Showing papers in "International Review of Hydrobiology in 2001"
TL;DR: The type of riparian vegetation has the potential to control the diversity and abundance of shredders and changes in Riparian vegetation have the Potential to affect the assemblages of aquatic invertebrates.
Abstract: Leaves entering low order streams are subject to physical abrasion, microbial degradation and invertebrate fragmentation. Aquatic invertebrates feeding on leaves are known as shredders and their densities tend to be correlated with the spatial and temporal accumulation of organic matter in streams. Shredders discriminate among the variety of leaves normally found in the stream; this discrimination may be related to differences in leaf toughness, plant nutrient content of leaves and the presence of secondary compounds. Shredders also consume leaves preferentially after the establishment of a well-developed microbial community. This preference may be the result of changes in leaf matrix carried out by the microbial community or the presence of fungal hyphae with a higher nutrition value than the leaves themselves. The immediate consequence of invertebrate feeding on leaves is the incorporation of plant material into secondary production and the fragmentation of leaves. The relative importance of fungi and invertebrates in the decomposition process depends upon the density of shredders, which, in turn, may depend on litter accumulation in streams. Therefore, the type of riparian vegetation has the potential to control the diversity and abundance of shredders and changes in riparian vegetation have the potential to affect the assemblages of aquatic invertebrates.
738 citations
TL;DR: The watershed of Big Hurricane Branch, Coweeta Hydrologic Laboratory, North Carolina, USA, was logged in 1976 as discussed by the authors, and leaf breakdown rates have been consistently faster than before logging and faster than in a reference stream.
Abstract: The watershed of Big Hurricane Branch, Coweeta Hydrologic Laboratory, North Carolina, USA, was logged in 1976 We measured breakdown rates of experimental leaf packs in this second-order stream prior to logging, during logging, soon after logging, and 3 additional times since then Leaf breakdown was slow just after logging, apparently due to leaf burial by sediments Thereafter, leaf breakdown rates have been consistently faster than before logging and faster than in a reference stream These differences may be related to 3 factors First, the post-logging nitrate concentration has been about 3–10 times higher than pre-logging values in Big Hurricane Branch and 5 times higher than in a reference stream The high nutrient concentration may be stimulating microbial decomposition processes in leaf packs Second, dominance of litterfall by “medium” and “fast” processing leaves from the recovering forest coupled with relatively high sediment loads during storms may hasten breakdown through physical abrasion Third, the interaction of high nutrients and high quality leaves may be attractive to leaf-shredding invertebrates whose feeding activities may also hasten the breakdown rates
83 citations
TL;DR: In this paper, the authors examined the limnological features that characterize the shallow ponds on Bathurst Island, Nunavut, Canada through chemical analyses and multivariate statistical methods as part of a larger on-going survey to document and monitor environmental changes in these remote and sensitive areas.
Abstract: The limnological features that characterize the shallow ponds ( 2 m deep) on Bathurst Island, Nunavut, Canada were examined through chemical analyses and multivariate statistical methods as part of a larger on-going survey to document and monitor environmental changes in these remote and sensitive areas. All sites were relatively oligotrophic and alkaline. Nutrient ratios indicated that nitrogen could be limiting algal growth to a greater degree than phosphorus in over 63 % of the sites. Principal components analysis (PCA) was used to explore the patterns of variation in the limnological dataset. The three dominant limnological gradients were: major ion content and dissolved organic carbon (DOC) levels along Axis 1; and pH along Axis 2.
75 citations
TL;DR: In this article, the authors used the Secchi depth as a simple operational measure of the effective depth of the photic zone, which can be used for more precise estimates of fundamental lake properties and for many practical issues of lake management, e.g., predictions of fish catch.
Abstract: General relationships between phytoplankton production, chlorophyll, total, dissolved and particulate phosphorus, Secchi depth, humic level, trophic level, fish production and latitude are described by regression equations using an extensive “Soviet” data base covering a wide domain of lake characteristics and a European data base. New systems for defining lake trophic and humic status are presented. The results may be used for more precise estimates of fundamental lake properties and for many practical issues of lake management, e.g., predictions of fish catch. We have used strict chlorophyll-a concentrations for every trophic class and we have omitted Secchi depth from the trophic classes, since Secchi depth and other variables strongly related to water clarity (like suspended particulate matter and particulate organic carbon) depend on autochthonous production, allochthonous influences and resuspension. We have used the Secchi depth as a simple operational measure of the effective depth of the photic zone. It has also been shown that among these lakes there exist a very strong relationship between primary production and latitude. In fact, 74% of the variability among the lakes in mean summer primary production can be statistically related to variations in latitude. These data also show a strong relationship between primary production and fish yield, which can be used to address many fundamental issues in lake management, like “normal and abnormal fish production”.
