Hydromorphologic survey and assessment of the lakeshore of Lake Scharmützelsee as a prerequisite for the development of a lakeshore utilization strategy

Bachelorarbeit von Ranjin Fernando

Abstract:

Lakeshores are ecotones between aquatic and terrestrial habitats with a high economic and socio-economic significance. For many years, lake conservation focused on biological and chemical conditions and while improvements on these fields have been achieved, the anthropogenic pressures on European lakeshores have rather increased in recent years. Against this background, the development of utilization and protection strategies for lakeshores is urgently needed. A precondition for this is a standardized survey and assessment of the hydromorphological status which is also required by the European Water Framework Directive under certain circumstances. For this thesis, the lakeshore of Lake Scharmützelsee, the largest lake in the German state of Brandenburg, was classified according to the GIS-based Hydromorphology Lake (HML) protocol of Ostendorp (2008). Since the HML protocol was at the time still in a testing phase, methodical modifications were applied and recommendations for an improvement of the protocol are given. Deviating from the HML protocol, the eulittoral zone was delineated with a constant width of five meters and the sublittoral zone according to the potential maximum water depth where the available light permits the growth of submerged macrophytes. A detailed on-site mapping and a separate assessment of linear and planar objects in the eulittoral zone enhanced the quality of the data further. For Lake Scharmützelsee, the assessment showed an expected increase in anthropogenic structural modifications from sublittoral (impact = 1.3) to eulittoral (impact = 1.7) to epilittoral (2.5). A correlation analysis between the impacts in different zones and the mapped objects was carried out and showed inter alia that the main reasons for structural deficits in the eulittoral zone are shore stabilizations and that in the presence of large piers and marinas a reinforced shore is more likely than in the presence of small piers and marinas. Further analysis showed that small marinas and piers can impair approximately 25% of the emergent reed belt area. The results qualify to designate conservation zones for continuous natural or near-natural lakeshore sections and to identify sections with a potential for restoration. The results of this thesis were already used by local authorities to design a blueprint for a lakeshore utilization strategy.

Table of Contents:

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Chapter 2.8, Mapping and classification of objects:

Objects in the sublittoral, eulittoral and epilittoral were mapped by analyzing the DOP40 images as well as the other primary data provided. Additionally shore stabilizations in the eulittoral were mapped based on the data of the on-site mapping. Deviant from Ostendorp et al., linear and planar objects in the eulittoral zone were mapped and assessed separately.

The mapping of areas was realized by creating polygons that enclosed objects seen on the DOP40 images. For the mapping of shore stabilizations as linear objects, the shoreline was divided into sections with a length corresponding to the shore stabilizations. Following the creation of polygons and polylines, they were classified as one of the objects defined in the catalog of objects by ascription of the corresponding ID.

An example how objects in the sublittoral and epilittoral were mapped and classified is shown in Figure 17 and Figure 18. The proceeding regarding the classification of linear and planar objects in the eulittoral is illustrated by Figure 19 and Figure 20.

2.8.1, Mapping of objects:

Sublittoral zone:

The polylines displaying the piers and marinas served as an orientation of the objects’ location, and the polylines of the lakeward boarder of the reed belt were used to generate polygons. Additionally, the generated map of submerged macrophytes was used to identify areas with submersed macrophytes and areas without. In accordance to recommendations by Ostendorp (pers. Communication) not the actual area of marinas and piers was delineated but rather a broader area that also included potential areas of landing boats.

Eulittoral zone (planar mapping):

Since the eulittoral zone was extremely narrow, an approach not defined by Ostendorp et al. was applied. First, the eulittoral zone was divided into two halves, a lakeward part and a landward part. Secondly, each half was cut into subparts so that polygons enclosing the objects were created. Hereby, in the lakeward part the same objects that occurred in the sublittoral zone were mapped, more precisely if an object was mapped in the sublittoral zone it was also mapped in the eulittoral zone.

Eulittoral zone (linear mapping):

The trackpoints set in Fugawi Global Navigator during the on-site mapping were exported to an ESRI shapefile and imported to the ArcMap project. Based on the trackpoints and the notes on the aerial images, the beginnings and endings of shoreline stabilizations were identified. Since many trackpoints that were recorded form the boat were not directly located at the shoreline but parallel to it, they had to be projected to the shoreline by dropping perpendiculars. Next, each section of the shoreline-polyline was cut into subsections so that for each mapped object in each segment a polyline was created. Additionally to the recorded shore stabilizations of the on-site mapping at each marina and pier seen on the DOP40 images a shore stabilization of approximately 2.5 m was mapped.

Epilittoral zone:

The biotope and habitat map was used as orientation for identifying objects in the Epilittoral. Additionally, maps available at Google Maps were used to identify roads and in some cases to get a colored view of objects. After objects were identified, polygons enclosing them were created.