Nutrient dynamics and successional changes in a lentic freshwater biofilm

SUMMARY 1. Colonisation, species composition, succession of microalgae and nutrient dynamics in biofilms grown under light and dark conditions were examined during the initial phases of biofilm development in a lentic freshwater environment.
2. Biofilms were developed on inert (perspex) panels under natural illuminated and experimental dark conditions and the panels were retrieved for analysis after different incubation periods. Analysed parameters included biofilm thickness, algal density, biomass, chlorophyll a , species composition, total bacterial density and nutrients such as nitrite, nitrate, phosphate and silicate.
3. Biofilm thickness, algal density, biomass, chlorophyll a and species richness were significantly higher in light-grown biofilms, compared with dark-grown biofilms. The light-grown biofilms showed a three-phased succession pattern, with an initial domination of Chlorophyceae followed by diatoms (Bacillariophyceae) and finally by cyanobacteria. Dark-grown biofilms were mostly dominated by diatoms.
4. Nutrients were invariably more concentrated in biofilms than in ambient water. Nutrient concentrations were generally higher in dark-grown biofilms except in the case of phosphate, which was more concentrated in light-grown biofilms. Significant correlations between nutrients and biofilm parameters were observed only in light-grown biofilms.
5. The N : P ratio in the biofilm matrix decreased sharply in the initial 4 days of biofilm growth; ensuing N-limitation status seemed to influence biofilm community structure. The N : P ratios showed significant positive correlations with the chlorophycean fraction in both light and dark-grown biofilms, and low N : P ratio in the older biofilms favoured cyanobacteria. Our data indicate that nutrient chemistry of biofilm matrix shapes community structure in microalgal biofilms.     

Labile and Recalcitrant Organic Matter Utilization by River Biofilm Under Increasing Water Temperature

Microbial biofilms in rivers contribute to the decomposition of the available organic matter which typically shows changes in composition and bioavailability due to their origin, seasonality, and watershed characteristics. In the context of global warming, enhanced biofilm organic matter decomposition would be expected but this effect could be specific when either a labile or a recalcitrant organic matter source would be available. A laboratory experiment was performed to mimic the effect of the predicted increase in river water temperature (+4?°C above an ambient temperature) on the microbial biofilm under differential organic matter sources. The biofilm microbial community responded to higher water temperature by increasing bacterial cell number, respiratory activity (electron transport system) and microbial extracellular enzymes (extracellular enzyme activity). At higher temperature, the phenol oxidase enzyme explained a large fraction of respiratory activity variation suggesting an enhanced microbial use of degradation products from humic substances. The decomposition of hemicellulose (β-xylosidase activity) seemed to be also favored by warmer conditions. However, at ambient temperature, the enzymes highly responsible for respiration activity variation were β-glucosidase and leu-aminopeptidase, suggesting an enhanced microbial use of polysaccharides and peptides degradation products. The addition of labile dissolved organic carbon (DOC; dipeptide plus cellobiose) caused a further augmentation of heterotrophic biomass and respiratory activity. The changes in the fluorescence index and the ratio Abs(250)/total DOC indicated that higher temperature accelerated the rates of DOC degradation. The experiment showed that the more bioavailable organic matter was rapidly cycled irrespective of higher temperature while degradation of recalcitrant substances was enhanced by warming. Thus, pulses of carbon at higher water temperature might have consequences for DOC processing.     

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.     

A new dynamic method for the rapid determination of the biodegradable dissolved organic carbon in drinking water

A new method for the determination of biodegradable dissolved organic carbon (BDOC), which may be useful to the water industry, is proposed. It is a dynamic method that measures the BDOC of circulating water continuously pumped across a biofilm attached to a special support that fills a system of two glass columns. The BDOC value corresponds to the difference in DOC between inlet and outlet water samples. The sampling may be intermittent or continuous, but the process is continuous. The biofilms give good performances over periods of at least 1 year. The analytical results are not significantly different from those of other bioassays based on the use of indigenous bacteria and the total duration of analysis is between 2 and 3 h.     

