Recent developments in tracking technology resulted in the mapping of various marine spawning migration routes of the European eel (Anguilla anguilla). However, migration routes in the North Sea have ...rarely been studied, despite many large European rivers and hence potential eel growing habitat discharge into the North Sea. In this study, we present the most comprehensive map to date with migration routes by silver European eels in the North Sea and document for the first time successful eel migration through the English Channel. Migration tracks were reconstructed for 42 eels tagged in Belgium and 12 in Germany. Additionally, some eels moved up north to exit the North Sea over the British Isles, confirming the existence of two different routes, even for eels exiting from a single river catchment. Furthermore, we observed a wide range in migration speeds (6.8-45.2 km day
). We hypothesize that these are likely attributed to water currents, with eels migrating through the English Channel being significantly faster than eels migrating northward.
GCMs (general circulation models) are main tools for generating climate projections for climate change research in hydrology and water resources. Accordingly, evaluating the performance of these ...models in simulating future climate is very important for choice of proper models. In this study, performance of 20 Coupled Model Intercomparison Project Phase 5 (CMIP5) model series was assessed using a technique for order performance by similarity to ideal solution (TOPSIS)-based approach together with normalized root mean square error (NRMSE), the Taylor skill score (
S
Taylor
), and two probability density function (PDF) skill scores. Precipitation and temperature data during 1976 to 2005 from three river basins including Zard River (ZR), Bakhtegan (BKH), and Ghareso (GH) in west and southwest Iran were used to select the best model. In general, models showed superiority in simulating temperature over precipitation. Based on the GCM ranking results for the ZR Basin, MIROC-ESM and IPSL-CM5A-LR were selected as the best and the weakest model, respectively. For the BKH Basin, the best model was BCC-CSM1.1 and the weakest IPSL-CM5A-MR and CCSM4. In other words, BCC-CSM1.1 had the maximum relative closeness to ideal solution. Based on the TOPSIS results, BCC-CSM1.1 and CanESM2 were the best models and IPSL-CM5A-MR the weakest model with a minimum relative closeness to the ideal solution in simulating temperature and precipitation for the GH basin. The approach presented in this study can be utilized to select appropriate climate models in other regions for future studies of climate change.
•Mesopelagic animals formed a deep scattering layer at the Arctic-Atlantic gateway.•Segregation of epi- and mesopelagic animals under sea ice during the midnight sun.•Higher mesopelagic ...backscattering strength than previously reported in the Arctic.•Link between mesopelagic backscattering strength and Atlantic water circulation.
Changes in vertical and spatial distributions of zooplankton and small pelagic fish impact the biological carbon pump and the distribution of larger piscivorous fish and marine mammal species. However, their distribution and abundance remain poorly documented at high latitudes because of the difficulties inherent to sampling relatively fast-moving organisms in ice-covered waters. This study documents the under-ice distribution of epipelagic and mesopelagic organisms at the Arctic-Atlantic gateway in spring, during the midnight sun period, using ice-tethered and ship-based echosounders. An epipelagic surface scattering layer composed of copepods consistently occupied the top 60 m and was associated with cold polar surface water (mean temperature of −1.5 °C). A mesopelagic deep scattering layer (DSL), partly composed of fish, persisted between 280 m and 600 m and was associated with modified Atlantic water. Backscattering strength within the DSL was higher than previously reported in the Arctic and north Atlantic, and increased by two orders of magnitude over the continental slope where one of the Atlantic water pathways enters the Arctic Ocean. Mesopelagic organisms did not perform diel vertical migrations. The consistent segregation between copepods at the surface and their predators at mesopelagic depths suggests limited predator–prey interactions during the midnight sun period, even under the ice cover. Predation on copepods by mesopelagic organisms, including fish, could thus be limited to very pulsed events during the seasonal vertical migration of copepods to and from overwintering depths. This suggests that the arctic mesopelagic food web may be decoupled from secondary production in the epipelagic layer throughout most of the year.
Abstract
Anoxic zones, regions of the water column completely devoid of dissolved oxygen, occur in open oceans and coastal zones worldwide. The Baltic Sea is characterized by strong salinity-driven ...stratification, maintained by occasional water inflows from the Danish Straights and freshwater input from rivers. Between inflow events, the stratification interface between surface and deep waters hinders mixing and ventilation of deep water; consequently, the bottom waters of large regions of the Baltic are anoxic. The onset of the anoxic zone is closely coincident with the depth of the halocline and, as a result, the interface between oxic and anoxic waters corresponds to a strong impedance contrast. Here, we track acoustic scattering from the impedance contrast utilizing a broadband split-beam echosounder in the Western Gotland Basin and link it to a dissolved oxygen level of 2 ml/l using ground truth stations. The broadband acoustic dataset provides the means to remotely observe the spatiotemporal variations in the oxic–anoxic interface, map out the extent of the anoxic zone with high resolution, and identify several mechanisms influencing the vertical distribution of oxygen in the water column. The method described here can be used to study other systems with applications in ongoing oceanographic monitoring programs.
