Efficient sampling methodologies for lake littoral invertebrates in compliance with the European Water Framework Directive

Lake shores are characterised by a high natural variability, which is increasingly threatened by a multitude of anthropogenic disturbances including morphological alterations to the littoral zone. The European Water Framework Directive (EU WFD) calls for the assessment of lake ecological status by monitoring biological quality elements including benthic macroinvertebrates. To identify cost- and time-efficient sampling strategies for routine lake monitoring, we sampled littoral invertebrates in 32 lakes located in different geographical regions in Europe. We compared the efficiency of two sampling methodologies, defined as habitat-specific and pooled composite sampling protocols. Benthic samples were collected from unmodified and morphologically altered shorelines. Variability within macroinvertebrate communities did not differ significantly between sampling protocols across alteration types, lake types and geographical regions. Community composition showed no significant differences between field composite samples and artificially generated composite samples, and correlation coefficients between macroinvertebrate metrics calculated with both methods and a predefined morphological stressor index were similar. We conclude that proportional composite sampling represents a time- and cost-efficient method for routine lake monitoring as requested under the EU WFD, and may be applied across various European geographical regions

A global synthesis of human impacts on the multifunctionality of streams and rivers

Human impacts, particularly nutrient pollution and land-use change, have caused significant declines in the quality and quantity of freshwater resources. Most global assessments have concentrated on species diversity and composition, but effects on the multifunctionality of streams and rivers remain unclear. Here, we analyse the most comprehensive compilation of stream ecosystem functions to date to provide an overview of the responses of nutrient uptake, leaf litter decomposition, ecosystem productivity, and food web complexity to six globally pervasive human stressors. We show that human stressors inhibited ecosystem functioning for most stressor-function pairs. Nitrate uptake efficiency was most affected and was inhibited by 347% due to agriculture. However, concomitant negative and positive effects were common even within a given stressor-function pair. Some part of this variability in effect direction could be explained by the structural heterogeneity of the landscape and latitudinal position of the streams. Ranking human stressors by their absolute effects on ecosystem multifunctionality revealed significant effects for all studied stressors, with wastewater effluents (194%), agriculture (148%), and urban land use (137%) having the strongest effects. Our results demonstrate that we are at risk of losing the functional backbone of streams and rivers if human stressors persist in contemporary intensity, and that freshwaters are losing critical ecosystem services that humans rely on. We advocate for more studies on the effects of multiple stressors on ecosystem multifunctionality to improve the functional understanding of human impacts. Finally, freshwater management must shift its focus toward an ecological function-based approach and needs to develop strategies for maintaining or restoring ecosystem functioning of streams and rivers

Water diversion and pollution interactively shape freshwater food webs through bottom-up mechanisms

[EN] Water diversion and pollution are two pervasive stressors in river ecosystems that often co-occur. Individual effects of both stressors on basal resources available to stream communities have been described, with diversion reducing detritus standing stocks and pollution increasing biomass of primary producers. However, interactive effects of both stressors on the structure and trophic basis of food webs remain unknown. We hypothesized that the interaction between both stressors increases the contribution of the green pathway in stream food webs. Given the key role of the high-quality, but less abundant, primary producers, we also hypothesized an increase in food web complexity with larger trophic diversity in the presence of water diversion and pollution. To test these hypotheses, we selected four rivers in a range of pollution subject to similar water diversion schemes, and we compared food webs upstream and downstream of the diversion. We characterized food webs by means of stable isotope analysis. Both stressors directly changed the availability of basal resources, with water diversion affecting the brown food web by decreasing detritus stocks, and pollution enhancing the green food web by promoting biofilm production. The propagation of the effects at the base of the food web to higher trophic levels differed between stressors. Water diversion had little effect on the structure of food webs, but pollution increased food chain length and trophic diversity, and reduced trophic redundancy. The effects at higher trophic levels were exacerbated when combining both stressors, as the relative contribution of biofilm to the stock of basal resources increased even further. Overall, we conclude that moderate pollution increases food web complexity and that the interaction with water abstraction seems to amplify this effect. Our study shows the importance of assessing the interaction between stressors to create predictive tools for a proper management of ecosystems.Ministerio de Economia, Industria y Competitividad, Gobierno de Espana, Grant/Award Number: GL2016-77487-R; European Social Fund; Diputacion Foral de Bizkaia; Serra Hunter Fellow; Labex, Grant/Award Number: ANR-10-LABX-41; H2020 European Research Council; Eusko Jaurlaritza; Consejo Nacional de Investigaciones Cientificas y Tecnicas; FRAGCLIM Consolidator, Grant/Award Number: 72617

