Multiple stressor effects act primarily on microbial leaf decomposers in stream mesocosms.

At the global level, stream ecosystems are influenced by multiple anthropogenic stressors such as eutrophication, habitat deterioration, and water scarcity. Multiple stressor effects on stream biodiversity are well documented, but multiple stressor effects on stream ecosystem processes have received only limited attention. We conducted one mesocosm (stream channel) and one microcosm (feeding trial) experiment to study how combinations of reduced flow, increased nutrient concentrations, and increased fine sediment coverage would influence fungal and macroinvertebrate decomposer assemblages and their active contribution to leaf decomposition.

European river typologies fail to capture diatom, fish, and macrophyte community composition.

Typology systems are frequently used in applied and fundamental ecology and are relevant for environmental monitoring and conservation. They aggregate ecosystems into discrete types based on biotic and abiotic variables, assuming that ecosystems of the same type are more alike than ecosystems of different types with regard to a specific property of interest. We evaluated whether this assumption is met by the Broad River Types (BRT), a recently proposed European river typology system, that classifies river segments based on abiotic variables, when it is used to group biological communities.

Weed cutting in a large river reduces ecosystem metabolic rates in the case of River Gudenå (Denmark).

Problems related to extensive macrophyte growth are widespread both in modified and man-made canals and streams, and in streams with natural morphology and rich vegetation. The weed cutting is a common management practice in order to reduce flood risk and enhance water conveyance. Although the short- and long-term impacts on the stream physical habitats and biota have been extensively studied, only little information exists on the effects of weed cutting on ecosystem metabolism, especially for larger rivers.

Periphyton biomass and life-form responses to a gradient of discharge in contrasting light and nutrients scenarios in experimental lowland streams.

Climate-induced changes in precipitation and land-use intensification affect the discharge of streams worldwide, which, together with eutrophication and loss of riparian canopy, can affect periphyton biomass and composition, and therefore, ultimately the stream functioning. We investigated the responses of periphyton biomass and life-forms (i.e.

Small-sized omnivorous fish induce stronger effects on food webs than warming and eutrophication in experimental shallow lakes.

Warming, eutrophication, and increased omnivory by small-sized fish are global change processes that induce major effects on the food web structure and primary producers of shallow lakes. Despite the key relevance of phytoplankton and periphyton in freshwaters, the combined and potential synergistic effects of fish omnivory, warming and eutrophication, especially on periphyton, remains little addressed, particularly for subtropical shallow lakes. We experimentally tested the food web effects on phytoplankton and periphyton induced by small visually feeding omnivorous fish (Rhodeus ocellatus), high nutrient enrichment and warming (+4.

Danish wetlands remained poor with plant species 17-years after restoration.

For more than two decades, wetland restoration has been successfully applied in Denmark as a tool to protect watercourses from elevated nutrient inputs from agriculture, but little is known about how the flora and fauna respond to restoration. The main objective of this study was therefore to: (1) examine plant community characteristics in 10 wetland sites in the River Odense Kratholm catchment, restored between 2001 and 2011 by re-meandering the stream and disconnecting the tile drains, and (2) explore whether the effects of restoration on plant community characteristics change with the age of the restoration. Specifically, we hypothesised that plant community composition, species richness and diversity would improve with the age of the restoration and eventually approach the state of natural wetland vegetation.

Microbial biofilm community dynamics in five lowland streams.

Stream biofilms are complex aggregates of diverse organism groups that play a vital role in global carbon and nitrogen cycles. Most of the current studies on stream biofilm focus on a limited number of organism groups (e.g.

Influence of plant habitats on denitrification in lowland agricultural streams.

The aim of this study was to assess potential differences in denitrification in contrasting stream habitats in agricultural lowland streams located in Denmark. The study focused on three types of habitats i) vegetated habitats with emergent plants, ii) vegetated habitats with submerged plants, iii) bare sediments. Denitrification rates were measured in situ using denitrification chambers and nitrogen isotope pairing technique three times during a growing season.

