Influence of variable inundation regimes on soil collembola

Soil collembola in floodplain habitats are known to react dynamically to inundation, showing direct negative effects of inundation as well as rapid regeneration after flooding. Unknown, however, are how these communities react to variable inundation and the role that spatial and temporal habitat heterogeneity plays. Therefore, the small-scale spatio-temporal dynamics of soil collembolan communities after varying inundation were studied in floodplain habitats in the Upper Rhine Valley in Germany. After frequent flooding, significant differences in density and species richness were found between different floodplain levels of the same location. Due to different species’ responses, major differences occurred in community structure. After infrequent inundation the densities and species richness of the same sites and especially hygrophilous components decreased dramatically. Between neighbouring sites, species exchange occurred and community structures became more similar. The results show that at the same locality soil collembola react dynamically as well as differentially to changes in the hydrological regime. Small-scale landscape heterogeneity allows a mixture of differentially reacting species to occur within the same regional metacommunity. Long-term stability of collembolan communities despite the high spatio-temporal heterogeneity of floodplains is thus maintained by metacommunity dynamics.     

Effect of hydrologic regime and forest age on Collembola in riparian forests

The principal objective of the study was to assess factors of primary importance for collembolan community variability measured in riparian forest stands of different age after traditional clear cutting within natural and altered hydrologic regimes. The study was conducted in the Ukrainian part of the Latorica river floodplain where the largest stands of the highly protected medio-European Querco—Ulmetum minoris fluvial forests can be found. Six oak forest stands were investigated on the river floodplain: three in a natural section (inside levee) of the floodplain, which have their original features preserved with periodical inundation, and three in a section separated by a flood control embankment (outside levee) and subjected to serious damage by drainage. In each section the three stands sampled were represented by different ages regenerated with clear-cutting (>3 years, >8 years and >112 years).Differences in hydrologic regimes were central to identification of a predictable and explainable percentage of variation in species composition of Collembola communities in fluvial forests. The hydrologic regime factor was correlated with the basic structural attributes of collembolan communities, such as abundance, species richness and some ecological traits. Season accounted for a higher degree of variation in collembolan communities than did the age of forest stands. We conclude that differences in hydrologic regime are of much higher importance in structuring collembolan communities in riparian forests than are the ages of stands.     

Frog communities and wetland condition: relationships with grazing by domestic livestock along an Australian floodplain river

Frogs are in decline worldwide, and are known to be sensitive indicators of environmental change. Floodplains of the Murray-Darling Basin in southeastern Australia have been altered in many ways by livestock grazing, by the introduction of exotic fish, and by changes to flooding regimes. These changes have led to declines in wetland condition and hence to the availability of habitat for wetland frogs. This study examined relationships between frogs, wetland condition and livestock grazing intensity at 26 wetlands on the floodplain of the Murrumbidgee River. Frog communities, species richness, and some individual species of frogs declined with increased grazing intensity. Wetland condition also declined with increased grazing intensity, particularly the aquatic vegetation and water quality components. There were clear relationships between frog communities and wetland condition, with several taxa responding to aquatic and fringing vegetation components of wetland condition. Thus, grazing intensity appeared to influence frog communities through changes in wetland habitat quality, particularly the vegetation. Reduced stocking rates may result in improved wetland condition and more diverse frog communities. River management to provide natural seasonal inundation of floodplain wetlands may also enhance wetland condition, frog activity and reproductive success.     

Does forest type and vegetation patchiness influence horizontal distribution of soil Collembola in two neighbouring forest sites?

