Karl-Otto Rothhaupt

Ecological effects of water-level fluctuations in lakes: an urgent issue

Water-level fluctuations (WLF) affect the ecological processes and patterns of lakes in several ways. Aquatic habitats and feeding or breeding grounds are gained or lost, as light, climate and wave impacts change to mention only a few phenomena. While the phenomenon of WLF has been studied in many rivers (better known as flood pulse, Junk & Wantzen, 2004) and environmental flows (Coops et al., 2003), so far it has not received due attention in lakes (Coops et al., 2003). A potential reason for why WLF in lakes have been overlooked for such a long time may be that central Europe and North America—the cradles of limnological research—are situated in landscapes which have been shaped by man for long time. Most central European lakes have been regulated since the middle ages; therefore, naturally fluctuating lakes such as Lake Constance (Fig. 1) are rare today.

An extension of the floodpulse concept (FPC) for lakes

This paper delivers a conceptual framework for the ecological functioning and biodiversity patterns of lakes that is based on the floodpulse concept (FPC). The specific characteristics of rivers and lakes considering water-level fluctuations are compared, with respect to catchment linkages, temporal patterns, and hydraulic forces of flooding and drawdown. The influences of floodpulses on element cycles, biodiversity, and adaptations of lake biota are analyzed, and the importance of multi-annual flooding cycles is highlighted. The degree by which these water-level fluctuations influence lake ecosystems strongly depends on lake morphology, where shallow lakes or those with large shallow margins are the most sensitive. Although floodpulses play a major role for ecosystem services such as lake management and climate change mitigation schemes, this issue is only scarcely dealt with. Tenets of the extended FPC for lakes are formulated in order to overcome this problem.

Effects of the invasive bivalve Corbicula fluminea on settling juveniles and other benthic taxa

Abstract The Asian clam Corbicula has become established worldwide in a wide range of freshwater ecosystems. Corbicula fluminea invaded Lake Constance (Central Europe) between 2000 and 2002 and has reached densities up to 3520 individuals >5 mm in length per square meter in sandy areas. However, the effect of this species on other benthic invertebrates remains unclear. Here, we show that ecosystem engineering via shell production by C. fluminea in Lake Constance considerably increases availability of hard surfaces in primarily soft-bottomed habitats. We studied effects of C. fluminea on littoral communities of sandy habitats using boxes containing bare sand, sand with C. fluminea shells (2000/m2), and sand with live clams (1000/m2). After 2 mo of exposure, the overall benthic community did not differ among treatments, but density of the mayfly Caenis spp. increased in boxes containing shells compared to the boxes containing sand or sand with live clams (analysis of variance [ANOVA], p < 0.0001). The density of shells greatly increased after mass mortality of C. fluminea populations. Our results indicate that shells can provide valuable hard surfaces for species that prefer structured habitats, especially in unstructured soft-bottomed habitats. In addition, density of juvenile C. fluminea was lower in boxes containing live adult clams than in boxes containing sand or sand and shells (ANOVA, p = 0.0048), possibly because of a chemical cue that might hinder settlement of juveniles in areas with high intraspecific concurrence.

Effects of zebra mussels on a native amphipod and the invasive Dikerogammarus villosus: the influence of biodeposition and structural complexity

