Fundamental and Applied Limnology / Archiv für Hydrobiologie

Published by E Schweizerbart Science Publishers
Print ISSN: 1863-9135
Publications
The aim of this study was to better understand the relationships of within- and among-lake variability of macroinvertebrate carbon stable-isotope ratios with both lake trophic potential and lake trophic functioning. Two approaches based on the macroinvertebrate communities were undertaken on 11 French lakes: the Lake Biotic Index (LBI), a lake biological quality assessment method (Verneaux et al. 2004 a), and the carbon isotopic signatures of macroinvertebrates expressed by metrics of dispersion (standard deviation of the littoral macroinvertebrate mean δ13C values and differences between littoral and deep mean δ13C values (Δδ13C)). The littoral macroinvertebrate mean δ13C values obtained ranged from -11.7 ‰ to -38.6 ‰. This great among-lake variability can be partially explained by different geological substrata on which the lakes are located and, potentially, by the lake organic matter recycling activity. Moreover, the depth-related differences in macroinvertebrate community δ13C (Δδ13C values) or macroinvertebrate taxa (taxon 13C depletion: TΔδ13C) were highly correlated to the values of a LBI sub-index, which was itself correlated to hypolimnion oxygenation and deep sediment organic matter contents. This result suggests that the studied lakes showed various degrees of deep recycled carbon assimilation. The depth-related macroinvertebrate 13C depletion may then be considered as describing the result of lake trophic functioning. However, because no correlation was observed between littoral macroinvertebrate δ13C variability and lake trophic potential, it seemed difficult to conclude as to the influence of different carbon sources on this potential.
 
Map of the Macun catchment showing the location of study sites within each basin.
Results of a principal components analysis based on the relative abundances of macroinvertebrate taxa collected each summer in 2001-2004 from each site. Taxa labeled along each axis loaded > 0.70 for that axis. A negative sign before a taxon indicates a negative relationship of that taxon with the axis. Symbols represent the mean (± SD) factor scores for each site. Axis-1 explained 25 % and axis-2 15 % of the variation among samples. Numbers represent site numbers as in Fig. 1 and tables.
Results of a principal components analysis based on the relative abundances of the top 11 chironomid species collected from the study sites in July (a), August (b), and September (c) 2002. Taxa labeled along each axis had factor loadings > 0.70 for that axis. A negative sign before a taxon indicates a negative relationship of that taxon with the axis. Numbers represent study sites and letters the respective month. Top panel includes sites from the south basin and site 9 (Immez outlet) and site 10 (Zeznina), and the bottom panel includes sites from the north basin. A minus sign before a species indicates a negative relationship of that species along the axis. Axis-1 explained 18 % and axis-2 16 % of the variation among samples.
Macroinvertebrate assemblages of inlet and outlet streams were examined in a high elevation cirque comprising two basins in the Swiss Alps. Average taxon richness, with chironomids included as a single taxon, was < 8 at most sites. Chironomids represented between 26 and 85 % of the individuals and at least 50 % of the species collected at the different sites with over 22 chironomid species identified in total. No differences in the relative abundance of common macroinvertebrate taxa were found between inlet and outlet streams, but composition differed between the north and south basin of the cirque. The north basin was mostly fed by groundwater and snowmelt, whereas the south basin was dominated by glacier-melt from rock glaciers. Chironomids were 26 % more abundant and had more species in south basin than north basin streams, whereas the simuliid Prosimulium latimucro was 24 % more abundant in north basin streams. Other common taxa, e.g., Nemoura sp., Dicranota sp., Crenobia alpina and Pseudopsilopteryx zimmeri, also showed substantial differences in abundance between the two basins. Diamesinae and Orthocladiinae were the most common chironomid subfamilies collected with Diamesa zernyi/cinerella, Pseudodiamesa branickii, Pseudodiamesa arctica, Corynoneura scutellata, and Tvetenia calvescens together representing on average >10 % of the assemblage at most sites. Chironomid abundance typically was higher in outlets than inlets. An exception was Diamesa zernyi/cinerella, which had greater relative abundances in inlets (24 %) than outlets (6 %). The results suggest that alpine macroinvertebrates, chironomids in particular, are sensitive to subtle differences in habitat conditions and may thus make good sentinels of environmental change to alpine waters.
 
This paper describes the life cycle of Pisidium henslowanum living in Lake Piediluco (southwestern Umbria, Italy). Morphological and histological analysis of samples taken monthly over a period of two years (February 1993 - February 1995) allowed us to follow the annual changes in the gonad tissues, and to ascertain that the species is fertile for most of the year with two peak periods, which occur in July and November, when there is massive gamete release. A short period of non-fertilization takes place in January and February when few spermatozoa occur and no ova are produced. Through the monitoring of the ontogenetic stages of P. henslowanum in Lake Piediluco, it was possible to determine the average life span of two distinct generations per year to be 12-14 months for the main one (winter generation) and 14-16 months for the subsidiary one (summer generation). The population is semelparous and bivoltine, with hatchings in late spring and late autumn. Self-fertilization was documented in many specimens, since a large number of free spermatozoa and ova were observed within the female follicles.
 
Detailed morphology of three North American species of the genus Alona Baird, 1843: A. bicolor Frey, 1965, A. circumfimbriata Megard, 1967 and A. setulosa Megard, 1967 was studied for the first time. The taxonomic status of these species is now clarified. A. bicolor belongs to the costata-group. Unlike to other species of the group, it demonstrates strong adaptation to benthic habitats - incl. thick carapace, a elongated rostrum and reduced eye. A. circumfimbriata is a member of rectangula-group, and its closest relative is the tropical A. monacantha Sars, 1901, differing in morphology of postero-ventral angle of valves and exopodite of limb III. A. setulosa has numerous characters in common with the species of the pulchella-group, but the relationship is more distant than in two other discussed species.
 
The copepodid phases and adults of Acanthocyclops trajani and Acanthocyclops einslei were studied to record their distinguishing characteristics. Morphological examination showed that copepodids of both species were very similar, and showed an identical pattern of articulation and ornamentation of appendages and antennules. Differences in the distal endopodid of the fourth swimming leg and antennal ornamentation were found in later stage copepodids of both species. A. trajani had a higher ratio of apical spines on the distal endopodid of the fourth swimming leg compared to A. einslei, as well as a higher segment length/width ratio, and site of lateral spine insertion, which is more distal in A. einslei compare to A. trajani. Based on morphological descriptions of the copepodids of A. trajani and A. einslei, reported in this study, discrimination of later stage copepodids is feasible and may serve as a tool for basic ecological studies of zooplankton communities that is not dependent on the presence of adult specimens.
 
We examined subfossil Cladocera (crustacean) assemblages and ephippia in a high-resolution sediment core from a small acidified boreal lake, Lake Pieni Majaslampi, in southern Finland, with a focus on community and reproductive responses during a period of environmental disturbances. The results showed a significant community shift ∼1970-1980 AD as planktonic taxon Eubosmina, together with littoral chydorids Acroperus harpae, Alonella excisa, and Alona rustica increased and populations of Alonella nana and Alona affinis declined. In addition, a concurrent and significant change in reproductive patterns occurred, as sexual reproduction of Eubosmina, A. affinis, and A. harpae increased. It appears likely that these ecological shifts were a response to multiple environmental stressors related to severe acidification that took place in this sensitive lake and culminated during the 1980s. Acidification of Lake Pieni Majaslampi resulted in dramatic changes in the food-web structure; perches (Perca fluviatilis) were extirpated and invertebrate predation predominated from the 1980s onwards and after this Eubosmina, which is known to be a desirable prey item for perches in acidic lakes, was apparently favored in the fish-free ecosystem. Furthermore, the observed reproductive shifts were perhaps adaptive responses to either increased invertebrate predation or to increased toxicity of the environment. As the analysis of subfossil ephippia allowed us to detect behavioral shifts in the cladoceran community related to lake acidification, ephippium analysis can provide a powerful tool to integrate ecology and paleoecology, and to enhance our understanding of changes in aquatic ecosystems determined from paleolimnological studies.
 