Human impacts on the structure and ecological function of littoral macroinvertebrate communities in lakes

Das litorale Makrozoobenthos ist eine bedeutende biotische Komponente in Seen und trägt substantiell zur Biodiversität und Funktion von Seeökosystemen bei. Allerdings unterliegt das Litoral zunehmenden anthropogenen Nutzungen, deren ökologische Auswirkungen jedoch kaum quantifiziert wurden. In dieser Doktorarbeit wurde untersucht, welche Bedeutung maßgebliche Umweltfaktoren auf die Zusammensetzung des litoralen Makrozoobenthos haben, und wie sich anthropogene Nutzungen auf die Zusammensetzung und Funktion des Makrozoobenthos auswirken. Die Zusammensetzung des Makrozoobenthos wurde durch die Uferstruktur, Trophie und das hydrodynamische Regime bestimmt. Die faunistische Ähnlichkeit zwischen Habitaten war jedoch signifikant geringer als zwischen Trophiestufen, so dass die Uferstruktur, und nicht die Trophie, einen größeren Einfluss auf das Makrozoobenthos hat. Strukturelle Degradation führte zu einer Reduktion der Habitatheterogenität, was eine signifikante Verringerung der Diversität und eine signifikant veränderte Artenzusammensetzung verursachte. Infolgedessen war die Komplexität der Makrozoobenthos-Nahrungsnetze an degradierten Ufern signifikant geringer als an natürlichen Ufern. Erhöhte Wasserstandsschwankungen führten zum Ausfall von Wurzelhabitaten und der damit assoziierten Makrozoobenthos-Gemeinschaft. Schiffsinduzierter Wellenschlag führte zur Verdriftung des Makrozoobenthos von ihren Habitaten bereits bei geringen Sohlschubspannungen. Die Effekte von Wasserstandsschwankungen und schiffsinduziertem Wellenschlag wurden jedoch durch Habitate mit hoher struktureller Komplexität verringert. Mit dieser Doktorarbeit konnte ich ein mechanistisches Verständnis darüber erarbeiten, wie anthropogene Nutzungen die Wirkungsbeziehungen zwischen Umweltfaktoren und Artengemeinschaften verändern und welche ökologischen Auswirkungen dies hat. Diese Kenntnisse können als wissenschaftliche Basis zur Bewertung von anthropogenen Beeinträchtigungen des Litorals dienen.Littoral macroinvertebrates are an important biotic component of lakes by contributing substantially to the biodiversity and functioning of lake ecosystems. Humans alter the littoral and riparian areas for various purposes, but the resulting ecological impacts on littoral macroinvertebrates have not been quantified. In this thesis, I investigated the significance of key environmental factors for littoral macroinvertebrate communities and how human alterations of these environmental factors impact the structure and function of macroinvertebrate communities. Macroinvertebrate community composition was significantly related to littoral structure, trophic state and the hydrodynamic regime. The significantly higher compositional dissimilarities among habitats than among trophic state suggested that littoral structure was the more important driver of community composition. Structural degradation caused a significant reduction of habitat heterogeneity and resulted in a significant reduction of species diversity and a significant altered community composition. This caused a significant reduction of macroinvertebrate food web complexity and substantial alterations of the trophic base of the food webs. Climate-change induced water level fluctuations resulted in the loss of root habitats and the specific community associated with this habitat. Ship-induced waves had substantial direct effects, since macroinvertebrates were detached from their habitats by waves even at moderate shear stress levels. However, the impacts of water level fluctuations and ship-induced waves were mitigated by the presence of habitats with high structural complexities. This thesis provided a mechanistic understanding of how human activities alter relationships between environmental factors and biotic communities. This knowledge can be used to develop scientifically sound approaches to assess the persistent human impacts on lake ecosystems