Abstract In the last decades, zebra mussels (Dreissena polymorpha) have invaded many freshwater systems with severe consequences for entire communities. Most benthic macroinvertebrates, especially amphipods and chironomids, increase in abundance in the presence of zebra mussels. Increased structural complexity and an unknown biotic factor lead to this effect. Dreissena-associated factors that might influence populations of the native Gammarus roeselii and the invader Dikerogammarus villosus in Lake Constance, Central Europe, were investigated in laboratory experiments. These factors were: 1) increased structural complexity related to mussel shells, 2) Dreissena biodeposition, 3) chironomids, the presence of which is increased by biodeposited matter, and 4) Dreissena kairomones. In habitat-choice experiments, the native and omnivorous amphipod G. roeselii showed a preference for mussel shells with biodeposited material and for mussel shells with biodeposited material with chironomids, whereas the invasive and predatory amphipod D. villosus showed a preference only for mussel shells with biodeposited material with chironomids. In a kairomone y-maze experiment, both amphipods avoided zebra-mussel-conditioned lake water. These results indicate that habitat complexity and food availability, mediated directly or indirectly through biodeposited material, are the factors by which amphipod abundances are increased in the presence of Dreissena. Thus, biodeposited material can form an important new food resource, translocated from the pelagic zone to the benthos by zebra mussel filtration, and this biodeposited material might support a new detritus-based food web in the benthos.

Effects of water-depth and water-level fluctuations on the macroinvertebrate community structure in the littoral zone of Lake Constance

In a 2-year field study, abundance, biomass and community structure of benthic macroinvertebrates and their seasonal dynamics were assessed along the depth gradient in the stony littoral zone of Lake Constance, Central Europe. The macroinvertebrate community patterns differed significantly between the depth zones, partly because of species turnover, but mostly as a result of different dominance structures. These distinct differences should be considered when designing surveys of benthic invertebrates also for applied purposes, since sources of variation should be kept small and particularly on hard substrates, extensive efforts are required to obtain sufficient data for a powerful statistical analysis. A large seasonal variability in the macroinvertebrate communities of the eulittoral zone indicates a strong influence of physical disturbances, particularly of water-level fluctuations. The community pattern of the drift line samples was influenced by the previous development of the water level. The cumulated water-level fluctuations and their net tendency accounted for three quarters of the variation in a PCA. Since Lake Constance is the only large pre-alpine lake whose water level is not extensively regulated, the uniqueness of the littoral community should have implications for nature conservation measures.

Complex spatial and temporal patterns of littoral benthic communities interacting with water level fluctuations and wind exposure in the littoral zone of a large lake

The spatial and temporal organisation of benthic invertebrate communities was studied in a large oligotrophic lake in central Europe. Three shallow littoral sites at 0.4 m depth were sampled monthly from May 2002 to April 2003. On a spatial scale, the benthic community composition at all sites and in all samplings significantly differed in both abundance and biomass. On a temporal scale, the benthic communities at all sites gradually changed each month; monthly samples always significantly differed, but samples from consecutive months were more similar to each other than to samples of non-consecutive months. The observed variability within benthic communities corresponded with changes in the abiotic parameters water level and wind exposure, but was best explained by short- and long-term fluctuations in the water level. Effects of wind exposure were most pronounced in the winter months, when high wind events most often occurred. However, wind effects were masked by stronger effects, such as water-level fluctuation within the shallow littoral zone, or diminished by parameters with opposite effects, e.g. slope vs. exposure. Wind-induced shear stress in the upper eulittoral zone directly influenced the abundance and biomass of the benthic community to a lesser extent. We conclude, however, that this stress alters habitats constantly (e.g. substrate composition, periphyton growth, resuspension vs. sedimentation) and is therefore the driving force for the reported permanent site differences. Furthermore, benthic communities were well adapted to frequent minor changes and also to regular major changes of their habitat, as bare substrates were rapidly recolonised within a month.

Temporal variation in zebra mussel (Dreissena polymorpha) density structure the benthic food web and community composition on hard substrates in Lake Constance, Germany

