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Changes in chlorophyll-a in English rivers over the last 49 years
Full text linkOngoing anthropogenically-driven environmental change in rivers (e.g. increasing air temperature, changing river flow extremes, increases in some key nutrients and decreasing concentrations of other key nutrients) is expected to impact ecological status and the magnitude and frequency of river algal blooms. In this study we considered 49 years of data from up to 161 river sites across England using water-column chlorophyll-a as a measure of suspended algal biomass and used a Bayesian hierarchical model to explore the potential drivers of changing river chlorophyll-a concentrations. Over a period of five decades the changes in chlorophyll-a concentrations in rivers across England showed a mixed pattern in relationships with key environmental variables and are almost evenly divided between significant increases and decreases in those chlorophyll-a concentrations. Most river sites showed no significant change in the probability of algal bloom events (chlorophyll-a > 15 μg/l; > 30 μg/l or 45 μg/l) over the last 49 years. These results indicate that there has been no clear directional response in algal bloom events across England’s rivers to the changing pressures, including climate change and large-scale reductions in P concentrations achieved over the last 49 years from improved wastewater treatment. By identifying these differing patterns in chlorophyll-a trends and responses across England, this large-scale spatio-temporal analysis provides a basis for exploring the multiple pressures driving chlorophyll-a responses at local to regional scales
Sub-Antarctic fjord circulation and associated icefish larval retention in a changing climate
Full text linkClimate change is impacting high-latitude fjord circulation with consequences for the transport of marine biota essential for supporting local ecosystems. Currently, little is understood about oceanographic variability in sub-Antarctic island fjords such as Cumberland Bay, the largest fjord on the island of South Georgia in the Southern Ocean. Cumberland Bay is split into two arms, West Bay and East Bay, and is a key spawning site for the ecologically and commercially important mackerel icefish. Through the use of a high-resolution three-dimensional hydrodynamic model, the seasonal cycle in Cumberland Bay is found to be driven by a combination of boundary forcing influencing shelf exchange and deep inflow, atmospheric forcing influencing near surface temperatures and flows and freshwater forcing via subglacial discharge driving upwelling and strong outflow. There is a complex three-dimensional flow structure with a high degree of variability on short timescales due to wind forcing. Using model flow fields to drive an individual-based model parameterised for mackerel icefish larvae spawned in Cumberland Bay, we identify West Bay as a key retention zone. Successful retention of mackerel icefish larvae is found to be sensitive to complex circulation patterns driven by winds, freshwater and fjord-shelf exchanges and to changes in physical processes linked to climate change such as meltwater runoff and föhn wind events. This study highlights the importance of oceanographic variability in influencing ecological processes in fjords in our changing climate
Combined effects of a pyrethroid insecticide and azole fungicide on lepidopteran growth analysed with DEB-TKTD modelling
No full textThe co-application of insecticides and fungicides is common in crop protection. Several studies in bees have identified synergism between pyrethroid insecticides and azole fungicides for mortality and sublethal endpoints. However, there are no studies that detail this synergism in Lepidopteran species. Here, we conduct a mixture exposure with cypermethrin and the fungicide prochloraz to assess their joint effects on mortality and sublethal endpoints for the moth Mamestra brassicae. The effects of pesticide exposure on sub-lethal endpoints over the life-cycle was simulated using energy budget TK/TD models from the DEBtox family. The model describes how organisms acquire and use energy for maintenance, growth, and reproduction, and how toxicants impact these processes. The approach could reliably simulate growth and survival of control and exposed moth larvae. The threshold for effects on survival was 0.92 mg/kg for cypermethrin and 2.78 mg/kg for prochloraz, and the threshold for energy budget (growth) was 1.7 10− 5 mg/kg for cypermethrin and 0.002 mg/kg for prochloraz. Prediction of mixture effects using additive assumptions frequently underestimated observed effects, indicating a pattern indicative of synergism, especially in lower concentration cypermethrin exposures. The success of the overall experimental and modelling approach, support the further applications of the methods and models used here for pesticide testing for other lepidopteran species. This approach may help improve the ecological risk assessment for pesticide mixtures
Mercury concentrations, habitat and trophic position of Antimora rostrata and Macrourus holotrachys from South Georgia (Southern Ocean)
