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

Bachelorarbeit 2010 91 Seiten

Ingenieurwissenschaften - Geotechnik

Leseprobe

Table of Contents

List of Figures

List of Tables

1. Introduction
1.1 Importance and deterioration of lakeshores
1.2 Lakeshores and hydromorphology in the WFD
1.3 Hydromorphology Lake (HML) protocol
1.4 Motives and objectives
1.4.1 Motives
1.4.2 Objectives
1.5 Structure of thesis

2. Methods
2.1 Characterization of Lake Scharmützelsee and main anthropogenic pressures
2.2 Acquisition of primary data
2.3 Setting up of GIS-project
2.4 Delineation of subzones and segments
2.4.1 Generalization of shoreline
2.4.2 Delineation of subzones
2.4.3 Modifications of subzones and exclusion of islands
2.4.4 Delineation of segments
2.5 On-site mapping of shoreline stabilizations
2.5.1 Prearrangements and execution
2.5.2 Documentation by photographs
2.6 Digitalization of a submerged macrophytes map
2.7 Adaptation of catalog of objects
2.8 Mapping and classification of objects
2.8.1 Mapping of objects
2.8.2 Classification of objects
2.9 Computation of impacts
2.9.1 Formulas for the calculation
2.9.2 Implementation of a database for the calculation of impacts

3. Results
3.1 Zoning, segmentation and numbering
3.2 Mapped objects and derived impacts
3.2.1 Sublittoral zone
3.2.2 Eulittoral zone
3.2.3 Epilittoral zone
3.3 Outline of classification
3.3.1 Lakeshore section 1
3.3.2 Lakeshore section 2
3.3.3 Lakeshore section 3
3.3.4 Lakeshore section 4
3.3.5 Lakeshore section 5
3.3.6 Lakeshore section 6
3.3.7 Lakeshore section 7
3.3.8 Outline of the distribution of selected objects
3.4 Graphical illustration of classification
3.5 Statistical analysis
3.5.1 Overview of the classification by subzone
3.5.2 Correlation between impacts in subzones and presence of objects
3.6 Further analysis
3.6.1 Estimation of reed bed area impeded by small piers and marinas
3.6.2 Occurrence of objects depending on reed bed area

4. Discussion and conclusion
4.1 Discussion of applied methods
4.1.1 Limitations
4.1.2 Methodical modifications of the HML-protocol
4.1.3 Suggestions for modifications and improvements of the HML-protocol
4.2 Discussion of results
4.2.1 Main hydromorphological pressures
4.2.2 Lakeshore hydromorphological status
4.3.3 Implications for lakeshore conservation and utilization concepts

5. References

Appendix I - Catalog of objects

Appendix II - Object profiles

List of Figures

Figure 1: Scheme of status classification according to the WFD

Figure 2: Main process steps of HML protocol

Figure 3: Depth contour lines of Lake Scharmützelsee

Figure 4: Non-generalized shoreline

Figure 5: Generalized shoreline

Figure 6: Delineation of sublittoral, eulittoral end epilittoral

Figure 7: Zoning before the removal of islands

Figure 8: Zoning after removal of islands

Figure 9: Unmodified perpendiculars

Figure 10: Modified perpendiculars

Figure 11: Delineation of segments

Figure 12: On-site mapping of shore stabilizations from land

Figure 13: On-site mapping of shore stabilizations by boot

Figure 14: Detailed view of internet-based photo album

Figure 15: Overview of internet-based photo album

Figure 16: Detail of submersed macrophytes map

Figure 17: Mapped objects

Figure 18: Classified objects

Figure 19: Classification of objects in the eulittoral by polygons

Figure 20: Classification of shore stabilization in the eulittoral by polylines

Figure 21: Structure of database

Figure 22: Borders and numbering of segments

Figure 23: Distribution of impacts for segments in the sublittoral

Figure 24: Distribution of impacts for segments in the eulittoral zone

Figure 25: Distribution of impacts for segments in the epilittoral zone

Figure 26: Lakeshore sections of the lakeshore

Figure 27: On-site photograph of segment 26

Figure 28: View of segment 26 in GIS

Figure 29: On-site photograph of segment 32

Figure 30: View of segment 32 in GIS

Figure 31: On-site photograph of segment 62

Figure 32: View of segment 62 in GIS

Figure 33: On-site photograph of segment 70

Figure 34: View of segment 70 in GIS

Figure 35: On-site photograph of segment 81

Figure 36: View of segment 81 in GIS

Figure 37: On-site photograph of segment 100

Figure 38: View of segment 100 in GIS

Figure 39: On-site photograph of segment 3

Figure 40: View of segment 3 in GIS

Figure 41: Distribution of emergent reeds, sedges and rushes

Figure 42: Distribution of small, large and multi-user piers and marinas

Figure 43: Distribution of shore stabilizations

Figure 44: Distribution of built-up areas of rural and provincial characteristic

Figure 45: Classification of the lakeshore by segments in sublittoral, eulittoral and epilittoral zone (five degree scale)

Figure 46: Classification of the lakeshore by segments in sublittoral, eulittoral and epilittoral zone (seven degree scale)

Figure 47: Classification of the lakeshore by segments in sublittoral, eulittoral and epilittoral zone with modified widths (five degree scale)

