Increased Nutrient Inputs Research Articles

Quaternary floodings in the Zanzibar Channel (NW Indian Ocean, Tanzania) – Identifying palaeoceanographic patterns and palaeoenvironment using a multiproxy study

Multiproxy palaeoenvironmental analyses represent a promising tool for complex reconstructions of continent-sea or air-sea interactions in shallow marine environments. This is in particular illustrated by the case of strong climatic variations in the late Pleistocene to mid-Holocene. A unique combination of geochemical proxies (143Nd/144Nd, 87Sr/86Sr, δ18O and δ13C isotope analyses, n-alkane analysis and biomarker study) together with micropalaeontological data (foraminifera, calcareous nannoplankton and diatoms) allowed to precisely characterise two marine floodings (mid-Holocene and late Pleistocene) in the Zanzibar Channel (NW Indian Ocean, Tanzania). The climate of the late Pleistocene interval was arid compared to the Holocene. The fully oligotrophic environment characteristic of the late Pleistocene flooding (∼115–130 ka) was episodically interrupted by intervals of intense rainfall with episodes of increased nutrient input during the mid-Holocene (∼5–10 ka). The dominance of seaweed meadows in the Holocene and late Pleistocene contrasts with the modern environment dominated by seagrass ecosystems. Relatively non-radiogenic εNd signatures in the Zanzibar Channel during the Holocene and late Pleistocene indicate a strong influence of riverine input draining the Precambrian basement on the African mainland. The main inflow of seawater was from the south, consistent with the flow direction of the East African Coastal Current and the directions of the March to October monsoon winds. A promising tool for future applications as indicators of seagrass/seaweed meadow type ecosystems may be the presence of specific diatom taxa.

How do additions of submerged macrophytes, large-bodied cladocerans and nutrients impact tropical plankton communities? A mesocosm experiment

AbstractWe investigated the individual and combined impacts of manipulation of submerged macrophytes, large-bodied cladocerans, and nutrients on plankton communities in a tropical hypereutrophic shallow reservoir. We tested how the addition of the macrophyte Ceratophyllum demersum, the cladoceran Sarsilatona serricauda, and nutrients affected phytoplankton and zooplankton diversity, composition, and structure using mesocosms and a factorial design (3 × 3) with eight treatments. During the experiment, the reservoir experienced an intense bloom of algae (207 mg l−1 of biomass), mainly composed of cyanobacteria (> 98%). The submerged macrophytes were found to significantly reduce the biomass of cyanobacteria (by 85%), diatoms (80%), and green algae (78%), while the addition of zooplankton and nutrients led to a 96% reduction for diatoms. While both submerged macrophytes and the added cladocerans impacted the native zooplankton community, the macrophytes exerted stronger effects on phytoplankton and zooplankton diversity, composition, and structure. Intriguingly, nutrient addition did not alter the main effects of macrophytes and large cladocerans. Our findings reveal the positive potential of introducing submerged macrophytes in tropical shallow lakes, even at a low to moderate percentage of the volume inhabited, to control toxic cyanobacterial blooms. Under our experimental conditions, the method was effective even without extra zooplankton grazing and at increased nutrient input.

Watershed grassland fires drive nutrient increases in replicated experimental ponds

Kelly, AG, Harris, TD. 2024. Watershed grassland fires drive nutrient increases in replicated experimental ponds. Lake Reserv Manage. 40:303–316. Forest and grassland fires have been increasing in frequency due to anthropogenic climate change and fire suppression-focused land management practices. Fire has frequently been observed in lake watersheds, yet links between fire ecology and limnology are not well understood, especially in grassland ecosystems. We conducted a 21-d replicated whole pond experiment to determine the effects of burning on lakes within grassland ecosystems. We examined physicochemical parameters and the phytoplankton concentration and community composition in control and treatment (burned) ponds. Total phosphorus, total dissolved phosphorus, soluble reactive phosphorus, and nitrate increased significantly following burning. The total nitrogen:total phosphorus and total dissolved nitrogen:total dissolved phosphorus ratios decreased significantly following burning. Increased nutrient inputs from burned material led to greater mean phytoplankton concentrations in the treatment ponds compared to the control ponds; however, no statistically significant changes were observed in phytoplankton concentration nor the community composition. Increases in nutrient concentrations in the treatment ponds were observed within the first half of the study and were short-lived, whereas increases in phytoplankton concentrations were not observed until experiment day 21. Our results indicate that increased prevalence of fire may worsen eutrophication issues in grassland water bodies, but more research is needed to understand the persistence of these impacts in pond ecosystems.

