Production estimates of the dominant taxa of Chironomidae (Diptera) in the modified,River Widawka and the natural,River Grabia,Central Poland

Production and community composition of selected taxa of Chironomidae were estimated in cross-sections of the lower course of two lowland rivers, the Widawka and the Grabia. At the selected site, the Grabia has not changed its morphometry for many years, whereas the discharge of the Widawka has increased (mainly due to inputs of coal mine water) by 75% in comparison with its hypothetical natural discharge. In the Widawka, the production value, for 76.7% of total Chironomidae abundance, amounted to 12.45 g dry wt m^–2 yr^–1, while in the Grabia it amounted to 11.91 g dry wt m^–2 yr^–1 The annual P : B ranged from 14.5 for large-sized species (Chironomus in the Widawka) to 82.0 for small-sized species (Eukiefferiella in the Grabia). The similar production values estimated for both rivers, despite a three times higher density of Chironomidae in the Grabia, is noteworthy.     

Diel drift of Chironomidae in a large lowland river (Central Poland)

The diel drift patterns of Chironomidae larvae were investigated in a seventh order section of the Warta River (Central Poland) over two diel cycles during May 1989. Three nets (mesh size 400 m) were installed in a cross section of the Warta River.The estimated drift density was low, but was comparable to that calculated for other large rivers. Spatio-temporal fluctuations in abundance and composition of macroinvertebrate drift, including Chironomidae, were observed with the highest density of drifting macrobenthos recorded near the depositional bank of this river. The ratio benthosdrift indicated differing propensities for of the older instars of a given chironomid taxon to drift. Orthocladiinae larvae were the most abundant subfamily of Chironomidae in drift but not in benthos, reaching up to 73% of the total drifting chironomid larvae. More taxa but fewer individuals (about 20% of the chironomid larvae collected) belonged to the tribe Chironomini, the dominant group in benthos.A major part of chironomid drift collection may represent behavioural drift because the net mesh size used in the Warta River was insufficient to catch the earliest instars (distributional drift). Both at the family and subfamily level chironomid larvae exhibited a distinct nocturnal drift periodicity. Nocturnal periodicity was documented for the dominant species, but due to the low density of many chironomid species, it was impossible to determine their diel drift pattern. Some Chironomidae appeared to be aperiodic.     

A partial analysis of ecological segregation in the chironomid community of a bog lake

A small dystrophic lake was found to support 19 species of chironomid larvae, 13 of which are relatively abundant while the other six are classified as rare as they collectively constituted less than 0.25% of the total chironomid community. With the exception of one species pair, evidence of ecological segregation could be demonstrated for all abundant species that could be morphologically distinguished as larvae. Both members of the overlapping pair fed mainly upon coarse detritus, the most abundant food resource in the lake. Limited data on the six rare species failed to reveal ecological segregation from one or more of the abundant species.     

Diel emergence patterns of drifting chironomid (Diptera) pupal exuviae in the Aude River (Eastern Pyrenees,France)

Two diel emergence patterns (April and October 1990) of chironomids from a hyporhithral site (4th–5th order) in the Aude River are described. In April, 62 species were collected with a mean hourly richness of 31 (±4). The Orthocladiinae (91%) largely dominated the emergence. The total number of exuviae captured by one drift-net varied from 1300 to 11600 per one hour period. There was a clear bimodal pattern with peaks post dawn (07.00–09.00 hrs) and around sunset (18.00 hrs).In October, the total number of exuviae captured was much lower and varied from 150 to 540 per one hour period with post dawn (06.00–08.00 hrs) and post sunset (18.00 hrs) peaks. Nevertheless, the total species richness (65) was higher as was the mean hourly richness (37±4). The Orthocladiinae (68%) dominated less because of increases in the Tanytarsini (15%) and Chiromini (14%). A diel rhythm appeared in autumn emergence. Most of the Orthocladiinae exuviae were collected during daylight hours, whereas most of the Chironomini and Tanytarsini were sampled during darkness. A majority of the exuviae with a length below 3 mm emerged during daylight, but most of the exuviae above 5 mm length emerged during darkness. The exuviae with an intermediate length (3–5 mm) had an amodal diel emergence pattern. In spring and autumn, the majority of species had a bimodal emergence pattern either by day (Orthocladiinae) or by night (Chironominae). But the smallest species had either an unimodal (Thiennemaniella vittata) or bimodal (Neozavrelia fuldensis) daytime emergence. The diel emergence patterns of 10 of the most frequently recorded species are presented.     