Figure 48: Classification of sublittoral, eulittoral and epilittoral zone (five degree scale)

Figure 49: Classification of the lakeshore by segments in sublittoral, eulittoral and epilittoral zone with modified widths (seven degree scale)

Figure 50: Classification of sublittoral, eulittoral and epilittoral zone (seven degree scale)

Figure 51: Correlation between impacts in eulittoral and sublittoral

Figure 52: Correlation between impacts in epilittoral and sublittoral

Figure 53: Correlation between impacts in epilittoral and eulittoral

Figure 54: Correlation between impacts in sublittoral and area of small piers and marinas

Figure 55: Correlation between impacts in sublittoral and area of large and multi-user piers and marinas

Figure 56: Correlation between impacts in sublittoral and reed bed area

Figure 57: Correlation between impacts in sublittoral and areas free of submerged macrophytes

Figure 58: Correlation between impacts in sublittoral and areas of sublittoral-segment

Figure 59: Correlation between reed bed area and percentage of shore stabilization

Figure 60: Correlation between reed bed area and area of small piers and marinas

Figure 61: Correlation between reed bed area and area of large and multi-user piers and marinas

Figure 62: Correlation between reed bed area and impact in epilittoral

Figure 63: Correlation between impact in eulittoral and percentage of shore stabilization

Figure 64: Correlation between percentage of shore stabilization and area of small piers and marinas

Figure 65: Correlation between percentage of shore stabilization and area of large and multi-user piers and marinas

Figure 66: Correlation between percentage of shore stabilization and impact in epilittoral

Figure 67: Correlation between area of large and multi-user piers and marinas

Figure 68: Correlation between area of small piers and marinas and impact in epilittoral

Figure 69: Delineation of potential reed bed area in segment 89 and 90

Figure 70: Area of piers and marinas with increasing area of emergent reeds, sedges rushes

Figure 71: Percentage of shore stabilization with increasing area of emergent reeds, sedges and rushes

Figure 72: Classification of the lakeshore by arithmetic mean of sublittoral, eulittoral and epilittoral

Figure 73: Classification of the lakeshore by segments with arithmetic mean values of impacts in sublittoral, eulittoral and epilittoral

List of Tables

Table 1: Hydrologic and morphologic characteristics of Lake Scharmützelsee

Table 2: Primary data

Table 3: Geographic coordinate system used

Table 4: Projected coordinate system used

Table 5: Amendments to the catalog of objects

Table 6: Mapped objects in the sublittoral zone

Table 7: Overview of impacts for segments in the sublittoral zone

Table 8: Mapped linear objects in the eulittoral zone

Table 9: Mapped planar objects in the eulittoral zone

Table 10: Overview of impacts for segments in the eulittoral zone

Table 11: Mapped objects in the epilittoral zone

Table 12: Overview of impacts for segments in the epilittoral zone

Table 13: Overview of classification by subzone

Table 14: Correlation matrix for selected variables of the classification

Table 15: Difference of potential and mapped reed bed area

Table 16: Order of lakeshores sections from least to worst modified

Table 17: Catalog of objects for sublittoral zone (subzone A)

Table 18: Catalog of objects for eulittoral zone (subzone B)

Table 19: Catalog of objects for epilittoral zone (subzone C)

1. Introduction

1.1 Importance and deterioration of lakeshores

Lakeshores are ecotones between aquatic and terrestrial habitats. A generally accepted definition for lakeshores however does not exist. Ostendorp (2004) proposes to understand lakeshores as a zone that comprises the riparian zone, the shoreline and the littoral zone. Additionally Ostendorp (2004) introduces the term ‘lakeshore region’ as the landside area adjacent to the lakeshore from which direct pressures for the lakeshore arise.

Besides being a habitat with a high grade of diversity in its biocoenosis and species abundance (Naiman & Décamps, 1990; Wetzel, 2001), lakeshores are of high ecological and socio-economic significance. Important ecological functions include: (i) function as buffer for diffuse terrestrial nutrient input (Bratli et al., 1999), (ii) uptake of nutrients by biofilms in the benthic zone and by periphyton attached to submerged macrophytes or reed bed (Woodruff et al., 1999), (iii) function as maturation area for fish (Winfield, 2004), (iv) function of littoral macrophytes and epiphytes as the basis for the littoral food web (Wetzel, 2001) and (v) protection against shore erosion by vegetation on both sides of the waterline (Beeson & Doyle, 1995; Ostendorp et al., 1995). In addition, the terrestrial and aquatic compartments of the lakeshore are of high socio-economical value as they are a preferential location for human settlement, recreation, tourism, fishing and industry (Liddle & Scorgie, 1980; Ostendorp et al., 2004; Schmieder, 2004).