The influence of forest type and heterogeneity of understory vegetation on the horizontal distribution of soil living Collembola was studied in two neighbouring mountain forest sites—a 180-year old beech forest and a 70-year old natural spruce forest. Four homogenous patches with different understory vegetation were chosen within each forest site and sampled 12 times between 1997 and 1998. A total of 56 collembolan species were identified, 51 in the beech forest and 48 in the spruce site. Twenty-three species were rare—they were recorded with low constancy and density. Although both forest sites differed in soil type, humus form and soil chemical parameters, the species composition of their collembolan communities was quite similar (77% shared species). Nevertheless, soil collembolan communities of both forest sites were clearly delimited on both qualitative (presence–absence) and quantitative (in density of individual species) levels as well as in terms of total collembolan density. Mean collembolan density reached 26 650–44 030 ind/m² in the beech patches compared to 44 470–68 050 ind/m² found in the spruce patches. Considerably higher densities of several species in one forest site may indicate more suitable habitat. In spite of similar species composition and minor differences in qualitative parameters among different vegetation patches within one forest site, there was clear variation in density of individual species, particularly between patches with and without herb vegetation. This could reflect different microclimatic conditions, additional litter supply from herbs or indirect interactions of Collembola with their roots.     

Changes in collembolan species composition in Eastern German mine sites over fifty years of primary succession

Brown-coal opencast mining provides a virgin soil substratum at a scale of square kilometres that is open to primary succession. Focusing on this process, we investigated changes in collembolan species composition in a long-term study that lasted almost 40 years (1960–1998) at mine sites, afforested with deciduous trees. The geological overburden, which characterises the soil quality, consisted mainly of Pleistocene and Tertiary sands, interspersed with lignite and dark Tertiary loam and clay.

According to their appearance during the primary succession, we established eight colonising groups, representing 90 of 113 species found. Results from soil samples as well as from pitfall traps were taken into account for the definition of the groups. Thus, edaphic and epedaphic life forms were equally regarded. Generally, “initial”, “pioneer” and “woodland” groups were discernible.

Largest changes in species composition occurred during the first ten years, as indicated by decreasing species turnover rates and increasing alpha diversity. A comparison with other (essentially shorter) studies on Collembola of mine sites (12 in Europe, 3 in other parts of the world) showed that some pioneer species are cosmopolitan whilst others seem to be regionally specific. Important events in the ecosystem development of mine sites, as indicated by the collembolan community, are the first occurrence of other humiphagous soil animal groups, especially that of earthworms, followed by a disappearance of the ectohumus layer. The similarity between collembolan communities of mine sites and of adjacent native woodlands is greatest ten years after afforestation. Fifty years after afforestation, the collembolan community still differed markedly from that of native stands. Thus, a gradual development of the mine site collembolan communities to a comparable native woodland community is not evident from the data.     

Species-specific earthworm population responses in relation to flooding dynamics in a Dutch floodplain soil

Earthworms dominate the animal biomass in moist floodplain soils. They are known to survive long periods in aerated water, but little is known about earthworm population dynamics in floodplain systems with changing inundation frequencies. This study determined earthworm population dynamics in a floodplain system, in relation to frequency and duration of flooding events. From October 2000 to May 2003 earthworms were hand sorted in the ‘Afferdensche en Deestsche Waarden’, a floodplain on the south bank of the river Rhine, near Druten, The Netherlands. Earthworm numbers and biomasses per age class (adult, subadult, juvenile) were recorded. Numbers and biomasses tend to decrease during flooding. Lumbricus terrestris was found in high numbers (>10/m²) only at the end of a flooding period. Allolobophora chlorotica was hardly affected by flooding; their biomass remained stable during the year. Aporrectodea caliginosa showed fluctuating numbers and biomasses during the sampling period that did not correlate with flooding frequency. Numbers and biomasses of Lumbricus rubellus were strongly reduced at the end of each flooding event, but their population densities fully recovered until next flooding event. Earthworm populations in floodplains fluctuate in time, depending on the season and on the time, duration and frequency of flooding. Different earthworm species react differently towards these flooding dynamics.     

