Low Salinity Research Articles

Mitigation of soil salinity by addition of different rice straw biochar doses in salt-affected acid soil

The current study was carried out to evaluate the effect of rice straw biochar amendment and to identify the appropriate dose of biochar application to reduce soil acidity, salinity, toxicity, and sodicity in salt-affected acid soils. The rice straw biochar at 4 different rates of 0%, (control) 1%, 3%, and 5% (w/w) was mixed with 6 salt-affected acid soils: S1 (non-saline), S2 and S3 (low saline), and S4, S5, and S6 (moderate saline). The mixture was continuously shaken in distilled water for 7 days. The biochar application significantly increased soil pH and saturated electrical conductivity (ECe) with an increasing biochar application rate compared with the control. Significant decreases in sodium adsorption ratio (SAR) and exchangeable sodium percentage (ESP) values below the critical level of sodicity were observed above the biochar application rate of 1%. Soluble chloride (Cl–) and soluble and exchangeable sodium (Na+) were significantly reduced above the biochar application rate of 1%. The biochar application (≥ 1%) led to a significant increase in soluble and exchangeable potassium (K+) and declines in soluble and exchangeable calcium (Ca2+) and magnesium (Mg2+). This study concluded that the biochar application rate of 1% was suitable for reducing soil acidity to a safe level for rice plants. The rice straw biochar application improved soil toxicity and sodicity by reducing soluble Cl– and soluble and exchangeable Na+, decreasing SAR and ESP. The biochar application also increased available K+, essential for rice plant growth and development in salt-affected soils.

Sample Preservation Solution Increases Nucleic Acid Yield and Environmental RNA Quality in Sediments Across an Estuarine Salinity Gradient

ABSTRACTEnvironmental nucleic acid‐based assessments are powerful tools for understanding microbial ecology, and environmental degradation in aquatic environments. This approach is particularly useful in guiding restoration in estuaries, some of the most degraded ecosystems in the world. The recent popularity of this approach has been accompanied by a parallel increase in the diversity of applied methods. A range of best practice methods exist across the field that can be employed and are selected based on environmental considerations such as physicochemical gradients, maximizing yield, and quality of nucleic acids sampled across sites within a study area. A consistent approach to intra‐study nucleic acid sampling also ensures accurate comparison between those sites. This study evaluates environmental nucleic acid (eNA) sampling methods across salinity gradients in aquatic ecosystems, focusing on the impact of preservation techniques on environmental DNA (eDNA) yield and environmental RNA (eRNA) yield and quality. Fieldwork was conducted at three sites within the Coorong estuary system in South Australia, representing low salinity, marine, and hypersaline conditions. Snap freezing and LifeGuard preservation solution treatments were applied in situ to compare their effects on nucleic acid yields and eRNA integrity. Snap freezing enhanced eDNA yield in low salinity sediments but negatively impacted eRNA integrity in marine and hypersaline conditions. Conversely, treatment with preservation solution consistently improved both eDNA and eRNA recovery across all salinity levels, which makes this approach a good candidate for preserving eNA molecules across environmental gradients. The study underscores the necessity of tailoring sample preservation methods to specific environmental conditions for accurate eNA‐based microbial community assessments in coastal ecosystems. These findings contribute to the development of robust eNA sampling protocols for benthic communities under varying salinity conditions.

Insights on CDI parametric controls and dependencies using gloabal sensitivity analysis

Capacitive deionization (CDI) emerges as a promising desalination technology due to its high energy efficiency and potential for energy recovery. Its performance improvement and application extension highly require understanding how variations in multiple input parameters, as well as their interactions, lead to variations in output, which is not straightforward in the complex system of CDI. In this work we use the extended Fourier amplitude sensitivity test (eFAST) method to conduct a global sensitivity analysis (GSA) in order to examine the effects of several parameters, including material properties, operating conditions, and ionic properties, on the energy consumption and salt removal efficiency of CDIs. The research reveals that high capacitance and efficient mass transfer are crucial for CDI advancement, with a trade-off between desalination rate and energy efficiency. The interplay between input parameters is revealed by factorial design and GSA, which show that no single parameter alone determines salt adsorption capacity but that feedwater salt concentration and current density are important when considering both individual and coupled effects. The study suggests that the specific application and feedwater characteristics should be taken into consideration when deciding between the CC and CV modes of desalination. While CC mode excels in water production and energy efficiency for high salinity feedwater pretreatment, CV mode is better at treating low salinity waterr. The comprehensive parametric analysis provides valuable insights into optimizing CDI design and operating conditions to balance desalination capacity and energy efficiency.

