Feeding ecology of the freshwater detritivore Ptychoptera paludosa (Diptera, Nematocera)

1. We examined selected aspects of the nutritional ecology of larval Ptychoptera paludosa and their role in nutrient cycling in the Breitenbach, a first-order stream in Hesse, Germany.
2. Food preference experiments demonstrated significant preference for sediments with a high organic matter content and live bacteria.
3. pH was circumneutral in all sections of the gut.
4. Enzymatic activity (β-glucosidase and amino-peptidase) in different parts of the gut was measured using 4-methylumbelliferyl-β- D -glucopyranoside (MUF-Glc) and leucine-4-methylcoumarinyl-7-amide (Leu-MCA). β-glucosidase activity was highest in the hindgut.
5. The mean larval gut passage time was between 7 and 8 h.
6. The egestion rate of last instar larvae was about 0.35 mg dry weight (DW) faeces per larva h^–1 and about 1.25 mg ash-free dry weight (AFDW) faeces per mg larval AFDW day^–1.
7. Larval faeces contained at least 4–18 times more organic matter than the average in the sediments in which they were feeding, that is, larvae fed selectively, extracting organic matter from sediments.
8. P. paludosa larvae are important in the dynamics of detritus in slow-flowing reaches of the Breitenbach. They gather organic material from the sediment to a depth of 3 cm, and release it as faeces onto the sediment surface. A total of 770 g DW faeces m^–2 yr^–1, comprising about 16% organic matter, was produced by the Ptychoptera population.     

Regulation of b- and a-Glycolytic Activities in the Sediments of a Eutrophic Lake

Temporal changes in α-and β-glucosidase activities, dissolved organic matter content, and bacterial biomass were studied in the superficial sediment layer of a eutrophic lake during the period of anoxia. The mean α-and β-glucosidase activities were 30.7±11.0 and 15.1±6.2 nmol h⁻¹ g⁻¹ of dry sediment, respectively. The specifc β-glucosidase activity seemed to be stimulated by carbohydrates (r=0.80, P<0.05), whereas the specifc α-glucosidase activity was negatively correlated with the dissolved protein concentration (r=−0.72, P<0.10). To test the effect of organic matter on hydrolytic activities under controlled conditions, changes in specific activities were studied in relation to the concentrations of different types of organic matter: phytoplankton, polymers (proteins, cellobiose, and starch) and monomers (glucose and amino acids). The specifc α-and β-glucosidase activities were strongly induced by their natural substrates (starch and cellobiose, respectively) (P<0.05) and were not inhibited by glucose. Proteins inhibited these activities (P<0.05), whereas supplementation with amino acids had no effect on specifc glycolytic activities.     

Organic Carbon in a Eutrophic Fishpond

Accumulation of dissolved organic carbon (DOC) was studied in a eutrophic pond and in cultures of Scenedesmus abundans. Samples of pond water and media were treated with a cation exchanger in Na cycle and chromatographed on Sephadex G 25 and G 10. — UV spectra of the peak fractions were recorded. In the pond about half of the organic carbon is in fractions with an apparent molecular weight (AMW) of 500–1000, while in the algal medium (after cultivation) most of organic carbon has an AMW of about 120. These and spectral data did not suggest that aromatics and compounds with conjugated double bonds were major organic constituents of DOC.     

Microcalorimetric Approach to Determine Relationships between Energy Supply and Metabolism in River Epilithon

In a study to determine the relative importance of various apparent molecular weight fractions to the metabolism (heat output) of attached microorganisms in rivers, a marked lack of response to gross changes in the external organic matter supply was noted over the course of several hours. Such a response by a mixed autotrophic-heterotrophic community could be attributed to the autotrophs being the sole organic energy source for the heterotrophs. However, substantial metabolic activities were noted in attached microbial communities grown in darkness (algae free), thus indicating that riverborne organic matter was a major energy source. This paradox was attributed to a proposed lag in the availability of dissolved and colloidal organic matter to the heterotrophic microorganisms.     