Genetic and ecological impacts of heavy metal and flooding stress on the earthworm Lumbricus rubellus in floodplains of the Rhine river

In the highly polluted river Rhine system, earthworms face environmental stress resulting from flooding and elevated heavy metal concentrations in the floodplain soil. Previous field studies have revealed adaptation to flooding for the earthworm species Lumbricus rubellus as this species matures at a lower weight in floodplain sites with a high frequency of flooding compared to less frequently flooded sites. Also heavy metals have effects on L. rubellus and heavy metals are influencing the genetic composition of this species. In this study, it was tested whether flooding and heavy metals had an impact on the genetic composition of L. rubellus living in floodplains along the river Rhine system. Earthworms were sampled at three sites previously studied along the river to assess earthworm diversity, biomass, density, and individual weight, and developmental status of L. rubellus. The genetic variation by means of isozymes was studied for 175 individuals. The results showed lowest density of L. rubellus adult and sub-adult life-stages and lowest individual weight of these life-stages at the frequent inundated site. The genetic composition, however, showed no effects of flooding on the genetic composition, but effects of heavy metals could not be ruled out.     

Soil Oribatida and Collembola communities across a land depression in an arable field

A small-scale field study of oribatid and collembolan communities was conducted in the floodplain area of the Ondava River in the East-Slovak Lowland, to assess the role of temporary water pools in microdepressions with heavy soils for microarthropod distribution in an agricultural landscape. Soil samples were taken from five sites across a microdepression without water outflow located in a cultivated field. For comparison, willow field margin was included into the study. Results from ordination analysis showed specific communities at the pool-shore, clearly different from those of the arable field and willow margin sites. Pool-shore communities were mainly affected by soil pH (positive correlation) and dominated by oribatid mites Subiasella quadrimaculata and Microppia minus, together with Collembola Folsomia quadrioculata and Lepidocyrtus cyaneus. The soil surrounding freshwater pools is assumed to be a temporary microhabitat for several microarthropod species that contribute to the biodiversity of the agricultural landscape.     

Collembolan community dynamics during deciduous forests regeneration in Japan

The structure and feeding group composition of collembolan communities were studied in secondary deciduous forests of different ages to investigate the collembolan community response to environmental changes associated with forest cycles. The study was carried out at eight sites forming a chronosequence (1, 4, 12, 24, 51, 54, 71 and 128 years after clear cutting) of deciduous forest stands in northern Ibaraki (Japan). Total collembolan density and species richness was low at the 1-year-old site, and there was little difference in density among sites over 4 years of age. The density of sucking feeders was especially low at the 1-year-old site. Species richness of trees of a diameter at breast height (DBH)<5 cm positively correlated with the density of fungal feeders. Species richness of total Collembolans and of sucking feeders correlated positively with the water content of the organic layer. Ordination of the collembolan community with Canonical Correspondence Analysis suggested that species richness of larger trees (DBH 5 cm) contributed to the differences in species composition of fungal feeders and sucking feeders. We conclude that total abundance and species richness of collembolans recovered within 4 years after clear-cutting, but species composition of fungal feeders and sucking feeders took longer to recover.     

Earthworm communities of flooded grasslands in Matsalu,Estonia

Earthworm communities in the soil of flooded (coastal and floodplain grasslands) and non-flooded (boreo-nemoral) meadows were studied. The average number of species in coastal and floodplain meadows was low, earthworm communities of boreo-nemoral meadows were diverse and the average number of species was high. Specific composition of earthworm communities varied between the three types of meadows. Earthworm communities of flooded meadows possess specific characteristics being low in both numbers and species due to periodical anaerobic conditions during over flooding and negative effect of sea water in coastal meadows.     

Effects of microhabitat diversity and geographical isolation on oribatid mite (Acari: Oribatida) communities in mangrove forests

The effects of microhabitat diversity and geographical isolation on the structure of oribatid communities were studied in mangrove forests on the Ryukyu Islands of Japan. The study took place at three sites on two islands 470 km apart. Oribatid mites (Oribatida) were extracted from leaves, branches, bark of trunks (0-50, 50-100, and 100-150 cm high) and of knee roots, and from forest-floor soil and littoral algae, each defined as a microhabitat of oribatid mites. At the 0-50 cm height, the species composition of the oribatid communities on the knee-root bark and the bark of trunks of Bruguiera gymnorrhiza differed significantly from that on the other microhabitats. This difference was attributed to tidal flooding of the mangrove forests. Cluster analysis showed that oribatid communities in the same microhabitat at different sites tended to be more similar than those on different microhabitats at the same site. This implies that the species composition of oribatid communities in mangrove forests is more likely to be affected by factors responsible for microhabitat diversity (characterized specifically by the flooded trunks) than by geographical distance between the islands.     