For many years the focus for lake conservation was based on the phenomena of eutrophication (Grüneberg et al., 2010). However, the pressures on lakeshores go beyond those of eutrophication, they are also highly sensitive to human induced hydrologic and morphologic changes (Ostendorp et al., 2004). Alterations to water levels including its natural patterns of fluctuations are very common throughout the world and might be due to the construction of dams and reservoirs for hydro-power generation, flood control and water abstraction for various purposes like irrigation (Kampa & Hansen, 2004; Nilsson et al., 2005). Frequency and amplitude of water-level-changes determine the structural variation of macrophytes in the littoral zone (Naiman & Décamps, 1990) and if unnaturally high may lead to their loss and subsequently affecting macrozoobenthos and shore-erosion (Keddy & Reznicek, 1986; Palomaki, 1994; Valdovinos et al., 2007; Aroviita & Hamalainen, 2008). Considering morphological changes, several publications exist suggesting that physical damage to aquatic ecosystems has considerable dimensions (e.g. Ostendorp et al., 2003; Kampa & Hansen, 2004). Ostendorp (2008) specifies the main structural modifications at central European lakeshores as (i) shore reinforcement structures (e.g. sheet pilings, concrete walls or rock fillings), (ii) land fillings and dredgings, (iii) transverse constructions from the shoreline into the lake (e.g. moles), (iv) soil sealing (e.g. buildings and roads) and (v) harbors, piers and marinas.

It is known that hydromorphological pressures have effects on reed beds (Ostendorp, 1989; Ostendorp, 1990), littoral macroinvertebrates (Brauns et al., 2007) and submersed macrophytes (Elias & Meyer, 2003). However knowledge regarding the relation between certain pressures on the lakeshore and their specific impacts is not profound (Ostendorp, 2004). The incomplete knowledge is jointly responsible that while improvements of water quality have been achieved in recent years, the pressures on the lakeshores have rather increased (Walz et al., 2003; Grüneberg et al., 2010). Today lakeshore development represents a mayor danger for the ecological integrity of lakeshores (Ostendorp et al., 2004; Schmieder, 2004). Hence, as a basis for future decision making processes regarding the protection and restoration, an assessment of the morphological impacts at lakeshores can be of great value.

1.2 Lakeshores and hydromorphology in the WFD

The European Water Framework Directive (WFD, 2000/60/EC) came into force on December 22nd 2000 and became thereby the legal basis for the water policy in the European Union (Chave, 2001).

The protection of lakeshores is not explicitly mentioned, however Article I (a) states that the framework “prevents further deterioration and protects and enhances the status of aquatic ecosystems and, with regard to their water needs, terrestrial ecosystems and wetlands directly depending on the aquatic ecosystems”(WFD, 2000, Article 1 a). The WFD describes hereby the lakeshore in its compartments: the sublittoral zone as aquatic ecosystem, the eulittoral zone as wetland directly depending on the aquatic ecosystems and the landside zone as terrestrial ecosystems directly depending on the aquatic ecosystems.

Part of the WFD are legally binding environmental objectives. It obligates the EU member states (i) to prevent the deterioration of the status of all surface water bodies, (ii) to achieve by 2015 for all natural surface waters a good ecological status or (iii) in the case of artificial or heavily modified surface waters a good ecological potential (WFD, 2000, Article 4 a). For the assessment of the ecological status and ecological potential are quality elements (QEs) introduced. Preferential consideration is given hereby to biological QEs. Additionally, physico-chemical and hydromorphological QEs having a supportive function for the biological elements are considered (Chave, 2001; WFD CIS, 2005).

Given below is the scheme that defines how the ecological status and ecological potential are to be classified. As seen an assessment of the hydromorphological conditions is necessary for the assignation of the high ecological status to a water body, i.e. to downgrade from the high to the good status.

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Figure 1: Scheme of status classification according to the WFD

Source: (WFD CIS, 2005)

For the classification statuses other than high the WFD requires the hydromorphological conditions to be “consistent with the achievements of the values specified (WFD, 2000, Table 1.2.2, page 51) for the biological elements”. The Common Implementation Strategy (CIS) of the WFD further concretizes in the guidance document No. 13 Overall Approach to the Classification of Ecological Status and Potential (WFD CIS, 2005) that “if the biological quality element values relevant to good, moderate, poor or bad status/potential are achieved, then by definition the condition of the hydromorphological quality elements must be consistent with that achievement and would not affect the classification of ecological status/potential” (WFD CIS, 2005, page 3). Furthermore, it concludes that “the assignment of water bodies to the good, moderate, poor or bad ecological status/ecological potential classes may be made on the basis of the monitoring results for the biological quality elements and also, in the case of the good ecological status/potential the physic-chemical quality elements“ (WFD CIS, 2005, page 3).

Hence, it can be concluded that according to the WFD an assessment of the hydromorphological conditions is mandatory when (i) the biological and physico-chemical conditions are classified as high and (ii) in accordance with Article 4 a, to prove that a high status of a water body hasn’t deteriorated.

1.3 Hydromorphology Lake (HML) protocol

The HML protocol is a GIS-based method for the identification and classification of structural pressures at lakeshores with relevancy for the WFD and nature conservation. Though the procedure does not classify the lakeshore according to the status classification of the WFD, the results can be used as a foundation to do so. It enables to visualize the presumable impacts to biotopes and biocoenosis at the lakeshore in a spatial context. The procedure relies therefore primarily on the assessment of aerial images and other available geodata (Ostendorp et al., 2008; Ostendorp et al., 2009).

