Kurz- und langfristige Sukzession in intermittierenden Flüssen : Struktur mikrobieller Sedimentgemeinschaften und biogeochemische Trajektorien

Intermittent rivers and ephemeral streams (IRES) experience drying events, and they are becoming increasingly common due to climate change and anthropogenic water withdrawal. Despite their prevalence, IRES have been less studied than non-drying rivers, and more research is needed to understand their dynamics. This dissertation examines drying events' effects on the sediment microbial community structure and biogeochemistry in temperate IRES. First, a research study was carried out using an outdoor mesocosm setup to track changes in bacterial and fungal communities, microbial functions and properties of sediment-dissolved organic carbon during three different drying events. Results showed that drying duration and intensity and sediment organic matter content regulated river Spree sediment microbial community composition and biogeochemical processes during drying. The associated sediment respiration, assessed as CO2 flux, rapidly declined during all drying treatments, and Bacilli class became the most dominant bacteria after 90 days of drying, except in non-enriched sediment under the most intense drying. Second, a microcosm experiment was conducted to understand how sediment drying history and properties influence biogeochemical dynamics during an IRES expansion phase. Sediment respiration and nutrient release/retention rates were measured through flow resumption, and results showed that drying duration and intensity and sediment organic matter content regulated the dynamics of nutrients and respiration upon flow resumption. Under the most intense and prolonged drying, non-enriched sediment showed a lag response in respiration during the first day after flow resumption, while all other treatments had either a linear increase or a fast pulse in respiration. Finally, the long-term microbial succession in IRES sediment and soil in the experimental catchment of Chicken Creek was investigated. In 2008 and 2018, the sediment of three ephemeral streams and their adjacent soil was analyzed for the structure of the bacterial and fungal communities and microbial functions across different seasons. Results showed that environmental factors, such as vegetation type and organic matter content, mediated sediment and soil microbial succession in Chicken Creek. Ephemeral streams under spare and sporadic flow events remained unique ecosystems with distinctive microbial communities and biogeochemical dynamics, different from its riparian soil. Overall, this dissertation concludes that temperate IRES are dynamic ecosystems where dry-wet cycles and environmental factors modulate their sediment microbial community structure and function trajectories in the short- and long term.Periodisch wiederkehrende Bäche und Flüsse (IRES, intermittent rivers and ephemeral streams) sind Gewässerkörper die episodisch austrocknen und durch Klimawandel und anthropogener Wasserentnahme zunehmend häufiger werden. Obwohl sie weit verbreitet sind, sind IRES bisher weit weniger erforscht worden als dauerhaft wasserführende Flüsse. Die vorliegende Dissertation untersucht Auswirkungen von Trockenperioden in IRES der gemäßigten Klimazone auf biogeochemische Parameter des Sediments sowie bakterielle und pilzliche Gemeinschaften. Zum einen wurde in einem Mesokosmen-Experiment im Freiland die bakterielle und pilzliche Diversität, sowie Eigenschaften von sedimentären, gelösten organischem Kohlenstoff und mikrobiellen Funktionen für verschiedene Austrocknungsintensitäten untersucht. Die Dauer und Intensität der Austrocknung, sowie die Konzentration an organischer Substanz, bewirkten maßgeblich eine Veränderungen der Struktur der mikrobiellen Gemeinschaft sowie der biogeochemischen Prozesse im Spree-Sediment während der Trockenphasen. In allen Austrocknungsintensitäten nahm die Respiration aus dem Sediment, gemessen als CO2 Emissionen, schnell ab; wobei die Ordnung Bacilli nach 90 Tagen Trockenzeit dominant wurde. Ausnahme war hier Sediment das nicht mit organischer Substanz angereichert war. Zum anderen wurde in Mikrokosmen der biogeochemische Effekte von vergangenen Austrocknungsepisoden und deren Eigenschaften während der Erweiterungsphase der IRES untersucht. Respiration im Sediment, sowie Freisetzung und Rückhalt von Nährstoffen wurden nach wieder einsetzenden des Wasserflusses gemessen. Eigenschaften wie Dauer und Intensität der Austrocknungsepisoden, sowie der Gehalt an organischer Substanz, bestimmten hier Nährstoffflüsse und Respiration; speziell in den ersten Tagen nach wiederkehren des Wasserflusses. Bei sehr intensiver und andauernden Austrocknung zeigte das Sediment ohne Anreicherung mit organischer Substanz eine verzögerte Reaktionszeit in der Respiration. Letzteren wurde die langfristige Auswirkung und mikrobielle Sukzession von IRES auf Sedimente und Böden im Einzugsgebiet Hühnerwasser in der Jahren 2008 und 2018 untersucht. Analysiert wurden die Struktur der mikrobiellen Gemeinschaften und Funktionen aus Sediment der wiederkehrenden Bäche und angrenzenden Uferböden in beiden Jahren. Vegetationsform und organische Substanz regulierten die mikrobielle Sukzession im Einzugsgebiet des Hühnerwassers. Die IRES bleiben auch bei nur geringem Wasserfluss eigenständige Systeme, die sich auch hinsichtlich ihrer mikrobiellen Struktur und Biogeochemie von den Böden in Gewässernähe unterscheiden. Schlussfolgernd für diese Dissertation steht, dass IRES in der temperten Klimazone dynamische Ökosysteme sind. Besonders Nass-Trocken-Zyklen und Umweltfaktoren regulieren die Struktur der mikrobiellen Gemeinschaften im Sediment und ihre Funktionen auf kurz- und langfristige Sicht