70 citations
TL;DR: A strong linear correlation was observed between total number of attached bacteria and sediment grain size in sandy fractions of lotic, lentic and subsurface environments, and biofilm-porewater ratios are suggested as valuable indicators for the characterization of sediment systems.
Abstract: An improved assessment for the enumeration of aquatic sediment bacteria is introduced. Sediment samples were stained with DAPI and counterstained with SYBR Green II. This, for the first time, allows the researcher to clearly distinguish between bacteria and nonspecifically stained bacteria-like particles. A strong linear correlation was observed between total number of attached bacteria and sediment grain size in sandy fractions of lotic, lentic and subsurface environments. This trend did not continue into the silt and clay fraction. Ratios of attached to free-living bacteria in our studies spanned three orders of magnitude and varied with sediment type. Sediment habitats which were exposed to anthropogenic disturbance and/or contamination always had lower biofilm-porewater ratios than obviously undisturbed sites. Biofilm-porewater ratios are therefore suggested as valuable indicators for the characterization of sediment systems.
63 citations
TL;DR: In this article, the breakdown rates of Alnus glutinosa leaves and the structure of macroinvertebrate communities were used to evaluate the impact of the village of Montalegre (Portugal) on the water quality of the Cavado river.
Abstract: The breakdown rates of Alnus glutinosa leaves and the structure of macroinvertebrate communities were used to evaluate the impact of the village of Montalegre (Portugal) on the water quality of the Cavado river. Chemical and microbial analyses of stream water indicated a high organic load in the vicinity of the village. The abundance of macroinvertebrates associated with leaves increased along the pollution gradient, whereas richness of the community decreased. Biotic indices and multivariate analysis applied to aquatic macroinvertebrate communities discriminated polluted from non-polluted sites. Exponential breakdown rates of alder leaves were high (0.014 to 0.060 day -1 ) and the differences observed among sites suggested that nutrient enrichment stimulated leaf breakdown significantly. Leaf breakdown rates have not reflected improved biotic conditions as assessed by biotic indices at the most downstream site. These results suggest that both data from the structure and function of a stream are important for assessing water quality.
59 citations
TL;DR: Lower Mystic Lake, Massachusetts, USA, has an anoxic black water layer just below the top of the chemocline (15.5-16.0 m) as discussed by the authors.
Abstract: Lower Mystic Lake, Massachusetts. USA, has an anoxic black water layer just below the top of the chemocline (15.5-16.0 m). Bacterial concentrations averaged 10.4 x 10 6 cells/ml in the black water layer and 4.0 x 10 6 cells/ml below 17 m. Below the chemocline, microbial concentrations were linearly correlated to the vertical light absorption coefficient, r = 0.82. Phototrophic bacteria were not detected below the top of the chemocline, due to a low PAR that never exceeded 0.0001 % surface illumination. Sulfate-reducing bacteria and methanogens were enriched from the monimolimnion in selective media. Below the chemocline, H 2 S concentrations were in excess of 11 mmoles/l and Fe, Mn, CH 4 and CO 2 concentrations were elevated compared to the mixolimnion. Nuisance releases of H 2 S occurred from the lake in 1965. Although the monimolimnion remains a highly reduced environment rich in H 2 S, the potential of further nuisance releases is small due to the diminished volume of the monimolimnion and the relatively deep chemocline.
53 citations
TL;DR: The structure and function of present day streams are influenced by forest disturbances that occurred over six decades ago, including large inputs of chestnut following the chestnut blight in the 1930s and inputs of early successional species such as black locust following extensive timber harvesting in the early 1920s.
Abstract: We excluded litter (leaves and wood) inputs to an Appalachian headwater stream for 5 years. Leaves disappeared from the streambed very rapidly ( 10 cm diameter) from the wetted perimeter of the stream. Five annual estimates of LWD mass made with line intersect methods exceeded those of complete removal by a factor of about 2x, although total wood removed was within the 95% confidence interval of that estimated by the line intersect method. Species of wood removed from the stream displayed weak similarity (percent similarity = 45 to 49%) with recent (1993 and 1972) measures of basal area of tree species in the surrounding forest, but stronger similarity (65%) with tree species measured in 1934. About 37% of the LWD removed consisted of American chestnut, Castanea dentata, (∼24%) and black locust, Robinia pseudoacacia, (∼14%), which currently represent < 1.5 % of the basal area of the surrounding forest. LWD in the stream reflects large inputs of chestnut following the chestnut blight in the 1930s and inputs of early successional species such as black locust following extensive timber harvesting in the early 1920s. These earlier disturbances to the forest were important sources of LWD that remain in the stream today. Thus, the structure and function of present day streams are influenced by forest disturbances that occurred over six decades ago.
