Global Change Abstracts The Swiss Contribution - SCNAT

Global Change Abstracts – The Swiss Contribution | Oceans and Fresh Water Systems
of dissolved seawater Cd by phytoplankton. A
few samples do not follow this trend, as they exhibit
extremely low Cd contents (= 900 in depth, despite of Cd concentrations
that display the expected increase along
the global deep-water pathway from the Atlantic
(similar to 0.3 nmol/kg) to the Pacific Ocean (similar
to 0.9 nmol /kg). This indicates that the biomass,
which is remineralized in the deeper ocean,
is also characterized by a very constant Cd isotope
composition. This observation is in accord with
the interpretation that the Cd distribution in
surface waters is primarily governed by Rayleigh
fractionation during near-quantitative uptake of
dissolved seawater Cd.
Earth and Planetary Science Letters, 2007, V261,
N3-4, SEP 30, pp 670-684.
08.1-273
Density-dependent life history differences in
a stream mayfly (Deleatidium) inhabiting permanent
and intermittent stream reaches
Robinson C T, Buser T
Switzerland
Marine & Freshwater Biology , Ecology , Zoology
A life-history response by the mayfly Deleatidium
(Ephemeroptera: Leptophlebiidae) from a permanent-fl
owing and an intermittent- flowing reach
of the Selwyn River, New Zealand, to failing water
conditions was examined using field populations
and laboratory experiments in January 2006.
Field populations had similar densities under
flowing water conditions, but size distributions
were skewed towards larger larvae in the intermittent
reach relative to the permanent reach. Under
field conditions of falling water at the intermittent
reach, more larvae were caught in the drift
during the day and more adults at dusk at the
intermittent than at the permanent reach. A desiccation
study in the laboratory showed that larvae
survived up to 3 days under moist conditions,
whereas larvae died within 3 h under dry conditions.
Another laboratory experiment revealed
that both populations increased emergence under
falling water in the high density treatment
but not in the ambient density treatment. We
conclude that a density increase caused by falling
water cues late instar larvae to hasten emergence,
141
an adaptive trait that may reduce population
mortality from stream drying.
New Zealand Journal of Marine and Freshwater
Research, 2007, V41, N3, SEP, pp 265-271.
08.1-274
Macroinvertebrate assemblages of a high elevation
stream/lake network with an emphasis
on the Chironomidae
Robinson C T, Hieber M, Wenzelides V, Lods Crozet B
Switzerland
Limnology , Marine & Freshwater Biology ,
Hydrology , Zoology
Macroinvertebrate assemblages of inlet and outlet
streams were examined in a high elevation cirque
comprising two basins in the Swiss Alps. Average
taxon richness, with chironomids included as a
single taxon, was < 8 at most sites. Chironomids
represented between 26 and 85 % of the individuals
and at least 50 % of the species collected at the
different sites with over 22 chironomid species
identified in total. No differences in the relative
abundance of common macroinvertebrate taxa
were found between inlet and outlet streams,
but composition differed between the north and
south basin of the cirque. The north basin was
mostly fed by groundwater and snowmelt, whereas
the south basin was dominated by glacier-melt
from rock glaciers. Chironomids were 26 % more
abundant and had more species in south basin
than north basin streams, whereas the simuliid
Prosimulium latimucro was 24 % more abundant
in north basin streams. Other common taxa, e.g.,
Nemoura sp., Dicranota sp., Crenobia alpina and
Pseudopsilopteryx zimmeri, also showed substantial
differences in abundance between the two
basins. Diamesinae and Orthocladiinae were the
most common chironomid subfamilies collected
with Diamesa zernyilcinerella, Pseudodianiesa
branickii, Pseudodiamesa arctica, Corynoneura
scutellata, and Tvetenia calvescens together representing
on average > 10 % of the assemblage at
most sites. Chironomid abundance typically was
higher in outlets than inlets. An exception was Diamesa
zernyilcinerella, which had greater relative
abundances in inlets (24 %) than outlets (6 %). The
results suggest that alpine macroinvertebrates,
chironomids in particular, are sensitive to subtle
differences in habitat conditions and may thus
make good sentinels of environmental change to
alpine waters.
Fundamental and Applied Limnology, 2007, V169,
N1, pp 25-36.