PERIPHYTIC DIATOM ASSEMBLAGES FROM BATHURST ISLAND, NUNAVUT, CANADIAN HIGH ARCTIC: AN EXAMINATION OF COMMUNITY RELATIONSHIPS AND HABITAT PREFERENCES

Diatoms are potentially the most important biomonitors of environmental change in high arctic lakes and ponds, but to date few autecological data are available. Because of the shallow nature of many of these water bodies, a large proportion of taxa are periphytic and planktonic diatoms are absent for the most part. By determining the microhabitat and substrate preferences of these benthic diatom taxa, the potential exists to infer past changes in available habitats from fossil diatom assemblages collected from sediment cores and ultimately to reconstruct past environmental and climatic changes responsible for these shifts in habitat availability. To refine our understanding of high arctic diatom habitat preference, the common diatom taxa found on submerged moss (bryophyte), sediment, and rock substrates from lakes and ponds on Bathurst Island, Nunavut, Canadian High Arctic were examined. The relationships among key limnological variables and the common taxa from each habitat were examined. Many diatom taxa exhibited varying degrees of microhabitat preference, with moss representing the more unique habitat. In addition, the following limnological variables significantly ( P ≤ 0.05) explained the species variance for each of the three substrates: Na ⁺ and total nitrogen for moss; total phosphorus (filtered) and pH for rock; and Fe^{3 +} , total phosphorus (unfiltered), total nitrogen, temperature, and pH for sediment. These data can be used to help interpret monitoring and paleolimnological studies in this environmentally sensitive region.     

PERIPHYTIC DIATOM ASSEMBLAGES FROM HIGH ARCTIC PONDS1

Epiphytic, epilithic, and surface sediment diatom assemblages were identified and enumerated from 35 study ponds on CapeHerschel (78°37″N, 74°42″W), east-central Ellesmere Island, Canada. All the sites are shallow (maximum depth <2 m), clear, oligotrophic, and freshwater. The ponds freeze completely for 10 months of the year. Major ion concentrations are relatively similar among the 35 sites, although environmental gradients exist. Over 130 diatom taxa from 28 genera were identified in the periphyton samples. Marked differences in species composition were evident among the ponds. Moreover, many of the diatoms exhibited varying degrees of microhabitat specificity. Variance partitioning by canonical correspondence analysis showed that 26% of the total variance exhibited by diatom species composition could be accounted for by the measured environmental variables (i.e. 10.2% by habitat and 15.8% by water chemistry). Pondwater alkalinity best explained the distribution of taxa, and weighted averaging regression and calibration were used to develop a transfer function to infer pondwater alkalinity from the diatom assemblages. Other important environmental variables included [Na⁺] for the epilithic and [SiO₂] for the epiphytic assemblages.     

Evaluating diatom community composition in the absence of marked limnological gradients in the high Arctic: a surface sediment calibration set from Cornwallis Island (Nunavut,Canada)

Fossil diatom assemblages preserved within the sedimentary record in Arctic lakes provide the potential to reconstruct past changes in important limnological variables. During the summers of 1992 and 1993, we examined previously unstudied freshwater ecosystems on Cornwallis Island, Arctic Canada, with the specific objectives of (1) documenting the limnology and modern diatom assemblages from this region, and (2) determining which environmental variables most influence diatom species distributions. The Cornwallis Island study sites displayed the least amount of variance in measured water chemistry variables in comparison to nearly all of our labs’ previous freshwater surveys in the Arctic. The small limnological gradients precluded the development of a statistically robust diatom inference model, but perhaps more importantly, allowed us to explore variations in diatom composition in the absence of marked variations in water chemistry. Diatom species turnover was minimal, with the most common diatom taxa being Achnanthidium minutissima, Nitzschia perminuta, N. frustulum, with lesser percent abundances of Chaemaepinnularia soehrensis, Navicula chiarae, Psammothidium marginulata, and A. kryophila. A small number of study sites differed from the majority with respect to water chemistry (e.g., coastal sites with high specific conductivities) and habitat availability (e.g., ephemeral ponds with extensive moss habitats), and these sites had markedly different diatom assemblages. These data reinforce previous observations that water chemistry and other climate-related factors are the primary environmental controls influencing diatom distributions at high latitudes. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Diatoms and their relationship to environmental variables from lakes and ponds on Bathurst Island, Nunavut, Canadian High Arctic