Bacterial consortia at sediment-water interfaces (SWIs) conduct metabolic processes that affect lake and reservoir organic matter cycling and nutrient composition. Seasonal reservoir dynamics such as stratification and overturn influence SWI bacterial activity and bacterial biomass production. We measured SWI bacterial uptake rates of tritium-labeled L-serine (Ser) to assess SWI bacterial activity and production in a monomictic, eutrophic reservoir. Total microbial Ser uptake (Sertot) and uptake in the protein fraction (Serpro) were measured seasonally. Serpro was approximately 40 percent of Sertot which demonstrated that Ser was incorporated into cellular material other than protein. Highest bacterial Sertot and Serpro occurred during the onset of summer stratification (Jun 2005) followed by late-season stratification (Oct 2005). Lower Sertot and Serpro were observed after the onset of autumnal overturn (Oct 2004) and during winter mixing (Feb 2005). Higher SWI temperature, lower dissolved oxygen, and decreasing redox potential, which are a function of summer stratification, were associated with higher Sertot and Serpro. Estimates of SWI bacterial production and growth rates indicated that highest production and fastest community generation times also occurred at onset of summer stratification and during late-season stratification. These data suggest summer stratification, and not autumnal overturn and winter mixing, is responsible for higher SWI bacterial metabolism, even under anoxic conditions during which bacteria utilize less energetically favored electron acceptors. We conclude that stratification is an important event that increases SWI bacterial metabolism, which results in increased carbon mineralization and nutrient cycling from sediments to the water column that affects water quality and reservoir trophic status.
 
Cercopagis predation rate to prey concentration for different species: results from single prey species experiments. Func- tional response is shown for the prey species where more prey concentrations were tested. Filled symbols show the median, the top of the box above the median represents the 75 percentile and the bottom below the median the 25 percentile. The whiskers show the 95 and 5 percentile, the open symbols are outliers, not included in the analysis. Zm veligers means zebra mussel ( Dreissena polymorpha ) veligers. 
Overview of single prey species experiments.
Clearance rate (mean ± standard error of mean) of Cercopagis for different prey in concentration 20 ind. L-1. Number of replicates for each prey species is shown above error bars. Bo = Bosmina longirostris, Eu = Eubosmina coregoni, Da = Daphnia retrocurva, Ch = Chydorus sphaericus, na = nauplii, di = diaptomids, Pl = Ploesoma truncatum, zm = zebra mussel (Dreissena polymorpha) veligers.
Overview of selectivity experiments
Body length of Cercopagis in different instars used in experiments. Filled symbols show the median, the top of the box above the median shows the 75 percentile and the bottom below the median shows the 25 percentile. The whiskers show the 95 and 5 percentile, the open symbols represent outliers.
We carried out a comprehensive exploration of predation by the invasive predatory cladoceran Cercopagis pengoi in the laboratory. A range of potential prey was offered to the predator, including all major summer nearshore zooplankton taxa in Lake Michigan; we used prey in different concentrations from 5 to 100 ind. L–1. We found that Cercopagis is a generalist capable to consume a variety of prey species, including small and large prey, and slowly and rapidly swimming prey. Consumption rates increased with concentration in several species, but did not saturate even at the highest concentration tested (40 or 100 ind. L–1). Cladocerans were consumed at a higher rate than copepods. Cercopagis was able to catch and handle prey of nearly its own body size to prey about seventeen times smaller; however, it did not show any clear size preference within this range. In contrast to most indigenous Great Lakes zooplankton, Cercopagis can efficiently feed on veligers of the zebra mussel, another invader from the Ponto-Caspian region.
 
Light absorbing constituents are important regulators of the underwater light field and the signal available for remote sensing of water quality. The spectral characteristics, magnitude and variability of the components of light absorption are documented and contrasted here for the broad range of conditions manifested in the 11 Finger Lakes of New York. The absorption coefficient, a (m-1), was partitioned according to the additive components of colored dissolved organic matter (aCDOM), non-algal particles (aNAP), phytoplankton (aφ), and water itself (aw; known), using laboratory spectrophotometric protocols on near surface samples collected monthly in 2004. Bulk in-situ measurements included Secchi disc depth (SD), irradiance profiles to determine the diffuse attenuation coefficient (Kd, m-1), and the beam attenuation coefficient at 660 nm [c(660)]. The average exponential slope values for CDOM (0.0175 nm-1) and NAP (0.0121 nm-1) were nearly equivalent to, and spectral features of aφ were similar to, those reported by Babin et al. (2003b) for coastal marine waters around Europe. Order of magnitude differences in study average values of aCDOM, aNAP, and aφ were observed amongst the study lakes. The largest component in each of the lakes, for the commonly adopted reference wavelength of 440 nm, was CDOM; it represented from 48 to 68 % of a amongst the study lakes. The aNAP and aφ components were approximately of equal importance, with aNAP(440) exceeding aφ(440) in 6 of the lakes. The value of a, from summation of the measured components, was a strong predictor of Kd differences amongst the lakes, and it had significant relationships with average values of SD and c(660). The ratio of the watershed area to the lake volume was found to be a strong predictor of the major differences in both aCDOM(440) and aNAP(440) amongst the lakes indicating the importance of terrigenous inputs of these constituent.
 
Features of light absorption are critical to optical aspects of water quality and in regulating the signal available in the emergent flux from the surface. Spectral characteristics, dynamics, and relationships with optically active constituents and common optical metrics, are documented for three light absorbing components in culturally eutrophic Onondaga Lake, New York, U.S.A., based on the results of a 5 year study. The absorption coefficient, a(m−1), is partitioned according to the additive components of colored dissolved organic matter (aCDOM), non-algal particles (aNAP), phytoplankton (aφ), and water itself (aw; known), based on laboratory measurements for near surface samples collected weekly for the spring to fall interval over the 2004-2008 period. Supporting bulk measurements included dissolved organic carbon, total suspended solids (TSS) and its organic and inorganic (FSS) fractions, the concentrations of total phosphorus and chlorophyll-a ([Chl]), downwelling irradiance profiles to determine the diffuse attenuation coefficient (Kd), the beam attenuation coefficient at 660 nm [c(660)], and Secchi disc depth. The average exponential slope values for aCDOM (0.0168 nm−1) and aNAP (0.0126 nm−1) were very similar to those reported for other case 2 systems. The shapes of aφ spectra, represented by the ratio aφ(440):aφ(676), were found to negatively depend on [Chl]. The largest component of a at 440 nm, the reference wavelength, in each of the 5 years was aCDOM (∼45 to 60 %), the smallest was aNAP (∼15 to 25 %). Progressive decreases in yearly average aφ, particularly over the last three years are documented in response to decreases in [Chl], driven by increased nutrient limitation and Daphnia grazing (2008 only). Wide short-term variations are demonstrated within years for the components of a, particularly in response to the timing of runoff and Daphnia grazing events. Strong positive relationships are reported between aNAP and both TSS and FSS, aφ (at both λ = 440 and 676 nm) and [Chl], and ap (aNAP plus aφ) and both TSS and c(660). The summation of the absorbing components at 440 nm is demonstrated to be a strong predictor of Kd. The utility of the information in supporting a model for Kd and SD and advancing monitoring of water quality through measurements of surface reflectance is described.
 
Monitoring data for the northern station Kigoma in Lake Tanganyika. (A) Potential energy anomaly (PEA) calculated for the upper 100 m and the mixing depth over euphothic depth ratio Zm:Zeu. (B) Soluble reactive phosphorus (SRP) and nitrate (NO 3 -N) concentrations at a depth of 20 m (C to F) temporal changes in biomass at a depth of 20 m for: (C) phytoplankton size classes, (D) biomass of phytoplankton groups obtained from inverted microscope (≥ 5 µm), (E) bacterial and HNF biomass, (F) biomass of different ciliate groups.  
Monitoring data for the southern station Mpulungu in Lake Tanganyika. Panels as in Fig. 2.  
Map of Lake Tanganyika with indication of the sampling sites. Open circles indicate the sampling sites (Kigoma and Mpulungu) during the seasonal monitoring (Feb. 2002 to Aug. 2004). Filled circles indicate the sites sampled during three north-south transects (Jul. 2002, Jul. 2003, Feb. 2004).  
This study aims to evaluate the seasonal and interannual variability in the importance of the microbial food web in Lake Tanganyika. Phytoplankton, bacteria and protozoa (heterotrophic nanoflagellates and ciliates) were monitored at two contrasting pelagic sites (Kigoma and Mpulungu) during 3 consecutive years. In addition, spatial variation was studied along 3 north-south transects during contrasting seasons. The study period covered a wide range of limnological conditions, with mixing depth ranging from 13 to >100 m and euphotic depth from 14 to 65 m. The consistently high bacterial biomass (up to 62 μg C l−1 ) and the high contribution of small phytoplankton (< 5 μm) to the total phytoplankton biomass (on average 50 % in Kigoma and 84 % in Mpulungu) point to an important role of the microbial food web in the lake throughout the year. Total phytoplankton biomass increased during periods of low water column stability, with an increased biomass of small eukaryotic phytoplankton (2 to 5 μm) at both stations, together with autotrophic prokaryotic picoplankton at the southern station Mpulungu and diatoms at the northern station Kigoma. Heterotrophic bacteria, heterotrophic nanoflagellates (0.06 to 11.01 μg C l−1 ) and ciliates (up to 8.16 μg C l−1 ) did not show this seasonality. The main seasonal and spatial variability in the importance of the microbial food web seems therefore primarily linked to the contribution of small phytoplankton, which may be better adapted to lower average light intensities and higher N:P ratios during periods of deep mixing.
 