Riparian vegetation directly or indirectly affects many important structural and functional processes in stream ecosystems. We used a contiguous paired-reach approach in ∼4 km of open and shaded ...reaches in 8 boreal streams to study the effects of canopy cover on in-stream physicochemical (temperature, nutrients), substratum, and biotic assemblages (benthic diatom, macrophyte, invertebrate). Canopy cover, woody debris, and summer temperatures differed between paired reaches. Variation partitioning (partial redundancy analysis) showed that benthic diatom traits, but not species composition, were related strongly to canopy cover (33% of the variance was explained by canopy cover alone). In contrast, using variation partitioning, we found no support for the hypothesis that canopy cover was a strong predictor of macrophyte or benthic invertebrate assemblages. However, multivariable regression (redundancy analysis) showed that canopy cover was a significant predictor of invertebrate taxonomic and trait composition (explaining ∼26% of the variability), after accounting for covariance with other environmental variables. In agreement with predictions, univariate analyses revealed that macrophyte traits related to light and growth forms were correlated negatively with canopy cover. Our findings that canopy cover resulted in lower summer temperatures, higher amounts of woody debris, and differences in community structure and traits support the importance of riparian buffer strips as a management tool for maintaining biodiversity and for managing stream ecosystems for the warmer future.
This expert opinion study examined the current status of the intertidal zone in the Western Indian Ocean (WIO) and ranked and discussed future management approaches. Information was gathered from ...scientists, practitioners, and managers active in the WIO region through a questionnaire and a workshop. The experts stated that the productive intertidal environment is highly valuable for reasons such as recreation, erosion protection, and provision of edible invertebrates and fish. Several anthropogenic pressures were identified, including pollution, harbor activities, overexploitation, and climate change. The experts considered the WIO intertidal zone as generally understudied, undermanaged, and with poor or no monitoring. The most important management strategies according to the expert opinions are to develop and involve local people in integrated coastal zone management (ICZM), to increase knowledge on species–environment relationships, and to develop awareness campaigns and education programs. To improve coastal environmental management and conservation, we argue that the intertidal zone should be treated as one organizational management unit within the larger framework of ICZM.
•Salts in frozen soils impact freezing point and vary with time during freezing.•Couplings in water, heat and energy processes were found in frozen soils simulation.•Boundary conditions were found to ...impact surface water and energy balance.•Salts transport was underestimated by the model.
Soil freezing/thawing is an important mechanism to control soil water and heat redistribution in mid-to-high latitudes. Salt in the agricultural soil from mid-to-high latitudes can alter characteristics of soil freezing/thawing cycle and then affect soil thermal and hydrological processes in winter and finally cause salinization in spring. To quantify the impacts of soil salinization on soil water and heat transport in saline soils, we conducted field experiments on soil water and heat dynamics in two typical agricultural regions of northern China with different climate and soil conditions. The coupled soil heat and water model—CoupModel has been extended to account for the dynamic impacts of salt on freezing point depression. The newly-added module improved the representation of soil freezing point depression by significantly improving model performance between simulated and measured soil temperatures, especially around freezing point, with mean error (ME) for the soil temperature at various depths reduced by 16% to 77% for the entire winter period. With a systematic model calibration approach, processes related to energy balance and soil freezing/thawing have been well constrained for both study sites with different characteristics for soil hydrology and energy balance. The model generally showed good performance with respect to soil moisture and temperature for both the calibration and validation periods. Our study has demonstrated a new modeling approach to successfully account for the impacts of salt on soil freezing/thawing and the new module can be a useful tool to address the salinization problems in mid-to-high latitudes with respect to climate change and water management.
Anthropogenic transformation of land globally is threatening water resources in terms of quality and availability. Managing water resources to ensure sustainable utilization is important for a ...semiarid country such as South Africa. Bayesian networks (BNs) are probabilistic graphical models that have been applied globally to a range of water resources management studies; however, there has been very limited application of BNs to similar studies in South Africa. This article explores the benefits and challenges of BN application in the context of water resources management, specifically in relation to South Africa. A brief overview describes BNs, followed by details of some of the possible opportunities for BNs to benefit water resources management. These include the ability to use quantitative and qualitative information, data, and expert knowledge. BN models can be integrated into geographic information systems and predict impact of ecosystem services and sustainability indicators. With additional data and information, BNs can be updated, allowing for integration into an adaptive management process. Challenges in the application of BNs include oversimplification of complex systems, constraints of BNs with categorical nodes for continuous variables, unclear use of expert knowledge, and treatment of uncertainty. BNs have tremendous potential to guide decision making by providing a holistic approach to water resources management.
The change in Soil Moisture Content (SMC) is one of the most crucial variables for regulating and analyzing basic hydrological processes, including runoff, evaporation, carbon and energy cycles, ...infiltration of water resources, droughts and floods, and desertification. This study aimed to detect and map the global SMC change using microwave remote sensing observations. Monthly SMC data from the Soil Moisture Ocean Salinity (SMOS) with a spatial resolution of 25 km were used to assess the SMC change from January 2010 to December 2021. Various trend patterns, including linear, quadratic, cubic, and concealed, were examined by applying a parametric polynomial fitting-based algorithm (Polytrend). In particular, approximately 16.93% of global land is subjected to soil moisture dynamics, of which 8.33% has become drier and 8.60% has become wetter. Both linear and nonlinear trends were observed in the global land areas that have experienced statistically significant changes. The concealed and linear trends were however the dominant trend patterns globally. The obtained trend results were further investigated using a well-known non-parametric trend test, Mann-Kendall, which showed 93.20% agreement, demonstrating the robustness and reliability of the observed trends.
PDF
