Roumen Kalchev

Some allometric and non-allometric relationships between chlorophyll-a and abundance variables of phytoplankton

We analysed data from three Bulgarian reservoirs, with trophic status from meso to eutrophic. Two kinds of relations (non-allometric and allometric) of chlorophyll with phytoplankton density, biovolume and surface area were investigated. The non-allometric relationships compare these phytoplankton variables with chlorophyll-a concentration, while the allometric ones include comparisons of average individual volume (AIV) of phytoplankters with chlorophyll-a content per individual (Chl.N−1), per unit biovolume (Chl.BV−1) and per unit surface area (Chl.SA−1).Maximum values of the rank correlation of the three non-allometric relationships were found in the eutrophic reservoir. The highest allometric correlation coefficients were observed in the mesotrophic reservoir. Two non-allometric relationships, Chl with N and Chl ith BV calculated on unified data from all three reservoirs showed lower significance and a non-linear character. Chl-SA relationship was always statistically significant and varied from linear to slightly non-linear when calculated on weighed values. Two allometric relationships, AIV with Chl.BV−1 and AIV with Chl.N−1 seem to be linear. A third AIV and Chl.SA−1 was described by a polinomial of the second degree, indicating that the smallest and largest phytoplankton individuals have a similar chlorophyll content per unit surface area. At the highest trophy, the Chl.SA−1 seemed lowest.The frequently investigated relationship between chlorophyll-a and biovolume ranged from statistically not significant in the mesotrophic to highly significant in the eutrophic reservoir. This tendency was generalized by obtaining a statistically significant rank correlation between the levels of significance of chlorophyll-biovolume correlations and the corresponding chlorophyll-a concentrations. The non-linear character of the chlorophyll-biovolume relationship over a wide range of trophy was probably caused by changes in surface area-biovolume ratio.

Trophic Relationships and Status of Reservoirs with and without Occurrence of Dreissena ssp. (Mollusca, Bivalvia) Built on Bulgarian Danube River Tributaries

Abstract The trophic status and relationships between Secchi depth transparency (SD) chlorophyll-a (CHL) and total phosphorus (TP) concentrations from nine non-infested and five infested areas with invasive alien species, Dreissena ssp. reservoirs, situated on the Bulgarian Danube River tributaries were studied. The trophic status index (TSI) values after Carlson (1977), and showed statistically significant differences for all three variables between infested and non-infested reservoirs. The three linear regression equations between SD × CHL, CHL × TP and SD × TP were statistically significant for the group of non-infested reservoirs, while in the infested reservoirs only the SDxCHL regression was statistically significant for P < 0.05. Our results showed that the Dreissena invasion destroyed the linear relationship between CHL × TP and SD × TP and seems to affects the accurate application of Carlson TSI.

Trophic Status and Phytoplankton Limitation Conditions in a Few Bulgarian and Hungarian Danube River Wetlands

Abstract The phytoplankton limitation conditions in a few Bulgarian and Hungarian wetlands and in two more sampling sites, one for each Danube stretch, were investigated by means of trophic state index of Carlson (1977) for phytoplankton chlorophyll-a (CHL), Secchi disk depths (SD), total phosphorus (TP), and total nitrogen (TN) concentrations. Phytoplankton of both river sites was not limited by non-algal turbidity, nor was they phosphorus and nitrogen limited. In summer months the studied wetlands were predominantly nitrogen limited, while in spring and autumn limitation by non-algal turbidity prevailed.

The Effect of Dreissena polymorpha on Bacterioplankton, Nematode Fauna and their Relations to Environmental Factors in Ogosta Reservoir (Danube Basin)

Abstract Spatial, seasonal, and annual bacterioplankton dynamics in recently infested by the species Dreissena polymorpha Ogosta Reservoir were studied for the first time during three year period. Bacterioplankton total number was higher in spring in ecotone zones, than in summer at thermocline. NH4-N, PO4-P, turbidity, dissolved oxygen, COD and chlorophyll-a correlate positively, while transparency and Ca2+ negatively with bacteria. Nematode species composition, included 22 species studied (13 rarely found and Rhabditis brevispina new for Bulgaria) belonging to nine families. The D. polymorpha impact is positive on nematodes and phytoplankton, negative on zooplankton and bacterioplankton, but weak positive on larger bacteria, rods and attached bacteria.

Bacterioplankton from Two Hungarian Danube River Wetlands (Beda-Karapancsa, Danube-Drava National Park) and its Relations to Environmental Variables

Abstract Seasonal and spatial distribution of bacterioplankton from two Hungarian oxbow lake type wetlands, Mocskos-Danube and Riha, was studied. They were both covered by macrophytes and they had different hydrological connectivity to the Danube. The six sampling campaigns from April to October 2014 included parallel samples from the Danube River at Mohács, Hungary. Bacterial abundance was the highest in spring and in Mocskos-Danube, followed by Mohács and Riha. Positive relationships existed between bacterioplankton and temperature on one hand and suspended solids, pH, PO4-P and chl-a on the other. Negative correlations were with DOC, dissolved oxygen and NH4-N.