@phdthesis{Morling2017,
  author    = {Morling, Karoline},
  title     = {Import and decomposition of dissolved organic carbon in pre-dams of drinking water reservoirs},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-399110},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xii, 151},
  year      = {2017},
  abstract  = {Dissolved organic carbon (DOC) depicts a key component in the aquatic carbon cycle as well as for drinking water production from surface waters. DOC concentrations increased in water bodies of the northern hemisphere in the last decades, posing ecological consequences and water quality problems. Within the pelagic zone of lakes and reservoirs, the DOC pool is greatly affected by biological activity as DOC is simultaneously produced and decomposed. This thesis aimed for a conceptual understanding of organic carbon cycling and DOC quality changes under differing hydrological and trophic conditions. Further, the occurrence of aquatic priming was investigated, which has been proposed as a potential process facilitating the microbial decomposition of stable allochthonous DOC within the pelagic zone. To study organic carbon cycling under different hydrological conditions, quantitative and qualitative investigations were carried out in three pre-dams of drinking water reservoirs exhibiting a gradient in DOC concentrations and trophic states. All pre-dams were mainly autotrophic in their epilimnia. Discharge and temperature were identified as the key factors regulating net production and respiration in the upper water layers of the pre-dams. Considerable high autochthonous production was observed during the summer season under higher trophic status and base flow conditions. Up to 30\% of the total gained organic carbon was produced within the epilimnia. Consequently, this affected the DOC quality within the pre-dams over the year and enhanced characteristics of algae-derived DOC were observed during base flow in summer. Allochthonous derived DOC dominated at high discharges and oligotrophic conditions when production and respiration were low. These results underline that also small impoundments with typically low water residence times are hotspots of carbon cycling, significantly altering water quality in dependence of discharge conditions, temperature and trophic status. Further, it highlights that these factors need to be considered in future water management as increasing temperatures and altered precipitation patterns are predicted in the context of climate change. Under base flow conditions, heterotrophic bacteria preferentially utilized older DOC components with a conventional radiocarbon age of 195-395 years before present (i.e. before 1950). In contrast, younger carbon components (modern, i.e. produced after 1950) were mineralized following a storm flow event. This highlights that age and recalcitrance of DOC are independent from each other. To assess the ages of the microbially consumed DOC, a simplified method was developed to recover the respired CO2 from heterotrophic bacterioplankton for carbon isotope analyses (13C, 14C). The advantages of the method comprise the operation of replicate incubations at in-situ temperatures using standard laboratory equipment and thus enabling an application in a broad range of conditions. Aquatic priming was investigated in laboratory experiments during the microbial decomposition of two terrestrial DOC substrates (peat water and soil leachate). Thereby, natural phytoplankton served as a source of labile organic matter and the total DOC pool increased throughout the experiments due to exudation and cell lysis of the growing phytoplankton. A priming effect for both terrestrial DOC substrates was revealed via carbon isotope analysis and mixing models. Thereby, priming was more pronounced for the peat water than for the soil leachate. This indicates that the DOC source and the amount of the added labile organic matter might influence the magnitude of a priming effect. Additional analysis via high-resolution mass spectrometry revealed that oxidized, unsaturated compounds were more strongly decomposed under priming (i.e. in phytoplankton presence). Given the observed increase in DOC concentrations during the experiments, it can be concluded that aquatic priming is not easily detectable via net concentration changes alone and could be considered as a qualitative effect. The knowledge gained from this thesis contributes to the understanding of aquatic carbon cycling and demonstrated how DOC dynamics in freshwaters vary with hydrological, seasonal and trophic conditions. It further demonstrated that aquatic priming contributes to the microbial transformation of organic carbon and the observed decay of allochthonous DOC during transport in inland waters.},
  language  = {en}
}
@misc{ZibulskiWesenerWilkesetal.2017,
  author    = {Zibulski, Romy and Wesener, Felix and Wilkes, Heinz and Plessen, Birgit and Pestryakova, Luidmila Agafyevna and Herzschuh, Ulrike},
  title     = {C / N ratio, stable isotope (δ 13 C, δ 15 N), and n-alkane patterns of brown mosses along hydrological gradients of low-centred polygons of the Siberian Arctic},
  series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  journal   = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  number    = {672},
  issn      = {1866-8372},
  doi       = {10.25932/publishup-41710},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-417104},
  pages     = {14},
  year      = {2017},
  abstract  = {Mosses are a major component of the arctic vegetation, particularly in wetlands. We present C / N atomic ratio, delta C-13 and delta N-15 data of 400 brown-moss samples belonging to 10 species that were collected along hydrological gradients within polygonal mires located on the southern Taymyr Peninsula and the Lena River delta in northern Siberia. Additionally, n-alkane patterns of six of these species (16 samples) were investigated. The aim of the study is to see whether the inter-and intraspecific differences in C / N, isotopic compositions and n-alkanes are indicative of habitat, particularly with respect to water level. Overall, we find high variability in all investigated parameters for two different moisture-related groups of moss species. The C / N ratios range between 11 and 53 (median: 32) and show large variations at the intraspecific level. However, species preferring a dry habitat (xero-mesophilic mosses) show higher C / N ratios than those preferring a wet habitat (meso-hygrophilic mosses). The delta C-13 values range between 37.0 and 22.5\% (median D 27.8 \%). The delta N-15 values range between 6.6 and C 1.7\%(median D 2.2 \%). We find differences in delta C-13 and delta N-15 compositions between both habitat types. For some species of the meso-hygrophilic group, we suggest that a relationship between the individ-ual habitat water level and isotopic composition can be inferred as a function of microbial symbiosis. The n-alkane distribution also shows differences primarily between xeromesophilic and meso-hygrophilic mosses, i. e. having a dominance of n-alkanes with long (n-C29, n-C31 /and intermediate (n-C25 /chain lengths, respectively. Overall, our results reveal that C / N ratios, isotopic signals and n-alkanes of studied brown-moss taxa from polygonal wetlands are characteristic of their habitat.},
  language  = {en}
}