The spatial and temporal patterns in concentration and character of dissolved organic matter (DOM) in karst basins in Slovenia and the United States were characterized. DOM in the shallow aquifer, or epikarst, waters was characterized by low, stable concentration and compounds of low aromaticity and humification. There was strong temporal coherence in DOM character, but not concentration, across locations within the epikarst. DOM in sinking streams, cave streams, and resurgence springs typically had higher DOM concentration and aromaticity. Fluorescence and parallel factor analysis of DOM revealed that humic or fulvic-like substances in soils, surface and cave streams, and springs were the dominant fluorophores. However, DOM extracted from soils was chemically different from that present in the stream and spring waters. Epikarst water contained humic-like and protein-like DOM, and had fluorescence characteristics indicative of microbial uptake and release of DOM in the epikarst. These data show that there are substantial basin-scale patterns in DOM concentration and character and that aquifer structure influences the spatial patterns of DOM in karst groundwater.
 
We investigated the vertical distribution and dynamics of viral abundance in the euphotic epilimnion and aphotic hypolimnion during periods of stratification in Lake Biwa, Japan. The abundance of virus-like particles (VLPs) was lower and more constant in the hypolimnion than in the epilimnion. Simple correlation analysis demonstrated that during periods of stratification, VLP abundance in the hypolimnion was positively correlated with chlorophyll-a concentration, the bacterial abundance of the >0.8-μm fraction, and water temperature. On the other hand, VLP abundance in the epilimnion was also positively correlated with chlorophyll-a concentration and the bacterial abundance of the >0.8-μm fraction, but was negatively correlated with the bacterial abundance of the 0.2-0.8-μm fraction and was not correlated with water temperature. We observed no correlation between VLP abundance and total bacterial abundance in either the epilimnion or the hypolimnion. Multiple regression analysis indicated that VLP abundance was explained by chlorophyll-a concentration in both the epilimnion and the hypolimnion. Aphotic environment and abundance of phytoplankton and bacteria in the hypolimnion, suggesting that main host of viruses is bacteria rather than phytoplankton. However our results suggest that VLP abundance in the hypolimnion related to the other factors as well as bacterial abundance.
 
Summary of comparisons of crab carapace width (CW) among habitat types. Analyses were carried out after pooling all site data within habitat classes. Key: NS = not sig- nificant (P> 0.05).
Little is known about population densities of freshwater crabs, or their ecological importance, in African rivers. This study aimed to quantify crab abundance in rivers draining Mt Kenya. Invertebrates were sampled from 21 sites on 19 rivers. Sample sites were divided into: open sites in agricultural land from which trees were mainly absent; shaded sites, in agricultural land, with cultivated catchments but heavy shading by riparian trees; and forest sites, still dominated by natural vegetation. Crabs, mainly Potamonautes odhneri, were recorded from 14 of the 21 sites, including all forest sites, and were significantly more abundant in forest sites than in either type of agricultural site. However, there was no difference in biomass among habitat types, because individual crabs were significantly smaller on average in forest sites. This was due to the large numbers of small juvenile crabs recorded in forest sites, whereas small juveniles were almost absent from all agricultural sites. Although numerically unimportant relative to other macroinvertebrates, crabs accounted for at least 70 % of total macroinvertebrate biomass from forest and shaded agricultural sites, and averaged around 40 % in open agricultural sites. It is possible that crab reproduction occurs mainly or exclusively in forested areas, which would therefore act as a recruitment source for populations farther downstream in agricultural areas.
 
Leaf litter inputs, an essential driver of river ecosystem structure, are heavily influenced by local and basin wide changes. Urbanization can impact leaf litter inputs at both scales, but the consistency of ecosystem response is unknown. In this study, we investigated relationships between basin land use coverage, reach-scale canopy conditions, and macroinvertebrate shredder metrics in 42 streams across a gradient of landuse in the Piedmont of Georgia, USA. We then evaluated how urbanization affects vertical leaf litter inputs and also autumn and spring leaf litter availability in a subset of 13 streams. Reach-scale riparian conditions controlled canopy cover and vertical litter inputs, but leaf litter standing crop dynamics were more complex and seemed to be controlled at the catchment level by factors beyond land use coverage. Overall, sites with less urbanization had greater litter standing crops during December; however, higher rates of retention occurred in more urbanized areas. We infer that urban streams balance litter export with additional horizontal inputs from storm drains that act to increase the litter source area. Macroinvertebrate shredder taxa richness was negatively affected by watershed landuse, but shredder abundance and percent composition were not. Shredder abundance and composition were not correlated to litter availability. The apparent importance of horizontal leaf litter inputs to urban stream detritus budgets indicates that further studies are warranted to characterize and quantify litter inputs from storm drains and to gain a better understanding of how these inputs effect shredder populations.
 
Lebertia (Brentalebertia nov. subgen.) hygropetrica nov. spec. is described from deutonymphs and adults of both sexes collected in a cascade spring in the Brenta-Adamello Natural Park (Trentino, Italy). The new taxon differs from all known species of the genus in having doubled acetabula (in adults resulting in three pairs of acetabula on each side of the gonopore), in the shape of the anterior coxal tips (finely pointed and bent downwards), the gnathosoma (very slender and elongated), and palp (stout, with thickened P-4).
 
Given the increasing problems with invasive aquatic plants in many freshwaters, more research on macrophyte acceptability by herbivores is warranted. Our study deals with the comparison of the acceptability in different seasons of a naturalised (Elodea canadensis) and a recently introduced species (Elodea nuttallii) originating from North America, for an omnivorous shredder, the amphipod Gammarus roeseli. It also compares acceptability trends of various plant parts (apex, defoliated stem and foliated stem) in the case of E. nuttallii. Two determinants of plant palatability (the plant dry matter content and the carbon/nitrogen ratio) were measured at each season for the two macrophytes. Our results show contrasting seasonal patterns for the two Elodea species. The main result is the highly contrasting acceptability of the two Elodea species in summer. Moreover, the consumption of the macrophytes tends to increase from spring to autumn. The lower acceptability of E. canadensis could be explained by a higher dry matter content, reflecting higher physical and chemical defences than those of E. nuttallii. The contrasting consumption patterns between the two macrophytes observed in summer could indicate different strategies against the herbivores that should be related to their introduction history. The lower carbon/nitrogen ratio in autumn could explain the increase of acceptability of both Elodea species in this season. The transition towards dormancy of both macrophytes and the subsequent decrease in defence mechanisms may induce colonisation by epiphytes and microbial decomposers and therefore the increase of nitrogen content.
 
The effects of organic matter in sediment on phosphorus release were studied by field investigations in eight Chinese shallow freshwater lakes with different trophic status and a laboratory experiment. The sediment organic matter content paralleled the trophic status, ranging from 6.1 to 173.0 g kg−;1 (dry weight), with the mean value of 63.1 g kg−1 (dry weight). It was positively proportional to soluble reactive phosphorus concentration in the interstitial water in a form of exponential function, but inversely related to the sediment Fe/P ratio. The sediment alkaline phosphatase activity was significantly related not only to the organic matter content (r = 0.829, P < 0.01, n = 120), but also to the soluble reactive phosphorus concentration in interstitial water (r = 0.454, P < 0.01, n = 42). In the laboratory experiment, the addition of organic matter (dry materials of an aquatic macrophyte) into the sediment significantly enhanced alkaline phosphatase activity and soluble reactive phosphorus release. However, in the treatment with organic matter added and aeration, this release was generally prevented in spite of an increase in APA. Hence, sediment organic matter can effectively accelerate phosphorus release by enzymatic hydrolysis and anaerobic desorption. The latter mechanism seems to be more important.
 
Nutrient pollution effects are not always apparent in freshwater sediments, because increase of N and/or P concentrations in recent sediments is also a consequence of sediment diagenesis. In the present work, two cores of sediment have been extracted from Colgada lake (CL) (Lagunas de Ruidera Natural Park, central Spain), one of them dated using radiometric techniques, and their C, N and P contents determined at different depths. CL has experienced significant local P inputs and regional N groundwater inputs over the last 60 years. An analysis of N and organic carbon content and their accumulation rates in the cores is performed in order to ascertain the relative importance of the two processes - mineralization and pollution - in the organic C and N profiles. CL sediments were significant middle- and long-term organic N and C sinks (about 10 g C m-2 y-1 and 1 g N m-2 y-1). This sink has intensified in the last 20-25 years to about 23 g C m-2 y-1 and 3.8 g N m-2 y-1. Relatively low C/N of sediments indicated a predominantly in-lake phytoplankton source of the sedimented organic matter over the last 50 years. A diagenesis model has been applied to the organic C profile, trying to discern recent lake eutrophication from organic carbon mineralization. In spite of massive N inputs in the last 50 years, observed increases of organic C and N in sediments in these years, although parallel to the increase of lake pollution, could be satisfactorily explained with the diagenesis model, with no visible influence of lake trophic status change during that period.
 
