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The genus Eurytemora is a diverse group of copepods found in coastal, estuarine, brackish, and freshwater environments. The main research has focused on Eurytemora affinis (Poppe, 1880) and revealed it to be a species complex. Eurytemora velox (Liljeborg, 1853) has only recently been characterized in the Scheldt estuary but never within a global phylogenetic context. This study integrated nearly all European Eurytemora species sequences available, along with original ones from the Scheldt. A total of 351 sequences were analyzed using one mitochondrial gene (CO1) and one nuclear gene (nITS), with sequencing performed specifically on the CO1 gene. Phylogenetic reconstructions were performed using the Maximum Likelihood method, along with haplowebs and genetic diversity indices. A significant subdivision between six European species was observed. The monophyletic clade status of the E. affinis complex was confirmed alongside the existence of three geographically isolated lineages of the E. affinis species, the East Atlantic, the North Sea/English Channel, and the Baltic lineages, each exhibiting pronounced genetic differentiation. The population of E. velox from the Urals differs significantly from the European ones. These results provide both an overview of the genetic structure of the genus in geographic Europe as well as new insights on E. velox. [ABSTRACT FROM AUTHOR]

Policy makers increasingly acknowledge the importance of considering ecosystem services (ESs) and biodiversity in impact assessment (IA) to reduce ecosystem degradation and halt ongoing losses of biodiversity. Recent research demonstrates how ESs can add value to IA, i.e., by shifting the focus from avoiding negative impacts to creating opportunities, by linking effects on ecological functioning to benefits for society, and by providing a multi-disciplinary framework that allows to consider cross-sectoral effects. However, challenges exist to its implementation in practice. The most commonly used ES models do not consider interactions among ESs. This restricts their capacity to account for cross-sectoral effects. Integrating ESs into IA also increases time investments as they cover a wide variety of disciplines and need detailed information. This paper presents a pragmatic approach that tackles these challenges and may facilitate the inclusion of ESs into IA. The approach focuses on ecosystem processes as the driver of ESs and biodiversity and the basis to evaluate effects of a project. Using the Belgian coastal ecosystem, we illustrate how the approach restricts data needs by identifying the priority ESs, how it improves the coverage of cross-sectoral effects in IA, and how it contributes to a more objective selection of impacts. [ABSTRACT FROM AUTHOR]

There is increasing recognition that soils fulfil many functions for society. Each soil can deliver a range of functions, but some soils are more effective at some functions than others due to their intrinsic properties. In this study we mapped four different soil functions on agricultural lands across the European Union. For each soil function, indicators were developed to evaluate their performance. To calculate the indicators and assess the interdependencies between the soil functions, data from continental long‐term simulation with the DayCent model were used to build crop‐specific Bayesian networks. These Bayesian Networks were then used to calculate the soil functions' performance and trade‐offs between the soil functions under current conditions. For each soil function the maximum potential was estimated across the European Union and changes in trade‐offs were assessed. By deriving current and potential soil function delivery from Bayesian networks a better understanding is gained of how different soil functions and their interdependencies can differ depending on soil, climate and management. Highlights: When increasing a soil function, how do trade‐offs affect the other functions under different conditions?Bayesian networks evaluate trade‐offs between soil functions and estimate their maximal delivery.Maximizing a soil function has varied effects on other functions depending on soil, climate and management.Differences in trade‐offs make some locations more suitable for increasing a soil function then others. [ABSTRACT FROM AUTHOR]

Many estuaries exhibit seasonality in the estuary-scale distribution of suspended particulate matter (SPM). This SPM distribution depends on various factors, including freshwater discharge, salinity intrusion, erodibility, and the ability of cohesive SPM to flocculate into larger aggregates. Various authors indicate that biotic factors, such as the presence of algae and their excretion of sticky transparent exopolymer particles (TEP), affect the flocculation and erosion processes. Consequently, seasonality in these biotic factors may play a role in the observed seasonality in SPM. Whereas the impact of abiotic factors on seasonality in SPM is well studied, the relative contribution of biotically induced seasonality is largely unknown. In this study, we employ two approaches to assess the aggregated importance of biotically induced seasonality in flocculation and erosion on seasonality in SPM in the Scheldt estuary. In the first approach, we focus on seasonality of in situ observations in the Scheldt estuary of turbidity, floc size, Chlorophyll-a, and TEP, showing that the abiotic parameters show seasonality, while seasonality in TEP is ambiguous. The second approach concerns a reverse engineering method to calibrate biotically affected parameters of a coupled sediment transport-flocculation model to turbidity observations, allowing us to compare the modeled SPM concentrations to the observations. Driven by seasonality in freshwater discharge, the model captures the observed seasonality in SPM without requiring biotically induced seasonality in flocculation and erosion, which is supported by the absence of seasonality in TEP. [ABSTRACT FROM AUTHOR]

Estuaries often show regions in which Chlorophyll-a (Chl-a) accumulates. The location and magnitude corresponding to such accumulation result from a complex interplay between processes such as river flushing, salinity, nutrients, phytoplankton grazing, and the light climate in the water column. Of particular interest is the long-term evolution of the estuary-scale Chl-a distribution in the Scheldt estuary (Belgium/Netherlands) in spring. From 2004-2007, we observed a limited spring-bloom in the brackish region. This bloom intensified in 2008-2014 and disappeared after 2015. This long-term evolution in Chl-a has been linked to simultaneous long-term trends in the suspended particulate matter (SPM) distribution and the improvement of the water quality, which affects grazing of Chl-a by zooplankton. However, this hypothesis has not been systematically investigated. In this paper, we apply two approaches to test this hypothesis. In the first approach, we analyze long-term in situ observations covering the full estuary. These observations include the SPM concentration, zooplankton abundance, and other variables affecting the Chl-a concentration, and show a long-term estuary-scale evolution in not only the SPM distribution but also in zooplankton abundance, freshwater discharge, and maximum photosynthetic rate. In the second approach, we apply a model approach supported by these observations to determine which of the changed conditions may explain the observed change in Chl-a. Our results suggest that a change in SPM alone cannot explain the Chl-a observations. Instead, mortality rate and grazing by zooplankton mainly explains the long-term estuary-scale evolution of Chl-a in spring. Our results highlight that insight into the zooplankton dynamics is essential to understand the phytoplankton (cf. Chl-a) dynamics in the Scheldt estuary. [ABSTRACT FROM AUTHOR]

Macrophytes are important organisms in running water systems, having a decisive role in ecological processes and interactions. Their temporal and spatial distribution in streams can be highly variable, and this is often determined by flow velocity. In this study, macrophyte growth, morphology and nutrient stoichiometry were studied monthly during one growing season in reaches with different flow velocity and flow velocity distribution and, as a result, different distributional plant patterns in an Austrian lowland stream, dominated by evergreen macrophyte species, Berula erecta. Flow velocity, water depth, fine sediment layer depth and metabolism were measured in the stream and the correlation with plant biomass and morphological traits was tested. We aimed to study differences between reaches with different distributional plant patterns and whether common interactions between macrophytes and flow velocity can also be observed when vegetation is evergreen. Plant biomass showed seasonal variation, with the highest values in June and the lowest in February. In the reach with low flow velocity and homogeneous macrophyte distribution, biomass peaked in summer and plant morphology changed with the seasons, whereas biomass and morphology in the reach with high flow velocity and patchy distribution were more constant throughout the year. Plant carbon, nitrogen and phosphorus content were higher in spring and autumn than in summer, whereas biogenic silica accumulated over the course of the growth season. Stream metabolism was strongly correlated with macrophyte biomass, and this correlation was stronger in the reach with homogeneous macrophyte distribution than in the reach with a patchy distribution. Moreover, average leaf area and stem length were positively correlated with fine sediment layer depth, and negatively with flow velocity. The results stress the importance of macrophyte growth and morphology in river processes like metabolism, hydromorphology and nutrient dynamics: especially plant morphology plays an important role in macrophyte–flow interactions. [ABSTRACT FROM AUTHOR]