Short-period hydrological regimes override physico-chemical variables in shaping stream diatom traits, biomass and biofilm community functions.

Despite increasing interest in hydrological effects on riverine ecosystems, few studies have documented the impact of hydrology on biofilm community functions, and those existing have typically focused on annual-based hydrological indices. In this study, we conducted monthly samplings during a year in five lowland streams with different flow regimes and investigated the impacts of hydrological conditions and physico-chemical variables on the trait composition of diatoms growing on artificial substrates, biomass (chlorophyll a and ash free dry weight), and biofilm community functions (biochemical processes, i.e.

Impacts of multiple stressors on freshwater biota across spatial scales and ecosystems.

Climate and land-use change drive a suite of stressors that shape ecosystems and interact to yield complex ecological responses (that is, additive, antagonistic and synergistic effects). We know little about the spatial scales relevant for the outcomes of such interactions and little about effect sizes. These knowledge gaps need to be filled to underpin future land management decisions or climate mitigation interventions for protecting and restoring freshwater ecosystems.

Effects of low flow and co-occurring stressors on structural and functional characteristics of the benthic biofilm in small streams.

Low flow and co-occurring stress is a more and more frequent phenomenon these years in small agricultural streams as a consequence of climate change. In the present study we explored short and longer term structural responses of the stream benthic algae community and biofilm metabolism to multiple stress in small streams applying a semi-experimental approach. We hypothesized that i) a reduction in flow in combination with secondary stress (nutrients and sediments) have immediate effects on the benthic algae community in terms of biomass (chlorophyll a, biovolume), taxonomic and trait (lifeform and size distribution) compositions as well as on metabolism (GPP and CR), and ii) that changes in the benthic algae community persist due to altered environmental settings but that functional redundancy among benthic algae species provides a high level of resilience in metabolism (GPP and CR).

Management Options to Reduce Phosphorus Leaching from Vegetated Buffer Strips.

Vegetated buffer strips (VBS) between agricultural areas and surface waters are important retention areas for eroded particulate P through which they may obtain critically high degrees of P saturation imposing high risk of soluble P leaching. We tested topsoil removal and three harvesting frequencies (once, twice, or four times per year) of natural buffer vegetation to reduce P leaching with the aim to offset erosional P accumulation and high degrees of P saturation. We used a simple numerical time-step model to estimate changes in VBS soil P levels with and without harvest.

Protecting and restoring Europe's waters: An analysis of the future development needs of the Water Framework Directive.

The Water Framework Directive (WFD) is a pioneering piece of legislation that aims to protect and enhance aquatic ecosystems and promote sustainable water use across Europe. There is growing concern that the objective of good status, or higher, in all EU waters by 2027 is a long way from being achieved in many countries. Through questionnaire analysis of almost 100 experts, we provide recommendations to enhance WFD monitoring and assessment systems, improve programmes of measures and further integrate with other sectoral policies.

The future of European water management: Demonstration of a new WFD compliant framework to support sustainable management under multiple stress.

The Water Framework Directive (WFD), which is the most comprehensive instrument of EU water policy, is more relevant than ever. Sixty percent of Europe's surface water bodies still fail to achieve good ecological status and a multitude of new stressors continue to emerge. A sustained and wholehearted water management effort is therefore of highest priority.

Responses of Aquatic Plants to Eutrophication in Rivers: A Revised Conceptual Model.

Compared to research on eutrophication in lakes, there has been significantly less work carried out on rivers despite the importance of the topic. However, over the last decade, there has been a surge of interest in the response of aquatic plants to eutrophication in rivers. This is an area of applied research and the work has been driven by the widespread nature of the impacts and the significant opportunities for system remediation.

Structural and functional responses of plant communities to climate change-mediated alterations in the hydrology of riparian areas in temperate Europe.