Influence of drought and litter age on Collembola communities

A field experiment was carried out to study the impact of drought and litter quality on the structure and performance of collembolan communities. The hypothesis was tested that changes in substrate humidity and resource quality significantly influence decomposition processes via alterations in soil faunal community structure. Litterbags (1000 μm mesh size) containing either freshly fallen or aged spruce litter were placed on the floor of a German spruce forest for one year. The bags were exposed to either ambient conditions (control) or drought (covered with roofs). Drought-induced changes in biological parameters were associated with a strong reduction in decomposition rates. Moreover, drought stress decreased Collembola abundance and species richness. The influence of drought on some microbiological parameters strongly depended on the litter age. A comparison of the two litter treatments revealed major effects of litter age on microbiological and physico-chemical parameters, but no effects on Collembola abundance and species richness. A detailed analysis of the collembolan community structure showed that certain species are highly adapted to specific characteristics of the substrate and thus rapidly respond to changes in microhabitat conditions.     

Collembolan communities in deciduous forests of different origin in Finland

The aim of the study was to compare the collembolan communities in anthropogenous birch stands of different origin with each other and with natural forests at the same latitude. Nine sites were investigated: three birch stands (Betula pendula) planted ca. 30 years prior to the study after clear-cutting of spruce stands, three birch stands planted ca. 30 years earlier on arable soil that had been under cultivation until reforestation, and three natural deciduous forests. These were sampled in August and October 1998, and microarthropods were extracted, counted and identified. Thirty years after reforestation, the collembolan communities of “Birch after Spruce” and “Birch after Field” differed significantly, but nevertheless, in comparison to some other soil faunal groups, were relatively similar to each other, and also to the communities of “Natural Deciduous” forests. Average population densities and species diversity were lowest in “Birch after Field”. The communities of deciduous forests, either natural or planted, were also relatively similar to those of coniferous forests at the same latitude. Past land-use history, organic matter content, soil structure and texture, acidity and water holding capacity were the most important factors in explaining the observed community structure.     

Collembolan community organization and its temporal predictability

Long-term investigations on Collembola in Russian forests revealed that both stable and fluctuating communities can exist in natural ecosystems. Stable collembolan communities are characteristic of mesic moisture conditions, whilst fluctuating communities are typical of either xeric or hygric habitats. Stable communities are determined by between-year constancy in species and ecological structures, though other characteristics (for instance, total collembolan abundance or number of species) can vary. Stability of collembolan communities is externally stimulated by the constancy of environmental conditions or by their cyclic changing. Stable collembolan communities are best suited for the bioindication of long-term anthropogenic impacts on natural ecosystems, whereas fluctuating communities better reflect short-term environmental changes. A temporal predictability is possible only for stable communities.     

Dam construction and ecological change in the riparian forest of the Hadejia – Jama'are floodplain,Nigeria

Riparian forests in the Sahel zone of Africa are of considerable importance for human resource use and for their ecological and conservation value. Typical riparian forest tree species are dependent on river flows and a shallow aquifer, and the community and population structure of riparian forests is related to spatial and temporal patterns of flooding at a site. Therefore, changes in hydrology caused by dams cause changes in floodplain vegetation. This paper explores the spatio-temporal complexity of these changes through an analysis of regeneration in a Nigerian floodplain affected by dams built in the early 1970s. The study shows that under certain conditions, and given sufficient time, riparian forests may be changing to forest types more characteristic of unflooded, upland areas. The results of the study have implications for the way in which the sustainability of developments downstream of large dams are analysed, suggesting that assessment of impacts must take place within temporal parameters relevant to ecological processes and at spatial scales that encompass spatial variation in floodplain ecosystems.     