Climate change can result in multiple indirect alterations of the environment in riverine ecosystems, due to changes in precipitation and runoff. Flow velocity, concentrations of CO2 and nutrients are thereby expected to change, and consequences of the combination of those effects for macrophytes, a key organism group, are still poorly understood. This was tested in a racetrack flume experiment on macrophyte species Berula erecta, an amphibious species growing fully submerged in the experiment. In a full-factorial design, plants were exposed to two different CO2 concentrations, two nutrient concentrations (N, P and Si) and two flow velocities. Apart from individual dose–response tests, two climate change scenarios were tested: a wet scenario simulating heavy precipitation and runoff with high flow velocity, high CO2 and high nutrient concentrations and a dry scenario simulating evapotranspiration with low flow velocity, high CO2 and high nutrient concentrations. Growth rate, biomass, morphology, chlorophyll and nutrient content were measured. Berula erecta responded strongly to both scenarios. Biomass and relative growth rate increased, leaf BSi content decreased, and especially in the wet scenario macrophytes had shorter stems and formed stolons with new ramets: the plants invested in horizontal growth to avoid hydrodynamic stress. Moreover, the C/N ratio was higher, leading to lower quality of macrophyte tissue as food source, and chlorophyll concentration was lower in the high CO2 treatment. It can be concluded that combined stressors caused by climate change strongly affect macrophytes, which may indirectly have consequences for other organisms of the aquatic ecosystem that depend on macrophytes. [ABSTRACT FROM AUTHOR]

Sediment transport in estuaries and the formation of estuarine turbidity maxima (ETM) highly depend on the ability of suspended particulate matter (SPM) to flocculate into larger aggregates. While most literature focuses on the small-scale impact of biological flocculants on the formation of larger aggregates, the influence of the flocculation process on large-scale estuarine SPM profiles is still largely unknown. In this paper, we study the impact of flocculation of SPM on the formation of ETM. For this, a semianalytical width-integrated model called iFlow is utilized and extended by a flocculation model. Starting from a complex one-class flocculation model, we show that flocculation may be described as a linear relation between settling velocity and suspended sediment concentration to capture its leading-order effect on the ETM formation. The model is applied to a winter case in the Scheldt estuary (Belgium, Netherlands) and calibrated to a unique, long-term, two-dimensional set of turbidity (cf. SPM) observations. First, model results with and without the effect of flocculation are compared, showing that the spatial and temporal variations of the settling velocity due to flocculation are essential to reproduce the observed magnitude of the suspended sediment concentrations and its dependence on river discharge. Second, flocculation results in tidally averaged land-inward sediment transport. Third, we conduct a sensitivity analysis of the freshwater discharge and floc breakup parameter, which shows that flocculation can cause additional estuarine turbidity maxima and can prevent flushing of the ETM for high freshwater inflow. [ABSTRACT FROM AUTHOR]

The Chinese mitten crab (Eriocheir sinensis) is a damaging invader which is designated as a species of Union Concern within the European Union. A negative impact of the crabs on macrophyte vegetation in lowland rivers is suspected but not yet proven or quantified. We have performed a mesocosm study that combines a density gradient of Chinese mitten crabs (0, 0.3, 1.0 and 2.5 ind. m−2) with chemical stress (2350 µg EDTA L−1 + 258 µg glyphosate L−1) or light limitation stress (− 70% irradiance compared to control) on water plants (Myriophyllum spicatum). The results clearly demonstrate that the crabs are capable of removing plant shoots effectively which can lead to a complete elimination of the vegetation. Generally, the higher the crab density, the sooner the plants started to disappear and the sooner the vegetation was completely removed. Additional light and chemical stress accelerated this process: plant disappearance at a crab density of 0.3 ind. m−2 compared to 1.0 ind. m−2 in the control treatments. Video recording, plant strength and crab pinch strength measurements and stable isotope signatures of δ13C and δ15N in the Chinese mitten crabs and their possible food sources showed that directly eating the plants is causing only minor damage to the plants. Most damage comes from the movement of the crabs and crab–crab interactions during which they use their chelae to grasp the shoots. We conclude that a decline of vegetation as a consequence of Chinese mitten crab behaviour can be a realistic scenario in freshwater ecosystems and warrants close attention and monitoring. Being primary producers and ecological engineers, macrophytes are key species in these ecosystems, whose services are lost when they disappear and are difficult to restore. [ABSTRACT FROM AUTHOR]

The weathering of silicates is a major control on atmospheric CO2 at geologic timescales. It was proposed to enhance this process to actively remove CO2 from the atmosphere. While there are some studies that propose and theoretically analyze the application of rock powder to agricultural land, results from field experiments are still scarce. In order to evaluate the efficiency and side effects of Enhanced Weathering (EW), a mesocosm experiment was set up and agricultural soil from Belgium was amended with olivine-bearing dunite ground to two different grain sizes, while distinguishing setups with and without crops. Based on measurements of Mg, Si, pH, and DIC, the additional weathering effect of olivine could be confirmed. Calculated weathering rates are up to 3 orders of magnitude lower than found in other studies. The calculated CO2 consumption by weathering based on the outlet water of the mesocosm systems was low with 2.3–4.9 tCO2km-2a-1 if compared with previous theoretical estimates. Suspected causes were the removal or dilution of Mg as a weathering product by processes like adsorption, mineralization, plant uptake, evapotranspiration, and/or preferential flow, not specifically addressed in previous EW experiments for CO2 consumption. The observation that Mg concentrations in the upper soil layers were about 1 order of magnitude higher than in the outlet water indicates that a careful tracking of weathering indicators like Mg in the field is essential for a precise estimate of the CO2 consumption potential of EW, specifically under global deployment scenarios with a high diversity of ecosystem settings. Porewater Mg/Si molar ratios suggest that dissolved Si is reprecipitating, forming a cation-depleted Si layer on the reactive mineral surface of freshly ground rocks. The release of potentially harmful trace elements is an acknowledged side effect of EW. Primarily Ni and Cr are elevated in the soil solution, while Ni concentrations exceed the limits of drinking water quality. The use of olivine, rich in Ni and Cr, is not recommended, and alternative rock sources are suggested for the application. [ABSTRACT FROM AUTHOR]

Aquatic macrophytes can have a significant impact on their associated community of epiphytic algae and bacteria through the provisioning of structural habitat complexity through different growth forms, the exudation of nutrients and the release of allelochemicals. In turn, this effect on epiphytic biofilm biomass and nutrient content has a potential effect on the macroinvertebrates that depend on epiphyton as a food source.We studied the effect of living macrophytes and their growth form on biofilm development in a semi‐controlled replicated microcosm experiment. Conditions of a nutrient‐poor water layer and nutrient‐rich sediment were created to study the effects of nutrient exudation by living macrophytes. We compared biofilm quantity and quality on structurally simple (Vallisneria spiralis) versus complex (Egeria densa) living plants and artificial analogues. Subsequently, the biofilm that had developed on the plants was fed, in a laboratory growth experiment, to two species of macroinvertebrate grazers (the snail Haitia acuta and the mayfly nymph Cloeon dipterum). This enabled us to assess if and how the macrophyte‐induced effects on the epiphyton can influence macroinvertebrate grazers.Living macrophytes were found to have a significant effect on epiphytic algal cover, which was mostly expressed by a lower cover on living macrophytes compared to their artificial analogues. Additionally, epiphyton cover on artificial macrophytes was found to be higher on complex structures compared to simple ones, yet this was not observed on living macrophytes. Plant specific traits, such as the release of allelopathic substances, competition for nutrients and DIC, and the amount of CaCO3 deposition on plant surfaces might explain these results.The density of epiphytic bacteria was found to be negatively correlated with biofilm Ca content from macrophytes in every treatment except living E. densa, which differed in leaf anatomy from the other plants by possessing polar leaves. Furthermore, biofilm on living macrophytes had lower C:N:P molar ratios compared to that on artificial plants, which is likely to be explained by nutrient exudation by the living plants. Although it was expected that a more nutritious biofilm would lead to increased grazer growth, this was observed only for H. acuta on E. densa. Because biofilm quantity was not a limiting factor, this lack of effect may be caused by compensatory feeding.It can be concluded that, depending on their traits, living macrophytes can have a positive effect on macroinvertebrate grazers by providing a large surface area for colonisation by epiphytic algae and bacteria, by improving biofilm stoichiometry and by stimulating bacterial growth. [ABSTRACT FROM AUTHOR]

