Search

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.

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.

The pleistocenic landscape in North Europe, North Asia and North America is spotted with thousands of natural ponds called kettle holes. They are biological and biogeochemical hotspots. Due to small size, small perimeter and shallow depth biological and biogeochemical processes in kettle holes are closely linked to the dynamics and the emissions of the terrestrial environment. On the other hand, their intriguing high spatial and temporal variability makes a sound understanding of the terrestrial-aquatic link very difficult. It is presumed that intensive agricultural land use during the last decades has resulted in a ubiquitous high nutrient load. However, the water quality encountered at single sites highly depends on internal biogeochemical processes and thus can differ substantially even between adjacent sites. This study aimed at elucidating the interplay between external drivers and internal processes based on a thorough analysis of a comprehensive kettle hole water quality data set. To study the role of external drivers, effects of land use in the adjacent terrestrial environment, effects of vegetation at the interface between terrestrial and aquatic systems, and that of kettle hole morphology on water quality was investigated. None of these drivers was prone to strong with-in year variability. Thus temporal variability of spatial patterns could point to the role of internal biogeochemical processes. To that end, the temporal stability of the respective spatial patterns was studied as well for various solutes. All of these analyses were performed for a set of different variables. Different results for different solutes were then used as a source of information about the respective driving processes. In the Quillow catchment in the Uckermark region, about 100 km north of Berlin, Germany, 62 kettle holes have been regularly sampled since 2013. Kettle hole catchments were determined based on a groundwater level map of the uppermost aquifer. The catchments were not clearly related to topography. Spatial patterns of kettle hole water concentration of (earth) alkaline metals and chloride were fairly stable, presumably reflecting solute concentration of the uppermost aquifer. In contrast, spatial patterns of nutrients and redox-sensitive solutes within the kettle holes were hardly correlated between different sampling campaigns. Correspondingly, effects of season, hydrogeomorphic kettle hole type, shore vegetation or land use in the respective catchments were significant but explained only a minor portion of the total variance. It is concluded that internal processes mask effects of the terrestrial environment. There is some evidence that denitrification and phosphorus release from the sediment during frequent periods of hypoxia might play a major role. The latter seems to boost primary production occasionally. These processes do not follow a clear seasonal pattern and are still not well understood.

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.

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”.