Bachelor's programme in Environmental Sciences: 57 pp. (first reviewer)

The aim of the thesis is to analyse the vegetation in largely human-influenced salt marshes of different deposition areas at the Jade Bay. Various site parameters and their interrelationships were analysed.

The studies were carried out in three salt marsh areas in the western (Petersgroden), southern (Schweiburg) and eastern Jade Bay (Stollhamm), in which the vegetation was first recorded. In addition, the sediments of the identified vegetation units were analysed for their grain size distribution and the respective elevation was measured. The current utilisation of the areas was also taken into account. The environmental characteristics and their interrelationships were analysed descriptively and evaluated taking into account relevant literature.

There are general differences in the vegetation structure of the three sites. Some plant communities occur in all areas, but often in different areas of the salt marsh and in different forms. There are also differences at the species level. In Petersgroden, the vegetation zonation is relatively typical. There is an extensive area with lower salt marsh communities and also a middle and an upper salt marsh. The vegetation sequence in Schweiburg and in Stollhamm is characterised to a large extent by communities of the Middle and Upper Salt Marsh, while the Lower Salt Marsh is only present to a small extent.

The sediments of the study areas reflect the different current conditions. The coarse-grained sediments in the eastern Jade Bay correlate with the higher wave intensities and, conversely, the calmer currents in the western Jade Bay are characterised by smaller grain sizes. The sediments of the area in the southern Jade Bay indicate the calmest currents within the Jade Bay due to their fine grain size. With regard to the plant communities present, only a slight correlation could be established. If the vegetation units of the sites are compared with each other, the measured grain sizes rarely coincide. Localised distributions of communities within an area, for example due to proximity to tidal creeks, can be explained on the basis of the grain sizes. In some places, the different occurrence of species can be attributed to the distribution of sediments.

In general, the transect in Schweiburg is higher than the one in Petersgroden. This means that most of the plant communities also tend to be higher. The communities of the lower salt marsh are found at approximately the same altitudes, while those of the upper salt marsh are higher in Schweiburg than in Petersgroden. The elevation profile thus clearly confirms the recorded vegetation pattern. The middle salt marsh is particularly elevated and extensive in Schweiburg, while the area of the lower salt marsh is very limited. Overall, the measured elevations fit in well with the existing literature, especially for Lower Salt Marsh communities.

The utilisation of the areas also has an influence on the vegetation composition. The areas in Petersgroden and Schweiburg, which are extensively utilised by mowing in late summer, are dominated by grasses. The unused area in Stollhamm is colonised by some species that are particularly sensitive to grazing, such as Atriplex portulacoides and Artemisia maritima. Another species that is heavily displaced when utilised is couch grass. It dominates the unused middle salt marsh in Schweiburg. In this case, it could also be the result of advanced succession due to silting up.

The hypothesis that plant communities only occur in connection with certain sediments could not be confirmed. In further studies, horizontal sampling instead of surface sampling, in which the direct substrate of the plant roots is analysed, could lead to further findings. In addition, it was not possible to determine the salt concentration and nutrient availability in the soil during the course of the work. In subsequent studies, the determination of sedimentation rates in the different deposition areas could be helpful in clarifying the development and succession of salt marshes.

The development of salt marshes therefore depends on various abiotic and biotic factors. In addition, anthropogenic influences must always be taken into account when studying the vegetation of salt marshes.

Bachelor's programme in Environmental Sciences: 77 pp. (first reviewer)

The aim of the thesis is to analyse the growth dynamics of salt marshes in different depositional areas on the basis of geological profiles. The investigations are mainly based on diatomological studies, which are considered in relation to different site parameters. The investigations focus on three study sites (Petersgroden, Schweiburg and Stollhamm), which are characterised by different deposition conditions due to the flow processes in the Jade Bay.

As a result of the geological investigations, the profile in Stollhamm (eastern Jade Bay) turned out to be unsuitable. On the other hand, the investigations at the Petersgroden (western Jade Bay) and Schweiburg (southern Jade Bay) sites yielded significant findings. The analyses included geological profile surveys, which provide a general overview of the salt marsh structure and were used to develop a sampling strategy for analysing the diatom communities. Furthermore, horizontal samples for analysing the grain size spectrum and organic matter were taken from the profiles largely parallel to the diatom samples, as the distribution of the diatoms correlates with the grain size of the material, among other things.

