Interaction effects of flow velocity and oxygen metabolism on nitrification and denitrification in biofilms on submersed macrophytes

Effects of water flow velocityon nitrification, denitrification, andthe metabolism of dissolved oxygen andinorganic carbon in macrophyte-epiphytoncomplexes were investigated in the presentstudy. The metabolic rates were measured inmicrocosms containing shoots of Potamogeton pectinatus L. with epiphyticbiofilms in the light and dark with no flow orwith the flow velocities of 0.03 and 9 cms^–1. Photosynthesis and respirationincreased with increasing water flow velocity.Rates of oxygen respiration were positivelycorrelated to the oxygen concentration of thewater. Nitrification was not significantlyaffected by flow velocity, but nitrificationwas higher in light than in dark at 0.03 cms^–1, but not at 9 cm s^–1.Denitrification was higher in stagnant waterand at 9 cm s^–1 than at 0.03 cm s^–1 inthe absence of oxygen, possibly due to complexeffects of water flow velocity on the supply oforganic matter to the denitrifying bacteria.Denitrification was always inhibited in light,and negatively correlated to the oxygenconcentration in dark. Epiphyticdenitrification occurred only at low oxygenconcentrations in flowing water, whereas instagnant water, denitrification was present inalmost oxygen saturated water. Therefore,because there are little of water movements andhigh oxygen consumption in dense stands ofsubmersed macrophytes, significant rates ofepiphytic denitrification can probably be foundwithin submersed vegetation despite high oxygenconcentrations in the surrounding water. Inconclusion, this study shows that the waterflow and oxygen metabolism within submersedvegetation have minor effects on nitrification,but significantly affect denitrification inbiofilms on submersed macrophytes.     

Preconditioning of leaves by solar radiation and anoxia affects microbial colonisation and rate of leaf mass loss in an intermittent stream

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Plant community structure determines primary productivity in shallow,eutrophic lakes

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Influence of hydraulics on the uptake of ammonium by two freshwater plants

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Responses of periphyton to changes in current velocity, suspended sediment and phosphorus concentration

SUMMARY.

• 1 Research was performed in laboratory streams to evaluate periphytic biomass accrual, export, and community composition over a range of limiting nutrient (phosphorus) concentrations with variable velocity, and suspended sediment addition, in comparison to constant velocity and no suspended sediment. In fixed-velocity treatments, velocity increase to 60 cm s^?1 significantly enhanced biomass accrual, but further increase resulted in substantial biomass reduction. Average biomass loss rates did not change significantly over a velocity range of 10–80 cm s^?1. Diatoms were favoured at relatively high velocities and low phosphorus concentrations, whereas the blue-green Phormidium tended to dominate at higher SRP concentrations and the green Mougeotia seemed to prefer lower velocities.
• 2 Sudden increases in velocity raised instantaneous loss rates by an order of magnitude or more, but these high rates persisted only briefly. As a result, marked biomass reductions were not apparent a day after the velocity change. Dominance change from filamentous green or blue-green to diatoms immediately after the increase was reversed within 2 days. Loss rate increases due to solids addition were much smaller than those accompanying velocity increase, but simultaneous velocity elevation and solids addition produced instantaneous loss rates approximately double those with velocity increase alone.
• 3 The experiments demonstrated that an elevation in velocity, above that to which algae were accustomed, led to increased loss rates and temporarily reduced biomass. However, recolonization and growth after biomass reduction were apparently rapid. Substantial export of periphyton following solids addition required erosion of the protective boundary layer accompanied by a velocity increase. These results arc applicable to understanding the response of lotic periphytic algae to elevated, turbid storm discharges and similar runoff or high-flow events.
• 4 Areal uptake rates of P by algae growing in the laboratory streams increased with soluble reactive phosphorus (SRP) concentration, up to approximately 15 μg I^?1 in overlying water. They also increased above 35 cm s ^?1. Overall, uptake rate seemed to vary inversely with biomass. The ralio of areal uptake rate/biomass was significantly less where mean biomass was 411±6 mg chl a m^?2 compared to 223±17 mg chl a m^?2.
• 5 The results suggested that although nutrient uptake is primarily a surface phenomenon, diffusion to interior cells can also determine the responses of attached communities. Both diffusion and uptake rate were stimulated by increasing nutrient concentration and velocity up to certain levels, but became limited by biofilm thickness and scouring.

     

Leaf‐cutting ants as ecosystem engineers: topsoil and litter perturbations around Atta cephalotes nests reduce nutrient availability

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Macroinvertebrate size-distributions of two contrasting freshwater macrophyte communities

SUMMARY.