Assessment of biological activity and fate of organic compounds in a reactor for the measurement of biodegradable organic carbon in water

A new, rapid method for the determination of biodegradable dissolved organic carbon (BDOC), especially suited to water industry needs, was recently proposed by the authors. This dynamic method measured the BDOC of circulating water continuously pumped over a biofilm attached to a special support (sinterized porous glass) that fills a system of two glass columns. The BDOC value corresponds to the difference in dissolved organic carbon (DOC) between inflow and outflow water samples. The analytical results are not significantly different from those of other bioassays that use indigenous bacteria, and the total duration of the analysis is less than 3 h. However, a problem common to all the BDOC methods based on attached bacteria is the extent to which the decrease in DOC during the BDOC analysis is due to true biodegradation or to adsorption of organic matter to the reactor. In the present study, a reasonable support is provided for the hypothesis that this decrease, at least in the dynamic method, is predominantly due to microbiological activity. After comparing the support (sinterized porous glass) with a good physical adsorbent (granular activated carbon), the influence of temperature, residual chlorine and sodium azide on the reactor performance was tested, and a sensitivity only attributable to biological activity was observed. Another set of experiments were performed to assess the fate and specific elimination of different organic substances, explicable assuming that biodegradation processes were involved.     

Uptake of dissolved organic carbon by biofilms provides insights into the potential impact of loss of large woody debris on the functioning of lowland rivers

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A new dynamic method for the rapid determination of the biodegradable dissolved organic carbon in drinking water

F. RIBAS, J. FRIAS AND F. LUCENA. 1991. A new method for the determination of biodegradable dissolved organic carbon (BDOC), which may be useful to the water industry, is proposed. It is a dynamic method that measures the BDOC of circulating water continuously pumped across a biofilm attached to a special support that fills a system of two glass columns. The BDOC value corresponds to the difference in DOC between inlet and outlet water samples. The sampling may be intermittent or continuous, but the process is continuous. The biofilms give good performances over periods of at least 1 year. The analytical results are not significantly different from those of other bioassays based on the use of indigenous bacteria and the total duration of analysis is between 2 and 3 h.     

Seasonal Dynamics of Soil Labile Organic Carbon and Enzyme Activities in Relation to Vegetation Types in Hangzhou Bay Tidal Flat Wetland

Soil labile organic carbon and soil enzymes play important roles in the carbon cycle of coastal wetlands that have high organic carbon accumulation rates. Soils under three vegetations (Phragmites australis, Spartina alterniflora, and Scirpusm mariqueter) as well as bare mudflat in Hangzhou Bay wetland of China were collected seasonally. Seasonal dynamics and correlations of soil labile organic carbon fractions and soil enzyme activities were analyzed. The results showed that there were significant differences among vegetation types in the contents of soil organic carbon (SOC) and dissolved organic carbon (DOC), excepting for that of microbial biomass carbon (MBC). The P. australis soil was with the highest content of both SOC (7.86 g kg^-1) and DOC (306 mg kg^-1), while the S. mariqueter soil was with the lowest content of SOC (6.83 g kg^-1), and the bare mudflat was with the lowest content of DOC (270 mg kg^-1). Soil enzyme activities were significantly different among vegetation types except for urease. The P. australis had the highest annual average activity of alkaline phosphomonoesterase (21.4 mg kg^-1 h^-1), and the S. alterniflora had the highest annual average activities of β-glycosidase (4.10 mg kg^-1 h^-1) and invertase (9.81mg g^-1 24h^-1); however, the bare mudflat had the lowest activities of alkaline phosphomonoesterase (16.2 mg kg^-1 h^-1), β-glycosidase (2.87 mg kg^-1 h^-1), and invertase (8.02 mg g^-1 24h^-1). Analysis also showed that the soil labile organic carbon fractions and soil enzyme activities had distinct seasonal dynamics. In addition, the soil MBC content was significantly correlated with the activities of urease and β-glucosidase. The DOC content was significantly correlated with the activities of urease, alkaline phosphomonoesterase, and invertase. The results indicated that vegetation type is an important factor influencing the spatial-temporal variation of soil enzyme activities and labile organic carbon in coastal wetlands.     