Thermodynamics-based unsaturated hydro-mechanical-chemical coupling model for wellbore stability analysis in chemically active gas formations

A thermodynamics-based unsaturated hydro-mechanical-chemical (HMC) coupling model is developed to analyze the coupled response and stability of boreholes in chemically active gas formations. The newly coupled constitutive relations are formulated by incorporating the chemical effect into the solid-gas-liquid unsaturated framework to account for the interactions between rock deformation, gas-liquid two-phase flow, and chemical potential difference. Compared with previous models, the present model shows significant prediction differences in field variables and wellbore stability evolution. The maximum absolute difference of pore pressure, effective radial stress, effective tangential stress, and collapse pressure can reach 8.98 MPa, 7.64 MPa, 7.29 MPa, 7.65 MPa, respectively. It is more conservative to select a long-term wellbore collapse pressure rather than a short-term one to guide drilling operations. The two-phase flow behavior, jointly controlled by wellbore pressure, capillary pressure, and chemical osmosis effect, provides a more realistic observation of the mud intrusion process. Compared with low salinity muds, high salinity muds can effectively impede the mud intrusion into the formation, which is more conducive to preventing wellbore collapse, but at the same time increases the risk of wellbore fracture. Sensitivity analysis shows that solute diffusion and reflection coefficients affect early wellbore stability through pore pressure and solute transport, while the chemical swelling coefficient has a long-term effect through chemically induced deformation. The results can provide theoretical guidance for quantitative optimization of mud parameters and prevention of wellbore instability when drilling in chemically active gas formations.

Significant effect of salinity on zinc adsorption on tropical coastal and floodplain soils

AbstractRising sea levels due to climate change are causing increased salinisation of low‐lying coastal and floodplain soils, and the impact of this process on the bioavailability of plant nutrients needs to be understood as mitigation strategies are adapted. Zinc (Zn) is an element of particular importance due to its function as a micronutrient for plants including rice and other staple foods. In the current study, our aim was to investigate the effects of salinisation on zinc adsorption onto soils representing at‐risk coastal and floodplain environments, addressing in particular our knowledge gap concerning the roles that solution chemistry and soil composition play. To this end, we conducted batch adsorption experiments in the laboratory and ran geochemical models in saline solutions up to 0.7 mol L−1 ion strength incorporating both (i) a multi surface model (MSM) for surface reactions containing three phases, that is iron hydroxides, organic matter and phyllosilicate clays, and (ii) aqueous‐phase complexation to dissolved organic and inorganic ligands. Surface reactions were modelled using the diffuse double layer model, the NICA–Donnan model and an ion exchange model using the Gaines–Thomas convention. We combined the experimentally determined mass composition of surface phases with generic modelling parameters taken from the literature. We first show that increasing salinity enhances the formation of aqueous Zn‐chloride complexes in the presence of dissolved organic matter and bicarbonate, thereby decreasing the availability of free Zn2+ and supressing the partitioning of zinc to the adsorbed phase. We demonstrate using batch adsorption experiments with a calcareous hydraquent and a tropaquept, that salinity decreases zinc adsorption strongly in the pH range between 3 and 6. Satisfactory agreement between experiments and model calculations was achieved with root‐mean‐square errors ranging for different salinities between 2.88% and 2.92% for the hydraquent and between 4.59% and 2.74% for the tropaquept soil. Model predictions of adsorption were slightly inferior at low salinity for the hydraquent soil and at high salinity for the tropaquept soil, pointing possibly to an incomplete geochemical model or to a need to parametrise surface adsorption models at higher ionic strengths. Present surface models have been largely parametrised at lower ionic strength. We lastly apply the MSM to examine zinc adsorption in five endoaquepts soils, representing soil series from Bangladesh. We show that increasing salinity decreases zinc adsorption to the soil organic matter and the clay fractions. We conclude from our findings that increased soil salinity due to rising sea levels and climate change will have a significant impact on zinc cycling and possibly other micronutrients in areas where coastal soils and floodplain soils overlap, such as deltas and estuaries. In particular, we predict a decrease in zinc adsorption in acidic to neutral soils. The availability of zinc for biouptake through the roots of crop plants including rice will be significantly disturbed following salinisation, most likely affecting crop production. Our study demonstrates the potential that geochemical modelling combined with experimental data has to improve our capability to assess the effects of salinity due to rising seawater levels in vulnerable regions of the world.