Sedimentation-induced eutrophication in large river floodplains – An obstacle to restoration?

Conservation and restoration of floodplain ecosystems and their specific functions often suffer from a deficient knowledge on basic processes and dynamics such as sedimentation and related nutrient inputs. In this study, we present the results of a joint analysis of site conditions and vegetation of alluvial meadows along a gradient of increasing distance to the main channel of the river Rhine. In particular we scrutinized whether the flooding frequency mediated by the ground elevation or the distance to the river channel determines the degree of eutrophication by river water and sediments.We found a remarkably strong transversal gradient in the functional floodplain. Extremely high concentrations of CAL-soluble phosphorous (more than 150 mg kg⁻¹) were measured in close proximity to the main channel. These sites were characterized by low vascular plant species richness and a significantly higher proportion of species with high nutrient demands. At a distance of 300 m from the main channel P concentrations in the soil dropped to a quarter of this figure, whereas the average species richness per plot strongly increased. Contrary to our expectations, the influence of the flooding duration was of minor importance for the nutrient status. We can specify that strong eutrophication effects induced by sediment deposits are confined to the close proximity to the main channel within a distance of 200–300 m. At more distant sites, target vegetation of flood meadows was obviously not affected by recent nutrient input in the course of flooding. Concerns by conservationists that the restoration of active floodplains by the removal of dykes will generally lead to unwanted eutrophication by river water and sediments require revision and thorough specification.     

Species abundance distribution of collembolan communities in forest soils polluted with heavy metals

The species frequency of collembolan communities along a gradient of heavy metal pollution in soil of pine forest soils was studied. Sampling plots were established in forests 1, 3, 5, 8, 11, 68 and 148 km from the Miasteczko Śląskie zinc smelter. At each plot the plant associations, physicochemical characteristics of soil, and collembolan species composition and abundance were examined. The structure of collembolan communities was analyzed with regard to species distribution, testing geometric series, broken-stick, logarithmic series, log-normal and negative binomial distribution models. Most of the collembolan communities occurring both in contaminated and in uncontaminated soils had structure similar to a negative binomial distribution. In the samples from the oldest forest, the species frequencies could also be fitted to a log-normal distribution. The species frequency model was independent of the degree of soil pollution. Under the assumption of a negative binomial distribution of Collembola from soil samples, it is possible to estimate the theoretical number of collembolan species in the habitats studied. The difference between estimated and empirical numbers of species (the number of species not revealed in samples) was linearly correlated with metal concentrations in soil, indicating the elimination of a number of rare species from severely polluted forests.     

Type-specific reference conditions of fluvial landscapes: A search in the past by 3D-reconstruction

River/floodplain restoration programs are often based on type-specific reference conditions of the respective river section. Most large rivers in the industrialized world are heavily degraded and lack near-natural reference sites. For that reason, historical analyses of the pre-channelization state have been used to define adequate restoration targets at the Austrian Danube section in the Alluvial Zone National Park downstream from Vienna. This study compares new reference data derived from 3D-reconstructions in the form of digital terrain models from two historical Danube river landscapes: the Machland floodplain in 1812 and the former floodplain in Vienna in 1849. The focus is on the original hydrological surface and subsurface connectivity of the river-floodplain systems related to different flow situations. Here, we use water cover, shorelines, depth of the groundwater table and inundation depth as surrogates for measuring connectivity. The results show that the two study sites naturally constituted extreme formations of the Austrian anabranching Danube sections. The Machland section was one of the narrowest floodplains but highly dynamic, and the Vienna/Lobau section was one of the broadest, whereby only the central part close to the main channel originally showed high morphological turnover. The analyses of hydrological surface connectivity relative to total floodplain extension reveal significant differences due to their basic geological and geographical conditions. Despite these basic differences, both study sites – in absolute numbers – showed similar extensions of the water bodies at low and mean flow. The depths of the groundwater table related to mean flow were also comparable. Prior to channelization, the groundwater conditions in both floodplains favored the formation of wet to moist alluvial forest communities.     

