δ15N Values Research Articles

Stable isotopic and stomach content analyses reveal changes in the trophic level and feeding habit of large-head hairtail (Trichiurus lepturus) in the northern South China Sea

The feeding habit of large-head hairtail (Trichiurus lepturus) in the northern South China Sea was investigated through isotopic and stomach content analyses. The isotopic features of the hairtail at the same body size differed among regions, with the fish in coastal waters presenting higher δ15N and δ13C values compared to those in the open sea, indicating different trophic levels (TL), food habits, and isotopic baselines. According to the partial correlation of water depth with δ15N values, the sampling stations were divided into three regions based on the depth of water: coastal (20–40 m), near coastal (60–80 m), and open sea (100–200 m) regions. In the coastal region, the hairtail from stations affected by the Pearl River plume exhibited lower δ15N and δ13C values. The stomach content analysis indicated different feeding habits of the hairtail from different regions. The hairtail in the coastal and near coastal waters fed more on fish and less on crustaceans compared to the hairtail in the open sea. The relationship between δ15N and fish size exhibited two contrary patterns. First, the δ15N values increased with increasing preanal length in the hairtail sampled from the water depth of 30–40 m in section F (in fish with preanal length < 200 mm) and those samples from the water depth of 100–200 m. This finding reflected an ontogenetic shift in diet and TL. However, the δ15N values tended to decrease with the increasing preanal length of the hairtail samples collected from the water depth of 30–40 m in section F (fish with a preanal length of ~200–300 mm). These findings suggested that under the conditions of insufficient availability of high-quality prey, the larger hairtail fed more on low-TL prey to compensate for the increase energy demand, arising due to growth, which led to the observed decrease in δ15N values.

Seasonal variations of macrozoobenthic community trophic structure in the waters adjacent to the seaweed beds of Dalian Island in the North Yellow Sea.

To investigate the effects of algal detritus export on the trophic structure of macrozoobenthic community in the adjacent benthic habitat during the bloom and decline of macroalgae, we collected macrozoobenthos from the adjacent sea area of Dalian Island in the North Yellow Sea in May (the algal bloom period) and August (the algal decay period) of 2020. We quantifyied the seasonal changes in the trophic structure of macrozoobenthic community by using carbon and nitrogen stable isotope techniques. Results showed that δ13C and δ15N values of macrozoo-benthos in May ranged from -23.14‰ to -14.24‰, 6.21‰ to 12.90‰, respectively, and -22.36‰ to -14.13‰, 5.33‰ to 12.00‰, respectively in August. Results of PERMANOVA analysis showed that δ13C values of macrozoobenthos differed significantly between the two months, while δ15N values were not significantly different. Based on the Euclidean distance, the macrozoobenthic communities in both months could be classified into five trophic functional groups. The trophic levels of macrozoobenthos ranged from 2.00 (Nitidotellina minuta) to 3.97 (Glycera onomichiensis) in May and from 2.00 (N. minuta) to 3.96 (G. onomichiensis) in August. The δ13C range, δ15N range, mean centroid distance, total area and corrected standard ellipse areas which represented community trophic structure indices in August were higher than those in May. Our results indicated that the trophic diversity level and trophic niche width of the macrozoobenthic community in the adjacent sea area of the seaweed bed were higher in the algal decline season.

A review of recent compound-specific isotope analysis studies applied to food authentication.

Compound-specific stable isotope analysis (CSIA) of food products is a relatively new and novel technique used to authenticate food and detect adulteration. This paper provides a review of recent on-line and off-line CSIA applications of plant and animal origin foods, essential oils and plant extracts. Different food discrimination techniques, applications, scope, and recent studies are discussed. CSIA δ13C values are widely used to verify geographical origin, organic production, and adulteration. The δ15N values of individual amino acids and nitrate fertilizers have proven effective to authenticate organic foods, while δ2H and δ18O values are useful to link food products with local precipitation for geographical origin verification. Most CSIA techniques focus on fatty acids, amino acids, monosaccharides, disaccharides, organic acids, and volatile compounds enabling more selective and detailed origin and authentication information than bulk isotope analyses.. In conclusion, CSIA has a stronger analytical advantage for the authentication of food compared to bulk stable isotope analysis, especially for honey, beverages, essential oils, and processed foods.