The above- and below-ground biomass and fruit production of Vallisneria natans plants were measured in relation to length of the growing season, based on six treatments (April/May/June planting in relation to October/November harvest) in a microcosm experiment. Above- and below-ground biomass generally increased with length of growing season. There were no significant differences between early and late harvest measures for each start date, except for the earliest planting date, where above-ground biomass was significantly less in November compared to October. There were no significant differences in the dry weight production of fruits between any of the treatments, nor in the ratio of unripe to mature fruits produced in each treatment. The biomass of mature fruits and the ratio of mature to unripe fruits were significantly higher (approximately double) amongst November harvested plants compared to October harvested plants across all start dates, suggesting reduced seed production as a result of early harvesting. There was a significant increase in the dry weight of mature fruits with length of growing season. Based on these results, shortening of the inundation periods experienced by Vallisneria natans plants in Yangtze River ephemeral wetlands (more so in autumn than in spring) will reduce annual biomass production, and advances in autumn desiccation date will reduce investment in viable seed production in this submerged macrophyte.
 
The genus Pinnularia Ehr. (Bacillariophyceae, Bacillariophyta) is very frequently found in algal communities of acidic environments. Several Pinnularia strains isolated from the thermal acidic area of Pisciarelli (Naples, Italy) have been investigated by using a combination of morphological, ecophysiological and molecular techniques and have been compared with 15 Pinnularia strains from acidic and neutral environments, obtained from Loras College Freshwater Algal Collection. Electron microscopy (EM) observations showed the presence of a single Pinnularia species in Italian isolates, Pinnularia obscura. The complete identity between the strains of P. obscura isolated from the thermo acidic hydrosystem of Pisciarelli and from freshwater environments revealed the ability of this species to disperse throughout the globe, colonizing both acidic and neutral habitats. Overall, the genus Pinnularia has been confirmed to show a very weak morphological variation between species; in fact, the main morphological traits helpful to discriminate among them have been identified only by EM. Low pH values were tolerated by the majority of Pinnularia strains and species, both from acidic and neutral environments. As shown by a 18S rDNA phylogenetic analysis, acid-tolerance within Pinnularia is homoplasious, as a reversion from intolerance to tolerance is documented at least in P. gentilis.
 
The European Union Water Framework Directive (WFD) aims to achieve good ecological status of its waterbodies by 2015 through the determination of reference state to provide a measure of perturbation by human impacts based on taxonomic composition and abundance of aquatic species. Collections of floating pupal exuviae discarded by emerging adult midges (Diptera: Chironomidae) provide a cost-effective method for obtaining representative ecological data from lakes. Chironomid and environmental data were collected from 203 lake surveys of all WFD types found in Britain. Canonical Correspondence Analysis provided species optima and niche breadths in relation to acidity measures. An acidification score derived from species optima was produced for each lake survey and compared with the lake's reference score modelled on physical characteristics. The Ecological Quality Ratio (EQR) of observed to reference scores were classified into WFD quality bands based on the relative frequency of sensitive to tolerant chironomid species. Sampling variation of EQR was used to determine the confidence of each lake survey classification. Species-based EQR provided a sensitive measure of lake perturbation from high ecological status. Analyses were repeated with generic data obtained in much less time. Precision obtaining generic EQR was lower but still acceptable for providing a high confidence of classification at High, Good and Moderate status.
 
Sediment cores from acidified Lake Gaffeln and Lake Lilla Hästevatten, SW Sweden, were analysed to test if the occurrence of subfossil Chaoborus mandibles were coupled to extinction of fish in the early 1970s. Mandibles of C. flavicans were found throughout the sediment cores while mandibles of C. obscuripes occurred in more recent sediments only. The appearance of C. obscuripes mandibles was accompanied by an increase of C. flavicans mandibles in both lakes, indicating reduced fish predation and eventual fish loss. The increase in Chaoborus flavicans density confirms earlier studies that this species is favoured by the loss of fish in acidified lakes. Since C. obscuripes is a strong indicator of fish-free conditions, we propose that this species can be used in paleo-studies as an indicator of fish absence in the same way as C. americanus in North America. However, mandibles of C. obscuripes were scarce in the sediment cores, and it will likely be of best use as indicator in shallow and humic lakes, i.e. its preferred lake type.
 
Chemical recovery of anthropogenic acidified streams is being observed in North Hemisphere countries, while biological recovery processes are delayed and appear to be complex. Here, we conducted a one year survey on several Baetis species, a known acid-sensitive genus, highlighting how developmental strategies could influence the presence and abundance of their populations in streams of varying acid levels. We found contrasting sensitivity of Baetis species to acidification, ranging from "very" acid-sensitive (B. melanonyx) and "slightly" acid-sensitive (B. alpinus and B. rhodani) to "acid-benefiting" (B. vernus). The study highlighted that both B. alpinus and B. rhodani showed similar patterns under acidic conditions. Occurrence and abundance appeared unequivocally related to the high level of plasticity of their bivoltine cycle. On the contrary, the univoltine B. vernus and B. melanonyx demonstrated opposite responses to acidification revealing strong differences in their sensitivity at early stages. Our findings underline the importance of life cycle knowledge in considering species specific responses to freshwater acidification and its implication on the understanding and monitoring of biological recovery processes.
 
As acidification changes from chronic to more episodic in nature, study focus shifts from lakes, where the basin moderates acidity, to streams where acid episodes occur. To assess the effects of acid stress, several macroinvertebrate indices have been used in Scandinavia and elsewhere, based on the presence or absence of species. Benthic diatoms are strongly linked to water quality with small spatial influence, and display a broad spectrum of species. An acidity index for streams based on benthic diatoms could refine assessment resolution, which is required as the acidification declines. During the autumns of 2004 and 2005, 99 benthic diatom samples were collected from 75 humic streams in Sweden that were monitored by monthly water sampling. The relationships between benthic diatoms and measured environmental variables were explored using canonical correspondence analysis. Acidity was the principal factor influencing the diatoms, with the highest eigenvalues noted for pH, alkalinity, and inorganic aluminium. Several weighted averaging (WA) models were developed to infer stream pH, both using 50 streams from 2004 as a calibration dataset cross-validated with 49 streams from 2005 as an independent dataset, and by modeling all 99 streams. The predictive power of the WA models was good. The model with all streams showed a high correlation for mean pH (r2 = 0.85) and minimum pH (r2 = 0.74) values. An acidity index for diatoms, ACID, was proposed. The correlations to mean and minimum pH values were strong, at r2 = 0.85 and 0.77, respectively. Our results confirmed a strong link between benthic diatoms and water quality, particularly acidity. By employing different approaches we demonstrated that diatoms are excellent acidity indicators. The proposed ACID index can be used to assess the acidity state of a stream. ACID is more convenient to use than a WA model for pH and has equal precision.
 
(a) Experimental fl umes and their common reservoir and (b) schematic graph of one fl ume. Note that the fl umes were slightly tilted (i.e. the straight lines and curved sections had a slope) and that they were covered with black, regularly perforated plastic sheets (and not mosquito nets as in (a)).  
Mean density in the box traps of (a) D. villosus and (b) G. pulex, showing data of three fl ume replicates per date and shear stress. The squared symbols indicate the two fl umes where we found one specimen each of the predator Rhantus at the end of the experiment. (c) Models of the box trap density as a function of time and shear stress for (a) D. villosus and (b) G. pulex. See text for equations and statistics.  
Plots of abundance vs. shear stress (τ) for (a) Dikerogammarus villosus and (b) Gammarus pulex in the same season (winter) and for running waters that were identical (a) or resembled (b) the running water from which we collected our experimental organisms. Note that it required to log-transform τ here (but not in subsequent fi gures) to illustrate the data distribution along the x-axis.  
Plots of mortality (over the six weeks of the entire experiment ) vs. shear stress for (a) D. villosus and (b) G. pulex. The dytiscid symbols indicate the two fl umes where we found one specimen each of the predator Rhantus at the end of the experiment.  
Mean alder leaf-litter decay. See Fig. 3 for further de- tails.  
The Ponto-Caspian gammarid Dikerogammarus villosus currently expands its range and replaces native gammarid populations in many large rivers of Europe. Results of small-scale, still-water experimentation fostered the idea that D. villosus reduces native gammarid populations in large rivers through predation. However, in large rivers, the prevailing flow conditions (potentially harsh or benign for predator and/or prey) and related flow-refuge use (potentially concentrating predator and prey in small spaces) could interfere in this predator-prey interaction. We combined a field survey with a mesocosm-flume experiment to assess flow-refuge use, mortality, and associated effects on leaf-litter decay through potential shredding by the gammarids of coexisting D. villosus and native Gammarus pulex across a shear stress (τ) gradient. In real running waters, both species had no well defined preference for a narrow τ range, suggesting that D. villosus would effectively prey on G. pulex across a wide τ range. In our experiment, however, the concentration of D. villosus and G. pulex in flow refuges increased with τ and decreased with the duration of the experiment (decrease of D. villosus < G. pulex). Overall mortality over the entire experiment was higher in G. pulex than in D. villosus and tended to decrease with τ in D. villosus, whereas it tended to increase with τ in G. pulex. Decay of alder leaf litter decreased with τ and time; however, the difference (low vs. high τ) of the temporal decay-rate drop was low. Our experimental results support the idea that at higher τ, both D. villosus and G. pulex are concentrated in flow refuges, which facilitates predation of the former on the latter. These flow effects on the interaction between D. villosus and a native gammarid (and potentially other rheophilic invertebrates) have particularly important implications for restoration projects that increase the discharge in by-passed sections of large regulated rivers, as the concurrent or future invasion of D. villosus could imperil the restoration of rheophilic invertebrate populations.
 
