Freshwater Ecosystems

Preventing insect nuisance in wetlands, amongst others mosquitoes (Culicidae), biting midges (Ceratopogonidae) and horse flies (Tabanidae), can be facilitated by applying ecological knowledge. We develop prevention schemes and study the autoecology of biting insects.

Highlights

Monitoring of biting insects and developing prevention schemes

The restoration of former wetlands and the expansion of existing wetlands as well as the use of arable land in stream and river valleys to alleviate flooding is important to adapt to the impacts of climate change, to meet goals in achieving WFD water quality objectives, to provide increased wetland habitat for wildlife and an outdoor space for human ‘well-being’.

More and more, concerns are raised over the potential impacts that such initiatives might have on biting insect population development and its associated nuisance and disease risk. It is important to ensure that biodiversity gain and habitat restoration can advance without inadvertently elevating the risks from disease vectors.

Biting insect management always starts with monitoring of the species involved, followed by applying knowledge on the ecology of the respective species when developing potential measures that can be taken to reduce larval habitats. Furthermore communication to those involved is essential in successful insect nuisance prevention. The guideline ‘Leidraad Risicomanagement Overlast Steekmuggen en Knutten’ can be very helpful in this approach.

Mirroring self-purification in nature (biomimicry), our innovative Aquafarm concept uses chains of organisms to ‘polish’ effluent and produce high-added value components.

Highlights

Floating treatment wetlands
Floating treatment wetlands (FTWs) may provide an appealing alternative to the more conventional (sub)surface flow wetlands to solve problems associated with eutrophication in urban surface waters, because they do not claim additional space.

We showed that total removal of TN and TP from the tanks planted with Iris was 54 times higher for TN and 10 times higher for TP removal compared to the control treatment. FTWs planted with Iris can be applied in a temperate climate to overcome problems with excessive algae growth in surface waters.

Not only floating wetlands also both wetlands with helophytes purifying water or floodplain or swamps either with helophytes or with willows and alder can purify, especially run off from adjacent agricultural land. A new, innovative approach of managed bioremediation is termed AquaFarm. The concept behind AquaFarm is based on optimising monocultures of organisms in a cascade of basins to purify waste water while at the same time the organisms are yielded to gain valuable components, like proteins, for multiple use in industry.

Our nature-based trans-disciplinary analysis integrates ecology-based water management and spatial land use planning. We use novel tools to bridge disciplines and integrate knowledge.

Highlights

5-S-Model

In order to make the proper choices in ecological river and catchment management one has to understand the key abiotic and biotic processes (dominance and feedback interactions). To simplify this ecological complexity, while recognising the importance of scale and hierarchy, the 5-S-Model was designed. This conceptual model provides guidelines for catchment management (Verdonschot et al., 1998, 2000, 2014). Five groups of key factors are distinguished, hierarchically ordered for streams: System conditions (the processes related to climate, geology and geomorphology), Stream hydrology (the hydrological and hydraulic processes), Structures (the morphology related processes like erosion and sedimentation), Substances (the biochemical processes) and Species (the response to the functioning of all above mentioned groups of key factors expressed in the community functioning). Species and their communities are the actual goal of ecological stream management and rehabilitation.

Ecosystem resilience

By improving the understanding of ecosystem functioning using ecological resilience and resistance as integrated measures makes ecological concepts applicable in the practice of restoration and the delivery of ecosystem services, like biodiversity. Benthic macroinvertebrates of lowland streams evolved under natural hydrologic disturbance regimes and carry traits to either resist high flows (resistance traits) or to recover quickly (resilience traits). Understanding the trait adaptations associated responses of macro-invertebrates under different disturbance regimes will enhance our understanding of survival mechanisms under multiple stress conditions and will tell about resilience and resistance. In stream mesocosms, we mimicked lowland stream spates by increasing current velocity above organic habitat patches and observed the response of Trichoptera larvae. It appeared that each combination of morphological and behavioural adaptations developed individually for each species under niche- specific conditions (Verdonschot et al. 2012, 2014). Furthermore, more tolerant species from the disturbed end of the gradient showed more mobility and flexibility than the species occurring under more or less natural stream conditions. This is consistent with the hypothesis that mobility is an adaptation of tolerant, ubiquitous species. Mobility is an resistance adaptation of r-strategists while seeking refuges is a resilience adaptation.