Long-term management of rice agroecosystem towards climate change mitigation

The Intergovernmental Panel on Climate Change recognize to agriculture the responsibility for about 15 % of global anthropogenic greenhouse gas (GHG) emissions, contributing to global warming. The increasing nutrient inputs in industrial agriculture affect the GHG concentration in the atmosphere and varies substantially due to rate and type of fertilizers applied to the crops, making the management more or less sustainable. In this perspective, this study has investigated at small scale the effect of different adjusted agricultural management practices, based on different nutrient dosage, to optimize the effect of rice cropping systems on carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) emissions. Farmyard manure (FYM), rice stubbles and Azolla integrated with chemical fertilizers have been correlated with microbial and enzymatic activities, and with different carbon and nitrogen fractions in acid Inceptisol. Results have revealed that the integrated nutrient management used in rice-rice agroecosystem yielded a peak for CO2 and CH4 emissions, whereas two peaks for N2O emission. This study has shown an increase in greenhouse gas emission intensity (GHGI) and grain yield of rice in the following order: rice stubbles > FYM > Azolla and it has confirmed CH4 emission as the dominant contributor to GHGI from the rice-rice agroecosystem. When analyzed together GHGs emission and soil properties, a positive correlation was found with biological properties as well as with the different carbon and nitrogen fractions in soil. The highest GHGI has been highlighted in the treatment where recommended dose of chemical fertilizers has been combined with rice stubbles, primarily due to the increase in CH4 emissions. In contrast, the lowest GHGI has been exhibited in Azolla treated plot, probably due to the cumulative effects of the photosynthetic rate of Azolla, the release of oxygen from the Azolla roots, and the physical protection capacity of the Azolla cover, which partially avoid the CH4 diffusion from the standing water. The seasonality did not affect the estimated rates of GHGI that have been lower both in case of winter and autumn rice compared to previous studies, probably for dissimilarities in management practices. Further research is required in other cropping sequences for addressing the ecological contribution of smallholder agriculture to help reducing GHG emissions, thus, mitigating global warming with actions at local scale.

A benthic foraminifera perspective of the Late Miocene-Early Pliocene Biogenic Bloom at ODP Site 1085 (Southeast Atlantic Ocean)

The Late Miocene-Early Pliocene Biogenic Bloom (ca. 9.0–3.5 Ma) was a phase of high marine biological productivity documented globally at multiple ocean sites, related to an increase in nutrient input and/or a significant reorganization of nutrients in the oceans. Here, we studied the Biogenic Bloom at Ocean Drilling Program (ODP) Site 1085 in the Southeast Atlantic Ocean, additionally providing an updated age model based on calcareous nannofossil biostratigraphy. During the event, we identified four intervals characterised by distinct benthic foraminiferal assemblages, suggesting changes in paleoenvironmental/paleoceanographic conditions. The Biogenic Bloom extends from 8.1 to 3.0 Ma at Site 1085, as detected by different proxies such as linear sedimentation rates, carbonate mass accumulation rates, benthic foraminiferal indices and assemblage data. The inferred paleoenvironmental changes allowed us to differentiate four intervals within the Biogenic Bloom. From 8.1 to 5.2 Ma and from 3.8 to 3.0 Ma, the high benthic foraminiferal accumulation rates (BFARs) and the abundance of phytodetritus-exploiting taxa point to highly seasonal phytoplankton blooms. Between 5.2 and 4.8 Ma, we document short-term fluctuations between well‑oxygenated conditions with transient input of phytodetritus and phases of low oxygen eutrophic conditions. Between 4.8 and 3.8 Ma, a decrease in opportunistic species and an increase in eutrophic taxa likely suggest a switch to a higher food supply to the seafloor. Our data shows that the onset of the Biogenic Bloom was synchronous with other global well-dated records and its end appears to align with other Atlantic records. Lastly, our findings support the hypothesis that the Biogenic Bloom was not a single productivity event, but a complex event made up of several short-lived, high-productivity regimes with different driving forces.

