Bachelor programme Environmental Sciences, 78 pages (first reviewer)

The aim of this bachelor thesis was to investigate possible causal relationships between anthropogenic and natural events, mainly in the last eight years, and fluctuations in the maintenance dredged material in the tidally influenced area of Emden harbour. The main focus here was on the fluctuating quantities and the increased proportion of sand in the dredged material in recent years. Based on the investigation of the interdependencies, an attempt was made to formulate hypotheses that could possibly explain the fluctuations in maintenance dredging in Emden harbour.

In order to investigate the research question as holistically as possible, two research methods were chosen. On the one hand, a data analysis was carried out. For this purpose, the previously defined events were compared with data on the quantities of maintenance dredging in the tidally influenced area of Emden harbour. In addition, data was consulted that provided information on the densities, shear forces and oxygen content. On the other hand, expert interviews were conducted in which reference was made to almost the same events.

It was found that natural events such as storm surges and extreme weather events in particular had an effect on the tidally influenced area of Emden harbour. In particular, the increased oxygen content in the water column caused by storm surges may be the reason for a reduced amount of dredging. In contrast, extreme weather events may result in higher dredging activity due to the consequences of a higher headwater discharge, among other things.

Anthropogenic events usually only resulted in a temporary change in the quantity or composition of the dredged material. During the construction of the Ems barrage, the dolphin berth and the deepening of the Ems estuary, there was a temporary increase in dredging activity and sand content, mostly in specific areas. However, ship transfers by Meyer Werft and the Sandmotor, a coastal protection project in the Netherlands, had no impact.

Bachelor's degree programme in Environmental Sciences, 53 pages (first and second assessor)

Hooksiel is a small village in the municipality of Wangerland in Lower Saxony (North-West Germany). It reflects the vegetation of the rural, but touristically influenced places on the North Sea coast. Due to climate change, the native vegetation is getting more and more influenced by the establishment of neophytes. On the East Friesian Islands, the distribution of neophytes has already been observed and investigated several times. To be able to effectively record the adjacent natural area of the mainland coast, a different method of surveying the neophytes is required than is used on the islands.

The aim of this work is to test a method for mapping the neophytes of the mainland coast. Therefore, two methods for Vegetation assessment are presented and applied in the study area Hooksiel. In the first method, random points are set in the study area to record the neophytes prior to the field survey. To be able to evaluate whether method l reflects the distribution of neophytes in the study area, method 2 is applied during the field survey. In the second method, points are selected preferentially during the field survey. The results of both methods are then analysed and compared.

The comparison of the methods suggests that the Vegetation assessment by random points with method l, represents a real distribution pattern of neophytes for rural areas. The results of method l represent the most common neophytes and their distribution patterns in the study area. The method can be transferred to other study areas after the points of criticism have been considered. For the study area it can be stated that up to this point the number of neophytes is still very small compared to the islands and urban areas. However, an increase in the number of neophytes in rural areas due to climate change is expected.

Master's programme Marine Environmental Sciences, 73 pages (first reviewer)

The Pacific oyster Crassostrea gigas (Thunberg, 1973) is a highly resilient, adaptable and comparatively undemanding oyster species, that originates from Japan, but has -accidentally and purposely - been introduced to many parts of the world. Nowadays, it is among the most globalised marine invertebrate species and the most widely cultivated oyster species for human consumption. Oyster reefs provide an abundance of ecosystem services and are commonly used as a natural coastal protection measure due to their ability to attenuate hydrodynamic energy.

In the southwest of the Netherlands, an estuarine area that encompasses different lakes, a bay and an estuary, is located. Here, the river Scheldt meets the North Sea in the Western Scheldt estuary. In this estuary, only very few natural oyster reefs exist, which is attributed to its high turbidity and low salinity.

Contrary to expectations, dense aggregates of C. gigas have recently been found in several salt marshes in the upper intertidal of the Western Scheldt, but not on the surrounding mudflats. This discovery is not only unexpected with respect to turbidity and salinity, but also inundation frequency. Previously, C. gigas was assumed to only establish in the lower intertidal and shallow subtidal.

This study aims at investigating what mechanisms enable C. gigas to establish inside the salt marshes which do not seem to be provided on the bare mudflats. As a first step, their distribution pattern was investigated. Based on the findings, the following hypotheses were suggested and investigated by means of various experiments and measurements: (i) salt marshes promote diatom growth, (ii) salt marshes decrease turbidity which improves filter-feeding efficiency, (iii) salt marshes provide stable settlement substrates.

Whilst the first hypothesis remains open to investigation, the measurements and experiments conducted for the latter two have delivered conclusive results. It can be assumed that salt marshes decrease turbidity and provide stable settlement substrates for oyster spat by attenuating hydrodynamic forces. Hence, they provide an environment in which oyster spat can settle and grow undisturbed and is also able to filter-feed efficiently in all stages of life.