Opportunistic consumption of marine pelagic, terrestrial, and chemosynthetic organic matter by macrofauna on the Arctic shelf: a stable isotope approach.

Macrofauna can contribute substantially to the organic matter cycling on the seafloor, yet the role of terrestrial and chemosynthetic organic matter in the diets of microphagous (deposit and suspension) feeders is poorly understood. In the present study, we used stable isotopes of carbon and nitrogen to test the hypothesis that the terrestrial organic matter supplied with river runoff and local chemosynthetic production at methane seeps might be important organic matter sources for macrofaunal consumers on the Laptev Sea shelf. We sampled locations from three habitats with the presumed differences in organic matter supply: "Delta" with terrestrial inputs from the Lena River, "Background" on the northern part of the shelf with pelagic production as the main organic matter source, and "Seep" in the areas with detected methane seepage, where chemosynthetic production might be available. Macrobenthic communities inhabiting each of the habitats were characterized by a distinct isotopic niche, mostly in terms of δ13C values, directly reflecting differences in the origin of organic matter supply, while δ15N values mostly reflected the feeding group (surface deposit/suspension feeders, subsurface deposit feeders, and carnivores). We conclude that both terrestrial and chemosynthetic organic matter sources might be substitutes for pelagic primary production in the benthic food webs on the largely oligotrophic Laptev Sea shelf. Furthermore, species-specific differences in the isotopic niches of species belonging to the same feeding group are discussed, as well as the isotopic niches of the symbiotrophic tubeworm Oligobrachia sp. and the rissoid gastropod Frigidoalvania sp., which are exclusively associated with methane seeps.

Isotopic niche shift in the sea urchins Echinometra lucunter and E. viridis after massive arrivals of Sargassum in the Mexican Caribbean

In the Mexican Caribbean, the decomposition of unusual amounts of Sargassum (Sargassum fluitans and S. natans) has caused changes in the benthic community. The aim of this study was to evaluate the impact of massive pelagic Sargassum arrivals on the trophic structure of sea urchins Echinometra lucunter and E. viridis, using stable isotopes of carbon (δ13C) and nitrogen (δ15N) to identify variations in relative proportions of assimilated primary producers in two reef lagoons (Xahuayxol and Xcalak) in the southern Mexican Caribbean. The survey considered two scenarios: (1) with massive Sargassum arrivals (WIMA) in 2018 and (2) without massive Sargassum arrivals (WOMA) in 2017. Results revealed a decreased in δ15N and δ13C values during WIMA in primary producers and sea urchins. Furthermore, the isotopic mixing models (MixSIAR) indicated that both E. lucunter and E. viridis preferably consumed Halimeda spp. and Thalassia testudinum. The isotopic niche width obtained from Stable Isotope Bayesian Ellipses in R (SIBER) analysis showed differences between species and localities. In Xahuayxol during WIMA the corrected standard ellipse area (SEAc) of E. lucunter increased while that of E. viridis decreased. However, the latter species had a significant increase in trophic level. In Xcalak during WIMA, for both sea urchins, the SEAc increased and overlapped while the trophic levels increased significantly. Results suggest that E. viridis in Xahuayxol was better adapted to changes in resource availability, while the niche expansion of E. lucunter in Xahuayxol and E. lucunter and E. viridis in Xcalak suggest that sea urchins exhibited a starvation stage due to a decrease in food resources.

Trophic response of fishes to rainfall variability in a temperate estuarine system of Korea: A stable isotope approach

To assess the basal resources supporting food webs impacted by rainfalls, we compared stable isotope ratios (δ13C and δ15N) of fish consumers and organic matter sources between up- and down-sites in an estuary between seasons (June and September) and years (2018 and 2019) that showed different patterns of summer monsoon. Our study showed seasonal differences in the δ13C and δ15N values of basal resources and fish consumers in both years. At the up-site, significant differences of δ13C values of fish consumers were found between years, resulting from changing rainfall period, thereby causing a shift in food availability from terrigenous organic matter to periphyton. In contrast, at the down-site, the consistent isotopic values of fishes were observed in both years, suggesting that rainfall shift has a negligible impact on resources for fishes. Overall, the annual shift in resources for fishes in the estuary may be controlled by contrasting rainfall events.

