Bachelor's programme in Environmental Sciences, 50 pages (first reviewer)

English version see below.

The cockle (Cerastoderma edule) is one of the most common species of macrozoobenthos in the North Sea and plays an important role in the food web. For bird species such as oystercatchers (Haematopus ostralegus) and eider ducks (Somateria moltissima) , it serves as a main food source alongside the common mussel (Mytilus edutis) . The populations of mussel-eating bird species have been declining dramatically since the beginning of the 21st century. Despite their central role in the Wadden Sea ecosystem, there is little long-term data on cockle populations in the North Sea. For this reason, the nature conservation and research organisation "Mellumrat e.V." has been conducting an annual survey in the south mudflats of the island of Mellum since 2005. In 2020, 33 sampling sites were sampled along six transects using a sampling cylinder. Due to a cockle die-off in August, samples were taken again in September.

Data on the abundance, shell length and biomass of the mussels as well as the grain size composition of the sediment were recorded and analysed. During the sampling in August, the average cockle density was 125.6 individuals/m² and the average shell length was 13.7 mm. The results show that the density and shell length of C. edute vary greatly at the different sampling sites and in the different years. In addition, skewness and sorting of the sediment contribute to the distribution of the population. It was found that C. edule occurs more frequently in coarser and well-sorted sediment.

A comparison of the data from the first and second sampling revealed that the population density had fallen sharply, while the biomass had not changed. In order to be able to record these and other population changes and link them to changes in the environment, the annual survey of mussels in Mellum's south mudflats should be continued.

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The cockle(Cerastoderma edule) is one of the most common species of macrozoobenthos in the North Sea and has an important role in the food web. For bird species such as oystercatchers(Haematopus ostralegus) and eider ducks(Somateria mollissima), it serves as a main food source alongside the blue mussel(Mytilus edulis). Populations of shell-eating bird species have been declining rapidly since the beginning of the 21st century. Despite their central role in the Wadden Sea ecosystem, little long-term data exists on the cockle populations of the North Sea. For this reason, the nature conservation and research association "Mellumrat e.V." has been conducting an annual inventory in the southern mudflats of Mellum Island since 2005. In 2020, 33 sampling sites were sampled along six transects with the help of a piercing cylinder. Due to a cockle die-off in August, samples were taken again in September.

Data on abundance, shell length and biomass of the mussels as well as the grain size composition of the sediment were recorded and evaluated. During the August sampling, the mean cockle density was 125.6 individuals/m² and the mean shell length 13.7 mm. The results show that the density and shell length of C. edule varies greatly at the different sampling sites and in the different years. In addition, skewness and sorting of the sediment contribute to the distribution of the population. C. edule was found to be more abundant in coarser and well-sorted sediment.

The comparison of the data of the first and second sampling showed that the population density had strongly decreased, while the biomass had not changed. In order to be able to record such and other population changes and to correlate them with changes in the environment, the annual inventory of mussels in the south mudflats of Mellum should continue to be carried out.

Master's programme in Landscape Ecology, 124 pages (first and second reviewer)

As a key factor in invasion phenomena, humans have contributed significantly to the spread of non-native plant species through the intensification of global trade relations, the development of increasingly effective transport links, the growing interest in new crop and ornamental plants, and the abandonment of traditional agriculture (cf. böckbr et al. 1998). In a very short time, geographical barriers could be removed that would not be overcome naturally by neobiota, or only very slowly. Effects triggered by humans should therefore be investigated more closely in order to deal more consciously with the invasion processes triggered, particularly in view of the fact that changes in plant occurrence will occur as a result of climate change effects.

To this end, this study focuses on the urban centre of biodiversity: "the city" , as the urban space is the hub of human trade relations and thus the gateway and springboard for non-native species worldwide (cf. kowarik 2010). Wilhelmshaven as a coastal town on the Jade Bay and as a transshipment centre through the deep-water container port Jade-Weser-Port is a suitable place to take a closer look at the situation of neophyte distribution in the coastal area on the mainland. With the aim of obtaining a suitable representation of the situation regarding the occurrence and distribution of neophytes in urban areas, the Wilhelmshaven study area was investigated in various utilisation areas using a mapping method of our own choice. For this purpose, the questions of which biotope types and thus utilisation areas are affected by neophytes, which species are involved and which species are most frequently found as invasive species were addressed.

