This paper aims at quantifying current riverine fluxes of microplastics (MPs) in two Mediterranean river catchments, a large one and a small one, namely the Rhône and the Têt, which are discharging ...to the Gulf of Lion in the Northwestern Mediterranean Sea. MP fluxes change markedly through time and space in both river systems. However, no clear relationships between MP concentrations and hydroclimatic conditions have been observed. In the Rhône River a non-linear dilution pattern of MPs in total suspended matter (TSM) during flood conditions could be observed. Although dilution is important, samples during floods exert a strong control on average MP fluxes. Compared to the Rhône River, average MP concentrations in the Têt River were throughout greater and more variable in shape and polymer composition. However, as the study year was exceptionally dry, the average specific MP flux, 76 g km−2 y−1, is only slightly larger than the non-flooding value of the Rhône River. We further monitored MP concentrations in shoreline sediments at the mouth of the Têt River to test whether these sediments can represent MP transport in the river. Besides fibers, which probably are easily washed out and transported offshore, MP concentrations and compositions are in agreement with MP loads upstream the river. We also examined the potential role of atmospheric deposition as a source of MP to the Têt River. The average atmospheric MP deposition of 6 kg km−2 y−1 exceeds by far the river average specific MP flux. Moreover, all MPs in atmospheric deposits were fibers, which in terms of mass are of minor importance in the bulk river fluxes. Atmospheric MP deposits may either have been overestimated and/or may be removed from surface waters by efficient removal processes (such as waste water treatment plants).
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•Under regular conditions, relationships between concentrations and hydroclimatic parameters are difficult to establish.•Flood samples could influence the calculation of average microplastic fluxes.•Accumulations in riverbank sediments could be good indicators for average riverine microplastic loads.•Atmospheric transport of microplastic fibers to the sea is potentially significant.•Microplastics show different shape distributions in the matrices under consideration.
Microplastics are small (<5mm) fragments of plastic debris that are ubiquitous in coastal areas and in open ocean. We have investigated the occurrence and composition of microplastics in beach ...sediments from the micro-tidal Northwestern Mediterranean Sea. Samples were collected on two beaches (northern and southern site) of the western Gulf of Lion showing markedly different characteristics. Sampling was performed along depositional lower, mid and upper beaches and repeated after 1month. Concentrations of microplastics in the northern and southern site were highly variable, ranging from 33 to 798 and from 12 to 187 microplastics per kg of dry sediment, respectively. Highest concentrations were found at three specific locations: nearby a local river mouth, within an accretionary area and in a depositional upper beach. The spatial and temporal distribution of beached microplastics seems to be directly dependent on external forcing such as wind, swell, precipitation, outflow and river mouth proximity.
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•Fibers are the main shape of beached microplastics.•Only 45% of sorted items are spectroscopically validated as plastic polymers.•Same range of MP concentrations than elsewhere along the Mediterranean coast•High small-scale heterogeneity and rapid shifts in MP distribution•River mouth proximity influences the beached MP abundance.
An experiment was carried out during summer 2015 in the inner part of the Kongsfjorden to study the inputs of meltwater and behaviour of associated suspended particles. We used a wide range of ...oceanographic instruments to assess the hydrological and hydrodynamic characteristics of coastal waters. The transfer of suspended particles occurs from a large surface plume fed by two main sources: the most important one is the upwelling of fresh and turbid water coming from a tide-water glacier: the Kronebreen, and the second one from a continental glacier: the Kongsvegen. We estimated that these two sources discharged about 2.48 ± 0.37 × 106 t of suspended sediments during the two months of melting. The major part of these sediments is deposited within the first kilometre due to flocculation phenomena. Flocculation is initiated below the surface turbid plume and is mainly caused by the salinity gradient and high suspended particle concentration. Finally, our estimates of suspended particle fluxes by a typical Arctic coastal glacier showed the need to consider suspended sediment fluxes from high-latitude areas into global budgets in the context of climate change.
