Short-term effects of macrophyte removal on aquatic biodiversity in rivers and lakes

Mass development of macrophytes is an increasing problem in many aquatic systems worldwide. Dense mats of macrophytes can negatively affect activities like boating, fishing or hydropower production and one of the management measures often applied is mechanical removal. In this study, we analyzed the effect of mechanical macrophyte removal on phytoplankton, zooplankton, and macroinvertebrate (pelagic and benthic samples) assemblages. Our study covered five sites in four countries in Europe and Africa with highly variable characteristics. In all sites, dense mats of different macrophyte species (Juncus bulbosus in a river in Norway; a mix of native macrophytes in a German river, Elodea nuttallii in a lake in Germany, Ludwigia spp. In a French lake and Pontederia crassipes in a South African lake) are problematic and mechanical removal was applied. In every country, we repeated the same BACI (Before-After-Control-Impact) design, including “before”, “one week after”, and “six weeks after” sampling in a control and an impact section. Repeating the same experimental design at all sites allowed us to disentangle common effects across all sites from site-specific effects. For each taxonomic group, we analyzed three structural and three functional parameters, which we combined in a scoring system. Overall, the removal of macrophytes negatively affected biodiversity, in particular of zooplankton and macroinvertebrate assemblages. In contrast, plant removal had positive effects on the phytoplankton assemblages. Effects were more pronounced one week after removal than six weeks after. Consequently, we suggest a stronger consideration of the effect of plant removal on biodiversity to arrive at more sustainable management practices in the future.acceptedVersio

Redox potential is a robust indicator for decomposition processes in drained agricultural peat soils:A valuable tool in monitoring peatland wetting efforts

Peat decomposition driven by soil metabolic processes is responsible for approximately 2 % of global annual anthropogenic greenhouse gas emissions. A peat soil's redox potential (Eh) and pH reflect its biogeochemical state and are therefore linked to the rate of peat decomposition and greenhouse gas production. In this study, we aim to establish if continuous Eh measurements are an effective tool to monitor metabolic peat decomposition processes and thus to quantify the effects of peat wetting efforts. We applied continuous in-situ Eh measurements (&gt;150 sensors 2020–2022) as a proxy for metabolic peat decomposition processes, which we validated under field conditions with extensive sampling of porewater chemistry (pH, NO3–, SO42−, Mn(II), Fe(II), S2− and CH4, &gt;2000 samples) for five agricultural, drained, minerotrophic peatland sites in the Netherlands. These 5 sites consisted of plots with and without subsoil irrigation (SSI), where SSI aims to raise groundwater levels and thus wet the peat soil. We found that in-situ continuous Eh measurements closely reflected spatial and temporal heterogeneity in pore water chemistry. Therefore, we concluded that Eh is a robust proxy for peat decomposition processes. Building on this result, we used continuous Eh measurements to study the prevalence of specific metabolic processes from site-to-site in relation with groundwater level changes. We found that, while groundwater levels are an important driver for (an)aerobic conditions, groundwater levels do not explain the full dynamics and extent of (an)aerobic conditions. O2 intrusion was mostly limited to approximately 0.5 m depth at deep (&gt;0.8 m) groundwater levels, likely due to air diffusion limitation. Higher and more constant groundwater levels year-round at SSI plots decreased oxygen intrusion and tended to deplete porewater Fe(II) and SO42−, which led to more reducing Eh and higher porewater CH4 concentrations. The depletion of electron acceptors and occurrence of methanogenesis differed from site to site. In summary, high-frequent Eh monitoring is found to be an effective tool to monitor metabolic peat decomposition processes and quantify the effects of peatlands wetting efforts. Therefore, this methodology is suitable to evaluate and further optimize peatland monitoring and preservation.</p

How invasive macrophytes affect macroinvertebrate assemblages and sampling efficiency: Results from a multinational survey

International audienceMacrophytes play an important role in the functioning and structuring of aquatic environments but rapid mass development of invasive macrophytes is causing global concerns. Macroinvertebrate richness and abundance are strongly influenced by macrophytes as macrophytes offer habitats and food resources, increase structural heterogeneity, and provide refuges. Meanwhile, the presence of macrophytes affects the efficiency of standard sampling methods for macroinvertebrates. These effects are not well studied but are leading to biased management decisions. To fill in this knowledge gap, we analysed macroinvertebrate communities from four lakes in four countries in Europe and Africa with mass development of invasive macrophytes. We compared macroinvertebrate communities in sediment samples from a plant-free part of the lake with those in sediment and sweep samples taken within macrophyte stands. We showed that taxa richness and density were higher in sediment samples beneath invasive macrophyte stands compared to plant-free habitats. Unique taxa were found in each sample type. Sampling efficiency of each sampling method varies greatly across lakes especially when replication is low. The taxonomic richness of macroinvertebrates within invasive macrophyte stands is often underestimated compared to open water sections with the same number of samples. To reach a high sampling coverage, a higher number of samples is necessary for sampling within invasive macrophytes. Our findings call for the development of a method that allows for comparable sampling within and outside of macrophyte stands. Such method will be the foundation for future research and management of aquatic systems