Midges (Diptera: Chironomidae) from the upper reaches of a spate river

The species of Chironomidae (Diptera) encountered in an upland ‘spate’ river are listed. Notes on larval biology are given and the midge fauna compared with that of other kinds of river.     

The effect of trophic/contaminant interactions on chironomid community structure and succession (Diptera: Chironomidae)

The effects of contaminants and organic pollution on the chironomid communities of two basins in Lac St. Louis, a river-lake on the St. Lawrence River above Montreal, Quebec, were assessed and compared using lake classification theory techniques and morphological deformity indices based on the ligulae and antennae ofProcladius, the dominant surviving component of the south-shore communities. Contaminants from the industrial complex around Beauharnois, Quebec, have seriously degraded communities along the south-shore gradient while the introduction of untreated domestic wastes from Laprairie, Quebec, has seriously affected the communities of the Laprairie basin. The interaction between trophic and contaminant effects constitutes a classic example of the setback or deflection in the trajectory of ecological succession in biological communities hypothesized by ODUM (1981, 1985).     

Deformities in chironomid larvae as indicators of pollution (pesticide) stress

Chironomid larvae (Chironomus spp.,Dicrotendipes conjunctus andProcladius paludicola) collected from Cox Creek and Aldgate Creek, South Australia, showed morphological abnormalities similar to those reported in other studies elsewhere in the world. The sediment of Cox Creek contained high concentrations of pesticides and there was a significant correlation between the occurrence of mouthpart and antennal deformities in larvae and the concentration of DDT and the herbicide, Dacthal®.Laboratory experiments were conducted using a culture ofChironomus sp. to determine whether or not a causal relationship existed between exposure to pesticides and the occurrence of deformities in larvae. Results showed a positive relationship between the concentration of DDT and the percentage of deformed mouthparts (menta). The results for the effect of DDT on antennae and those for the effect of Dachthal® were less clear, but generally showed a higher incidence of deformity for treatments compared with controls.To compare these results to a natural population (i.e. from an unpolluted area) the incidence of deformities was measured for larvae collected from Deep Creek Conservation Park, an area virtually free of pollution. The significance of this work is discussed with regard to its wider application as a useful environmental monitoring technique for freshwater systems.     

Density,production and life cycle of Brachycentrus subnubilus Curtis (Trichoptera: Brachycentridae) in a lowland river,Central Poland

The annual mean density of Brachycentrus subnubilus a trichopteranspecies with a univoltine life-cycle was 572 ind. m^-2. Itconstituted of only 2.1% of the total macrozoobenthos abundance,while this species in terms of biomass exceeded 11.9% of the totalbenthic biomass. Production of Brachycentrus subnubilus was estimated bysize-frequency method was 26.56 g wet weight m^-2 and theturnover ratio was 5.7.     

Chironomids as water quality indicators in the River Mignone (Central Italy)

Chironomids of the River Mignone (Central Italy) were studied in order to examine their community structure and their relationship to some common biological indices (Biotic Score, Extended Biotic Index, Indice Biotique de Qualité Générale) utilizing the total macroinvertebrate fauna (chironomids generally at family level) for water quality assessment in rivers.A total of 36 taxa belonging to Tanypodinae (2 taxa), Orthocladiinae (22 taxa) and Chironominae (12 taxa) was collected at seven stations four times during a year. The results support the importance of the chironomid identification in water quality assessment studies in rivers, and demonstrate the usefulness of the factorial correspondence analysis as ordination technique based on both qualitative and quantitative chironomid data to determine environmental quality gradients.The value as bioindicator of some taxa was discussed, and chironomid assemblages were related to biological water quality of the river according to functional feeding groups.This study forms part of a larger Research project supported by MPI and CNR grants and is aimed at the biological water quality assessment of the river and at the analysis of the total macrobenthic community.     