Conceptual model of the particle dynamics of a typical glacial upwelling system in front of the Kronebreen glacier into the Kongsfjorden. Display omitted
•Meltwaters from Arctic glaciers highly stratify fjord waters.•Melting Arctic glaciers produce large turbid plumes spreading into the fjords.•Upwelling systems are the major source of water and sediments in Arctic fjords.•Flocculation processes enhance and favor the settling of surface fine particles.
Microbial-driven organic matter (OM) degradation is a cornerstone of benthic community functioning, but little is known about the relation between OM and community composition. Here we use Rhône ...prodelta sediments to test the hypothesis that OM quality and source are fundamental structuring factors for bacterial communities in benthic environments. Sampling was performed on four occasions corresponding to contrasting river-flow regimes, and bacterial communities from seven different depths were analyzed by pyrosequencing of 16S rRNA gene amplicons. The sediment matrix was characterized using over 20 environmental variables including bulk parameters (for example, total nitrogen, carbon, OM, porosity and particle size), as well as parameters describing the OM quality and source (for example, pigments, total lipids and amino acids and δ(13)C), and molecular-level biomarkers like fatty acids. Our results show that the variance of the microbial community was best explained by δ(13)C values, indicative of the OM source, and the proportion of saturated or polyunsaturated fatty acids, describing OM lability. These parameters were traced back to seasonal differences in the river flow, delivering OM of different quality and origin, and were directly associated with several frequent bacterial operational taxonomic units. However, the contextual parameters, which explained at most 17% of the variance, were not always the key for understanding the community assembly. Co-occurrence and phylogenetic diversity analysis indicated that bacteria-bacteria interactions were also significant. In conclusion, the drivers structuring the microbial community changed with time but remain closely linked with the river OM input.
Ecosystem responsible aquaculture practices are today imperative to feed the world increasing population. The culture of extractive species such as oyster with fed species such as fish is a promising ...solution to recycle waste streams, which would be otherwise lost and discharged into the surrounding environment. In Mediterranean earthen ponds, meagre (Argyrosomus regius), white seabream (Diplodus sargus) and grey mullet (Mugil cephalus) are three fish species of different trophic levels that are good candidates to be raised in integrated multi-trophic aquaculture (IMTA) pond with oysters (Magallana gigas) and macroalgae (Ulva flexuosa). Trophic links between species raised in IMTA ponds were inferred using the analysis of body fatty acid composition as well as in carbon and nitrogen stable isotopes. A combination of 3 treatments was tested: fish, oysters, phytoplankton and macroalgae (T1); fish, oysters and phytoplankton (T2); fish, phytoplankton and macroalgae (T3). Our results highlighted that the three fish species were in competition for food sources as they mainly fed on commercial feed whatever the treatment. However, grey mullet also consumed polychaetes that naturally grown in ponds. Macroalgae were not used by fish. In T1 and T2, oysters actively consumed the excess of phytoplankton. In T2, the absence of macroalgae reduce nutrient competition for phytoplankton growth and oysters have more available food. In earthen ponds, the production of fish with macroalgae or fish with oyster should be privileged compared to usual semi-intensive fish polyculture as the presence of extractive species reduced fish wastes.
•Integrated Multi-Trophic Aquaculture is promising to preserve environment.•Fish are good candidates to be raised with oysters and macroalgae.•Trophic link between organisms were elucidated using fatty acids and stable isotopes.•The 3 fish species were in competition for food sources (commercial feed).•Macroalgae removal reduce competition with phytoplankton that beneficiate to oyster.