The hydrology of riparian areas changes rapidly these years because of climate change-mediated alterations in precipitation patterns. In this study, we used a large-scale in situ experimental approach to explore effects of drought and flooding on plant taxonomic diversity and functional trait composition in riparian areas in temperate Europe. We found significant effects of flooding and drought in all study areas, the effects being most pronounced under flooded conditions.

Structural and functional characteristics of buffer strip vegetation in an agricultural landscape - high potential for nutrient removal but low potential for plant biodiversity.

Vegetated buffer strips constitute a transition zone between terrestrial and aquatic ecosystems and provide several ecosystem services. Buffer strips are often applied as a mitigation measure against diffuse pollution in agricultural areas, primarily because they may retain nutrients and in this way help protect the aquatic environment. Additionally, they can improve biodiversity in an otherwise homogenous landscape and may therefore have a value in their own right.

Headwater streams in the EU Water Framework Directive: Evidence-based decision support to select streams for river basin management plans.

Headwater streams are important contributors to aquatic biodiversity and may counteract negative impacts of anthropogenic stress on downstream reaches. In Denmark, the first river basin management plan (RBMP) included streams of all size categories, most being <2.5m wide (headwater streams).

Multiple stress response of lowland stream benthic macroinvertebrates depends on habitat type.

Worldwide, lowland stream ecosystems are exposed to multiple anthropogenic stress due to the combination of water scarcity, eutrophication, and fine sedimentation. The understanding of the effects of such multiple stress on stream benthic macroinvertebrates has been growing in recent years. However, the interdependence of multiple stress and stream habitat characteristics has received little attention, although single stressor studies indicate that habitat characteristics may be decisive in shaping the macroinvertebrate response.

Effects of increased flooding on riparian vegetation: Field experiments simulating climate change along five European lowland streams.

In many parts of the world, the magnitude and frequency of cold-season precipitation are expected to increase in the near future. This will result in an increased magnitude and duration of winter and spring flooding by rain-fed streams and rivers. Such climate-driven increases in flooding are likely to affect riparian plant communities, but future vegetation changes are hard to predict due to current lack of data.

Trait Characteristics Determine Pyrethroid Sensitivity in Nonstandard Test Species of Freshwater Macroinvertebrates: A Reality Check.

We exposed 34 species of stream macroinvertebrates, representing 29 families, to a 90 min pulse of the pyrethroid λ-cyhalothrin. For 28 of these species, no pyrethroid ecotoxicity data exist. We recorded mortality rates 6 days post-exposure, and the behavioral response to pyrethroid exposure was recorded using automated video tracking.

Plant trait characteristics vary with size and eutrophication in European lowland streams.

Previous studies investigating community-level relationships between plant functional trait characteristics and stream environmental characteristics remain scarce. Here, we used community-weighted means to identify how plant traits link to lowland stream typology and how agricultural intensity in the catchment affects trait composition.We analysed plant trait characteristics in 772 European lowland streams to test the following two hypotheses: (i) trait characteristics differ between plant communities in small and medium-sized streams, reflecting adaptations to different habitat characteristics, and (ii) trait characteristics vary with the intensity of agricultural land use in the stream catchment, mediated either directly by an increase in productive species or indirectly by an increase in species that efficiently intercept and utilize light.

Functional trait composition of aquatic plants can serve to disentangle multiple interacting stressors in lowland streams.

Historically, close attention has been paid to negative impacts associated with nutrient loads to streams and rivers, but today hydromorphological alterations are considered increasingly implicated when lowland streams do not achieve good ecological status. Here, we explore if trait-abundance patterns of aquatic plants change along gradients in hydromorphological degradation and eutrophication in lowland stream sites located in Denmark. Specifically, we hypothesised that: i) changes in trait-abundance patterns occur along gradients in hydromorphological degradation and ii) trait-abundance patterns can serve to disentangle effects of eutrophication and hydromorphological degradation in lowland streams reflecting that the mechanisms behind changes differ.