Pt variations seem to reflect variations in hydrodynamics and grain size composition. Since the early 2000s, Pt concentrations in the Loire and the Rhone River sediments tend to increase (>2.5 μg kg−1) and were attributed to the use of car catalytic converters, an emerging technology since the 1990s using >50 % of European Pt demand. High and variable historical Pt concentrations (up to 14.6 μg kg−1) in the Seine River sediments may reflect legacy Pt sources due to former anthropogenic activities in this watershed, such as the use of Pt-based catalysts for petroleum refinery since the end of the 1940s, coal handling and precious metals refining, probably concealing the likely presence of an emerging traffic-related Pt signal. This first comparison of historical Pt concentration trends in sediments from contrasting watersheds allows to distinguish signals originating from different natural and anthropogenic sources (background level, historical sources, road traffic).

Temporal trends of plastic additive contents in sediment cores of three French rivers (Loire, Meuse and Moselle) over the last decades

Sediment cores from three major French watersheds (Loire, Meuse and Moselle) have been dated by 137Cs and 210Pbxs from 1910 (Loire), 1947 (Meuse) and 1930 (Moselle) until the present in order to reconstruct trajectories of plastic additive contaminants including nine phthalate esters (PAEs) and seven organophosphate esters (OPEs), measured by gas chromatography–mass spectrometer (GC–MS–MS). Historical levels of ∑PAEs were higher than those of ∑OPEs in the Loire and the Moselle sediments, while ∑PAEs and ∑OPEs contents were of the same order of magnitude in the Meuse sediments. Although increases in concentrations do not evolve linearly, our results clearly indicate an increase in OPEs and PAEs concentrations from the 1950–1970 period onwards, compared with the first half of the 20th century. Our results show that, ∑OPE contents increase gradually over time in the Loire and Meuse rivers but evolve more randomly in the Moselle River. Trajectories of ∑PAEs depend on the river and no generality can be established, suggesting sedimentary reworking and/or local contamination. Data from this study allowed comparisons of contents of ∑OPEs and ∑PAEs between rivers, with ∑OPE concentrations in the Moselle River > Meuse River > Loire River, and concentrations of ∑PAEs in the Loire River > Moselle River > Meuse River. Among all PAEs, di(2-ethylhexyl) phthalate (DEHP) was the most abundant in all sediment samples, followed by diisobutyl phthalate (DiBP). Tris (2-chloroisopropyl) phosphate (TCPP) was the most abundant OPE in sediments of the three rivers. In addition, strong positive Pearson correlations were observed between organic matter (OM) parameters and OPE concentrations, and to a lesser extent, between OM parameters and PAE concentrations. This is particularly true for the Moselle River and for the Loire River, but less so for the Meuse River.

Characterization of periods of high and low hydrological activity in the Loire River, France, between the 14th and mid-19th centuries

The Loire River watershed accounts for a fifth of metropolitan France. Nevertheless, knowledge of past floods of the Loire River and its tributaries is still very limited. This study aimed to carry out an unprecedented census of floods in the Loire River, during the Little Ice Age (LIA), from the 14th century to the mid-19th century, in order to detect periods of high and low hydrological activity. The abundant historical archives in the cities of Nevers and Decize, as well as other archives consulted, enabled us to record 303 flood events, including 220 in the study area between Digoin and Nevers in Burgundy. This census is heterogeneous over the centuries, with the majority of newly recorded flood events taking place during the 14th and 15th centuries, first half of the 16th century, and 18th and 19th centuries. The use of two types of flood indexes enabled this study to overcome the documentary bias, and detect several decadal periods of high or low hydrological activity during the LIA in the Loire River. Almost all these periods can be found on other rivers in both France and Europe, the Loire River being exposed to the confluence of several climatic influences, as confirmed by comparisons with the North Atlantic Oscillation (NAO), Grand Solar minima and temperature fluctuations. Nevertheless, the coldest periods of the LIA, coupled with negative NAO positions, correspond to periods of high hydrological activity in the Loire River. The study of flood seasonality also reveals a high degree of variability during the LIA, with a higher proportion of flood events occurring in summer and autumn compared with the current seasonal pattern.