The approach of the HML protocol is to investigate compartments of the lakeshore separately regarding the occurrence of predefined objects. The areas and lengths of objects together with specific impacts for each type of object are then used to derive impacts for each compartment. Figure 2 illustrates the main process steps of the HML protocol according to Ostendorp (2008):

- Preliminarily, geospatial data of the investigation area has to be acquired; most important are digital orthophotos (DOP), topographic maps, a map of the lake’s depths contour lines and land-use maps.
- Three subzones are created; (i) a subzone A (sublittoral zone) that stretches from the shoreline lakeward to the transition from deep water waves to shallow waves or the maximal depth occurrence of closed submerse macrophytes respectively, (ii) a subzone B (eulittoral zone) as the area between the high and low annual water levels and (iii) a subzone C (epilittoral zone) that includes the area that can have a direct impact on ecological conditions in the others subzones (a minimal width of 100 m is recommended).
- The three subzones are sub-divided into segments respectively of constant length (e.g. 250 m).
- If necessary the catalog of objects including the specific impacts has to be adapted to the special conditions at the lakeshore. Objects it shall include are for example vegetation cover, land-uses, marinas, shore stabilizations etc.
- Objects are identified according to the catalog of objects. In each segment, the area of objects has to be estimated. Additionally in segments of the eulittoral zone the percentage of stabilized shoreline is estimated and in the sublittoral zone the percentages of areas where water-current is affected by anthropogenic structures.
- Impacts for segments are generally computed as the sum of proportional impacts by all objects of the catalog of objects. The proportional impact by an object is thereby defined as the product of its percentage of area with the object’s specific impact. The area of affected water-current and percentage of shore stabilization are integrated to the segments’ impacts by the application of weighting factors (see Chapter 2.9.1)
- Finally, the three subzones of the lakeshore can be classified graphically and statistically based on the impacts of the segments.

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Figure 2: Main process steps of HML protocol

Source: According to Ostendorp (2008)

The three subzones of the HML protocol are based on the understanding of the lakeshore as a zone and the existence of a lakeshore region as noted in this thesis’s introduction. The general understanding of epilittoral is extended to include also the lakeshore region.

Nameable other methods for assessing the hydromorphology of lakeshores are the Lake Habitat Survey (LHS) (Rowan et al., 2006) and the procedure of the Landesamt für Umwelt, Naturschutz und Geologie Mecklenburg-Vorpommern (LUNG M-V) (Kollatsch et al., 2006). Distinctive features of the HML protocol are that it assesses the whole lakeshore by segments of constant lengths and that a preliminary definition of a reference state for the lakeshore is not required. The reference state is simply achieved if all occurring objects are natural. Additionally, mapping and classification are separate process steps which allows accessing the empirical data for purposes of modification or further analysis. The utilization of an extendable hierarchically structured catalog of objects and the independence regarding the type of lakeshore makes the HML protocol potentially applicable at many natural and artificial standing waters (Ostendorp et al., 2008).

1.4 Motives and objectives

1.4.1 Motives

This thesis can be considered as the first part of a larger investigation at the department of Freshwater Conservation to assess how morphological modifications at the lakeshore contribute to a degradation of ecological functions and affect biotopes and biocoenosis. Therefore assessments of the lakeshore-morphology of different years are planed so that the changes in morphology and the resulting changes to the biotopes can be documented. One goal is to support the establishment of guidelines and concepts for a lakeshore utilization strategy.

A current matter of controversial debate at Lake Scharmützelsee is the impact of certain land uses in respect to nature and water protection. So justifies the responsible environmental authority decisions to not extend permits for private marinas and piers with concerns over their impacts on flora and fauna. The authorities rather promote the construction of large multi-user marinas. The perception of many residents however is contrary; they argue that the small private marinas only occupy an insignificant area and pointed out to an increase of reed bed in recent years.

1.4.2 Objectives

As a prerequisite for the establishment of a lakeshore utilization strategy, the degree of hydromorphological alteration of the lakeshore of Lake Scharmützelsee is to be determined. For this purpose a classification of the lakeshore according to the HML protocol is applied including the incorporation of data from an on-site mapping. Since the HML protocol is still in a testing phase, this thesis includes an examination of the procedure and proposes adaptations. Additionally, the aforementioned problematic concerning marinas and piers is to be assessed by an analyzing the data collected by the HML protocol. The main questions to be answered by this thesis are:

- What are the main hydromorphological pressures at the lakeshore?
- Where are the most and least modified sections of the lakeshore?
- Is the occurrence of reed bed impeded by the presence of marinas and piers?

1.5 Structure of thesis

Placed in front of this thesis is a characterization of Lake Scharmützelsee regarding its ecology, morphology and hydrology. It follows a documentation of the applied methods with images and descriptions of the proceeding. The catalog of objects, which represents the basis for the classification of pressures, is to be found in Appendix I. Furthermore, profiles for the mapped objects are listed in Appendix II. The results are presented by outlining distinctive sections of the lakeshore and maps showing the distribution of impacts along the lakeshore. Subsequently, the applied methodology will be discussed before analyzing and discussing the results.