Invasive species often influence existing biocenoses by altering their environment or facilitating the ecology of other species. Here we combined stable isotope analysis with quantitative benthic community sampling to investigate temporal variation in the influence of biodeposition of organic material (biodeposits) by the zebra mussel (Dreissena polymorpha) on the benthic food web in hard substrate habitats of Lake Constance, Germany. The accumulation of organic material excreted by zebra mussels (faeces and pseudofaeces) is hypothesised to implement a biodeposition based food web. By means of stable isotope analyses, we found that the feeding strategy of amphipods was dependent on the availability of zebra mussel biodeposits. The proportion of pelagic resources contributing to the diet (by δ13C) and trophic position (by δ15N) of amphipods were significantly and positively correlated to the production of zebra mussel biodeposits. Also, the benthic community in Lower Lake Constance showed a shift towards higher densities of the mayfly Caenis spp., Chironominae, and the caddisfly Ecnomus tenellus, which might act as links to higher trophic levels when more zebra mussel biodeposits were available. These results demonstrate that temporal variation in zebra mussel density, and thus in organic biodeposition, have a strong impact on the benthic communities and food web structure associated with hard substrates to the extent that there may be dependence on zebra mussel occurrence in such habitats in Lake Constance.

An efficient in situ method for sampling periphyton in lakes and streams

We present an efficient in situ sampling device that allows a simple and quantitative sampling of natural periphyton communities. The Brush Sampler is based on a previously developed sampler, which was improved by the addition of an external water supply, ball valve closing mechanism, and special exchangeable stiff brushes to solve previously reported problems of biomass overestimation and underestimation. The Brush Sampler was tested under ambient conditions in the field at four different sampling sites in a lentic and a lotic system and compared to the old sampler and control samples. The tests revealed a high inaccuracy of the old sampler and showed that biomass estimates (ash-free dry mass and chlorophyll-a content) obtained with the improved Brush Sampler did not significantly differ from biomass values determined from scrapings of control samples collected at the same sites. Therefore, our modified sampling device can be used as a tool for quantitative and qualitative epilithon community analyses.

Alteration of Kairomone-Induced Antipredator Response of the Freshwater Amphipod Gammarus roeseli by Sediment Type

The importance of sediment type and of kairomones released by juvenile burbot (Lota lota) on behavioral responses of the freshwater amphipod Gammarus roeseli was studied in laboratory experiments. In the absence of kairomones, G. roeseli preferred coarse substrates; the highest preference was shown for the most coarse sediment. In the presence of kairomones, the amphipods preferred the less-coarse substrate pebbles over gravel. This difference is an effective antipredator response; G. roeseli is able to hide efficiently in the interstices of the pebbles. Juvenile burbot have a low foraging efficiency on pebbles and preferentially forage in the interstices of coarser sediments. G. roeseli responded differently to kairmones in different sediment types. The amphipods decreased their activity only in pebbles. In gravel, the rate of exploration behavior increased, and on a bare surface, the area containing fish kairomones was avoided.

Ecological effects of water-level fluctuations in lakes.

Ecological effects of water-level fluctuations in lakes: an urgent issue.- Potential effects of water-level fluctuations on littoral invertebrates in lowland lakes.- Effects of water-level regulation on the nearshore fish community in boreal lakes.- Natural lake level fluctuation and associated concordance with water quality and aquatic communities within small lakes of the laurentian great lakes region.- Climate change and lakeshore conservation: a model and review of management techniques.- The impact of water-level regulation on littoral macroinvertebrate assemblages in boreal lakes.- Quantitative trends of zebra mussels in Lake Balaton (Hungary) in 2003-2005 at different water levels.- Patterns, origin and possible effects of sediment pollution in a mediterranean lake.- Temporal scales of water-level fluctuations in lakes and their ecological implications.- Effects of water-depth and water-level fluctuations on the macroinvertebrate community structure in the littoral zone of lake constance.- Flooding events and rising water temperatures increase the significance of the reed pathogen pythium phragmitis das a contributing factor in the decline of phragmites australis.- Leaf litter degradation in the wave impact zone of a pre-alpine lake.- Use of the water-level fluctuation analysis tool (Regcel) in hydrological status assessment of finnish lakes.- Mass mortality of the invasive bivalve Corbicula fluminea induced by a severe low-water event and associated low water temperatures.- An extension of the floodpulse concept (FPC) for lakes.- Effects of water-level fluctuations on lakes: an annotated bibliography.