The Stratification of Pools in the Alluvium of the River Lužnice

Abstract

The stratification of two shallow and small pools, situated in a floodplain ecosystem, was investigated.A new methodological approach was applied. The parameter called summarized chemical and biological stratification (SCB), was derived from basic limnological parameters in order to evaluate the global intensity of chemical and biological stratification and to compare it with a thermal one.Three situations were described when the seasonal courses of thermal and SCB stratification were compared: 1. Both SCB and thermal stratification are present. 2. The water column is homogeneousthere is no stratification in the pool. 3. SCB stratification is present, but the water is homoiothermic. The thermal stratification is very unstable because of the small volume of the pools and frequent floods. The SCB stratification is of higher stability and it may persist in a homoiothermic water column. In comparison with temperate deep lakes, the thermal stratification does not play such an important role in initiating the chemical and biological stratification. The surfacekolume ratio and the depth in the pools are lower, which cause the "bottom-initiated" quick renovation of stratification even in homoiothermic water.The differences in oxygen regime, volume and localization of both investigated pools cause the differences in stratification patterns. Frequent oxygen depletions in one of the pools increase the intensity of stratification and influence its character. The anaerobic conditions lead to steeper gradients of basic nutrients, pH, alkalinity and water color.The occurrence of a unique phytoplankton community (Cryptophyceae) is probably closely related to the described stratification patterns.

Spatial and temporal diversity of small shallow waters in river Lužnice floodplain

“…Concentrations of NH 4 -N, NO 3 -N, and PO 4 -P were determined using a Tecator flow injection analyser (FIA Star 5010, Tecator, Sweden; Ruzicka & Hansen, 1981) in samples filtered through Whatman GF/C filters. Total nitrogen (TN) and total phosphorus (TP) were determined in samples filtered through 100 lm mesh after mineralisation by persulphate as NO 3 -N and PO 4 -P (for details, see Pithart & Pechar, 1995). Chlorophyll-a concentration was estimated spectrophotometrically or fluorometrically after extraction in an acetone-methanol mixture (Pechar, 1987).…”

“…Similarly, the relative impact of terrestrial vegetation-with its effect of shading and leaf litter-increases with decreasing area. The small, shallow lakes and pools can be relatively deep, with a tendency towards intense stratification and oxygen deficits, influencing the whole aquatic community, and in particular the fish (Pithart & Pechar, 1995;Pechar et al, 1996).…”

Xanthophyceaen assemblages during winter–spring flood: autecology and ecophysiology of Tribonema fonticolum and T. monochloron

“…In the Czech Republic, several studies were performed in inundation river areas (e.g. the middle Elbe River, Frič & Vávra, 1901;Hrbáček & Novotná-Dvořáková, 1965), along the Dyje river (Ošmera, 1973) and in the Lužnice River floodplain (Pithart & Pechar, 1995;Pechar et al, 1996;Pithart, 1999). However, all of these studies were performed in permanent pools and oxbows, and were focused on zooplankton, phytoplankton ecology and water chemistry.…”

Appearance of Planktothrix rubescens Bloom with [D-Asp3, Mdha7]MC–RR in Gravel Pit Pond of a Shallow Lake-Dominated Area

“…They emphasized that absolute depth alone is not a sound criteria to define shallow or deep lakes; moreover, the stratification is also not decisive, because various stratification patterns can develop in shallow lakes both in space and time. Shallow lakes are generally considered polymictic [ 47 , 48 , 49 ] because wind-induced mixing continuously sets back the thermal stratification of the shallow water column [ 50 , 51 ]. However, recent studies suggest that even in shallow lakes, periods with stratification can occasionally be observed [ 26 , 52 ].…”

“…Intensive study of shallow lakes’ stratification started only in the last few decades [ 38 , 45 ]. Pithart and Pechar [ 51 ] found weak stratification in floodplain pools of Lužnice River. Fonseca and Bicudo [ 53 ] described a persistent stratification for a few weeks in a tropical shallow reservoir.…”