52 citations
TL;DR: The analysis of invertebrate assemblages revealed differences between alder and the other two species related to nitrogen and microbial abundance, whereas in alder, they became more abundant.
Abstract: Decomposition of three leaf species (Alnus glutinosa, Eucalyptus globulus and Quercus robur) were examined in a headstream. During two months decomposing leaves were periodically analysed for nutrient content, soluble sugars, phenols, protein precipitation capacity, total fiber, weight loss, microbial and macroinvertebrate colonisation. The leaves of the three species showed similar patterns in dynamics of soluble sugars, tannins and phenols. Bacteria numbers per foliar dry mass were constant in oak during the experiment, but increased linearly in eucalyptus. Total heterotrophic colony forming units (bacteria and fungi) were similar in eucalyptus and oak and constant during incubation, whereas in alder, they became more abundant. The analysis of invertebrate assemblages revealed differences between alder and the other two species related to nitrogen and microbial abundance.
51 citations
TL;DR: The community structure and succession of autotrophic picoplankton in several oligotrophic to hypertrophic German freshwater ecosystems were studied and phylogenetic analyses of the rbcL genes revealed that these organisms evolved independently within several green algal lineages.
Abstract: The community structure and succession of autotrophic picoplankton in several oligotrophic to hypertrophic German freshwater ecosystems were studied with emphasis on the occurrence and characterization of chlorophyte picoplankton. Depending on the trophic status and the time of the year, the relation of green eukaryotic picoplankton to picocyanobacteria, the contribution of the picoplankton to the total phytoplankton biomass, and the succession and dominance of picoplankton groups changed considerably. A significant correlation between the picoplankton abundances, their biomass and their biomass contribution could not be found. Although the chlorophyte picoplankton were similar with respect to their ultrastructure, phylogenetic analyses of the rbcL genes revealed that these organisms evolved independently within several green algal lineages. The most common picoplanktonic green algae in the lakes that were studied belong to the genera Choricystis and Pseudodictyosphaerium. Considering the new molecular biological findings, the systematics of picoplanktonic green algae from freshwater and marine habitats are discussed.
48 citations
TL;DR: In this paper, the macrocrustacean fauna from an alluvial aquifer in the French Pyrenees was investigated using 15 wells scattered over the floodplain.
Abstract: The macrocrustacean fauna from an alluvial aquifer in the French Pyrenees was investigated using 15 wells scattered over the floodplain. Wells were sampled at three contrasting periods for faunal, phy-sical and chemical variables to investigate relationships between amphipod, isopod distributions and environmental factors.
The assemblages, dominated by stygobite amphipod species, showed an overall persistence between the sampling dates. Groundwater quality exhibited between-site variations related to agriculturally-induced pollution. Low correlations existed between water quality and fauna distribution patterns. At the scale of the aquifer, groundwater contamination did not influence the macrocrustacean distribution. The spatial distribution of amphipods and isopods was clearly related to hydrogeology and hydrodynamics: strong relationships were found between the assemblages composition and the hydrological context of the stations (wells from the alluvial plain and from the alluvial terrace). With respect to spatial and temporal scales and providing adequate sampling methods, macrocrustaceans then constitute natural indicators of groundwater hydrodynamics in the Ariege aquifer.
TL;DR: The role of macrophytes in the terrestrialization process of an oxbow lake of the river Danube, where a thick sediment layer has developed since river regulation, is investigated and the fast decomposition of submerged Macrophytes indicates a low contribution to the terrestrialized process.
Abstract: Ecological alterations of wetlands due to anthropogenic influence are a central topic of discussions focussing on the restoration of these disturbed ecosystems. In this context we investigated the role of macrophytes in the terrestrialization process of an oxbow lake of the river Danube, where a thick sediment layer has developed since river regulation. One third of the oxbow lake is covered by a reed belt, fuelling about 140 tons of plant material per year into the detritus pool. From submerged macrophytes the system receives about 48 tons. Degradation of emergent macrophytes is slow due to early burial by sediment, leading quickly to anaerobic conditions. Thus emergent macrophytes contribute significantly to the terrestrialization process. The fast decomposition of submerged macrophytes indicates a low contribution to the terrestrialization process.
