Factors affecting the abundance and activity of the bacterioplankton in lowland forest springs in north-eastern Poland

Abstract

The paper summarises the results of bacteriological and hydrochemical studies on the lowland springs in the big forest complex of the Podlasie region in NE Poland. In this area, 75 springs were investigated in the summer period of 2014 and 2015 to determine bacterial number, biomass and hydrolytic activity. All investigated objects were categorized by direct catchment land use and hydrobiological type. The number and biomass of bacteria in the water of the investigated springs is much smaller than in other types of surface water in lowland areas and ranges from 0.29 to 2.94 106 cells cm−3. The best reflection of the habitat quality within lowland groundwater outflows is their hydrobiological typology (helocrene, rheocrene and limnocrene). Despite differing development of spring niches, their hydrology, as well as the geological material and its graining cause unification of the bacterial numbers. The number of bacteria cells were correlated with the concentration of some nitrogen compounds (NH4+, NO2−), and the hydrolytic activity of bacteria with phosphorus compounds mainly dissolved phosphorus. The presence of dissolved organic carbon compounds turned out to be the most disturbing factor in the development of bacterioplankton. Concentrations of these parameters were found to be conditioned by the management of the direct outflow catchment. Furthermore in rheocrene springs, bacterial activity during hydrological stress is clearly lower, despite a large number of bacterial cells in the water (r=-0.38; p<0.005). Our results show that lowland springs are a very sensitive objects to changes in land use, which has a significant impact on water quality and thus the number and activity of bacteria.