Ecological catchment system analysis

Restoration of ecosystems has moved from individual sites, single lakes or stream stretches towards landscapes and catchments. Therefore, we distinguish Operational Restoration Units (ORUs). That is a natural system based delimitation of the spatial borders of a restoration project, and encompasses the wider socio-economic drivers. An ecological catchment (or ORU) system analysis differentiates between three cycles: an abiotic, a biotic and a socio-economic or societal cycle. Within the abiotic cycle the system conditions, hydrology, morphology and chemistry of the catchment or ORU are analysed for the current and future situation. The biotic cycle focusses on the key ecological processes and responses driving the ecosystem functioning. The societal cycle includes the direct and indirect socio-economic actors that affect the current and future ‘surroundings’ of the project. With this conceptual approach multiple stressors can be identified and multiple measures advised based on an integrated approach over different spatial and temporal scales to reach a sustainable nature-based functioning (eco)system.

Improving biodiversity, reducing management costs and preventing insect nuisance in wetlands can be facilitated by applying ecological knowledge. We develop smart mowing regimes, floating helophyte mats and nuisance insects prevention schemes to attain these goals.

Highlights

Tools for ecological water management

Ecological water management is still strongly based on the use of structure parameters to typify, assess, evaluate and select measures. Driven by the Water Framework Directive (WFD) a number of typologies, descriptions of reference conditions, assessment techniques, and Decision Support Systems (DSS) to diagnose and select measures for restoration were developed. The EKO tools to classify water bodies, to evaluate current status and to predict the outcome of measures were develop on a regional basis for about a quarter of the areas in the Netherlands. The DSS tools ‘MaatregelWijzer Waterbeheer’ and ‘Waternood DAN’ can assist to select measures for rehabilitation and restoration. The novel ‘Leidraad Natuurontwikkeling’ includes a DSS that is based on ecological theory and is applicable for a number of water bodies and their surrounding landscapes.

Aquatic plants as natural weirs: a nature-based solution

Studies showed that omission of mowing watercourses do not necessarily lead to flooding. Especially, when omission of maintenance is accompanied by a level drop due to the removal of weirs. Still, it remains difficult to predict if and when problems with floods can be expected. The biomass of plants reaches its optimum in the summer, however, the base flow and groundwater level are lower in the summer. The key solution is to determine how the water level at base flow rises due to water plants in the wet profile. During spates, the peak discharge itself is not the problem, but the additional increase in the average water level caused by the obstruction of the watercourse by aquatic plants can be. At a peak discharge the water seeks the path of least resistance and will flow over the water plants. But at the same moment the, submerged aquatic plants will bend, so the flow resistance is reduced. To further study and model flow-water plant growth relationships we will combine water safety with sustainable, cost-effective water management.

Invasive species

Non-indigenous invertebrates are common in fresh waters in The Netherlands. Based on data from the local water authorities, approximately 60% of the sampling locations contained one or more non-indigenous species. We study their impact on the native macroinvertebrate assemblages. Our studies showed that many non-indigenous species are fitting in the already present macroinvertebrate assemblage instead of displacing indicator species or disrupting the whole community.

We develop new cost-effective techniques, such as QuickScan sampling (e.g. activity traps, eDNA), that are applicable in effective monitoring schemes in space and time. Water quality assessment is innovated using trait-based diagnostic tools (e.g. Multimetric Amoebe), passive sampling and effect-directed analysis.

Highlights

Monitoring design

Both national and European approaches to assess ecological water quality require an unbiased estimate of the quality exceeding that of a single site or reach. The selection of sampling sites is often based on its assumed representativeness for the entire water body or on more practical matters, like accessibility of the site. The problem with such a non-probability site choice is that statistically-based inferences about trends at higher/lower spatial scales cannot be made and the selection bias can result in erroneous conclusions. Probability sampling is well suited to eliminate selection bias since, by construction, every site has a known nonzero probability of being selected. Since we are obliged in the Netherlands to make inferences at water body/national level we need to apply probability sampling to draw statistically sound conclusions. By developing a ‘Quick Scan’ methodology that can be used in a probability sampling scheme to scan larger regions for ecological problems both cost-effectiveness and spatial coverage are strongly improved.

Multimetric AMOEBE: diagnostic assessment tool

Tools to not only assess but also to diagnose the ecological status of streams and drainage ditches in The Netherlands are currently lacking. Therefore, multimetric indices based on functional features of macroinvertebrates were developed. Based on a large datasets from regional water district managers degradation gradients were composed. Subsequently, a stepwise process was used to evaluate the discriminatory efficiency of a variety of diversity, abundance/ composition, tolerance/ sensitivity, and functional metrics for assessing ecological degradation. After evaluating metric range, strength of correlation to the stressor gradient, degree of redundancy, and sample- and seasonal repeatability, metrics were selected for incorporation into the multimetric index. We represent the multimetric-indices graphically with the AMOEBE technique, to provide a quick overview of the relative contribution of different types of disturbances to ecological degradation.