TL;DR: The dynamics of leaf weight loss and microorganisms associated with Salix pedicellata leaves decaying at the four sites were compared for the first time during the same period over this permanent and intermittent system.
Abstract: Leaf degradation was investigated at four sites in the Zegzel/Cherraa river system (Oueds). Two sites (Upper Zegzel and Lower Zegzel) carry water throughout the year and two (Upstream and Downstream Cherraa) are dry for 5–7 months each year.
The dynamics of leaf weight loss and microorganisms associated with Salix pedicellata leaves decaying at the four sites were compared for the first time during the same period over this permanent and intermittent system. Overall decay rates of leaves were significantly higher in the permanent Zegzel stream sections (k = 0.0094 d–1 upstream and 0.0056 downstream) than in the intermittently flowing Cherraa sites (k = 0.0046 upstream, and 0.0036 downstream). In the latter, decay was much slower during dry than during wet periods (Upstream Cherraa: k = 0.0028 and 0.0446, respectively; Downstream Cherraa, k = 0.0008 and 0.0357, respectively).
Similar gradients from permanent to intermittent sites were observed in numbers of bacteria per unit area or per weight of decaying leaves (direct counts by epifluorescence microscopy), in numbers of fungal species and in sporulation rates, from leaves recovered at the four sites. Ten hyphomycete species were new for Morocco.
TL;DR: In this article, the authors used the litter bag technique to study leaf decomposition in the large forested eutrophic (160.9 μmol l -1 DIN, 1.7 µm l −1 SRP) Ebro river and in the forested Senia (12.8 µm L -1 RSP), Air dried leaves (3g) of Phragmites australis were used in both watercourses while Populus alba leaves were studied in the Ebro River only, and Populus nigra leaves and a submerged
Abstract: The litter bag technique was used to study leaf decomposition in the large forested eutrophic (160.9 μmol l -1 DIN, 1.7 μmol l -1 SRP) Ebro river and in the forested Senia (12.8 μmol l -1 DIN, 0.7 μmol l -1 RSP), Air dried leaves (3g) of Phragmites australis were used in both watercourses while Populus alba leaves were studied in the Ebro river only, and Populus nigra leaves and a submerged rooted macrophyte (stems and leaves), Potamogeton coloratus, were studied only in the Senia stream. Litter bags of 100 μm and 1 mm mesh size were collected on days 0, 3, 15, 30, 90 and 120 and 5 mm mesh bags were sampled once after 30 days. Macroinvertebrates inside the leaf bags were retrieved and ash free dry weight and carbon and nitrogen contents of the remaining detritus were determined. Litter decomposition rates, k, were estimated using a simple exponential model. No significant differences in decomposition rates were observed between 100 μm and I mm mesh bags. In 100 μm litter bags, decomposition of P. nigra leaves from the Senia stream (0.0104 day -1 ) was faster than that of P. alba leaves from the Ebro river (0.0049 day -1 ) (ANCOVA, p < 10 -5 ). The decomposition rate of P. australis was higher in the Ebro river (0.009 ± 0.002 day -1 ) than in the Senia stream (0.0056 ± 0.0004 day -1 ) for the first 30 days of decomposition, but no differences were observed from day 30 onwards. The number of macroinvertebrates increased over time and were mainly collectors-gatherers of the genus Chironomus. Percentage of detritus nitrogen increased in litter that had initially high C/N ratios (28.7 in P. alba and 64.7 in P. nigra) and decreased when initial C/N ratios were low (12.6 and 14.6 for P. australis from the Senia and Ebro river respectively).
TL;DR: Meiobenthicabundances from the area of investigations, were up to ten times lower than those reported from non-ice covered deep-sea regions, however a significant water depth depending decrease of meiOBenthic abundances was stilldetectable.