Fertilizer restrictions are not sufficient to mitigate nutrient pollution and harmful algal blooms in the Indian River Lagoon, Florida

In Florida's Indian River Lagoon (IRL), anthropogenic eutrophication has resulted in harmful algal blooms and catastrophic seagrass losses. Hoping to improve water quality, policy makers enacted fertilizer bans, assuming that this would reduce the nitrogen (N) load. To assess the effectiveness of these bans, seawater and macroalgal samples were collected at 20 sites “pre” and ~ five-years “post” bans and analyzed to determine concentrations of dissolved nutrients and stable nitrogen isotope values (δ15N). Higher concentrations of ammonium and nitrate were observed post-ban and macroalgal δ15N values increased. A comparison of nutrient concentrations and δ15N between brown tide (Aureoumbra lagunensis) blooms indicated that the post-ban bloom was more strongly N-enriched with higher δ15N values than the pre-ban bloom, which had depleted values in the range of fertilizers. These data indicate a primary role of human waste influence in the IRL, suggesting that current management actions have been insufficient at mitigating eutrophication.

Hg bioaccumulation in the aquatic food web from tributaries of the Three Gorges Reservoir, China and potential consumption advisories

The Three Gorges Reservoir (TGR) holds the distinction of being China's largest reservoir, and the presence of pollutants in the fish from the reservoir have a direct impact on the health of local residents. Thus, 349 fish specimens of 21 species and 1 benthos (Bellamya aeruginosas) were collected from four typical tributaries of the TGR from 2019 to 2020. These specimens were analyzed for the concentrations of total mercury (THg) and methylmercury (MeHg), and some representative samples were tested for δ13C and δ15N values to reveal the characteristics of bioaccumulation and biomagnification. The maximum safe daily consumption was estimated based on the oral reference dose (0.1 μg kg−1 bw/day according to US-EPA, 2017). The results showed that the mean THg and MeHg concentrations in fish from the TGR tributaries were 73.18 ± 49.21 ng g−1 and 48.42 ± 40.66 ng g−1, respectively, with the trophic magnification factors (TMFs) of THg and MeHg being 0.066 and 0.060, respectively. Among all the fish species in the tributaries, the highest daily maximum safe consumption amount was 1253.89 g for S. asotus consumed by adults, while the lowest was 62.88 g for C. nasus consumed by children.

Sources of Polycyclic Aromatic Hydrocarbons in Fecal Pellets of a Marphysa Species (Annelida: Eunicidae) in the Yoro Tidal Flat, Japan.

The fecal pellets of Marphysa sp. E sensu Abe et al. (2019) (Annelida, Eunicidae) living in the Yoro tidal flat (Ichihara, Chiba, Japan) contain high levels of polycyclic aromatic hydrocarbons (PAHs), and the concentrations rapidly decrease over time. To investigate the origin of the high-concentration PAHs in the fecal pellets and food sources of the worms, the PAH concentrations, carbon and nitrogen stable isotope ratios (δ13C and δ15N), total organic carbon, and total nitrogen for two types of sediment (sands and reduced muds), fecal pellets, and the body of the worms were determined. The PAH concentrations and chemical properties of the fecal pellets were similar to those of the reduced muds (20-30 cm sediment depth). The δ13C, δ15N, and C/N values of reduced muds were the same as the typical values of terrestrial C3 plants, suggesting that reduced muds were derived from terrestrial plants. These data indicated that the worms selectively take up reduced muds containing high levels of PAHs. The δ13C and δ15N values of the worm bodies indicated that the worms did not use the organic carbon derived from terrestrial C3 plants as primary nutrition. Taking into consideration their selective uptake of reduced muds, excretion, and subsequent rapid decrease of PAHs in the fecal pellets, the worms could contribute to the remediation of chemical pollutants in the tidal flat sediments.