Smart passive sampling by using activity traps

We tested the effectiveness of activity traps for macroinvertebrate monitoring in shallow, heavily vegetated drainage ditches was tested. Based on the taxon accumulation curves, a trapping duration of 168 h was highly efficient and resulted in a large number of taxa collected. Of the attractants offered in the traps, only bait caused differences in the macroinvertebrate assemblage recorded when short trapping time was used. Because of their relatively low labour requirements and high level of standardization, activity traps appear to be a valuable tool in lentic biodiversity surveys, especially when deployed for a longer period than has usually been reported. The use of bait is advisable only if capture of specific taxa is required and not for standard monitoring purposes.

Understanding key determinants of stream ecosystem functioning is crucial to biodiversity and to mitigate global and climate change. Our field and laboratory experimental research quantifies the effects of e.g. addition of wood and sand, the role of buffer strips, dispersal barriers, and re-introduction of ecosystem engineers in stream restoration. Furthermore, attention goes to ecosystem services of streams and their valleys.

Highlights

Wood and sand addition to streams

Stream restoration often benefits more from initiating natural processes instead of large technical interferences. Therefore, the results of applying re-meandering as a restoration measure are often disappointing. Designing a watershed to store and retain water in the upstream areas, for example, by reconnecting incised streams to their valleys by adding sand to the streams, and adding dead woody debris to increase micro)habitat and flow diversity, have proven to be far more successful.

Restoration on a valley-wide scale

Nature-based solutions in stream management will provide more robust ecosystems that are less vulnerable to climate change. Restoration on a stream valley-wide scale makes use of the buffer capacity of the valley, which delivers a number of ecosystem services. Not only do stream valleys store water in the soil and retain water in the inundated areas, but they also are capable of removing nutrients from adjacent agricultural lands before they enter the stream. Furthermore, stream valleys are biodiversity hotspots, which in turn strengthens, among others, recreational and health services.

Stream valleys as ‘sponges’

River and stream valleys store water in the soil, retain water in inundated areas and delay downstream transport of water by increasing the length of the flow path and slowing the speed and force of the current. Such water system based measures on catchment scale are sustainable, but call for a novel approach in landscape planning. Under the flag of ‘Building with Nature’ such solutions are embraced as they provide a robust and cost-effective base for future generations.

Reintroduction of ecosystem engineers

Currently many species characteristic of stream ecosystems of a good ecological quality are not able to reach restored sites. This might influence ecosystem functioning, given that some macroinvertebrates are important drivers of ecosystem processes in streams. Reintroduction might be an option for restored streams which could not be reached by its typical fauna. We study the feasibility of this approach by looking at population development and dispersal and we investigate the ecological mechanisms and processes associated with species introductions.

Guided by ecological theory, we develop knowledge on novel restoration measure-effect relations. Examples include building new islands (Marker Wadden) in lake Marker and rehabilitating stream valley marshes. Furthermore, the effects of climate and global change are taken into account.

Highlights

Shading streams to mitigate the effects of climate change

Forested riparian zones appeared to be effective to mitigate the stream water temperature rise in small streams induced by climate change in North-western Europe. Furthermore, among other benefits, it helps to maintain or restore the habitat for coldstenothermic stream organisms. We study the effects of shaded-to-open and an open-to-shaded transitions on stream water temperature and on the biological communities inhabiting these streams.

Wetland construction

Fine sediments are abundant in urbanized deltas around the world and provide a potential source of building material for wetland construction. In the Netherlands, the MarkerWadden project has embarked aiming at creating a dynamic wetland system in lake Markermeer with gradients in topography, sediments, and rich benthic and wetland biodiversity. Fine sediments will be accumulated into atolls, which eventually develop into valuable ecosystems. We study the interplay of biological, chemical and physical interactions in lake Markermeer. The acquired scientific knowledge will be used to assess which ecosystem services will evolve and how such systems should be managed.

Recovery processes in rivers, lakes, estuarine and coastal waters

Knowledge of responses of aquatic assemblages to recovery processes that occur after measures have been taken to reduce major stressors is urgently required. In a systematic literature review we comparatively assessed recovery measures across the four major water categories. Despite the many studies only few provide evidence of how ecological knowledge might enhance restoration success. We plea to bridge the gap between ecological theory / knowledge and water management in practice.