Abstract: Abundance, biomass and activity of the small-sized benthic organisms (bacteria to meiofauna, includingforaminifera) was studied in summer 1998 during the expedition ARK XIV/1a to the Amerasian area of theperennially ice covered central Arctic Ocean. With the help of two icebreakers, the German research vesselPOLARSTERN and the Russian nuclear-powered ARCTICA, it was possible to reach this remote, heavilyice-covered region in order to carry out the first benthic investigations. These focus on effects on the benthiccommunity of the expected low food availability under perennial ice coverage. Bacterial and meiofaunalabundances were determined by direct counting. Biomass determinations on bacteria and nematodes wereundertaken by size-imaging techniques. In addition biochemical analyses were carried out to estimate foodavailability (as sediment-bound chloroplastic pigments indicating phytodetritus) at the sea floor, the total microbialbiomass (TMB; i.e. the total amount of sediment inhabiting bacteria, flagellata, protozoa and small metazoa,estimated by phospholipid quantification) and the potential bacterial activity (turnover rates of ester-cleavingexoenzymes). Concentrations of chloroplastic pigment equivalents (CPE) in the main target area (Alpa-Ridge)ranged between 0.10 ± 0.02 and 0.17 ± 0.04 g/ml. A 2-3 times higher concentration was determined at astation on the Lomonosov Ridge crest (0.40 ± 0.15 g/ml). The standing stock of meiobenthic organisms(including foraminiferans) was extremely low and varied between 72 ± 17 individuals 10 cm-2 in the deepMakarov Basin (3,170 m) and 190 ± 56 individuals 10 cm-2 on the Alpha Ridge (1,470 m). Significantly highernumbers (U-test, p = 0.049) were found on the Lomonosov Ridge (297 ± 82 individuals 10 cm-2). Meiobenthicabundances from the area of investigations, were up to ten times lower than those reported from non-ice covereddeep-sea regions. However a significant water depth depending decrease of meiobenthic abundances was stilldetectable.A comparison of biomass data determined by volumetric measurements and biochemical methods showed thatabout 67% of the TMB are held by organisms of nanofauna size (2-32 m), approx. 32% belongs to bacteria.Only 0.5-1.5% of the TMB were held by metazoan meiofauna.
TL;DR: This article performed a seven-month study on beech leaf breakdown and associated fauna along a forested stream showing a gradient in acidification level (4 stations with mean pH ranging from 53 to 72).
Abstract: We performed a seven-month study on beech leaf breakdown and associated fauna along a forested stream showing a gradient in acidification level (4 stations with mean pH ranging from 53 to 72) We completed this approach by comparing in situ the shredding efficiency of the main invertebrate species present at each station, the acid-tolerant Protonemura sp (Plecoptera: Nemouridae) and the acid-sensitive Gammarus fossarum (Amphipoda: Gammaridae) Results showed that beech leaf breakdown rate was severely depressed under acidic conditions Not only did the acidic station show lower biomass of shredders, but Protonemura sp, the main shredder presented significantly lower feeding activity than G fossarum in the non-acidic stations At the other three stations, feeding activities of G fossarum were similar and differences in litter breakdown rates appeared to be related to G fossarum densities By combining both fine-resolution studies of individual species and ecosystem level studies, our results suggest that the functional role played by G fossarum in the studied system seems to be unique and not fulfilled by other species in the acidified upper part of the stream
TL;DR: The importance of seasonal abundance and life-history characteristics of mayfly nymphs (e.g., emergence and recruitment) on density estimates relative to the mayfly-density management goal is discussed in this paper.
Abstract: After an absence of 40 years, mayfly nymphs of the genus Hexagenia were found in sediments of western Lake Erie of the Laurentian Great Lakes in 1993 and, by 1997, were abundant enough to meet a mayfly-density management goal (ca. 350 nymphs m -2 ) based on pollution-abatement programs. We sampled nymphs in western Lake Erie and Lake St. Clair, located upstream of western Lake Erie, to determine the importance of seasonal abundance and life-history characteristics of nymphs (e.g., emergence and recruitment) on density estimates relative to the mayfly-density management goal. Two types of density patterns were observed: (1) densities were relatively high in spring and gradually decreased through late summer (observed in Lake Erie and Lake St. Clair in 1997 and Lake St. Clair in 1999) and (2) densities were relatively high in spring, gradually decreased to mid summer, abruptly decreased in mid summer, and then increased between summer and late fall (Lake Erie and Lake St. Clair in 1998 and Lake Erie in 1999). Length-frequency distributions of nymphs and observations of adults indicate that the primary cause for the two density patterns was attributed to failed (first pattern) and successful (second pattern) reproduction and emergence of nymphs into adults in mid summer. Gradual declines in densities were attributed to mortality of nymphs. Our results indicate that caution should be used when evaluating progress of pollution-abatement programs based on mayfly densities because recruitment success is variable both between and within years. Additionally, the interpretation of progress toward management goals, relative to the restoration of Hexagenia populations in the Great Lakes and possibly other water bodies throughout the world, is influenced by the number of years in which consequtive collections are made.
TL;DR: In this article, the authors compared the biofilm removal of the optimal ultrasound exposure time previously obtained using the ultrasonic bath with the removal by a method using a narrow tip ultrasonic generator.