2. Methods

2.1 Characterization of Lake Scharmützelsee and main anthropogenic pressures

Lake Scharmützelsee is located approximately 50 km south-east of Berlin and is the largest lake in the state of Brandenburg (Hämmerling & Nixdorf, 2004). Figure 3 shows the lake’s topology and neighboring settlements and Table 1 summarizes the lake’s hydrologic and morphologic characteristics. Simplified the lake can be described as consisting of two basins separated by a peninsula which allows only limited water exchange (Grüneberg et al., 2007); the polymictic northern basin with shallow water-depths up to 7 m stretches from north to south and the dimictic southern basin with a north-eastern to south-western orientation and depths up to 29 m. 88 % of inflow to the lake is from groundwater (Grüneberg et al., 2007), and the water discharge is controlled by a water gate at Wendisch Rietz (Nixdorf et al., 2004).

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Figure 3: Depth contour lines of Lake Scharmützelsee

Source: Background-map taken and modified from Google Maps

Table 1: Hydrologic and morphologic characteristics of Lake Scharmützelsee

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Lake Scharmützelsee has experienced a large degree of anthropogenic pressures including discharge of sewage as well as shore development. From the end of the 1960s until 1990, increasing amounts of phosphorus mainly sewage water and to a lesser extend of agricultural origin were introduced into the lake resulting in eutrophication (Hämmerling & Nixdorf, 2004). Due to a number of measures, the trophic level has considerably improved since 1990. By 2003 the lake had recovered to its natural mesotrophic (LAWA, 1999) state (Hilt et al., 2010).

Despite the improvement of the eutrophication problem, the anthropogenic pressures on the lakeshore have steadily increased. Due to its proximity to Berlin the lake is a popular tourist attraction, there is a broad overture for activities such as shipping, sailing, water skiing, fishing, bathing, tennis as well as various accommodation possibilities, a leisure park and a large thermal-spa (Tourismusverein Scharmützelsee e.V., 2010). The department for statistics in Berlin and Brandenburg states the number of visitors with almost 90.000 for the year 2009 which is an increase of more than 5 % compared to 2008 (Amt für Statistik Berlin-Brandenburg, 2010). In 2009 the population of the communities Bad Saarow, Diensdorf-Radlow and Wendisch-Rietz totaled 6785 (Amt für Statistik Berlin-Brandenburg, 2009). Additionally, new residential areas have been created in recent years right at the lake shore where previously forest areas were located (e.g. on the peninsula Husareninsel, see www.husareninsel.com).

2.2 Acquisition of primary data

As a basis for the GIS-Project, digital orthophotos of the years 2006 and 2007 with a resolution of 40 cm (DOP40) in grayscale where purchased from the regional land surveying office. Depth contour lines of the lake derived from an assessment with an echo sounder were supplied in the form of an ESRI-shapefile. A biotope and land-use map of the state of Brandenburg was obtained from the Landesumweltamt Brandenburg in the form of an ESRI-shapefile. The shoreline, the lakeward boundary of the reed belt and occurrences of piers and marinas were mapped during a previous study project (Donath, 2009) and were also available in the form of ESRI-shapefiles. Additionally, distribution data of submerged aquatic macrophytes was assessed.

Table 2: Primary data

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2.3 Setting up of GIS-project

For setting up the GIS-model the software ArcGIS 9.3.1 with an ArcEditor License was used. The two main applications used were ArcMap for processing the geospatial data and ArcCatalog for carrying out file management tasks. The spatial data was organized in a personal geodatabase and an ArcMap-document was created which was used for the following map based operations.

Primary data No. 1-5 had an error in the specification of their projected coordinate system at the point they were handed over from the Department of Freshwater Conservation and hence had to be corrected.

The geographic coordinates (Table 3) were according to the European Terrestrial Reference System 1989 (ETRS89) and the projection (Table 4) was based on the Universal Transverse Mercator (UTM) coordinate system. Since the object area was in the UTM zone 33 (15th meridian), eight-digit longitude coordinates were to be used. The primary data however was using seven-digit longitude values which is a specific practice in Brandenburg. In order to visualize these coordinates correctly the false easting parameter had to be changed to 3.500.000 m (Gassert pers. comm.).

Table 3: Geographic coordinate system used

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Table 4: Projected coordinate system used

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2.4 Delineation of subzones and segments

As a basis for delineating the sublittoral, eulittoral and epilittoral as well as the segments served the polyline that represented the shoreline. By the application of buffers the subzones were created and for the segmentation into segments perpendiculars to the shoreline were dropped. The area enclosed by a subzone and the perpendiculars was then used to create a polygon for each segment in a subzone.

2.4.1 Generalization of shoreline

As the shoreline inherited a large degree of irregularities it had to be generalized first so that perpendiculars would not intersect. After several values have been tested, it was decided to apply a smoothing tolerance of 50 m for the generalization because with lower values relatively many perpendiculars would have intersected and therefore been subject to adjustment.

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Figure 4: Non-generalized shoreline

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Figure 5: Generalized shoreline

The generalized shoreline was used for all further process steps which however resulted in imprecision since the generalized shoreline was less accurate. At two locations (14.057753° E, 52.290180° N and 14.042925° E, 52.284453° N) the generalized shoreline was considerably diverging from the shoreline seen on the orthophotos. This deflection was corrected by replacing the generalized shoreline by the non-generalized shoreline at those locations.

