Arable Weeds at the Edges of Kettle Holes as Overwintering Habitat for Phytopathogenic Fungi

Weeds in agricultural landscapes can serve as alternate hosts for phytopathogenic fungi and promote the spatial and long-term distribution of these fungi. Especially, semi-natural habitats such as kettle holes are considered as a source of fungal pathogens because they are a permanent habitat for various weed species in arable lands. In our study, we investigated the suitability of nine different weed species and families at the edges of 18 kettle holes in two consecutive autumn/winter seasons as alternate hosts for Fusarium and Alternaria. We detected a fungal infestation with both genera on every weed species investigated with significantly higher abundances of these fungi in the second, notably wetter season. Eight weed species were described as non-host plants for Fusarium and Alternaria in agricultural landscapes in Brandenburg, Germany for the first time. In both autumn/winter periods, weeds harbored more Alternaria than Fusarium. The study revealed a high Fusarium species diversity in weeds and a community structure of up to 12 Fusarium species at the edges of kettle holes. Grasses showed the highest diversity and often the highest fungal abundances compared to herbaceous plants. Therefore, these habitats in arable lands can act as ecosystem disservice and promote the spread of fungal diseases in the surrounding crop fields.Peer Reviewe

A New tool for the assessment of severe anthropogenic eutrophication in wetlands under increasing human pressure

It is about time the assessment of trophic state in wetlands is no longer estimated through the regressions and thresholds modelled for deep-stratified lakes where sediment nutrient recycling was purposely neglected. We are in badly need of a system trophic indicator to be used as a reference for biological indicators. The recent use of biological communities (macro-invertebrates, diatoms, etc) for the evaluation of the “ecological state” of a water body implicitly requires the assessment of its “trophic state”

Auswirkung von Seeufermodifikation auf die Struktur und Sekundärproduktion der Makroinvertebraten in einem großen nordostdeutschen Tieflandsee