Abstract: Two types of ultrasound applications are commonly used in order to remove bacteria from sediment for subsequent direct enumeration: ultrasonic baths and narrow tip ultrasonic generators. By measuring four parameters (total number of bacteria, number of ETS-active bacteria, amount of proteins and weight of fine sediment obtained in sonicated juices), we compared the biofilm removal of the optimal ultrasound exposure time previously obtained using the ultrasonic bath with the removal by a method using a narrow tip ultrasonic generator. To obtain comparable removal efficiencies estimated by protein contents in sonicated juices, the ultrasonic bath method required an ultrasound exposure time more than 10 times that with a narrow tip ultrasonic generator. Furthermore, the two methods provided significantly different bacterial counts because of an alteration of the sediment with the ultrasonic bath. Thus, a narrow tip ultrasonic generator is more suitable than an ultrasonic bath for the analysis of biofilms developed on sand.
TL;DR: The 18S rRNA targeted fungal oligonucleotide probe FUN1429 was designed and evaluated for the identification of in situ metabolically active Eumycota and showed clear fluorescence hybridization signals after visualization with confocal laser scanning microscopy (CSLM).
Abstract: Based on computer assisted comparative sequence analysis, the 18S rRNA targeted fungal oligonucleotide probe FUN1429 was designed and evaluated for the identification of in situ metabolically active Eumycota. The general accessibility of fungal cells for fluorescent oligonucleotides was tested by whole cell hybridizations. Additionally, the influences of different growth media, age of the fungal specimen and the composition of permeability buffers were assessed. All strains showed clear fluorescence hybridization signals after visualization with confocal laser scanning microscopy (CSLM). In contrast fluorescence hybridization signals were hardly detectable by conventional epifluorescence microscopy due to strong fungal autofluorescence. The inherent autofluorescence emitted from the strains increased with the age of cultures, but was significantly decreased by chitinase treatment prior to in situ hybridization. The composition of the growth media showed no measurable effect on signal intensity.
TL;DR: The spatial succession of the reservoir microbial food webs was followed downstream by maximum densities of their potential predators among zoo-plankters – rotifers, and early developmental stages of copepods.
Abstract: We studied the planktonic food web in eutrophic Sau Reservoir (Catalonia, NE Spain). Along the longitudinal axis from the Ter River downstream to the dam, we characterized a microbial succession of food web dominance of bacteria-HNF-ciliates. The Ter River transports a large load of organic material into the reservoir, with a bacterial density of ∼9 · 106 large cells per ml. While at the first lacustrine station of the Reservoir HNF were the dominant bacterial consumers, at the others, an oligotrich ciliate, Halteria grandinella, was the main protozoan bacterivore. Most of the bacterial production in the reservoir epilimnion was consumed by grazing. The spatial succession of the reservoir microbial food webs was followed downstream by maximum densities of their potential predators among zoo-plankters – rotifers, and early developmental stages of copepods.
TL;DR: Experiments showed that 9 out of 10 species, which were observed to produce resting eggs during the aquatic phase, were able to survive the terrestrial phase through dormancy in the desiccated floodplain soils.
Abstract: The floodplains of the River Oder are inundated in winter and spring and are desiccated during summer. The plankton community developing towards the end of winter is dominated by monogonont rotifers. Some species maintain populations on the flooded areas as well as in the remaining permanent waters after flooding. Other species are found during the inundation period only. These species produce drought-resistant diapause stages, beginning at low population densities between 5 to 36 females L -1 . Experiments showed that 9 out of 10 species, which were observed to produce resting eggs during the aquatic phase, were able to survive the terrestrial phase through dormancy in the desiccated floodplain soils. Other species colonise the temporarily inundated areas from the permanent waters again during each flooding period.
TL;DR: Considerable differences were observed in the macroinvertebrate community of the two sampling sites and several taxa were present with considerably higher individual number in either the stem or the leaf litter bags.
Abstract: Stem and leaf litter of Phragmites australis were enclosed in litter bags and submerged in a vigorous and a die-back reed stand of Lake Ferto/Neusiedler See (Hungary). Species composition and individual number of the macroinvertebrates within the litter bags were recorded between April, 1996 and July, 1998. Thirty one taxa were found during the two and a half year experiment. Considerable differences were observed in the macroinvertebrate community of the two sampling sites. Chironomidae (collector) were predominant at site 5 (vigorous), while Isopoda and Gastropoda (shredder, grazer-scraper) were the predominate taxa at site 3 (die-back). The individual number and the number per gram dry mass were higher in the leaf litter bags than in the stem litter bags. Several taxa were present with considerably higher individual number in either the stem or the leaf litter bags.