Aquatic hyphomycetes play an essential role in the conditioning and breakdown of imported leaves, needles and other plant detritus in running waters. Most research on their diversity and function has been done in temperate regions and very little in South and Central America. Current knowledge suggests that fungal diversity in tropical streams is comparable to that in temperate waters. Due to increasing anthropogenic stress threatening stream communities in the tropics, we risk losing irreplaceable information. We investigated aquatic hyphomycetes on leaves decaying in 15 streams in the Republic of Panama. The streams were classifi ed as pristine, rural, or urban. Multivariate analyses of physico-chemical and riparian vegetation parameters separated the pristine streams from the other two groups. Pristine streams generally had the lowest levels of several inorganic nutrients and turbidity and the widest buffer zones of riparian vegetation. Multivariate analysis of aquatic hyphomycete communities separated the pristine streams from rural and urban streams. Both numbers of fungal species and conidia released per unit leaf mass were generally highest in pristine streams. A total of 34 fungal taxa was recovered. Of these, 32 were assigned to described aquatic hyphomycete taxa, with 29 being new records for the Republic of Panama.
 
Physical and chemical limnological variables were measured from 40 ponds and 6 lakes across Melville Island, Nunavut/N.W.T., Canadian high Arctic, an environmentally sensitive region where very limited limnological data were available. Mean values of most variables were mid-range when compared to other high Arctic limnological surveys, yet the ranges of most measured variables were amongst the largest yet encountered in Canadian high Arctic regional surveys. The first two axes of a Principal Components Analysis explained 55.2 % of the variation in the environmental data. Variables most strongly associated with axis one were pH, dissolved organic carbon, total dissolved nitrogen, specific conductivity and related variables, while axis two represented gradients of other nutrients and trace metals. High elevation sites near permanent ice caps recorded the lowest specific conductivity and Ca2+ values yet reported in high Arctic systems. High phosphorus values (>20 μg/L) in some of the Melville Island sites are likely indicative of re-suspended sediments, rather than eutrophic conditions. Total nitrogen to total phosphorus ratios suggest that ∼50 % of the sites are P limited, while 33 % are N limited, supporting previous research which suggests N limitation is more commonly encountered in Arctic than in temperate freshwater ecosystems. Finally, when freshwater sites on Melville Island were grouped according to predefined bioclimatic zones, only the most lushly vegetated zone appeared to affect limnological conditions. with these sites having higher mean total dissolved nitrogen, pH, and specific conductivity.
 
Organic matter transport and retention were evaluated in 14 small streams representing a range of riparian vegetation disturbance and watershed development levels in the Puget Lowland of western Washington. To determine relative transport and retention, diamond-shaped acetate strips of similar size and density to leaves were released in riffles during low-flow conditions. Simultaneous dissolved tracer releases were used to measure hydraulic characteristics of each reach. Both reach-averaged velocity and hydraulic dispersion predicted median leaf-surrogate material travel distance (R2 = 0.87, p < 0.001) and characterized transport and retention over longer reach lengths than in traditional organic matter release experiments. Relative organic matter transport distance increased as the pool/riffle ratio decreased, reach-averaged velocity increased, and dispersion increased. Because urban development affects hydraulic characteristics, urbanization enhances organic matter transport in small streams, reducing the retention of organic matter available for biotic processes.
 
Implementation of policies about the conservation and restoration of aquatic ecosystems' biodiversity and ecological integrity requires rapid assessment methods. The landscapes of the Carpathian Mountains, spanning an unusually steep gradient of land-use intensity from a European perspective, offer great opportunities for evaluating such methods. Focusing on the orders Ephemeroptera, Plecoptera and Trichoptera (EPT), we evaluated three approaches for assessing macroinvertebrate species richness in second and third order streams: (1) the use of data at higher taxonomic levels, (2) the use of species-level data, and (3) the use of abundance data. The number of families was a reliable indicator of species richness within EPT. Species richness of Trichoptera was strongly correlated to species richness in Ephemeroptera and Plecoptera, and thus in the EPT group as a whole, whereas species richness in Ephemeroptera and Plecoptera did not perform as well. We found little evidence for the usefulness of abundance data as a surrogate for species richness within orders, except in Plecoptera. Taxa richness in EPT was generally positively related to forest cover in the catchments and negatively related to the proportion of agricultural land. EPT taxa richness could be used to distinguish between High/Good quality classes and those of lower ecological quality according to the EU Water Framework Directive. Our results suggest that assessments focusing on the family level provide a cost-efficient alternative to species-level assessments in second and third order streams, and point at Trichoptera as a potential indicator group.
 
The location of three-dimensional fl uorescence peaks for the LB-EPS extracted sample. Regions I, II, IV are biogenic aromatic proteins containing tyrosine, tryptophan and complexed tryptophan & protein-like compounds (EX = 210 nm – 280 nm, EM = 280 nm – 380 nm); Region III represents fulvic acid-like compounds (EX: 210 nm – 250 nm, EM = 380 nm – 425 nm); Region V contains humic acid-like structures. A & B peaks: aromatic proteins, soluble microbial by-product-like; C peak: humic substance-like compounds.  
Sorption of Cu 2+ by LB-EPS under calcium precipitation (a) sorption of Ca 2+ in Cu 2+ solutions; (b) where a-e represent the Cu 2+ concentrations of 5, 10, 20, 50 mg l –1 , respectively.  
Photomicroscopic images (1,000×) of crystal structure and confi guration: the dissolution of LB-EPS with an increase of calcium ions: (a) 80 mg l –1 ; (b) 160 mg l –1 ; (c) 300 mg l –1 ; (d) 600 mg l –1 . LB-EPS and copper concentrations for all samples were 48 mg l –1 and 5 mg l –1 , respectively.  
Cu2 + adsorption effi ciencies (a) by LB-EPS, binding constant K of Cu 2+ ; (b) under changing calcium concentrations according to the Model (1) and k values amount to the [ML] / [M][L].  
The behavior and fate of copper binding with extracellular polymeric substance (EPS) from activated sludge, under varying calcium concentrations, was studied. Results showed that the degree of LB-EPS sequestering with calcium had a strong differential effect on copper sorption. At lower Ca2+ concentrations (≤ 80 mg · l-1), the Langmuir equation was able to model adsorptive processes between Cu2+ and EPS, which showed competitive adsorption between free Cu2+ and Ca2+ ions. However, at higher Ca2+ concentrations (> 80 mg · l-1), the competitive sorption between Cu2+ and Ca2+ was replaced by calcium precipitation which isolated Cu2+ from EPS. Three-dimensional fluorescence spectrum and Fourier transform-infrared spectra analysis of loosely bound extracellular polymeric substance (LB-EPS) indicated that the EPS sample was composed of humic acid-like and proteins-like complexes containing proteins, polysaccharides, and lipids that reacted with the investigated metal ions. Microscopic images of crystal structure and configuration, with the increase of Ca2+ concentrations, showed that calcification needles gradually grew and the aggregating EPS inchmeal dissolved. In essence, EPS are potential good for sequestering free Cu2+ from freshwaters. However in the presence of Ca2+, LB-EPS also acts as a nucleation site for precipitation “marl” deposition which reduces Cu2+ adsorption. Bio-lithification layer formation in combination with high calcium bio-adsorption levels significantly reduced, but did not eliminate, copper adsorption in EPS.
 
