TemBi 2014 mesocosm study: Summer storm effect on phytoplankton community composition and functional groups in Lake Stechlin

We simulated an experimental summer storm in large-volume (~1200 m3, ~16m depth) enclosures in Lake Stechlin (https://www.lake-lab.de) by mixing deeper water masses from the meta- and hypolimnion into the mixed layer (epilimnion). The mixing included the disturbance of a deep chlorophyll maximum (DCM) which was present at the same time of the experiment in Lake Stechlin and situated in the metalimnion of each enclosure during filling. Phytoplankton community composition and biomass of phytoplankton functional groups were monitored for 42 days after the experimental disturbance event in addition to water physical variables and water chemistry. Mixing disrupted the thermal stratification, increased concentrations of dissolved nutrients and CO2 and changed light conditions in the epilimnion. Mixing stimulated phytoplankton growth and changes phytoplankton community composition, resulting in higher biomass of Cryptophyceae (within one week after mixing), Nostocales (mainly Dolichospermum sp.; 2-3 weeks after mixing) and thereafter Bacillariophyceae (mainly Asterionella sp.)

Long-term phytoplankton community dynamics in Lake Stechlin (north-east Germany) under sudden and heavily accelerating eutrophication

Climate warming and legacy phosphorus (P) in sediments are two main factors counteracting current efforts to prevent eutrophication of temperate freshwater lakes and reservoirs. Climate warming impacts lacustrine thermal regimes, accelerates harmful cyanobacterial growth, and increases the probability of periodic anoxic bottom conditions. Legacy P in sediments becomes influential over eutrophication because of its reactivation under anoxic conditions.Lake Stechlin is a deep glacial lake of the Baltic Lake area, Germany in which artificial external P loading has been effectively blocked for more than 3 decades. The lakes trophic status was oligotrophic, until roughly 2 decades ago when it accelerated toward higher trophic levels. Here we analyse the temporal dynamics of Lake Stechlin phytoplankton biomass and composition in relation to chemical and hydrological covariates, based on monitoring data from 1994 to 2019 at sampling frequency of c. 27 samples per year.Our results show an assemblage change toward cyanobacterial dominance that took place at several temporal scales. Intra-annual compositional change became more pronounced over the study period, mainly because of changes during the autumn and winter seasons.Results from a structural break point analysis of the phytoplankton time series with covariates, and from a hierarchical cluster analysis show that major changes occurred in 2007-2011. An analysis of early warning indicators did not unambiguously support this period as a critical transition. The change rather occurred as a rapid succession of major events during these years.Results from convergent cross-mapping causality tests are consistent with the hypothesis that increasing relative water column stability may drive eutrophication, and additionally, that the intra-annual timing of the biomass change plays an important role in the lakes P loading.Although quantitative data on internal P loading are unavailable, internal P mobilisation from sediments appears to be the most plausible mechanism behind the increased phytoplankton biomass. Lake Stechlin, therefore, is an example of the challenges that legacy P poses to the management of freshwater ecosystems in the context of climate warming, even when external P sources are effectively blocked, and local protective measures are in place.Peer reviewe

The potential of exact sequence variants (ESVs) to interpret and assess the impact of agricultural pressure on stream diatom assemblages revealed by DNA metabarcoding

International audienceLand-use imposes an important potential threat on the aquatic ecosystems of riverine habitats. In this study, DNA metabarcoding was used to assess the effect of land-use on diatom assemblages, with a special focus on cropland area as an integrative proxy for several direct-acting pressures. The so-called taxonomy-free approach was tested using exact sequence variants (ESVs) without pre-clustering and without assigning them to traditional taxonomy. Our hypothesis is that the taxonomy-free approach gives better interpretation of the effect of agricultural land use and it provides a more efficient index to indicate agricultural stress than the classical method with taxonomical clustering. Classical ordination techniques (PCA, NMDS) were performed to study the effects of cropland area proportion on diatom assemblages and a modified version of the Zelinka-Marvan equation for the index development. Results showed that (i) although ESVs provided better results when studying land-use effects on diatoms, taxonomic assignment after analysis was necessary to give ecological interpretations and that (ii) a better performing index could be developed by using the taxonomy-free approach. By using ESVs without taxonomic assignment, information on the ecology of sequences belonging to the same species and of unassigned sequences could be kept. New types of clustering methods are welcome in the future of biomonitoring where the delimitation of taxonomic units should be refined based on a higher emphasis on their ecology rather than on morphological or genetical criteria