Isotopic reconstruction of the early life experience of individuals from the early Bronze age Vliněves site (Czech Republic)

This paper provides information on the early life experience of people from the Central European Early Bronze Age, reconstructed on the basis of the stable carbon (δ13C) and nitrogen (δ15N) isotopic values from dentine serial sections of individuals from Vliněves (Czech Republic). This site yielded the largest known quantity of human remains from the Únětice culture, coming from both regular graves and settlement features. In this pilot study 27 individuals aged between 7 and 30–40 years were investigated.The average value of maximal nitrogen isotopic offset within the isotopic profile (Δ15Nmax) was 4.1 ± 1.2 ‰, which is higher than the recommended range for weaning under healthy circumstances. The reported ages at the first decrease in δ15N values, as well as at the final smoothing of the nitrogen isotopic curve, suggest that all individuals were weaned before 2.2 years of age. Most individuals (n = 20) showed positive covariance between δ15N and δ13C values during infancy and early childhood, which is the typical isotopic pattern of breastfeeding. Post-weaning isotopic values were typical for a terrestrial C3 based diet and suggest limited access to animal protein on the part of individuals buried in settlement pits. The mild increase in δ15N values in later childhood suggests that the explanation of the increased Δ15Nmax lies rather in the special character of the early childhood diet than in the common presence of nutritional/physiological stress. The similarities in the isotopic profiles of individuals from multiple burials suggest the shared dietary behaviour of these individuals.

The formation environment of Carboniferous karstic bauxite deposits in the central North China Craton: Insights from nitrogen isotopes and geochemical proxies

Over 5 billion tons of karstic bauxites are hosted in the Late Carboniferous Benxi Formation in the North China Craton (NCC). However, the bauxite formation environment in the central NCC remains unknown. The geological, mineralogical, geochemical, nitrogen concentrations, and δ15N isotope evidence of the Huilong and Shangwutou bauxite deposits in the central NCC was conducted, aiming to clarify the formation environments. Typically, bauxites in the central NCC contains three layers from bottom to top: Fe-bearing claystone/clayey ironstone, bauxite ore, and bauxitic claystone. The Fe-bearing claystone/clayey ironstone is composed of kaolinite, goethite, and hematite; the bauxite ore is composed of diaspore, kaolinite, but also minor hematite, ilmenite, and svanbergite; and the bauxitic claystone consists of kaolinite, but also some diaspore and goethite. Diaspores coexisted extensively with hematite, anatase, and svanbergite, forming cryptocrystalline matrix of bauxites, suggesting that they may be formed during early diagenesis. Geochemical discriminant diagrams also indicated that two deposits were primarily affected by the hydrogenous deposition and early diagenesis, and no sedimentary recirculation. The ∑REEs concentrations and fractionation (Prn/Ybn) features along the profiles mainly concentrated in the bottom bauxite ore, which reflected that the pH values could be alkaline in bottom bauxite ore, and decreased weakly acidic for the central bauxite ore to bauxitic claystone along the profiles upwards. Combining the δ15N data with two geochemical redox proxies, and the widely coexistence of diaspore and hematite, indicated that the two deposits mainly formed under suboxic conditions, and thus denitrification was the predominant process in nitrogen cycling. The δ15N values are positively correlated with paleosalinity proxies, indicating that the higher saline bottom water may lead to a strong vertical density differential and water-column stratification, conducing to forming suboxic restricted pore-water environments.

Stable Nitrogen Isotopes as an Effective Tool for Estimating the Nitrogen Demand of Broussonetia papyrifera (L.) Vent Seedlings under Variable Nitrate Concentrations

