The harpacticoid assemblages (Copepoda: Harpacticoida) in the Western Carpathian spring fens in relation to environmental variables and habitat age

Harpacticoids are an important component of meiofaunal assemblages in springs. No information so far has been available on harpacticoid assemblages of the Western Carpathian spring fens, unique biotopes of high conservation value which cover a very long gradient of mineral content of groundwater, due to the variable geological background setting. Spring fens are isolated habitats of different age which can be assessed by radiocarbon dating of their basal sediment layers. This enables to test a possible effect of habitat age on species composition and species richness. In this study, we examined harpacticoid assemblages in 50 permanent tree-less spring fens (helocrenes) in the Western Carpathians (Slovakia and Czech Republic) in terms of species composition, total abundance, species density, and species richness. We tested mainly the effect of 12 explanatory variables describing water chemistry and temperature, climatic conditions, amount of nutrients, organic carbon, sediment structure, habitat age and size, using Canonical Correspondence Analyses (CCA) with stepwise forward selection. For the computation of species richness rarefaction was used. In total, 20 harpacticoid species were recorded with the total median density of 950 individuals in m⁻². Three significant explanatory variables, Ellenberg Indicator Values of plant community for nutrients, in situ measured pH, and average January temperature, explained together 19.0% (adj. 13.7%) of the total variance in the species composition data. The relationships of harpacticoids to these three explanatory variables were species specific and no uniform response of the total assemblage to the environmental variables was found (in terms of total abundance and number of species). The only exception was the influence of overall unfavourable conditions in the mineral-poor acidic Sphagnum-fens. Pilocamptus pilosus was significantly associated with a higher amount of nutrients and warmer climate. Nutrient enrichment was clearly indicated by a decrease or absence of crenophile Bryocamptus cuspidatus, and accompanied by an increase in ubiquitous Attheyella crassa. Moraria brevipes was confined to low pH, B. cuspidatus showed a high tolerance for low pH, whereas Bryocamptus echinatus preferred alkaline conditions. Despite a significant correlation between habitat age and species density we found no clear evidence that any colonisation driven process could influence the number of harpacticoid species within the tested time scale. We hypothesize that rather other habitat characteristics connected with age, i.e. habitat heterogeneity and stability, may be determinant for species richness. The occurrence of some species (e.g. P. pilosus, B. cuspidatus) was clearly geographically limited, but due to the spatial structuring of significant environmental variables no conclusion on dispersal limitations could be made.     

Emergence patterns and microhabitat preference of aquatic dance flies (Empididae; Clinocerinae and Hemerodromiinae) on a longitudinal gradient of barrage lake system

Aquatic dance flies (Empididae; Clinocerinae and Hemerodromiinae) are important components of freshwater assemblages, especially in running waters. They are predators as larvae and adults and thus essential for understanding aquatic food webs. This study was conducted in Plitvice lakes National Park (Croatia) representing a wide variety of freshwater habitats (springs, streams, lakes and tufa barriers). Adults were collected monthly from March 2007 until March 2009 using pyramid-type emergence traps at 13 locations. A total of 3865 specimens comprising 18 species were collected. The dominant genus was Chelifera, while the most abundant species was Hemerodromia unilineata. All species were univoltine except Chelifera precabunda, Chelifera pyrenaica and Chelifera stigmatica that were bivoltine. Considerable differences in composition and structure of aquatic dance flies assemblages were recorded along a longitudinal gradient of studied sites, primarily related to differences in physical and chemical parameters of water. Water temperature was the main factor influencing the timing of emergence. Hemerodromia species preferred variable water temperature throughout the year while the majority of the Chelifera species preferred stable water temperature characteristic of spring sites. Furthermore, discharge affected assemblage composition of aquatic dance flies. The highest abundance of aquatic dance flies was recorded in lotic habitats with fast water current over substrates of moss, gravel and particulate tufa with detritus. These results give a new insight on microhabitat preference and their distribution on unique karstic habitats.     