The results show that the neophyte species occurring in the individual utilisation areas investigated are not randomly distributed throughout the urban area, but are linked to specific site conditions and to specific locations in the various land use categories. The complex mechanisms of the distribution and spread of neophytes in the study area can only be explained in part in this study, as the complexity of invasion processes means that it is only possible to contribute to an understanding of the mechanisms of action. Urban areas are characterised by a high degree of dynamism, which will continue to increase in the future, meaning that the diversity of species in a city is never stable and should continue to be monitored by research studies.

Master's programme Marine Environmental Sciences, 36 pages (first reviewer)

German version see below.

The microphytoplankton is at the bottom of the marine food web and thus, essential for the zoobenthos in the Wadden Sea. The macrozoobenthos, especially Cerastoderma edule has been studied for several years at Mellum. Mellum is an uninhabited island in the German Wadden Sea, located in the proximity of the Jade Bay. The cockle population at Mellum underlies seasonal and annual changes, that are studied at six transects in the southera tidal flat (Carla Faber 2015). In order to understand these fluctuations, it is important to investigate the benthic diatom community. The purpose of this study is, to examine the benthic diatom community in the southera tidal flat of Mellum and its dependencies on habitat characteristics, cockle population, contribution to biopoductivity and reverse, the effect of cockles on these. For this, diatom, grain size and chlorophyll a samples were taken from 22 sites of the transect from 10.10. - 16.10.2020. The cockle samples were taken from 11.8. - 27.8.2020 by Maike Haan (unpublished). They were analysed for differences among the studied transects, correlation and redundancy analysis.

As the studied region is a sandy intertidal flat, it is dominated by epipsammic diatoms, that live attached to sand grains. The most abundant species were Achnanthes spec., Navicitla perminuta, Opephora spec. and Amphora spec. Epipelic diatonis were mostly more abundant at sites with higher silt proportions, congruent with higher bioproductivity and species richness at these sites. The cockle density was highest at 750- and 1000- metre distance to the high tide.

The grain size influenced the diatom population and diversity, as reported in earlier studies. Grain size therefor had an indirect effect on chlorophyll a production. A positive relation between low chlorophyll a proportions at sites with high abundance of small diatoms like Achnanthes spec. and Navicula perminuta underpins the hypothesis, that bioproductivity is influenced by the cell size of diatoms. No evidence for a dependency of cockles on benthic photosynthesis, benthic diatom diversity and -population at Mellum could be found.

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In the Wadden Sea, the basis of the food web is formed by microphytoplankton. It is therefore essential for all living organisms in the Wadden Sea at higher trophic levels, such as the zoobenthos. Zoobenthos, in particular Cerastoderma edule, has been studied in the Wadden Sea off the island of Mellum for many years. Mellum is an uninhabited bird sanctuary island located in the Jade Bay. Every year, 6 transects are used to record the cockle population there. This is subject to seasonal and annual fluctuations (Carla Faber 2015) and Maike Haan (unpublished). In order to understand these fluctuations, it is important to analyse the population of microphytobenthos, especially diatoms, on site. The aim of this study is to investigate the link between diatoms, habitat characteristics (sediment), bioproductivity and the cockle population off Mellum.

Therefore, sediment, chlorophyll and diatom samples were taken from 22 sites in the transects for the study from 10.10. - 16.10.2020. The mussel samples were taken by Maike Haan from previous sampling from 11.8. - 27.8.2020. The data were then analysed for differences along the transects and correlations with each other using a redundancy analysis.

The southern mudflats off Mellum consist largely of fine sand and medium sand and are therefore dominated by episammic diatoms. The most common species were Achnanthes spec., Navicula perminuta, Opephora spec. and Amphora spec. Epipelic diatoms were mostly found at sampling sites with a higher silt content, which was also associated with a higher number of species and a higher chlorophyll a content. Mussel density was highest at sampling sites 750 and 1000 metres from the high tide line on the transect.

It was found that grain size is a significant factor influencing the diatom population and diversity, which is also consistent with previous studies. This means that grain size also has an indirect influence on bioproductivity. A positive correlation between small diatom species and low chlorophyll a production supports the hypothesis that bioproductivity is influenced by the size of the diatoms. An influence of benthic chlorophyll a production, diatom diversity and population on cockle density off Mellum could not be proven.