Poor growth is often observed in artificial young forests due to insufficient inorganic nitrogen in karst soils. However, little is known about the assimilatory demand of the whole plant for nitrate and the partitioning of nitrate assimilation in roots and leaves in woody plants grown in karst habitats. In this study, Broussonetia papyrifera (L.) Vent (B. papyrifera) seedlings were grown under nearly hydroponic conditions. The isotope mass balance approach was employed to quantify the δ15N values of the N assimilates in plant organs and in whole plants for B. papyrifera seedlings grown at different nitrate concentrations. The δ15N values of the N assimilates in the whole B. papyrifera seedlings showed a rising trend with increasing nitrate concentration. Increasing the supply of nitrate decreased the leaf–root difference in the δ15N values of the N assimilates for B. papyrifera seedlings. Quantifying the δ15N values of N assimilates in the whole B. papyrifera seedlings grown under different nitrate concentrations contributes to estimating the assimilatory demand of the B. papyrifera seedlings for nitrate. The leaf–root difference in the δ15N values of the N assimilates can be used to estimate the partitioning of nitrate assimilation in the roots and leaves.

Trophic ecology of Angolan cold-water coral reefs (SE Atlantic) based on stable isotope analyses

Cold-water coral (CWC) reefs of the Angolan margin (SE Atlantic) are dominated by Desmophyllum pertusum and support a diverse community of associated fauna, despite hypoxic conditions. In this study, we use carbon and nitrogen stable isotope analyses (δ13C and δ15N) to decipher the trophic network of this relatively unknown CWC province. Although fresh phytodetritus is available to the reef, δ15N signatures indicate that CWCs (12.90 ± 1.00 ‰) sit two trophic levels above Suspended Particulate Organic Matter (SPOM) (4.23 ± 1.64 ‰) suggesting that CWCs are highly reliant on an intermediate food source, which may be zooplankton. Echinoderms and the polychaete Eunice norvegica occupy the same trophic guild, with high δ13C signatures (-14.00 ± 1.08 ‰) pointing to a predatory feeding behavior on CWCs and sponges, although detrital feeding on 13C enriched particles might also be important for this group. Sponges presented the highest δ15N values (20.20 ± 1.87 ‰), which could be due to the role of the sponge holobiont and bacterial food in driving intense nitrogen cycling processes in sponges’ tissue, helping to cope with the hypoxic conditions of the reef. Our study provides first insights to understand trophic interactions of CWC reefs under low-oxygen conditions.

Promoting the use of non-lethal sample collection for analysing the trophic relationships of inshore flatfish populations using stable isotope analysis

Trophic studies on inshore flatfish populations usually rely on stomach content analyses and/or stable isotope analysis (SIA) of dorsal white muscle that involves the collection of samples from euthanised fishes. To promote the use of non-lethal sampling methods in inshore flatfish populations of relatively high intrinsic angling and/or ecological value, the applicability of using fin tissue and/or epidermal mucus as non-lethal alternatives to muscle in SIA studies was assessed for European flounder Platichthys flesus, plaice Pleuronectes platessa and common sole Solea solea. In all species, the results indicated that there were significant differences in the δ13C and δ15N values of dorsal muscle versus their fin and mucus samples. These significant differences were, however, predictable by linear regression, with regression coefficients produced for converting fin and mucus SI values to the equivalent muscle SI values. The use of combined data across the species also provided regression coefficients for converting fin and mucus SI to equivalent muscle values for flatfish populations more generally. These results indicated that there are tissue alternatives to dorsal muscle that can be applied to the SIA of flatfish populations, with these tissues able to be collected using non-lethal sampling methods.

Sources of organic matter and carbon stocks in two mangrove sediment cores and surface sediment samples from Qinglan Bay, China

The carbon stocks (Corg stocks) in mangrove sediments and the distribution and source changes of sedimented organic matter in Qinglan Bay are not understood as the mangrove forests decrease. In this paper, we collected two sediment cores in the interior mangrove and 37 surface sediment samples from mangrove-fringe, tidal flat and subtidal habitats and then analysed the total organic carbon (TOC), total nitrogen (TN), and the stable organic carbon isotope (δ13C) and nitrogen isotope (δ15N) in the sediment samples to obtain the organic matter sources and carbon stocks in two different mangrove sediment cores from Qinglan Bay. The δ13C and TOC/TN values showed that mangrove plants and algae were the main sources of organic matter. Relatively high contributions of mangrove plants (>50 %) were distributed in the mangrove areas in Wenchang estuary, the northern region of Bamen Bay and the eastern side of the Qinglan tidal inlet. The enriched δ15N values might be related to anthropogenic nutrient inputs, including increased aquaculture wastewater, human sewage and ship wastewater. The Corg stocks in cores Z02 and Z03 were 357.79 Mg C ha−1 and 265.78 Mg C ha−1, respectively. This Corg stock difference might have been related to the salinity and the benthos activities. The high Corg stock values measured in Qinglan Bay were caused by the mangrove maturity and stand age. The total Corg storage of the mangrove ecosystem in Qinglan Bay was estimated to be approximately 263.93 Gg C. This study contributes to organic carbon stocks and sources of sedimented organic matter in global mangroves.