Benthic foraminiferal assemblages from Moreton Bay, South-East Queensland, Australia: Applications in monitoring water and substrate quality in subtropical estuarine environments

We assess species composition, assemblage structure and distribution of the benthic foraminiferal assemblages from diverse substrates in Moreton Bay, South-East Queensland, Australia. Analysis of 47 surface sediment samples revealed 69 species, three distinct foraminiferal assemblages and six sub-assemblages. The assemblages from the western Bay are characterized by stress tolerant taxa and the lowest diversity, whereas the assemblages from the eastern Bay are characterized by symbiont-bearing taxa and high diversity. We found a correlation between foraminiferal assemblages and substrate conditions that was indicative of strong environmental gradients (substrate type, water quality and salinity), from an urban-impacted assemblage in the westernmost part of the Bay, to a hyposaline, estuarine-influenced assemblage in the western Bay to a nearly normal marine to hypersaline assemblage in the eastern Bay. The FORAM Index was consistent with the changes in water and sediment quality gradient, from the western shoreline to the eastern Bay. Thus the foraminiferal assemblages of Moreton Bay make excellent bio-indicators of environmental changes in a subtropical, estuarine setting in eastern Australia.     

Ground water sustenance of Nebraska's unique Sand Hills peatland fen ecosystems

Many ecosystems have evolved under conditions where ground water is critical to the survival of the unique species contained therein. One example is Nebraska's Sand Hills fens. The Sand Hills region comprises lush interdunal valleys amid grass-stabilized dunes. One valley type, fens, are ground water-fed wetlands that have several meters of saturated, organic soils comprising peat formed under anaerobic conditions where plant growth exceeds decomposition. These fens support unique flora and fauna such as rush aster and northern redbelly dace that are typically found in more boreal regions of North America. This study characterized the hydrogeology of a representative fen in the Jumbo Valley to explore how these relict species survive in a hot, arid climate and to understand present and historical relations between ground water and these unique ecosystems. Results indicate that ground water's present role in sustaining the fens is twofold: (1) wetland plant transpiration of shallow ground water across the valley creates a cooler, humid microclimate that sustains the fens in the region's hot, arid climate and (2) the large volume of ground water pumped through the fens by plant transpiration transports necessary nutrients to the root zone. Results suggest that, in the past, in addition to its sustaining role, ground water also played a vital role in fen development and in fen preservation through nearly 15,000 years of existence. Thus, as with like ecosystems, the role of ground water must be considered in future Sand Hills fen protection, restoration, and management.     

Fish assemblages in forest drainage ditches: Degraded small streams or novel habitats?

Artificial drainage of forested wetlands to increase timber production has profoundly altered the hydrology of North-European landscapes during the 20th century. Nowadays, drainage ditches and small dredged streams can comprise most fluvial water bodies there, but the resulting ecological effects are poorly documented. In the current study, we explored, using fish as an indicator group, consequences of the transformation of natural stream networks to a mixture of natural and artificial watercourses. We asked whether the transformation results in impoverishment, enrichment or re-assembling of the communities both at watercourse and the landscape scales. We sampled fish in 98 sites in five well-forested regions in Estonia where ditches formed 83–92%, dredged streams 4–7%, and natural streams 3–10% of the total length of small watercourses. Based on a total of 6370 individual fish of 20 species, we found that, compared to natural streams, ditches had an impoverished fauna at both scales and both in terms of species richness and assemblage composition. Only natural streams hosted characteristic species (with Barbatula barbatula, Lampetra planeri and Lota lota emerging as significant indicators), while dredged streams had intermediate assemblages. The habitat factors explaining those drainage-related differences included a reduced flow velocity, loss of stream channel variability, less transparent water, and abundant aquatic vegetation. Hence, for stream-dwelling fish, drained forest landscapes represent degraded habitats rather than novel ecosystems, which contrasts with the transformation of terrestrial assemblages. Future studies should address whether that reflects the situation for whole aquatic assemblages, and how is the functioning of the hydrological systems affected. We suggest that the critical management issues for environmental mitigation of ditching effects on fish include basin scale spatial planning, protecting of the remaining natural streams, and rehabilitation of ditch channels in flat landscapes lacking beavers.     