Environmental variables measured during the long-term study on the springs of the Adamello-Brenta Nature Park. Note that the full correspondence of yrs bars are between the couples Fumo and Levade (above) and Borzago and Nambi (below). CV = coefficient of variation.  
Comparison of species accumulation curves between real samples (white circles) and simulated ones (black symbols) to show the effect of random sampling process. Dispersion around the mean is the standard deviation. Species richness over the years is marked by black squares; 'Tot sp' is the total species number recorded.  
Switch of importance between Eunotia intermedia and E. exigua in the spring Fumo.  
It is thought that long-term monitoring is an essential tool through which conservationists and managers (i) are alerted when the system departs from the natural state, (ii) can check their environmental policy, and (iii) can detect disturbance effects. However, while long-term studies are growing in number, the lack of information on the background rates of natural changes could lead to a biased interpretation of results. In this study we analyzed the diatom composition of yearly samples (14-16 yrs) in four springs with the following goals: (1) to estimate the consequences of sampling-related processes on the species composition and relative abundance; (2) to determine the form of the assemblages' variation, evaluating whether the assemblages can be predicted by cyclic, directional, or stochastic changes; (3) to test if, and to what extent, the diatom variability (variation in species composition, relative abundance and diversity) on a temporal scale is driven by the environment; (4) to evaluate the degree of temporal concordance among the diatom assemblages inhabiting four springs. Results showed that because the effect of sampling was inversely proportional to the species abundances, the presence of the least abundant species over the years were mainly a result of chance. The analyses allowed us to discriminate between stochastic and directional patterns, revealing the ongoing changes in two out of four springs. Because the environmental variables did not explain a significant portion of this variability, other hypotheses are put forward. The assemblages' dynamics of species composition over time were significantly synchronous in two out of six couples of springs, and regardless of the environment. This result can suggest that internal, within springs, drivers may be more important than extrinsic forces operating over regional spatial scales. Overall, these results provide a benchmark of diatom variability over time and in natural conditions delimiting the "limits of acceptable changes".
 
Cladocera and calanoid Copepoda are ubiquitous in surface freshwater, each with about 500-600 species and subspecies distributed worldwide. Both groups also contain some subterranean species, which occur in karst and porous aquifers. The first stygobiotic calanoid, Microdiaptomus cokeri, was described in 1942, and the first cladoceran, Alona smirnovi, in 1973. Currently, seven species of Cladocera are confirmed and three more are possible stygobionts. In Calanoida, nine species are recognized stygobionts and three more are possible. In the last few years the number of described stygobiotic taxa has increased and may continue to do so, as caves and gravel-beds are more intensively studied. Stygobionts are probably derived from a Miocene fauna that, under the constraint of a worsening climate, took advantage of the development of caves and found subterranean refugia. The Pleistocene glaciations accelerated this colonization process, which persists to the present. Both groups do not contribute much to the overall subterranean biodiversity, but they exhibit adaptations that may help to reveal the mechanisms of colonization of the subterranean realm. Some of their characteristics are related to feeding and to maintaining their position during cave floods, and are shared with other stygobionts. In addition, stygobiotic Cladocera and Calanoida have distinct life-histories and morphological adaptations. In karst-dwelling Cladocera, parthenogenesis supports fragmented populations, whereas karst-dwelling Calanoida are planktonic, a unique way of life among freshwater stygobionts.
 
Concentration of dissolved and particulate organic carbon (DOC and POC) in different treatments (C = control, H = humic water added, S = cane sugar added) of the experiments (mean ± SD) with water from Lake Pääjärvi (PJexp) and from Alinen Mustajärvi (AMexp). Vertical dashed lines indicate when DOC additions were made. 
Mean ( ± SD) of primary production of phytoplankton (PP), bacterial production (BP) and stable carbon isotope values of dissolved inorganic carbon ( δ 13 C-DIC) in different treatments (mean ± SD) of the PJexp and AMexp. Note different scales for δ 13 C- 
NMS plot of LH-PCR results for the bacterial community in PJexp (A) and AMexp (B) . In the legend, B refers to samples taken at the beginning of the experiment and concentrated either with tangential fi ltration (TF) or Filtropur fi lters (FF) (see Methods for details). C, H and S refer to samples taken at the end of the experiments from the three different treatments (see Fig. 1). 
Stable carbon and nitrogen isotope values (mean ± SD) of particulate organic matter (POM), and of cladoceran (Cla) and copepod (Cop) zooplankton initially in the PJexp (PJ) and AMexp (AM), and in the different treatments (C, H, S) at the end of these experiments. 
We studied the response of pelagic community metabolism, bacterial community structure and the origin of crustacean zooplankton carbon following additions of two different sources of dissolved organic carbon (DOC), natural humic water and cane sugar, in two mesocosm experiments lasting 15-18 days. Experimental water with the natural plankton community originated from two boreal lakes in southern Finland having similar total organic carbon (ca. 11 mg L-1) and total phosphorus (ca. 13 μg L-1) content, but differing in total nitrogen content (ca. 1450 and 440 mg L-1). The experiments demonstrated limitation of bacterial activity mainly by biodegradable DOC in the high nitrogen lake water, and by nitrogen in the low nitrogen lake water, which was also refl ected in total pelagic energy metabolism and zooplankton productivity. DOC additions caused changes in the bacterial community structure, shown by length heterogeneity analysis of the PCR amplified 16S rRNA gene (LH-PCR). Cane sugar, differing in stable carbon isotope value (δ13C ca. -11 ‰) from that of humic matter of boreal terrestrial vegetation (δ13C ca. -28 ‰), proved to be a good tracer of DOC via bacteria to metazooplankton, especially in the nitrogen- limited conditions. Utilization of detrital particulate terrestrial organic matter by zooplankton was also evident, but it appeared to be a poor quality food. Our results show that an increased loading of allochthonous DOC to boreal lakes as predicted under future climate scenarios will not necessarily stimulate bacterial production and hence carbon transfer up the food web. Whether this happens will be strongly dependent on the stoichiometry (C : N:P ratios) of the available resources.
 
A total of 30 shallow lakes, located along the middle and lower reaches of the Yangtze River, were studied to assess the relative importance of nutrients and zooplankton biomass in determining the phytoplankton biomass in subtropical China. Zooplankton biomass and nutrients both varied greatly in these lakes. Factor analysis and multiple linear regression showed that phytoplankton biomass was positively correlated with TN, NH4+, NO3− and TP, while it did not show any negative relationship to zooplankton biomass. Meanwhile, the phytoplankton biomass showed contrary relationships to the mass ratio of TN/TP in spring and summer, suggesting that in nutrient-richer lakes the dominant phytoplankton species have different preferences for TN/TP ratio. The insignificant top-down control of phytoplankton biomass may be attributed to the dominance of small-sized crustaceans and low crustacean biomass resulting from cyanobacterial dominance and planktivorous fish predation as well as other factors. Thus, it is likely that nutrients were more important than zooplankton biomass in explaining the total variance of phytoplankton biomass in these subtropical lakes.
 
The distribution and dispersal of adult mayflies, stoneflies and caddisflies were investigated in an approximately 5 ha area of montane forest and grassland-scrub in the South Island, New Zealand. Low-flying insects were collected in 28 Malaise traps set along stream channels, in dry valleys and on hillsides for 8 weeks in late summer. Adult assemblages differed in forest and grassland and along valleys depending on distance from streams that were their probable sources. Stoneflies and mayflies occurred predominantly in forest and were taken mainly above the stream or very close to it. In contrast, caddisfly species exhibited a wide range of distribution patterns with some restricted to forest and others being found in both forest and grassland up to 300 m from the nearest likely source. Many females of several species that were taken well away from their natal stream (e. g., Pycnocentria evecta and Aoteapsyche colonica), were not fully developed, reproductively, suggesting they were dispersing inland to mature, whereas others packed with eggs (e. g., most Hydrobiosis parumbripennis) were more likely to be searching for oviposition sites. Many more male and female caddisflies were trapped in valleys than on hillsides, even where surface-water was absent, suggesting that valleys provide important corridors for dispersal, at least of low-flying individuals.
 
Intersexes of Gammarus fossarum and several other gammarid species seem to be functional females, however, knowledge on reproduction variables, which are of crucial importance for the existence of populations, in intersexes is still scarce. We proposed several hypotheses regarding body length (of singles and in precopula pairs), precopula behaviour (e.g. reduced pairing success) and fecundity (e.g. reduced brood size) of intersexes. Data obtained from G. fossarum populations in the streams Friedrichsbach and Lockwitzbach (Germany) were used to examine these hypotheses. At the Friedrichsbach and one of the two sampling sites of the Lockwitzbach, intersex singles were only in tendency larger than female singles. At the other Lockwitzbach site, intersex singles were significantly larger compared to female singles. Pairing success of intersexes was not reduced. Absolute brood size as well as the brood size normalised to body length did not differ significantly between females and intersexes regarding early stages, late stages or pooled data from all stages of egg development before hatching. For females and intersexes, the number of eggs (stage 1-5) in the marsupium did not significantly decrease during egg development. Hence, intersexes might not be a disadvantage for the population at least with regard to the examined reproduction variables in these populations of this gammarid species.
 
