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Abstract Despite a vast amount of literature has focused on trace element (TE) contamination in Antarctica during the last decades, the assessment of the main pathways driving TE transfer to the biota is still an overlooked issue. This limits the ability to predict how variations in sea-ice dynamics and productivity due to climate change will affect TE allocation in the food web. Here, food web structure of Tethys Bay (Terra Nova Bay, Ross Sea, Antarctica) was first characterised by analysing carbon and nitrogen stable isotopes (δ13C, δ15N) in organic matter sources (sediment and planktonic, benthic and sympagic primary producers) and consumers (zooplankton, benthic invertebrates, fish and birds). Diet and trophic position were also characterised using Bayesian mixing models. Then, relationships between stable isotopes, diet and TEs (Cd, Cr, Co, Cu, Hg, Ni, Pb and V) were assessed in order to evaluate if and how horizontal (organic matter pathways) and vertical (trophic position) food web features influence TE transfer to the biota. Regressions between log[TE] and δ13C revealed that the sympagic pathway drives accumulation of V in primary consumers and Cd and Hg in secondary consumers, and that a coupled benthic/pelagic pathway drives Pb transfer to all consumers. Regressions between log[TE] and δ15N showed that only Hg biomagnifies across trophic levels, while all the others TEs showed a biodilution pattern, consistent with patterns observed in temperate food webs. Although the Cd behavior needs further investigations, the present findings provide new insights about the role of basal sources in the transfer of TEs in polar systems. This is especially important nowadays in light of the forecasted trophic changes potentially resulting from climate change-induced modification of sea-ice dynamics. Graphical abstract Image 1 Highlights • Horizontal and vertical food web structure was characterised using δ13C and δ15N. • Trace element (TE) transfer was assessed in the Antarctic food web. • Sympagic and pelagic pathways drove Cd and Hg transfer to invertebrates. • Benthic pathway (sediment and phytodetritus) drove Pb to invertebrates. • Hg concentration increased along trophic levels and biomagnified. Depiction of trace element transfer in the Antarctic food web highlighted an important role of both sympagic and pelagic pathways, suggesting that forecasted modification of sea-ice dynamics due to climate change may alter contaminant accumulation and biomagnification patterns. [ABSTRACT FROM AUTHOR]

We investigated the space-time dynamics of N pollution in a Mediterranean gulf (Gulf of Gaeta) by means of δ 15 N variation in seaweed fronds ( Ulva lactuca ) previously collected from an unpolluted habitat. We used a comprehensive deployment grid that enabled the generation of isotopic seascapes (isoseascapes) describing the topography of N pollution in coastal waters and identifying N input hotspots and their pathways of dispersion at sea. The δ 15 N values of U. lactuca increased during 48 h of exposure to the gulf waters, indicating anthropogenic N inputs from wastewater-derived sources. Comparison of the isoseascapes between two years differing in terms of rainfall identified coastal and offshore areas that were vulnerable to freshwater-transported nutrients, consistent with terrestrial hydromorphology and sea surface-water circulation. Isoseacapes were robust enough to reduce deployment effort, representing a powerful tool for monitoring and management strategies and useful for Environmental Protection Agencies, the main target audience of applied ecological research. [ABSTRACT FROM AUTHOR]

Effects of two chemical forms of Nitrogen (NH 4 + and NO 3 − ) on δ 15 N in Ulva lactuca were analysed separately and in mixture at two concentrations. We assessed whether the δ 15 N values of U. lactuca discriminate between Nitrogen from synthetic fertilisers (inorganic) and from fresh cow manure (organic), and the isotopic ability of the macroalga to reflect Nitrogen concentrations. Isotopic signature and N content of the macroalga reflected different nitrogenous sources and their concentrations after 48 h. The inorganic Nitrogen source (NH 4 NO 3 ) altered the isotopic values of the macroalgae more than Nitrogen from fresh cow manure (NO 3 − ). δ 15 N values observed in the mixed solution did not differ from those displayed in NH 4 NO 3 treatment alone. We conclude that stable isotope analysis of U. lactuca collected in an unpolluted site and experimentally submerged in sites suspected of being affected by disturbance is a useful tool for rapid monitoring of anthropogenic discharges of Nitrogen pollutants. [ABSTRACT FROM AUTHOR]