Many lake water bodies not attained the goal of the European Water Framework Directive (WFD) to achieve a good ecological state by 2015. This is, among other things, because the assessment and improvement of hydromorphological conditions of lakeshores has been neglected as an important component ensuring the ecological integrity of lake ecosystems. In recent years, macroinvertebrates were emphasized to be useful indicators for the assessment of lakeshore hydromorphology. Hence, in Europe macroinvertebrate-based assessment methods were developed to evaluate the hydromorphological conditions of lakeshores. In this thesis, some of the uncertainties and missing aspects of existing macroinvertebrate-based assessment methods were addressed. The results were obtained by sampling macroinvertebrates and macrophytes at natural shores and at shores modified by marinas and beaches in three depth zones between April and November 2011 in a large lowland lake (Lake Scharmützelsee, Germany). Firstly, I clarified that upper littoral macroinvertebrates should be used for assessing the hydromorphology of lakeshores. It was shown that the effect of lakeshore modification on macroinvertebrate diversity and community composition was most pronounced in the upper littoral and decreased to the profundal zone. Secondly, I demonstrated that a single seasonal sampling is sufficient to capture the compositional differences of macroinvertebrate communities associated with human lakeshore modification. Seasonal effects on upper littoral macroinvertebrate diversity and composition were less important than shore type in comparison with the middle littoral and profundal zone. Thirdly, upper littoral macrophyte communities were also affected by lakeshore modification and at the same time the most important variable structuring macroinvertebrate communities. Hence, the effects of different shore types on macrophytes were transferred to macroinvertebrates, but artificial substrates were also able to partly substitute macrophyte habitats as it was shown for the studied marinas. Since lakeshore modification affected macrophytes slightly differently than macroinvertebrates, macrophytes should be considered as an additional component in lakeshore assessment. Finally, secondary production as proxy to determine the effect of lakeshore modification on the functioning of macroinvertebrates was estimated. Estimation of secondary production requires the determination of biomass. Biomass was indirectly determined by using length-mass regressions established for macroinvertebrates from temperate lakes of the central European lowland. The result showed that total secondary production and secondary production of native taxa in the upper littoral was substantially lower at the studied beaches compared to natural sites. In contrast, upper littoral secondary production at marinas did not differ to natural sites, but secondary production of non-native taxa was significantly higher at marinas. No effects of lakeshore modification on secondary production were found with increasing depth. Different scenarios based on upscaling of site-specific production to whole lake ecosystem level gave evidence that the observed local impacts of lakeshore modification can translate into alterations of the functioning of macroinvertebrates at whole lake ecosystem level. In addition, it was emphasized that secondary production as a functional measure is more sensitive in detecting hydromorphological alterations than the structural measures diversity or biomass. Secondary production should therefore be included in existing lakeshore assessment methods. In order to obtain a comprehensive overview about the changes in the functioning of macroinvertebrates following lakeshore modification, it is recommended to consider not only total secondary production but also secondary production of functional groups. With these results, this thesis contributes to the mechanistic understanding of the effect of lakeshore modification on the functioning of macroinvertebrates and the consequences for the functioning of the whole lake ecosystem. The newly generated knowledge helps to optimize the development of successful lakeshore assessment tools and identification of management measures.Viele stehende Gewässer haben es nicht geschafft, das Ziel der Europäischen Wasserrahmenrichtline (WRRL) bis 2015 einen gut ökologischen Zustand zu erreichen. Dies liegt unter anderem an dem Versäumnis die Bewertung und Verbesserung des hydromorphologischen Zustands von Seeufern in bisherige Ansätze zu integrieren. Seeufer stellen eine wichtige Komponente von Seeökosystemen dar, um die Intaktheit dieser zu gewährleisten. In den vergangenen Jahren wurden Makroinvertebraten als brauchbare Indikatoren für die Bewertung der Seeuferhydromorphologie hervorgehoben. Daraufhin wurden in Europa einige Bewertungsmethoden basierend auf Makroinvertebraten entwickelt, um den hydromorphologischen Zustand von Seeufern beurteilen zu können. In dieser Doktorarbeit werden einige Unsicherheiten und fehlende Aspekte existierender Makroinvertebraten-basierenden Bewertungsmethoden adressiert. Die Ergebnisse wurden erzielt, in dem Makroinvertebraten an natürlichen Seeufern und an Seeufern, modifiziert in Form von Häfen und Strände, in drei Tiefenzonen zwischen April und November 2011 an einem großen Tieflandsee (Scharmützelsee, Deutschland) beprobt wurden. Als Erstes konnte ich aufzeigen, dass die Makroinvertebraten des oberen Litorals zur Bewertung der Hydromorphologie von Seeufern herangezogen werden sollten. Die Auswirkungen anthropogen modifizierter Seeufer auf die Diversität und Zusammensetzung der Makroinvertebraten waren am stärksten im oberen Litoral und nahmen zum Profundal hin ab. Zum Zweiten konnte ich nachweisen, dass eine Beprobung pro Jahr ausreicht, um die Unterschiede in der Makroinvertebraten-Gesellschaft als Folge von Seeufermodifikationen zu erfassen. Jahreszeitliche Einflüsse auf die Diversität und Zusammensetzung der Makroinvertebraten wurden im oberen Litoral von den Auswirkungen der modifizierten Seeufer überlagert, jedoch nicht mehr im mittleren Litoral und im Profundal. Drittens konnte ich zeigen, dass die Makrophyten-Gesellschaften des oberen Litorals ebenfalls von den Modifikationen des Seeufers beeinflusst waren. Gleichzeitig wurden Makrophyten als die bedeutendste Variable, die Makroinvertebraten-Gesellschaften strukturiert, identifiziert. Demnach übertrugen sich die Auswirkungen von Seeufermodifikationen auf Makrophyten weiter auf die Makroinvertebraten. Makropyhten-Habitate konnten jedoch teilweise durch künstliche Substrate ersetzt werden, wie an den Häfen aufgezeigt. Da sich Seeufermodifikationen etwas anders auf Makrophyten auswirkten als auf Makroinvertebraten, sollten Makrophyten als zusätzliche Komponente zur Bewertung von Seeufern herangezogen werden. Abschließend wurde die Sekundärproduktion als Proxy zur Bestimmung der Auswirkungen von Seeufermodifikationen auf die Funktionalität von Makroinvertebraten abgeschätzt. Die Abschätzung der Sekundärproduktion erfordert die Bestimmung der Biomasse. Diese wurde indirekt mit Hilfe von Längen-Massen-Regressionen bestimmt. Die Längen-Massen-Regressionen wurden anhand von Makroinvertebraten aus Seen des zentraleuropäischen Tieflands erstellt. Im Ergebnis zeigte sich, dass die gesamte Sekundärproduktion und die Sekundärproduktion heimischer Taxa des oberen Litorals an den untersuchten Stränden, im Vergleich zu den natürlichen Stellen, beträchtlich verringert waren. Dagegen änderte sich die gesamte Sekundärproduktion an den untersuchten Häfen des oberen Litorals, im Vergleich zu den natürlichen Stellen, nicht. Der Anteil der Produktion von nichtheimischen Arten an den Häfen war jedoch höher gegenüber natürlichen Ufern. Keine Auswirkungen von Seeufermodifikationen auf die Sekundärproduktion konnte in den tieferen Wasserzonen gefunden werden. Unterschiedliche Szenarien, die auf Basis von Hochrechnung der standortspezifischen Sekundärproduktion auf Ebene des gesamten Sees erzeugt wurden, belegen, dass lokale Auswirkungen von Seeufermodifikationen auch auf Ebene des gesamten Seeökosystems bemerkbar werden. Zusätzlich wurde bestätigt, dass die Sekundärproduktion als Maß für die Funktionalität eine höhere Sensitivität aufweist, Auswirkungen von Seeufermodifikationen zu erkennen, als die strukturellen Maße Diversität und Biomasse. Deshalb sollte die Sekundärproduktion in existierende Bewertungsmethoden für Seeufer aufgenommen werden. Um einen umfassenden Überblick über die Änderungen der Funktionalität von Makroinvertebraten als Folge von Seeufermodifikationen zu erhalten, wird nicht nur empfohlen die gesamte Sekundärproduktion, sondern auch die Sekundärproduktion funktioneller Gruppen zu berücksichtigen. Mit diesen Ergebnissen trägt die vorliegende Doktorarbeit zum mechanistischen Verständnis der Auswirkungen der Seeufermodifikation auf die Funktionalität der Makroinvertebraten und der Konsequenzen für das gesamte Seeökosystem bei. Das neu generierte Wissen hilft, die Entwicklung von erfolgsversprechenden Methoden für die Seeuferbewertung und Identifikation von Managementmaßnahmen zu optimieren

