Wolfgang Ostendorp

‘Die-back’ of reeds in Europe — a critical review of literature

Abstract Reed decline phenomena have been detected in more than 35 lakes in Europe. About 110 publications and reports, which have dealt with this subject, are evaluated in this paper. The localities and the circumstances that go with the reed ‘die-back’ are listed. The methods of investigation are discussed. Probable causal factors are grouped into five categories: direct destruction, mechanical damage, grazing, water and sediment quality, lake regulation and related effects. Deficiencies of the present state of research are pointed out.

Water level variability and trends in Lake Constance in the light of the 1999 centennial flood

The extreme flood of Lake Constance in 1999 focused attention on the variability of annual lake levels. The year 1999 not only brought one of the highest floods of the last 180 years but also one of the earliest in the season. The 1999 extreme event was caused by heavy rainfall in the alpine and pre-alpine regions. The influence of precipitation in the two distinct regional catchments on lake level variations can be quantified by correlation analysis. The long-term variations in lake level and precipitation show similar patterns. This is seen through the use of spectral analysis, which gives similar bands of spectral densities for precipitation and lake level time series. It can be concluded from the comparison of these results with the analysis of climate change patterns in northern Europe, i.e. the index of the North Atlantic Oscillation, that the regional effects on lake level variations are more pronounced than those of global climate change.

Auswirkungen des Extremhochwassers 1999 auf die Flächendynamik und Bestandsstruktur der Uferröhrichte des Bodensees

Abstract In consequence of the extreme flood at Lake Constance in 1999 the reed belts showed a severe loss in vitality so that a permanent damage could be expected. The monitoring project presented here focuses the documentation of the damage following the disturbance event, the identification of co-factors, and is designed to find out significant stressors that may impede the recovery of the reeds. The monitoring is based on CIR aerial photo interpretation, quantitative GIS-analyses and field data. The design of the study implies the definition of five degrees of damage using the interpretation of CIR aerial photo series from July 2000. The aquatic reed beds were digitised and areal sums were calculated. These data were compared with the corresponding data from 1999 and 1993. Stand structural and biomass attributes were investigated in 50 randomly distributed permanent plots covering all site types and damage degrees. The results showed a loss of about 24 hectares of aquatic reeds at Lake Constance Untersee alone. The stands which had survived showed a great patchiness in terms of culm density, shoot population composition, culm architecture, and aboveground biomass production. Severely damaged stands were mainly composed of secondary shoots, whereas primary and insect infested shoots dominated in less damaged stands. One co-factor which explained the patchiness was the vertical position of the stand, i.e. the probability of being severely damaged increased with increasing distance below mean water level. The monitoring programme will be continued till 2003.

Dynamik der Schilfröhrichte am Bodensee unter dem Einfluss von Wasserstandsvariationen

Abstract On the basis of different sets of aerial photos the dynamics of the reed bed areas of Lake Constance were investigated in relation to the dynamics of the water levels. The objectives of the study were to quantify the changes of reed areas due to different flood events in the last decades and their recovery in the time periods between these events. The results should given information of the relevance of water level variations on reed bed dynamics and the regeneration times of reed beds after extreme disturbance events. Following the extreme flood at Lake Constance in 1999 the reed belts of Lake Constance lost approximately 30 ha (24%) of the lakeside reed beds. The loss is comparable to the situation in the late 1960s, when approximately 40 ha died back due to the extreme flood in 1965 and the high spring water levels in the subsequent years. In the time period between the extreme floods of 1965 and 1999, the reed areas expanded to nearly 85% of the area before 1965. The expansion rates increased with increasing distance to the flood event of 1965. Especially in periods with series of years of low spring water level the expansion rates were high. The damage degrees of the reed areas in the years 2000 and 2002 showed a clear relation to the elevation (i.e. average water level) of the stands. The damage degree increased with decreasing elevation. Furthermore the regeneration process of severely damaged stands was related to the elevation level of the stands. Whereas stands at high elevation regenerate fast, those at low elevation died off completely in the years after the extreme flood. This supports the hypothesis that the water level flutuations play a major role in the reed dynamics of Lake Constance. As a consequence of the climate change an increase in the frequency of high spring water levels is expected. Thus, it seems unlikely that reed stands will ever expand again to the same area as before 1965.

Estimation of mechanical resistance of lakeside Phragmites stands

Abstract The power of resistance of reed stands against mechanical impact by waves and drifting matter is assessed using the mechanical properties of the stem wall (modulus of elasticity, breaking stress), the dimensions of the stems cross section (diameter, momentum of inertia), and the culm density. The power of resistance of an individual stem (pmr) was found to be proportional to the bending stiffness ( M E ) and to the breaking strength ( M S ) in the internode position where maximum deflection or breaking occurs. The power of mechanical resistance of reed stands (PMR) was found to be proportional to the sum of individual M E values (or M S values, respectively) per unit surface (1 m 2 ). Two predictive models, based on the pmr and the PMR values were tested using mechanically damaged stands in the field; the pmr model fits observed values in 70–90% of all cases (damaged culms), the PMR model explains 53–67% of the variability in percentage of damaged biomass.