Increase in marginal sea alkalinity may impact air–sea carbon dioxide exchange and buffer acidification

AbstractTotal alkalinity (TA) has increased in the Baltic Sea, with implications for atmospheric CO2‐induced acidification and CO2 uptake. We compiled extensive data of TA in surface waters of the Baltic Sea, aiming to (i) identify new tendencies in the relationship between TA and salinity (TA–S relationship), (ii) update the TA trend analysis, (iii) investigate spatial–temporal patterns, and (iv) discuss potential drivers and implications. We observed a progressive decrease in the slopes and increase in the intercepts of the TA–S overtime due to the persistent process of TA enhancement. A weak seasonal pattern was identified, with warmer months presenting lower salinity and TA. Lower rates of TA increase were observed in high salinities (Skagerrak–Kattegat; +1.00 to +2.20 μmol kg−1 yr−1), intermediate trends in low salinities (Gulf of Bothnia; +3.28 to +3.57 μmol kg−1 yr−1), and maximal trends in the Central Baltic Sea (+3.70 to +4.57 μmol kg−1 yr−1) and Bornholm Basin (+4.82 to +5.32 μmol kg−1 yr−1). The increase in the intercept of the TA–S in the Gulf of Bothnia suggests a progressive increase in the external supply of TA, although lower than previously thought. The maximum trend in the Bornholm Basin suggests an increase in external supply from the Southern catchment and/or the accumulation of internal production. The positive TA–phosphorus correlations underscore a significant internal source. The TA increase amplifies the CO2 uptake by 1.8–7.8% during spring/summer and reduces the CO2 outgassing by 3.4–7.7% in autumn/winter. The TA enhancement has the potential to buffer CO2‐induced acidification by 39–60% by 2050.

Hindcasting Estuarine Bottom Salinity Using Observing Systems Data and Nonlinear Regression, as Applied to Oysters in Delaware Bay

Salinity is a major environmental factor that influences the population dynamics of fish and shellfish along coasts and estuaries, yet empirical methods for hindcasting salinity at specific sampling stations are not widely available. The specific aim of this research was to predict the salinity experienced by juvenile and adult oysters (Crassostrea virginica) collected at sampling stations in Delaware Bay. To do so, empirical relationships were created to predict salinity at five oyster bed stations using observing systems data. These relationships were then applied to construct indices of salinity exposure over an oyster’s lifetime. Three independent salinity data sources were used in conjunction with observing systems data to construct and validate the predictive relationships. The root mean square error (RMSE) of the models ranged from 0.5 to 1.6 psu when model predictions were compared with the three independent data sets. Results demonstrated that data from an observing system near the head of Delaware Bay could be used to predict salinity within ± 2 psu at oyster bed stations as far down-estuary as 39 km. When these models were applied to estimate low salinity exposure of 2-year-old oysters via the metric of consecutive days below 5 psu, the indices suggested that there could be as much as a 42-day difference in low salinity exposure for oysters at stations just 31 km apart. The approach of using observing systems data to hindcast salinity could be applied to advance understanding of salt distribution and the effect of low salinity exposure on organisms in other estuaries, especially bottom-associated species.

Theoretical and experimental investigation of the impact of oil functional groups on the performance of smart water in clay-rich sandstones