The production of five genera of Chironomidae (Diptera) in Lake Norman,a North Carolina reservoir

The production of five genera of chironomids collected at 4- and 8-m depths at four stations in Lake Norman, North Carolina, was estimated using the size-frequency method. To correct for multivoltinism, the estimates were adjusted by multiplying by 365/Cohort Production Interval. Ranges of production estimates (P) in milligrams dry mass m^-2 yr^-1 and production/mean annual biomass ratios (P/B ratios) for each genus over both depths were: Tanytarsus, P = 744 to 8788, P/BB = 66 to 176; Cladotanytarsus, P = 74 to 2387, P/B = 69 to 100; Stempellina, P = 19 to 412, P/ B = 74 to 132; Chironomus, P = 166 to 7293, P/ B = 50 to 70; Cryptochironomus, P = 92 to 398, P/ B = 71 to 221. These estimates are among the highest reported for chironomids, due primarily to the rapid larval development times estimated for these genera.     

Incidence of deformed chironomid larvae (Diptera: Chironomidae) in Swedish lakes

The occurrence of deformed mouth parts in recent and subfossil material of mostly Chironomus, Micropsectra and Tanytarsus increased from less than 1 % of the larvae at unpolluted sites or time periods to figures in the range of approx. 5–25% at strongly polluted sites. Deformities occurred in species that are widely separate in taxonomic position and way of living. Several heavy metals are suspected causative agents. Deformities in various mouth parts are illustrated by SEM photographs.     

Allergens of non-biting midges (Diptera: Chironomidae): a systematic survey of chironomid haemoglobins

Various genera of non-biting midges (Diptera: Chironomidae) possess haemoglobins in larvae and adults. For certain species, these haemoglobins have been implicated in human allergic disease in several countries. The present study confirms and extends observations that haemoglobin is present in many species of Chironomidae, establishes that it is retained from the larval to the adult stage and shows that haemoglobin persists both in live and in dead dry flies. Previous suggestions that Chironomidae should be seen as important environmental and occupational allergens are clearly substantiated.     

Analysis of chlordane-impacted streams using chironomid pupal exuviae (Diptera: Chironomidae)

A method of rapidly assessing streams and rivers using chironomid pupal exuviae was tested on a chlordane-impacted stream near St. Louis, Missouri. Various concentrations of chlordane were found in sediments of Grand Glaize Creek, most likely resulting from soil runoff around housing and business developments throughout the stream's course. Chironomid pupal exuviae and sediment samples were collected concurrently from Grand Glaize Creek on two separate occasions, once in 1988 and again in 1990. Cluster analysis of samples at sites, based on the percent abundances of taxa within habitats and by subfamilies, produced two distinct clusters; one grouping samples with lower chlordane concentrations and the other grouping samples with higher chlordane concentrations. Further analysis showed a trend towards lower percent abundances of taxa living in depositional and transitional/depositional zones (Chironominae and some Tanypodinae) at the higher chlordane site, while the lower chlordane sites had lower percent abundances of taxa within erosional and erosional/transitional zones (Orthocladiinae and some Tanypodinae). These findings support the hypothesis that taxa living in close association to fine organic sediments will be exposed to higher concentrations of chlordane in the stream and more negatively affected than taxa feeding and living in habitats removed from chlordane-bound sediments. Comparisons from the present study were made to related studies revealing similar patterns among the Chironomidae.     

Horizontal migration of zooplankton in a littoral zone of the lowland Sulejow Reservoir (Central Poland)

Horizontal migrations of zooplankton between macrophyte patches and open areas were investigated in the sparsely vegetated littoral zone of the Sulejow Reservoir in June-July 2000 and 2001, using one-litre plastic traps. Large-bodied zooplankton: daphnids and copepods generally swam towards the open water at dusk and towards submerged macrophytes at dawn. Small-bodied zooplankton (Bosmina sp., Chydorus sp.) did not show any pattern of horizontal movement. At the time of the research the phytoplankton community was dominated by eatable diatoms (Cyclotella sp.), whose biomass reached 14 mg l⁻¹. Thus, bottom-up forces (food scarcity) are not likely to be responsible for the observed zooplankton migrations. Analyses of fish stomach contents showed high contribution of large zooplankters to the food of juvenile roach (Rutilus rutilus) and perch (Perca fluviatilis) which densely inhabited the littoral zone of reservoir. High fish pressure in the littoral zone along with high density of the predatory cladoceran, Leptodora kindtii in the open water, suggest that top-down forces (predatory pressure) were responsible for the migration of large zooplankton. At dusk predatory pressure of fish fry exceeded that of L. kindtii, forcing endangered zooplankton to escape from macrophytes towards open water. The opposite situation occurred at dawn. The consequences of the relationships for both zooplankton and fish fry communities dynamics are discussed.