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

Dynamic of Dominant Plant Communities in Kettle Holes (Northeast Germany) during a Five-Year Period of Extreme Weather Conditions

Understanding the ecosystem functions and services of central European kettle holes (small wetlands) requires knowledge about their spatiotemporal dynamics. A lot of existing research has been conducted on the wet–dry cycles of North American potholes, but much less is known about kettle holes. Based on the extreme weather conditions between 2015 and 2020, we aimed to quantify differences among dominant plant communities of kettle holes using unmanned aerial systems. Different dominant plant communities were differently affected by dry and wet intervals with a major increase in terrestrial plants. Multivariate analysis showed strong variability in plant community composition for permanent and semi-permanent kettle holes, where hydrophytes decreased and nitrophilous perennials increased. Although we cannot provide quantitative results in succession over a five-year observation period, we found indications of progressive succession towards irreversible alternative stable states with woody plants for some kettle holes, especially of the “storage type”. Therefore, we assume stronger changes in proportion of wetland types in kettle holes compared to potholes and we expect the proportion of wood-dominated kettle holes to increase in the central European landscape in the future, leading to enhanced homogenization of the landscape accompanied by a loss of ecosystem functions and services

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

Allometric relationships for selected macrophytes of kettle holes in northeast Germany as a basis for efficient biomass estimation using unmanned aerial systems (UAS)

Quantifying plant biomass in ecosystems is an essential basis for many ecological questions. A direct estimation of macrophyte biomass proves to be difficult for the large number of kettle holes in Pleistocene landscapes, due to their strong heterogeneities. This study compared a classical non-destructive method for biomass estimation based on allometric relationships built from a larger selection of plant trait variables with regressions only based on plant height and cover of four macrophyte species typical for kettle holes in northeast Germany (i.e. Carex riparia, Phalaris arundinacea, Persicaria amphibia, Rorippa amphibia). Their predictive power and potential applicability for remotely sensed biomass estimation using unmanned aerial systems (UAS) was evaluated. The usage of several in-situ measured plant traits of individual plants revealed best macrophyte biomass predictions (R² = 0.84 to 0.95). Yet, using only plant height and cover to predict biomass still showed a moderate to good correlation (R² = 0.52 to 0.81). Using P. arundinacea as an example, we demonstrated for one kettle hole the potential of calculating plant patch height from digital surface models (DSM) derived from UAS RGB images processed with structure-from-motion (SfM) photogrammetry. After applying a site-specific correction factor for discrepancies between reference field measurements of plant heights and DSM derived plant heights, we were able to calculate P. arundinacea biomass of the entire kettle hole based on allometric relationships using plant height and cover. Finally, we briefly discuss how further methodological development can improve UAS-derived plant height as predictor variable for biomass estimation