Mean number (± SD, n = 2 or 3) of nanofl agellates (size groups < 4 µm and 4–8 µm) in treatments with different Daphnia densities, at the onset (t 0 or t 1 ) and end (t 25 or t 49 ) of Experiments I and II.  
We tested the hypothesis that grazing by bacterivorous zooplankton might suppress methanotrophic activity in small stratified, humic lakes. During two series of replicated laboratory experiments, densities of methane-oxidising bacteria (MOB) in water from a small, polyhumic lake were measured in the presence of different densities (range 0-200 individuals l−1) of a large bacterivorous cladoceran, Daphnia longispina. Grazing by Daphnia and by nanoflagellates reduced the proportion of MOB in the microbial community and the methanotrophic activity decreased significantly at higher Daphnia densities. Thus, the hypothesis arising from previous field observations was supported experimentally, but field studies are required to quantify the influence of grazers on methanotrophic activity and CH4 effluxes of lakes.
 
Streams polluted with uranium mine drainages are abundant in Central Portugal with over 50 abandoned mines. We investigated the effect of stream water contaminated with uranium mine effluents on oak leaf (Quercus robur) decomposition and associated decomposer communities and its impacts on the feeding ecology of larva of the caddisfly shredder Sericostoma vittatum. Leaf mass loss, toughness and fungal biomass in oak leaves did not differ between reference and contaminated water. However, microbial respiration was significantly higher in leaves exposed to contaminated waters. Shredders preferentially consumed leaves exposed to reference rather than contaminated stream water. Although 100% survival was observed in both treatments, consumption and relative growth rate decreased to half in larvae provided with leaves incubated in contaminated water. This may be due to less palatable leaf-microbial assemblages and/or to higher contents of metals accumulated by the leaves. We hypothesize that uranium mine drainages impair stream ecosystem function through their effects on shredders rather than on microbial processing.
 
We investigated whether the conversion of riparian land use from indigenous forest to pasture influences Chironomidae (midge) community composition in two Brazilian rivers. Our study was conducted in the main rivers (São José dos Dourados 6th order, Aguapeí 7th order) of two large catchments in the State of São Paulo. Both are dominated by agricultural ecosystems but retain substantial patches of native riparian forest. Replicated artificial substrates (baskets filled with coarse clay gravel) were exposed at one forested reach and one pasture reach in each river. Each respective land use had to be present for at least 500 m along both river banks above and alongside the study reach, and the riparian forest at the forested reaches had to be at least 50 m wide. Colonisation baskets were sampled after 44 days and all midge larvae sorted and identified to the lowest level possible (a total of 5,286 individuals belonging to 27 taxa). Land use affected midge communities, but not as expected. Densities of three dominant midge genera were significantly higher in pasture reaches than in forested reaches, possibly in response to moderate nutrient enrichment at the pasture reaches. Total midge density and taxon richness were similar across land uses. These results imply that land-use related changes in habitat conditions were not severe enough to represent a stressor (with negative effects) for the midge communities in the investigated large rivers, but rather acted as a subsidy, with mainly positive effects.
 
The objective of the present study was to analyse the effects of drainage water from an abandoned gold mine on the breakdown of Alnus glutinosa leaves mediated by aquatic fungi and invertebrates. We analysed three sites (P = polluted, R = reference, and RP = intermediate) in the winters of 2002 and 2004. The sites had similar pH (6-7) but differed in the concentration of heavy metals (As, 0.4 mg L−1; Fe, 4.9 mg L−1; Mn and Zn, 1.2 mg L−1 in site P) and PO43− (0.04 mg L−1 in site P). The breakdown of alder leaves was low, both in the absence (fine mesh bags) or presence (coarse mesh bags) of invertebrates. Sites did not differ (ANCOVA) in breakdown rates mediated by aquatic fungi (k = 0.0016 to 0.0080), but sporulation rates were significantly higher at site R in 2002 (up to 2488 spores mg AFDM−1d−1). In the presence of shredding invertebrates, breakdown was significantly lower at the polluted sites in both years (k < 0.0160 vs. k > 0.0191), in spite of similar shredder biomass in all sites. The dominant shredder caddisfly Allogamus ligonifer discriminated between leaves exposed in sites R and RP in 2002 (consumption rates of 0.60 vs. 0.35 mg mg−1 AFDM day−1). In situ experiments revealed that shredders from site RP consumed leaves at lower rates than in site R (0.46 vs. 0.35 mg mg−1AFDM day−1). Our results suggest that although pollution was not enough to suppress microbial growth and invertebrate survival, sub-lethal effects affected the ecosystem function, even when interannual variation was prominent.
 
We examined litter breakdown and fungal communities at three sites along a small mountain stream affected by mine drainage in Colorado. One site was located in the drainage from an abandoned mine, and the 2 other sites were upstream and downstream of the confluence of the drainage with a pristine stream. At the 2 sites affected by the mine drainage, pH was depressed, zinc concentration was elevated, and metal hydroxides were deposited onto the stream bottom and leaf litter. At these sites, litter breakdown was slower, shredding invertebrates were absent, and microbial activity was also lower compared to the upstream site. Conidia production by aquatic hyphomycetes was limited at all sites, but indicated differences in species diversity and identity. The mining sites were both dominated by Varicosporium elodea, while the upstream site had several taxa that produced conidia. Molecular analysis by denaturing gradient gel electrophoresis of PCR-amplified ITS regions showed similar patterns, but revealed more taxa at the upper and lower sites than seen with conidia examination. In these stressed streams, litter breakdown was slower and associated biota, including shredders and fungi, reflected changes from the suite of stressors associated with acid mine drainage.
 
Surface sediment samples were collected from 35 lakes on the Yunnan Plateau as part of an investigation into the relationship between surface sediment subfossil chironomid distribution and lake environmental variables. This region of China is unique as it contains large temperature gradients, from the subtropics to the foothills of the Himalaya, but also contains lakes that have been heavily impacted by anthropogenic activities. The chironomid communities were dominated by 8 taxa, which together accounted for 77.7 % of the fauna. The statistical analyses indicated that mean July air temperature and water depth were the most significant variables affecting the distribution of chironomids across these sites. After removing 3 major outliers from axis 1 in the ordination data set, temperature lost its significance but water depth and reductions in bottom dissolved oxygen (DO) were still found to be significant. In addition the diversity of the dataset was found to be low compared with other chironomid training sets throughout the world, suggesting that this region in China has different characteristics governing the abundance and distribution of chironomids compared with other parts of the world, hence the need for regional training sets within China. This is the first subfossil chironomid data set from this region and the understanding of key environmental influences on contemporary faunas will aid interpretations of palaeolimnological data sets to reconstruct past trends and magnitude of environmental change over a range of timescales.
 
We investigated how riparian logging affects the food webs of coastal streams in northern Sweden by comparing streams surrounded either by clear-cuts or old-growth forests. Specific hypotheses were that: (i) algal standing stocks are higher in clear-cut streams, whereas detrital standing stocks are higher in old-growth streams; (ii) algal-based (autotrophic) pathways contribute more to consumer (aquatic insect) body carbon in clear-cut streams than in old-growth streams; (iii) a higher autotrophic contribution reflects a combination of numerical (increased abundance of herbivore taxa) and functional (shift in diet by generalist taxa) responses of insect taxa to logging; and (iv) potential predators function more strictly as true predators, and reduce propensity to omnivory in clear-cut relative to old-growth streams. The standing stocks of algae and fine particulate organic matter (FPOM) were similar between treatments, whereas the standing stock of coarse particulate organic matter (CPOM) was higher in old-growth streams. Stable isotope analysis suggested that the autochthonous contribution to aquatic insect carbon per individual taxon was greater in clear-cut than in old-growth streams; although the difference was not statistically conclusive the large effect size suggests that it is biologically meaningful. Greater reliance on autotrophic pathways in clear-cut streams seemed to be caused by a decrease in the relative consumption of detritus by the generalist species Leuctra hippopus, an increase in the abundance of the specialist herbivore Baetis rhodani, and a diffuse increase in the consumption of algae across all functional feeding groups except gathering-collectors. Resources and consumers were enriched in 15N in clear-cut relative to old-growth streams, suggesting that forestry affects the microbial processing of organic nitrogen, which in turn causes an increased availability of 15N to algae. The enrichment in 15N in clear-cut relative to old-growth streams was apparent in all functional feeding groups except for gathering-collectors. In summary, our results show that riparian logging affects the balance of aquatic vs. terrestrial carbon sources and the cycling of nutrients in streams, with effects reverberating to the aquatic consumers.
 