Baseline and historical environmental data are sparse in the High Arctic, however diatom assemblages preserved in high arctic lake and pond sediment profiles can provide proxy data of past environmental changes. Ecological data, however, are still sparse. Diatom taxa preserved in the surficial sediment of lakes and ponds on Bathurst Island (75° 42 N, 97° 21 W), Nunavut, Canadian High Arctic, and their relationship to 34 environmental variables were examined using multivariate statistics. A total of 148 diatom taxa were identified from the surface sediments of 29 study sites. Five environmental variables, Fe³⁺, Total Phosphorus (Unfiltered) (TPU), Total Nitrogen (TN), Temperature (TEMP) and pH significantly (P0.05) accounted for most of the variation in the diatom assemblages. TN was also significantly correlated to other variables (e.g. TPF, DOC, POC). A CCA constrained to TN indicated that this variable best explained the species distributions, and a weighted-averaging (WA) model was developed to infer nutrient levels from the relative abundances of the 58 dominant taxa. Interestingly, previous limnological work indicated that nitrogen most likely limited algal production in some of these high arctic sites. This model may be used to quantitatively estimate past TN levels from diatom assemblages preserved in sediment cores from Bathurst Island, and may provide a means to track past environmental changes in the High Arctic.     

RELATIONSHIPS BETWEEN LITTORAL DIATOMS AND THEIR CHEMICAL ENVIRONMENT IN NORTHEASTERN GERMAN LAKES AND RIVERS1

We explored statistical relationships between the composition of littoral diatom assemblages and 21 chemical and physical environmental variables in 69 lakes and 15 river sites in the lowland of northeastern Germany. Canonical correspondence analysis with single treatment and with forward selection of environmental variables was used to detect 11 important ecological variables (dissolved inorganic carbon [DIC], Na ⁺ , total phosphorus [TP], dissolved organic carbon [DOC], total nitrogen [TN], pH, oxygen saturation, dissolved iron, SO₄^{2 ?} , NH₄ ⁺ , soluble reactive silicium) and maximum water depth or Ca^{2 +} or soluble reactive phosphorus that most independently explain major proportions of the total diatom variance among the habitats. Monte Carlo permutation tests showed that each contributed a significant additional proportion (P < 0.05) of the variance in species composition. Together, these 11 most important environmental variables explained 34% of the total variance in species composition among the sites and captured 73% of the explained variance from the full 21 parameters model. Weighted‐averaging regression and calibration of 304 indicator taxa with tolerance down‐weighting and classic deshrinking was used to develop transfer functions between littoral diatoms and DIC, pH, TP, TN, and Cl ^? . The DOC:TP ratio was introduced and a weighted‐averaging model was developed to infer allochthonous DOC effects in freshwater ecosystems. This diatom‐DOC/TP model was significant (P < 0.001) and explained 7.6% of the total diatom variance among the sites, surpassing the inferential power of the diatom‐TP‐transfer function (7.3% explained variance). The root‐mean‐square errors of prediction of the models were estimated by jack‐knifing and were comparable with published data sets from surface sediment diatom samples. The data set of littoral diatoms and environmental variables allows use of the diatom‐environmental transfer functions in biomonitoring and paleolimnological approaches across a broad array of natural water resources (such as floodplains, flushed lakes, estuaries, shallow lakes) in the central European lowland ecoregion.     