Integrating ecosystem and contaminant models to predict the effects of ecosystem fluxes on contaminant dynamics

AbstractEnvironmental contamination is one of the major drivers of ecosystem change in the Anthropocene. Toxic chemicals are not constrained to their source of origin as they cross ecosystem boundaries via biotic (e.g., animal migration) and abiotic (e.g., water flow) vectors. Meta‐ecology has led to important insights on how spatial flows or subsidies of matter across ecosystem boundaries can have broad impacts on local and regional ecosystem dynamics but has not yet addressed the dynamics of pollutants in recipient ecosystems. Incorporating meta‐ecosystem processes (i.e., flux of materials across ecosystem boundaries) into contaminant dynamics can elucidate how contaminants may reverberate among local food chains. Here, we derive a modeling framework to predict how spatial ecosystem fluxes can influence contaminant dynamics and how this influence is dependent on the type of ecosystem flux (e.g., herbivore movement vs. abiotic chemical flows). We mix an analytical and numerical approach to analyze our integrative model which couples two subcomponents that have previously been studied independently of each other—an ecosystem model and a contaminant model. We observe an array of dynamics for how chemical concentrations change with increasing nutrient input and loss rate across trophic levels. When we tailor our range of chemical parameter values (e.g., environmental uptake of contaminant and assimilation efficiency of the contaminant) to specific organic chemicals, our results demonstrate that increasing nutrient input rates can lead to trophic dilution in pollutants such as polychlorinated biphenyls across trophic levels. However, increasing nutrient loss rate causes an increase in the concentrations of chemicals across all trophic levels. A sensitivity analysis demonstrates that nutrient recycling is an important ecosystem process impacting contaminant concentrations, generating predictions to be addressed by future empirical studies. Importantly, our model demonstrates the utility of our framework for identifying drivers of contaminant dynamics in connected ecosystems including the importance that (1) ecosystem processes and (2) movement, especially movement of lower trophic levels, have on contaminant concentrations.

The influence of flow, nutrient enrichment and aquatic macrophytes on benthic microalgal dynamics in a perched temporarily closed estuary

This study investigated the benthic microalgal dynamics in a temporarily closed microtidal estuary situated along a degraded stretch of coastline, where estuaries are impacted by development, flow modification, and nutrient pollution. The near natural, perched uMdlotane Estuary experienced regular high flow conditions that maintained the open mouth state for 40% of the study period. Increased nutrient input originated from agricultural-return flow derived from the extensive catchment sugarcane farming (55.9%). No notable temporal differences were recorded for the benthic microalgal biomass (range: 0–41.3 mg m−2). The benthic diatom diversity and evenness indices ranged between 0.6 and 3.1 H′ and 0.2–1 J′, respectively. Higher benthic microalgal biomass (14.9 ± 15.6 mg m−2) coincided with lower diatom diversity (1.3 H’) in the lower reaches. The habitat stability provided by the rooted Stuckenia pectinata facilitated benthic microalgal accumulation, while the absence of sediment disturbance contributed to the decrease in the benthic diatom diversity. The benthic diatom species Cocconeis lineata, Halamphora acutiuscula, and Hantzschia amphioxys largely dominated the community. Temporal differentiation in benthic diatom composition was driven by salinity, water temperature, phosphate, and photic depth changes. The pollution tolerant species Cyclotella atomus increased in abundance (sub-dominant RA = 5%) in response to increased phosphate availability. The presence of nutrient tolerant taxa serves as an early warning of impending environmental deterioration. Implementation of an adaptive management approach supported by monitoring is required to facilitate timely interventions to prevent the loss of ecosystem functionality induced by nutrient enrichment.

Effect of NPK fertilizer on the biochemical response of tomatoes (Solanum lycopersicum L.)