Monitoring the Active Conformation of Green Fluorescent Protein (GFP) and β-Glucosidase Adsorbed on Soil Particles

In order to determine the effect of various soil components on the activity of proteins, we monitored the fluorescence and the enzymatic activity of, respectively, green fluorescent protein (GFP) and β-glucosidase adsorbed on fine soil particles. We also monitored the activity of these proteins in the presence of components that are representative of soil colloids: a montmorillonite clay, goethite and organic matter extracted from soil. Upon adsorption on clay and goethite, GFP lost its fluorescence properties while β-glucosidase suffered only a partial loss of its catalytic activity. Extractable organic matter had an inactivating role on GFP while it did not cause inactivation of β-glucosidase. When GFP and β-glucosidase adsorbed on particles from natural soil samples, their behaviour was consistent with the behaviour observed for these proteins in the presence of the separate components, suggesting that the macroscopic activity of proteins adsorbed on soil particles corresponds to an average of the activities of proteins adsorbed on a mixture of surfaces. The monitoring of the proteins on soil particles with different organic matter contents has also shown that organic matter can have different effects (protecting or inactivating) on different proteins.     

Regulation and Seasonal Dynamics of Extracellular Enzyme Activities in the Sediments of a Large Lowland River

We tested whether seasonal changes in the sources oforganic substances for microbial metabolism were reflected changes in the activities of five extracellular enzymes in the eighth order lowland River Elbe, Germany. Leucine aminopeptidase showed the highest activities in the water column and the sediments, followed by phosphatase > β-glucosidase > α-glucosidase > exo-1,4-β-glucanase. Individual enzymes exhibited characteristic seasonal dynamics, as indicated by their relative contribution to cumulative enzyme activity. Leucine aminopeptidase was significantly more active in spring and summer. In contrast, the carbohydrate-degrading enzymes peaked in autumn, and β-glucosidase activity peaked once again in winter. Thus, in sediments, the ratio of leucine aminopeptidase/β-glucosidase reached significant higher medians in spring and summer (5-cm depth: ratio 7.7; 20-cm depth: ratio 10.1) than in autumn and winter (5-cm depth: ratio 3.7, 20-cm depth: ratio 6.3). Therelative activity of phosphatase in the sediments was seasonally related to both the biomass of planktonic algae as well as to the high content of total particulate phosphorus in autumn and winter. Due to temporal shifts in organic matter supply and changes in the storage capacity of sediments, the seasonal peaks of enzyme activities in sediments exhibited a time lag of 2–3 months compared to that in the water column, along with a significant extension of peak width. Hence, our data show that the seasonal pattern of extracellular enzyme activities provides a sensitive approach to infer seasonal or temporary availability of organic matter in rivers from autochthonous and allochthonous sources. From the dynamics of individual enzyme activities, a consistent synoptic pattern of heterotrophic functioning in the studied river ecosystem could be derived. Our data support the revised riverine productivity model predicting that the metabolism of organic matter in high-order rivers is mainly fuelled by autochthonous production occurring in these reaches and riparian inputs.     

Activity profiles of bacterioplankton in a eutrophic river

1. The significance of microbial diversity in processing dissolved organic matter (DOM) is largely unknown. We investigated the range of functional diversity in the bacterioplankton from a eutrophic river by profiling extracellular enzyme activities (EEA) and substrate-induced respiration (SIR) patterns.
2. The EEA profiles consisted of assays for 21 hydrolases, measured using fluorogenic substrates arrayed on 96-well microplates. Commercially available BiOLOG^® GN and ECO plates, which contained 120 different substrates, were used for the SIR profiles.
3. The EEA data were more dynamic than the SIR. Five enzymes, leucine aminopeptidase, alkaline phosphatase, alanine aminopeptidase, arginine aminopeptidase and β-glucosidase, showed consistently high activity; ten others were ubiquitous at lower activity levels; the remainder were detected intermittently. The SIR data showed less temporal variability. With one exception (citrate), the 20 substrates that generated the largest responses were all saccharides or their derivatives.
4. The EEA and SIR data did not generally correlate. Both methods were effective for ordinating bacterioplankton although, unlike the SIR, the EEA ordination followed a clear temporal trajectory.
5. Because the SIR profiles are based on a culture response, whilst the EEA profiles measure activity of the extant community, the latter appear to be more directly linked to the mechanics of DOM processing.     

Hydrolytic extracellular enzyme activity in heterotrophic biofilms from two contrasting streams

SUMMARY. 1. Extracellular hydrolytic enzyme activities and cell densities were monitored during undisrupted biofilm formation on pristine surfaces in two contrasting river sites in North Wales: an oligotrophic mountain stream (Nant Waen) and a mildly eutrophic river (River Clywedog).
2. Bacterial densities generally increased at both sites over a 33-day monitoring period. Densities in the eutrophic site were approximately 14 times greater than in the mountain stream.
3. Using fluorescent substrate analogues, biofilms from Nant Waen produced low, variable xylosidase and β-glucosidase activities. Biofilms from the more eutrophic River Clywedog produced higher xylosidase and β-glucosidase activities and detectable endopeptidase, though these activities also fluctuated during the colonization period.
4. Unlike the other activities measured, esterase activities in the River Clywedog were correlated with cell densities ( P <0.05). When extracellular esterase activities per cell were calculated, the oligotrophic biofilm was found to contain about twice as much extracellular esterase activity as the more eutrophic River Clywedog biofilm.     