This research investigated the effect of ion concentration on the performance of low salinity water under different conditions. First, the effect of injection water composition on interparticle forces in quartz-kaolinite, kaolinite-kaolinite, and quartz-oil complexes was tested and modeled. The study used two oil samples, one with a high total acid number (TAN) and the other with a low TAN. The results illustrated that reducing the concentration of divalent ions to 10 mM resulted in the electric double layer (EDL) around the clay and quartz particles and the high TAN oil droplets, expanding and intensifying the repulsive forces. Next, the study investigated the effect of injection water composition and formation oil type on wettability and oil/water interfacial tension (IFT). The results were consistent with the modeling of interparticle forces. Reducing the divalent cation concentration to 10 mM led to IFT reduction and wettability alteration in high TAN oil, but low TAN oil reacted less to this change, with the contact angle and IFT remaining almost constant. Sandpack flooding experiments demonstrated that reducing the concentration of divalent cations incremented the recovery factor (RF) in the presence of high TAN oil. However, the RF increment was minimal for the low TAN oil sample. Finally, different low salinity water scenarios were injected into sandpacks containing migrating fines. By comparing the results of high TAN oil and low TAN oil samples, the study observed that fine migration was more effective than wettability alteration and IFT reduction mechanisms for increasing the RF of sandstone reservoirs.

Unforeseen green tide of floating tubular Ulva meridionalis, a lethal threat to oyster farming, along the west coast of Taiwan: tracking its origin and ecophysiological insights

Abstract Ulva green tides have adversely affected coastal ecosystems. In June 2023 in Changhua County, Taiwan, an unprecedented floating tubular Ulva bloom spanning about 30 km of coastline caused about 30 % reduction in oyster yield as reported by local farmers. Understanding its taxonomic and ecological basis is crucial for preemptive and remedial measures. Based on molecular (rbcL and tufA) and morphological evidence, U lva meridionalis was the cause of this green tide. Haplotype network analysis (based on ITS) suggests that this green tide originated from northern China via the China Coastal Current. Historical survey data indicate that U. meridionalis arrived in Taoyuan Algal Reef (about 150 km north of the bloom area) as far back as 2018. Our ecophysiological experiments revealed that U. meridionalis exhibited a rapid daily growth rate with biomass increment up to 13–21 % when subjected to local nutrient-rich waters under lower salinity and spring-like conditions. Although historical ecological and poultry/livestock data analyses showed no noticeable change in sea surface temperature and rainfall over the past decade, a gradual rise in agricultural nitrogen and phosphorus output was observed. This taxonomic and ecological background lays the groundwork for long-term ecological monitoring. Moreover, this study exemplifies the detrimental impact of an unforeseen Ulva bloom on oyster farming.

Political Economic Role in Natural Quality Management and its Impact on Plant Ecology: Why Arar-Juniper Plants Disappeared

Wadi-Arar is a unique region that has lost some of its most important natural features within 200 years, including plants, geographical lakes, and valleys. The study aimed to investigate the disappearance of the juniper plant, a vital species in Saudi Arabia, in recent decades. The research highlighted various factors influencing the quality of life for the juniper plant and its habitats. It sought to identify the primary factors causing changes in the natural conditions of the plant and those influencing its growth. The findings indicated a significant impact of the Suez Canal on the Arar region, the sole connection between Africa and Asia, and Europe. This influence extends beyond geopolitical factors in the surrounding area, as the existence of the Suez Canal disrupted the natural life cycle of many animal species over thousands of years of migrations and coexistence across Earth's continents. These animals previously provided natural organic fertilizer to the soil, supporting plant growth. However, due to low rainfall resulting in low natural nutrients and high salinity, the plants' viability has diminished, reflecting a history of administrative and geopolitical decisions.

Persistent interactive effects of developmental salinity and temperature in Atlantic killifish (Fundulus heteroclitus)

Climate change alters multiple abiotic environmental factors in aquatic environments but relatively little is known about their interacting impacts, particularly in developing organisms where these exposures have the potential to cause long-lasting effects. To explore these issues, we exposed developing killifish embryos (Fundulus heteroclitus) to 26 °C or 20 °C and 20 ppt or 3 ppt salinity in a fully-factorial design. After hatching, fish were transferred to common conditions of 20 °C and 20 ppt to assess the potential for persistent developmental plasticity. Warm temperature increased hatching success and decreased hatch time, whereas low salinity negatively affected hatching success, but this was only significant in fish developed at 20 °C. Temperature, salinity, or their interaction affected mRNA levels of genes typically associated with thermal and hypoxia tolerance (hif1a, hsp90b, hsp90a, hsc70, and hsp70.2) across multiple developmental timepoints. These differences were persistent into the juvenile stage, where the fish that developed at 26 °C had higher expression of hif1a, hsp90b, hsp90a, and hsp70.2 than fish developed at 20 °C, and this was particularly evident for the group developed at both high temperature and salinity. There were also long-lasting effects of developmental treatments on body size after four months of rearing under common conditions. Fish developed at low salinity or temperature were larger than fish developed at high temperature or salinity, but there was no interaction between the two factors. These data highlight the complex nature of the developmental effects of interacting stressors which has important implications for predicting the resilience of fishes in the context of climate change.