Increasing nutrient inputs affect plants and soil. Long-term, repeated mineral fertilizer applications may alter the agro-ecosystem. The application of the right amount of fertilizer is primordial to maintaining and improving sustainable plant productivity. The physiological response of the plant provides meaningful information on yield and makes it possible to better choose the doses of fertilization amendments. In order to determine the adequate dose of NPK fertilizer under economically profitable and more environmentally sustainable conditions, we investigated the impact of the chemical fertilizer amended at different NPK fertilizer doses (15, 20, and 25 kg ha-1) on the growth parameters, oxidative metabolism, and yield of Solanum lycopersicum. A complete random block experimental set-up with three doses and four replicates was performed for a greenhouse tomato crop. The results showed that NPK fertilizer influences morphological parameters, and phenolic compounds with the best data correlated to the medium treatment. Likewise, the content of flavonoids, lycopene, and β-carotene in tomato fruits displays a similar trend of variation with all treatment doses. The biochemical responses of plants to mineral fertilizer indicate that a medium dose is suitable, without overuse of fertilizers and pesticides, to reduce the negative impact on the agro-ecosystem.

Fluctuation in the diversity of mayflies (Insecta, Ephemerida) as documented in the fossil record

Due to their aquatic larvae, the evolution of mayflies is intricately tied to environmental changes affecting lakes and rivers. Despite a rich fossil record, little is known about the factors shaping the pattern of diversification of mayflies in deep time. We assemble an unprecedented dataset encompassing all fossil occurrences of mayflies and perform a Bayesian analysis to identify periods of increased origination or extinction. We provide strong evidence for a major extinction of mayflies in the mid-Cretaceous. This extinction and subsequent faunal turnover were probably connected with the rise of angiosperms. Their dominance caused increased nutrient input and changed the chemistry of the freshwater environments, a trend detrimental mainly to lacustrine insects. Mayflies underwent a habitat shift from hypotrophic lakes to running waters, where most of their diversity has been concentrated from the Late Cretaceous to the present.

Soil aggregate-associated organic carbon mineralization and its driving factors in rhizosphere soil

Understanding the determinants of soil carbon mineralization at both the aggregate and rhizosphere levels is crucial for providing precise feedback on climate change. However, the specific patterns and relative contributions of rhizosphere effects on carbon mineralization at the aggregate scale remain unclear. To address this, we conducted an incubation experiment to examine the impact of warming on soil carbon mineralization. We also assessed variations in microbial activities and soil properties across different aggregates in both rhizosphere and non-rhizosphere soils, while exploring how the rhizosphere effects modulated the response of soil respiration to warming. Our findings revealed that rhizosphere soil provides a favorable environment for microbial activities through increased nutrient input and aggregate stability, leading to significant increases in microbial biomass and enzyme activity, thus promoting soil carbon mineralization. Moreover, the spatial heterogeneity of soil aggregates contributes to the differentiation and diversity of microbial community distribution, which further enhances the diversification of carbon mineralization at the aggregate level. Notably, macroaggregates play a significant role in soil carbon flux, making a substantial contribution to carbon turnover in the ecosystem. The partial least squares (PLS) path analysis indicated that the rhizosphere positively increased the contributions of soil properties and microbial variables to the overall amount of soil cumulative mineralization, with soil nutrients playing a crucial role among these factors. These findings highlight the complex regulatory role of substrate quality in soil carbon mineralization dynamics at the aggregate scale, underscoring its far-reaching implications for accurately predicting the feedback to climate change in soil carbon mineralization.

Methanotrophic potential of Dutch canal wall biofilms is driven by Methylomonadaceae.

Global urbanization of waterways over the past millennium has influenced microbial communities in these aquatic ecosystems. Increased nutrient inputs have turned most urban waters into net sources of the greenhouse gases carbon dioxide (CO2) and methane (CH4). Here, canal walls of five Dutch cities were studied for their biofilm CH4 oxidation potential, alongside field observations of water chemistry, and CO2 and CH4 emissions. Three cities showed canal wall biofilms with relatively high biological CH4 oxidation potential up to 0.48mmol gDW-1 d-1, whereas the other two cities showed no oxidation potential. Salinity was identified as the main driver of biofilm bacterial community composition. Crenothrix and Methyloglobulus methanotrophs were observed in CH4-oxidizing biofilms. We show that microbial oxidation in canal biofilms is widespread and is likely driven by the same taxa found across cities with distinctly different canal water chemistry. The oxidation potential of the biofilms was not correlated with the amount of CH4 emitted but was related to the presence or absence of methanotrophs in the biofilms. This was controlled by whether there was enough CH4 present to sustain a methanotrophic community. These results demonstrate that canal wall biofilms can directly contribute to the mitigation of greenhouse gases from urban canals.