Microhabitat suitability models are useful tools to enhance the reintroduction success of fish. Since 2008, a translocation and reintroduction program has been carried out in Flanders to prevent substantial loss of genetic variability in the Cottus perifretum (bullhead) population, and to meet the goals set by the Habitat Directive. To this end, habitat suitability of potential headstreams was assessed on a macrohabitat and microhabitat scale prior to the reintroduction. On a macrohabitat scale, water quality, habitat structure, food availability, and fish community were screened. Based on microhabitat models for bullhead in the summer period, microhabitat suitability was assessed in headstreams where macrohabitat characteristics showed a high potential for success. Both macro‐ and microhabitat assessment showed that reintroduction of bullheads in the Nellebeek, Bruelbeek, and Mollendaalbeek would most likely lead to self‐sustaining populations. For the Sint‐Annabeek, the microhabitat suitability model, considering depth and stream velocity, estimates that 7.5–9.5% of the headstream is suitable for bullhead. However, when substratum is taken into account, the microhabitat suitability index shows that only 4.3–5.8% of the brook is suitable. The current habitat quality and quantity in the Sint‐Annabeek is estimated to support a mean total population of 812 bullheads. However, the microhabitat suitability can be substantially improved by the artificial deposition of medium‐sized gravel (5–50 mm) and large gravel (50–100 mm). By doing so, the mean estimated population size could increase up to 1,330 individuals. Our results show that habitat improvement is necessary prior to the reintroduction of bullheads in the Sint‐Annabeek. [ABSTRACT FROM AUTHOR]

There are many different anthropogenic causes of wetland degradation, such as disturbances which affect the physical structure of wetlands, resulting in erosion (altered fire regimes, road and railway building through wetlands, channelization of wetlands), pollution, land-cover change, and climate change. These different types of degradation have various impacts, depending on the type of wetland, soils, biochemistry and other factors. We researched a poorly-studied South African valley-bottom peatland that is dominated by the ecosystem engineer Palmiet: Prionium serratum. We ask the question: what is the impact of degradation by gully erosion, pollution and alien tree invasion on biochemistry and plant community composition of palmiet wetlands? In 39 plots from three palmiet wetlands situated approximately 200 km apart we found that channel erosion, through a loss of alluvium, has probably resulted in leached soils with lower soil organic matter and water content, less able to retain nutrients and cations. Soil leaching is a possible explanation for the groundwater of degraded wetlands having higher electrical conductivity and pH than that of pristine wetlands and a lower soil cation exchange capacity (21.3 ± 5.80-7.7 ± 4.91 meq/100 g). The loss of alluvium typically resulted in a completely new plant community, composed mostly of pioneer species and several alien species. The increase in base saturation (17.5 ± 8.46-30.2 ± 17.85%) and soil pH (4.8 ± 0.51-5.1 ± 0.50) with degradation was hypothesized to be the result of liming practices. Once extremely degraded, i.e. all the alluvium is lost, it is unlikely that these sensitive palmiet wetlands will recover original vegetation communities and lost functions, except on long timescales. We recommend conservation of the few pristine wetlands that remain, and rehabilitation of those that still retain some of their original function. [ABSTRACT FROM AUTHOR]

Many macrophyte species in lowland streams exhibit signs of grazing and herbivore damage, even though herbivory by aquatic macroinvertebrates and fish is generally considered to be of little importance. In this study, we collected evidence for the hypothesis that herbivory on macrophytes by macroinvertebrates and fish is more widespread than assumed. We measured the dual stable isotope signatures (δ13C and δ15N) of organic matter, epiphyton, submerged macrophytes, macroinvertebrates and fish in a Belgian lowland stream. There was a clear distinction in isotopic signatures of the different basal resources, allowing the use of the SIAR mixing model. These calculations revealed the consumption of macrophyte tissue not only by the phytophagous larvae of Nymphula nitidulata Hufnagel (Lepidoptera: Crambidae), but also by Baetidae nymphs (Ephemeroptera), Orthocladiinae larvae (Diptera: Chironomidae), the crayfish Orconectus limosus Rafinesque (Decapoda: Cambaridae) and the fish Gobio gobio L. (Cypriniformes: Cyprinidae) which are classified as feeding on other resources. Although the potential share of macrophyte biomass in the diet of macroinvertebrates and fish was demonstrated to be up to 49%, this amount is only a small percentage of the total standing macrophyte biomass in a lowland stream. However, the impact of this herbivory may still be substantial because consumption may comprise a significant fraction of the daily primary production. Additionally, small-scale herbivory may still have a negative impact on macrophyte growth and survival, for example through consumption of apical meristems and the increased susceptibility to diseases and toxins if the macrophyte’s epidermis is damaged. [ABSTRACT FROM AUTHOR]

The weathering of silicates is a major control on atmospheric CO2 at geologic time scales. It was proposed to enhance this process to actively remove CO2 from the atmosphere. While there are some studies that propose and theoretically analyze the application of rock powder on agricultural land, results from field experiments are still scarce. In order to evaluate the efficiency and side effects of Enhanced Weathering, a mesocosm experiment was set up and agricultural soil from Belgium was amended with olivine-bearing dunite ground to two different grain sizes, while distinguishing setups with and without crops. Based on measurements of Mg, Si, pH, and DIC, the additional weathering effect of olivine could be confirmed. Calculated weathering rates are up to three orders of magnitude lower than found in other studies. The calculated CO2 consumption by weathering was comparably low with 2.3 to 4.9 CO2tkm−2a−1. One identified cause was preferential flow leading to a low water-rock interaction time for a significant water volume in the setup, not addressed in previous Enhanced Weathering experiments for CO2 consumption. Correction for preferential flow leads to fluxes about a magnitude higher, confirming that this process and surface runoff in the field must be included in assessments for the CO2 consumption potential of Enhanced Weathering in general. Pore water Mg/Si molar ratios suggest that dissolved Si from the added minerals stays in the system over the observation period, because a cation depleted Si layer forms on the reactive mineral surface of freshly ground rocks. This layer has not reached equilibrium thickness within the first two years. The release of potentially harmful trace elements is an acknowledged side effect of Enhanced Weathering. Primarily Ni and Cr are elevated in soil solution, while Ni concentrations exceed the limits of drinking water quality. The use of olivine, rich in Ni and Cr, is not recommend and alternative rock sources are suggested for the application. [ABSTRACT FROM AUTHOR]