BENTHIC DIATOM AUTECOLOGY AND INFERENCE MODEL DEVELOPMENT FROM THE CANADIAN HIGH ARCTIC ARCHIPELAGO1

Diatom assemblages were analyzed from 64 lakes and ponds from Alert, Ellesmere Island and Mould Bay, Prince Patrick Island in the Canadian High Arctic Archipelago. Diverse water chemistry conditions and diatom communities were present in these sites. Small benthic taxa typically dominated diatom communities; however, assemblages were markedly different between Alert and Mould Bay sites in response to disparate water chemistry characteristics in the two regions. The most abundant taxa belonged to the genera Navicula, Cymbella, Achnanthes, Nitzschia, and Pinnularia. Canonical correspondence analysis indicated that pH, specific conductivity, dissolved organic carbon, and total phosphorus were the most important limnological variables in determining species composition. Diatom inference models were developed for pH, specific conductivity, and dissolved organic carbon using weighted averaging and weighted averaging partial least squares techniques; these had root mean square error of prediction/r²_boot values of 0.40/0.77, 0.28/0.70, and 0.24/0.55, respectively. These models are applicable to sites with large ranges of taxonomic and limnological variation and will allow the reconstruction of past changes of climate‐related limnological parameters from biostratigraphic records in future paleolimnological studies.     

DIATOM COMMUNITIES FROM A DELAWARE SALT MARSH 1,2

Edaphic diatoms were collected from 5 representative habitats of Canary Creek salt marsh, Lewes, Delaware, from 24 July 1969 to 21 July 1970. Of the 104 taxa encountered, 32 had a general distribution on the marsh and 41 were endemic to one of the 5 habitats sampled. Three of the habitats supported stands of grasses: tall Spartina alterniflora Loisel., dwarf S. alterniflora, and Distichlis spicata (L.) Greene; and these habitats possessed the highest species diversity (H') and the greatest number of diatom species. The remaining 2 habitats, a bare bank and a panne, were devoid of macroscopic vegetation. The diatoms of these last 2 habitats were exposed to hypersaline conditions during warmer periods of the year and this was considered a contributing factor to the lower values observed for the aforementioned parameters of community structure. A comprehensive examination of the community structure characterizing the 5 habitats, employing statistical analyses and the distribution of species, showed each habitat to support its own unique and easily recognizable edaphic diatom community. A multiple regression analysis indicated that the differences between the 5 communities were closely related to differences in temperature and elevation between the habitats, and also a result of significant interactions between edaphic diatoms and filamentous algae.     

Distribution of benthic diatoms in relation to environmental variables in lowland streams

The composition (% relative abundance) of diatom assemblages from soft bottom sediments was studied at 75 sites situated in 46 rivers, brooks, and ditches in the islands of Hiiumaa and Saaremaa and in the lowland of West Estonia. Although the total number of recorded taxa was 205, the studied diatom assemblages consisted of 54, 55, 48, and 50 constant species in the drainage basin of Moonsund, the Gulf of Riga, Hiiumaa, and Saaremaa, respectively. The habitats of the dominating taxa were heterogenous and the most widespread species were Achnanthidium minutissimum, Martyana martyi, Meridion circulare, Cocconeis placentula, Planothidium lanceolatum, and Amphora pediculus. The Shannon–Weaver diversity (H) index varied from 2.09 to 4.63. Multivariate analyses were used to identify the environmental variables governing the composition and structure of the benthic diatom assemblage. Principal Component Analysis (PCA) and Redundancy Analysis (RDA), based on 56 most abundant taxa, indicated differences in the composition and structure of diatom assemblages between different drainage basins as well as between the upper and lower stream courses. In the headwaters there prevailed small epipsammic diatoms (Martyana, Planothidium, Staurosira, Staurosirella). Different motile epipelic species from the genera Amphora, Navicula, Nitzschia, etc. were distributed abundantly in the lower courses of the streams. There was a positive correlation between order of the stream site and trophic level of water (R=0.35; p<0.05). Along a river system, the increasing order of the stream was accompanied by higher trophic level of water.     