Estimation of Hypoxic Areas in the Western Baltic Sea with Geostatistical Models

Dissolved oxygen is essential for all marine life, especially for benthic organisms that live on the seafloor and are unable to escape if oxygen concentrations fall below critical thresholds. Therefore, near-bottom oxygen concentrations are a key component of environmental assessments and are measured widely. To gain the full picture of hypoxic areas, spatial gaps between monitoring stations must be closed. Therefore, we applied two spatial interpolation methods, where estimated near-bottom oxygen concentrations were solely based on measurements. Furthermore, two variants of the machine learning algorithm Quantile Regression Forest were applied, and any uncertainties in the results were evaluated. All geostatistical methods were evaluated for one year and over a longer period, showing that Quantile Regression Forest methods achieved better results for both. Afterward, all geostatistical methods were applied to estimate the areas below different critical oxygen thresholds from 1950 to 2019 to compute oxygen-deficient areas and how they changed when faced with anthropogenic pressures, especially in terms of increased nutrient inputs.

Use of historical isoscapes to develop an estuarine nutrient baseline.

Coastal eutrophication is a prevalent threat to the healthy functioning of ecosystems globally. While degraded water quality can be detected by monitoring oxygen, nutrient concentrations, and algal abundance, establishing regulatory guidelines is complicated by a lack of baseline data (e.g., pre-Anthropocene). We use historical carbon and nitrogen isoscapes over ~300 years from sediment cores to reconstruct spatial and temporal changes in nutrient dynamics for a central California estuary, Elkhorn Slough, where development and agriculture dramatically enhanced nutrient inputs over the past century. We found strong contrasts between current sediment stable isotopes and those from the recent past, demonstrating shifts exceeding those in previously studied eutrophic estuaries and substantial increases in nutrient inputs. Comparisons of contemporary with historical isoscapes also revealed that nitrogen sources shifted from a historical marine-terrestrial gradient with higher δ15N near the inlet to amplified denitrification at the head and mouth of the modern estuary driven by increased N inputs. Geospatial analysis of historical data suggests that an increase in fertilizer application - rather than population growth or increases in the extent of cultivated land - is chiefly responsible for increasing nutrient loads during the 20th century. This study demonstrates the ability of isotopic and stoichiometric maps to provide important perspectives on long-term shifts and spatial patterns of nutrients that can be used to improve management of nutrient pollution.

Investigating the impact of climate change on the lake ecosystem during the late Holocene using a sedimentary record from the southern Arabian Desert, Yemen

Lake systems respond physically, chemically, and biologically to hydro-climatic change and variability, and these responses are documented in the sediments. Individual proxies and lacustrine environments may respond to climate variations in a nonlinear way, making it difficult to determine the direction and extent of a climatic shift. Here we investigate the response of lake ecosystem to climatic and environmental changes using a suite of paleo-proxies including ostracods, chironomids, and n-alkanes distribution from paleolake ‘Gayal el Bazal (Yemen)’. A previous study from this site has provided a continuous, and high-resolution dataset providing an understanding of precipitation during the last ca 1200 years, particularly during Medieval Climate Anomaly (MCA) and Little Ice Age (LIA). However, the response of the lake ecosystem to these changing hydro-climate conditions, including water-level, salinity, and productivity, remains unknown. The n-alkanes dataset shows that during pluvial interval such as the MCA, the lake experienced an increase in nutrient input resulting in enhanced aquatic productivity. Concurrently, ostracods assemblage displays an increased abundance of swimmer species (like Bradleytriebella lineata and Fabaeomiscandona cf. breuili), suggesting an indirect response between ostracods and climate shifts. The chironomid community during the MCA interval is dominated by taxa belonging to the subfamilies of Chironomini, suggesting a warm, shallow, productive environment with macrophyte vegetation. The LIA interval is marked by increased abundance of higher-chain length n-alkanes, suggesting increased contribution from higher plants. Furthermore, ostracod distribution revealed increased abundance of non-swimmer species like Vestalenula cylindrica., which thrive under saline conditions in the lake. Changes in abundances of Tanytarsini during the LIA interval, which are associated with higher oxygen levels, suggest changes in lake productivity. As a result, the overall patterns in biological indicators reveal that their individual abundance and species/tribe distribution fluctuates in response to changes in the climate and hydrological conditions.