The analysis of diatom assemblages proved to be a pioneering field of research in the Jade Bay, so the analyses had to clarify fundamental relationships between the habitat selection of the diatoms. The investigations are based on various methodological approaches, which were applied in combination to the study area. The application of the methodology of VOS and DE WOLF (1988), according to which ecological groups are classified, revealed great similarities between the ecosystem of the Dutch North Sea and that of the Jade Bay. Nevertheless, it is clear that the diatom associations differ at the species level.

Which species in particular are typical for the Dutch North Sea and do not occur in the Jade Bay and which species can be assigned to the ecological groups in the Jade Bay must be clarified by further investigations on Jade Bay samples. However, the method has provided valuable information for a general assessment of the site conditions. As the dominance of the ecological groups Navicula digitoradiata var.minima and Achnanthes delicatula in the profiles shows, the system is characterised by mesohalobic conditions. The Navicula digitoradiata var. minima group, which is represented by a particularly high number of individuals in Petersgroden, emphasises the clayey-silty conditions of the site, whereas the dominance of the Achnanthes delicatula group in Schweiburg indicates a certain proportion of sand. These results were verified by analysing the grain size. A graphical analysis was used to identify "local diatom zones" in the profiles, each of which is made up of a specific combination of species and describes the different stratigraphic conditions. Species that occur in a spatially limited distribution in a "Local Diatom Zone" have proven to be of particular importance for differentiating the site conditions. In order to precisely record the characteristics of the "Local Diatom Zones", a more closely meshed sampling strategy within the drilling profile is recommended.

As it has been confirmed that the habitat selection of diatoms varies in different coastal systems, further sampling should be carried out to establish correlations between diatom distribution and environmental factors. Ultimately, it would be desirable to adapt the system of VOS and DE WOLF (1988) to the conditions of the Jade Bay. Figure 5.5 of this bachelor thesis provides a good basis for this, in which character types of both profiles are summarised.

Overall, the profile structure in Petersgroden is more homogeneous compared to the profile structure in Schweiburg, so that a continuous growth of the salt marsh can be assumed. The same correlation is made clear by the distribution of the diatoms, which indicate differences in the facies areas due to the dominance distribution and form comparatively uniform associations. In contrast, the boundaries of the "Local Diatom Zones" in Schweiburg are less clearly defined, a result that also correlates with the geological profile survey. The occurrence of a few species is clearly limited to one area of the profile in Schweiburg, whereas many species were assigned to two or more zones.

In order to be able to compare the profiles further, parallelisation of the drilling profiles is absolutely necessary. The sand layers in both profiles are possibly due to the same storm surge events, so that the profile sections can be parallelised on the basis of the sand layers. In order to verify this assumption, a temporal dating of the profiles with stable isotopes is a conceivable possibility.

Ultimately, a renewed profile investigation in Stollhamm and, if possible, at other salt marsh sites in the Jade Bay is recommended. The Stollhamm site is very interesting for further investigations because, as the analyses of the grain size spectrum have shown, the sedimentological conditions in the eastern Jade Bay differ greatly from the recorded sample sites.

In order to take into account the influence of agricultural utilisation, further studies on pollen deposits are desirable. Scientists already have valuable knowledge about the effects of agricultural use on vegetation communities, so that paleoecological distribution patterns at pollen level can be used to estimate the conditions of use and their influence on vegetation growth.

The geological profile images illustrate a detailed picture of the salt marsh structure and indicate further fields of investigation. Unfortunately, the capacities of this work are filled by the diatomological evaluations, but additional geochemical and pedological analyses would round off the results very well. The intercalated sand layers and peat fragments would be a very interesting aspect of investigation.

The work makes it clear that the growth of salt marshes is dependent on various biotic and abiotic factors and is also characterised by human influence. Since hardly any studies on the salt marshes in the Jade Bay have been carried out to date, particularly at the palaeoecological level, this work only forms a basis for the analysis and instead opens up further fields of research.

