 |
| Titel |
The effect of flow reduction on microphytobenthos development in an alpine river stretch using novel fluorescence techniques |
| VerfasserIn |
A. Ganglbauer, E. Bondar-Kunze, T. Hein, B. Zeiringer |
| Konferenz |
EGU General Assembly 2009
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250030939
|
|
|
|
|
|
| Zusammenfassung |
| Many European river systems are affected by flow alterations leading to significant
differences of the pristine discharge regime at different temporal scales. Flow regulation
measures and water abstraction are changing the extent and frequency of water level changes.
In concert with river bed regulation this could affect the hydromorphological situation of river
systems and key ecosystem functions.
Microphytobenthos is a major component in the physical, chemical and biochemical
processes, which occur in river systems and the associated riparian zones. They are
significant primary producers in rivers, because of their high turnover rate, rapid colonization
along the aquatic-terrestrial boundary, transform nutrients and support via their biomass the
food webs in the river and adjacent ecosystems. The developed structure and composition of
microphytobenthos is controlled by the hydromorphological conditions and thus, indicates
environmental changes. The guiding question for the presented research was to what extent
changes in the variability of flow affect microphytobenthos development in a river stretch and
to what extent the structure and composition of microphytobenthos changed at the micro
scale.
To investigate these effects under natural conditions we compared a residual flow
section impacted by a hydropower plant with one unaffected section of the River
Ybbs, a tributary to the Danube River. The river stretch investigated was a 33 km
long stretch between the villages Göstling and Opponitz in Lower Austria. The
River Ybbs is draining a catchment of 1,300 km2 and has a mean discharge of
20 m3 s-1.The main benthic algal group are diatoms, which are typical for low
order rivers in the Alpine area, characterized by low temperatures throughout the
year.
We expected that flow velocity explain the extent of microphytobenthos development at the
river stretch scale and especially low flow conditions affect the structure and composition of
algal biomass at the micro scale.
The measurements included field surveys and two experimental settings. During May 2008
we conducted an in-situ experiment with artificial substrata to investigate the effect of flow
velocity changes. We exposed glass slides in baskets along two transects in the River Ybbs at
two sampling sites and eight different positions. After a period of about four weeks with
weekly recurrent measurements including flow velocity, water depth, chlorophyll a content
and electron transport rate (ETR) we started our experiment. Glass slides were
taken from each position and were exposed in a flow reduced impounded area in the
river Ybbs near Göstling. There low flow velocity was used to test the effect on
microphytobenthos development. The next ten days daily measurements of flow
velocity, water depth, chlorophyll-a content and electron transport rate (ETR) with the
pulse amplitude modulated fluorescence method and microscopic analysis were
undertaken. Based on these daily measurements under almost stable environmental
conditions we could ascertain a shift in the benthic algae community. To assess the
distribution along a river stretch we measured 70 sampling points at each sampling
side.
To characterize the biomass and activity of the microphytobenthos we used Pulse Amplitude
Modulated Fluorescence (PAM-Fluorescence). Using this technique allow to measure the
biomass (Chlorophyll a) and the ETR (electron transport rate) simultaneously without
destroying the structure. With this technique it is possible to The PAM technique measure
directly the fluorescence of chlorophyll a in the photosystem two. The quantum
yield you get is the probability that a photon can be used photochemically. The
quantum yield offers the possibility to illustrate the fitness of algae. Based on these
measurements short term responses can be measured and combined with the results of field
surveys.
These analytical results were used for a habitat modelling approach to describe the
microphytobenthos development at 2 scales. First results of the research will be
presented. |
|
|
|
|
|
|