Despite the importance of water purification to society, it is one of the more difficult wetland ecosystem services to quantify. It remains an issue in ecosystem service assessments where rapid estimates are needed, and poor-quality indicators are overused. We attempted to quantify the water purification service of South African palmiet wetlands (valley-bottom peatlands highly threatened by agriculture). First, we used an instantaneous catchment-scale mass balance sampling approach, which compared the fate of various water quality parameters over degraded and pristine sections of palmiet wetlands. We found that pristine palmiet wetlands acted as a sink for water, major cations, anions, dissolved silicon and nutrients, though there was relatively high variation in these trends. There are important limitations to this catchment-scale approach, including the fact that at this large scale there are multiple mechanisms (internal wetland processes as well as external inputs) at work that are impossible to untangle with limited data. Therefore, secondly, we performed a small field-scale field survey of a wetland fragment to corroborate the catchment-scale results. There was a reasonable level of agreement between the results of the two techniques. We conclude that it appears possible to estimate the water purification function of these valley-bottom wetlands using this catchment-scale approach. [ABSTRACT FROM AUTHOR]

The reliability of large-scale particle image velocimetry (LSPIV) methodology to measure a 2D surface velocity field in a vegetated lowland stream is evaluated. To this end, measurements of the free-surface flow field obtained with LSPIV are compared with measurements with an electromagnetic current meter (ECM) close to the surface at four different locations. The measurements were performed monthly, allowing the evaluation of the LSPIV measurements in relation to different vegetated conditions. The difference observed between the mean velocities measured with ECM and LSPIV remains low in winter, whereas an increase is observed in summer. Inappropriate particle seeding density and unsteadiness of the flow are the main sources of LSPIV reliability reduction. Nonetheless, the seasonal average frequency of reliable LSPIV measurements is 97%, 95% and 78% in winter, spring and summer, respectively. The results illustrate that LSPIV is an inexpensive methodology, which provides high-resolution and reliable data to study the flow-field distribution in vegetated rivers, provided some considerations are taken into account to deal with the added complexity of the vegetation presence and the field conditions. [ABSTRACT FROM AUTHOR]

Freshwater ecosystems are confronted with the effects of climate change. One of the major changes is an increased concentration of aquatic carbon. Macrophytes are important in the aquatic carbon cycle and play as primary producers a crucial role in carbon storage in aquatic systems. However, macrophytes are affected by increasing carbon concentrations. The focus of this review lies on dissolved organic carbon (DOC), one of the most abundant forms of carbon in aquatic ecosystems which has many effects on macrophytes. DOC concentrations are rising; the exact cause of this increase is not known, although it is hypothesized that climate change is one of the drivers. The quality of DOC is also changing; for example, in urban areas DOC composition is different from the composition in natural watersheds, resulting in DOC that is more resistant to photo-degradation. Plants can benefit from DOC as it attenuates UV-B radiation, it binds potentially harmful heavy metals and provides CO2 as it breaks down. Yet plant growth can also be impaired under high DOC concentrations, especially by humic substances (HS). HS turn the water brown and attenuate light, which limits macrophyte photosynthesis at greater depths. This leads to lower macrophyte abundance and lower species diversity. HS form a wide class of chemicals with many different functional groups and they therefore have the ability to interfere with many biochemical processes that occur in freshwater organisms. Few studies have looked into the direct effects of HS on macrophytes, but there is evidence that HS can interfere with photosynthesis by entering macrophyte cells and causing damage. DOC can also affect reactivity of heavy metals, water and sediment chemistry. This indirectly affects macrophytes too, so they are exposed to multiple stressors that may have contradictive effects. Finally, macrophytes can affect DOC quality and quantity as they produce DOC themselves and provide a substrate to heterotrophic bacteria that degrade DOC. Because macrophytes take a key position in the aquatic ecosystem, it is essential to understand to what extent DOC quantity and quality in surface water are changing and how this will affect macrophyte growth and species diversity in the future. [ABSTRACT FROM AUTHOR]

Tidal marsh (re)creation on formerly embanked land is increasingly executed along estuaries and coasts in Europe and the USA, either by restoring complete or by reduced tidal exchange. Ecosystem functioning and services are largely affected by the hydro-geomorphologic development of these areas. For natural marshes, the latter is known to be steered by feedbacks between tidal inundation and sediment accretion, allowing marshes to reach and maintain an equilibrium elevation relative to the mean sea level. However, for marsh restoration sites, these feedbacks may be disturbed depending on the restoration design. This was investigated by comparing the inundation-elevation change feedbacks in a natural versus restoration site with reduced tidal exchange in the Scheldt estuary (Belgium). This study analyzes long-term (9 years) datasets on elevation change and tidal inundation properties to disentangle the different mechanisms behind this elevation-inundation feedback. Moreover, subsequent changes in sediment properties that may affect this feedback were explored. In the restoration area with reduced tidal exchange, we found a different elevation-inundation feedback than on natural marshes, which is a positive feedback on initially high sites (i.e., sediment accretion leads to increasing inundation, hence causing accelerating sediment accretion rates) and a gradual silting up of the whole area. Furthermore, there is evidence for the presence of a relict consolidated sediment layer. Consequently, shallow subsidence is less likely to occur. Although short-term ecological development of the tidal marsh was not impeded, long-term habitat development may be affected by the differences in hydro-geomorphological interactions. An increase of inundation frequency on the initially high sites may cause inhibition of habitat succession or even reversed succession. Over time, the climax state of the restoration area may be different compared to natural marshes. Moreover, sediment-related ecosystem services, such as nutrient and carbon burial, may be positively influenced because of continuing sedimentation, although flood water storage potential will decrease with increasing elevation. Depending on the restoration goals, ecosystem trajectories and delivery of ecosystem services can be controlled by adaptive management of the tidal volume entering the restoration area. [ABSTRACT FROM AUTHOR]

Abstract: Tidal marsh vegetation is increasingly valued for its role in ecosystem‐based coastal protection due to its wave dissipating capacity. As the efficiency of wave dissipation is known to depend on specific vegetation properties, we quantified how these morphological, biochemical, and biomechanical properties of tidal marsh vegetation are, in turn, affected by wave exposure. This was achieved by field measurements at two locations, with contrasting wave exposure, in the brackish part of the Scheldt Estuary (SW Netherlands), where Scirpus maritimus is the dominant pioneer species. Our results show that shoots from more wave‐exposed conditions developed significantly shorter and thicker stems than the ones growing in more sheltered conditions. Furthermore, we show that the more exposed shoots are more flexible whereas the shoots growing in more sheltered conditions are stiffer. This may indicate plasticity in response to wave exposure following a stress‐avoidance strategy. Increasing stiffness was shown to be related to enhanced biogenic silica and lignin contents of the shoot tissue. These properties might affect the wave‐attenuating capacity of the marsh as stiff plants are known to mitigate waves more effectively than flexible ones. However, we also found higher shoot densities on the exposed site, which may partly explain why higher relative wave attenuation rates were found on the exposed site, despite the presence of more flexible individual shoots. This study highlights that the efficiency of wave attenuation by tidal marsh vegetation ultimately depends on mutual interactions between waves and plasticity in morphological, biochemical, and biomechanical plant properties. [ABSTRACT FROM AUTHOR]

Habitat structural complexity provided by aquatic macrophytes in lowland streams affects the associated epiphytic macroinvertebrate assemblages in both direct (increased microhabitat diversity, refuge against predation) and indirect ways (e.g. current attenuation by physical structures). In a correlative field study carried out in two different years in a Belgian stream, we investigated the effects of the factors macrophyte identity, macrophyte complexity (represented as fractal complexity) and current velocity on the composition of the macroinvertebrate community associated with monospecific macrophyte patches, consisting of plants with differing structural complexity; Sparganium emersum Rehmann (least complex), Potamogeton natans L. (intermediate) and Callitriche obtusangula Le Gall (most complex). In addition to significantly lower within-patch current velocity being observed, vegetation stands consisting of complex macrophytes also harboured significantly richer macroinvertebrate communities than stands of simpler macrophytes. A significant part of the variation in the macroinvertebrate community composition could be explained by plant identity, macrophyte complexity and current velocity. However, it was not possible to determine the relative importance of these three factors, because of their high degree of intercorrelation. Additionally, the explanatory power of these factors was higher under conditions of high current velocity, suggesting a role of macrophyte patches as instream flow refugia for macroinvertebrates. [ABSTRACT FROM AUTHOR]