The application of a plug-flow reactor to measure the biodegradable dissolved organic carbon (BDOC) in seawater

Most of the ambient dissolved organic carbon (DOC) is refractory to microbial degradation; bacteria can consume a minor but variable part of the DOC pool over periods of hours and days. It is important to increase our knowledge of the dynamics of the biodegradable fraction of DOC (BDOC) to understand the global carbon budget.Several methods for determining BDOC have been developed; however, the problem of most of them is the time (days/weeks) required for the colonization and/or determination.In this paper, we describe the application to seawater of a plug-flow bioreactor to measure BDOC within 3–4 h. The bioreactor was built following Søndergaard and Worm [Søndergaard, M., Worm, J., 2001. Measurement of biodegradable dissolved organic carbon (BDOC) in lake water with a bioreactor. Water Res. 35, 2505-2513.] protocols for the measurement of BDOC in lake water. We analyzed BDOC on samples collected in the Gulf of Trieste during autumn–winter and summer 2003–2004. BDOC concentrations varied from 8 to 24 μM and represented from 10.3% to 25.5% of the total DOC. To evaluate the effectiveness of this method, we compared bioreactor BDOC measurement with data obtained from batch cultures. The results indicate that BDOC in coastal seawater can be measured rapidly and reliably with this bioreactor.     

Seasonal relationships between planktonic microorganisms and dissolved organic material in an alpine stream

The relationships between the abundance and activity of planktonic, heterotrophic microorganisms and the quantity and characteristics of dissolved organic carbon (DOC) in a Rocky Mountain stream were evaluated. Peak values of glucose uptake, 2.1 nmol L⁻¹ hr⁻¹, and glucose concentration, 333 nM, occurred during spring snowmelt when the water temperature was 4.0°C and the DOC concentration was greatest. The turnover time of thein situ glucose pool ranged seasonally from 40–1110 hours, with a mean of 272 hr. Seasonal uptake of³H-glucose, particulate ATP concentrations, and direct counts of microbial biomass were independent of temperature, but were positively correlated with DOC concentrations and negatively correlated with stream discharge. Heterotrophic activity in melted snow was generally low, but patchy. In the summer, planktonic heterotrophic activity and microbial biomass exhibited small-scale diel cycles which did not appear to be related to fluctuations in discharge or DOC, but could be related to the activity of benthic invertebrates. Leaf-packs placed under the snow progressively lost weight and leachable organic material during the winter, indicating that the annual litterfall in the watershed may be one source of the spring flush of DOC. These results indicate that the availability of labile DOC to the stream ecosystem is the primary control on seasonal variation in heterotrophic activity of planktonic microbial populations.     

Seasonal trends in river biofilm storage products and electron transport system activity

SUMMARY. 1. Glycogen, poly-beta-hydroxyalkanoate (PHA) and electron transport system (ETS) activity levels were monitored seasonally in light- and dark-grown biofilms from a North Wales river.
2. A spring peak was evident in glycogen, PHA and ETS activity levels per cm² and per cell, with the exception of PHA per cell, which peaked in the winter.
3. There was a seasonal shift in the type of storage product found, perhaps reflecting seasonal changes in carbon sources.
4. The light-grown spring biofilm yielded the greatest amount of bio-film storage products per cm². This should be taken into account during caloric studies of river biofilms as a food source for grazing invertebrates.
5. A model is presented of factors influencing storage product deposition in river biofilms. The thickness and cell packing of river biofilms should be noted in future studies. Storage product deposition can occur deep within thick biofilms, irrespective of the river water chemistry.     