TemBi 2014 mesocosm study - Impact of summer storms on long-term lake ecosystem dynamics

Extreme weather and disturbance events are expected to increase, influencing plankton community structure and biogeochemical element cycling in lakes. We simulated an experimental summer storm by mixing deeper water masses from the meta- and hypolimnion into the mixed layer (epilimnion). The mixing included the disturbance of a deep chlorophyll maximum (DCM) which was present at the same time of the experiment in the deep clear-water Lake Stechlin and situated in the metalimnion of each enclosure during filling. Plankton community structure, water physical variables and biogeochemical cycling was monitored for 42 days after the experimental summer storm disturbance event. The experiment was performed in large-volume (~1200 m3, ~16m depth) enclosures in Lake Stechlin (LakeLab; https://www.igb-berlin.de/en/lakelab)

The ecological role of permanent ponds in Europe: a review of dietary linkages to terrestrial ecosystems via emerging insects

Permanent ponds are valuable freshwater systems and biodiversity hotspots. They provide diverse ecosystem services (ES), including water quality improvement and supply, food provisioning and biodiversity support. This is despite being under significant pressure from multiple anthropogenic stressors and the impacts of ongoing global change. However, ponds are largely overlooked in management plans and legislation, and ecological research has focused on large freshwater ecosystems, such as rivers or lakes. Protection of ponds is often insufficient or indirectly provided via associated habitats such as wetlands. This phenomenon is likely exacerbated due to lacking a full-scale understanding of the importance of ponds. In this review, we provided a detailed overview of permanent ponds across Europe, including their usages and the biodiversity they support. By discussing the concepts of pondscape and metacommunity theory, we highlighted the importance of connectivity among and between ponds and identified fluxes of emerging insects as another ES of ponds. Those insects are rich in essential nutrients such as polyunsaturated fatty acids (PUFA), which are delivered through them to the terrestrial environment, however the extent and impact of this ES remains largely unexplored. Several potential stressors, especially related to ongoing global change, which influence pond diversity and integrity were discussed. To conclude this review, we provided our insights on future pond management. Adaptive measures, taking into account the pond system per se within the pondscape, were found to be the most promising to mitigate the loss of natural ponds and restore and conserve natural small water bodies as refuges and diversity hotspots in increasingly urbanized landscapes

The ecological role of permanent ponds in Europe ::a review of dietary linkages to terrestrial ecosystems via emerging insects

Permanent ponds are valuable freshwater systems and biodiversity hotspots. They provide diverse ecosystem services (ES), including water quality improvement and supply, food provisioning and biodiversity support. This is despite being under significant pressure from multiple anthropogenic stressors and the impacts of ongoing global change. However, ponds are largely overlooked in management plans and legislation, and ecological research has focused on large freshwater ecosystems, such as rivers or lakes. Protection of ponds is often insufficient or indirectly provided via associated habitats such as wetlands. This phenomenon is likely exacerbated due to lacking a full-scale understanding of the importance of ponds. In this review, we provided a detailed overview of permanent ponds across Europe, including their usages and the biodiversity they support. By discussing the concepts of pondscape and metacommunity theory, we highlighted the importance of connectivity among and between ponds and identified fluxes of emerging insects as another ES of ponds. Those insects are rich in essential nutrients such as polyunsaturated fatty acids (PUFA), which are delivered through them to the terrestrial environment, however the extent and impact of this ES remains largely unexplored. Several potential stressors, especially related to ongoing global change, which influence pond diversity and integrity were discussed. To conclude this review, we provided our insights on future pond management. Adaptive measures, taking into account the pond system per se within the pondscape, were found to be the most promising to mitigate the loss of natural ponds and restore and conserve natural small water bodies as refuges and diversity hotspots in increasingly urbanized landscapes