Diploma Programme Landscape Ecology: 76 p. (first reviewer)

On the East Frisian island of Wangerooge, the current total populations of the neophytic species late weeping cherry(Prunus serotina) and narrow-leaved ragwort(Senecio inaequidens) were mapped in the summer of 2009. Almost all individuals of Prunus serotina were recorded as point coordinates in four different size classes in order to take into account age differences for possible control measures. The stands of Senecio inaequidens were divided into five size classes. In order to identify any signs of displacement of indigenous plant species, phytosociological mapping was carried out and compared in near-natural vegetation with and without the presence of Senecio inaequidens.

In the area of dwarf shrub heath dominated by heather(Calluna vullgaris), the current distribution of the neophytic potato rose(Rosa rugosa) was documented and plant sociological surveys were used to determine the extent to which Rosa rugosa has spread in the Calluna heath. In addition, the species compositions of various plant communities with and without the presence of Rosa rugosa were analysed with the help of the vegetation surveys in order to determine the extent to which the species composition changes in the presence of Rosa rugosa. In addition, soil samples were taken under dominant stands with Calluna vulgaris and Rosa rugosa, as well as in a mixed community of the species mentioned. An analysis of the soil samples should show whether Rosa rugosa favours or changes certain soil properties.

The results show that Rosa r ugosa has a high risk potential, can establish itself in almost all areas of the dune biotope types and, in addition to further degeneration and scrub encroachment, poses a serious threat to the Calluna heath. The analysis of the soil samples only shows a tendency of Rosa r ugosa towards less acidic sites than those favoured by Calluna vulgaris.

Like Rosa rugosa, Prunus serotina can also be described as a problematic neophyte from a nature conservation point of view. Because of its strong tendency to spread and its successful establishment outside anthropogenic habitats, Prunus serotina poses a high potential threat to near-natural habitats.

Only Senecio inaequidens does not appear to have any negative effects on the species composition of the plant communities into which it invades, despite its increased spread and establishment in semi-natural habitat types. However, this species could pose an increased threat in the near future if the mass populations that have been established are not displaced again in the course of succession.

Bachelor's programme in Geoecology at the University of Bayreuth: 65 pp. (First reviewer)

Two types of mudflats, the sand and mixed mudflats, were analysed for the microscale spatial distribution of benthic diatoms. It was expected that the species composition of the diatoms on the two types of mudflats would differ due to the different sediment composition and general conditions. The colonisation density of the diatoms was also investigated.

Since, according to C. Brockmann (1950), the finer and more watery the sediment, the larger the diatom populations, it was assumed that the bed colonisation on the mixed mudflats is denser than that of the sandflats. As diatoms are very small organisms, it was also of interest whether small-scale structures within the different types of mudflats affect the species composition and the density of colonisation. To this end, the microscale morphological structure of the ripples in the sandflats was examined. The hypothesis was put forward that different species compositions and colonisation densities develop on the windward and leeward sides of the ripples as well as at the top of a ripple and in the valley between two ripples. This theory is based on the fact that the different areas of the ripples are presumably subject to different forces, for example from the water. The protected leeward side can be expected to be more densely populated than the windward side, which is impacted by the water. It can also be assumed that diatom species with stronger shells are found on the windward side than on the leeward side of a ripple. In the valley between two ripples, greater water saturation is expected at low tide than on the peaks, which should also result in a denser colonisation.

On the mixed mudflats, a small-scale structure can be recognised by eye, which needs to be clarified. A pattern of spots caused by the brown-coloured diatoms can often be seen. The differently coloured areas could be due to the species composition, with stronger or weaker coloured species. Another hypothesis is that dark-coloured areas have a higher density of colonisation than light-coloured areas.

The study showed that the benthic diatom population of the sandflats differs from that of the mixed mudflats in terms of species composition and presumably also in terms of colonisation density. These differences are primarily due to the nature of the sediment. The surface structure of the tidal flats, on the other hand, has no influence on the species composition of the diatom population. The colonisation density of the differently shaped surface could not be meaningfully evaluated within the scope of this study.

