In book: Chironomids- From genes to ecosystems, Publisher: C.S.I.R.O., Canberra, Australia
Our objective is to elucidate the influence of oxygen on the spatial distribution of the benthic fauna in shallow waters. In this study, our attention was focussed on the Chironomidae that are abundant in our study site - a small euthrohic pond in Belgium. It is well known that oxygen controls the specific occurence and macrodistribution of chironomid larvae in standing waters (Heinis, 1993). However, it is unclear how the "respiratory environment" (Brundin, 1951) of these organisms is defined. Our study of the oxygen microstratification is intended to elucidate its significance for the vertical distribution of the chironomid larvae. Therefore, we have measured the oxygen concentration at several locations above and in the sediment as well as in the water column.
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"fine substrates) affect the benthic oxygen availability. Some genera belonging to this chironomid tribe observed in this study (Table 1) were associated with oxygen depletion processes in previous studies (Int Panis et al., 1995, 1996; Granados & Toro, 2000; Francis, 2001; Little & Smol, 2001; Brodersen & Quinlan, 2006). The second most relevant variable was temperature . "
[Show abstract][Hide abstract] ABSTRACT: The distribution of different macroinvertebrate
groups inhabiting the littoral zone of 82
mountain lakes in the Pyrenees was investigated in
relation to the altitudinal environmental gradient. For
each lake, altitude, longitude and latitude, together
with 28 environmental variables, relating to chemical
and physical characteristics and to lake general
productivity, were considered. Using Principal Component
Analysis (PCA) we showed that the altitudinal
environmental gradient (i.e. altitude and altituderelated
variables) represented the largest gradient of
environmental variability. We found that incidence
was related to altitude in about 50% of macroinvertebrate
groups, most relationships being inverse, and
also that the number of macroinvertebrate groups
found per lake was better described by a second-order
polynomial function than by simple linear regression.
However, this relationship was linear for a subset of
high-altitude lakes above 2,500 m a.s.l., suggesting
an ecological threshold around this altitude. Redundancy
Analyses (RDAs) showed the importance of
environmental factors varying with altitude for the distribution of macroinvertebrate groups. Organic
matter, salmonid presence, fine substrate dominance,
macrophyte coverage, temperature and altitude by
itself were, in this order, the most relevant factors.
Partial RDAs showed that different combinations of
these variables contributed to the explanation of the
distribution of each group. However, the variable that
uniquely explained most variability differed from
group to group. We conclude that the altitudinal
gradient is a multi-faceted ecological factor, which
impinges on each group by means of some specific
environmental variable(s) that are particularly
relevant for the life history of that group.
"A hand corer with an area of 40 cm 2 was used for quantitative sediment sampling . Four replicates were taken at each station, one of which was used for a microprofile measurement of sediment oxygen concentration (Int Panis et al., 1994a) . The three remaining cores from each station were horizontally sliced at depths of 1, 2, 3, 4, 5, 7 and 10 cm and subsequently fixed with neutralised formalin within 15 min after the sample was taken . "
[Show abstract][Hide abstract] ABSTRACT: Animals that dwell at different depths in the sediment, are adapted to different respiratory environments. It is possible that animals that occur deep in the sediment have a higher hemoglobin concentration than surface-dwelling animals. To test this hypothesis, hemoglobin concentrations and weights of eight chironomid species that dwell in the littoral zone were measured. High hemoglobin concentration and weight both seemed to contribute to an ability to cope with low oxygen concentrations, and determined the vertical distribution of chironomids in the sediment. A multiple regression equation, including these factors, was derived. It may be used to predict the median depth of occurrence for species that were not included in this study. High sensitivity of small animals to oxygen stress is discussed from a theoretical point of view.
[Show abstract][Hide abstract] ABSTRACT: Lake St. Croix is a natural impoundment located at the southern end of the St. Croix River. Land use changes since European settlement (c. 1850) have resulted in nutrient runoff, eutrophication, and periodic oxygen depletion in the hypolimnion of Lake St. Croix. Establishing sound lake management practices requires knowledge of historical conditions obtained through paleoecological studies. Remains of non-biting midges (Insecta: Diptera Chironomidae) in lake sediments have been shown to be reliable indicators of past hypolimnetic oxygen conditions. Cores from two sub-basins in the lake were collected in 2006. Midge analysis indicated that shifts in species assemblages correspond to the times of land use change. Chironomus and Procladius, which are tolerant of low oxygen levels, increased in relative abundance as land use changes adversely impacted the St. Croix River’s watershed. Volume-weighted hypolimnetic oxygen concentrations were estimated using a transfer function developed for southern Ontario. Mean post-settlement chironomid reconstructed average volume-weighted hypolimnetic oxygen values were 0.73 mg/L lower than mean pre-settlement values for sub-basin 1, near Prescott, WI and 0.45 mg/L lower for sub-basin 3, near Lakeland, MN. These results indicate that oxygen depletion has occurred in the lake since the time of European settlement, and are supported by increases in the relative abundance of eutrophic midge bioindicators and the decrease in relative abundance of bioindicators of less productive conditions since the 1850s. This study, in conjunction with other historical and paleoecological studies of Lake St. Croix, provides historical data for setting management goals and strategies for Lake St. Croix.