Analysis of foraminifera assemblages and sediment geochemical properties to characterise the environment near Araçá and Saco da Capela domestic sewage submarine outfalls of São Sebastião Channel, São Paulo State, Brazil

Superficial bottom samples were collected near diffusers of domestic sewage submarine outfalls at Araçá and Saco da Capela, São Sebastião Channel, Brazil. The goal of this study was to investigate the distribution and composition of live benthic foraminifera assemblages and integrate the results obtained with geochemical analyses to assess human-induced changes. According to the results obtained no environmental stress was observed near the Saco da Capela submarine outfall diffusers. The foraminifera assemblage is characterised by species typical of highly hydrodynamic environments, with well-oxygenated bottom waters and low nutrient contents. In contrast, near Araçá submarine outfall, organic enrichment was denoted by high phosphorus, sulphur and, to a lesser extent, total organic carbon content. Harmful influences on foraminifera could be identified by low richness and specific diversity, as well as the predominance of detritivore feeder species, which are associated with higher organic matter flux and low oxygen in the interstitial pore water.     

Environmental drivers of biotic traits and phenology patterns of Diptera assemblages in karst springs: The role of canopy uncovered

Springs are stable environments with constant abiotic factors and therefore of use in variety of ecological experiments. We investigated the influence of canopy coverage on abundance, diversity, phenology and feeding guilds among Diptera assemblages at two rheocrene karst springs located near each other. The springs differed by canopy coverage while physicochemical characteristics of the water were similar. We set six emergence traps for one year at each spring covering all available microhabitats proportionally. We hypothesized that canopy coverage will have a strong effect on assemblage composition of Diptera as well as on diversity, abundance, phenology and feeding guilds composition between sites and that it will have a stronger effect than microhabitat characteristics. Similarity of species composition among springs was only 37.5%, with 23 common species/taxa out of 74 species/taxa. Abundance of Diptera was 8.5× higher at the open canopy spring, while diversity and number of species/taxa was higher at closed canopy spring. Emergence started earlier at open canopy site and was prolonged even in winter months. The majority of species were detritus feeders followed by collectors and there was no substantial difference among sites. We conclude that at springs with similar water characteristics, canopy coverage is the main driver of Diptera assemblage structure, with water velocity as a complementary factor. Substrate and other physicochemical factors seem less important.     

Environmental determinants of leech assemblage patterns in lotic and lenitic habitats

Leeches (Clitellata: Hirudinida) are abundant predators or ecto-parasites inhabiting various freshwater habitats; however many biotic and abiotic drivers of their assemblage patterns have been deduced rather than directly tested. To study species richness and composition changes in leech assemblages, 109 sites of running and stagnant water bodies were sampled in three regions of the Czech Republic in 2007–2010, together with several explanatory variables that are known or expected to be important predictors of leech distribution. In total, 17 species of leeches were recorded, varying between 0–7 and 0–9 species in lotic and lenitic sites, respectively. These differences in species richness of lotic and lenitic sites were highly significant, contrary to the abundances, which varied between 0–283 and 0–295 individuals. The main change in species composition was controlled by water temperature and morphological characteristics (e.g. substrate and cover of macrophytes), mostly reflecting the differences between lotic and lenitic habitats. We found the density of benthos (i.e. prey availability) to be the best predictor of species composition in both lotic and lenitic sites, together with the percentage of canopy cover. However, the other significant predictors (i.e. the substrate and water conductivity found to be significant in lotic sites, and the mean annual temperature and PO₄^3? in lenitic sites), differed between these habitats. Other than mean annual temperature and water temperature, which had different effects on species richness in lotic and lenitic sites, there were no other differences between lotic and lenitic sites in terms of how species richness and abundance responded to all other analyzed predictors. Our results stress the importance of prey availability and canopy for leech distribution patterns. Differences in the significant predictors of leech assemblage patterns between lotic and lenitic sites raise fundamental questions about the underlying mechanisms and ecological constraints to leech distribution in these main types of aquatic systems.     