Bachelor's programme in Environmental Sciences: 41 pp. (First reviewer)

The distribution of benthic biatoms in the surface sediments along a transect through a tideway in the Jade Bay was investigated. In addition, the abiotic parameters pH, salinity and temperature of the tidewater were recorded and the grain size and loss on ignition of the sediments were determined.

The sediments of the tideway consisted mainly of silt, the clay fraction was up to 11 %, whereby the southern side of the tideway tended to have finer grain sizes. The determination of the diatoms revealed 64 species and 13 higher order taxa, with the benthic diatoms showing the highest species diversity. The dominant species in all samples was the tychoplankter Cymatosira belgica. Some species could be assigned exclusively to the slope, shoulder and centre zones of the tideway. These species could be suitable as indicators for a location within a tidal flat.

Diploma programme in Geography at the University of Göttingen: 103 p. (second reviewer)

The north-western beach of the island of Langeoog has experienced an intensive phase of negative sand balance over the last 10 to 15 years. Among other things, this has led to severe erosion of the dunes in the area of the Pirolatal on the seaward side of the beach. In 1997, an artificial dune belt was built for the first time to protect the drinking water wells located behind the Pirolatal, which was intended to prevent the natural dunes from breaking through, which would lead to the salinisation of the drinking water. Due to the ongoing erosion, this coastal protection measure had to be continuously extended in the following years. By 2006, the erosion had progressed so far that the artificially constructed areas were already under attack. By 2009, a total of six artificial dunes had been created. The material used for this consists of beach sand, which is extracted from the island's beach and piled up in the Pirolatal. As the material in the artificial dunes is unsorted marine material, it is to be expected that there are inevitably differences to the aeolian transported dune sand. The most obvious indication of this is mussel shells, which can be found everywhere in the artificial dunes.

This Diplom thesis examines the differences in sedimentology, vegetation composition and chemistry between the artificial and natural dunes and to what extent it is possible to predict the development of the artificial dunes and their vegetation on the basis of these differences. Langeoog is a suitable study area as the artificial dunes in the Pirolatal had already been in use as protective measures for eleven years in 2009 and can therefore be traced back over a sufficient period of time. A transect through the natural dunes at the eastern end of the island in the Meierei area along the Falkenweg is used as a reference section. The data collected in the Pirolatal will be analysed in relation to the data from the dunes classified as natural.

The investigations include the recording of the abiotic site parameters (altitude, salinity, pH value, carbonate and humus content, storage density and grain size composition and distribution) and the recording of the vegetation (species, cover, plant communities, frequency and indicator values). On the basis of the grain size analysis, a poorer grain size sorting and a coarser grain size composition can be confirmed on the artificial dunes. In contrast, the storage density and the chemical composition of the material show no differences to the natural dunes. The analyses of the humus and carbonate content and the pH value even confirm the same processes of humus accumulation, lime leaching and acidification on the artificial as on the natural dunes.

This picture of comparability and differences can also be found in the vegetation analyses. While the admission of plant communities and the frequencies of plant species do not show any similarities, the respective increase in vegetation cover is comparable with the age of the dunes. A prognosis for the further development of the artificial dunes is only possible to a limited extent. Progressive carbonate leaching and humus accumulation can be assumed. Depending on this, the pH values will continue to fall. The onset of soil formation is to be expected as a result of acidification and humus accumulation. The vegetation will change to the extent that the lack of over-sanding will end the dominance ofAmmophila arenaria (common marram grass) in favour of better-adapted species. In addition, a tendency towards "scrub encroachment" can be recognised, as species such as Hippophae rhamnoides (sea buckthorn), Rubus caesius (cranberry) or Rosa rugosa (potato rose) increase over time. The direct dependence of the vegetation on the site conditions definitely rules out the development of artificial dunes in the sense of natural dune genesis.