Patches are of central interest to many areas of environmental science because they provide a lower limit of structural detail in synoptic studies, and an upper limit of contextual structure for point measurement-based studies. Identification and delineation of macrophyte patches however, is often arbitrary and case-specific. In this paper we propose a widely-applicable set of guidelines for delineating a “patch” and “patch matrix” – the latter implying a collection of interacting patches – which could standardise future research. To support this proposal, we examine examples from eco-hydrological studies, focusing on interactions between plants, water flow, sediment, and invertebrates. We discuss three aspects that are key to the delineation of a patch: (1) constitution (variable(s) whose values define the patch), (2) spatial properties (patch boundaries), and (3) distinction (of isolated single patches from multiple separate-but-interacting patches). The discussion of these aspects results in guidelines for identifying and delineating a patch which is applicable to any aquatic habitat, and covers a broad range of disciplines such as plant and animal ecology, biogeochemistry, hydraulics, and sedimentology. [ABSTRACT FROM AUTHOR]

Accelerated mass loss from the Greenland ice sheet leads to glacier retreat and an increasing input of glacial meltwater to the fjords and coastal waters around Greenland. These high latitude ecosystems are highly productive and sustain important fisheries, yet it remains uncertain how they will respond to future changes in the Arctic cryosphere. Here we show that marine-terminating glaciers play a crucial role in sustaining high productivity of the fjord ecosystems. Hydrographic and biogeochemical data from two fjord systems adjacent to the Greenland ice sheet, suggest that marine ecosystem productivity is very differently regulated in fjords influenced by either land-terminating or marine-terminating glaciers. Rising subsurface meltwater plumes originating from marine-terminating glaciers entrain large volumes of ambient deep water to the surface. The resulting upwelling of nutrient-rich deep water sustains a high phytoplankton productivity throughout summer in the fjord with marine-terminating glaciers. In contrast, the fjord with only land-terminating glaciers lack this upwelling mechanism, and is characterized by lower productivity. Data on commercial halibut landings support that coastal regions influenced by large marine-terminating glaciers have substantially higher marine productivity. These results suggest that a switch from marine-terminating to land-terminating glaciers can substantially alter the productivity in the coastal zone around Greenland with potentially large ecological and socio-economic implications. [ABSTRACT FROM AUTHOR]

The role of in-stream aquatic vegetation as ecosystem engineers in the distribution of organic matter was investigated in the Okavango Delta, one of the world's largest oligotrophic wetlands. The Okavango channel beds are covered up to 50% with submerged macrophyte patches. By accumulating and concentrating organic matter in the sediments below the patches, macrophytes are likely able to locally forestall a deficiency of nutrients. Up to 21 times more N, 18 times more C, 13 times more P and 6 times more Si can be found in vegetated sediments compared to non-vegetated sediments. Nutrient specific accumulation relates to its relative scarcity in the overlaying water. There is a depletion of dissolved N relative to P, whereas Si is relatively abundant. The Okavango Delta water can generally be characterised as oligotrophic based on plant species composition (e.g. presence of carnivorous plants and absence of floating plants), low plant N:P ratios, and low nutrient- and element-concentrations. Local mineralization and intensified nutrient cycling in the sediments is hypothesized to be crucial for the macrophytes' survival because it provides a key source of the essential nutrients which plants otherwise cannot obtain in sufficient quantities from the nutrient poor water. By engineering the ecosystem as such, channel vegetation also retards the loss of elements and nutrients to island groundwater flow, contributing to one of the key processes driving the high productivity of the Okavango Delta, making it unique among its kind. [ABSTRACT FROM AUTHOR]

Land use change (deforestation) has several negative consequences for the soil system. It is known to increase erosion rates, which affect the distribution of elements in soils. In this context, the crucial nutrient Si has received little attention, especially in a tropical context. Therefore, we studied the effect of land conversion and erosion intensity on the biogenic silica pools in a subtropical soil in the south of Brazil. Biogenic silica (BSi) was determined using a novel alkaline continuous extraction where Si = Al ratios of the fractions extracted are used to distinguish BSi and other soluble fractions: Si = Al > 5 for the biogenic AlkExSi (alkalineextractable Si) and Si = Al < 5 for the non-biogenic AlkExSi. Our study shows that deforestation can rapidly (< 50 years) deplete the biogenic AlkExSi pool in soils depending on the slope of the study site (10-53%), with faster depletion in steeper sites. We show that higher erosion in steeper sites implies increased accumulation of biogenic Si in deposition zones near the bottom of the slope, where rapid burial can cause removal of BSi from biologically active zones. Our study highlights the interaction of erosion strength and land use for BSi redistribution and depletion in a soil toposequence, with implications for basin-scale Si cycling. [ABSTRACT FROM AUTHOR]

The presence of vegetation in stream ecosystems is highly dynamic in both space and time. A digital photography technique is developed to map aquatic vegetation cover at species level, which has a very high spatial and a flexible temporal resolution. A digital single-lens reflex (DSLR) camera mounted on a handheld telescopic pole is used. The low-altitude (5 m) orthogonal aerial images have a low spectral resolution (red-green-blue), high spatial resolution (∼1.9 pixels cm, ∼1.3 cm length) and flexible temporal resolution (monthly). The method is successfully applied in two lowland rivers to quantify four key properties of vegetated rivers: vegetation cover, patch size distribution, biomass and hydraulic resistance. The main advantages are that the method is (i) suitable for continuous and discontinuous vegetation covers, (ii) of very high spatial and flexible temporal resolution, (iii) relatively fast compared to conventional ground survey methods, (iv) non-destructive and (v) relatively cheap and easy to use, and (vi) the software is widely available and similar open source alternatives exist. The study area should be less than 10 m wide, and the prevailing light conditions and water turbidity levels should be sufficient to look into the water. Further improvements of the image processing are expected in the automatic delineation and classification of the vegetation patches. [ABSTRACT FROM AUTHOR]

Quantification of ecosystem services ( ES) is an important step in operationalizing the concept for management and decision-making. With the exponential increase in ES research, ES have become a 'catch-all phrase', which some suggest has led to a poorly defined, impractical and ambiguous concept. An overview of the methods used in ES quantification is needed to examine their scientific rigour and provide guidelines for selecting appropriate measures., We present a systematic review of 405 peer-reviewed ES research papers to address the question: 'Is the biophysical and socio-economic reality of ES adequately quantified? First, we considered whether ES measures are scientifically rigorous enough by considering four predefined criteria (the type of data used, quantification of uncertainty, validation done and data reported). Secondly, using a novel approach, we determined which part of the ES cascade was measured: the ecosystem property, function, service, benefit or value., Our results showed that each of the 21 ES analysed had on average 24 different measures, which may indicate the complex reality of ES and/or suggest a potential lack of consensus on what constitutes an ES. We found that uncertainty is often not included and validation mostly missing., When analysing which part(s) of the ES cascade each measure corresponded to, we found that for regulating ES, ecosystem properties and functions (ecological aspects) are more commonly quantified (67% of measures). Conversely for provisioning ES, benefits and values (socio-economic aspects) are more commonly quantified (68%). Cultural ES are predominantly quantified using scores (35%)., In conclusion, ES appear to be poorly quantified in many cases, as often only one side of the cascade is considered (either the ecological or socio-economic side) and oversimplified and variable indicators are often used., Policy implications. This review provides a detailed overview of ecosystem services ( ES) quantification (ranging from simple scores to advanced methods) with the aim to support future ES quantification and ultimately the successful application of the ES concept. [ABSTRACT FROM AUTHOR]

