Succession of aquatic vegetation driven by reduced water‐level fluctuations in floodplain lakes

Abstract

Summary 1.In recent years, interest has grown in restoring floodplain function of regulated rivers. Successful rehabilitation of riparian systems requires knowledge of how regulation of river flow affects biodiversity and ecosystem function. The effects of changes in the river's low water-level regime on aquatic ecosystems in floodplains has received little attention so far. 2. The aquatic vegetation of 215 floodplain lakes along the Lower Rhine (the Netherlands) was analysed in relation to lake characteristics and lake water-level fluctuations in 1999-2000. 3. Vegetation composition was related to lake morphology and age, cattle access to the shoreline, the amount of time the river was in flood, and lake sediment area exposed at low water level (drawdown). Surprisingly, vegetation composition was correlated more strongly with lake age and occurrence of drawdown than the amount of time the river was in flood. 4. In older lakes, water-level fluctuations are reduced due to an accumulation of clay and silt that 'seals' sediment, preventing drawdown during periods of low river levels. Our results suggest that this clay sealing process is a major driving force for aquatic vegetation succession in floodplain lakes along the Lower Rhine, as succession drives from desiccation-tolerant species (e.g. Chara spp.) in young lakes to desiccation-sensitive species (e.g. Nuphar lutea ) in old lakes. 5. Water levels were stable in lakes along a river branch that was impounded below mean flow only. Here, the original low water-level regime has been replaced by an artificial regime with higher water levels than would be expected naturally. Consequently, in these lakes drawdown was rare or absent, and the aquatic macrophyte vegetation was characterized by low species richness and frequent dominance by the invasive species Elodea nuttallii . 6. Synthesis and applications . Our results show that stabilization of river water levels during low flow may negatively affect vegetation composition and succession in floodplain lakes adjacent to these rivers. A management scheme including incidental temporary lowering of the river water level, which results in drawdown of floodplain lakes, would enhance the ecological status of those rivers with stabilized water levels during low flow.

Towards a more precisely defined macrophyte-dominated regime: the recent history of a shallow lake in Eastern Poland

“…In the following stages of succession, at the turn of the 21 st century, there was dominance by C. globularis, with a gradually increasing contribution of C. delicatula. Our research supports the finding reported from periodically flooded oxbow lakes (Van Geest et al, 2005), where charophyte beds responded to increased water level fluctuations by changes in balance between C. vulgaris, resistant to hydrological disturbances and non-resistant C. globularis. We suggest that this pattern may serve as a useful tool for determining periods of substantial changes in water level.…”

“…It has been shown in several European lakes that the macrophyte-dominated state can cyclically shift into the phytoplankton-dominated state and back every several years with no evident external stimuli (Rip et al, 2005;Van Geest et al, 2005;Hargeby et al, 2007;van Nes et al, 2007). A similar phenomenon was observed in Boreal lakes of northern Canada (Bayley et al, 2007).…”

“…1). They were formed, however, not by C. globularis as in the 1950s, but by C. vulgaris, a species tolerant of water level fluctuations (Van Geest et al, 2005) and of turbid and nutrient-rich conditions (Van den Berg et al, 1997;Van den Berg & Coops, 1999).…”

Mapping Aquatic Vegetation in a Large, Shallow Eutrophic Lake: A Frequency-Based Approach Using Multiple Years of MODIS Data

“…The lake topography affects the water depth of the lake, which is considered responsible for variation in the biomass and species composition of aquatic vegetation in many freshwater ecosystems of the world [54][55][56]. The optimum depth for the growth of the aquatic vegetation in Lake Taihu has been reported as less than 2.0 m [14,41].…”

The Biomass and Physiological Responses of Vallisneria natans (Lour.) Hara to Epiphytic Algae and Different Nitrate-N Concentrations in the Water Column

“…The decline of submerged macrophytes is often accompanied with a high planktonic algae density in the eutrophic lakes [25,26]. However, the overgrowth of epiphytic algae was seen to occur earlier than planktonic algae in eutrophic lakes and the reduction of submerged macrophytes was connected with a high epiphytic algae density [27,28]. In previous studies by Jones and Sayer [29] and Bécares et al [30], a 50% reduction of submerged macrophyte biomass occurred when epiphytic algal biomass exceeded 50 and 90 mg Chl-a m −2 , respectively.…”