New approaches to integrated quality assessment of lakeshores

The EU Water Framework Directive (WFD) requires the ecological assessment of water bodies. Since the littoral zones and the lakeshores are part of lakes as water bodies as defined by the WFD, a new scheme for ecological quality assessment of lakeshores should be established. It is proposed that this scheme should go beyond the formal requirements of the WFD, as it includes aspects of nature conservancy, landscape protection, and regional planning and development. Some of these aspects are subject to other EU legislation (e.g. Habitats Directive) and some are subject to national legislation. Ten general Quality Elements (QEs) are proposed, which can be refined and reified through several levels of detail, depending on the specific aims of a study. A list of eleven topics, which should be discussed in the establishment of the lakeshore quality assessment scheme, is given. The more complex ones are the implementation of other EU legislation, the definition of lakeshore types and reference conditions, the stipulation of best aggregation procedures, and a better understanding of the significance of hydrological and morphological impacts on the biota.

Impact of winter reed harvesting and burning on the nutrient economy of reed beds

The fringing reeds (Phragmites australis (Cav.) Trin. ex Steud., Poaceae) at Lake Constance-Untersee were mown or burnt in winter thereby drastically reducing the addition of decomposable organic matter to the sediment. The purpose of this study was to test whether or not this management significantly decreased the contents of organic matter and nutrients in the surface sediment layer and if the oxygen conditions in the withinreed water body improved. Hypotheses were tested by monitoring 6 treated reed beds and 3 reference fields over a period of up to 4 years. The sediment/water system of reed beds was found to be well buffered against the removal of the current years crop of dead Phragmites straw, because only slight, and mostly insignificant, differences between treated and untreated reeds were detected. Hence, the benefit of winter reed harvesting to reduce nutrient overloading of the reed-belts and the ‘die-back’ of reeds remains dubious.

Die ökologische Bewertung von Seeufern in Deutschland

ZusammenfassungZiel und AbsichtObwohl die Seeufer als Übergangsbiotop zwischen Land und See wichtige ökologische Funktionen erfüllen, ist über diese Leistungen im einzelnen wenig bekannt. Zudem müssen die Seeufer einen hohen Nutzungsdruck aushalten und sind dadurch bereits vielfach stark verändert. Während die stofflichen Belastungen geringer werden, steigen die strukturellen Veränderungen. Leider gibt es hier ein Defizit: Es fehlt bisher an umsetzbaren Bewertungsverfahren und Entscheidungshilfen.SchwerpunkteDiesem Defizit hat auch die EU-Wasserrahmenrichtlinie nicht abgeholfen, da hier die Seeufer nur implizit behandelt werden. In diesem Artikel werden einige bestehende Bewertungsverfahren und ihre Konzeptionen benannt. Allerdings wurden alle diese Verfahren nicht für Seeufer entwickelt. Daher werden Kriterien vorgeschlagen, die ein seeuferspezifisches Bewertungsverfahren erfüllen sollte. Ein Seeufermanagement sollte strukturelle und biologische Parameter berücksichtigen und die Akzeptanz der Bevölkerung einbeziehen.Ergebnisse und SchlussfolgerungenNeben der eher gängigen Biodiversität könnte die biologische Funktion der Seeufer durch ein funktionierendes Nahrungsnetz, z.B. des Makrozoobenthos, dargestellt werden. Aber schon bei der Biodiversität treten erhebliche Probleme auf, wie man sie quantifizieren kann. Ein einfacher Biodiversitätsindex kann den Forderungen nach der vollständigen Erfassung einer komplexen Situation, dazu gekoppelt mit Informationen zu Struktur, Praktikabilität, Kosten, und dergleichen mehr, nicht genügen und kann nicht für die Bewertung einer Maßnahme herangezogen werden.Empfehlungen und AusblickEin möglicher Ansatz, der oben genannten Komplexität gerecht zu werden, ist, mathematische Modellansätze und ordnungstheoretische Verfahren in die Betrachtung einzubeziehen.AbstractGoal and ScopeDetails about the ecological function of lake shores as ecotones between land and lakes are not well-known. These ecotones are also heavily exploited and, in part, considerably changed. Whereas anthropogenic nutrient loading is decreasing, structural changes are increasing. Unfortunately, there is a deficit in methods of evaluation and decision processes.Main FocusEven the EU-water framework directive was no remedy for this deficit, as lake shores were included only implicitly. In this article several evaluation methods and their conceptual groundwork are presented. However, these methods were not developed for lake shore research. Therefore, criteria are proposed which could fulfill the specific demands of lake shore assessments. The management of lakes shores should consider structural and biological parameters, and be agreeable to local residents.Results and ConclusionsIn addition to conventional biodiversity methods, the ecology of lake shores could also be represented by a functional food net, for example in benthic invertebrates. But even quantification of biodiversity alone creates many problems. A simple biodiversity index cannot meet all the demands placed on a method of evaluation in complex situations, especially when coupled with additional information on structure, practicability, costs, etc. For these reasons, assessments for future management cannot be based on such an index.OutlookA possible approach to include this complexity in assessments is to apply mathematical models and theoretical order concepts.