Agricultural ecosystems provide a range of benefits that are vital to human well-being. These benefits are dependent on several soil functions that are affected in different ways by legislation from the European Union, national, and regional levels. We evaluated current European Union soil-related legislation and examples of regional legislation with regard to direct and indirect impacts on five soil functions: the production of food, fiber, and fuel; water purification and regulation; carbon sequestration and climate regulation; habitat for biodiversity provisioning; and the recycling of nutrients/agro-chemicals. Our results illustrate the diversity of existing policies and the complex interactions present between different spatial and temporal scales. The impact of most policies, positive or negative, on a soil function is usually not established, but depends on how the policy is implemented by local authorities and the farmers. This makes it difficult to estimate the overall state and trends of the different soil functions in agricultural ecosystems. To implement functional management and sustainable use of the different soil functions in agricultural ecosystems, more knowledge is needed on the policy interactions as well as on the impact of management options on the different soil functions. [ABSTRACT FROM AUTHOR]

The values of watershed services from watersheds has for many years been neglected, underestimated and not factored in land use decisions for sustainable management. Sustainable management of watersheds and environmental friendly economic activities are vital for sustained water flow, steady supply of ecosystem services for societal needs and enhancement of aquatic vegetation and animal species. The problem of the failure to capture actual values of ecosystem services from watersheds and incorporate them in the national income accounting is profound in developing countries which are characterized with constrained budget for financing conservation programs. To resolve this problem attention has moved to market based instruments such as payment for watershed services (PWS). However, the approach to elicit the necessary information for PWS to kick off is still lacking. Furthermore, Ecohydrology, defined as an integrative sustainability science using the interactions between hydrology, biota and natural processes as management tools to reinforce ecosystem services on a broad range of landscapes (Zalewski, 2015) is a basis for the development and application of market-based approaches in watershed conservation. This study investigated small holder farmers' willingness to pay (WTP) for watershed services in Pangani River Basin. A contingent valuation method was employed to elicit the willingness to pay for watershed conservation. A probit model was used to determine respondents' response to WTP and factors conditioning the maximum amount they are WTP. Findings indicates that majority of respondents are willing to pay for watershed services. Similarly, result reveals that marital status, household size and distance from the water source positively influence smallholder farmers' WTP and the maximum amount to be paid. Equally important occupation, household size, income from irrigation, and amount paid for irrigation were found to negatively influencing smallholder farmers' WTP. The result also revealed that education level, total land size and yield from irrigated farm plot positively influence smallholder farmers' WTP. These results therefore, indicate that establishment of PWS is feasible. [ABSTRACT FROM AUTHOR]

Purpose: The main objective of this study is to enhance our knowledge about the interplay between the plant Si content and the plant nutrient content as well as the nutrient stoichiometry for a broad range of submerged and emergent wetland plants. Methods: We investigated the carbon, nitrogen, phosphorus and silicon content of 16 species (10 submerged and 6 emergent) along a transect within the Biebrza river (Poland) at 10 locations for the years 2006 and 2007. In addition, the relationships between silicon and carbon, nitrogen and phosphorus content as well as the calculated nutrient ratios (C/N, C/P and N/P) were analyzed. Results: We found evidence for a significant relation of Si to major nutrients carbon and nitrogen (negative correlation) and phosphorus (positive correlation) within wetland plants. Our results show that especially submerged plants are able to substitute carbon compounds in a significant share by silicon compounds. Nitrogen however is partially substituted by Si for emergent plants. This change in plant nutrient content in turn alters the nutrient stoichiometry of C : N : P. Conclusion: Our data is the first showing a possible important effect of plant Si content on plant nutrition and nutrient cycling in wetlands. Plant Si has to be considered in plant ecology, physiology and biogeochemistry of wetland plants, because of its effects on the plant nutrient state. Furthermore, Si may also possibly affect the carbon and nutrient turnover via altered plant nutrient content and subsequently via litter decomposition. [ABSTRACT FROM AUTHOR]

The trade in soybean, an important animal feed product, exemplifies the environmental and socio-economic impact of global markets and global agricultural policy. This paper analyses the impact of increasing production of soybean in the exporting countries (deforestation and grassland conversion) as well as in importing regions (decrease in permanent grassland by substitution of grass as feed). Ecosystem services monetary values were used to calculate the environmental and socio-economic impact of observed land use changes. This is balanced against the economic value of the global soybean trade. The results prove that consumption choices in one region have real effects on the supply of ecosystem services at a large spatial scale. Conclusively, solutions to make this global market more sustainable are discussed. [ABSTRACT FROM AUTHOR]

In-stream submerged macrophytes have a complex morphology and several species are not rigid, but are flexible and reconfigure along with the major flow direction to avoid potential damage at high stream velocities. However, in numerical hydrodynamic models, they are often simplified to rigid sticks. In this study hydraulic resistance of vegetation is represented by an adapted bottom friction coefficient and is calculated using an existing two layer formulation for which the input parameters were adjusted to account for (i) the temporary reconfiguration based on an empirical relationship between deflected vegetation height and upstream depth-averaged velocity, and (ii) the complex morphology of natural, flexible, submerged macrophytes. The main advantage of this approach is that it removes the need for calibration of the vegetation resistance coefficient. The calculated hydraulic roughness is an input of the hydrodynamic model Telemac 2D, this model simulates depth-averaged stream velocities in and around individual vegetation patches. Firstly, the model was successfully validated against observed data of a laboratory flume experiment with three macrophyte species at three discharges. Secondly, the effect of reconfiguration was tested by modelling an in situ field flume experiment with, and without, the inclusion of macrophyte reconfiguration. The inclusion of reconfiguration decreased the calculated hydraulic roughness which resulted in smaller spatial variations of simulated stream velocities, as compared to the model scenario without macrophyte reconfiguration. We discuss that including macrophyte reconfiguration in numerical models input, can have significant and extensive effects on the model results of hydrodynamic variables and associated ecological and geomorphological parameters. [ABSTRACT FROM AUTHOR]

UAVs and other low-altitude remote sensing platforms are proving very useful tools for remote sensing of river systems. Currently consumer grade cameras are still the most commonly used sensors for this purpose. In particular, progress is being made to obtain river bathymetry from the optical image data collected with such cameras, using the strong attenuation of light in water. No studies have yet applied this method to map submergence depth of aquatic vegetation, which has rather different reflectance characteristics from river bed substrate. This study therefore looked at the possibilities to use the optical image data to map submerged aquatic vegetation (SAV) depth in shallow clear water streams. We first applied the Optimal Band Ratio Analysis method (OBRA) of Legleiter et al. (2009) to a dataset of spectral signatures from three macrophyte species in a clear water stream. The results showed that for each species the ratio of certain wavelengths were strongly associated with depth. A combined assessment of all species resulted in equally strong associations, indicating that the effect of spectral variation in vegetation is subsidiary to spectral variation due to depth changes. Strongest associations (R2-values ranging from 0.67 to 0.90 for different species) were found for combinations including one band in the near infrared (NIR) region between 825 and 925 nm and one band in the visible light region. Currently data of both high spatial and spectral resolution is not commonly available to apply the OBRA results directly to image data for SAV depth mapping. Instead a novel, low-cost data acquisition method was used to obtain six-band high spatial resolution image composites using a NIR sensitive DSLR camera. A field dataset of SAV submergence depths was used to develop regression models for the mapping of submergence depth from image pixel values. Band (combinations) providing the best performing models (R2-values up to 0.77) corresponded with the OBRA findings. A 10% error was achieved under sub-optimal data collection conditions, which indicates that the method could be suitable for many SAV mapping applications. [ABSTRACT FROM AUTHOR]