Characterization of nitrogen emissions for freshwater eutrophication modelling in life cycle impact assessment at the damage level and urban scale

Human interventions mobilize massive nitrogen (N) emissions to freshwater and result in serious eutrophication impacts. Life cycle impact assessment (LCIA) provides a reliable quantitative tool to address the challenges of potential ecological impact induced by increasing nutrient inputs. However, characterization procedures that relate N emissions to ecological damage in freshwater ecosystems in LCIA methodology are still lacking. This study aims to propose a spatially explicit characterization model (1 km × 1 km) for N-induced freshwater eutrophication. A complete cause-effect chains linking the N emission with species loss endpoint impact was constructed, in which the site-specific fate factor modelling contained transfer and removal processes in terrestrial and freshwater compartments, and the mechanistic modelling of ecosystem exposure and damage effect were quantified with species loss. The eutrophication characterization was conducted with a case study in Guangzhou, China, and 1 km × 1 km spatial differentiation of eutrophication susceptibility was intuitively demonstrated, with higher values in the Pearl River Estuary area. Method comparisons and further improvements were discussed in support of model generalization and further application.

Negative spill-over effects of agricultural practices on plant species conservation in nature reserves

Nature reserves are one of the most important instruments for biodiversity protection and to limit regional species extinctions. However, these functions can only be fulfilled if environmental influences from the surroundings, such as agrochemical inputs do not negatively affect the protected habitats.Here, we compare the effectiveness of conservation measures under the influence of yield-optimized cultivation in Germany using vegetation analyses of transects from the edge to the core of protected areas at 21 sites. By analysing nitrogen and phosphate deposition, herbicide number and concentration in soil and vegetation as well as Ellenberg indicator values of plant communities as a function of the distance from the field margin at each site, we aimed at assessing the impact of these stressors in different environmental settings.The results indicate strong chemical edge effects and negative influences for plant communities resulting from increased nutrient input and amounts of herbicide residues closer to the edge of the agricultural fields. Concordantly, the number of endangered plants species decreased with increasing proximity to the field edge. The strong influence of yield-optimized cultivation on the edges of nature reserves which decrease with distance show that nature protection needs effective buffer zones surrounding conservation areas, especially if nature reserves are only small and narrow. To prevent spill-over effects the application of fertilizer and herbicides on croplands adjacent to conservation areas has to be reduced. This could be achieved most effectively through organic farming and targeted agricultural subsidies.

Machine Learning for Detection of Macroalgal Blooms in the Mar Menor Coastal Lagoon Using Sentinel-2

The Mar Menor coastal lagoon in southeastern Spain has experienced a decline in water quality due to increased nutrient input, leading to the eutrophication of the lagoon and the occurrence of microalgal and macroalgal blooms. This study analyzes the macroalgal bloom that occurred in the lagoon during the spring-summer of 2022. A set of machine learning techniques are applied to Sentinel-2 satellite imagery in order to obtain indicators of the presence of macroalgae in specific locations within the lagoon. This is supported by in situ observations of the blooming process in different areas of the Mar Menor. Our methodology successfully identifies the macroalgal bloom locations (accuracies above 98%, and Matthew’s Correlation Coefficients above 78% in all cases), and provides a probabilistic approach to understand the likelihood of occurrence of this event in given pixels. The analysis also identifies the key parameters contributing to the classification of pixels as algae, which could be used to develop future algorithms for detecting macroalgal blooms. This information can be used by environmental managers to implement early warning and mitigation strategies to prevent water quality deterioration in the lagoon. The usefulness of satellite observations for ecological and crisis management at local and regional scales is also highlighted.