In the study of food webs, the existence and explanation of recurring patterns, such as the scale invariance of linkage density, predator–prey ratios and mean chain length, constitute long-standing issues. Our study focused on litter-associated food webs and explored the influence of detritivore and predator niche width (as δ 13 C range) on web topological structure. To compare patterns within and between aquatic and terrestrial ecosystems and take account of intra-habitat variability, we constructed 42 macroinvertebrate patch-scale webs in four different habitats (lake, lagoon, beech forest and cornfield), using an experimental approach with litterbags. The results suggest that although web differences exist between ecosystems, patterns are more similar within than between aquatic and terrestrial web types. In accordance with optimal foraging theory, we found that the niche width of predators and prey increased with the number of predators and prey taxa as a proportion of total taxa in the community. The tendency was more marked in terrestrial ecosystems and can be explained by a lower per capita food level than in aquatic ecosystems, particularly evident for predators. In accordance with these results, the number of links increased with the number of species but with a significantly sharper regression slope for terrestrial ecosystems. As a consequence, linkage density, which was found to be directly correlated to niche width, increased with the total number of species in terrestrial webs, whereas it did not change significantly in aquatic ones, where connectance scaled negatively with the total number of species. In both types of ecosystem, web robustness to rare species removal increased with connectance and the niche width of predators. In conclusion, although limited to litter-associated macroinvertebrate assemblages, this study highlights structural differences and similarities between aquatic and terrestrial detrital webs, providing field evidence of the central role of niche width in determining the structure of detritus-based food webs and posing foraging optimisation constraints as a general mechanistic explanation of food web complexity differences within and between ecosystem types. [ABSTRACT FROM AUTHOR]

The Bosphorus Strait is a dynamic and complex system. Recent evidences showed nitrogen and heavy metal concentrations to follow opposite patterns across the Strait, suggesting a complex spatial organisation of the anthropogenic disturbance in this system. Here, we provide isotopic information on the origin and transportation of dissolved nitrogen along the Bosphorus. C and N isotopic and elemental analyses were performed on specimens of Ulva lactuca and associated epiphytes sampled in five locations across the Strait. Variations in C and N isotopic signatures were observed in U. lactuca , pointing to a decrease in the availability of anthropogenic organic dissolved nitrogen along a north-south direction. Conversely, epiphytes did not show isotopic or elemental patterns across the Strait. These results suggest that preliminary stable isotope surveys in extended costal systems basing on U. lactuca can represent a valuable tool to focus meaningful targets and hypotheses for pollution studies in the Mediterranean region. [ABSTRACT FROM AUTHOR]

Measuring C and N stable isotopes at natural abundance can provide information on the role of fungi associated with litter decay in the nutrient cycle of freshwater ecosystems. However, uncertainty regarding isotopic fractionation by decomposer fungi during uptake or metabolic turnover is a serious limitation, weakening the description of taxon-specific ecological differences in nutrient transfer in aquatic detritus-based systems. We performed two laboratory experiments to assess C and N isotopic changes during leaf litter colonization by: (1) mixed fungal communities on three different leaf litter species, and (2) four different fungal strains growing on the same leaf litter. Our approach served to decouple the isotopic effects of different fungal taxa from those arising from structural changes occurring in leaf litter during decomposition. N isotopic changes were directly related to fungal biomass accrual on litter, whereas carbon isotopic changes were mainly dependent on the remaining lignin fraction. Isotopic mixing model equations enabled us to calculate strain-specific isotopic fractionation, indicating that fungi were enriched in 15 N by 3.6–5.9‰ with respect to bulk N litter. [ABSTRACT FROM AUTHOR]

Highlights: [•] Ulva lactuca and Cystoseira amentacea δ15N values were assessed in the Gulf of Gaeta. [•] U. lactuca was more responsive than C. amentacea to environmental pollution. [•] Comparison of fragments from the same frond overcomes natural isotopic variability. [•] Spatial analysis indicated areas in the Gulf differently affected by N inputs. [ABSTRACT FROM AUTHOR]

Abstract: Upland forested areas of watersheds undergo changes due to many factors including ecological succession, natural disturbances and human activity. The rate of natural and man-induced ecological changes in these landscapes is a function of the structural and functional characteristics of the component ecosystems. Analyzing spatial patterns and detecting fragile areas are thus crucial for making previsions about the chance and rate of disturbance propagation within and between the ecosystems. In this study we have tested the hypothesis of occurrence of a relationship between the extent of temporal change and spatial heterogeneity of mixed forested areas in the watershed of two Italian volcanic lakes by using remotely sensed data. Landsat images were acquired in summer 1987, 1992 and 2000, when Nature Reserves were established, and the temporal variation in the Normalized Difference Vegetation Index (NDVI) was determined by the change detection analysis. To analyze the spatial variability of NDVI, semivariograms were calculated using data from five randomly chosen forested areas (10km2-wide) per watershed. Results show that NDVI varied greatly across the two study sites and most of the variation was spatially structured. NDVI varied also over time. A linear positive relationship was observed between the number of pixels changing between dates and the semivariogram range, as the maximum distance of spatial dependence estimated from the starting NDVI image. Spatial homogeneity of NDVI is thus suggested as an indicator of intrinsic fragility (i.e. susceptibility to change) of mixed forests and the semivariogram range as a rapid estimator that can be considered by forest managers and agencies. [Copyright &y& Elsevier]