With climate change, the strong seasonality and tight pelagic-benthic coupling in the Arctic is expected to change in the next few decades. It is currently unclear how the benthos will be affected by ...changes of environmental conditions such as supplies of organic matter (OM) from the water column. In the last decade, Kongsfjorden (79°N), a high Arctic fjord in Svalbard influenced by several glaciers and Atlantic water inflow, has been a site of great interest owing to its high sensitivity to climate change, evidenced by a reduction in ice cover and an increase in melting freshwater. To investigate how spatial and seasonal changes in vertical fluxes can impact the benthic compartment of Kongsfjorden, we studied the organic matter characteristics (in terms of quantity and quality) and prokaryotic distribution in sediments from 3 stations along a transect extending from the glacier into the outer fjord in 4 different seasons (spring, summer, autumn and winter) in 2012–2013. The biochemical parameters used to describe the sedimentary organic matter were organic carbon (OC), total nitrogen, bulk stable isotope ratios, pigments (chorophyll-a and phaeopigments) and biopolymeric carbon (BPC), which is the sum of the main macromolecules, i.e. lipids, proteins and carbohydrates. Prokaryotic abundance and distribution were estimated by 4′,6-diamidino-2-phenylindole (DAPI) staining. This study identifies a well-marked quantitative gradient of biogenic compounds throughout all seasons and also highlights a discrepancy between the quantity and quality of sedimentary organic matter within the fjord. The sediments near the glacier were organic-poor (<0.3%OC), however the high primary productivity in the water column displayed during spring was reflected in summer sediments, and exhibited higher freshness of material at the inner station compared to the outer basin (means C-chlorophyll-a/OC ~5 and 1.5%, respectively). However, sediments at the glacier front were depleted in BPC (~0.2–0.3mgCg−1DW) by 4.5 and 9 times compared to sediments from the inner and outer stations. δ13C values in sedimentary organic matter of Kongsfjorden varied between −23.8 and −19.3‰ and reflected distinct sources of organic matter between basins. Bacterial total cell numbers in sediments of Kongsfjorden were <2×108cellsml−1 and the prokaryotic community structure was strongly influenced by the marked environmental biogenic gradients. Overall, the spatial variability prevailed over the seasonal variability in sediments of Kongsfjorden suggesting that glacier inputs prominently control the functioning of this benthic ecosystem and its communities.
Regional index terms: Norway, Svalbard, Kongsfjorden.
•Organic matter quantity, quality and sources were spatially and seasonally examined.•Well-marked glacier-outer fjord quantitative gradients of OM throughout all seasons•Spring events of surface primary production well recorded in sediments•Discrepancy between quantity and quality of the sedimentary OM within the fjord•Biogenic gradients influenced the prokaryotic distribution in the sediments.•Spatial variability prevailed over seasonal variability in Kongsfjorden's sediments.
In temperate fish polyculture, common carp (Cyprinus carpio) and roach (Rutilus rutilus) are two fish species commonly reared in the same ponds. In the natural environment, these two species are ...considered omnivorous and may compete for food sources. However, few is known about their trophic behavior in polyculture ponds. The aim of our study was to use carbon and nitrogen stable isotope analysis to characterize trophic niche partitioning between both fish species reared in semi-intensive (fed) and extensive (non-fed) ponds. Fish growth performance was higher in semi-intensive than in extensive ponds. In semi-intensive ponds, δ13C and δ15N values of fish indicated that carp consumed mainly formulated feed, whereas roach also consumed natural food sources. In extensive ponds, δ13C and δ15N values of carp and roach indicated that both fish species did not use the same food sources. Regardless of the type of pond, standard ellipse areas, proxies of the estimated trophic niche size, were significantly smaller for carp than for roach and did not overlap, confirming that roach had more trophic plasticity than carp. Results of this study confirmed that carp and roach are good candidates to be rear in the same pond because they are able to adapt their trophic behavior to reduce trophic competition.
•Common carp and roach are two fish species commonly raised in the same ponds.•As these species are omnivorous, they may compete for food sources.•δ13C and δ15N values of fish were analyzed in semi-intensive or extensive ponds.•Stable isotope data show that fish adapt their trophic behavior to reduce competition.
