Zooplankton community response to enhanced turbulence generated by water‐level decrease in Lake Balaton, the largest shallow lake in Central Europe

Abstract

During the unusually long European drought between 2000 and 2003, the water level of the large and shallow Lake Balaton, Hungary (area 5 596 km 2 , mean depth 5 3.25 m), decreased by 28%. Although food availability for zooplankton remained unchanged, and the fish stock declined more than the water mass, the density of populations of several planktonic rotifers, cladocerans, calanoid copepodes, and veligers decreased by 60-90% simultaneously with the water-level decrease and regenerated only after the drought. The generally strong turbulence of the lake was intensified during the four consecutive years of low water, as verified by instrumental monitoring of the turbulence intensity and by the estimation of the turbulent kinetic-energy dissipation rate. In our tank experiments, turbulence conditions similar to those that existed in the lake during low water were simulated, but mineral suspended material was minimized and food was regularly resupplied. Under these experimental conditions, zooplankton taxa showing the highest mortality were the same as those that were most susceptible in situ. Increased turbulence coupled with the water-level decrease is especially unfavorable for rotifer Keratella, the cladoceran Daphnia, Bosmina, and copepodit and adult stages of the calanoid copepod Eudiaptomus gracilis in this lake.Moderate turbulence intensity is beneficial for zooplankton, because it increases the producer-consumer encounter rate, and improves consumers' capture efficiency, feeding, and growth rates (Saiz and Alcaraz 1991; Visser and Stips 2002;Visser et al. 2009). High turbulence, however, interferes with the feeding current of the suspension feeders, erodes the remote detection of prey by their predators, inhibits their food ingestion, and increases their metabolic energy expenditures Kiørboe and Saiz 1995;Peters and Marrasé 2000). And finally, very high turbulence could disorientate the movement, lead to uncontrolled vertical drifting, and could even injure the largest bodied organisms (Reynolds 1992;Visser et al. 2009).Earlier we proved experimentally and quantified the relationship between frequently resuspended fine mineral sediment (mineral turbidity) of Lake Balaton and inhibition of the effective food collection and development of cladocerans, especially Daphnia, even if food abundance exceeded threshold concentrations (G.-Tó th 1984; G. -Tó th et al. 1986). However, the direct physical effect of turbulence on the zooplankton was never established in Lake Balaton or any other shallow lake.Lake Balaton is the largest shallow lake in Central Europe. Because the lake is very shallow, the vertical space for the dissipation of the kinetic energy content of the water mass induced by the wind is very limited, and so dissipation per unit of volume is very high. Higher than 4 m s 21 wind velocity occurs, on average, every third day and causes a turbulence sufficient to resuspend sediments. Wind faster than 10 m s 21 occurs , 12-15 times annually, resulting in sediment resuspension up to 600 mg dry wei...

Effects of turbulence on alkaline phosphatase activity of phytoplankton and bacterioplankton in Lake Taihu

“…The different levels of turbulence intensities used in this study were based on actual conditions previously observed in Lake Taihu on summer 2013. In Taihu, the ɛ varied between 6.01 × 10 −8 and 2.39 × 10 −4 m 2 s −3 (Table 1), which corresponded to the range of values (from 1.07 × 10 −7 to 6.67 × 10 −3 m 2 s −3 ) previously measured by G. -Tóth et al (2011) in the large shallow Lake Balaton. The calm condition (0 cm s −1 ) which is without any hydrodynamic turbulence was the control.…”

“…Because Lake Taihu is very shallow, it is strongly influenced by wind wave turbulence and the turbulent kinetic-energy content are much higher than those in stratified deep lakes and even in the open ocean (G. -Tóth et al 2011). However, In Taihu, the cyanobacterial blooms have occurred every summer and threaten the supply of drinking water and fisheries-related products for more than 8 million people,…”

“…However, the inducible threshold of APA is restricted to a certain level of Pi concentration, which depends on the ecosystem and its physico-chemical characteristics (Labry et al, 2005;G.-Tóth et al, 2011). In Taihu, when the concentration of SRP is less than 0.02 mg L −1 or when the mass ratio of TN over TP is above 22, the APA significantly increases (Gao et al, 2006), suggesting it is characteristic of P limitation.…”

The hydraulic retention time on the particle removal efficiency by Daphnia magna filtration on treated wastewater

“…However, the Daphnia survival is doubtful in situations where the water flow is high and with a high level of turbulence (Tóth et al 2011). The proposed model could predict fairly well the removal efficiency for all the HRT studied except for the smallest HRT of 3 h. The reason for this could be due to the fact that the flow entering the container at HRT = 3 h generated a high level of turbulence in the system.…”

“…The proposed model could predict fairly well the removal efficiency for all the HRT studied except for the smallest HRT of 3 h. The reason for this could be due to the fact that the flow entering the container at HRT = 3 h generated a high level of turbulence in the system. It is known that turbulence may affect Daphnia swimming behavior (Seuront et al 2004), Daphnia morphology (Laforsch and Torllrian 2004) and (Tóth et al 2011). Wickramarathna et al (2014 found Daphnia swimming velocities of 1.54 cm s -1 for Daphnia cells 2 mm long.…”