Drivers of Perceived Nuisance Growth by Aquatic Plants

International audienceMass developments of macrophytes occur frequently worldwide and are often considered a nuisance when interfering with human activities. It is crucial to understand the drivers of this perception if we are to develop effective management strategies for ecosystems with macrophyte mass developments. Using a comprehensive survey spanning five sites with different macrophyte species in four countries (Norway, France, Germany and South Africa), we quantified the perception of macrophyte growth as a nuisance among residents and visitors, and for different recreational activities (swimming, boating, angling, appreciation of biodiversity, appreciation of landscape and birdwatching). We then used a Bayesian network approach to integrate the perception of nuisance with the consequences of plant removal. From the 1234 responses collected from the five sites, a range of 73-93% of the respondents across the sites considered macrophyte growth a nuisance at each site. Residents perceived macrophytes up to 23% more problematic than visitors. Environmental mindedness of respondents did not influence the perception of nuisance. Perceived nuisance of macrophytes was relatively similar for different recreational activities that were possible in each case study site, although we found some site-specific variation. Finally, we illustrate how Bayesian networks can be used to choose the best management option by balancing people’s perception of macrophyte growth with the potential consequences of macrophyte removal

Water isotope values in shore samples collected in March and July 2020 from northeastern German lake systems

Water isotopes (δ2H and δ18O) were analyzed in samples collected in lakes associated to major riverine systems in northeastern Germany throughout 2020. This sub-dataset is derived from water samples collected from lake shores. Samples were taken in March and July 2020 with a pipette from 40-60 cm depth below water surface and directly transferred into a measurement vial. Stable isotope analysis was conducted at IGB Berlin, using a Picarro L2130-i cavity ring-down spectrometer. The data give information about the seasonal isotope amplitude in the sampled lakes and about spatial isotope variability in different branches of the associated riverine systems

Short-term effects of macrophyte removal on aquatic biodiversity in rivers and lakes

Mass development of macrophytes is an increasing problem in many aquatic systems worldwide. Dense mats of macrophytes can negatively affect activities like boating, fishing or hydropower production and one of the management measures often applied is mechanical removal. In this study, we analyzed the effect of mechanical macrophyte removal on phytoplankton, zooplankton, and macroinvertebrate (pelagic and benthic samples) assemblages. Our study covered five sites in four countries in Europe and Africa with highly variable characteristics. In all sites, dense mats of different macrophyte species (Juncus bulbosus in a river in Norway; a mix of native macrophytes in a German river, Elodea nuttallii in a lake in Germany, Ludwigia spp. In a French lake and Pontederia crassipes in a South African lake) are problematic and mechanical removal was applied. In every country, we repeated the same BACI (Before-After-Control-Impact) design, including “before”, “one week after”, and “six weeks after” sampling in a control and an impact section. Repeating the same experimental design at all sites allowed us to disentangle common effects across all sites from site-specific effects. For each taxonomic group, we analyzed three structural and three functional parameters, which we combined in a scoring system. Overall, the removal of macrophytes negatively affected biodiversity, in particular of zooplankton and macroinvertebrate assemblages. In contrast, plant removal had positive effects on the phytoplankton assemblages. Effects were more pronounced one week after removal than six weeks after. Consequently, we suggest a stronger consideration of the effect of plant removal on biodiversity to arrive at more sustainable management practices in the future

Water isotope values in time series samples (March 2020 - January 2021) from Müggelsee, Germany

Water isotopes (δ2H and δ18O) were analyzed in samples collected in lakes associated to major riverine systems in northeastern Germany throughout 2020. This sub-dataset is derived from water samples taken before the outflow of Müggelsee. Sampling was conducted biweekly from March 2020 to January 2021. Samples were taken with a pipette from 40-60 cm below water surface and directly transferred into a measurement vial. Isotope analysis was conducted at IGB Berlin, using a Picarro L2130-i cavity ring-down spectrometer. The data give information about the seasonal isotope amplitude at Müggelsee over the studied time period

Water isotope values from a spatial campaign conducted in four northeastern German lakes in September 2020

Water isotopes (δ2H and δ18O) were analyzed in samples collected in lakes associated to major riverine systems in northeastern Germany throughout 2020. This sub-dataset is derived from water samples taken at multiple spatially distributed spots in four selected lakes. A Limnos water sampler was used to obtain samples from 1 m below water surface on 29th and 30th September 2020. Isotope analysis was conducted at IGB Berlin, using a Picarro L2130-i cavity ring-down spectrometer

Water isotope values in time series samples (March - October 2020) collected at buoys deployed in northeastern German lake systems

Water isotopes (δ2H and δ18O) were analyzed in samples collected in lakes associated to major riverine systems in northeastern Germany throughout 2020. This sub-dataset is derived from water samples taken at buoys temporarily installed in deep parts of the lake. Samples were taken monthly to bimonthly from March to October 2020. A Limnos water sampler was used to obtain samples from 1 m below water surface. Isotope analysis was conducted at IGB Berlin, using a Picarro L2130-i cavity ring-down spectrometer. The data give information about the seasonal isotope amplitude in the sampled lakes and about spatial isotope variability in different branches of the associated riverine systems

Water isotope values from northeastern German lake systems

Water isotopes (δ2H and δ18O) were analyzed in samples collected in lakes associated to major riverine systems in northeastern Germany throughout 2020. The dataset is derived from water samples taken at a) lake shores (sampled in March and July 2020); b) buoys temporarily installed in deep parts of the lake (sampled monthly from March to October 2020); c) multiple spatially distributed spots in four selected lakes (in September 2020); d) the outflow of Müggelsee (sampled biweekly from March 2020 to January 2021). At shores, water was sampled with pipette from 40-60 cm below water surface and directly transferred into a measurement vial, while at buoys a Limnos water sampler was used to obtain samples from 1 m below surface. Isotope analysis was conducted at IGB Berlin, using a Picarro L2130-i cavity ring-down spectrometer. The data give information about the seasonal isotope amplitude in the sampled lakes and about spatial isotope variability in different branches of the associated riverine systems