A summary of the work will be published shortly. (Status: 10/2015)

Diploma Programme Marine Environmental Sciences: 115 p. (second reviewer)

Since the 1970s man made ozone depletion causes an increase of ultraviolet radiation (UVR), especially UVB on the earth surface. In the second half of the^19th century the rise of industrialisation has provoked an increase in burning of fossil fuels, which cause continuously increasing CO₂ concentration in the atmosphere. Current average atmospheric CO₂ concentrations are about 380 ppm and may exceed 1000 ppm by the end of this century. The increased partial pressure of CO₂ in the atmosphere causes an increased dissolution of CO₂ in the world oceans and hence an increase of dissolved inorganic carbon (DIC) in the water, which leads to the process known as ocean acidification. The momentary average pH of the surface ocean will fall by 0.3 to 0.5 units to an average value of 7.7 - 7.9 by the year 2100, if global emission of CO₂ continue to rise based an current trends.

UVR may cause various changes in the photosynthetic response, as well as on growth and reproduction of marine macroalgal species. Additionally increased DIC in the oceans may have especially influence on all photoautotrophic organisms, as well as a calcifying species. lt may increase the rate of photosynthetic carbon fixation and hence of growth, by an increased supply of carbon to Rubisco, the carbon fixing enzyme. However, most macroalgae exhibit carbon concentrating mechanisms (CCMs), thus their photosynthesis is carbon saturated at present atmospheric CO₂ levels. As the carbon dissolution state of the ocean decreases with decreasing pH, disadvantages of ocean acidification may especially occur to calcifying species.

In the present study four red algae species (including one calcifying species) inhabiting the lower intertidal on the coast of southern Spain were examined according to changes in their ability to acclimate to increased photosynthetic active radiation (PAR) and UVR under increased COAST conditions in a two factorial design. To study the different responses of the species to the treatment conditions alterations in photosynthesis and pigment composition, as well as carbon and nitrogen tissue concentrations were examined. Each factor (CO₂ or UVR) was established in two different levels: CO₂ was set to ambient concentrations and enriched concentrations, of about 1000 ppm CO₂. For each level of CO₂ one treatment with UVR and one with UVR depleted conditions was established, thus four different treatments per species resulted. For two species an additional low light control treatment was set, to study the deleterious influence of high irradiance on the species. All species answered with photoinhibition to the experimental light conditions in a diurnal pattern, whereby a decrease of photosynthetic performance could be found after light treatment and an increase after 10 -12 h of recovery in darkness. All species showed a delay of recovery due to UVR in the beginning of the experiment. Further, in two of four species the experimental light conditions permanently exceeded the capacity of their photosystem, leading to chronic photoinhibition, obvious in decreasing values of optimum quantumyield (FV/FM) over the experiment and a decrease of chlorophyll a concentration in one of the species. The ability to acclimate to enhanced irradiation and UVR was found to be related to the functional-form, the external and internal morphological constitution of the species. Thus it was found that species exhibiting a leathery cellstructure(Gymnogongrus sp. and Gelidium corneum) are more resistant against high irradiances and UVR, as they were able activate recovery and protection mechanisms more efficiently than the calcareous species(Corallina elongata) and the species showing smooth fronds(Plocamium cartilagineum). In general it has been found that the deleterious influence of UVR exceeded those of CO₂ in all species, despite of in the calcareous one. In Gymnogongrus sp. additional_{CO2 mitigates} the negative influence of UVR during acclimation, as it leads to increased recovery of the respective treatment. In C. elongata the influence of CO₂ was contrarily, once significantly increasing photosynthetic efficiency, once significantly decreasing it. As in calcifying species processes of photosynthesis are linked with those of calcification and the influence of ocean acidification includes the deleterious effect of increased dissolution of calcium carbonate (CaCO₃) on the one hand, and stimulation of calcification by increased DIC concentrations on the other hand, results may have different origin. In P. cartilagineum almost no treatment induced effects could he found and in G. corneum treatment affects where dominated by effects of UVR.

Overall, a mitigating effect of enriched CO₂ concentration duringacclimation to UVR could be found in every species, despite of P.cartilagineum, what seems to be correlated to the thickness of the thalli. Hence, further investigations especially on the interactive effects of UVR and CO₂ in correlation to species morphology are necessary, to understand in which extend future driven increases of CO₂ in the atmosphere might favour some species in their acclimation ability to enhanced irradiation and increased UVR, making the survival of more shade adapted species in higher irradiated places possible.