Toward the first documented extinction of a marine macroalga in the Mediterranean Sea?

Fucus virsoides is a glacial relict-species endemic to the Adriatic that was widespread from northern Italy to southern Albania. In recent decades, however, it has suffered an alarming decline. In this study, all available records were reviewed to reconstruct its historical and current occurrence and to investigate the possible causes of its decline. Comprehensive mapping revealed a continuing decline with a significant shift, leaving only about 20 fragmented populations. While the species is already classified as critically endangered in Albania, F. virsoides could be considered functionally extinct in Istria (Croatia), critically threatened with extinction in Italy and Montenegro and locally extinct in Slovenia. The status of the species in the rest of Croatia is still unclear. The remaining populations are located in areas characterised by low temperatures, low salinity and high nutrient concentrations. Long-term analyses of these key abiotic factors revealed profound changes that suggest a link to the species' decline. This study provides a thorough assessment of the overall status of F. virsoides and argues for its inclusion on the IUCN Red List. Immediate conservation measures are needed for the long-term survival of this species.

Sediment water content drives movement of intertidal crab Helice tientsinensis more strongly than salinity variations

Intertidal wetlands undergo dynamic water and salinity variations, creating both promising and challenging habitats for diverse organisms. Crabs respond strongly to these variations by means such as altering their movements, thereby restructuring their spatial distribution and influencing coastal ecosystem resilience. However, the movements of crabs under varying environmental conditions require further elucidation. We conducted a systematic mesocosm experiment using the ubiquitous intertidal crab species Helice tientsinensis with four amount levels and six salinity levels of sprayed water applied through a custom apparatus, with a primary focus on crab movement. Crab movement from the experimental side of the apparatus (with altered conditions) to the control side (resembling field conditions of the intertidal wetlands of China's Yellow River Delta) and vice versa was recorded. The results revealed significant differences in moving out of the experimental side and moving in among the different water and salinity conditions, both separately for the two factors and simultaneously. Decreases in water content had a more pronounced effect on crab movement, leading to an increased number of crabs moving out of the experimental side of the apparatus. Conversely, as the experimental side became wetter, crabs tended to move towards it, and this movement was intensified by increases or decreases in water salinity. A structural equation model revealed that the moving-out and moving-in played fundamental roles in determining the number of resident crabs at the end of each experiment. While crabs preferred moist sediment with lower salinity, changes in salinity alone had minimal direct effect compared to sediment water contents. Our results clarify crab movements under varying water and salinity conditions, offering valuable insights to support adaptive interventions for crab populations and inform adaptive conservation and management strategies in intertidal wetlands.

Insights on physiological, antioxidant and flowering response to salinity stress of two candidate ornamental species: the native coastal geophytes Pancratium maritimum L. and Eryngium maritimum L

Increasing seawater influence in coastal areas is an ongoing environmental issue. Gardening is a widespread activity mainly in touristic areas such as the Mediterranean coasts. However, the use of exotic species well adapted to salinity encompasses the risk of invasive species introduction. This study aimed to evaluate salinity tolerance of native geophytes, Pancratium maritimum L. and Eryngium maritimum L., to assess their use as ornamental species in salt affected coastal areas. Experiments were conducted using cultivated plants for flowering response and physiological and enzymatic antioxidant response. Six treatments were applied for two months, exposing plants to seawater (SW) dilutions (Tap-Water, 6.25%SW, 12.5%SW, 25%SW, 50%SW and 100%SW). Taxa decreased inflorescence production being this effect more architectonical in E. maritimum and affecting all inflorescence integrity in P. maritimum. Flowering time was strongly delayed and reduced in P. maritimum, while E. maritimum showed smaller effects among treatments. Physiological and biochemical response showed at moderate salinity levels (1/4SW) variation concomitant with late stress response and senescence in P. maritimum, with decreased water use efficiency, NPQ values, and enzymatic activity, and increased malondialdehyde (MDA) levels. In contrast, E. maritimum showed early stress response with steady gas exchange response, increasing NPQ values and catalase (CAT) and superoxide dimutase (SOD) activity, and decreasing MDA levels with salinity. Glutathione enzymes showed limited participation in both species. The results of this study suggest that neither species can be classified as halophytes, but they exhibit tolerance to low and moderate salinity levels, making them suitable for ornamental use.