Enhanced in vitro and in vivo antioxidant activity and mobilization of free phenolic compounds of soybean flour fermented with different β-glucosidase-producing fungi

Aims:  To evaluate the soybean polyphenol glucosides bioconversion to aglycone forms by different β-glucosidases-producing filamentous fungi to enhance their antioxidant activity.
Methods and Results:  Soybean defatted flour was submitted to solid-state fermentation with Aspergillus niger , Aspergillus niveus and Aspergillus awamori . The fungi studied produced approximately the same β-glucosidase activity units amount when p- nitrophenyl-β- d -glucopyranoside was used as substrate for the assay. However, electrophoretic analysis, using 4-methylumbellipheryl-β- d -glucopyranoside as substrate, showed that β-glucosidase produced by A.   niveus was more active. Fermented methanolic extracts showed an increase in polyphenol and genistein contents and antioxidant activities. The highest genistein content was found in soybean fermented by A. niveus . Methanolic extracts of the soybean fermented by the different fungi showed a similar capacity of scavenging H₂O₂ generated in vivo by the tumour promoter 12- O- tetradecanoyl phorbol-13-acetate.
Conclusions:  A.   niveus synthesized a β-glucosidase with higher specificity to hydrolyse genistin β-glycosidic bond than those produced by A .  awamori and A. niger .
Significance and Impact of the Study:  The utilization of these β-glucosidases-producing fungi in soybean fermentation processes resulted in the obtaining of methanolic extracts with different antioxidant potentials that could be used either therapeutically or as an antioxidant in nonphysiological oxidative stress conditions, as the one induced in skin by UV radiation.     

Input, movement and exchange of organic matter within a subtropical coastal black water river-flood plain system

SUMMARY. 1. Inputs, movements and exchanges of particulate organic matter were measured on two contrasting floodplains of the Ogeechee River, Georgia, U.S.A. A model, which incorporated measurements of standing crop, respiration, litterfall, inundation, and litter processing rates, was used to estimate annual exchanges of organic matter between the river and floodplains.
2. Annual litterfall was higher on the East floodplain than on the lower elevation West floodplain (902 v. 784 g ash-free-dry-mass [AFDM] m⁻²).
3. Experiments with tagged leaves and sticks demonstrated that litter was readily displaced during floods. The distance and direction of displacement varied within and between floodplains but tended to be higher closer to the river and was generally parallel to the river.
4. The model indicated that both floodplains lost organic matter to the river. The lower elevation floodplain (East) lost more organic matter to the river (208 g AFDM m⁻² year⁻¹) than did the higher elevation (West) floodplain (79g AFDM m⁻² year⁻¹).
5. Inputs of organic matter from the floodplain to the river exceeded the amount of litterfall typically entering heavily forested high gradient headwater streams (5.5 v. 0.4-0.6 kg AFDM m⁻² year⁻¹).
6. Floodplain organic matter inputs may exert a greater influence upon structure and function within these streams than do upstream inputs or primary production. Consequently, current conceptualizations of stream structure and function need to be modified to account for the effects of floodplain inputs on stream channel processes within large, low-gradient rivers.     

Effect of primary producers on the heterotrophic metabolism of a stream biofilm

1. ,The influence of benthic algae on heterotrophic metabolism in a forested Mediterranean stream was investigated. Bacterial density and ectoenzymatic activities, as well as algal biomass (chlorophyll- a ) and metabolism (the rate of ¹⁴C incorporation), were measured during colonization over 60 days of artificial substrata (clay tiles) under light and dark conditions.
2. ,Chlorophyll- a and the rate of ¹⁴C incorporation were significantly higher in light-grown than in dark-grown biofilms. Bacterial density and ectoenzymatic activity (especially β-glucosidase) were also significantly higher in light-grown biofilms.
3. ,Regressions of chlorophyll- a and ¹⁴C incorporation values on the ectoenzymatic activities were significant. The slopes of regression lines obtained for dark-grown biofilms were significantly higher than those obtained for light -grown biofilms.
4. ,The differences in the slope (of the regression lines) between dark and light-grown biofilms suggest that the response of the heterotrophs is faster in biofilms with low algal biomass accrual and slows down when algal biomass is increased.
5. ,It is concluded that algal accumulation in the epilithic biofilm influences the use of organic matter by the heterotrophic community by increasing the amount of organic substrate available for bacteria.     