Effects of human disturbance and riparian conditions on Odonata (Insecta) assemblages in eastern Amazon basin streams

Riparian vegetation is an important determinant of the physical, chemical, and biological condition of streams, and odonates are useful indicators of riparian condition. To identify environmental factors that structure Odonata assemblages in tropical forest streams, we collected adult odonate specimens and habitat data from 50 stream sites located in the Brazilian municipality of Paragominas (Pará state). We collected 1769 specimens representing 11 families, 41 genera, and 97 species. Of these species, 56 were Zygoptera, and 41 were Anisoptera. Improved environmental condition was reflected in increased Zygoptera species richness and reduced Anisoptera species richness. Channel shading was strongly and positively related to Zygoptera richness, and negatively to Anisoptera richness. Zygoptera species richness, but not Anisoptera species richness, was related positively to bank angle, quantity of wood in the stream bed, electrical conductivity, and decreased water temperature. Altered riparian vegetation structure was the principal determinant of odonate assemblage structure. Our results indicate that maintaining intact riparian vegetation is fundamental for conserving or re-establishing aquatic odonate assemblage structure.     

太湖流域直湖港支流龙延河水系鱼类集群现状

分别于2009年8月和2010年5月对直湖港支流龙延河水系的鱼类集群现状及其影响因素进行研究.结果表明,研究区域有多种鱼类存在,共采集到31种,隶属于5目9科22属;春、夏两季鱼类集群的种类数没有明显差异,但春季的鱼类多度和生物量均显著高于夏季;主干支流、次级支流和支流末端等不同区位的鱼类组成也有一定差异;水体透明度、...     

The role of an extreme flood disturbance on macrophyte assemblages in a Neotropical floodplain

Aquatic macrophytes produce large amounts of organic matter and have an essential structuring role in floodplains. This process highlights the importance of this community to aquatic biodiversity maintenance. We investigated the role of a flood disturbance on the response of macrophyte assemblages in regional and local structuring in the Upper Paraná River floodplain. Plant species were recorded before (November 2006) and after (March 2007) an uncommon increase in water level caused by the El Niño South Oscillation, which is considered a disturbance. Samples were taken in lakes and backwaters located in the floodplain and connected to three distinct rivers (that differentiate three sub-systems). Species richness and the assemblage structure of macrophyte patches underwent significant changes after the flood disturbance, depending on the specific sub-system (rivers) to which the lakes were connected. In addition, flood disturbance had a strong impact on community organization at the local scale. However, regionalization with respect to sub-systems remained significant after the flood disturbance. Our results emphasize the importance of connection to the river on macrophyte community composition and richness, and suggest that flood events in the Upper Paraná River floodplain disrupt community organization only at fine (local) scales.     

HYDROLOGICAL FUNCTION OF A MOUNTAIN FEN AT LOW ELEVATION UNDER DRY CONDITIONS

Mountain fens are limited in their spatial extent but are vital ecosystems for biodiversity, habitat, and carbon and water cycling. Studies of fen hydrological function in northern regions indicate the timing and magnitude of runoff is variable, with atmospheric and environmental conditions playing key roles in runoff production. How the complex ecohydrological processes of mountain fens that govern water storage and release as well as peat accumulation will respond to a warmer and less snowy future climate is unclear. To provide insight, we studied the hydrological processes and function of Sibbald fen, located at the low end of the known elevation range in the Canadian Rocky Mountains, over a dry period. We added an evapotranspiration function to the Spence hydrological function method to better account for storage loss. When frozen in spring and early summer, the fen primarily transmits water. When thawed, the fen's hydrological function switches from water transmission to water release, leading to a summertime water table decline of nearly 1 m. Rainfall events larger than 5 mm can transiently switch fen hydrological function to storage, followed by contribution, depending on antecedent conditions. The evapotranspiration function was dominant only for a brief period in late June and early July when rainfall was low and the ground was still partially frozen, even though evapotranspiration accounted for the largest loss of storage from the system. This research highlights the mechanisms by which mountain peatlands supply baseflow during drought conditions, and the importance of frozen ground and rainfall in regulating their hydrological function. The study has important implications for the sustainability of low elevation mountain fens under climate change.     