TL;DR: Densities of lesions were highest in Bolinao, intermediate in Puerto Galera, and lowest in El Nido, which pattern is parallel to intensity of human reef exploitation and opposite to that in colony size, live coral cover and Acropora cover.
Abstract: Partial mortality or tissue necrosis was quantified in the massive scleractinian coral Porites at three sites in The Philippines (Bolinao, NW Luzon; Puerto Galera, Mindoro; and El Nido, N Palawan). Overall, 15 ± 1 (mean ± 1 standard error, 642 replicates) percent of colony area was dead, mean colony area was 1135 ± 127 cm 2 , and lesion density was 1.7 ± 0.1 dm ‐2 . Total live coral cover varied between 20 and 63% in belt transects, and Porites and Acropora cover were inversely correlated. ANOVA models incorporating effects of site, colony size, sedimentation rates, wave exposure and depth were highly significant but explained only a small proportion of the variation observed in lesion density and percent dead area (respectively 8 and 2%). Lesion density was found to vary significantly with site (contributed 29% to this explained variance), decrease with increasing colony area (33%), and increase with increasing sedimentation (23%) and wave exposure (14%). Colony size was significantly explained by the factor site (contributing 61% to the total 29% explained variance) and depth (34%), with the smallest colonies being observed in Bolinao and the largest in El Nido. Densities of lesions were highest in Bolinao, intermediate in Puerto Galera, and lowest in El Nido. This pattern is parallel to intensity of human reef exploitation and opposite to that in colony size, live coral cover and Acropora cover. Since only a small part of the observed variance in partial mortality estimators was explained by the ANOVAs, other factors not quantified here must have been more important (e.g. disease incidence, predation, human exploitation).
TL;DR: In this paper, the authors measured leaf input, leaf breakdown, and benthic leaf standing stock in Hugh White Creek, a second-order, Appalachian Mountain stream in North Carolina, U.S. A.
Abstract: We measured leaf input, leaf breakdown, and benthic leaf standing stock in Hugh White Creek, a second-order, Appalachian Mountain stream in North Carolina, U. S. A. Leaf input and leaf breakdown data were used in a computer model to predict standing stocks. Predicted standing stocks were then compared with measured values. Once the model was modified to include leaves in four breakdown rate categories, leaf blow-in, and temperature effects on leaf breakdown, agreement between model prediction and measurement was quite good.
TL;DR: The success of the restoration was predominantly attributed to bottom-up forces as a result of the declining nutrient load and an intensified co-precipitation of phosphorus with calcite, however, the increased predation impact by the piscivorous fish may have caused a reduced nutrient recycling by the planktivorousFish thus contributing also to the improvement in water quality.
Abstract: A long-term biomanipulation has been performed in the stratified Feldberger Haussee since 1985. Prior to manipulation, nutrient load to the lake had declined due to waste water removal. Planktivorous fish were reduced by seining and by enhancement of piscivorous fish. Changes in transparency, nutrients, phytoplankton, zooplankton and fish were documented for both the premanipulation period (1978-1985) and the manipulation period (1986-1998). Transparency increased in response to the manipulation (+54%), but strong year-to-year fluctuations were observed. These fluctuations were correlated to chlorophyll a, primary production and the proportion of piscivores in the fish community. We conclude that the success of the restoration was predominantly attributed to bottom-up forces as a result of the declining nutrient load and an intensified co-precipitation of phosphorus with calcite. However, the increased predation impact by the piscivorous fish may have caused a reduced nutrient recycling by the planktivorous fish thus contributing also to the improvement in water quality.
TL;DR: Zooplankton in the main channel of the Nakdong River and in three tributaries was sampled from June 1994 to September 1995 as discussed by the authors, and Planktonic rotifers (Brachionus spp, Keratella spp., and Polyarthra spp.), cyclopoid nauplii and small cladocerans (Bosmina longirostris) were numerically dominant.
Abstract: Zooplankton in the main channel of the Nakdong River and in three tributaries was sampled from June 1994 to September 1995. Planktonic rotifers (Brachionus spp., Keratella spp., and Polyarthra spp.), cyclopoid nauplii and small cladocerans (Bosmina longirostris) were numerically dominant. There was considerable longitudinal variation of zooplankton biomass in the main channel as well as spatial heterogeneity among the major tributaries. In the middle region of the main channel, between river kilometer (RK) 170 and 150 above the estuary dam, total zooplankton abundance sharply increased from less than 100 ind. L -1 to more than 1,000 ind. L -1 . In a downstream direction toward the estuary dam, phytoplankton biomass increased while total zooplankton biomass decreased. However, as shown by the increasing transport of zooplankton biomass, zooplankton was diluted in the reach of the estuary dam. Advective effects from major tributaries appear to be the contributory factor for the higher zooplankton biomass in the middle region. Overall, rather the external factors (flushing, retention) than internal factors (e.g., phytoplankton) appear to be responsible for changes in zooplankton abundance toward the river mouth.