Paleoenvironmental changes during the Middle-Late Ordovician transition, Northwestern Tarim Basin, NW China and implications for the great Ordovician Biodiversification Event

• Black shales of Saergan Formation had a mainly felsic source region likely in an active continental margin. • The paleoenvironment exhibited a semiarid climate with high salinity and anoxic marine conditions during the Middle–Late Ordovician in the Awati Sag. • The Middle–Late Ordovician was a transition period which the paleoenvironment changed greatly. • The GOBE may be triggered by supergreenhouse climate. The changes in the geological environment during the Middle–Late Ordovician transition are well documented by geochemical evidence. We study the paleoenvironmental changes during the Middle–Late Ordovician and their effects on the Great Ordovician Biodiversification Event (GOBE) through the analysis and testing of the major elements, trace elements and rare earth elements (REEs) present in 21 samples from the Middle–Upper Ordovician Saergan Formation in the Awati Sag, Northwestern Tarim Basin, NW China. Compared with post-Archaean Australian Shale, the Saergan Formation is enriched in Ca, P, U and REEs. The total abundance of REEs ranges from 107.3 to 674.8 ppm, with obvious enrichment of light REEs and negative Eu anomalies, as well as Ce shows a weak negative anomaly. Furthermore, the parent rock of Saergan Formation is mainly felsic. Combined with the provenance attributes and tectonic background, the source area is considered to be mainly in an active continental margin tectonic environment. The black shales underwent moderate weathering and simple cyclical sorting, with an immature composition. Multiple geochemical indicators show that the Middle–Late Ordovician is a transition period and the paleoenvironment had semiarid climate and hypersaline anoxic marine conditions. The supergreenhouse climate may accelerate chemical weathering and increase nutrient inputs. In addition, the warm climate melting of the polar ice sheet which leads to the relative shallowness of the sea surface temperature gradient, sea level rise and expansion of marine habitats. The resultant environmental changes could have accelerated the diversification of benthos, which provides an ancient analogue for anthropogenic climate change.

Vertically Resolved Pelagic Particle Biomass and Size Structure Across a Continental Shelf Under the Influence of a Western Boundary Current

AbstractContinental shelves are key to societal interactions with the oceans, supporting >90% of the world's fisheries through highly productive ecosystems. Previous research has shown that phytoplankton biomass is generally higher on the inner continental shelves, often due to increased nutrient inputs from upwelling or coastal run‐off. However, consistency in observed vertical and horizontal gradients (in abundance, biomass or size) of larger particulates, including zooplankton, on continental shelves has not been established. Using an optical plankton counter and CTD mounted on an undulating towed body, we present high‐resolution vertically resolved profiles of pelagic particle size structure across a continental shelf. Biomass was highest inshore, declining with distance from shore and with depth in the top 100 m of the water column, although the presence of frontal zones can alter this pattern. In the region adjacent to the East Australian Current (EAC), uplift generated by either the EAC interacting with the continental slope or upwelling‐favorable winds, correlated with smaller geometric mean sizes and steeper size spectrum slopes, particularly in the presence of frontal features. South of the EAC separation, the continental shelf water mass was more homogenous but still displayed the same horizontal and vertical patterns in particulate biomass and mean size. By combining our observations in a global comparison, we demonstrate consistent particulate distributions on continental shelves where the inner shelf has higher biomass with a steeper size spectrum slope compared to offshore. The highly productive inner shelf supports zooplankton communities vital to temperate ecosystems and coastal fisheries, through their consistently high biomass.

Hindcasting harmful algal bloom risk due to land-based nutrient pollution in the Eastern Chinese coastal seas

Harmful algal blooms (HABs) have been increasing in frequency, areal extent and duration due to the large increase in nutrient inputs from land-based sources to coastal seas, and cause significant economic losses. In this study, we used the “watershed-coast-continuum” concept to explore the effects of land-based nutrient pollution on HAB development in the Eastern Chinese coastal seas (ECCS). Results from the coupling of a watershed nutrient model and a coast hydrodynamic-biogeochemical model show that between the 1980s and 2000s, the risk of diatom blooms and dinoflagellate blooms increased by 158% and 127%, respectively. The spatial expansion of HAB risk caused by dinoflagellates is larger than that of diatoms. The simulated suitability of the habitat for bloom of Aureococcus anophagefferens, a pico-plankton of non-diatom or dinoflagellate, in the Bohai Sea is consistent with observations spatially and temporally. To halt further nutrient accumulation in the ECCS, reductions of dissolved inorganic nitrogen (DIN) (16%) and dissolved inorganic phosphorus (DIP) (33%) loading are required. To improve the situation of distorted DIN:DIP ratios, even larger reductions of DIN are required, especially in the Bohai Sea. Our approach is a feasible way to predict the risk of HABs under the pressure of increasing anthropogenic nutrient pollution in coastal waters.