Effects of augmentation of coarse particulate organic matter on metabolism and nutrient retention in hyporheic sediments

SUMMARY 1. Metabolic and biogeochemical processes in hyporheic zones may depend on inputs of coarse particulate organic matter. Our research focused on how differing quantity and quality of organic matter affects metabolism and nutrient retention in the hyporheic zone of a first-order Appalachian stream.
2. Sixteen plots were established on a tributary of Hugh White Creek, NC, U.S.A. Sediment was extracted and treated with leaves, wood, plastic strips or remained unamended. Following treatment, sediment was returned to the stream and, approximately 3 months later, samples were removed from each plot.
3. Aerobic and anaerobic metabolism were measured as the change in O₂ and CO₂ in recirculating microcosms. At the same time, we monitored other possible terminal electron accepting processes and changes in nutrient concentrations. Aerobic metabolism was low in all treatments and respiratory quotients calculated for all treatments indicated that metabolism was dominated by anaerobic processes.
4. Rates of anaerobic respiration and total (combined aerobic and anaerobic) respiration were significantly greater ( P  < 0.05) in plots treated with leaf organic matter compared to controls.
5. Addition of leaves, which had a low C:N ratio, stimulated respiration in hyporheic sediments. Anaerobic processes dominated metabolism in both control and amended sediments. Enhanced metabolic rates increased retention of many solutes, indicating that energy flow and nutrient dynamics in the subsurface of streams may depend upon the quantity and quality of imported carbon.     

厌氧发酵液中溶解性有机物对活性污泥合成聚羟基脂肪酸酯影响的研究进展

利用活性污泥微生物将剩余污泥发酵液中的挥发性脂肪酸(Volatile fatty acids,VFAs)转化为聚羟基脂肪酸酯(Polyhydroxyalkanoates,PHA)是目前环境生物技术领域的研究热点.但针对发酵液中非VFAs物质(主要是溶解性有机物,Dissolved organic matter,DOM)...     

Extracellular enzyme activity: Indications for high short-term variability in a coastal marine ecosystem

Extracellular -glucosidase, -glucosidase, and aminopeptidase activity variations (measured by use of fluorogenic substrate analogs) at a coastal station in the Mediterranean Sea were investigated over a 1-year period. A 27-h cycle and daily measurements were made in a summer situation. We observed strong relative diurnal variations, compared to seasonal variations, in - and -glucosidase. Within 24 h, 0–100% of both - and -glucosidase were found in the dissolved phase. The aminopeptidase activities did not show a strong diurnal variation, but day to day variations were similar in magnitude to seasonal changes. Consistently, high proportions of all three enzymes were found in the dissolved phase on a seasonal scale. Seasonal measurements at 50- and 100-m depths showed a weak negative dependency on depth for extracellular enzyme activity. The potential importance of both hourly and daily changes in extracellular enzyme activity and of free enzymes is considered. Correspondence to: M. Karner     

Scales of observation of riparian forests and distributions of suspended detritus in a prairie river

1. Detrital inputs from riparian forests can provide the main source of energy to aquatic consumers in stream communities. However, the supply of coarse organic detritus to stream communities is difficult to predict. Patchy riparian inputs and connectivity between reaches have complicated studies and disrupted patterns of the distribution of suspended coarse particulate organic matter within streams and rivers.
2. In this study we emphasize the importance of spatial and temporal scales in determining potential distribution of instream leaf litter. Although large pulses of detritus are transported by streams during storm flows, the main supply of benthic leaf litter used by shredders and of suspended particulate organic matter used by filter feeders is transported during prolonged periods of baseflow. The local, fine-scale distribution of this organic matter is determined by the location and continuity of leaf litter sources (riparian vegetation) and specific features of channel roughness (such as woody debris, roots and rocks).
3. Viewing riparian vegetation at several scales results in variable conclusions regarding the amount of potential source area of leaf detritus. The percentage of suspended whole leaves at sites in the Little Washita River, Oklahoma, U.S.A. was best explained by the percentage of riparian forest cover in 500 m and 1000 m reaches upstream of the sites, as viewed by remote sensing imagery. The amount of leaf fragments was best explained by distance downstream along the longitudinal gradient. Ash-free dry mass of suspended coarse particulate matter did not correlate with any measures of riparian cover.
4. Our results suggest that leaves originate over longer reach lengths than those generally considered as source areas. Scale is an important consideration in studies of riparian patterns and related instream processes because of the need to integrate point dynamics as well as upstream influences.     