Diatom, chrysophyte and protozoan distributions along a latitudinal transect in Fennoscandia

Diatoms, chrysophyte scales and cysts, and the siliceous plates of thecoamoebae were studied from the surface sediments of 20 freshwater habitats in Fennoscandia The study sites are distributed along a latitudinal transect extending from southern Finland to northern Norway, spanning boreal forest through arctic tundra vegetational zones Diatom assemblages were usually dominated by acidophilic, periphytic members of the genera Achnanthe, Fragilaria and Navicula Marked shifts in diatom assemblage composition were recorded along the latitudinal transect, whereas scaled chrysophytes were rare in all study sites Meanwhile, siliceous protozoa were common, but did not exhibit any noticeable trends in assemblage composition with changing latitude A comparison of the Fennoscandian diatom assemblages with those recorded from freshwater sites near Yellowknife (central Northwest Territories, Canada) revealed similar trends in diatom assemblage composition with changing ecoclimatic zones in both regions Moreover, canonical correspondence analysis showed that diatom assemblages in cold, dilute tundra sites were effectively separated from sites with forested catchments from both the Fennoscandian and Canadian transects The general similarity between the two regions suggests that autecological data and the resulting environmental transfer functions based on diatom assemblages may eventually be joined from North American and European regions     

Impact of the invasive moss Campylopus introflexus on carabid beetles (Coleoptera: Carabidae) and spiders (Araneae) in acidic coastal dunes at the southern Baltic Sea

Campylopus introflexus is an invasive moss in Europe and North America that is adapted to acidic and nutrient-poor sandy soils with sparse vegetation. In habitats like acidic coastal dunes (grey dunes) it can reach high densities, build dense carpets and modify habitat conditions. While the impact of the moss invasion on the vegetation is well analyzed, there is a lack of knowledge regarding possible effects on arthropods. In the present study we analyzed the impact of Campylopus introflexus on the ground-dwelling arthropods carabid beetles and spiders, as both taxa are known to be useful indicator taxa even on a small-scale level. In 2009 we compared species composition in a) invaded, moss-rich (C. introflexus) and b) native, lichen-rich (Cladonia spp.) acidic coastal dunes by using pitfall traps. A total of 1,846 carabid beetles (39 species) and 2,682 spiders (66 species) were caught. Species richness of both taxa and activity densities of spiders were lower in invaded sites. Species assemblages of carabids and spiders differed clearly between the two habitat types and single species were displaced by the moss encroachment. Phytophagous carabid beetles, web-building spiders and wolf spiders were more abundant in native, lichen-rich sites. Shifts in species composition can be explained by differences in the vegetation structure, microclimate conditions and most likely a reduced food supply in invaded sites. By forming dense carpets and covering large areas, the moss invasion strongly alters typical arthropod assemblages of endangered and protected (EU-directive) acidic coastal dunes.     

CHANGES IN THE PLANKTONIC DIATOM FLORA OF A LARGE MOUNTAIN LAKE IN RESPONSE TO FERTILIZATION1

Fertilization (phosphorus and nitrogen) of Kootenay Lake, British Columbia, was begun in 1992 in an attempt to increase food resources for declining stocks of kokanee salmon. In 1992 and 1993, significant changes in diatom abundance, species composition, diversity, and morphology of individual species were observed in the fertilized North Arm in comparison to the unfertilized South Arm. Effects of fertilization were most obvious during the spring. During summer stratification, fertilization did not result in significant changes in total abundance, but changes in species composition were observed. In 1993, with continued fertilization of the North Arm, diatom abundance in both spring and summer was significantly higher than at the same sites in 1992. No significant differences were observed in the unfertilized South Arm. Diatom abundance was significantly correlated with dissolved inorganic nitrogen (positive) and dissolved reactive silica (negative). Diatom assemblages in the fertilized North Arm in both the spring and summer of 1993 were dominated by Asterionella formosa and Fragilaria crotonensis, taxa considered mesotrophic. Abundance of the oligotrophic taxa Rhizosolenia eriensis and Cyclotella michiganiana was higher in the South Arm than in the North Arm. Differences in diatom assemblages between the two arms in both years were further summarized by multivariate statistical analyses. Morphological variations in two small Cyclotella species (C. comensis and C. cf. pseudostelligera) were observed between the fertilized and “control” stations. Populations of both species from fertilized stations exhibited stronger silicification with coarser striations and a smaller mean size.     

