Differential response of blue-green algal groups to phosphorus load reduction in a large shallow lake: Balaton, Hungary

Lake Balaton is the largest shallow lake in Central Europe. The elongated lake (length 77,9 km; average width: 7,2 km) has a surface area of 593 km(2), and has a mean depth of 3,14 m (maximum: 11m). The theoretical retention time is 3-8 years. The catchment area of the lake is 5182 km(2), the Zala River itself drains an area of 2622 km(2). As a result of the increased phosphorous load, the originally mesotrophic lake underwent rapid eutrophication in the 1960s-1970s (Herodek 1984). Between 1975 and 1981, the total P load was estimated as 2,47 g m(-2) year(-1) in the western part of the lake, and 0,31 g m(-2) year(-1) in the eastern part (Somlyódy and Jolánkai 1986). As a consequence of the morphometric and loading conditions, a sharp trophic gradient has developed in the lake. In the early 1980s, a large-scale eutrophication management program was started (Istvánovics et al. in press). So far, the program has resulted in about 30% reduction of the biologically available P (BAP) load of the lake. This load reduction was expected to reduce slightly the phytoplankton development in the lake (Herodek 1984). This paper describes phytoplankton changes between 1989 and 1994 in two basins of the lake (siófok Basin and Keszthely Basin) that are different in their trophic status. Special attention will be paid to Cylindrospermopsis raciborskii, a bloom-forming subtropical blue-green alga

Áramlási holtterek eloszlása és ökológiai jelentősége a Tisza magyar szakaszán = Distribution and ecological significance of aggregated dead zones along the Hungarian section of River Tise

A Tisza magyar szakaszán a fitoplankton biomasszáját és összetételét alapvetően a Szamos fitoplanktonja határozza meg. A Tisza heterogén, ám szokatlanul mély medrében az áramlási holtterek hatása jelentéktelen. A tiszalöki és a kiskörei duzzasztás miatt lelassuló vízből a kovaalgák kiülepednek, az óriási kiterjedésű holttérként funkcionáló Tisza-tóból bemosódó Cryptophyta és zöldalgák ezt a biomassza veszteséget nem tudják pótolni. Az áramlási holtterek akkor tudják jelentősen befolyásolni a folyó fitoplanktonját, ha az aljzatra ülepedő algák számára elegendő fény áll rendelkezésre a fotoszintézishez. Ilyen viszonyok jellemzőek a Szamos romániai szakaszára - és feltevésünk szerint számos olyan nagy folyóra - melynek kisvízi medrét nem szabályozták. A sekély áramlási holtterekben a kiülepedés - felkeveredés - kiülepedés spirálja révén sokszorosára növekszik az algák tartózkodási ideje a vízhez képest. Ez a mechanizmus a nagyobb méretű, gyorsabban ülepedő fajokat részesíti előnyben. A hazai vízfolyásokon általánosságban is igazoltuk, hogy a fitoplankton bioamasszáját nem a tápanyag ellátottság, hanem a tartózkodási idő határozza meg. Ezért a tápanyag kibocsátás csökkentése önmagában nem hatékony beavatkozás a vízfolyások ökológiai állapotának javítására. A vízhálózat fitoplankton szempontból vett topológiai viszonyai azonban lehetnek olyanok, hogy a tápanyagterhelésen keresztül csökkenthessük a hálózat algatermő képességét. | The import of algae from the Szamos River is the major determinant of the biomass and composition of phytoplankton along the Hungarian Tisza River (from rkm 686 to rkm 177). The impact of aggregated dead zones is negligible in the highly heterogeneous but exceptionally deep channel of the latter. As a consequence of diminutive flow velocities upstream of the two dams (rkm 523 and 402), the dominant diatoms sediment rapidly. The mass export of crypto- and chlorophytes from the shallow floodplain complex created by Dam 2 (maximum area 104 km2) cannot compensate for the biomass loss. To significantly influence the dynamics of riverine phytoplankton, the bottom of dead zones must be illuminated and sustain photosynthesis by sedimented algae. Such shallows are characteristic of the Romanian Szamos and presumably of several large rivers that escaped regulation of their low water channel. Repeated sedimentations and resuspensions ensure manifold longer residence time for phytoplankton relative to water. The mechanism selectively favors larger cells that sediment faster. Statistical analysis of long-term water quality data from Hungarian running waters revealed that algal biomass was independent of nutrient availability and was related to water residence time. Consequently, emission control is an inefficient measure to improve the trophic status of streams and rivers, unless the topology of the whole fluvial network is considered with respect to phytoplankton growth

The Global Lake Ecological Observatory Network (GLEON): the evolution of grassroots network science

Nine years later, with over 380 members from 40 countries, and 50 publications to its credit, GLEON is growing at a rapid pace and pushing the boundaries of the practice of network science. GLEON is really three networks: a network of lakes, data, and peopl

Growth and phosphorus uptake of summer phytoplankton in Lake Erken (Sweden)

The thermal stratification in Lake Erken was short and relatively unstable in 1989. Changes in the species composition of the phytoplankton between early May and August followed the general succession pattern outlined for other temperate lakes. Fast-growing, r-strategist cryptophytes, dominant in the early phase of succession, could be separated sufficiently by 12 mu m membrane filters from larger K-strategists like Ceratium hirundinella and Gleootrichia echinulata which dominated in July. Under more turbulent conditions, the biomass of diatoms increased, and these species were also >12 mu m. Growth rates of the phytoplankton and those of the two size groups were sensitive to the species composition, but fitted reasonably to the Droop model. Long turnover times of orthophosphate in the water, the Phosphorus Deficiency Indicator defined here as the ratio of the light-saturated rate of photosynthesis and the conductivity coefficient of phosphate uptake, and relative growth rates generally indicated low P-deficiency. Moderate deficiency was observed in late July, towards the end of the stratification period. Steady-state net P-uptake rates were calculated from the Droop model and compared with instantaneous net P-uptake rates estimated from P-32 uptake kinetics by the linear force-flow relationship of Falkner et al. (Arch. Microbiol., 152, 353-361, 1989). The two data sets showed surprisingly similar seasonal trends. Depletion of epilimnetic soluble reactive phosphorus (SRP) resulted in enhanced utilization of intracellularly stored P. Such periods were, however, interrupted by elevated SRP inputs to the epilimnion that led to luxury P uptake and a low incidence of P deficiency

Coupling high frequency dissolved oxygen and chlorophyll fluorescence data for a robust estimation of lake metabolism parameters

Gross primary production (GPP) and community respiration (R) are increasingly calculated from high-frequency measurements of dissolved O2 (DO) by fitting dynamic metabolic models to the observed DO time series. Since different combinations of metabolic components result in the same DO time series, theoretical problems burden this inverse modeling approach. Bayesian parameter inference could improve identification of processes by including independent knowledge in the estimation procedure. This, however, requires model development, because parameters of existing metabolic models are too abstract to achieve a significant improvement. As algal biomass is a key determinant of GPP and R, and high-frequency data on phytoplankton biomass are increasingly available, coupling DO and biomass time series within a Bayesian framework has a high potential to support identification of individual metabolic components. We demonstrate this in three lakes where both high frequency DO and chlorophyll fluorescence data were available. Phytoplankton data were digested via a sequential Bayesian learning procedure coupled with an error model that accounted for systematic errors caused by structural deficiencies of the metabolic model. This method provided ecologically coherent and therefore presumably robust estimates for biomass-specific metabolic rates. This can contribute to a better understanding of metabolic responses to natural and anthropogenic changes