2.4.2 Delineation of subzones

For the sublittoral, eulittoral and epilittoral each a polygon was to be digitalized that described the subzone. First, polylines depicting the boundaries of the subzones were created from which in a later step the polygons subzones were derived.

Sublittoral

For the northern lake basin a water depth of four meters and for the southern basin a depth of six meters was used to delimit the subzone. The water depths used represented the potential maximum depth of submerged macrophytes as calculated by Hilt et al. (2010). Basis for the calculations was the theoretical maximum colonization depth of submerged macrophytes at a light supply of 3 Em-2d-1 according to Sand-Jensen and Borum (1991).

Eulittoral

Due to the controlled discharge of water, seasonal water level changes are below 30 cm (Grüneberg, pers. comm.), so that the identification of the eulittoral zone according to Ostendorp (2008) was not possible. Therefore a constant buffer of 2.5 m on both sides of the shoreline was applied so that a five m wide subzone was created.

Epilittoral

Since the definition of this subzone (see Chapter 1.3) makes a clear distinction very difficult a constant value of 100 m, as suggested in the HML protocol, was chosen as range for the lakeshore region.

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Figure 6: Delineation of sublittoral, eulittoral end epilittoral

2.4.3 Modifications of subzones and exclusion of islands

It was agreed upon to exclude the two islands Großer Werl and Kleiner Werl from the survey and classification. For this reason, the sublittoral zone that included the Großer Werl was modified so that it did not include the island; the other subzones depicting the islands were then deleted.

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Figure 7: Zoning before the removal of islands

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Figure 8: Zoning after removal of islands

2.4.4 Delineation of segments

To sub-classify the subzones into segments, the shoreline was divided into sections and at the endpoints of these sections perpendiculars were dropped. The perpendiculars were then used to create the segments in all three subzones.

Sectioning the shoreline

The polyline representing the shoreline was to be divided into sections of 250 m length. Since the polyline had a length of 27.513 km and was not an even-numbered multiple of 250 m, 108 sections of 250 m were created while at one of the locations (14.057753° E, 52.290180° N) two longer sections were created, namely of 256.83 m length.

Dropping perpendiculars

Perpendiculars were dropped at the end of each section of the shoreline. As the perpendiculars were needed for creating segments in all three subzones they were extended so that they intersected with the borders of all subzones. In a second step all perpendiculars that did not serve to create meaningful segments were modified in a way that rectangular-like areas where enclosed with the boundary lines of the subzones.

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Figure 9: Unmodified perpendiculars

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Figure 10: Modified perpendiculars

Creating segments

Using the geometry described by the perpendiculars and the three subzones, the tool construct features served to create the segments in the form of polygons (Figure 11). To enable a unique identification of the segments, an ID-number was allocated to each polygon in its attribute table.

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Figure 11: Delineation of segments

2.5 On-site mapping of shoreline stabilizations

Position and type of shoreline stabilization were recorded for Lake Scharmützelsee on May 5th and 6th 2010. The motive for the on-site investigation was to incorporate a mapping of shore stabilization into the HML-protocol, thus it represented a deviation from Ostendorp (2008). The applied approach was not to classify according to the catalog of objects but to register as much information as possible and leave the classification to a later point in time.

2.5.1 Prearrangements and execution

Primarily 35 DIN A4 printouts of maps were created using ArcMap. The maps displayed the DOP40 images, the perpendiculars that separated the segments and for each segments its corresponding segment-ID. Each map covered three to four segments, i.e. an area of 750-1000 m along the shoreline.

Secondly, an outdoor-laptop equipped with a GPS receiver was prepared for the mapping by importing the DOP40 images to the software Fugawi Global Navigator 4.10. Important functions of the software were to display the current position on the DOP40 images and to set trackpoints that contained the actual GPS coordinates.

Mainly by boat and partly by foot, the whole shoreline was accessed to register shore stabilizations. Besides mapping the objects by marking their location and type on the physical maps, also the software’s function to set trackpoints was used. In this way the coordinates at the beginnings and endings of shore stabilizations were recorded.

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Figure 12: On-site mapping of shore stabilizations from land

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Figure 13: On-site mapping of shore stabilizations by boot

Note: the outdoor-laptop with the GPS sensor is seen on the boat

2.5.2 Documentation by photographs

During the on-site mapping the state of shoreline development was documented by photographs. A total of 305 digital photographs covering the whole lake were taken while smaller distances between photographs at inhomogeneous regions and larger distances at homogenous regions were chosen. The camera used was equipped with a build-in GPS sensor which allowed recording for each image the location where it was taken.

