Schweizerische Zeitschrift für Hydrologie

Synechococcus virga-rosea n. sp. andSynechococcus rubescens n. sp. were described in this study.

Photodamage of photosynthesis arises from oxidative damage. One of the protective mechanisms is to convert excessive absorbed energy into thermal radiation. Another mechanism could be to strengthen the antioxidative capacity of plants and algae. Selenium is important in antioxidation in humans and may play a role in antioxidative mechanisms in plants. The aim of this investigation was to study the role of selenium in "light-enhanced dark respiration" (LEDR) and photosynthesis in the flagellate Euglena gracilis, after exposure to ultraviolet radiation (UV-radiation). Selenium was added into the growth medium at different concentrations of selenite (10-7, 10-8, 10-9 and 10-10 M, Na2SeO3· 5H2O). E. gracilis were given six different light pulses with a photon fluence rate of 59, 163, 600, 1180, 2080 and 3340 μmol m-2 s-1 and periods of darkness between the light pulses. Photosynthetic saturation occurred at irradiances higher than 600 μmol m-2 s-1 and at the highest irradiance the photosynthetic rate decreased due to photoinhibition. Without any exposure to UV-radiation (UV-A, 320-400 nm, of 1.02 W m-2 plus UV-B, 280-320 nm, of 0.73 W m-2) LEDR increased with increasing photon fluence rate. After 40 min exposure to UV-radiation, photosynthetic rate and LEDR as functions of photon fluence rate were reduced. Neither in control (no UV-radiation) or when measured immediately after exposure to UV-radiation selenium had no stimulating effects on photosynthesis and LEDR. However, after UV-treatment and 24 h of recovery the presence of selenium led to an increase in photosynthesis and LEDR at higher irradiances. The results indicates that selenium might play a role in the repair mechanisms in E. gracilis after UV treatments.

The Velikaya River is the principal river flowing into the southern part of Lake Peipus, which is situated in the basin of the Gulf of Finland, an arm of the Baltic Sea. Lake Peipus is one of the largest and most productive freshwater bodies in Europe. An important population center in ancient Russia, the town of Pskov sits on the downstream part of the Velikaya. Here fisheries resources have been exploited for millennia. Local archaeological materials and historical documents provide unique opportunities for examining the historical ecology of this river and lake ecosystem. This study describes millennium-long changes in fish populations in the Velikaya River and Lake Peipus and discovers the factors responsible for them. We analyzed 5,981 fish remains dating from the 4th to the 18th centuries collected at two archaeological sites in Pskov and its surroundings. During this 1500-year period, three species predominated: pike, perch and bream together composed about three-quarters of identified bone elements. Fish sizes estimated from bone remains showed that target species, particularly bream and perch, tended to be larger before 1800 than in 20th century landings. Catch composition also changed over this long period, with increased contribution from smaller species such as whitebait, ruffe and vendace, especially in the 20th century. The main driver of the observed changes was fishing, with other human-induced factors and climate change being less important.

The mechanisms behind phytoplankton diversity patterns in natural ecosystems still remain elusive. In two shallow lakes with contrasting river connectivity, we first explored how diversity within each sampling (alfa diversity, α), among samplings (beta diversity, β1), and among hydrological seasons (β2) contributed to the diversity registered throughout the whole year (gamma diversity, γ). Then we estimated the importance of several environmental and temporal factors as structuring factors of these diversity patterns. To do this, we sampled the two lakes—one laterally isolated and other laterally connected lake with the Paraná River System—during a complete hydrological year. For the analyses, we considered both the species and the functional group level. At the species level, temporal variation (β1 + β2) made the main contribution for gamma diversity at the connected lake, possibly related to the constant species input from the river system. For the isolated lake, however, α was the main contributor. Regarding functional groups, α was the most important for both lakes, although no element of gamma diversity was different from the null model. Environmental factors like conductivity, turbidity, nutrient availability, and flood phases appeared as more relevant for the connected lake. Temporal processes (e.g., succession, ecological drift) were critical for the observed diversity patterns in both lakes. These results were consistent particularly considering the taxonomical approach. Our main findings are that the environment influences phytoplankton diversity patterns; however, other dynamics occurring on temporal scales may be more relevant for the phytoplankton community.

A study of the thermal regime of the Lower Ardeche River was carried out from July 1982 to December 1984 using a chemical method (sucrose inversion) and a continuous temperature recorder. Yearly, monthly and daily temperature fluctuations were analyzed. The main factors that influence thermal variations are air temperature and geomorphology of the canyon. The hydrological regime is responsible of the water temperature fluctuations between years Despite the low winter temperatures, the Lower Ardeche can be classified among Mediterranean rivers, which typically have a very high maximum in summer.

In the original publication, the incorrect GIS map projection was used to calculate lake surface areas and catchment areas that were presented