Global Change Abstracts The Swiss Contribution - SCNAT

Global Change Abstracts – The Swiss Contribution | Oceans and Fresh Water Systems
from the source. Using non-metric multidimensional
scaling and analysis of similarities, we detected
significant differences between the macroinvertebrate
assemblages of the investigated
sections in all spring ecosystems, even over short
distances. These results stress the importance of
distinguishing between the sequential habitats in
this upper region of headwaters. Although a complex
of abiotic factors is responsible for the distribution
of macroinvertebrates, we consider temperature
to be of special importance. Based on our
faunistic data, we propose that the rheocrene-like
springs in the Jura Mountains consist of two sections:
the springhead and the springbrook, with
the springhead consisting of the source and the
upper part of the adjacent downstream section.
In accordance with literature and our faunistic
and temperature data, we place the beginning of
the springbrook at approximately 5 m from the
springhead. With this distinction, we justify that
springheads and springbrooks are unique, discrete
ecosystems, and as such must be considered
in conservation legislation.
Fundamental and Applied Limnology, 2007, V169,
N1, pp 37-48.
08.1-283
Nitrate-depleted conditions on the increase in
shallow northern European lakes
Weyhenmeyer G A, Jeppesen E, Adrian R, Arvola
L, Blenckner T, Jankowski T, Jennings E, Noges P,
Noges T, Straile D
Sweden, Denmark, Germany, Finland, Switzerland,
Ireland, Italy, Estonia
Limnology , Geochemistry & Geophysics , Marine &
Freshwater Biology
We determined relative nitrate-nitrogen (NO 3- N)
loss rates in 100 north-mid-European lakes from
late spring to summer by using the exponential
function N-2 5 N-1e(-k)((t)(2) - (t)(2)), where N-1 and
N-2 are NO 3- N concentrations at the beginning
(t(1)) and the end (t (2)) of the time interval, respectively,
and k is the specific NO 3- N loss rate. We
found that k decreased with increasing lake depth.
Adjusting k to the lake depth (k(adj)), we observed
that k(adj) was positively related to spring NO 3-N
concentrations, but this relationship became insignificant
at mean lake depths exceeding 12.5 m.
A relationship between k(adj) and spring NO 3-N
concentrations in lakes shallower than 12.5 m implies
that changes in spring NO 3-N concentrations
influence the NO 3- N loss rate and thereby summer
NO 3- N concentrations. Time series from one
Estonian, one German, and 14 Swedish lakes shallower
than 12.5 m since 1988 revealed that May
to August NO 3- N concentrations have decreased
145
over time everywhere, and the number of time periods
exhibiting a NO 3- N depleted condition, i.e.,
NO3-N levels below 10 µ g L-1, in these lakes has
tripled since 1988. We explained the decreasing
NO 3- N concentrations by a reduction in external
nitrogen loading including atmospheric deposition,
and by changes in climate. The observed prolongation
of NO 3- N depleted conditions might be
one possible explanation for the increasing occurrence
of nitrogen- fixing cyanobacteria in a variety
of lake ecosystems.
Limnology and Oceanography, 2007, V52, N4, JUL,
pp 1346-1353.
08.1-284
Differential decline and recovery of haplochromine
trophic groups in the Mwanza Gulf
of Lake Victoria
Witte F, Wanink J H, Kishe Machumu M, Mkumbo
O C, Goudswaard P C, Seehausen O
Netherlands, Tanzania, Switzerland
Marine & Freshwater Biology , Biodiversity , Ecology
Zoology
Lake Victoria had a fish fauna dominated by 500+
species of haplochromine cichlids that made up
more than 80% of the fish mass. The five main
trophic groups caught with bottom trawlers in
the sub- littoral areas of the Mwanza Gulf were:
detritivores, zooplanktivores, insectivores, molluscivores
and piscivores. The detritivores (13+
species) formed the most important guild, making
up 60-80% of the number of individuals, followed
by the zooplanktivores (12+ species), which
comprised 10-30%. In the 1980s the haplochromines
from the sub-littoral and offshore areas (estimated
at some 200 species) vanished almost completely.
Commercial trawl fishery, the upsurge
of the introduced Nile perch, and an increase of
eutrophication were potential causes of this decline.
In the 1990s, when Nile perch was heavily
fished, a recovery of some haplochromine species
was observed. We studied the decline and partial
recovery of the different haplochromine trophic
groups in the northern part of the Mwanza Gulf.
The rate at which the trophic groups declined differed;
the relatively large piscivores, insectivores
and molluscivores were the first to disappear from
the catches. The small detritivores and zooplanktivores
declined at lower rates, especially the latter
group. From the beginning of the 1990s a resurgence
of both groups was observed. By 2001,
the zooplanktivores had reached their previous
level of abundance, but their diversity declined
from more than 12 species to only three. Though
four detritivorous species began being regularly
caught again, they constituted only about 15% of