Lakeshore Modification Reduces Secondary Production of Macroinvertebrates In Littoral But Not Deeper Zones

Littoral macroinvertebrates are an integral component of lake food webs, but their productivity may be affected by shoreline alteration. We hypothesized that human modification of lake shores simplifies habitat diversity, which, in turn, affects littoral macroinvertebrate production and patterns of depth–production relationships. Furthermore, we expected that lakeshore modification would favor nonnative species, potentially compensating for negative effects of lakeshore modification on production of native taxa. To test these ideas, we estimated benthic macroinvertebrate production in the upper littoral, middle littoral, and profundal zones of a large lowland lake (Lake Scharmützelsee) in Northeast Germany. We collected samples between April and November 2011 along depth transects established at both natural and modified shorelines. We found that production in the upper littoral zone was significantly lower at beaches than natural shores or marinas, but no difference existed between natural shorelines and marinas. The substantially lower production at beaches was correlated with lower habitat diversity, resulting from a lack of macrophytes. Additionally, production declined with increasing water depth at natural shores and marinas, but at beaches, production was highest in the middle littoral zone. Production of native taxa was lower at marinas than at natural shorelines, but production of nonnative species offset these declines. The increased productivity of nonnative species in upper littoral habitats at modified shorelines demonstrates that shoreline development has compromised the function of the littoral zone in Lake Scharmützelsee. Extrapolating depth- and habitat-specific production estimates to the entire lake showed that 33% of whole-lake benthic secondary production occurred in the upper littoral zone, even though this depth zone comprised only 7% of total lake area. Additionally, we estimated that completely replacing natural habitats with beaches would reduce whole-lake benthic secondary production by 24%. Our results highlight the crucial role of the littoral zone for whole-lake ecosystem functioning and the high susceptibility of littoral benthic secondary production to lakeshore modification by human activities

Lakeshore Modification Reduces Secondary Production of Macroinvertebrates In Littoral But Not Deeper Zones

Littoral macroinvertebrates are an integral component of lake food webs, but their productivity may be affected by shoreline alteration. We hypothesized that human modification of lake shores simplifies habitat diversity, which, in turn, affects littoral macroinvertebrate production and patterns of depth–production relationships. Furthermore, we expected that lakeshore modification would favor nonnative species, potentially compensating for negative effects of lakeshore modification on production of native taxa. To test these ideas, we estimated benthic macroinvertebrate production in the upper littoral, middle littoral, and profundal zones of a large lowland lake (Lake Scharmützelsee) in Northeast Germany. We collected samples between April and November 2011 along depth transects established at both natural and modified shorelines. We found that production in the upper littoral zone was significantly lower at beaches than natural shores or marinas, but no difference existed between natural shorelines and marinas. The substantially lower production at beaches was correlated with lower habitat diversity, resulting from a lack of macrophytes. Additionally, production declined with increasing water depth at natural shores and marinas, but at beaches, production was highest in the middle littoral zone. Production of native taxa was lower at marinas than at natural shorelines, but production of nonnative species offset these declines. The increased productivity of nonnative species in upper littoral habitats at modified shorelines demonstrates that shoreline development has compromised the function of the littoral zone in Lake Scharmützelsee. Extrapolating depth- and habitat-specific production estimates to the entire lake showed that 33% of whole-lake benthic secondary production occurred in the upper littoral zone, even though this depth zone comprised only 7% of total lake area. Additionally, we estimated that completely replacing natural habitats with beaches would reduce whole-lake benthic secondary production by 24%. Our results highlight the crucial role of the littoral zone for whole-lake ecosystem functioning and the high susceptibility of littoral benthic secondary production to lakeshore modification by human activities