Ecology of the Copepods at a Low Salinity Zone of the Ganges Estuary, India

Ecology of the Copepods at a Low Salinity Zone of the Ganges Estuary, India

Microbial and hydrothermal dolomite formation in Early Cretaceous lacustrine sediments in Yin'e Basin: Insights from petrology and geochemistry

Dolomite is widely present in geological history, but its origin has always been a prominent problem that troubles sedimentologists. For lacustrine dolomite, current research has not yet provided a reliable explanation for its complex genesis mechanism. The Early Cretaceous lakes in Northwest China host various morphological dolomites, providing valuable materials for exploring the origin of dolomites. According to their petrological and mineralogical characteristics, it can be divided into thick laminated dolomite, thin laminated dolomite, dolomitic mudstone, and vein dolomite. The ratios of trace elements and rare earth elements show that these dolomites precipitated in a brackish–suboxic environment. The high δ13C values (>8 ‰VPDB) of thick laminated dolomite and some thin laminated dolomite suggest the involvement of methane-producing microorganisms in the precipitation of dolomite, and the appearance of microscale/nanoscale spherical dolomite aggregates and the dispersed organic matter around dolomite particles jointly confirm that microbial-mediated biological activity promotes dolomite precipitation. The dolomite stoichiometry (mole % MgCO3) confirms that thick laminated dolomite was deposited in a restricted shallow water environment, while dolomitic mudstone is mainly deposited in relatively open water areas. The thin laminated dolomite in the shale laminae represents short-term or seasonal climatic and environmental fluctuations. In addition, some carbonate minerals of dolomitic mudstone in shallow water environment recrystallized by post-depositional hydrothermal effect, resulting in δ18O value decreased (<−10 ‰VPDB). The vein dolomite is characterized by high rare earth content and low δ13C and δ18O values, and its Sr isotope (0.712894 ± 0.000374) values reflect that the hydrothermal fluid may have been formed by the mixing of infiltrating lake water and crustal magmatic water. According to the characteristics of fluid inclusions, it is inferred that the hydrothermal fluid has the characteristics of low temperature (108.3 °C–159.8 °C), medium salinity (3.5 wt%–14.3 wt% NaCl) and high density (0.95–1.00 g/cm3). The microbial mediation and tectonic hydrothermal fluids play an important role in the formation of the Early Cretaceous lacustrine dolomite.

Seafloor alkalinity enhancement as a carbon dioxide removal strategy in the Baltic Sea

Carbon dioxide removal from the atmosphere and storage over long times scales in terrestrial and marine reservoirs is urgently needed to limit global warming and for sustainable management of the global carbon cycle. Ocean alkalinity enhancement by the artificial addition of carbonate minerals to the seafloor has been proposed as a method to sequester atmospheric CO2 and store it in the ocean as dissolved bicarbonate. Here, a reaction-transport model is used to scrutinize the efficacy of calcite addition and dissolution at a well-studied site in the southwestern Baltic Sea – a brackish coastal water body in northern Europe. We find that most calcite is simply buried without dissolution under moderate addition rates. Applying the model to other sites in the Baltic Sea suggests that dissolution rates and efficiencies are higher in areas with low salinity and undersaturated bottom waters. A simple box model predicts a tentative net CO2 uptake rate from the atmosphere of 3.2 megatonnes of carbon dioxide per year for the wider Baltic Sea after continually adding calcite to muddy sediments for 10 years. More robust estimates now require validation by field studies.

Interactive effects of temperature and salinity on metabolism and activity of the copepod Tigriopus californicus.