TL;DR: In this article, the authors investigated the breakdown of beech leaf litter and dynamics of particulate organic matter (POM) at five sampling stations along a 295 m altitudinal gradient of a 1 st to 5 th order undisturbed stream (the River Stradomka, southern Poland).
Abstract: Breakdown of beech leaf litter and dynamics of particulate organic matter (POM) were investigated at five sampling stations along a 295 m altitudinal gradient of a 1 st to 5 th order undisturbed stream (the River Stradomka, southern Poland) The gradual increase of stored POM with stream altitude was observed This was explained by changes in the stream substrata Beech leaves breakdown was faster in the downstream direction This tendency can be explained by physical fragmentation or by microbial activity but not by water chemistry The increase of stored total POM and coarse POM in transport reduced the breakdown of exposed beech leaves It is suggested that when physical and chemical variables of water cannot explain observed altitudinal patterns of leaf breakdown, other factors including different POM and biological parameters should he considered
TL;DR: In this article, the authors quantified the decrease of organic and trophic pollution in a constructed wetland used for tertiary sewage treatment, and found that the results of the saprobic zoning system were influenced by differences in nitrate concentrations.
Abstract: The present study quantified the decrease of organic and trophic pollution in a constructed wetland used for tertiary sewage treatment. Different diatom indices [the saprobic zoning system of LANGE-BERTALOT (1978, 1979), the saprobic index (SI) of ROTT et al. (1997), as well as the trophic indices of SCHIEFELE and KOHMANN (1993); KELLY and WHITTON (1995) and ROTT et al. (1999)] were tested for their effectiveness in detecting changes in water quality of highly organic and trophic waters. The saprobic zoning system detected nearly the same pollution levels as the chemical data, but the measured saprobic characteristics (e.g. TOC: Total Organic Carbon) did not correspond to significant changes in the diatom assemblages. The data suggested that the results of the saprobic zoning system were influenced by differences in nitrate concentrations. The trophic diatom indices correlated relatively well with the inorganic compound chemical data.
TL;DR: Food was better exploited after repeated gut passage, as evidenced by reductions in organic contents, proteins and carbohydrates in the faeces, and Tadpoles tended to gain weight when fed Scenedesmus or Aphanizomenon.
Abstract: This study examined the exploitation of several species of algae and other organisms by Rana dalmatina larvae, by comparing nutrient contents and pigment degradation of food algae to faeces and changes in larval weight.
Tadpoles gained weight when fed Oscillatoria limosa mats collected from the field. The high inorganic content of the Oscillatoria mats, combined with gut peristalsis, may have faciliated the cracking of the tough cell walls.
When fed Cladophora and Spirogyra, ash-free dry weight and protein content of tadpole faeces decreased whilst chlorophyll-degradation products increased in the faeces relative to the food. With Scenedesmus as food, pigment degradation occurred after gut passage. Tadpoles tended to gain weight when fed Scenedesmus or Aphanizomenon. The epipelic diatoms, Gongrosira, and the planktonic flagellates Cryptomonas and Chlamydomonas were exploited only in traces.
Food was better exploited after repeated gut passage, as evidenced by reductions in organic contents, proteins and carbohydrates in the faeces.
TL;DR: Results suggest an interaction between nutrient status/availability and UV sensitivity, and the dominant periphyton species, Anabaena circinalis RAB.
Abstract: Rising levels of ultraviolet radiation (UVR) striking the Earth's surface have led to numerous studies assessing its inhibitory effects on phytoplankton and periphyton in aquatic systems. Mineral nutrients such as nitrogen (N) and phosphorus (P) have been shown to increase aspects of algal metabolism and compensate for UVR inhibition. An in situ substratum enrichment technique and UV shielding was used to assess the effects of nutrient additions on periphyton exposed to different levels of UVR in Castle Lake, California during July-August, 1997. UV shielding had no effect on total periphyton biomass, but caused shifts in species composition. The dominant periphyton species, Anabaena circinalis RAB., demonstrated sensitivity to ambient levels of UV radiation possibly due to UV inhibition of N 2 -fixation. Total diatom biovolume decreased when shielded from UVR. Phosphorus additions continually elicited an increase in periphyton biovolume at all levels of analysis. These results suggest an interaction between nutrient status/availability and UV sensitivity.