     

Phenology and bathymetric distribution of the profundal chironomid fauna in Starnberger See (F.R. Germany)

Results of the first long-term investigation of the profundal chironomid fauna of Starnberger See, a prealpine lake are reported. Data are presented on the qualitative and quantitative composition of the chironomid fauna in the profundal of Starnberger See, on the spatial variation, and on the phenology of the dominant species, based on pupal occurrence and the seasonal distribution of larval instars. Twenty-five distinct chironomid taxa could be recorded in the profundal zone. Typical inhabitants of the profundal zone of Starnberger See are the larvae of the genus Micropsectra. The maximum abundance of Micropsectra larvae were found at 60 m with 5644 Ind.m⁻². Abundance, distribution and phenology of the dominant chironomid species are discussed in comparison with other lakes.     

Distribution and production of Chironomidae (Diptera) in the lower course of the Grabia River (Central Poland)

SUMMARY.

• 1 A fifth-order section of the Grabia River was investigated over two years: 1984/85 (low water level) and 1985/86 (high spate). Chironomidae (thirty-nine species) dominated the macrobenthos in both years.
• 2 In 1984/85 (mean annual water temperature 10.2°C), the number of Chironomidae species in coarse sediment was highest in spring (thirty-three species) while in sand it was highest in summer (fifteen species). A decrease in species richness was recorded in autumn and winter at each of the established sites. The estimated Chironomidae production for the whole river section was 5.37 g dry wt m^?2 yr^?1, but it differed widely amongst the study sites, ranging from 3.75 to 12.07 g m^?2 yr^?l.
• 3 In 1984/85 (mean annual temperature 8.1°C) there occurred a summer spate which was more intense than any recorded over the previous 20 years. This substantially reduced the number of species, the greatest reduction being in the coarse sediment, which was buried with sand during the spate. Production for the whole section decreased to 1.17 g m^?2 yr^?1, and the variability amongst sites ranged from 1.04 to 1.45 g m^?2 yr^?1.

     

Influence of dam removal on trichopteran assemblages in the lowland Drzewiczka River,Poland

The aim of this study is to assess the response of Trichoptera in a patchy tailwater stretch of the Drzewiczka River (Poland) to dam removal as compared to the previous pulse discharge disturbance. The study was carried out in the river at the end of a whitewater slalom canoeing track located downstream of the dam reservoir called Drzewieckie Lake (area 0.84 km²). Between February and April 2002, the dam reservoir was gradually emptied before its dredging, and the Drzewiczka River recovered its natural discharge (1.7–4.5 m³ s⁻¹) for several years (temporary renaturisation). Altogether, 120 monthly samples of macroinvertebrates and their environments were collected in two sampling cycles, S1 in 2000–2001 during high discharge fluctuations (2.1–12.0 m³ s⁻¹ daily) and S2 in 2002–2003 during renaturisation after emptying the reservoir, from the following five habitats: H_P—pool habitat, H_S—stagnant habitat, H_M—macrophyte habitat, H_B—bank habitat and H_R—riffle habitat. On the basis of trichopteran abundance, the patterns in their assemblages were recognised with use of a self-organising map that was a Kohonen artificial neural network. The obtained classification of trichopteran samples was found to be based in general on the spatial criterion, i.e. dependent on habitats, irrespective of which sampling cycle the samples originated from, which clearly showed that the habitat mosaic of the river bed was observed both in S1 and S2. In addition, a very important function was noted for riparian and land plants, which developed intensively at the bottom of the Drzewieckie Reservoir immediately after it was emptied. They restricted extensive transport of reservoir sediments to the downstream river reach, thus reducing differences between S1 and S2 in the tailwater. It is also worth noting that in S1, in comparison to S2, Cyrnus trimaculatus, Mystacides azurea and Lype reducta flowing downstream from the reservoir were observed more frequently in the river, which confirmed that impoundments can be conducive to the presence of certain species downstream of dams. Summing up, although artificial short-term flow fluctuations usually diminish the quality and quantity of benthos, the article presents a case in which they were small and short enough to allow the formation of a mosaic of bed patches and positively affected certain parameters of macrobenthic communities according to the intermediate disturbance hypothesis. Handling editor: David Dudgeon     