Impact of storm-flow on electron transport system activity in river biofilms

1. The effect of storm-flow on light- and dark-grown biofilms from a North Wales river was monitored using electron transport system (ETS) activity and epifluorescence cell counts. 2. Artificial substrata were colonized in the river, exposed to ambient-flow (60 cms^?1) or storm-flow (235 cms^?1 with suspended sediment addition) for 12h in a laboratory flow tank, and returned to the river to monitor the recovery period. 3. Total cell densities decreased in both the light- and dark-grown biofilms as a result of storm-flow. In addition, storm-flow ETS activity per cell increased significantly in the light-grown samples (2.7 times) but did not increase significantly in the dark-grown samples (1.6 times). 5. Within 48 h, storm-flow total cell densities and ETS activity levels had returned to ambient-flow levels in both light- and dark-grown biofilms. 6. Within each light regime, despite their different histories, both ambient and storm-flow samples responded the same to daily changes in the river environment, including a second disruption by natural causes, for the remainder of the 24-day experiment.     

DOC Release from Alder Leaves and Catkins during Decomposition in a Small Lowland Stream

Alder leaves and catkins were placed in a small stream, then retrieved in weekly intervals, and rates of release of dissolved organic carbon (DOC) and substantial DOC characteristics were determined. Decomposition rates of leaves and catkins were 0.026 d^–1 and 0.011 d^–1 on the streambed, and 0.017 d^–1 and 0.009 d^–1 in the sediments, respectively, during 5 weeks of decomposition. The rate of DOC release from leaves declined from 18.0% d^–1 to 0.7% d^–1, and had a higher proportion of low molecular weight compounds, more saturated and contained larger humic molecules than DOC from catkins, which rate of release declined from 10.6% d^–1 to 0.1% d^–1. In initial stages of the decomposition, leaf material produced more biodegradable DOC (BDOC) than catkins. During the period of low leaf litter input, DOC released from catkins can become an important instream source of labile DOC. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Availability of glucose and light modulates the structure and function of a microbial biofilm

We have studied the differences in the organic matter processing and biofilm composition and structure between autoheterotrophic and heterotrophic biofilm communities. Microbial communities grown on artificial biofilms were monitored, following incubation under light and dark conditions and with or without the addition of glucose as a labile organic compound. Glucose addition greatly affected the microbial biofilm composition as shown by differences in 16S rRNA gene fingerprints. A significant increase in β-glucosidase and peptidase enzyme activities were also observed in glucose-amended biofilms incubated in the dark, suggesting an active bacterial community. Light enhanced the algal and bacterial growth, as well as higher extracellular enzyme activity, thereby indicating a tight algal–bacterial coupling in biofilms incubated under illumination. In these biofilms, organic compounds excreted by photosynthetic microorganisms were readily available for bacterial heterotrophs. This algal–bacterial relationship weakened in glucose-amended biofilms grown in the light, probably because heterotrophic bacteria preferentially use external labile compounds. These results suggest that the availability of labile organic matter in the flowing water and the presence of light may alter the biofilm composition and function, therefore affecting the processing capacity of organic matter in the stream ecosystem.     

Hydrologic Drivers and Seasonality of Dissolved Organic Carbon Concentration, Nitrogen Content, Bioavailability, and Export in a Forested New England Stream

We present the results of a full year of high-resolution monitoring of hydrologic event-driven export of stream dissolved organic matter (DOM) from the forested Bigelow Brook watershed in Harvard Forest, Massachusetts, USA. A combination of in situ fluorescent dissolved organic matter (FDOM) measurement, grab samples, and bioassays was utilized. FDOM was identified as a strong indicator of concentration for dissolved organic carbon (DOC, r ² = 0.96), dissolved organic nitrogen (DON, r ² = 0.81), and bioavailable DOC (BDOC, r ² = 0.81). Relationships between FDOM and concentration were utilized to improve characterization of patterns of hydrological event-driven export and the quantification of annual export. This characterization was possible because DOM composition remained relatively consistent seasonally; however, a subtle shift to increased fluorescence per unit absorbance was observed for summer and fall seasons and percent BDOC did increase slightly with increasing concentrations. The majority of export occurred during pulsed hydrological events, so the greatest impact of bioavailable exports may be on downstream aquatic ecosystems. Export from individual events was highly seasonal in nature with the highest flow weighted mean concentrations (DOC_FW) being observed in late summer and fall months, but the highest total export being observed for larger winter storms. Seasonal trends in DOC export coincide with weather driven changes in surface and subsurface flow paths, potential for depletion and rebuilding of a flushable soil organic matter pool, and the availability of terrestrial carbon sources such as leaf litter. Our approach and findings demonstrate the utility of high frequency FDOM measurement to improve estimates of intra-annual temporal trends of DOM export.     