Metabolism after drying and bedform migration in the Spree River in 2018/2019

Sandy streambed sediments that had been exposed to either intense drying (90-day without rainfall) or bedform migration (periodically moving ripples) were placed in 250 µm mesh bags to the Spree River in Northeastern Germany on October 22, 2018, to initiate the recovery process from drying or migration stress. Subsamples from the recovering sediments were collected at eight dates within eight months and taken to the laboratory for further analysis. Community respiration and Net Community Production of sediment associated biofilms were measured as dissolved oxygen concentrations from sediment pore water in inundated microcosms. The aim of the experiment was to observe the long-term recovery of microbial communities in lowland streams from drying and bedform migration and to identify if stress effects persisted as legacy after the stress period

Community abundance after drying and bedform migration in the Spree River in 2018/2019

Sandy streambed sediments that had been exposed to either intense drying (90-day without rainfall) or bedform migration (periodically moving ripples) were placed in 250 µm mesh bags to the Spree River in Northeastern Germany on October 22, 2018, to initiate the recovery process from drying or migration stress. Subsamples from the recovering sediments were collected at eight dates within eight months and taken to the laboratory for further analysis. Community abundance was assessed on a heterotrophic (amplified bacterial and fungal gene copies) and on an autotrophic level (Chlorophyll a concentration and diatom cell count). The aim of the experiment was to observe the long-term recovery of microbial communities in lowland streams from drying and bedform migration and to identify if stress effects persisted as legacy after the stress period

Long-term recovery of metabolism, enzyme activity and community abundance after drying and bedform migration in the Spree river 2018/2019

Sandy streambed sediments that had been exposed to either intense drying (90-day without rainfall) or bedform migration (periodically moving ripples) were placed in 250 µm mesh bags to the Spree River in Northeastern Germany on October 22, 2018, to initiate the recovery process from drying or migration stress. Subsamples from the recovering sediments were collected at eight dates within eight months and taken to the laboratory for further analysis. Community respiration and Net Community Production of sediment associated biofilms were measured as dissolved oxygen concentrations from sediment pore water in inundated microcosms. Potential extracellular enzyme activities (Beta-Glucosidase, Xylosidase, Chitinase, Phosphatase, Leucine-Aminopeptidase, Phenol-Oxidase, and Peroxidase) were assessed by measuring fluorescence and absorbance after extraction from sediments. Community abundance was assessed on a heterotrophic (amplified bacterial and fungal gene copies) and on an autotrophic level (Chlorophyll a concentration and diatom cell count). The aim of the experiment was to observe the long-term recovery of microbial communities in lowland streams from drying and bedform migration and to identify if stress effects persisted as legacy after the stress period

Enzyme activity after drying and bedform migration in the Spree River in 2018/2019

Sandy streambed sediments that had been exposed to either intense drying (90-day without rainfall) or bedform migration (periodically moving ripples) were placed in 250 µm mesh bags to the Spree River in Northeastern Germany on October 22, 2018, to initiate the recovery process from drying or migration stress. Subsamples from the recovering sediments were collected at eight dates within eight months and taken to the laboratory for further analysis. Potential extracellular enzyme activities (Beta-Glucosidase, Xylosidase, Chitinase, Phosphatase, Leucine-Aminopeptidase, Phenol-Oxidase, and Peroxidase) were assessed by measuring fluorescence and absorbance after extraction from sediments. The aim of the experiment was to observe the long-term recovery of microbial communities in lowland streams from drying and bedform migration and to identify if stress effects persisted as legacy after the stress period