FRESHWATER DIATOMS FROM THE CANADIAN ARCTIC TREELINE AND DEVELOPMENT OF PALEOLIMNOLOGICAL INFERENCE MODELS1

Relationships between surface sediment diatom assemblages and measured environmental variables from 77 lakes in the central Canadian arctic treeline region were examined using multivariate statistical methods. Lakes were distributed across the arctic treeline from boreal forest to arctic tundra ecozones, along steep climatic and environmental gradients. Forward selection in canonical correspondence analysis determined that dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), total nitrogen (TN), lake surface area, silica, lake‐water depth, and iron explained significant portions of diatom species variation. Weighted‐averaging (WA) regression and calibration techniques were used to develop inference models for DIC, DOC, and TN from the estimated optima of the diatom taxa to these environmental variables. Simple WA models with classical deshrinking produced models with the strongest predictive abilities for all three variables based on the bootstrapped root mean squared errors of prediction (RMSEP). WA partial least squares showed little improvement over the simpler WA models as judged by the jackknifed RMSEP. These models suggest that it is possible to infer trends in DIC, DOC, and TN from fossil diatom assemblages from suitably chosen lakes in the central Canadian arctic treeline region.     

DIATOM COMMUNITY STRUCTURE: TAXONOMIC AND STATISTICAL ANALYSES OF A MISSISSIPPI SALT MARSH1

Edaphic diatoms were collected on a seasonal basis from beneath five monospecific stands of spermatophytes on Graveline Bay Marsh (Mississippi) from 14 October 1976 through 21 June 1977. Of the 119 diatom taxa encountered. only seven were restricted to a single edaphic habitat, and five of these accounted for 17.2%of the individuals comprising the community associated with Distichlis spicata (L.) Greene. The single most abundant diatom was Navicula tripunctata (Müll.) Bory, which accounted for 21.5%of all individuals counted during the study. Based on a 2-way ANOVA of species diversity (H’) and the number of taxa in a sample, edaphic diatom community diversity was highest beneath D. spicata and Spartina patens (Ait.) Muhl., lowest beneath Sp. alterniflora Loisel. and Juncus roemerianus Scheele, and somewhat intermediate for the Scirpus olneyi Gray habitat. Structural differences between selected community pairs were quantified using a similarity index (SIMI) and the values generated were exceedingly variable. A multiple regression analysis revealed that structural differences amongst edaphic diatom communities were related to differences in elevation, far red light energy, ammonia nitrogen, soil moisture, and tentatively, height of the spermatophyte canopy.     

The moss dwelling testacean fauna of Île de la Possession

An ecological study of the moss dwelling testacean fauna (Protozoa, Rhizopoda) on Île de la Possession (Crozet Archipelago, sub-Antarctica) revealed 83 taxa, belonging to 21 genera. The moss flora was dominated by cosmopolitan and ubiquitous taxa, such as Trinema lineare, T. enchelys, Euglypha laevis and E. rotunda. A cluster analysis and a correspondence analysis identified three communities: (1) a Corythion dubium assemblage found in a drier, slightly acidic terrestrial moss vegetation, (2) the Arcella arenaria, and (3) the Difflugiella crenulata assemblages, both characteristic of wetter, circumneutral habitats. The latter typified submerged mosses growing in running water, while the A. arenaria assemblage seemed to prefer mosses in standing waterbodies. Moisture conditions appeared to play a key role in determining the distribution pattern of testacean communities, while pH was only a secondary factor. A logistic regression emphasised the effect of the habitat type in controlling the variance in testacean assemblages. Moreover, the close relationship between bryophyte species and habitat type had a significant influence on the distribution pattern of the testate amoebae. Weighted averaging and calibration were used to estimate moisture optima and tolerances of the testate amoebae.     