A complete documentation of the shoreline by photographs was created as an internet-based photo album (see Figure 14 and Figure 15) which is available at following internet page:

http://picasaweb.google.com/lh/albumMap?uname=113880726831129796658&aid=5452666982926378001&authkey=Gv1sRgCKbVsPG4m479swE#map

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Figure 14: Detailed view of internet-based photo album

Source: Google (Google, 2010b), photos by Grüneberg (2010)

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Figure 15: Overview of internet-based photo album

Note: Each photo can be viewed in detail by clicking on it

Source: Google (Google, 2010b), photos by Grüneberg (2010)

2.6 Digitalization of a submerged macrophytes map

Data from the mapping of submerged macrophytes was used for creating a map of submerged macrophytes. The data comprised 50 transects with qualitative estimations of the abundance of various species. Their abundance was expressed on a five degree scale (1: very rare, 2: rare, 3: common, 4: frequent, 5: abundant) in four depth zones (0-1 m, 1-2 m, 2-4 m and >4 m). As the depth contour lines used in the GIS-project contained a high error probability in depths below 2 m, it was decided to combine the depth zones 0-1 m, 1-2 m and 2-4 m into a new zone spanning from 0-4 m. At the same time the abundances-values of the depth zones were averaged. To integrate the data into the HML protocol it was desired to classify areas as containing macrophytes or being free of macrophytes. Thus, the degree scale was reduced to a two degree scale (1-2: no macrophytes, >2: macrophytes).

The transects of the macrophytes-mapping were digitalized as polygons using the geographical coordinates provided. The polygons were then defined according to the new two degree scale as macrophytes containing and macrophytes-free areas. The macrophytes map was created based on the expansions of the sublittoral zone; hence it reached from the lakeward boundary line of the eulittoral zone to the four meter depth contour line in the northern basin and to the six meter contour line in the southern basin. A detail of the final submerged macrophytes map is given below.

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Figure 16: Detail of submersed macrophytes map

Note: Areas with macrophytes (green), areas free of macrophytes (red)

2.7 Adaptation of catalog of objects

The catalog of objects was extended by 18 objects since they were considered significant for the assessment and it was desired to map the lake with more detail as required by the HML protocol. The new objects are listed below in Table 5, the complete catalog of object that was used can be found in Appendix I. Additionally, for each object was a profile created to have a basis for the mapping and classification of the objects. The profiles provide a picture with a short description of each object and are to be found in Appendix II.

Table 5: Amendments to the catalog of objects

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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. (2008), 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. (2008) 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 (Google, 2010a) 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.

2.8.2 Classification of objects

Each polygon and polyline was classified by upgrading its dataset in the attribute table with the ID of the corresponding object. In addition to the object-ID, also the segment-ID in which the object was located in was saved.

At this point, as a result of the foregone process steps[1] [2] a large number of objects were subdivided into various polygons. Therefore, a fusing of objects was undertaken on the basis of the segment-ID and object-ID. In this manner, the multitude of polygons could be reduced as all polygons in one segment representing the same object were merged into one polygon.

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Figure 17: Mapped objects

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Figure 18: Classified objects

Note: 1: Reed bed; 2: small marina; 3: submersed macrophytes; 4: large marina; 5: area free of submersed macrophytes; 6: forest; 7: built-up area of rural characteristic

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Figure 19: Classification of objects in the eulittoral by polygons

Note: 1: small marina; 2: reed bed; 3: submersed macrophytes; 4: Multi-user marina; 5: grassland with shrubs; 6: grassland

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Figure 20: Classification of shore stabilization in the eulittoral by polylines

Note: 1: small marina; 2: no shoreline stabilization; 3: sheet pilings

2.9 Computation of impacts

2.9.1 Formulas for the calculation

According to Ostendorp et al. (2008), a segment’s impact (ISSG) is generally the sum of proportional impacts by all objects of the catalog of objects. The proportional impact by an object is thereby defined as the product of its percentage of area (AObj / ASSG) with the object’s specific impact (IObj). Deviant from Ostendorp et al. (2008) were the impacts of segments in the three subzones also averaged to derive impacts for a combined zone (ISG).

Sublittoral and epilittoral zone

Since objects affecting the water-current as described in Ostendorp et al. (2008) were not registered, no weighting factors were required for the calculations of impacts in the sublittoral zone. For calculating the impacts of segments in the sublittoral and epilittoral zone the following formula was applied:

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Eulittoral zone

An integration of the linear and planar mapping in the eulittoral zone to a combined impact for the segments’ of the eulittoral was recommended by applying weighting factors (Ostendorp pers. comm.). It was decided to weigh the linear mapping with 70 % and the planar mapping with 30 % to form a combined impact for segments. The impact of planar objects in a segment (IArea) was calculated in the same manner as the impacts of segments in the sublittoral and epilittoral zone. For computing the impact of linear objects in segments (ILength) the product of the percentage of length (sObj / sSSG) with IObj was summed up. Finally, ISSG for segments in the eulittoral was derived by applying weighting factors:

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Combined zone

The arithmetic mean of impacts in the sublittoral, eulittoral and epilittoral was formed:

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2.9.2 Implementation of a database for the calculation of impacts

The calculation of impacts was carried out with the field calculator tool and the summarize function of ArcMap. An important feature of ArcMap was that it automatically stored the areas and lengths of polygons or polylines in their tables of attributes. Within the personal geodatabase, geospatial data and tabular data was linked in a way so that the necessary values for the computation of impacts were available to the field calculator. An essential role played a table containing for all objects the object-ID and the corresponding specific impact. This table was linked via the object-ID with the layers containing the polygons and polylines. By linking the data, it was possible to calculate for each object in a segment the percentage of area or percentage of length and subsequently the percentage of impact. The percentages of impacts were then summarized based on the segment-ID. After the impacts have been calculated they were saved in tables and linked with the corresponding layers so that each segment got its impact ascribed. Figure 21shows the structure of the database used for the computations.