A neural network encoder-decoder for time series prediction: Application on 137Cs particulate concentrations in nuclearized rivers

Monitoring the impact of human activities on the environment is a major challenge as many pollutants can be found in the different ecosystems. This is the case of the caesium-137 that has been present in the environment for many decades as a result of atmospheric tests, accidents such as Chernobyl and release from nuclear industries. With the recent advance in data-driven models, this study evaluate the relevance of a deep learning tool for reconstructing caesium-137 chronics particulate concentration in rivers. An encoder-decoder neural network, “Hierarchical Attention-Based Recurrent Highway Networks”(HRHN), is proposed notably for its ability to extract the most relevant temporal and spatial information from the databases. Three monitoring stations were studied, one on the Rhône River and two on the Loire River, all of them downstream nuclear industries in these catchments affected by the global fallout and the accident of Chernobyl. The objective is to predict the future concentration from a set of variables providing past information on water discharge, washout flux and industrial radioactive releases. Once optimised, the model generates first results in agreement with the real concentration curves by correctly following the main trends, with a NSE of 0.89, 0.53 and 0.35 respectively for the Rhone station and the two stations on the Loire. The main reason of inaccuracies is due to the quantity of data available. The originality of this model is its capacity to make predictions on different catchment areas. In fact the training was conducted on the Rhône station as the range of the concentration was higher (from 265.4 to 2700.0 Bq/kg) and the testing on the two Loire station. Another encoder-decoder model DA-RNN (Dual-Stage Attention-Based Recurrent Neural Network) was also evaluate in order to compare the performance of an alternative architecture, without convolution layer. The conclusion is that HRHN remains more powerful in the predictions on the 3 systems. With these first interesting results for HRHN, further investigations should be taken into account for other pollutants than caesium-137 to better understand the robustness of the model.

Influence of local environmental gradients on ecological strategies of herbaceous communities in riverine side channels

AbstractQuestionsIn riverine side channels (secondary and former arms), the alternation of lotic, lentic and dry phases produces disturbance and resource gradients that filter species and community strategies. To better understand the impact of this alternation of functioning on plant communities at a fine spatial scale, we tested for the effects of elevation (linked to water level), slope, longitudinal position, light availability and sediment grain size on (i) taxonomic composition and (ii) competition, stress tolerance, and ruderal strategies (C, S and R strategies) at the community level. We hypothesized that fewer resources would increase the stress‐tolerant prevalence (i.e., community‐weighted mean value), while topographic gradients would affect ruderal prevalence. In addition, we hypothesized that strong and directional environmental filtering should reduce the co‐occurrence of species with different CSR strategy values (i.e., low C, S and R functional dispersion).LocationFourteen side channels on the lower reach of the Loire river (France).MethodsTaxonomic composition of the herb layer and environmental variables were assessed on 474 plots. The relations between species composition and environmental gradients were investigated by a constrained analysis of principal coordinates. The effects of environmental gradients on community CSR strategies were assessed using mixed‐effects models and a model‐averaging procedure.ResultsTaxonomic community composition was shaped mainly by light availability, topographic elevation and sediment grain size. Slope and the interaction between light and elevation influenced the community‐weighted mean and functional dispersion values of S and R strategies. Among other interactions, those involving sediment grain size shaped the dispersion values for C and R strategies.ConclusionThe study identified shading and fine sediment grain size as key drivers of biotic homogenization in the riverscape. Increasing the disturbance frequency and magnitude would limit the progression of the ecological succession and favor the co‐occurrence of taxonomically and functionally diverse communities within the side channels.

Digital Heritage and Mapping Renaissance Tours. Recent Research from the CESR

This article presents recent initiatives in the fields of Digital Heritage and digital mapping by researchers attached the Centre d'études supérieures de la Renaissance (CESR) in Tours, France. During the fifteenth and early sixteenth century the city of Tours, situated in the heart of France in the valley of the river Loire, was one of the main residences of the French kings and this had important consequences for the nature of artistic production and for social aspects of urban life. Making use of the latest developments in Digital and Spatial Humanities, researchers attached to the CESR have created an interactive digital map of historical Tours; several crosslinked databases of artworks and archival sources from Tours; an enriched 3D model of an artistic masterpiece, the funeral monument of deceased royal children; an interactive historical graphic novel; and a GPS-led app with an historical guided tour of the city. These digital projects all have in common that they bring together the outcomes of scientific historical and art historical research with digital applications, as a starting point for further research, and for public outreach activities.