Full text linkMercury (Hg) is a neurotoxic element that can harm marine wildlife. Hg can reach the Southern Ocean through atmospheric and oceanic currents. However, data on Hg in Southern Ocean deep-sea fishes remain scarce. Our study assessed the influence of biological and ecological factors on Hg bioaccumulation in two deep-sea species, blue antimora (Antimora rostrata) and bigeye grenadier (Macrourus holotrachys), inhabiting the South Georgia region. Specifically, we aimed to: 1) analyse the habitat and trophic position of both species; 2) understand how Hg concentrations vary between tissues (muscle, brain, liver and gills); 3) evaluate how biological (length and weight) and ecological characteristics (trophic position (δ15N) and habitat (δ13C)) influence Hg concentrations. Muscle tissue had the highest Hg concentrations in both species, while the liver in A. rostrata and gills in M. holotrachys had the lowest. Overall, A. rostrata exhibited lower Hg concentrations (51.0 ± 9.0) than M. holotrachys (62.0 ± 11.0). No significant relationships were found between Hg concentrations and length, weight nor trophic position of A. rostrata. In contrast, M. holotrachys showed a positive relationship between Hg concentrations and habitat in all tissues, whereas for length and weight this positive relationship was observed in most tissues except the brain. A. rostrata is a pelagic feeder, whereas M. holotrachys mostly feeds near the sea bottom, highlighting how feeding strategy and habitat influence Hg bioaccumulation. It also reveals unexpected patterns of Hg distribution among tissues, particularly in the brain, where M. holotrachys exhibited one of the highest Hg concentrations
Quantifying nutrient loss across particle size fractions in eroded tropical soils using 239+240Pu fallout radionuclides
Full text linkIn sub-Saharan Africa, where livelihoods depend on agriculture, steep valley slope cultivation intensifies soil erosion, threatening agricultural sustainability by depleting fertile topsoil of nutrients. This study measured soil erosion and deposition using 239+240Pu fallout radionuclides and associated macro- and micronutrient loss across particle size fractions in the Oroba Valley, Nandi Hills, Kenya. Three experimental plots were assessed: Plot 1 (conventional tillage) and Plot 2 (terraced agricultural system), both of which were cleared for cultivation in 1940, while Plot 3 (historically shrubland) was recently cleared in 2023. A stratified sampling design was used to collect soil samples, which were analysed for particle size distribution, organic matter (OM) content, pH, and total elemental composition using ICP-MS/MS. The MODERN model to estimate erosion and deposition rates using 239+240Pu inventories integrates nutrient losses across specific particle sizes to estimate the nutrients lost. There was severe soil erosion in Plots 1 and 2, with net losses of 13.68 t ha-¹ yr⁻¹ and 6.09 t ha-¹ yr⁻¹ , respectively, while Plot 3 showed minimal loss (0.32 t ha-¹ yr⁻¹), reflecting the protective effect of vegetative cover. Fine particles (100 µm) retained K and Mg. This study shows how 239+240Pu isotopes can be used as sensitive indicators of soil loss and fertility degradation, offering land management and conservation insights
Age of granitoid magmatism in South Georgia and correlations to southern Patagonia and the northern Antarctic Peninsula
Full text linkSouth Georgia forms one of the most isolated fragments of continental crust on Earth and lies in a remote location in the Southern Ocean. Its geology is dominated by Early Cretaceous back-arc turbidite successions that are in faulted contact with a late Palaeozoic – early Mesozoic accretionary complex. The accretionary complex includes fragments of a deformed accretionary prism and ophiolite that are intruded by a suite of granitoid plutons that are dated here. Granitoid magmatism has been identified from the Middle Jurassic (c. 163 Ma) and Late Cretaceous (c. 107 Ma, c. 86 Ma), which can be correlated with convergent margin magmatism from the southern (Fuegian) Andes and Cordillera Darwin of southern Patagonia, and the northern Antarctic Peninsula, with the Late Cretaceous magmatism restricted to the western parts of each area. These correlations support earlier findings that established a contiguous relationship between the southeast sector of South Georgia and southernmost Patagonia (south of the Magallanes fault zone) and the northern sector of Graham Land (Antarctic Peninsula)
Unpouching Peracarida relationships with ultraconserved elements
No full textPeracarida is a large group containing twelve orders of brooding crustaceans, including the large orders Amphipoda, Isopoda, Tanaidacea and Cumacea, and a series of smaller orders, some restricted to isolated habitats. The relationships of Peracarida have been disputed and little effo has been made to use extensive taxon sampling with a modern genetic approach. Here we present a novel probe set of ultraconserved elements (UCEs) developed for peracarids to investigate higher-level relationships using newly collected Antarctic material and collection-based specimens. Concatenated and coalescent-based analyses across different levels of occupancy matrices recovered strong support for the monophyly of Peracarida and for the clade Mancoida (Isopoda + Tanaidacea + Cumacea). Thermosbaenacea was consistently resolved as the sister group to all remaining peracarids. Within Amphipoda, our results contrast with previous phylogenies by placing Corophiida and Hyperiidea as early-branching lineages. In Isopoda, Oniscidea was recovered as monophyletic and concordant with morphological hypotheses. These findings provide one of the first phylogenomic frameworks for Peracarida and demonstrate the promise of UCEs for resolving long-standing questions in malacostracan evolution
