Die Ablaich- und Interstitialphase der Äsche (Thymallus thymallus L.) - Grundlagen und Auswirkungen anthropogener Belastungen -
Loading...
Files
Date
Authors
Publisher
Philipps-Universität Marburg
Supervisors
Abstract
The present study deals with the spawning and
intragravel period of the grayling (Thymallus thymallus L.)
-basics and anthropogenic influences- in a river with high
nutient load. In the River Lahn, a right-bank tributary of the
River Rhine in Germany, the number and structure of spawning
sites in three different river sections were noticed, the
spawning behaviour was observed and the number of swim-up-fry
was counted from 1995 to 1999. In two consecutive years with
different discharge (1996 and 1997) substrate samples were
taken at each spawning ground, oven-dried and sorted through
sieves from > 63 mm to < 0.063 mm according to standard
procedures. For the assessment of interstitial water
conditions, a multilevel tube-sample-system was buried at
natural spawning grounds. The pore water was extracted
simultaneously from three sediments depth (10, 20 and 30 cm)
and analysed for O2, CO2, alkalinity, NO3-N, NO2-N, NH4-N,
NH3-N, o-PO4-P, pH-value, temperature and conductivity.The
influence of different nutrient loads to the developing eggs
and larvae of the grayling was studied in the reach of an
waste-water-treatment plant (wwtp) effluent. Exposition boxes
with grayling eggs were buried into the sediment at three study
sites with different nutrient load. Simultaneously a
multilevel-tube-system was placed in the sediment.Daily
variations of temperature, oxygen concentration, pH-value,
turbidity and conductivity were registered every 5-minutes in
the surface water and recorded on computer. These data were
used to model the daily variations of the corresponding
parameters in the interstitial water. The exposition boxes were
retrieved at three different developing stages of the grayling
(eyed-eggs, hatching and emergence). The mortality of the eggs
and larvae was noticed and morphometric parameters were
measured using a dissecting microscope. In the River Lahn, the
spawning migration of the grayling took place at the beginning
of April. Male grayling defended rectangular-shaped territories
of 4.5 to 8 m². The spawning act started in the afternoon when
water temerature reached 8°C. The grayling used shallow areas
(mean water depth 41 cm) with a mean current velocity of 61
cm/s at the surface and 34 cm/s at the bottom of spawning.
Between spawning acts grayling rested in pools at the river
banks that were covered by overhanging branches and roots. The
Spawning areas were characterized by a gravely substrate. It
consisted mainly of coarse pebble (particle size 20-63 mm:
30-50%), some bigger stones (> 63 mm: 3-35 %) and coarse
gravel (6.3-20 mm: 14-30%). The percentage of fines (< 2 mm)
was low at all three spawning sites (5.3-12.3%). The duration
of the embryonic incubation period depended on water
temperature. The average incubation period lasted 156.3 day
degrees (16.9 days at 9.25 °C). The limiting factors of the egg
and larval period of the grayling in the River Lahn were
ammonia concentration and the percentage of fines in the
interstitial. At the obsevation field with the highest nutrient
load ammonia concentration reached a maximum value of 108 µg/l
NH3-N in the pre-hatch period and 52 µg/l NH3-N in the
post-hatch period. Not a single larvae survived in this
observation field until the end of the study. A toxic threshold
of 25 µg/l NH3-N is discussed for the post-hatch period. The
amount of alevins was significantly correlated with the
percentage of fines (particle size < 2 mm) at the natural
spawning grounds. The maximum percentage of fines at a natural
spawning ground was 23.7%. This high amount of fines was caused
by missing scouring of the interstitial due to the absence of a
flood in winter 1996. Consecutively the ammount of alevins was
reduced to the half compared to the corresponding value of the
year with winter flood. The water pH at natural spawning
grounds (sediment depth of 10 cm) was in the range of 8 to 8.9.
At observation fields a maximum pH of 9.9 was modelled for a
sediment depth of 10 cm. The pH of the surface water showed
great daily variations from 7.3 to 9.9 with maxima in the
afternoon. These maxima were caused by the increased
photosythetic activity of the algae, the growth of which was
strongly increased by the high nutrient load of the River Lahn.
Another result of the increased photosynthetic activity was the
high oxygen content of the surface water and interstitial water
at day time which ranged from 11.2 mg/l to 16.5 mg/l O2 and
11.7 mg/l to 15 mg/l O2 (sediment depth: 10 cm), respectively.
The dissolved oxygen levels always exeeded the saturation curve
at day time. At night time the respiration of the algea and
biofilm led to oxygen consumption. Values as low as 5.9 mg/l O2
were recorded at night time in the surface
water.
Review
Metadata
Contributors
Supervisor:
Dates
Created: 2003Issued: 2004-05-19Updated: 2011-08-10
Faculty
Fachbereich Biologie
Publisher
Philipps-Universität Marburg
Language
ger
Data types
DoctoralThesis
Keywords
eutrophicationintergravel stagegraylingLaichsubstratspawninglarvaepHalevinsubAbwasser , Thymallus thymallus ,dischargespawning sitepHsewagehabitatammonia
DFG-subjects
ÄscheHochwasser / AbflussLaichplatzAmmoniakHyporheisches InterstitialEutrophierungTLaichenLarve , HabitatKläranlage
DDC-Numbers
570
show more
Hübner, Dirk: Die Ablaich- und Interstitialphase der Äsche (Thymallus thymallus L.) - Grundlagen und Auswirkungen anthropogener Belastungen -. : Philipps-Universität Marburg 2004-05-19. DOI: https://doi.org/10.17192/z2004.0286.
License
This item has been published with the following license: In Copyright