Inter-annual Arcellinida (testate lobose amoebae) assemblage dynamics within lacustrine environments

Arcellinida (testate lobose amoebae) were examined from 22 surface-sediment samples collected from homogenous environments in eastern Canadian lakes (Lac du Castor Blanc, SW Quebec; Oromocto Lake, SW New Brunswick) to: 1) evaluate the faunal consistency of assemblages within the targeted environments; and, 2) assess the Arcellinida assemblage response evident in samples collected from Oromocto Lake in 2010 CE (n = 10) and 2012 CE (n = 6) to inter-annual changes in environmental conditions. Cluster analysis and detrended correspondence analysis (DCA), redundancy analysis (RDA), and Bray-Curtis Dissimilarity Matrix (BCDM) were used to identify the dominant arcellinidan assemblages, determine physicochemical controls over the Arcellinida distribution, and assess the assemblages’ faunal homogeneity, respectively. Cluster analysis, DCA, and BCDM results revealed two distinct and relatively homogenous arcellinidan assemblages: 1) Lac du Castor Blanc Assemblage; and 2) Oromocto Lake Assemblage, which could further be subdivided into Oromocto Lake 2010 CE (OL10), and 2012 CE (OL12) sub-assemblages. RDA results showed that 65.6% of the variance in the arcellinidan distribution could be attributed to four significant parameters; sand size fraction (32.1%), calcium (29.2%), manganese (2.7%), and organic content (1.5%). The OL10 and OL12 sub-assemblages aligned well with the respective sample collection dates of 2010 CE and 2012 CE, with proportions of the healthy-lake-indicating Diffluggiid taxa being higher in OL12, likely due to a concurrent slight increase in substrate organic content in the 2012 CE sediments. Our results confirm the faunal homogeneity of assemblages in limnologically similar environments, and demonstrate the rapid response of Arcellinida assemblages to changes in lake conditions at inter-annual time scales.     

The dynamic balance between organic acids and circumneutral groundwater in a large boreal peat basin

Large raised bogs and patterned fens cover 56% of the landscape in the Glacial Lake Agassiz region of northern Minnesota (USA). Organic acids supply most of the acidity in the surface water of the bogs, but groundwater upwelling from the underlying glacial deposits neutralizes these organic acids within deep peat. Substantial concentrations of organic acids also occur in the surface waters of fens mixed with variable amounts of inorganic solutes contributed by groundwater discharge. We used a triprotic analog model to determine the extent to which organic acids in fen and bog waters behave as strong or weak acids. The modeling approach optimized charge balance by calibrating estimates of mole site density in the DOC (dissolved organic carbon) of surface and pore waters with estimates of triprotic acid dissociation constants. Before the calibration process, all of the bog waters and 76% of the fen waters had more than +20% imbalance in charge balance. After calibration, more than 75% of all waters were electrochemically balanced within 20%. In the best calibration, the mole site denisty of bog DOC was estimated as 0.05 mmol/mmol C., approximately six times smaller than that estimated for fen DOC or the DOC in the fen deeper fen peats that underlie all bog landforms. The three modeled de-protonation constants were; pK_a1=3.0, pK_a2=4.5 and pK_a3=7.0 for the bog DOC, and; pK_a1=5.2, pK_a2= 6.5 and pK_a3=7.0 for the fen DOC. Bog DOC, behaves as a strong acid despite its small mole site density. The DOC in bog runoff can therefore theoretically acidify the surface waters in adjacent fens wherever these waters do not receive sufficient buffering alkalinity from active groundwater seepage.     

Terrestrial invertebrates of dry river beds are not simply subsets of riparian assemblages

Dry river beds are common worldwide and are rapidly increasing in extent due to the effects of water management and prolonged drought periods due to climate change. While attention has been given to the responses of aquatic invertebrates to drying rivers, few studies exist on the terrestrial invertebrates colonizing dry river beds. Dry river beds are physically harsh and they often differ substantially in substrate, topography, microclimate and inundation frequency from adjacent riparian zones. Given these differences, we predicted that dry river beds provide a unique habitat for terrestrial invertebrates, and that their assemblage composition differs from that in adjacent riparian zones. Dry river beds and riparian zones in Australia and Italy were sampled for terrestrial invertebrates with pitfall traps. Sites differed in substrate type, climate and flow regime. Dry river beds contained diverse invertebrate assemblages and their composition was consistently different from adjacent riparian zones, irrespective of substrate, climate or hydrology. Although some taxa were shared between dry river beds and riparian zones, 66 of 320 taxa occurred only in dry river beds. Differences were due to species turnover, rather than shifts in abundance, indicating that dry river bed assemblages are not simply subsets of riparian assemblages. Some spatial patterns in invertebrate assemblages were associated with environmental variables (irrespective of habitat type), but these associations were statistically weak. We suggest that dry river beds are unique habitats in their own right. We discuss potential human stressors and management issues regarding dry river beds and provide recommendations for future research.     