Distribution and production of chironomids (Diptera: Chironomidae) in a shallow, alkaline lake (Neusiedler See, Austria)

From July 1990 to July 1991 the benthic community of the open water zone of Neusiedler See, one of the largest shallow lakes in central Europe, was studied with special reference to the chironomids. Only 16 spp. of chironomids inhabited the sediment of the open water zone. The numerically dominant species were Tanypus punctipennis, Procladius cf. choreus, Microchironomus tener and Cladotanytarsus gr. mancus. Most invertebrates showed a distinct horizontal distribution. Species richness and abundance were highest on muddy and organically rich substrates near the reed belt. Chironomid densities in this area reached 54,000 ind m^–2 and biomass was 2.0 g dw m^–2. The two tanypod species accounted for more than 90% of the standing stock of the macrozoobenthos near the reed belt. The sediment of the open lake and of the eastern part of Neusiedler See was composed of compact clay and sand as a result of the erosion of fine material due to strong waves and currents. Individual densities in these areas were much lower. Production of the numerically dominant species T. punctipennis was estimated using the increment-summation method, whereas production of the remaining species was estimated using an empirically derived multiple regression. Mean annual production of chironomids exceeded 6 g dw m^–2 yr^–1 near the reed belt, but it reached only 0.55 g dw m^–2 yr^–1 in the open lake. These values are rather low compared with other lakes and can be explained by unfavourable sediment conditions due to wave action and by physiological stress due to the water chemistry.     

Comparison of bacterial production in sediments, epiphyton and the pelagic zone of a lowland river

1. The microbial metabolism of organic matter in rivers has received little study compared with that of small streams. Therefore, we investigated the rate and location of bacterial production in a sixth‐order lowland river (Spree, Germany). To estimate the contribution of various habitats (sediments, epiphyton, and the pelagic zone) to total bacterial production, we quantified the contribution of these habitats to areal production by bacteria. 2. Large areas of the river bottom were characterized by loose and shifting sands of relatively homogenous particle size distribution. Aquatic macrophytes grew on 40% of the river bottom. Leaf areas of 2.8 m² m^?2 river bottom were found in a 6.6 km river stretch. 3. The epiphyton supported a bacterial production of 5–58 ng C cm^?2 h^?1. Bacterial production in the pelagic zone was 0.9–3.9 μg C L^?1 h^?1, and abundance was 4.0–7.8 × 10⁹ cells L^?1. Bacterial production in the uppermost 2 cm of sediments ranged from 1 to 8 μg C cm^?3 h^?1, and abundance from 0.84 to 6.7 × 10⁹ cells cm^?3. Bacteria were larger and more active in sediments than in the pelagic zone. 4. In spite of relatively low macrophyte abundance, areal production by bacteria in the pelagic zone was only slightly higher than in the epiphyton. Bacterial biomass in the uppermost 2 cm of sediments exceeded pelagic biomass by factors of 6–22, and sedimentary bacterial production was 17–35 times higher than in the overlying water column. 5. On a square meter basis, total bacterial production in the Spree was clearly higher than primary productivity. Thus, the lowland river Spree is a heterotrophic system with benthic processes dominating. Therefore, sedimentary and epiphytic bacterial productivity form important components of ecosystem carbon metabolism in rivers and shallow lakes. 6. The sediments are focal sites of microbial degradation of organic carbon in a sand‐bottomed lowland river. The presence of a lowland river section within a river continuum probably greatly changes the geochemical fluxes within the river network. This implies that current concepts of longitudinal biogeochemical relationships within river systems have to be revised.