Habitat availability determines food chain length and interaction strength in food webs of a large lowland river

Many large rivers used for navigation have lost their hydromorphological heterogeneity, which has led to the widespread loss of native biodiversity and the concurrent establishment of non‐native communities. While the effects on biodiversity are well‐described, we know little about how the loss of natural habitats and the restructuring of communities cumulate into effects on riverine food webs. We constructed binary and ingestion webs for benthic macroinvertebrates and their resources in the Elbe River (Germany) and compared if food chain length, food web complexity, robustness, ingestion rates, and consumer‐resource interaction strength differ among three shoreline engineering practices. Food webs at profoundly altered shorelines were significantly less complex and had significantly shorter food chains than the food web at the semi‐natural shoreline. However, food web robustness to a simulated loss of species was comparable at all shorelines. Total ingestion rates were up to eight times lower at highly altered shorelines due to significantly lower ingestion rates by native species. Predator–prey interaction strength was comparable among shorelines due to higher shares of non‐native predators, indicating that non‐native predators can be functionally equivalent to native predators. We attributed the observed food web differences to the absence of complex habitats at profoundly altered shorelines and the accompanied absence of specialized consumers. Our study provides empirical evidence that hydromorphological modifications reduce the efficiency of food webs to control organic matter dynamics and may ultimately affect the provisioning of riverine ecosystem services

Areas of Protection

Within the context of the EU Water Framework Directive (EU-WFD), there is a demand for a holistic quality improvement of aquatic systems. Therefore, it is obvious that biodiversity is one of the quality components and hence has to be considered in detail. The ranking of habitats, based on biodiversity indices, depends on the specific measurement selected. It is postulated that a ranking of habitats by means of a biodiversity index may be ambiguous. Concepts to resolve this dilemma are demonstrated, and a graphical formalism is introduced which up to now has only been used in quantum mechanics, statistical mechanics, and theoretical chemistry: The YOUNG-diagram technique

Assessing the Utility of Hydrogen, Carbon and Nitrogen Stable Isotopes in Estimating Consumer Allochthony in Two Shallow Eutrophic Lakes.

Hydrogen stable isotopes (δ2H) have recently been used to complement δ13C and δ15N in food web studies due to their potentially greater power to separate sources of organic matter in aquatic food webs. However, uncertainties remain regarding the use of δ2H, since little is known about the potential variation in the amount of exchangeable hydrogen (Hex) among common sample materials or the patterns of δ2H when entire food webs are considered. We assessed differences in Hex among the typical sample materials in freshwater studies and used δ2H, δ13C and δ15N to compare their effectiveness in tracing allochthonous matter in food webs of two small temperate lakes. Our results showed higher average amounts of Hex in animal tissues (27% in fish and macroinvertebrates, 19% in zooplankton) compared to most plant material (15% in terrestrial plants and 8% in seston/periphyton), with the exception of aquatic vascular plants (23%, referred to as macrophytes). The amount of Hex correlated strongly with sample lipid content (inferred from C:N ratios) in fish and zooplankton samples. Overall, the three isotopes provided good separation of sources (seston, periphyton, macrophytes and allochthonous organic matter), particularly the δ2H followed by δ13C. Aquatic macrophytes revealed unexpectedly high δ2H values, having more elevated δ2H values than terrestrial organic matter with direct implications for estimating consumer allochthony. Organic matter from macrophytes significantly contributed to the food webs in both lakes highlighting the need to include macrophytes as a potential source when using stable isotopes to estimate trophic structures and contributions from allochthonous sources