Multi‐disciplinary study of a late Pleistocene woolly rhinoceros found in the Pannonian Basin and implications for the contemporaneous palaeoenvironment

ABSTRACTExcavation campaigns conducted at the Pécel‐Kis hársas site (Hungary) between 2014 and 2017 yielded the remains of a mature female woolly rhinoceros (Coelodonta antiquitatis) and six lithic artefacts. Radiocarbon dating confirmed that the rhinoceros died ca. 20.4k cal a bp, at the very end of the Last Glacial Maximum and, considering the position of the artefacts when found, it was probably killed by Epigravettian hunters. Based on dental analyses of the specimen, a vigorous lichen‐ (and possibly moss‐)consuming diet could be inferred for the end of the animal's lifetime. Based on Sr results, we can exclude the possibility of long‐range migration. In accordance with the optimum environmental demands of the foraging lichen, the low δ18O value of osseous material implies a relatively cold contemporaneous climate with a calculated mean annual air temperature of around 0.7 °C. Meanwhile, the extremely low δ15N value may have resulted from the proximity of the discontinuous permafrost zone and some intensive soil dislocation. Consequently, poor vegetation and an open, tundra‐like habitat can be assumed to have been dominant at the site at that time, which is also supported by palaeoenvironmental modeling experiments.

Using 15N to determine the metabolic fate of dietary nitrogen in North Pacific spiny dogfish (Squalus acanthias suckleyi).

Marine elasmobranchs are ureosmotic, retaining large concentrations of urea to balance their internal osmotic pressure with that of the external marine environment. The synthesis of urea requires the intake of exogenous nitrogen to maintain whole-body nitrogen balance and satisfy obligatory osmoregulatory and somatic processes. We hypothesized that dietary nitrogen may be directed toward the synthesis of specific nitrogenous molecules in post-fed animals; specifically, we predicted the preferential accumulation and retention of labelled nitrogen would be directed towards the synthesis of urea necessary for osmoregulatory purposes. North Pacific spiny dogfish (Squalus acanthias suckleyi) were fed a single meal of 7 mmol l-1 15NH4Cl in a 2% ration by body mass of herring slurry via gavage. Dietary labelled nitrogen was tracked from ingestion to tissue incorporation and the subsequent synthesis of nitrogenous compounds (urea, glutamine, bulk amino acids, protein) in the intestinal spiral valve, plasma, liver and muscle. Within 20 h post-feeding, we found labelled nitrogen was incorporated into all tissues examined. The highest δ15N values were seen in the anterior region of the spiral valve at 20 h post-feeding, suggesting this region was particularly important in assimilating the dietary labelled nitrogen. In all tissues examined, enrichment of the nitrogenous compounds was sustained throughout the 168 h experimental period, highlighting the ability of these animals to retain and use dietary nitrogen for both osmoregulatory and somatic processes.