DIATOM PALEOLIMNOLOGY OF TWO FLUVIAL LAKES IN THE ST. LAWRENCE RIVER: A RECONSTRUCTION OF ENVIRONMENTAL CHANGES DURING THE LAST CENTURY

Water quality degradation is a serious concern for the St. Lawrence River. While some environmental data are available for the St. Lawrence ecosystem, long-term monitoring data are generally lacking. To infer past environmental changes, we undertook a paleolimnological assessment of diatom assemblages preserved in four ²¹⁰Pb- and ¹³⁷Cs-dated sediment cores from two fluvial lakes in the river, and used diatom transfer functions to infer past shoreline habitat characteristics. At sites in Lake Saint-François, a fluvial lake downstream from Cornwall, water quality decreased this century in response to human impacts (e.g. macrophyte density and nutrient levels increased). These trends were apparent from an increase in epiphytic diatom taxa, followed by an increase in eutrophic planktonic taxa. Water quality, however, appears to have improved somewhat in response to rehabilitation measures during the last two decades. From a sediment core near Montréal (Lake Saint-Louis), we also noted a large proportion of eutrophic and epiphytic taxa, but less evidence was recorded of a recent improvement in water quality. The diatom-based inference model for habitat characteristics appeared to reconstruct environmental conditions in the St. Lawrence River during the last century. The most notable shift has been an increase in diatom taxa commonly associated with macrophyte substrates. Trends in some of the planktonic diatoms were similar to those recorded in paleolimnological investigations from Lake Ontario, but cores from the river also may be reflecting local environments. This study shows that diatom-based paleolimnological studies are possible in large river systems, if coring sites (e.g. fluvial lakes) are carefully selected.     

Ecology of terrestrial testate amoebae assemblages from coastal Lowlands on Devon Island (NWT,Canadian Arctic)

Summary Fifty-seven taxa belonging to 17 genera of testate rhizopods were recorded in samples of mosses, soils and lichens, collected from the Truelove and Sparbo Hardy Lowlands on the high arctic Devon Island (NWT, Canada). Different groups of habitats are characterized by particular assemblages of Testacea species, with the quantity and quality of the available water as important ecological parameters. The Assulina muscorum-Corythion dubium assemblage characterizes the most dry and acidic moss habitats, while the Paraquadrula irregularis assemblage is to be found in wet and rather neutral habitats. The sedge moss meadows with their more moderately coarse textured and poorly drained soils, bear a Plagiopyxis callida-Plagiopyxis declivis soil-dwelling testate amoebae assemblage. The Centropyxis minuta assemblage lives in the most coarsely textured soils. pH seems to play a subordinate role, not only in the mosses but also in the soils. Multivariate methods (cluster analysis and CANOCO) have been used to separate these different assemblages.     

Diatom Assemblages and their Associations with Environmental Variables in Oregon Coast Range Streams, USA