Movement response of Collembola to the excreta of two earthworm species: Importance of ammonium content and nitrogen forms

Several studies reported variable effects of earthworms on microarthropod density and variety. The present study tests the attraction of seven collembolan species belonging to four families, to the excreta of two earthworm species belonging to two families and two ecological categories, Aporrectodea giardi and Hormogaster elisae. Our objectives were (1) to better understand the impact of earthworms on the composition and density of Collembola communities, and (2) to dissect mechanisms involved in the attraction. Experiments were performed in Petri dishes containing two half-disks of filter paper, one with earthworm excreta, i.e. casts or a mix of mucus and urine, and the other with natural soil aggregates or water, respectively. Collembola were introduced half-way between the two half-disks and their number was counted on each half-disk and compared over 140 min. The content of ammonium in casts and mucus-urine of both earthworm species was analyzed to determine whether it altered the responses of Collembola faced with different types of earthworm excreta. The behaviour of Collembola varied strongly among the seven collembolan species, and with type of excreta and earthworm species. Six collembolan species were attracted to the mucus and urine of at least one earthworm species. The mucus-urine mixture of A. giardi, with low ammonium content, was generally more attractive than that of H. elisae, which was even repulsive in some cases, probably because of high levels of ammonium. The attraction to casts of the two earthworm species was less frequent and more variable. Folsomia candida was neither attracted to the casts nor to the mucus and urine of any earthworm species. Therefore, (1) earthworm species with different ecology, and different nitrogen excretion pathway impact differently the behaviour of collembolan species belonging to the same family or arising from the same habitat, and (2) variations in the sensitivity to ammonium among collembolan species partially explain the variable response of Collembola to earthworm excreta.     

Microbial diversity in three floodplain soils at the Elbe River (Germany)

Microbial communities in floodplain soils are exposed to periodical flooding. A long-term submerged Eutric Gleysol (GLe), an intermediate flooded Eutric Fluvisol (FLe), and a short-time flooded Mollic Fluvisol (FLm) at the Elbe River (Germany) with similar organic carbon contents (C_org) between 8.1% and 8.9% were selected to test the quality of phospholipid fatty acids (PLFA), soil microbial carbon (C_mic), basal respiration (BR), metabolic quotient (qCO₂), and C_mic/C_org ratio to characterize and discriminate these soils with microbial parameters.The three floodplain soils can be differentiated by C_mic and by total PLFA-biomass. Due to the different flooding durations and the time since the soils were last flooded C_mic and PLFA-biomass increase in the order GLe<FLe<FLm. Both parameters correlate significantly (r=0.999;p<0.05). The C_mic/C_org ratios are low in comparison to terrestrial soils and revealed the same ranking over the three soils like C_mic. Contrary, qCO₂ and BR are highest in GLe and lowest in FLm according to inundation regime. The diminished C_mic, high BR, and high qCO₂ values in GLe seem to be an unspecific response of aerobic soil microorganisms on the long flooding period and the resulting short time for developing after last flooding as well as the low pH value. Different plant communities and their residues may influence the microbial diversity additionally.The PLFA profiles were dominated by the group of saturated fatty acids that together constituted almost 62-72% of the total fatty acids identified in the soils. In GLe all groups of PLFA, inclusive monounsaturated fatty acids, are lowest and in FLm highest, while in FLe the PLFA fractions show an intermediary amount of the three soils. The FLm had most of the time aerobic conditions and revealed therefore the highest C_mic, PLFA-biomass, especially monounsaturated fatty acids, C_mic/C_org ratio as well as relatively low BR and qCO₂ value. These indicate that microorganisms in FLm are more efficiently in using carbon sources than those in GLe and FLe.All 26 identified PLFA were found in FLe and FLm, while the polyunsaturated fungi biomarker 18:2ω6,9c could not be detected in GLe. In this long-time submerged soil the environmental conditions which microorganisms are exposed might be disadvantageous for fungi.