Unifying occupancy-detection and local frequency scaling (Frescalo) models
Full text linkFrescalo’s “local frequency scaling” and classical occupancy-detection models both seek to recover true species-occurrence signals from imperfect data. In this paper, we show that the two approaches rest on the same underlying detection mathematics. Occupancy models treat each site’s repeat visits as independent detection trials and separately estimate occupancy probability and per-visit detectability. Frescalo, by contrast, pools data across ecologically defined neighbourhoods, standardises for uneven effort, and infers a single discovery rate per species plus a species-specific “time-factor” to capture time trends. The occupancy–detection Bernoulli formulation can be linked directly to Frescalo’s Poisson/discovery framework, where occupancy and detectability combine into one rate parameter (which, when sampling is light, closely matches the product of occupancy and per-visit detectability). This connection clarifies how Frescalo’s neighbourhood-scale and time corrections function as a coarser-scale analogue of repeat-visit models. By casting Frescalo in occupancy modelling terms, we hope to promote further investigation into the adoption of occupancy model diagnostics, extensions and other tests within Frescalo analyses, improving transparency and rigour when working with less-structured biodiversity data
Enhanced water stress on vegetation productivity with climate warming over the Northern Hemisphere
No full textWater stress is a major environmental factor limiting vegetation productivity, however, large interactions between atmospheric and soil dryness still hinder a complete understanding of the main cause of the widespread drought-related decreased vegetation productivity. In this study, we investigated inter-annual changes in gross primary productivity during 1982 to 1998 and 1998 to 2018 using two independent remote sensing products. We also analyzed the impacts of temperature, soil moisture, and vapor pressure deficit on gross primary productivity trends during 1982 to 1998 and 1998 to 2018 to explore the causes of gross primary productivity declines during recent decades. Results show that gross primary productivity trend during 1998 to 2018 tends to stall after the year 1998 concurrent with a significant enhancement of a positive vapor pressure deficit trend during 1998 to 2018, particularly in forests, grasslands, and warmer regions. In the Northern Hemisphere, whilst increasing vapor pressure deficit plays a dominant role in weakening the gross primary productivity trend from 1998 to 2018, changing soil moisture and temperature also influences the trends as identified in different regional responses. In addition, results from 8 dynamic global vegetation models showed that the dynamic vegetation models fail to capture the inter-annual changes in gross primary productivity, likely due to an overestimation of gross primary productivity responses to soil water
What controls current and future background vulnerability of rivers to eutrophication and pathogens?
No full textTo have confidence managing rivers under changing environmental pressures we must demonstrate thorough understanding of their response. Models express our understanding quantitatively. For 30 rivers in England, catchment attributes were combined with hydro-climatic time-series in hourly-resolution water quality model applications over a 15-year period. Retaining high-resolution input observations within simplified catchment representations makes geographically widespread application of process-based models achievable, whilst still representing diurnal cycles and quantifying ecosystem functioning. Background vulnerability assessments revealed eutrophic conditions (>30 µg chlorophyll-a L−1 as diatoms), oxygen stress (9 CFU mL−1 of the faecal indicator organism, Escherichia coli) in 10, three, and 11 rivers respectively. Pathogen risk only considered treated effluent sources, not covering intermittent discharges or livestock contributions. By 2050, under a backdrop of uncertain change in climate, river quality is expected to worsen by 4.7 % for 10th percentile DO and 27.5 % for 90th percentile E. coli, with urban influence strongly determining sensitivity to change. Whilst deoxygenation vulnerability appears not widespread, faster future deteriorations are projected than elsewhere, such as in the USA. Eutrophication shows much spatio-temporal variability in change (with an average 5.1 % decrease in 90th percentile chlorophyll-a), seemingly controlled by local hydraulic factors and top-down biotic interactions. Across all indicators, riparian condition and channel hydrodynamics appear more important in controlling variability than regional differences in hydro-climatology. Assessment of comprehensive government-mandated interventions suggests partial offsetting of worsening DO, and further eutrophication decrease. E. coli deteriorations are effectively offset, although land management actions alone lead to further worsening
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