Meroplanktic phytoplankton play a crucial role in responding to peak discharge events in the middle lowland section of the Loire River (France)

Meroplanktic phytoplankton play a crucial role in responding to peak discharge events in the middle lowland section of the Loire River (France)

Evolution of the middle Loire river course during Pleistocene in relation with geodynamic and first settlements of the Paris basin

Evolution of the middle Loire river course during Pleistocene in relation with geodynamic and first settlements of the Paris basin

Statistically derived morphological signatures of large river channels extracted from topo‐bathymetric LiDAR data

AbstractWith the development of LiDAR technology and the availability of topo‐bathymetric data of high quality, new methods are emerging to describe and understand more accurately fluvial geomorphology. We explore the capacities of probability density functions (PDFs) of detrended dimensionless elevations extracted from digital elevation models (DEMs) to document channels morphology and configuration. These DEMs were obtained from a topo‐bathymetric LiDAR survey of 450 km performed on the middle and lower reaches of the largest river of France: the Loire River. The objective is to propose a thorough and complete method for PDF analysis in order to assess the vertical structuration of river reaches presenting various fluvial patterns. The analysis was conducted on the PDFs of active channel belt of four sites selected for the diversity of their morphological configurations (anabranching, braided, channelized and meandering). Results showed that PDFs appear to be specific of a reach and that they are useful for describing its vertical structure. The simplification with Gaussian mixture model (GMM) is effective in slicing PDF and the resulting Gaussians components are related to morphological units (MUs). The distance between Gaussian curves obtained using GMMs can be considered as an indicator of topo‐bathymetric connectivity between MUs (e.g., main and side channels) on sites presenting multichannel or channelized channel configurations. The study showed the high potential of PDF and GMM analysis in the field of fluvial geomorphology and suggests interesting developments for river management and restoration.

Vanishing lead in the Loire River estuary: An example of successful environmental regulation

The behavior, and history of lead (Pb) contamination in the ecosystem of the Loire estuary was examined using elemental concentrations and Pb isotope data in water, sediment, bivalves, shrimps, and fish. In the estuary and in the surrounding coastal area, Pb concentrations in water and sediment decreased compared to concentrations determined in the 1980s, with concentrations ranging from 15.8 to 65.7 mg kg−1 in the surface sediment, 0.04–0.26 nM in the water column, and 48.0–77.9 mg kg−1 in suspended particles. Pb biomonitoring using blue mussels collected by the French Mussel Watch Program over the last 40 years showed a concentration decrease from 3.8 to 0.8 mg kg−1. A similar trend is observed in an estuarine sediment core. Changes in accompanying Pb isotope compositions strongly suggest a binary mixing process between Pb derived from terrigenous material and anthropogenic sources. Thus, environmental regulations restricting the release of lead into the environment contribute to a decrease in estuarine levels of this pollutant, which occurs on a decadal time scale.

Toxicity assessment of microplastics within the Loire River in the clam Corbicula fluminea exposed to environmentally relevant exposure conditions.

The dispersed pollution caused by microplastics (MPs) represents a current and global concern. While the fragmentation of plastic debris into smaller particles occurs in rivers, little MP research is done on freshwater species and is published compared to the marine environment. The Loire River is the longest river in France and is subject to moderate to high anthropic pressure while it represents major societal and economic issues. However, there are not many studies that have been put forward with regards to the effect of environmental MPs (EMPs) on aquatic organisms and no policies have been enacted to monitor the plastic pollution. In this study, freshwater bivalves, Corbicula fluminea, were exposed for 21 days to environmentally relevant concentrations of a mixture of <200 µm MPs generated from plastic litter collected directly along the banks of the Loire River. This mixture was composed of 40% polyethylene (PE), 40% polypropylene (PP), 10% polyethylene terephthalate (PET) and 10% polyvinylchloride (PVC) (mass percentage). Ecotoxicological effects were assessed from the individual to the molecular levels on several endpoints: condition index, filtration efficiency, enzyme activities, lipid peroxidation, energy reserves and gene expression. The ingestion of EMPs caused damages at the biochemical level. Indeed, we reported an increase in catalase activity in gills and digestive mass, a decrease in TBARs in gills, a decrease in acetylcholinesterase activity in the digestive mass, a decrease of glycogen and lipid contents in the whole organisms and a significant induction of the expression of gst, cat, mp, acp genes. The current results suggest therefore that long-term exposure to realistic doses of EMPs causes toxicity towards freshwater benthic biota. The analysis of biomarker activities and the analysis of gene expression are complementary to prevent the effects of a plastic contamination at higher biological levels in aquatic organisms.