Description of sampling sites, coordinates and dominant algal species and average bio volume at each sampling site over a period of one year. 
The relationships between water quality and the phytoplankton community within Lake Loskop and irrigation canals downstream were studied over a period of one year from April 2009 to March 2010. The phytoplankton assemblage in Lake Loskop during this sampling period was dominated by the phytoplankton Ceratium hirundinella, with the highest biovolume of 12.1 mm3 l-1 recorded in late summer during January 2010. From the data generated the algae assemblage showed a clear trend in the two canals during the study period and also among sampling stations. The filamentous macroalgae Cladophora glomerata dominated the phytobenthos of the two irrigation canals during the whole sampling period. However, much higher biovolumes (8.5; 6.3 mm3 l-1) of Cladophora glomerata and total phosphates were observed in the long and short irrigation canals during lake overturn in the months of March and September, while much lower average biovolumes (2.4; 1.5 mm3 l-1) were recorded during the summer months. The dominance of the water column phytoplankton assemblage in the two irrigation canals by Ceratium hirundinella, Fragilaria crotonesis, Closterium stellenboschense and Closterium polystictum during autumn and spring was related to the observed lake overturn. Withdrawal of irrigation water from the upper-hypolimnia during these two time periods transported phytoplankton species usually occurring in the epilimnion zone of Lake Loskop into the irrigation canals. This phenomonen resulted in these species becoming dominant during autumn in the water column of the two irrigation canals downstream of Lake Loskop. The phytoplankton assemblage data generated from this study can be used for management and control of nuisance macroalgae like Cladophora glomerata in irrigation canals.
 
Biodiversity was assessed and a synthesis on sponges belonging to the genus Eunapius from African inland waters was performed, with detailed descriptions, geographic distribution, ecological notes and a diagnostic key. The gemmular trait "network of spongin fibers in the inner portion of the gemmular theca" discovered by the SEM analysis is here reported for the first time in four species of the genus. A comparative analysis was made, based on a critical revision of original descriptions, recent investigations on materials from historical collections, and recent samplings. Eight taxa are here reported, namely the widespread Eunapius carteri and E. fragilis, and the African endemics E. aetheriae, E. ambiguus, E. carteri saharensis, E. michaelseni, E. nitens and Eunapius sp. The genus Eunapius is, among Spongillidae, the most common and widespread in Africa in North Africa, Sahara and Sub-Sahara up to South Africa and Namibia. Habitats range from extremely isolated waters in deserts to swamps, perennial rivers and lakes in highlands and coastal areas.
 
Many annual-plant and invertebrate species produce seeds or eggs that can survive in dormancy for many years before germinating or hatching. The ability of the resulting seed or egg banks to influence population dynamics is a function of the success and duration of germination or hatching and subsequent development. To explore this for Daphnia mendotae, I collected diapausing eggs from the sediments of Onondaga Lake, NY, incubated them in spring photoperiod and temperature conditions, and measured the duration of different life stages for eggs from recent (< 5 year-old) and older (15-20 year-old) sediments. A total of 432 D. mendotae hatched. Many of these hatchlings were inviable (39-44%), with a higher proportion of late hatchers from both egg ages showing inviability. The days to hatch for two eggs from a single ephippium (egg case) is highly positively correlated, indicating either a genetic or maternal component to survival. Older eggs take, on average, 8.6 days longer to hatch than recent eggs. When the total time to maturity is considered for the subset of animals surviving to reproduce, there is no significant difference between older and younger diapausing eggs in the time from when an egg first receives the hatching stimulus to the release of the hatchling's first brood. These results suggest that for those eggs receiving a hatching cue, neither egg age nor hatching timing alone is a good predictor of the potential impact of the egg bank on population dynamics, but both must be considered.
 
Agricultural practices have the potential to influence hyporheic exchange through increased fine sediment loads and through reduced hydraulic conductivity, bed roughness and morphological diversity. These impacts can reduce connectivity between stream and hyporheic waters to the detriment of salmonid embryos. Salmonids bury their eggs in streambed gravels, typically to depths of up to 300 mm and for incubation periods of up to 6 months. Embryo survival is dependant on a complex range of factors which critically includes the delivery of oxygen from surface waters. This paper investigates hyporheic zone exchange processes, oxygen concentration and embryo survival in a canalised agricultural stream at a range of nested spatiotemporal scales. Results are contrasted with those from the Girnock Burn, a relatively undisturbed catchment. Conservative tracer experiments were used to assess reach average hyporheic exchange using the USGS OTIS model. Artificial redds were used to assess reach scale variability in hyporheic processes. Incubation stacks were used to assess embryo mortality and hyporheic water quality with depth at the scale of individual redds. Optodes (optical dissolved oxygen sensors) were used at a sub-set of sites to assess fine scale temporal variability in hyporheic oxygen and temperature. Stream and hyporheic hydrochemistry were used to infer source water contributions and provenance. Data showed that reach average hyporheic exchange in the Newmills Burn was ca. five times less than in the Girnock Burn. Dissolved oxygen (DO) concentrations related strongly to spatiotemporal patterns of groundwater (GW) discharge. Embryo survival was significantly correlated with DO. It is suggested that low DO in the Newmills Burn relates to groundwater upwelling and limited hyporheic exchange caused by a combination of low morphological diversity, hydraulic conductivity and bed roughness. It is suggested that future studies of embryo survival should look beyond the single issue of fine sediment effects to include a broader understanding of hyporheic zone processes.
 
Sample-based rarefaction curve using pooled data from all samples taken in one year. Dashed curves represent the 95 % confi dence intervals: (–) lower confi dence level, (+) higher confi dence level. 
Abundance (A %) of the families in each type of bait. References: CEL: cellulosic baits; KER: keratinic baits; CHI: chitinic baits; SES: sesame seeds.
Principal component analysis (PCA) of the samples according to the seasonal abundance in each bait. CEL: cellulosic baits; KER: keratinic baits; CHI: chitinic baits; SEE: sesame seeds; FAL: fall; WIN: winter; SPR: spring; SUM: summer.
Abundance of the taxa in each sampling date and total abundance (Total A). The taxa are listed in decreasing order of total abundance.
Zoosporic true fungi and heterotrophic straminipiles are phylogenetically unrelated groups of microorganisms playing similar ecological roles in food webs in fresh water ecosystems. As saprotrophs they are important decomposers of organic matter of animal and vegetal origin. However, there is still little research on most aspects of the ecology of these microorganisms. In this study the species composition of zoosporic true fungi (Blastocladiomycota and Chytridiomycota) and heterotrophic straminipiles (Hyphochytriomycota and Peronosporomycota), and their frequency, abundance and diversity on different types of baits were analyzed. Samples for characterizing the species composition were collected over a four-year period and for characterizing the structure of the assemblages at four dates during a one-year period. The relationship between some biological and environmental parameters were analysed. We expected that fluctuations in environmental factors during the year might lead to changes in the species composition and structure of the assemblages. Sixty-eight taxa were recovered with the baiting technique during the four-year period. The species composition was dependent primarily on the type of bait used. The structure of the assemblages also appeared to be more influenced by the type of baits available for colonization than by other environmental parameters. Even though the abundance of the taxa was associated with pH, nitrite, sulfate, soluble reactive phosphorous and dissolved oxygen concentrations. We did not find any differences in their richness, frequency, abundance and diversity during the year as expected.
 
The relationship between diversity and function has only recently been investigated in stream ecosystems. Here we evaluated the effect of litter evenness on litter decomposition in single species and 2-species litter bags with Alnus glutinosa (L.) Gaertn. (A) and Eucalyptus globulus Labill. (E). The five evenness treatments (100 %A, 25 %E + 75 %A, 50 %A + 50 %E, 75 %E + 25 %A and 100 %E) simulated the relative proportions of both leaf species throughout the year in a eucalypt stream lined by alder trees. Decomposition rates of eucalypt were retarded in the presence of alder, while those of alder were stimulated in the presence of eucalypt. Differences in mass loss between treatments were unrelated to the initial quality of the mixtures. Globally, the effects of litter evenness on microbial parameters (O2 consumption, fungal biomass and sporulation) and invertebrate numbers ranged from undetectable to weak. This was probably due to high nutrient concentrations in the stream water that may have masked the potential stimulating effects promoted by the high quality of alder leaves on eucalypt biotic degradation. Although the effects of litter evenness on biotic parameters were idiosyncratic, the importance of species evenness on litter mass loss was suggested by the higher decomposition rates of the 50 %:50 % mixture, which is likely related to a trade-off between alder high nutrient quality and the stability promoted by eucalypt in the mixture. Alterations in litter evenness, resulting from changes in riparian composition and diversity, might affect litter decomposition, and consequently ecosystem function. These findings could be relevant for recovery and management of riparian zones.
 
Top-cited authors
Heikki Hämäläinen
  • University of Jyväskylä
Paul J. Wood
  • Loughborough University
Dean Jacobsen
  • University of Copenhagen
Felix Baerlocher
  • Mount Allison University
Kimmo T. Tolonen
  • Finnish Environment Institute