Based on an analysis in the frequency domain of the governing equation of oxygen dynamics in aquatic systems, we derive a new method for estimating gross primary production (GPP) from oxygen time series. The central result of this article is a relation between time averaged GPP and the amplitude of the diel harmonic in an oxygen time series. We call this relation the Fourier method for estimating GPP. To assess the performance and accuracy of the method, we generate synthetic oxygen time series with a series of gradually more complex models, and compare the result with simulated GPP. We demonstrate that the method is applicable in systems with a range of rates of mixing, air-water exchange and primary production. We also apply the new method to oxygen time series from the Scheldt estuary (Belgium) and compare it with 14C-based GPP measurements. We demonstrate the Fourier method is particularly suited for estimating GPP in estuarine and coastal systems where tidal advection has a large imprint in observed oxygen concentrations. As such it enlarges the number of systems where GPP can be estimated from in situ oxygen concentrations. By shifting the focus to the frequency domain, we also gain some useful insights on the effect of observational error and of stochastic drivers of oxygen dynamics on metabolic estimates derived from oxygen time series. [ABSTRACT FROM AUTHOR]

In hydrodynamically stressful environments, some species—known as ecosystem engineers—are able to modify the environment for their own benefit. Little is known however, about the interaction between functional plant traits and ecosystem engineering. We studied the responses of Scirpus tabernaemontani and Scirpus maritimus to wave impact in full-scale flume experiments. Stem density and biomass were used to predict the ecosystem engineering effect of wave attenuation. Also the drag force on plants, their bending angle after wave impact and the stem biomechanical properties were quantified as both responses of stress experienced and effects on ecosystem engineering. We analyzed lignin, cellulose, and silica contents as traits likely effecting stress resistance (avoidance, tolerance). Stem density and biomass were strong predictors for wave attenuation, S. maritimus showing a higher effect than S. tabernaemontani. The drag force and drag force per wet frontal area both differed significantly between the species at shallow water depths (20 cm). At greater depths (35 cm), drag forces and bending angles were significantly higher for S. maritimus than for S. tabernaemontani. However, they do not differ in drag force per wet frontal area due to the larger plant surface of S. maritimus. Stem resistance to breaking and stem flexibility were significantly higher in S. tabernaemontani, having a higher cellulose concentration and a larger cross-section in its basal stem parts. S. maritimus had clearly more lignin and silica contents in the basal stem parts than S. tabernaemontani. We concluded that the effect of biomass seems more relevant for the engineering effect of emergent macrophytes with leaves than species morphology: S. tabernaemontani has avoiding traits with minor effects on wave attenuation; S. maritimus has tolerating traits with larger effects. This implies that ecosystem engineering effects are directly linked with traits affecting species stress resistance and responding to stress experienced. [ABSTRACT FROM AUTHOR]

Diatoms are important primary producers in lake ecosystems and, as a sink for dissolved (DSi) and biogenic silica (BSi) originating from land, can significantly impact the global Si cycle. After burial in lake sediments, resistant diatom frustules can also be used for reconstructions of past ecosystem change. The BSi content of lake sediments is thus often used as a proxy for past diatom productivity, and measured using a time-step analysis of Si extracted in 0.1 M NaCO. However, studies in soils and ocean sediments have shown that also certain non-biogenic Si fractions are prone to dissolve in alkaline solutions, contributing to a potential overestimate of sedimentary BSi concentration. In lakes, volcanic and terrestrial Si compounds reactive at high pH are likely to interfere with the analysis. In this study we used a continuous analysis of Si and Al extracted in 0.5 M NaOH and a new mathematical model improved from Koning et al. (Aquat Geochem 8:37-67, ) to distinguish between biogenic and non-biogenic Si fractions in lake-sediment extracts. We tested this approach in 43 samples of a 19,000-year sediment sequence recovered from Lake Rutundu, a volcanic crater lake on Mt. Kenya. Our results show that a significant fraction of the extractable Si is of non-biogenic origin, especially in the part of the sequence deposited during the glacial period. We conclude that this technique is essential for the characterization of different Si phases, and in particular the diatom-derived BSi, in the sediment of lakes situated in volcanic catchments. It allows calculating a correction, based on the distinct Si:Al ratio of each of those Si phases, that eliminates the contribution from non-BSi fractions. [ABSTRACT FROM AUTHOR]

The biogeochemical cycling of silicon (Si) along the land-to-ocean continuum is studied by a variety of research fields and for a variety of scientific reasons. However, there is an increasing need to refine the methodology and the underlying assumptions used to determine biogenic silica (BSi) concentrations. Recent evidence suggests that contributions of nonbiogenic sources of Si dissolving during alkaline extractions, not corrected by standard silicate mineral dissolution correction protocols, can be substantial. The ratio between dissolved Si and aluminum (Al) monitored continuously during the alkaline extraction can be used to infer the origin of the Si fractions present. In this study, we applied both a continuous analysis method (0.5 M NaOH) and a traditional 0.1 M Na2CO3 extraction to a wide array of samples: (1) terrestrial vegetation, (2) soils from forest, cropland and pasture, (3) lake sediments, (4) suspended particulate matter and sediments from rivers, (5) sediments from estuaries and salt marshes and (6) ocean sediments. Our results indicate that the 0.1 M Na2CO3 extraction protocol can overestimate the BSi content, by simultaneously dissolving Si fractions of nonbiogenic origin that may represent up to 100% of the Si traditionally considered as biogenic, hampering interpretation especially in some deeper soil horizons, rivers and coastal oceanic sediments. Moreover, although the term amorphous Si was coined to reflect a growing awareness of nonbiogenic phases we show it is actually inappropriate in samples where silicate minerals may account for a large part of the extracted Si even after linear mineral correction. [ABSTRACT FROM AUTHOR]

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Recent research indicates that many ecosystems, including intertidal marshes, follow the alternative stable states theory. This theory implies that thresholds of environmental factors can mark a limit between two opposing stable ecosystem states, e.g. vegetated marshes and bare mudflats. While elevation relative to mean sea level is considered as the overall threshold condition for colonization of mudflats by vegetation, little is known about the individual driving mechanisms, in particular the impact of waves, and more specifically of wave period. We studied the impact of different wave regimes on plants in a full scale flume experiment. Seedlings and adult shoots of the pioneer Scirpus maritimus were subjected to two wave periods at two water levels. Drag forces acting on, and sediment scouring occurring around the plants were quantified, as these are the two main mechanisms determining plant establishment and survival. Depending on life stage, two distinct survival strategies emerge: seedlings present a stress avoidance strategy by being extremely flexible, thus limiting the drag forces and thereby the risk of breaking. Adult shoots present a stress tolerance strategy by having stiffer stems, which gives them a higher resistance to breaking. These strategies work well under natural, short period wind wave conditions. For long period waves, however, caused e.g. by ships, these survival strategies have a high chance to fail as the flexibility of seedlings and stiffness of adults lead to plant tissue failure and extreme drag forces respectively. This results in both cases in strongly bent plant stems, potentially limiting their survival. [ABSTRACT FROM AUTHOR]