Scales of observation of riparian forests and distributions of suspended detritus in a prairie river

1. Detrital inputs from riparian forests can provide the main source of energy to aquatic consumers in stream communities. However, the supply of coarse organic detritus to stream communities is difficult to predict. Patchy riparian inputs and connectivity between reaches have complicated studies and disrupted patterns of the distribution of suspended coarse particulate organic matter within streams and rivers.
2. In this study we emphasize the importance of spatial and temporal scales in determining potential distribution of instream leaf litter. Although large pulses of detritus are transported by streams during storm flows, the main supply of benthic leaf litter used by shredders and of suspended particulate organic matter used by filter feeders is transported during prolonged periods of baseflow. The local, fine-scale distribution of this organic matter is determined by the location and continuity of leaf litter sources (riparian vegetation) and specific features of channel roughness (such as woody debris, roots and rocks).
3. Viewing riparian vegetation at several scales results in variable conclusions regarding the amount of potential source area of leaf detritus. The percentage of suspended whole leaves at sites in the Little Washita River, Oklahoma, U.S.A. was best explained by the percentage of riparian forest cover in 500 m and 1000 m reaches upstream of the sites, as viewed by remote sensing imagery. The amount of leaf fragments was best explained by distance downstream along the longitudinal gradient. Ash-free dry mass of suspended coarse particulate matter did not correlate with any measures of riparian cover.
4. Our results suggest that leaves originate over longer reach lengths than those generally considered as source areas. Scale is an important consideration in studies of riparian patterns and related instream processes because of the need to integrate point dynamics as well as upstream influences.     

Groundwater controls on nutrient cycling in a Mojave desert stream

1. Groundwater fluxes of nitrogen and dissolved organic carbon (DOC) were investigated in Grape Vine Canyon Stream in the Mojave Desert focusing on the rate of inputs and the fate of groundwater-derived nutrients in the stream. Discharge rates from different ground waters were measured using an end-member mixing model coupled with injections of a conservative solute tracer into the stream channel.
2. In surface water, nitrate concentration averaged 1.13 mg N L^–1 and DOC concentration averaged 1.82 mg C L^–1.
3. Groundwater discharge into Grape Vine Canyon Stream was derived from three sources. Nitrate concentration varied among the three groundwater sources with mean concentrations of 0.56, 0.94 and 0.08 mg N L^–1. DOC, in contrast, did not vary among ground water sources, with an overall average concentration of 2.96 mg C L^–1.
4. In the surface stream, nitrate concentration was two-fold greater than the concentration predicted from groundwater input, indicating that in-stream processes generated nitrate. Stream DOC concentration was lower than predicted based upon groundwater input rate. The production of nitrate and loss of DOC suggest that DOC is lost through mineralisation of dissolved organic matter, possibly resulting in the mineralisation of dissolved organic nitrogen to ammonium and subsequent transformation to nitrate via nitrification. In further support of this hypothesised linkage, DOC loss explained 80–89% of the variance in nitrate production in Grape Vine Canyon Stream.     

Novel mathematical modeling on pilot-scale of plug-flow aerated submerged biofilm reactor for dissolved organic matter and nitrogen removal

The investigation aimed to present mathematical models for describing the dynamic behavior of the dissolved organic matter removal and nitrification in the Aerated Submerged Bio-Film (ASBF) for a plug-flow reactor. Based on the experimental data from the batch system of the ASBF pilot plant, mathematical models for the plug-flow reactor were developed to predict dissolved organic matter and ammonia nitrogen removal rates as a function of heterotrophic and autotrophic bacteria populations, dissolved organic matter concentrations, ammonia nitrogen concentrations, dissolved oxygen concentrations, and temperature. The mathematical models for dissolved organic matter and ammonia nitrogen removal in ASBF include two differential equations reflecting heterotrophic and autotrophic bacteria populations, and a number of kinetic parameters. Consequently, the results present a better insight into the dynamics behavior of heterotrophic and autotrophic biofilm growth and their practical application to wastewater for dissolved organic matter and ammonia nitrogen removal process. The mathematical model for ammonia nitrogen and dissolved organic matter removals present good results for the plug-flow reactor.