•Increasing salinity favored lipoxygenase induction in terrestrial higher plant debris.•Lipoxygenases initiated autoxidative degradation of terrestrial POM in estuaries.•Autoxidative degradation of ...terrestrial POM enhanced at low and high latitude.•In temperate zones autoxidative damage of terrestrial POM more limited.
There exists a substantial amount of research on abiotic (e.g. photochemical) degradation pertaining to organic matter (OM) in the marine realm. While recent research has shown its importance in the degradation of terrestrial particulate OM (TPOM), the mechanisms involved in the induction of autoxidation in estuaries remain unclear. In this study, we propose for the first time the involvement of lipoxygenase (LOX) activity in the induction of autoxidation in mixed waters. The observation of unusual profiles of palmitoleic acid oxidation products and the presence of jasmonic acid in suspended particulate matter (SPM) collected close to the Rhône River, as well as in samples from the Mackenzie and Amazon rivers, is attributed to strong LOX activity. We show the role played by salinity in the induction of this LOX activity and provide an explanation for the differences in estuarine autoxidation level. At high latitude, lower temperatures and irradiance favor photooxidative damage to higher plant debris and, consequently, hydroperoxide production. High hydroperoxide content strongly contributes to LOX activation in mixed waters. The high resulting LOX activity enhances alkoxyl radical production and thus autoxidation. On the contrary, at low latitude, photooxidative effects are limited, and riverine autoxidation is favored. The higher hydroperoxide content of TPOM may, as a consequence, thereby also contribute to a high level of LOX activity and autoxidation in estuaries. In temperate zones, land and riverine photooxidative and autoxidative damage is limited, unlike estuaries where we observed significant LOX-induced and autoxidative damage.
In the oligotrophic context of the Mediterranean Sea, riverine inputs of particulate organic matter represent an important source of food for benthic communities. However, since most of these inputs ...are delivered during short, but intense flood events, communities living in the vicinity of river mouths are also exposed to strong and frequent physical disturbances. A very tight and complex relationship links river dynamic and macrofaunal communities in Mediterranean deltas, but less is known on the response of meiobenthic communities to river regime. In 2010, sediments cores were collected in the Rhône River prodelta in winter and spring before the flooding of the Rhône River tributaries in June, and then twice in the early and late summer. The hypothesis was that increased runoff and export of terrigenous material would induce major changes in the sediment biochemistry, which would in turn trigger modifications in abundances and vertical distribution of the meiofauna. The origin and quality (lability, degradation state) of the different pools of organic matter preserved in these recent sediments were determined using bulk geochemical and molecular analyses (fatty acids, amino acids). Vertical profiles of descriptors for organic matter origin and quality revealed major changes in the nature of the inputs occurring at monthly time scales. Inputs of plant detritus from autumnal and winter flood events were still visible in the cores collected in February and April. A few days after the June 2010 high-discharge event, a newly deposit (~7 cm) containing soil organic matter has recovered the prodeltaic sediments and the resident meiofaunal community, but at the end of August only 2 cm of this deposit remained. Multivariate analyses furthermore highlighted that the meiofaunal community was driven by both the trophic conditions and the deposition of a new sediment layer driven by the hydrological regime of the Rhône River. In April, increased abundances of meiofauna were observed in response to the sedimentation of labile organic matter after the spring bloom. The June high-discharge event affected the meiofauna with a reduction of its abundance and the burial of the resident meiobenthic community. However, the meiofauna recovered in less than two months after this disturbance, showing the strong resilience of this component of the benthic ecosystem in this high energy environment.
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•Vertical distribution of sedimentary organics varies at a monthly time scale.•Origin determines organic matter quality.•Meiofaunal abundances are driven by trophic conditions and river regime.•Rapid response of meiofauna to the sedimentation of phytodetritus.•High resilience of meiofauna to flood disturbance.
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