In recent years, it has become increasingly clear that two-way interactions between organisms and landscape-forming processes play a key role in the evolution of many aquatic ecosystems. To be able to compare sedimentation processes among different environments, a standardized method that is generally applicable is necessary. Current methods are usually designed for one environment only or are unreliable in the presence of vegetation. This paper presents the functionality of a plate sediment trap with a lid in combination with a filter paper, which enables the measurement of sedimentation rates in both permanently subaqueous environments and periodically flooded wetlands. We first present the trap design and demonstrate its functionality. No significant differences were found between replicates, nor was there any indication of a trap size effect on the sedimentation rate. Secondly, we demonstrate its applicability in periodically flooded and permanently subaqueous environments and in the presence or absence of vegetation. It is concluded that the use of a standardized method and equipment makes it possible to compare (bio)geomorphological changes in totally different environments. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Watersheds and rivers are vital ecological features for the provision of hydrological services for the health, welfare and prosperity of human communities. Nevertheless, anthropogenic activities coupled with climate change and climate variability are blamed for degrading watersheds and rivers and decreasing their capacity to irrigate. To address the situation, it is important to understand why and how water shortages are occurring. This paper reports findings of a study carried out to identify and assess drivers of water shortages and adaptation strategies to climate change and variability in Pangani River Basin of Tanzania. To assess the influence of climate change and variability on hydrological flow and water shortages, time series data on rainfall and temperature were compiled from the Tanzania Meteorological Agency. We also used structured questionnaires to collect data on villagers’ perceptions about the drivers of water shortages and adaptation strategies. Results indicated a decreasing trend of water flow ( p < 0.05) at Kikuletwa–Karangai gauging station along Pangani River Basin. Trend analysis indicated a slight decrease of rainfall and increase of temperature. Although there is no empirical evidence to associate climate change with the decline of rainfall and water flow, adaptation measures need to be put in place in order to mitigate against increasing climate variability, reduced water flow, and projected climate change. Therefore, watershed conservation strategies should also focus on improving the welfare of local communities. Additionally, involvement of stakeholders in the entire PRB is crucial toward watersheds conservation for steady flow of hydrological services. [ABSTRACT FROM AUTHOR]

The response of aquatic plants to abiotic factors is a crucial study topic, because the diversity of aquatic vegetation is strongly related to specific adaptations to a variety of environments. This biodiversity ensures resilience of aquatic communities to new and changing ecological conditions. In running water, hydrodynamic disturbance is one of the key factors in this context. While plant adaptations to resource stress (nutrients, light...) are well documented, adaptations to mechanical stress, particularly flow, are largely unknown. The submerged species Egeria densa was used in an experiment to detect whether the presence or absence of hydrodynamic stress causes plant thigmomorphogenetic responses (i) in terms of plant biogenic silica (BSi), cellulose and lignin concentrations, and (ii) in terms of plant strength. Plant silica concentrations, as well as lignin concentrations were significantly higher in presence of hydrodynamic stress. These physiological changes are accompanied by some significant changes in stem biomechanical traits: stem resistance to tensile forces (breaking force and breaking strength) and stiffness were higher for plants exposed to hydrodynamic stress. We conclude that the response of this aquatic plant species to mechanical stress is likely the explaining factor for a higher capacity to tolerate stress through the production of mechanically hardened shoots. [ABSTRACT FROM AUTHOR]

We assessed the role of vegetation and hydrology in the Si cycle in the Okavango Delta. Our results show a large storage of biogenic Si (BSi) in vegetation and the sediments. The biological storage is among the highest observed so far for any ecosystem worldwide. Floodplain vegetation accumulates similar amounts of BSi in both the temporary floodplains and the permanent floodplains, with most values observed between 20 and 100 g Si m. This vegetation Si, after litterfall, contributes to a large biogenic Si storage in the sediments. In temporary floodplains, sediments contain less BSi (375-1950 g Si m in the top 5 cm) than in the permanent floodplains (1950-3600 g Si m in the top 5 cm). BSi concentrations in the floodplain sediments decline exponentially indicating rapid dissolution. In the occasional and seasonal floodplains, unidirectional solute transfer from floodplains to the islands will remove Si from the riverine systems. Our work clearly emphasizes the crucial role of floodplains and wetlands in Si transport through tropical rivers, and the potential interference of hydrology with this role. [ABSTRACT FROM AUTHOR]

ABSTRACT Aquatic plants (macrophytes) can have a large effect on river hydraulics and geomorphology. Though, the extent to how plant morphological plasticity actively influences these feedbacks has received little scientific attention. The nymphaeid macrophyte species Nuphar lutea (L.) Smith is characterized by a distinct leaf duality. Floating leaves shade most of the submerged leaves thereby limiting light penetration in the water. Despite their apparent negligible photosynthetic role, submerged leaves of N. lutea remain intact during summer and contribute a significant part to the total biomass. Our results indicate that the submerged leaves are crucial in plant-flow interactions and hence in the engineering potential of the plant, i.e. the capacity to locally reduce flow velocities and to promote sedimentation, including organic matter deposition. Plant individuals growing in running river water were compared to individuals from adjacent oxbow lake water. The number and size of submerged leaves were significantly higher for river standing individuals and the accumulated sediment contained significantly more organic matter, total nitrogen and total phosphorus, and was characterized by a lower carbon/nitrogen ratio and a finer grain size. We therefore argue that the submerged N. lutea canopy in rivers has the ability to create a high-nutrient, low hydrodynamic environment, resembling the conditions found in oxbow lakes. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Silicon (Si) is one of the most common elements in the earth bedrock, and its continental cycle is strongly biologically controlled. Yet, research on the biogeochemical cycle of Si in ecosystems is hampered by the time and cost associated with the currently used chemical analysis methods. Here, we assessed the suitability of Near Infrared Reflectance Spectroscopy (NIRS) for measuring Si content in plant tissues. NIR spectra depend on the characteristics of the present bonds between H and N, C and O, which can be calibrated against concentrations of various compounds. Because Si in plants always occurs as hydrated condensates of orthosilicic acid (Si(OH)4), linked to organic biomolecules, we hypothesized that NIRS is suitable for measuring Si content in plants across a range of plant species. We based our testing on 442 samples of 29 plant species belonging to a range of growth forms. We calibrated the NIRS method against a well-established plant Si analysis method by using partial least-squares regression. Si concentrations ranged from detection limit (0.24 ppmSi) to 7.8% Si on dry weight and were well predicted by NIRS. The model fit with validation data was good across all plant species (n = 141, R2 = 0.90, RMSEP = 0.24), but improved when only graminoids were modeled (n= 66, R2= 0.95, RMSEP = 0.10). A species specific model for the grass Deschampsia cespitosa showed even slightly better results than the model for all graminoids (n = 16, R2 = 0.93, RMSEP= 0.015). We show for the first time that NIRS is applicable for determining plant Si concentration across a range of plant species and growth forms, and represents a time- and cost-effective alternative to the chemical Si analysis methods. As NIRS can be applied concurrently to a range of plant organic constituents, it opens up unprecedented research possibilities for studying interrelations between Si and other plant compounds in vegetation, and for addressing the role of Si in ecosystems across a range of Si research domains. [ABSTRACT FROM AUTHOR]

The controlled reduced tide system (CRT) is a new technique for restoring tidal marshes and is being tested in the Schelde estuary (Belgium). Biogeochemical processes within a CRT were hypothesized to support and improve several estuarine functions such as sediment trapping and nutrient burial. In 2006, the first pilot CRT was implemented in the freshwater zone of the estuary. Fifteen sediment physicochemical descriptors were intensively monitored over 3 years in the newly created CRT and in reference habitats from the adjacent estuary. Soil transformed rapidly in the CRT; in the most frequently flooded zones, the formation of a nutrient-rich estuarine sedimentary substrate contrasted with the estuarine sand flats where shear stress is sustained by coastal squeeze. The temporal dynamics of the sediment descriptors were investigated to identify key processes involved in the flooding of the CRT sediment. Although many processes were specific to the CRT, both reference and CRT sediment characteristics experienced similar long-term oscillations. However, despite such variations, successful CRT nutrient trapping and fine particles burial were demonstrated. This study proves that the CRT, in accordance with restoration goals, can restore ecological functions in impacted estuaries. In addition, the results highlight the complex timing of abiotic patterns in intertidal sediments. [ABSTRACT FROM AUTHOR]