Natural oligotrophy vs. pollution-induced eutrophy on the SE Mediterranean shallow shelf (Israel): Environmental parameters and benthic foraminifera

The eastern Mediterranean is naturally highly oligotrophic, but urbanization along the Levant coast has led to raised organic and nutrient loads. This study tracks living foraminiferal assemblages at two sites near an activated sewage sludge outfall from 11/2003 to 5/2004. Oligotrophic site PL29 shows seasonal variations in O_2, chlorophyll a, and organic carbon, and has an abundant, diverse benthic foraminiferal assemblage living at various in-sediment depths. At eutrophic site PL3, ∼16 years of sludge injection favor a depleted assemblage primarily of opportunist foraminifera. This site shows less seasonality, is subjected to organic matter overload, O₂-stress, and periodic anoxia, foraminifera are less abundant and diverse, and live at shallower depths. The assemblages at both sites represent a common pool of species, with Ammonia tepida highly dominant. Benthic foraminifera were therefore found to be sensitive to trophic trajectories, respond on sub-seasonal time-scales, and track injection and dispersal of organic loads on the shelf.     

The ichthyoplankton assemblage and the environmental variables off the NW and N Iberian Peninsula coasts,in early spring

Ichthyoplankton and mesozooplankton were sampled and fluorescence and physical environmental variables were measured off the NW and N Iberian Peninsula coasts, during April 2005. A total of 51 species of fish larvae, belonging to 26 families, were recorded. Sardina pilchardus, with 43.8% and 58.7% of the total fish egg and larval catches, respectively, dominated the ichthyoplankton assemblage. The study area was divided by a cross-shelf frontal structure into two hydrographic regions that coincided with the Atlantic and Cantabrian geographic regions. Ichthyoplankton abundance was higher in the Cantabrian region while larval diversity was higher in the Atlantic region. This was the main alongshore variability in the structure of the larval fish assemblage. Nevertheless, the stronger variability, related with the presence of a shelf-slope front, was found in the central-eastern Cantabrian region where two major larval fish assemblages, an “outer” and a “coastal”, were distinguished. The Atlantic region, where the shelf-slope front was not found, was inhabited by a single larval fish assemblage. Canonical correspondence analysis revealed that, off the NW and N Iberian Peninsula coasts, the horizontal distribution of larval fish species in early spring may be explained by a limited number of environmental variables. Of these, the most important were the physical variables depth and sea surface temperature.     

An ecological and hydrochemical study of three springs in NE Iran with the emphasis on diatom diversity

Springs are complex and taxa rich ecosystems. Diatom assemblages have received very little attention in spring ecosystems in Iran; hence, the diatom assemblage in three selected springs in northeast Iran, were investigated using multivariate analysis together with hydro chemical measures. For this purpose, water and diatom samples collected during four seasons of 2019. Hydrochemistry results revealed that water-rock interaction is the most important factor in changing the water chemistry of studied springs and their waters produced from carbonate reservoir rocks (mainly calcite). As a result, Ca-HCO₃ is predominate water type in all three springs. In this study, 75 diatom taxa identified, from which 55 were included in the analysis. Cluster analysis based on diatoms relative abundance, clustered samples in two major groups and third small group. Results of the indicator species analysis for groups and DCA analysis were in the absolute conformity. Results revealed that the diatom assemblage dominated by combination of early colonizer taxa, spring indicator taxa and cosmopolitan taxa; most of them also reported from different spring types. The results also showed that the spring’s diatom composition influence by size and morphology of the springs.