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Figure 21: Structure of database

3. Results

3.1 Zoning, segmentation and numbering

Figure 22 illustrates the final delineation of the three subzones, the segments and the sequence of segment-IDs from 1 to 110.

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Figure 22: Borders and numbering of segments

Source: Background-map taken and modified from Google Maps

The width of the sublittoral varies considerably since it is based on depth contour lines. In the northern basin the subzone is at times just around 5 m wide (e.g. segment-ID 2, 104 and 108) while in the southern basin the subzone is generally wider with a maximum width of almost 700 m (i.e. segment-ID 16 and 17). Apart from that, most segments to the east of the southern basin have widths of 100 to 200 m and the segments to the west are 50 to 150 m wide.

3.2 Mapped objects and derived impacts

3.2.1 Sublittoral zone

Around 85 % of the sublittoral zone has been classified as submerged macrophytes[3] or emergent reed bed areas[4] (Table 6). Areas free of submersed macrophytes made up the great part of the remaining sublittoral areas while anthropogenic constructions such as piers and marinas made up less than 4 %.

Impacts derived for the segments in the sublittoral zone had values between 1.0 and 2.84 and the arithmetic mean was 1.31 (Table 7). A total of 87 out of 110 segments had values in the range of 1.0 and 1.5, another 21 segments received values between 1.5 and 2.5 and for two segments higher values were computed with the maximum being 2.84.

Table 6: Mapped objects in the sublittoral zone

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Table 7: Overview of impacts for segments in the sublittoral zone

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Figure 23: Distribution of impacts for segments in the sublittoral

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3.2.2 Eulittoral zone

The on-site mapping showed that around 27 %, i.e. 7.5 km, of the shoreline is reinforced (Table 8). Most prevalent were small scaled shore stabilizations of various types at privately owned properties with at total length of 1.8 km. Concrete walls and sheet pilings, both classified with the highest specific impact had a total length of 1.6 km and 0.5 km respectively. Punctual shore stabilization at piers and marinas made up more than 3 % due to their high number.

The planar objects that were mapped in the eulittoral zone were mainly reed bed and submerged aquatic vegetation on the lakeward side and green areas with trees, lakeshore trees, willow bushes and grassed areas on the landward side (Table 9). Only around 12 % of the area was assigned to objects with impacts greater than 2.0.

For 56 segments of the eulittoral zone were impacts between 1.0 and 1.5 calculated, for 39 segments values between 1.5 and 2.5 and 13 segments received impacts between 2.5 and 3.5. Two segments had higher impacts, among them the maximum impact in the subzone with a value of 3.96 (Table 10).

Table 8: Mapped linear objects in the eulittoral zone

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Table 9: Mapped planar objects in the eulittoral zone

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Table 10: Overview of impacts for segments in the eulittoral zone

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Figure 24: Distribution of impacts for segments in the eulittoral zone

3.2.3 Epilittoral zone

Table 11: Mapped objects in the epilittoral zone

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Around 66 % of the epilittoral zone was classified as settlement areas including residential areas, roads, parks and grassed areas (Table 11). Most common were thereby built-up areas of rural characteristic and provincial characteristic followed by forest settlements. 31 % of the area was classified as natural or near-natural vegetation.

Segments in the epilittoral zone where primarily classified with impacts close to the value of 3.0 (Figure 25) with the arithmetic mean ranging at 2.51 (Table 12). Impacts spanned from 1.00 to a maximum of 4.02. 17 segments had values between 1.00 and 1.5, 29 segments values between 1.5 and 2.5, 56 segments values between 2.5 and 3.5 and eight segments had higher values up to a maximum of 4.02.

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Table 12: Overview of impacts for segments in the epilittoral zone

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Figure 25: Distribution of impacts for segments in the epilittoral zone

3.3 Outline of classification

An outline of the classification of Lake Scharmützelsee’s lakeshore is given in the following in the form of seven shore sections. The lakeshore sections consist of adjacent segments with similar occurrence of objects and similar impacts ascribed. Figure 26 illustrates the location of the lakeshore sections, detailed coordinates are given in the description of each section.

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Figure 26: Lakeshore sections of the lakeshore

Note: Borders between lakeshore sections are indicated by black lines.

Source: Background-map taken and modified from Google Maps

[...]


[1] Using the polyline of the lakeward boundary of reed bed to generate polygons caused that several marinas and piers were subdivided into polygons.

[2] The standards for the mapping and classification changed in the process of this thesis. For several initially separately mapped objects, it was decided that they should be mapped as one object in the end.

[3] Including areas naturally without vegetation

[4] Including sedges and rushes

Details

Seiten
91
Erscheinungsform
Originalausgabe
Jahr
2010
ISBN (eBook)
9783842815766
Dateigröße
17.4 MB
Sprache
Englisch
Katalognummer
v228535
Institution / Hochschule
Brandenburgische Technische Universität Cottbus – Environmental Sciences and Process Engineering, Department of Freshwater Management
Note
1,4
Schlagworte
hydromorphological pressures lakeshore management littoral zone spatial planning european water framework directive

Autor

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