Posidonia oceanica is a seagrass endemic to the Mediterranean and it has been widely used as a bioindicator. We studied the layers of a 500-year-old matte using a multiproxy approach (δ13C, δ15N, 14C and C and N concentrations in seagrass debris) in order to evaluate the potential of P. oceanica as a long-term environmental indicator of N pollution and CO 2 emissions. From 1581 to 1800, accumulation rate was ca. 0.35 cm year−1, while in the last 100 years it has amounted to ca. 0.51 cm year−1. We observed increasing δ15N values with height in the vertical matte profile, indicating an increase in anthropogenic organic N inputs over time. In contrast, no clear trend in the δ13C values was observed. This study reconstructs the long-term impact of human activities on a seagrass meadow located off the Italian coast, yielding long-term background information that can help managers to implement efficient plans. • 14C dating of the matte revealed a chronological record dating back ca. 500 years. • Matte accretion rate was 0.35 cm year−1 (0.51 cm year−1 in the last 100 years). • P. oceanica δ15N increase over time, from ca. 0‰ to ca. 3‰ in the recent layers. • The highest δ15N in the recent layers is indicative of anthropogenic N inputs. • No clear temporal trend in the δ13C values of P. oceanica was observed. [ABSTRACT FROM AUTHOR]

Industrial, agricultural, and recreational activities dump several pollutants into the Caspian Sea, which is one of the main water bodies of Iran. Therefore, performing risk assessments would be required as part of the monitoring programs. Herein, non-cancer health risk assessment of the consumption of macroalgae was performed and the ecological risk assessment of metal pollution in sediments of the southern Caspian Sea was presented using sediment quality guidelines (SQGs), enrichment factors (EF), contamination factors (CF), contamination degrees (CD), pollution load indices (PLI), geo accumulation indices (I geo), and potential ecological risk indices (RI). Next, machine-learning approaches were used to predict the stable isotope value of nitrogen in macroalgae, in which physicochemical information of water and heavy metal levels in macroalgae were used separately and together as predictor variables. Results indicated that simultaneous use of physicochemical properties of water and heavy metal levels resulted in the best prediction of isotopic nitrogen content. • Ecological risk assessment of metal pollution in sediments of Caspian Sea was studied. • Maximum allowable consumption of macroalgae by human was detected. • Machine learning approaches were used to predict nitrogen content in macroalgae. • Water physicochemical properties and metal levels predicted isotopic nitrogen content. [ABSTRACT FROM AUTHOR]

Multi-tissue trace elements (TEs), C, N concentrations and stable isotopes (δ13C, δ15N) of chick carcasses and eggs of Adélie and Emperor penguins were studied to i) provide reference data before the recent institution of the Ross Sea Marine Protected Area (Antarctica), and ii) provide conversion factors that allow estimating C, N, δ13C and δ15N in edible tissues from non-edible ones, thus improving the use of stable isotopes in contamination and trophic transfer studies. Higher concentrations of As, Cd, Cr, Cu, Hg, Mn and Pb were found in chick carcasses than in eggs, suggesting increasing contamination in recent decades and high toxicity risks for penguin consumers. Isotopic conversion factors highlighted small differences among body tissues and conspecifics. These values suggest that chick carcasses are reliable indicators of the energy pathways underlying the two penguin species, their trophic position in the food web and their exposure to TEs. • Trace element level in penguin eggs and chick tissues was higher than in past studies. • Opportunistic penguin predators and scavenger may be exposed to high toxicity risks. • Low vs. high C and N isotopic variability was found among chick tissues and egg parts. • We provided isotopic and elemental conversion factors between tissues and egg parts. [ABSTRACT FROM AUTHOR]

In this investigation, δ13C and δ15N isotope ratios and heavy metal levels were assessed in macroalgae, sediment samples, and benthic species from northern parts of the Persian Gulf and the Gulf of Oman. The highest δ15N values in algal samples (11±0.42), indicative of anthropogenic organic N inputs, were detected in the Sadaf region, whereas the lowest values (3.17 ± 0.12), indicative of anthropogenic inorganic inputs, were detected in the Parvaz region. In addition to sediment quality guidelines (SQGs), contamination factors (CF), enrichment factors (EF), contamination degree (CD), pollution load index (PLI), geo accumulation index (Igeo), and potential ecological risk index (RI) were employed to assess the anthropogenic influence on sediment quality and to describe the sensitivity of the biota to toxic heavy metals. The obtained results demonstrate that the analyzed elements (Mn, Cr, Ni, Pb, Zn, Cu, Co, and V) had no ecological risk in the sampling area. • δ15N in bivalves closely matched those observed in macroalgae. • The highest δ15N was observed at Sadaf, indicative of anthropogenic organic N inputs. • TOC/TN in sediments was less than 10, indicative of marine origin of organic carbon. • SBAF showed that accumulation of metals in algae samples was independent of sediments. • High EF levels of Cr, Pb and Mg in sediments confirmed their anthropogenic source. [ABSTRACT FROM AUTHOR]