• 1 Macroinvertebrates (>0.1 mg, fresh weight) were collected every 2 weeks for 18 weeks from weedbeds dominated by either the macroalga Chara or rooted plants (mostly Isoetes sp., Potamogeton filiformis, Nuphar variegatum and Myriophyllum exalbescens) in Narrow Lake, Alberta, Canada. Significant differences in total biomass, taxonomic composition, and size-structure of the macroinvertebrate community were found between the two weedbed types.
• 2 Total biomass of macroinvertebrates in the Chara beds (seasonal mean 26.4 g m^?2) was consistently higher than in the rooted-plant weedbeds (seasonal mean 7.6 g m^?2).
• 3 The macroinvertebrate community of the Chara beds was dominated by chironomids, anisopterans, gastropods and sphaerid clams whereas amphipods dominated the community in the rooted-plant weedbeds.
• 4 On average, the proportion of total biomass in the various size-classes (biomass size-spectrum) of the macroinvertebrate community in Chara beds varied very little between 1 and 512 mg. In rooted plant weedbeds, the spectrum showed a strong peak in the 4–8 mg size-class, a weak peak in the 32–64 mg size-class, and proportionately low biomass in the 128–256 mg and 256–512 mg size-classes. The slope of the normalized size-spectrum for the macroinvertebrate community of the Chara beds (-0.89) was significantly different from that of the rooted plant community (-1.11). The biomass of large organisms (>64 mg) was 10 times greater in the Chara beds than in the rooted-plant weedbeds.
• 5 The species composition of aquatic macrophyte beds can greatly influence the abundance, taxonomic composition, and size-structure of the littoral zone macroinvertebrate community. Therefore, any changes in plant species composition of weedbeds, through introduction of exotic plant species or introduction (or loss) of an efficient grazer (e.g. crayfish), have the potential to alter greatly the structure of the macroinvertebrate community in a lake, with unknown consequences to fish and waterfowl dependent upon these prey.

     

The partitioning of nitrate assimilation between root and shoot of higher plants

Abstract The partitioning of nitrate assimilation between root and shoot of higher plant species is indicated by the relative proportions of total plant nitrate reductase activity (NRA) in the two plant parts and the relative concentrations of nitrate and reduced N in the xylem sap. These have been collated here from the literature and temperate and tropical species compared. Both the distribution of NRA and xylem sap nitrate: reduced N indicate that the following four generalizations can be made.

• 1 Temperate, perennial species growing in low external nitrate concentrations (about 1 mol m^?3) carry out most of their nitrate assimilation in the root. As external nitrate concentration increases (in the range found in agricultural soils, 1–20 mol m^?3), shoot nitrate assimilation becomes increasingly important.
• 2 Temperate, annual legume species growing in low external nitrate concentrations carry out most of their nitrate assimilation in the root. Shoot nitrate assimilation increases in importance as external nitrate concentration is increased.
• 3 Temperate, annual non-legume species vary greatly in their partitioning of nitrate assimilation between root and shoot when growing in low external nitrate concentrations. Regardless of the proportion carried out in the root at low external nitrate concentrations, nitrate assimilation in the shoot becomes increasingly important as external nitrate concentration is increased.
• 4 Tropical and subtropical species, annual and perennial, carry out a substantial proportion of their nitrate assimilation in the shoot when growing in low external nitrate concentrations. The partitioning of nitrate assimilation between root and shoot remains constant as external nitrate concentration increases.

It is proposed that a greater proportion of nitrate assimilation occurs in the shoot when an increase in the rate of nitrate uptake does not induce an increase in NR level in the root. Thus, a greater proportion of the nitrate taken up remains unassimilated and is passed into the xylem. A constant partitioning of nitrate assimilation between root and shoot is achieved by balancing NR levels in the root with rates of nitrate uptake. The advantages and disadvantages of assimilating nitrate in either the root or shoot are discussed in relation to temperate and tropical habitats.     