The Oregon Coast Range, rich in natural resources, is under increasing pressure from rapid development. The purpose of this study was to examine diatom species patterns in relation to environmental variables in streams of this region. Diatoms, water quality, physical habitat and watershed characteristics were assessed for 33 randomly selected stream sites. Watershed size, elevation, geology, vegetation and stream morphology varied substantially among sites. Streams were characterized by dilute water chemistry and a low percent of fine substrate. A total of 80 diatom taxa were identified. Taxa richness was low throughout the region (median 15, range 10–26). Assemblages were dominated by two adnate species, Achnanthidium minutissimum and Achnanthes pyrenaicum. Diatoms sensitive to organic pollution dominated the assemblages at all sites (median 85%). Non-metric multidimensional scaling (NMDS) and correlational analysis showed quantitative relationships between diatom assemblages and environmental variables. NMDS axes were significantly correlated with watershed area, watershed geology, conductivity, total nitrogen, total solids and stream width. Diatom-based site classification (Two-way Indicators Species Analysis, (TWINSPAN)) yielded 4 discrete groups that displayed weak correlations with environmental variables. When stream sites were classified by dominant watershed geology, overall diatom assemblages between groups were significantly different (Analysis of Similarity (ANOSIM) global R = 0.19, p < 0.05). Our results suggest that streams in the coastal region are in relatively good condition. High natural variability in stream conditions in the Oregon Coast Range ecoregion may obscure quantitative relationships between environmental variables and diatom assemblages. A bioassessment protocol that classifies sites by major landscape variables and selects streams along the major human disturbance gradient might allow for detection of early signs of human disturbance in environmentally heterogeneous regions, such as the Pacific Northwest.     

Long‐term limnological changes in the Ecuadorian páramo: Comparing the ecological responses to climate warming of shallow waterbodies versus deep lakes

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DIATOM ASSEMBLAGES OF STREAMS INFLUENCED BY WILDFIRE1

The Greater Yellowstone Area ecosystem experienced major wildfires in 1988, resulting in a substantial number of catchments being burned. We studied diatom assemblage structure at 14 sites over 5 years in catchments ranging from 0 to over 90% burned. Coefficients of variation for selected physical measures provided a good assessment of the degree of disturbance experienced by the various sites and correlated highly with percentage of catchment burned. Principal components analysis quantitatively estimated the degree of temporal change in diatom assemblages at a site. The more extensively burned catchments showed the greatest amount of structural change in diatom taxa among years. Navicula permitis Hust. and Nitzschia inconspicua Grun. were predominant in the heavily disturbed systems, whereas Achnanthes minutissima Kuetz., A. lanceolata (Breb.) Grun., Rhoicosphenia curvata (Kuetz.) Grun. ex Rabh., and Diatoma hiemale var. mesodon (Ehr.) Grun. were common in less disturbed streams. The results demonstrate that recovery trajectories of lotic diatom assemblages following major landscape-scale disturbances are a function of disturbance intensity resulting from differences in catchment characteristics.     

Benthic macrocrustacean and insect assemblages in relation to spring habitat characteristics: patterns in abundance and diversity

We studied variation in benthic macrocrustacean and insect assemblages in relation to spring habitat characteristics in six springs located in a single groundwater area in south-west Finland. We defined five habitat types in the studied springs according to water flow and benthic substrate characteristicsminerogenic brooks, organogenic brooks, helocrenes, floating moss carpets and limnocrene pools. Most studied invertebrate orders, as well as individual taxa, showed differences in relative abundances between the habitat types, but the most common taxa occurred in all springs and habitat types. The studied macroinvertebrates were most abundant in the moss carpet sites and least abundant in the pool sites, but the difference was not statistically significant. We did not observe significant differences in mean taxonomic richness per sample between habitat classes. The observed taxonomic richness in pooled samples of habitat classes was highest in moss carpet habitat and lowest in pool habitat, and the rarefied richness estimate was lowest in pool habitat. Benthic macrocrustacean and insect assemblages varied more between habitat types than between individual springs. In an Nonmetric Multidimensional Scaling ordination analysis, spring brook sites were separated from the moss carpet and pool sites, whereas helocrene sites were widely scattered among sites in other habitat classes. The strongest ecological gradients were related to water flow and the presence of minerogenic substrate, separating lentic and lotic habitats. Abundances of moss and coarse detritus accounted for most of the within-class variation. We identified several indicator species for minerogenic and organogenic brooks and for moss carpet and pool habitats, but none for the helocrenes. We found several occurrences of two crenobiont insect species considered threatened in Finland. We suggest that combined studies on macroinvertebrate and bryophyte assemblages would be a powerful approach in assessing the biodiversity of springs.