Shallows of the lower Danube as additional sources of potamoplankton

Abstract

This paper presents studies on the algal flora of the Bulgarian Danube section during three summer periods (1980)(1981)(1982) and during the four seasons of 1987/1988. The following variables were investigated: 1) species composition of the river phytoplankton and the phytobenthos; 2) frequency quotients of the species; 3) number of species at the investigated sites; 4) phytoplankton numbers and biomass; 5) floristic similarity between the sites. The data show the existence of a dynamic connection between phytoplankton and phytobenthos. The shallows in the midstream and river arms play an important role as potamoplankton sources during the periods of low waters. It is comparable with the role of the adjacent wetlands to which previously priority was given. This is especially so below 597th river kilometer.

Phytoplankton dynamics in relation to connectivity, flow dynamics and resource availability—the case of a large, lowland river, the Hungarian Tisza

“…1), but its Romanian section escaped the regulation of the low-water channel. Stoyneva (1994) convincingly demonstrated the role of shallows as sources of planktonic algae in the lower Danube. The same mechanism applied along the braided patches of the Szamos River, where the bottom was well illuminated (depth \ 0.5 m) in up to 60-70% of the cross section during low flow (Istvánovics et al, unpubl.).…”

“…Unregulated lowland rivers possess large, flowdependent storage capacity from inshore retention areas to shallows and to anabranching arms (Junk et al, 1989;Stoyneva, 1994;Reynolds, 2000;Ward & Tockner, 2001;Schiemer et al, 2001;Hein et al, 2003;Schöll & Kiss, 2008). Laminar flow in the boundary layer surrounding surfaces provides refuge to several species of riverine algae.…”

Phytoplankton growth in three rivers: The role of meroplankton and the benthic retention hypothesis

“…It is, however, interesting to note that in the Danube River the decrease in biomass and net production downstream of the Iron Gate (river km ,1700; Serbia) was followed by a conspicuous increase from about Nikopol, Bulgaria (river km ,600; Dokulil 2006). The latter reach was the one where Stoyneva (1994) observed the significant role of shallow areas in phytoplankton recruitment. Thus, benthic retention and meroplankty may better be predicted from channel depth than river size (cf.…”

“…They proposed a mechanism of overwintering resting stages of meroplanktonic species (having the ability to pass a part of the life cycle settled on the bottom) in relatively finegrained deposits (e.g., sand and silt). Subsequently, Stoyneva (1994) deduced from long-term phytoplankton records that shallow bottoms were important source areas of phytoplankton inoculation along the lower reaches of such a large river as the Danube. Convincing field evidence validating the role of aggregated dead zones (ADZs) as retentive habitats, however, was scarce, as were studies indicating an important role of meroplankton in rivers (Reynolds 2000).…”

Factors controlling the seasonal development and distribution of the phytoplankton community in the lowland course of a large river in Northern Italy (River Adige)

“…Wehr and Descy 1998). Such studies may be complicated by the heterogeneity of life cycles of river algae, which is enhanced by the presence of substrata and dead-zones constituting a source of organisms and resulting in alternation between periphytic and planktonic habitats (Stoyneva 1994;Leland et al 2001).…”