Biodegradation of Methyl Orange by alginate-immobilized Aeromonas sp. in a packed bed reactor: external mass transfer modeling

Azo dyes are recalcitrant and xenobiotic nature makes these compounds a challenging task for continuous biodegradation up to satisfactorily levels in large-scale. In the present report, the biodegradation efficiency of alginate immobilized indigenous Aeromonas sp. MNK1 on Methyl Orange (MO) in a packed bed reactor was explored. The experimental results were used to determine the external mass transfer model. Complete MO degradation and COD removal were observed at 0.20 cm bead size and 120 ml/h flow rate at 300 mg/l of initial dye concentration. The degradation of MO decreased with increasing bead sizes and flow rates, which may be attributed to the decrease in surface of the beads and higher flux of MO, respectively. The experimental rate constants (k _ps) for various beads sizes and flow rates were calculated and compared with theoretically obtained rate constants using external film diffusion models. From the experimental data, the external mass transfer effect was correlated with a model J _D = K Re ^?(1 ? n). The model was tested with K value (5.7) and the Colburn factor correlation model for 0.20, 0.40 and 0.60 bead sizes were J _D = 5.7 Re ^?0.15, J _D = 5.7 Re ^?0.36 and J _D = 5.7 Re ^?0.48, respectively. Based on the results, the Colburn factor correlation models were found to predict the experimental data accurately. The proposed model was constructive to design and direct industrial applications in packed bed reactors within acceptable limits.     

Fungal contributions to carbon flow and nutrient cycling during decomposition of standing Typha domingensis leaves in a subtropical freshwater marsh

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Structural and functional aspects of the Nuphar lutea (L.) Smith heterophylly: Ultrastructure and photosynthesis

The ultrastructure and functional characteristics of the photosynthetic apparatus of floating and submersed leaves of the heterophyllous plant Nuphar lutea (L.) Smith have been examined. Differences have been revealed in mesophyll cell chloroplasts, content of pigments, and chlorophyll fluorescence parameters between floating and submersed leaves and submersed leaves at different depths. A sharp decline in the PSII (photosystem II) efficiency of submersed leaves when exposed to an actinic light intensity of more than 60 ??mol m^?2 s^?1 has been noted. The described differences may be considered as an adaptation mechanism of submersed leaves to life in an aquatic environment with a reduced light intensity and changed light spectral composition.     

Leaf cell membrane stability‐based mechanisms of zinc nutrition in mitigating salinity stress in rice

• Excess salt affects about 955 million ha of arable land worldwide, and 49% of agricultural land is Zn‐deficient. Soil salinity and zinc deficiency can intensify plant abiotic stress. The mechanisms by which Zn can mitigate salinity effects on plant functions are not well understood.
• We conducted an experiment to determine how Zn and salinity effects on rice plant retention of Zn, K⁺ and the salt ion Na⁺ affect chlorophyll formation, leaf cell membrane stability and grain yield. We examined the mechanisms of Zn nutrition in mitigating salinity stress by examining plant physiology and nutrition. We used native Zn‐deficient soils (control), four salinity (EC ) and Zn treatments – Zn 10 mg·kg^?1 (Zn₁₀), EC 5 dS ·m^?1 (EC ₅), Zn₁₀+EC ₅ and Zn₁₅+EC ₅, a coarse rice (KS ‐282) and a fine rice (Basmati‐515) in the study.
• Our results showed that Zn alone (Zn₁₀) significantly increased rice tolerance to salinity stress by promoting Zn/K⁺ retention, inhibiting plant Na⁺ uptake and enhancing leaf cell membrane stability and chlorophyll formation in both rice cultivars in native alkaline, Zn‐deficient soils (P  <  0.05). Further, under the salinity treatment (EC ₅), Zn inputs (10–15 mg·kg^?1) could also significantly promote rice plant Zn/K⁺ retention and reduce plant Na⁺ uptake, and thus increased leaf cell membrane stability and grain yield. Coarse rice was more salinity‐tolerant than fine rice, having significantly higher Zn/K⁺ nutrient retention.
• The mechanistic basis of Zn nutrition in mitigating salinity impacts was through promoting plant Zn/K⁺ uptake and inhibiting plant Na⁺ uptake, which could result in increased plant physiological vigour, leaf cell membrane stability and rice productivity.