Master's programme Landscape Ecology, 31 pages (first reviewer)

The plankton communities of freshwater pond ecosystems in the high Arctic are in rapid transition due to changes associated with global warming and resulting species shifts. Warming could increase primary productivity by accelerating the biochemical and metabolic processes. On Svalbard the average annual temperature has increased more than 2°C over the last 35 years. Among other factors, rising temperatures are leading to an increase in waterfowl populations enriching the high Arctic freshwater ponds with nutrients. The dominant breeding geese population (Branta leucopsis) in the Kongsfjorden area has increased greatly over the last 40 years and is a dominant source of nutrient input via faeces. It was hypothesised that nutrient enrichment by barnacle goose faeces have cascading effects on phytoplankton community composition and biovolume as well as grazing pressure by zooplankton. An experiment was conducted involving a full-factorial combination of a warming treatment, nutrient enrichment and grazing by Daphnia spp. Submerged goose droppings rapidly released soluble reactive phosphorous (SRP), NO₃/NO2_and Si into the water increasing the nutrient levels. The increase in nutrients not only increased the phytoplankton biovolume and shifted the community composition to Chlorophyceae dominance but also altered the fitness of Daphnia spp. In addition, experimental warming shifted the phytoplankton community to Chromista as dominant taxa and reduced the phytoplankton and zooplankton biovolume. Furthermore, a simultaneous increase in water temperature and nutrients reduced both phytoplankton and zooplankton biovolume and favoured the taxa Ciliata. The results demonstrate a complex interplay of temperature rise and bird-induced nutrient enrichment on pelagic high Arctic freshwater plankton communities and their trophic interactions.

Bachelor's degree programme in Environmental Sciences, 54 pages (first reviewer)

Climate change caused by the increase in greenhouse gases (GHG) is intensifying research into the avoidance of emissions of climate-damaging gases. In order to achieve the climate goals of the Paris Agreement, compensation must take place in places where GHG emissions cannot be avoided. This study arose from the Wesermarsch district's land agency's desire for a regional and flexible instrument for financing measures to offset GHG emissions. Based on this, this bachelor's thesis examines whether the land agency can offer CO₂ compensation by means of land valorisation. A literature review is used to identify the compensation measures that are suitable for the area under investigation and which certificates can be awarded according to the political framework conditions. Furthermore, a quantitative survey was conducted with potential customers in order to establish a connection between existing customer interest and the implementation of the offer. The literature research showed that the area agency can currently issue C0₂ certificates without official quality standards such as Verified Carbon Standard (VCS) or Gold Standard. These admissions cannot be counted towards the EU Emissions Trading Scheme (EU ETS) or the national Emissions Trading Scheme (nETS).

The survey was answered by 15 companies and shows that interest in certificates for the voluntary carbon market is rather low on average. However, the companies with a rather high to high interest would generally want to offset the entire C0₂ footprint of their company. In relation to the study area, peatland renaturation would also be the most effective compensation measure due to the high occurrence of degraded peatland soils with a high GHG reduction potential of 10.67 tonnes of C0' equivalents per year (t C02 eq./a) in the Wesermarsch. With a possible renaturation area of 5-10 hectares (ha) per year, the land agency could offset 5,000-10,000 tonnes of C0₂-eq. for a management period of 100 years. At a price of €5-7 per m², a C0₂ certificate for one tonne of C0₂ would cost between €50.00 and €70.00.

The issue of CO₂ certificates for the voluntary carbon market is recommended as an instrument for financing the compensation measures. In order to satisfy the interests of customers, we recommend CO₂ offsetting by rewetting peatlands. However, the generation of further climate protection projects such as the acquisition of further moorland areas, reforestation with native deciduous forests and the rewetting of salt marshes are also necessary.

Bachelor programme Environmental Sciences, 32 pages (first reviewer)

German version see below.

Climate change has been a topic of global concern for a good number of decades. It has prompted large amounts of research and monitoring across the globe to study its causes and effects and make projections for the future. This thesis's objective was to identify and summarise the effects of climate change and permafrost on freshwater bodies in Svalbard, an archipelago in the high Arctic. For the research process, existing literature was reviewed and used as a basis for this thesis. Rising water temperatures, changing water tables, more light availability, and a higher nutrient input were found to be the main issues facing Svalbard's freshwater bodies, as an effect of climate change and permafrost thaw. The consequences of this will be reflected in a change in freshwater biota and the growing, shrinking, or desiccation of lakes and ponds. Continued monitoring of Svalbard's freshwater bodies is urgently necessary.

