Distribution of phytoplankton in a German lowland river in relation to environmental factors
In comparison to lentic systems, the species composition and community structure of phytoplankton in lotic habitats are still poorly understood. We investigated the spatial and temporal dynamics of the phytoplankton community in a German lowland river, the Kielstau catchment, and the relationships with environmental variables. Among the 125 taxa observed, Desmodesmus communis, Pediastrum duplex and Discostella steligera were dominant species at lentic sites while Tabellaria flocculosa, Euglena sp., Planothidium lanceolatum, Cocconeis placentula and Fragilaria biceps dominated at lotic sites. Remarkable spatial and temporal variations of the phytoplankton community were revealed by non-metric multidimensional scaling. Canonical correspondence analysis indicated that physical factors (e.g. hydrological variables) and major nutrients [e.g. total phosphorus, dissolved inorganic nitrogen (DIN)] were of equal importance controlling the variation in structure of riverine phytoplankton assemblages. Weighted averaging regression and cross-calibration produced strong models for predicting DIN, water temperature (WT) and total suspended solid (TSS), which enabled the selection of algal taxa as potentially sensitive indicators: for DIN, Ulnaria ulna var. acus, U. ulna, D. communis and Euglena sp.; for WT: D. steligera, Scenedesmus dimorphus, D. communis and Euglena sp.; for TSS, Nitzschia sigmoidea, D. communis and Oscillatoria sp. The results from this relatively small survey indicate the need for further monitoring to gain a better understanding of riverine phytoplankton and to capitalize on the environmental indicator capacity of the phytoplankton community. doi:10.1093/plankt/fbq139, available online at www.plankt.oxfordjournals.org. Advance Access publication November 9, 2010 # The Author 2010. Published by Oxford University Press. All rights reserved. For permissions, please email:
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I N T R O D U C T I O N
Phytoplankton have been studied extensively in lentic
fresh waters (lakes and reservoirs) where long residence
time and low flow velocity allow sufficient time for
growth and reproduction (e.g. Basu and Pick, 1997;
Sabater et al., 2008; Torremorell et al., 2009). However,
in comparison to lentic systems, the species
composition and community structure of phytoplankton in
lotic systems (streams and rivers) are still poorly
understood (Basu and Pick, 1996; Piirsoo et al., 2008). The
spatial and temporal pattern of a community are of
crucial importance for understanding ecosystem
functioning because they can affect ecosystem processes,
functioning and stability and reflect major shifts in
environmental conditions (Suikkanen et al., 2007; Zhou
et al., 2009a).
Distribution patterns of phytoplankton are strongly
correlated with environmental factors (Lepisto et al.,
2004). Possible factors may be physical [climate, water
temperature (WT), light intensity], chemical (nutrient
concentrations) (Reynolds et al., 1993; Torremorell et al.,
2009), hydrological (river morphology, discharge, water
residence time, precipitation) (Descy and Gosselain,
1994; Kiss et al., 1994; Skidmore et al., 1998) and biotic
(grazing, competition, parasitism) (Moss and Balls,
1989; Ha et al., 1998). Unfortunately, there is no general
consensus as to which factors regulate phytoplankton
communities in lotic habitats (Basu and Pick, 1995).
Besides, contributions of the main environmental
factors to phytoplankton variations are also unclear. For
example, hydrological factors are thought to be of
greater importance to planktonic development in rivers
than in lakes (Pace et al., 1992), whereas other
researchers concluded that river phytoplankton is more strongly
regulated by nutrient concentrations, such as total
phosphorus concentration (Soballe and Kimmel, 1987;
Moss and Balls, 1989; Basu and Pick, 1996; Van
Nieuwenhuyse and Jones, 1996). The response of
phytoplankton to environmental factors has become a central
topic of current research (Buric et al., 2007), and
identification of the main factors controlling phytoplankton in
a particular water body is essential for choosing an
appropriate management strategy for the maintenance
of a desired ecosystem state (Peretyatko et al., 2007).
Lowland rivers, characterized by specific properties,
such as low hydraulic gradients, shallow groundwater
and high potential for water retention in peatland and
lakes (Schmalz and Fohrer, 2010), are apparently
different from the habitats of lakes and mountain streams.
Until now, studies of phytoplankton communities in
lowland rivers, to our knowledge, are still scanty. In this
paper, we investigated the spatio-temporal variation of
the phytoplankton community and environmental
variables over a 1-year period (November 2008 August
2009) throughout a lowland river ecosystem in northern
Germany. The objectives of this study were to: (i)
describe the distribution patterns in the species
composition and biomass of phytoplankton in the Kielstau
catchment; (ii) stu (...truncated)