With a view to the future, there is potential to mimic the facilitative mechanisms provided by the salt marsh with three-dimensional artificial structures in order to establish oyster reefs for coastal protection in areas where they have not established naturally due to environmental constraints. In the Netherlands, a country which is heavily impacted by sea level rise and coastal erosion, these approaches can serve as a promising addition to previous coastal protection measures.

Bachelor's degree programme in Environmental Sciences, 46 pages (first reviewer)

Mangroves inhabit the intertidal zones of tropical and subtropical regions (Saint-Paul et al., 2017). Adaptations such as anchored aerial roots (Krause, 2011) and salt excretion enable them to live under saline and dynamic conditions (Gilbert et al., 2002). Besides providing a habitat for flora and fauna (Giri et al. 2011), they supply locals with food and goods (Saint-Paul et al., 2008). Due to their complex and stable root systems, mangrove forests act as a natural coastal protection (Losada et al., 2020). However, since 1980 more than 35% of the mangrove areas from back than have been destroyed, mostly through anthropogenic use of the areas (Valiela et al., 2001).

The following literature research highlights protection measures and management approaches for the conservation of mangrove forests in South- and Southeast Asia and Central- and South America. In the last decades the number of agreements, initiatives and projects dealing with the conservation and protection of mangrove areas has increased (Friess et al., 2020). The management system "Community Based Mangrove Management", in which the local community is involved in the management and maintenance of the mangrove forests (Sudtongkong et al., 2008), as well as the reforestation of the forests through "Ecological Mangrove Restoration", show success in the conservation, restoration and sustainable use of the forests since the 1990s (Brown et al. 2014). They are also promising methods for the future, which can and must be adapted worldwide in order to preserve the important mangrove forest ecosystem for future generations.

Master's programme Marine Environmental Sciences, 45 pages (first reviewer)

The sandy beach is a nutrient-poor habitat and strongly dependent on allochthonous inputs. The sandy beach is a hotspot for organic matter, which is colonised by a variety of microorganisms. This study investigates the spatial and temporal variability of the occurrence and composition of mudflats on the East Frisian island of Wangerooge at two selected beach sections.

For this purpose, the total dry weight, as well as the dry weight according to components of the daily deposits and the deposits from the winter were determined on a total of 34 days in the months of March, April and September to December 2019. With regard to the amount of scum, the dependence on water level and wind speed was also a sub-aspect of the analysis. In addition, the location of the deposits and the beach profiles were documented using GPS devices. The extent to which the deposits contribute to the nutrient input to the beaches was analysed by examining the beach sediments from areas with and without deposits. To this end, the potassium, phosphorus, ammonium and nitrate content of the sediment was determined on one day in each of the months of September to December 2019.

The main factors influencing the composition, location and quantity of sediment on Wangerooge are the weather conditions and the water level. The winter mudflats provide a large input of biomass. In the winter months, the mudflats consist primarily of terrestrial material, whereas algal material dominates the mudflat deposits in the summer months. The investigation has shown that the flushing fringes contribute to a statistically significant input of potassium and that increased amounts of ammonium and phosphorus can also be detected in areas with flushing fringe deposits. Nitrate, on the other hand, is not detectable in any sediment sample.

Accordingly, the mudflats of the East Frisian Islands must be protected as a habitat, food source and nutrient supplier for various organisms. Beach cleaning is one of the greatest dangers for mudflats and should be avoided or replaced by more sustainable beach cleaning concepts.

Bachelor's programme in Environmental Sciences, 33 pages (first and second reviewer)

Temme (2019) compared present and absent areas of the neophyte Campylopus introflexus as well as the distribution on the East Frisian Island Spiekeroog in Lower Saxony with the results from Dirk Hahn (2006) in between 2001 and 2002.The most important result was that the area with Campylopus introflexus only had 32% of the area between 2001 and 2003. This raises the question which effect C. introflexus has on the succession of the grey dune Vegetation and if C. introflexus an affects the soil parameters.

To study the succession of grey dunes, four categories were calculated out of the data from 2001 to 2002 and 2018: Areas where C. introflexus never occured, where it newly occurred in 2018, where it was found both in 2001 to 2002 and in 2018 and where it occurred in 2001 to 2002 but disappeared afterwards. For these categories pH-value and the carbon and nitrogen concentrations of the soil and the vegetation were examined and compared.

After a colonisation of C. introflexus there are two companions in these areas. One is the natural grass companion Violo-Corynephoretum canescentis which is almost like the companion before the C. introflexus establishment. The second companion is the Empetrum-pagan. It is typical for the north side of dunes and is different to the other companions. Also the soil parameters pH-value and carbon and nitrogen concentrations are different between the areas with Empetrum-pagan and the areas without Empetrum-pagan. The pH-value is significantly lower than before Empetrum nigrum colonisation and carbon and nitrogen concentrations are significantly higher.