Freshwater vertebrate and invertebrate diversity patterns in an Andean-Amazon basin: implications for conservation efforts

The Napo Basin in Ecuador is an important drainage of the Amazon Basin, the most biodiverse ecosystem for freshwater species. At the same time, this basin has conspicuous information gaps on its biodiversity patterns and human threats. Here, we estimated the diversity distribution patterns of freshwater vertebrates and invertebrates in the Napo Basin, as a tool for present and future management and conservation efforts. Also, we assessed the spatial congruence of the diversity patterns observed between aquatic vertebrates and invertebrates. For this, we compiled occurrence records for 481 freshwater vertebrate species (amphibians, birds, mammals, reptiles, and fish), and 54 invertebrate families obtained across an altitudinal gradient of the basin (200–4500 m). Using these occurrence records and environmental variables, we modeled the distribution of each vertebrate species and invertebrate family. Then, we stacked these distributions to build species richness maps for vertebrates, and a family richness map for invertebrates. We found that the most diverse areas for vertebrate species are the lowlands (\u3c600 m), whereas richness of invertebrate families peaks at higher elevations (lower montane forests). Congruence among species richness patterns of the five vertebrate groups was high (r = 0.66), with fish being the best predictor for vertebrates (r = 0.78). However, congruence decreased at higher elevations (r = 0.14), suggesting that specific species or habitat-based approaches should be used in the highlands. Also, we found a high correlation between species and family richness of freshwater invertebrates (r = 0.66), suggesting that family richness of invertebrates could be used as a surrogate of species richness in this basin. We highlight this correlation because, at the watershed scale, it allows working with family groups where species-level taxonomy is challenging. Our results provide the first comprehensive representation of freshwater biodiversity patterns at high resolution in an Andean-Amazon basin, and calls attention to the need for incorporating different taxonomic groups when assessing diversity patterns. Given these different diversity patterns, conservation programs for this basin should incorporate both vertebrate and invertebrate groups as biodiversity indicators. Finally, our study provides a practical methodological guidance in the estimation of freshwater diversity in regions of scarce information with high conservation priority, such as the Andean-Amazon basins

Freshwater vertebrate and invertebrate diversity patterns in an Andean-Amazon basin: implications for conservation efforts

<p>The Napo Basin in Ecuador is an important drainage of the Amazon Basin, the most biodiverse ecosystem for freshwater species. At the same time, this basin has conspicuous information gaps on its biodiversity patterns and human threats. Here, we estimated the diversity distribution patterns of freshwater vertebrates and invertebrates in the Napo Basin, as a tool for present and future management and conservation efforts. Also, we assessed the spatial congruence of the diversity patterns observed between aquatic vertebrates and invertebrates. For this, we compiled occurrence records for 481 freshwater vertebrate species (amphibians, birds, mammals, reptiles, and fish), and 54 invertebrate families obtained across an altitudinal gradient of the basin (200–4500 m). Using these occurrence records and environmental variables, we modeled the distribution of each vertebrate species and invertebrate family. Then, we stacked these distributions to build species richness maps for vertebrates, and a family richness map for invertebrates. We found that the most diverse areas for vertebrate species are the lowlands (<600 m), whereas richness of invertebrate families peaks at higher elevations (lower montane forests). Congruence among species richness patterns of the five vertebrate groups was high (<i>r</i> = 0.66), with fish being the best predictor for vertebrates (<i>r</i> = 0.78). However, congruence decreased at higher elevations (<i>r</i> = 0.14), suggesting that specific species or habitat-based approaches should be used in the highlands. Also, we found a high correlation between species and family richness of freshwater invertebrates (<i>r</i> = 0.66), suggesting that family richness of invertebrates could be used as a surrogate of species richness in this basin. We highlight this correlation because, at the watershed scale, it allows working with family groups where species-level taxonomy is challenging. Our results provide the first comprehensive representation of freshwater biodiversity patterns at high resolution in an Andean-Amazon basin, and calls attention to the need for incorporating different taxonomic groups when assessing diversity patterns. Given these different diversity patterns, conservation programs for this basin should incorporate both vertebrate and invertebrate groups as biodiversity indicators. Finally, our study provides a practical methodological guidance in the estimation of freshwater diversity in regions of scarce information with high conservation priority, such as the Andean-Amazon basins.</p