Biofilm development and invertebrate colonization of wood in four New Zealand streams of contrasting pH

1. Biofilm development and activity on wood substrata (Nothofagus menziesii) were examined at four forested sites in a South Island, New Zealand, river catchment over a period of 6 months. Two of the sites had brown waters and mean pH of 3.7 and 4.5, whereas the other two had clear waters and mean pH of 6.3 and 6.8. 2. Fungi and other filamentous heterotrophs were the dominant colonizers of wood at all sites; few algal cells were present. Incorporation of ¹⁴C-glucose by biofilms was greatest in all four streams after 3 months, whereas endocellulase activity fluctuated over time and temporal patterns differed among streams. 3. No clear relationship was found between the incorporation of ¹⁴C-glucose or endocellulase activity of biofilms and pH, although at one near-neutral pH site ¹⁴C-glucose uptake increased in response to nutrient (N + P) additions. 4. After 6 months, incorporation of ¹⁴C-glucose and endocellulase activity of biofilms on Pinus radiata dowels buried vertically in the stream beds did not differ at depths of 3–9 cm and 19–25 cm in each stream. 5. Radiotracer experiments with a grazing amphipod (Paraleptamphopus sp.) demonstrated that biofilms on wood from all four sites could be ingested and at least partially assimilated. Chironomid larvae and harpacricoid copepods were the most abundant invertebrates colonizing wood substrata at all sites. Different chironomid species dominated at acidic and near-neutral pH sites. 6. Overall, our findings provide little support for the hypothesis that microbial activity on organic substrata is necessarily lower in streams of low pH.     

Mineralisation of dissolved organic matter by heterotrophic stream biofilm communities in a large boreal catchment

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Relationships between DOC bioavailability and nitrate removal in an upland stream: An experimental approach

The Catskill Mountains of southeastern New York State have among thehighest rates of atmospheric nitrogen deposition in the United States. Somestreams draining Catskill catchments have shown dramatic increases in nitrateconcentrations while others have maintained low nitrate concentrations. Streamsin which exchange occurs between surface and subsurface (i.e. hyporheic) watersare thought to be conducive to nitrate removal via microbial assimilationand/ordenitrification. Hyporheic exchange was documented in the Neversink River inthesouthern Catskill Mountains, but dissolved organic carbon (DOC) and nitrate(NO₃ ^–) losses along hyporheic flowpaths werenegligible. In this study, Neversink River water was amended with natural,bioavailable dissolved organic carbon (BDOC) (leaf leachate) in a series ofexperimental mesocosms that simulated hyporheic flowpaths. DOC and N dynamicswere examined before and throughout a three week BDOC amendment. In addition,bacterial production, dissolved oxygen demand, denitrification, and sixextracellular enzyme activities were measured to arrive at a mechanisticunderstanding of potential DOC and NO₃ ^– removalalong hyporheic flowpaths. There were marked declines in DOC and completeremoval of nitrate in the BDOC amended mesocosms. Independent approaches wereused to partition NO₃ ^– loss into two fractions:denitrification and assimilation. Microbial assimilation appears to be thepredominant process explaining N loss. These results suggest that variabilityinBDOC may contribute to temporal differences in NO₃ ^–export from streams in the Catskill Mountains.     