Holocene relationships between climate, waterfowl, and lacustrine nutrient cycling at Kettle Lake, North Dakota, USA

Avian populations can substantially influence lacustrine nutrient loading and biogeochemical cycling through guano deposition. Here, we examine the influence of climate-forced avian migration throughout the Holocene on Kettle Lake, North Dakota, using stable nitrogen and carbon isotope values (δ15N, δ13C) of lake sediment organic matter. Carbon content and δ13C values are negatively correlated with δ15N and appear to be driven by changes in charcoal abundance and watershed vegetation, respectively. We find enriched δ15N values when the guano mineral struvite is present in the lake sediment core in the early to Mid-Holocene. A strong δ15N-percent Nitrogen content relationship during periods with struvite, relative to periods without struvite, indicates that guano deposition from mass bird visitations altered past nitrogen cycle processes, likely through enhanced denitrification. These results attest to the ability of waterfowl to alter lacustrine N-cycling in a mid-continental North American lake, and indicate that paleo-N data in this particular lake are recording a unique history that does not necessarily represent regional paleoenvironmental conditions. However, a significant, positive relationship between δ15N and Ambrosia and Amaranthaceae pollen abundance suggests avian visitation and its impacts on the N-cycle occurred during periods of anomalously wet summers superimposed on the background conditions of early to Mid-Holocene drought.

Study of filtration, digestion and absorption of Chlorella pyrenoidosa by juvenile Chinese mitten crab (Eriocheir sinensis)

While previous studies have reported that the zoea and megalopa stages of Eriocheir sinensis can filter phytoplankton in water bodies, it remains unclear whether juvenile crab (E. sinensis) possess the same ability. The objective of this study was to investigate whether juvenile crabs (average body weight 9.51 ± 1.57 g) can filter and absorb phytoplankton. Firstly, stomach and intestinal contents of juvenile crabs were analyzed, and their filter-feeding ability was tested under different pellet feed ratios using a blood cell counter. It was found that juvenile crabs cultured in Chlorella pyrenoidosa suspension contained large quantities of the algae in their stomach and intestinal contents compared to the control group, which were cultured with no C. pyrenoidosa. Additionally, the filtration rate of juvenile crabs to C. pyrenoidosa decreased with the increase of pellet feed proportion. Finally, the ability of juvenile crab to digest and absorb C. pyrenoidosa was studied through 15N stable isotope labeling technology. The δ15N values in muscle and intestinal tissue of group filtered with 15N labeled C. pyrenoidosa were significantly higher than group filtered with unlabeled C. pyrenoidosa and control group. The results indicated that juvenile crab could filter, digest and absorb C. pyrenoidosa, expanding our understanding of the feeding ecology of this species. This has significant implications for the ecological culture of E. sinensis and the potential for sustainable aquaculture practices.

The patchiness of soil 13C versus the uniformity of 15N distribution with geomorphic position provides evidence of erosion and accelerated organic matter turnover

Farming on hillslopes often affects the accumulation and loss of soil organic matter (SOM) depending on slope position and cropping patterns. Most hillslope studies focus on soil movement to characterize SOM turnover under erosive conditions. In this study, we trace erosion and characterize agronomic practices erosive impacts on SOM translocation and transformation along geomorphic positions. To achieve this, we assessed the horizontal distribution (upper 15 cm) and vertical distribution (to 100 cm profiles) of soil δ15N and δ13C isotope abundance individually. We mapped the spatial distribution of δ13C, δ15N, and SOM turnover indices as a novel approach to tracing erosion and degradation of SOM in the field. Except for tillage (conventional vs. reduced tillage), other individual agricultural practices (residue removal with no cover crop vs. retaining residuals, cover cropping, and fertilizer 0, 40, and 80 kg ha-1 nitrogen) caused no significant shifts in δ15N and δ13C values in topsoil (0–15 cm). Among the evaluated factors, topography and depth predicted soil δ15N and δ13C profiles. Trends in δ13C vs. δ15N showed a wider range of δ13C values in topsoil of upslope plots under reduced tillage, while in the depositional location, conventional tillage had the same effect. This suggests erosion under reduced tillage occurred. Erosion and accelerated decomposition gradually slowed δ13C enrichment with soil depth. Digital soil mapping approach depicted low continuity of δ13C vs. high continuity of δ15N with geomorphic position We attributed the intermediate δ13C values, and steeper slope of δ13C against logarithm of soil organic carbon (SOC) across the slope to erosion and high SOM turnover, particularly of recently added plant inputs. Current results support the prediction of intensive vs. conservation practices’ effects on upslope soil stability and the fate of SOM in both topsoil and at depth of sloping farmlands.