Dynamics of vegetation changes in oil and salt-contaminated oligotrophic ridge-hollow mire complexes after reclamation (Middle Pre-Ob region, Khanty-Mansi Autonomous Okrug – Yugra)

Oligotrophic ridge-hollow and ridge-hollow-pool complex mires are widely distributed in the central part of West Siberia, including many oil fields of the Middle Pre-Ob region. The article considers the dynamics of re-vegetation of oil and salt-contaminated areas of these mire types subjected to reclamation. Survey materials for 2–3 years and 15 years after reclamation allow to identify the main trends in vegetation restoration in the short and medium term. The reversible oligotrophication of ridges manifests in a relative decrease in the participation of the meso-eutrophic species on contaminated mire sites. In the hollows, however, the similar trend can be traced only in relation to oil-contaminated sites, whereas in the salt-contaminated hollows, the strong eutrophic conditions last. In the medium-term perspective, most typical oligotrophic hollow species, with the exception of Eriophorum russeolum and Oxycoccus palustris, were unable to recover. In the course of dynamic changes in the vegetation, the leading role in recovery successions gradually passes to mesotrophic and eutrophic species possessing massive root systems and aerenchyma – Eriophorum angustifolium, Phragmites australis, Carex rostrata, etc. Restoration of the moss layer is several years behind that of the grass layer, and due to the lack of competition, the participation of liverworts in it is of great importance, especially in salt spills. At the same time, among mosses as in the case of vascular species mesotrophic components are the main dominant ones15 years after reclamation.

Differentiated macrophyte types as a habitat for rotifers in small mid-forest water bodies

The rotifer community structure may be shaped by a variety of environmental factors, including biological parameters, such as predation or competition, as well as by physical-chemical factors, among which the kind of macrophyte substratum and parameters relating to the trophic state and to the catchment area conditions are of great importance. Another impact on rotifer composition, abundance and frequency may be expected when considering differentiated macrophyte types (including helophytes, nymphaeids and elodeids) within a group of eight ponds located within a mid-forest catchment area, which was the main aim of the present study. Detailed analysis on the participation of indicator eutrophic rotifer species provided an additional goal of this investigation in order to qualify the trophic state of this kind of water body located within the Wielkopolska region, in the central western part of Poland.The presence of 117 taxa, including 7 species that are rare or infrequently distributed in the Polish fauna was recorded. The number of taxa and rotifer abundance differed greatly in respect to the specific water body and to the type of substratum. The vegetated zones dominated by elodeids were characterised by the most various and most abundant rotifer communities as well as by the highest values of the Shannon-Weaver index. This reflects a positive relationship between the heterogeneity of habitat and the structure of rotifer communities. It was also found that helophytes and the open water zone possessed the highest, while elodeids the lowest percentage of eutrophic species.

Differences between Nearshore and Offshore Phytoplankton Communities in Lake Ontario

Differences between nearshore and offshore phytoplankton biomass and composition were evident in Lake Ontario in 1982. Phytoplankton biomass was characterized by multiple peaks which ranged over three orders of magnitude. Perhaps as a consequence of the three times higher current velocities at the northshore station, phytoplankton biomass ranged from 0.09 to 9.00 g∙m−3 compared with 0.10 to 2.40 g∙m−3 for the midlake station. Bacillariophyceae was the dominant group at the northshore station until September when Cyanophyta contributed most to the biomass (83%). Although Bacillariophyceae was the principal component of the spring phytoplankton community at the midlake station, phytoflagellates (49%) and Chlorophyceae (25%) were responsible for summer biomass, with the Chlorophyceae expanding to 80% in the fall. The seasonal pattern of epilimnetic chlorophyll a correlated with temperature. While chlorophyll a concentrations were similar to values from 1970 and 1972, algal biomass had declined and a number of eutrophic species (Melosira binderana, Stephanodiscus tenuis, S. hantzschii var. pusilla, and S. alpinus) previously found were absent in 1982.

Postsettlement Diatom Succession in the Bay of Quinte, Lake Ontario

Siliceous algal microfossil assemblages deposited in the Bay of Quinte prior to European settlement consist of low numbers of benthic diatoms and chrysophyte cysts. Early settlement activities are marked by qualitative changes in the flora and small increases in microfossil flux. Events associated with the Ambrosia horizon produced a rapid transition from assemblages characteristic of oligotrophy environments to those characteristic of eutrophic waters and a large increase in microfossil flux. This was followed by a period of decreasing siliceous microfossil flux and reestablishment of less eutrophic species ca. 1853–61. Minimum siliceous algal microfossil flux and highly atypical assemblages occurred in the period ca. 1879–88, which corresponds to the period of intensive mining activities in the Bay of Quinte watershed. Maximum flux of siliceous microfossils occurred ca. 1900 and declined thereafter, although composition of assemblages deposited indicates increasing eutrophy and displacement of summer-blooming species. We interpret this as evidence of beginning of summer silica limitation. Based on microfossil evidence, the modern eutrophic flora of the bay was established by 1928.