In natural environments, two or more abiotic parameters often vary simultaneously, and interactions between co-varying parameters frequently result in unpredictable, non-additive biological responses. To better understand the mechanisms and consequences of interactions between multiple stressors, it is important to study their effects on not only fitness (survival and reproduction) but also performance and intermediary physiological processes. The splash-pool copepod Tigriopus californicus tolerates extremely variable abiotic conditions and exhibits a non-additive, antagonistic interaction resulting in higher survival when simultaneously exposed to high salinity and acute heat stress. Here, we investigated the response of T. californicus in activity and oxygen consumption under simultaneous manipulation of salinity and temperature to identify whether this interaction also arises in these sublethal measures of performance. Oxygen consumption and activity rates decreased with increasing assay salinity. Oxygen consumption also sharply increased in response to acute transfer to lower salinities, an effect that was absent upon transfer to higher salinities. Elevated temperature led to reduced rates of activity overall, resulting in no discernible impact of increased temperature on routine metabolic rates. This suggests that swimming activity has a non-negligible effect on the metabolic rates of copepods and must be accounted for in metabolic studies. Temperature also interacted with assay salinity to affect activity, and with acclimation salinity to affect routine metabolic rates upon acute salinity transfer, implying that the sublethal impacts of these co-varying factors are also not predictable from experiments that study them in isolation.

First indication of platinum input into the southern North Sea via German Rivers

Platinum (Pt) is an emerging critical metal, but the long-term environmental impacts of anthropogenic Pt remain largely unknown. We report, for the first time, Pt input from three major German rivers (Ems, Weser and Elbe) into the southern North Sea. All three rivers were a major source of Pt, with a maximum of 6.3 pmol L−1 in the Elbe endmember, compared to generally <1.0 pmol L−1 in the North Sea samples. All samples measured in the North Sea were elevated in Pt (mean of ∼0.9 pmol L−1) relative to typical open-ocean values (∼0.2–0.3 pmol L−1 in the Atlantic and Pacific). Across the Weser and Elbe estuarine transect, an initial sharp drawdown of Pt concentrations at low salinity (S < 1.5) was observed, which correlated well with Fe and Mn concentrations, indicating adsorption and co-precipitation at low salinity. At higher salinities (S ≥ 3) Pt concentrations followed a more conservative distribution relative to salinity. In addition, we followed a 12 h tidal cycle in each of the rivers, which generally reflected an inverse correlation of Pt concentrations against salinity. This study indicates that Pt might be an emerging contaminant in the North Sea, requiring further study to define specific sources.

Environmental controls on bioluminescent dinoflagellate density, in Laguna Grande, Fajardo, Puerto Rico

Introduction: Bio bays in Puerto Rico play an important socio-economic role and declines in dominant bioluminescent dinoflagellate Pyrodinium bahamense are concerning. Studies show erratic blooms with is weak correlation to in situ environmental factors. Our study examines shorter field and longer proxy records on dinoflagellate density at Laguna Grande de Fajardo (LGF). Objectives: To quantify temporal changes in dinoflagellate density in a long-term monitoring study, understand how the marine environment modulates those changes, and determine the wider impacts of a fluctuating climate and extreme events on proxies for dinoflagellate density. Methods: Bimonthly samples were collected from 2016 to 2021 at three sampling sites in LGF. Dinoflagellates density was estimated by Sedgewick Rafter counting cells. Environmental conditions were obtained from Rio Fajardo 5007100 station and NOAA buoy 41056. Marine climate and biotic proxies were obtained from remote sensing measurements. Kruskal Wallis, Spearman correlations and cross-correlations in the shorter field and longer proxy records were used to evaluate environmental controls on LGF dinoflagellate blooms. Results: Six years of field monitoring densities found a low period in 2016-2017, frequent and intense blooms in 2018-2021 punctuated by hurricanes. Generally low values were recorded in late winter in contrast with higher values in late summer (Aug-Nov). Light winds and mixed layer response to seasonal warming in the form of high tides and low salinity, were found to sustain dinoflagellate reproduction. Conclusions: Bioluminescent dinoflagellates are vital to coastal tourism and require resource management. LGF results show that: 1) dinoflagellate counts fluctuate widely, 2) fluorescing dinoflagellates are sensitive to environmental conditions because of limited seasonality and narrow physiological range, 3) hurricanes play a role by ‘raking and refreshing’ the coastal lagoon for subsequent biotic reproduction, and 4) intra-seasonal fluctuations of density and proxies relate to air-sea thermodynamic conditions, the salinity budget and sea level.