Downstream alteration of the composition and biodegradability of particulate organic carbon in a mountainous,mixed land-use watershed

Despite increasing recognition of storm-induced organic carbon (C) export as a significant loss from the terrestrial C balance, little is known about the biodegradation and chemical transformation of particulate organic carbon (POC) in mountainous river systems. We combined analyses of C isotopes, solution-state ¹H NMR, and lipid biomarkers with biodegradable dissolved organic C (BDOC) measurements to investigate downstream changes of POC composition and biodegradability at a mountainous, mixed land-use watershed in South Korea. Water and suspended sediment (SS) samples were collected in a forested headwater stream, a downstream agricultural stream, and two downstream rivers during peak flow periods of four storm events, using either sequential grab sampling from the headwater stream to the most downstream river within a few hours around the peak flow or sediment samplers deployed during the whole storm event. DOC concentrations exhibited relatively small changes across sites, whereas POC concentrations were highest in the agricultural stream, and tapered along downstream reaches. The δ¹³C and δ¹⁵N of SS in the agricultural stream were distinct from up- and downstream signatures and similar to those for erosion source soils and lake bottom sediment, although increases in radiocarbon age indicated continuous compositional changes toward the lake. ¹H NMR spectra of SS and deposited sediment exhibited downstream decreases in carbohydrates and lignin but enrichment of organic structures related to microbial proteins and plant wax. The downstream sediments had more microbial n-alkanes and lipid markers indicating anthropogenic origin such as coprostanol compared to the forest soil n-alkanes dominated by plant wax. While the BDOC concentrations of filtered waters differed little between sites, the BDOC concentrations and protein- to humic-like fluorescence ratios of DOC leached from SS during a 13-day incubation were higher in downstream rivers, pointing to contribution of labile POC components to the enhanced biodegradation. Overall, inputs of microbial and anthropogenic origin, in interplay with deposition and mineralization, appear to substantially alter POC composition and biodegradability during downstream transport, raising a question on the conventional view of mountainous river systems as a passive conduit of storm pulses of POC.     

Microbial respiration within a floodplain aquifer of a large gravel-bed river

1. Aerobic respiration, productivity and the carbon turnover rate of microbial biofilms were determined at hyporheic and phreatic sites in the Kalispell Valley alluvial aquifer along a transect extending 3.9 km laterally from the main channel of the Flathead River, a sixth order river in Montana (U.S.A.). The effect of experimentally increasing bioavailable organic carbon (acetate) on the respiration rate of biofilms in this carbon‐poor [dissolved organic carbon (DOC) < 2 mg L^?1] aquifer was also measured. 2. Chambers containing natural substratum were placed in‐situ and allowed to colonise for 20 weeks. After 4, 12 and 20 weeks, they were taken to the laboratory where oxygen flux was measured in a computer‐controlled, flow‐through respirometry system. 3. Respiration ranged from 0.01 to 0.33 mg O₂ dm^?3 h^?1 across sites, with means ranging from 0.10 to 0.17 mg O₂ dm^?3 h^?1. Productivity estimates ranged from 0.18 to 0.32 mg C dm^?3 day^?1 (mean 0.25, SE 0.03). The total organic carbon (TOC) of the microbial biofilms ranged from 18.2 to 29.7 mg C dm^?3. Turnover rate ranged from 3.2 to 5.6 year^?1 with a mean of 4.2 year^?1. 4. At the hyporheic site very close to the river, respiration did not significantly increase when samples were supplemented with labile carbon. Respiration increased with increasing DOC addition at hyporheic sites more distant from the river, suggesting a carbon‐limitation gradient within the hyporheic zone. Microbes at the phreatic site did not respond to increasing DOC addition, suggesting that the phreatic biofilm is adapted to low carbon availability. 5. Comparing the volume of the alluvial aquifer (about 0.7 km³) to that of the river benthic sediments (to 0.25 m depth, which amounts to about 1.6 × 10^?4 km³) within the Flathead Valley, leads to the conclusion that interstitial microbial productivity is orders of magnitude greater than benthic productivity. Alluvial aquifers are often voluminous and microbial production is an enormous component of ecosystem production in rivers such as the Flathead.