Shoreline algal wash as a factor in reed decline in Lake Constance-Untersee

Abstract

165This paper assesses the chemical and mechanical impact of algal wash (Cladophora, Spirogyra, Chara) upon the lakeside reed belt (Phragmites australis) using field mapping methods, bioassays with Scenedesmus acutus in batch culture, and field experiments. Heavy mats of filamentous algae are correlated with a reduction in number ofthe outermost reed stalks. The water pressed from decaying heaps of Cladophora and Spirogyra reduced the growth rate of Scenedesmus significantly, but mats from Chara did not. It is assumed that the toxic substance is an organic compound. In field experiments the detrimental effect could not be clearly evidenced. The reasons for this are discussed. It is concluded that mechanical impact is of major importance.

Structure, growth dynamics and biomass of reed (Phragmites australis) – A review

“…Assessing the chemical and mechanical impact of algal wash on lakeside reed belt, Ostendorp (1992) found minor importance of chemical impact, while mechanical damage was decisive for reed growth. Stalks were bent and broken down by algal masses (also demonstrated by Kró likowska, 1987), thereby the aerenchyma channels became filled with water.…”

Estimation of mechanical resistance of lakeside Phragmites stands

“…that the yearly amount of biomass destroyed by these forces is equal to the yearly biomass increment the stand would have in a mechanically unaffected state (e.g. Ostendorp, 1992; Fig. 3).…”

“…(Lang, 1981). In late summer and autumn, when the water level is low and strong winds occur, the mats of senescent submerged plants are uprooted and washed ashore (Ostendorp, 1992). The water level is high in summer as a result of ice and snow melting in the inner alpine region, and low in winter.…”

“…The most abundant drifting matter consists of uprooted submerged plants and filamentous algae (Ostendorp, 1992), followed by mats of broken Phragmites stems from the previous years and a wide range of solid rubbish. Mechanical damage due to snow cover, drifting ice, trampling (cattle, holiday makers), and motor boat generated waves has been proved W. Ostendorp/ Aquatic Botany 51 (1995) 87-101 to be of little importance in Lake Constance.…”

“…Field mappings which were run over 3 years (partly published in Ostendorp, 1992) showed that the different types of mechanical threat to lakeside reeds in Lake ConstanceUntersee can be grouped according to their frequency and significance as follows: waves charged with drifting matter> wave action only> hail storm> resting birds> recreational activities> professional fishing> wind action only. Here, resting birds are flocks of starlings (Stumus vulgaris L.), recreational activities are swimming, surfing and boating, and professional fishing is eel-basket fishing.…”