How much information do we gain from multiple-year sampling in natural pond research?

Natural ponds are perceived as spatially and temporally highly variable ecosystems. This perception is in contrast to the often-applied sampling design with high spatial but low temporal replication. Based on a data set covering a period of six years and 20 permanently to periodically inundated ponds, we investigated whether this widely applied sampling design is sufficient to identify differences between single ponds or single years with regard to water quality and macrophyte community composition as measures of ecosystem integrity. In our study, the factor “pond”, which describes differences between individual ponds, explained 56 % and 63 %, respectively, of the variance in water quality and macrophyte composition. In contrast, the factor “year” that refers to changes between individual years, contributed less to understand the observed variability in water quality and macrophyte composition (10 % and 7 % respectively, of the variance explained). The low explanation of variance for “year” and the low year-to-year correlation for the single water quality parameter or macrophyte coverage values, respectively, indicated high but non-consistent temporal variability affecting individual pond patterns. In general, the results largely supported the ability of the widely applied sampling strategy with about one sampling date per year to capture differences in water quality and macrophyte community composition between ponds. Hence, future research can be rest upon sampling designs that give more weight to the number of ponds than the number of years in dependence on the research question and the available resources. Nonetheless, pond research would miss a substantial amount of information (7 to 10 % of the variance explained), when the sampling would generally be restricted to one year. Moreover, we expect that the importance of multiple-year sampling will likely increase in periods and regions of higher hydrological variability compared to the average hydrological conditions encountered in the studied period

Transition zones across agricultural field boundaries for integrated landscape research and management of biodiversity and yields

1. Biodiversity conservation and agricultural production have been largely framed as separate goals for landscapes in the discourse on land use. Although there is an increasing tendency to move away from this dichotomy in theory, the tendency is perpetuated by the spatially explicit approaches used in research and management practice. 2. Transition zones (TZ) have previously been defined as areas where two adjacent fields or patches interact, and so they occur abundantly throughout agricultural landscapes. Biodiversity patterns in TZ have been extensively studied, but their relationship to yield patterns and social–ecological dimensions has been largely neglected. 3. Focusing on European, temperate agricultural landscapes, we outline three areas of research and management that together demonstrate how TZ might be used to facilitate an integrated landscape approach: (i) plant and animal species’ use and response to boundaries and the resulting effects on yield, for a deeper understanding of how landscape structure shapes quantity and quality of TZ; (ii) local knowledge on field or patch-level management and its interactions with biodiversity and yield in TZ, and (iii) conflict prevention and collaborative management across land-use boundaries

Transition zones across agricultural field boundaries for integrated landscape research and management of biodiversity and yields

1. Biodiversity conservation and agricultural production have been largely framed as separate goals for landscapes in the discourse on land use. Although there is an increasing tendency to move away from this dichotomy in theory, the tendency is perpetuated by the spatially explicit approaches used in research and management practice. 2. Transition zones (TZ) have previously been defined as areas where two adjacent fields or patches interact, and so they occur abundantly throughout agricultural landscapes. Biodiversity patterns in TZ have been extensively studied, but their relationship to yield patterns and social–ecological dimensions has been largely neglected. 3. Focusing on European, temperate agricultural landscapes, we outline three areas of research and management that together demonstrate how TZ might be used to facilitate an integrated landscape approach: (i) plant and animal species’ use and response to boundaries and the resulting effects on yield, for a deeper understanding of how landscape structure shapes quantity and quality of TZ; (ii) local knowledge on field or patch-level management and its interactions with biodiversity and yield in TZ, and (iii) conflict prevention and collaborative management across land-use boundarie