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Climate change has been a recognised global problem for several decades. It is already being researched and monitored in many ways in order to understand its causes and consequences and to make predictions for the future. The aim of this work was to identify and summarise the effects of climate change and permafrost on the standing waters of Svalbard, an archipelago in the Arctic. The research was based on previously published literature, which was used to write this thesis. Rising water temperatures, changing water levels, increased light availability and increased nutrient input were identified as the main changes. These will affect the standing waters of Svalbard as a result of climate change and thawing permafrost. The effects of this will be seen in a change in aquatic biota, as well as the growth, shrinking or even drying up of lakes and ponds. Continued monitoring of Svalbard's standing waters is urgently needed.

Bachelor's programme in Environmental Sciences, 66 pages (first and second reviewer)

In this study the population of neophytes in the coastal location of Carolinensiel is examined. The aim is to analyze the effect of different types of human utilization, as well as to compare the population of neophytes in Carolinensiel to the population on the East Frisian Islands and discuss possible dispersion from coastal mainland to the islands.

To accomplish this, the results are compared to earlier studies about neophytes in the village Hooksiel (Kröger, 2020), on the highly touristic island Wangerooge (Reiff, 2019) and the uninhabited island Mellum (Wißmann, 2019), which are all located close to the study area. Not the whole study area, but sections of 100-metre length on public streets are examined. In total 157 sections are tested, half of which is selected randomly while the other half is selected by personal preference. Results show 43 different species of neophytes of which eight have invasive potential.

The highest number of different neophytic species appears in residential zones, while touristic and traffic zones show the lowest number. Areas that are used as forest and parks provide only slightly more neophytic species than areas that are used for tourism and traffic or for agriculture. The high number of neophytes in residential zones can most likely be explained by the variety of suitable habitats and frequent planting of neophytes by inhabitants.

In general, human planting plays a major role in neophyte appearance in the study area, as the origin of most of the neophytes with invasive potential probably lies in previous planting. The comparison of the four examined areas indicates few similarities between the sites. Only the four species Medicago sativa agg., Oenothera spp. Rosa rugosa and Senecio inaequidens are present in every location. The closest similarities, however, can be seen between the sites Carolinensiel, Hooksiel and Wangerooge, while Mellum clearly differs. The reason for this difference can mainly be explained by the absence of four species, which are all present in the other sites.

A possible explanation for that might be the fact that these species are dependent on humans either for long distance dispersal or for human-made habitats. Therefore, the extremely low presence of humans on Mellum might be the main reason for the neophytes' absence. Wangerooge on the other hand, shows a big variety of neophytes. Thus, the natural barrier of the island does not seem to prevent the dispersion of neophytes. Much more than this barrier, the intensity and modality of human utilisation might be the limiting factor for the appearance of many neophytes.

Bachelor's degree programme in Environmental Sciences, 37 pages (first and second reviewer)

Senecio inaequidens DC. is a neophyte native to South Africa that has been found in Europe since 1889. The seeds of S. inaequidens spread anemochorously, which is why the long-distance dispersal of this species is particularly promoted by air turbulence along roads, motorways and railway tracks. Since 1979, S. inaequidens has also been recorded in the coastal dunes of the Lower Saxony Wadden Sea National Park. Schmidt (2019) recorded a particularly high number of occurrences on the Spiekerooger Ostplate, which raised the question of whether the seeds of S. inaequidens hydrochor can be dispersed in the Lower Saxon Wadden Sea National Park.

To test the influence of transport in seawater on the germination rate of S. inaequidens seeds, seeds were placed in salt water for one, two and four weeks and sown on cotton pads. One group of seeds was not subjected to such pre-treatment to serve as a control. Since the seeds can be washed up in the soil after transport to different biotopes with different conductivity (salt content), the cotton pads on which the seeds were sown were doused with water of varying salinity. The number of seeds that germinated was documented from 30 July 2020 up to and including 1 September 2020. The results show that the seeds of S. inaequidens are still able to germinate after one week in salt water, although the germination rate is reduced by the effect of the salt water compared to the control. If the dwell time exceeded one week, hardly any seeds germinated. The highest germination rates were measured at low conductivities. Up to a conductivity of 24000 µS/ cm in the settlement substrate (cotton pad), the seeds of the control and the one-week pre-treatment were able to germinate.

Based on drifter data from wood drifters, it is assumed that the majority of the seeds landed in the North Sea can be washed to a new location within a week. However, they probably land mainly in areas where the conductivity in the soil is too high for germination, such as on mudflats or on the beach. However, it is possible for seeds to be washed up in unsuitable areas, dry and be transported further by the wind. Despite this, hydrochory is not considered as a possible transport route for S. inaequidens seeds in the Lower Saxon Wadden Sea National Park, as the quantity of successfully transported seeds is too small for this.