Diversity patterns of trait-based phytoplankton functional groups in two basins of a large, shallow lake (Lake Balaton, Hungary) with different trophic state

The application of functional approaches in understanding phytoplankton community-level responses to changes in the environment has become increasingly widespread in recent years. Eutrophication is known to cause profound modifications in ecosystem processes, however, the underlying relationships between environmental drivers and phytoplankton diversity and functioning are complex and largely unknown. Therefore, in the present study we investigated and compared the temporal diversity patterns of phytoplankton functional groups in the mesotrophic eastern and eutrophic western basin of the shallow Lake Balaton situated in Hungary. Diversity data were derived from taxonomic composition and biomass data corresponding to the years 2005-2006 and 2008-2009. With the use of cluster analysis phytoplankton species were classified into eight distinct groups representing different combinations of functionally relevant traits including greatest axial linear dimension, surface to volume ratio, photosynthetic pigment composition, N2-fixation, phagotrophic potential, growth form/complexity (unicell, filamentous, colony- or coenobiumforming) and motility. Our results have revealed that there is a significant inverse relationship between the functional group diversity used in our study and trophic state (total phytoplankton biomass) as opposed to species diversity, where no correlation was observed. In addition, group evenness showed an even stronger negative correlation with trophic state, while species evenness yielded only a weak relationship. The observed variability in functional group diversity suggests that such an approach could provide an efficient means of revealing structural changes in phytoplankton communities, establishing new hypotheses and highlighting fundamental points in ecosystem functioning

Társadalmi konfliktusokat generáló ökológiai történések a Balaton életében az utóbbi néhány évtizedben - A vízszintváltozás hatása a parti öv növényvilágára | Social Conflict Generating Ecological Developments in the Life of Lake Balaton in Recent Decades – Effect of water level fluctuation on the plants of the littoral zone

While the Hungarian public was primarily concerned with the water quality of Lake Balaton in the 1980s and 1990s, low water levels and their environmental effects became the focus of public attention in 2002, 2003 as well as 2012. Accurate and reliable monthly and yearly data about the water balance of Lake Balaton has been available since 1921. The amounts of water getting into the lake from the catchment area have been considerably less than average in nine percent of the period between 2001 and 2012; the water in the catchment area became scarce and the water levels of the lake notably decreased during the drier than average years of 2001-2004 and 2012. Cladophora glomerata (filamentous green alga) appeared in large quantities in the shallow waters of the south shore in the summer of 2002, 2003 as well as 2012. It is not a new phenomenon: the first documented Cladophora explosion in Lake Bala-ton was in 1934. Scientists at the Balaton Limnological Institute (Center for Ecologi-cal Research of the Hungarian Academy of Sciences) studied the Cladophora vegetation of the south shore in July 2003. They found that excessive Cladophora growth—harming tourism with its gooey green mats and rotting muck—appeared where the water depth was lower than 30 cm. This explosion, however, is not a consequence of water pollution but an unavoidable consequence of the low water levels. The results show that the photosynthetical apparatus of the main submerged macrophyte species have adapted to the semi-dark waters of Lake Balaton. The photosynthetical parameters of submerged macrophytes indicate that they can survive and disperse in parts of the lake where the water is no deeper than 2.2-2.3 m. It means that the area suitable for the establishment of submerged macrophytes increases by 60 percent with a 50 cm decrease in the water levels, while a 100 cm decrease means a threefold increase in the size of the area favourable for submerged macrophytes. The decrease in water levels contribute considerably to the spread of reed. This is due the increase in drier areas suitable for sexual reproduction on the one hand and to the oxidation of sediment on the other. The emerging of a reed-covered area out of the water—even if for a short period—contributes considerably to the prevention of reed decline. The artificial stabilization of the water levels in the past fifty years has greatly contributed to the slow degradation of the flora in the littoral zone. At the same time, the low water levels of the past decade have shown that low water levels do not damage the macrophyte populations of Lake Balaton

Extraction methods for phycocyanin determination in freshwater filamentous cyanobacteria and their application in a shallow lake

Phycocyanin (PC) is one of the water-soluble accessory pigments of cyanobacteria species, and its concentration in aquatic systems is used to estimate the presence and relative abundance of blue-green algae. PC concentration and the PC/Chl-a ratio of four N2-fixing filamentous cyanobacteria strains (Cylindrospermopsis raciborskii, Anabaena spiroides, Aphanizomenon flos-aquae and Aphanizomenon issatschenkoi) common to Lake Balaton (Hungary) were determined using repeated freezing and thawing. A strong linear correlation was found between the extracted PC and Chl-a concentrations for all strains at high Chl-a concentrations (almost stable PC/Chl-a ratio in the range of 20−100 µg l−1 Chl-a). Extraction of PC and Chl-a from samples with low biomass of cyanobacteria (less than 20 µg l−1 Chl-a) proved to be unreliable using the standard protocol of freeze–thaw cycles (coefficients of variation exceeding 10–15%). In order to find an extraction method that is robust in fresh waters characterized by low algae biomass (e.g. Lake Balaton), the effectiveness of four extraction methods (repeated freeze–thaw method and homogenization with mortar and pestle, Ultrasonic, and Polytron homogenizer) were compared using C. raciborskii. It was found that the efficiency of extraction of phycocyanin was highest when a single freeze–thaw cycle was followed by sonication (25% additional yield compared with using the freeze–thaw method alone). Applying this combined method to surface water samples of Lake Balaton, a strong correlation was found between PC concentration and cyanobacterial biomass (R 2 = 0.9436), whilst the repeated freezing–thawing method found no detectable PC content. Here we show that the combined sonication/freeze–thaw method could be suitable for measuring filamentous cyanobacteria PC content, even at low concentrations; as well as for the estimation of cyanobacterial contribution to total biomass in fresh waters

Missing observations in ARIMA models: skipping strategy versus additive outlier approach

Optimal estimation of missing values in ARMA models is typically performed by using the Kalman Filter for likelihood evaluation, "skipping" in the computations the missing observations, obtaining the maximum likelihood (ML) estimators of the model parameters, and using some smoothing algorithm. The same type of procedure has been extended to nonstationary ARIMA models in G6mez Maravall (1994). An alternative procedure suggests filling in the holes in the series with arbitrary values and then performing ML estimation of the ARIMA model with Additive Outliers (AO). When the model parameters are not known the two methods differ, since the AO likelihood is affected by the arbitrary values. We develop the proper likelihood for the AO approach in the general non-stationary case and show the equivalence of this and the skipping method. Computationally efficient ways to apply both procedures, based on an Augmented Kalman Filter, are detailed. Finally, the two methods are compared through simulation, and their relative advantages assessed; the comparison also includes the AO method with the uncorrected likelihood