     

Evaluation of passive solar heating and alternative flow regimes on nitrate removal in denitrification beds

Denitrification beds are a simple and relatively inexpensive technology for removing nitrate from point source discharges. To date, operational beds have used wood media as the carbon source, as it provides a sustained nitrate removal rate (2-10 g N m⁻³ of media d⁻¹) while maintaining permeability. In pilot-scale (2.9 m⁻³) denitrification beds receiving municipal wastewater effluent dosed with KNO₃, we looked at improving nitrate removal by using alternative carbon media (maize cobs) and increasing bed temperature through passive solar heating. The influence of flow regime (horizontal-point, horizontal-diffuse, downflow and upflow) on short-circuit flow was also investigated.The long-term nitrate removal rate (21.8 g N m⁻³ d⁻¹) of the maize cob beds over the 15-month period of the trial was 2-11-fold higher than sustained removal rates reported by other researchers for wood-based beds. While passive solar heating raised the mean bed temperature by 3.4 °C, it did not cause a measurable increase in the nitrate removal rate due to the variability in the removal rate exceeding the expected increase due to temperature.Horizontal flow had more short-circuiting than vertical flow. Short-circuiting in the horizontal flow was attributed to flow being concentrated near the top surface due to the buoyancy effect of warmer water. Greater short-circuiting in the solar heated horizontal and upflow beds than in the corresponding unheated beds was attributed to the buoyancy effect being more pronounced in the solar heated beds.Overall, downflow was deemed the most effective of the four tested flow regimes. It provided the highest increase in bed temperature due to solar heating, had the highest nitrate removal rate in the latter part of the trial and had more plug-flow characteristics. While passive solar heating raised bed temperature, we were unable to demonstrate a significant difference (at 95% CL) in nitrate removal rate between the unheated and solar heated beds because of the high variability in nitrate removal rate and the increase in short-circuiting in the solar heated horizontal and upflow beds.     

Regime shift in the littoral ecosystem of volcanic Lake Atitlán in Central America: combined role of stochastic event and invasive plant species

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Photosynthetic characteristics of Myriophyllum spicatum and six submersed aquatic macrophyte species native to Lake George, New York

SUMMARY.

• 1 The macrophyte community of Lake George, New York is diverse, composing of forty-eight submersed species representing a wide range of habitats, depth ranges and life-history strategies. The photosynthetic rates of seven representative submersed aquatic macrophytes were determined in laboratory studies using measurements of short-term changes in oxygen concentration at eight light intensities from 0 to 1000 μmol m^?2 s^?1 at 20°C. The species examined were: Elodea canadensis, Myriophyllum spicatum, Potamogeton amplifolius, P. gramineus, P. praelongus, P. robbinsii, and Vallisneria americana.
• 2 Comparisons of maximum net photosynthesis, Michaelis–Menten V_max and K_m for photosynthesis versus irradiance, and dark respiration rates correlated with changes in community composition and species distribution with depth.
• 3 In particular, Myriophyllum spicatum exhibited a high photosynthetic rate (V_max) and high light requirement (both in compensation point and higher half-saturation constant (K_m) indicative of a high light-adapted species. In contrast, the native species exhibited shade-tolerant characteristics.
• 4 Simple daily carbon balance models indicate that M. spicatum has a higher positive carbon balance near the surface than the native species, but carbon balance decreased more rapidly with decreased light. All species showed greatly reduced carbon balances under a simulated M. spicatum canopy, indicating that native species might not survive. Myriopyllum spicatum leaves would experience self-shading and eventual sloughing.

     

When is stream invertebrate drift catastrophic? The role of hydraulics and sediment transport in initiating drift during flood events

1. The term ‘catastrophic drift’ is used to describe the large‐scale displacement of invertebrates that occurs during periods of increased river discharge. However, the physical processes that lead to animals entering the water column at such times remain poorly understood. Specifically, the hypothesis that the movement of bed sediments during floods triggers a large increase in drift has lacked a rigorous field test. 2. Using a portable flume, the hydraulic conditions and rates of bedload transport associated with small, frequent floods were created in situ within a reach of a gravel bed river. Experiments focussed on the patches of fine sediment which are the dominant source of bed material transported during small floods. The flume produced near bed velocities of up to 2 m s^?1 over the patches, increasing shear stress, initiating sediment transport and causing invertebrates to enter the drift. 3. The total number of individuals lost from the bed, as well as the taxonomic composition of the drift, were influenced strongly by shear stress and bedload. The rate of loss from the bed was low at shear stresses <9 dynes cm^?2 (0–4 individuals min^?1 from the 0.5 m² flume bed area). Once shear stress exceeded 9 dynes cm^?2, the threshold that resulted in consistent bedload transport from the patches, the rate of loss of animals increased to a maximum of 56 individuals min^?1. When bedload transport rates were at their highest, the taxonomic composition of the drift was more similar to the benthos than it was to the drift observed when bed material was stable. 4. Absolute rates of bedload transport created by the manipulations were extremely low (<7 g m^?1 s^?1) and typical of those measured during small, frequent floods. Events of this magnitude do not break up the armour layer across the reach as a whole and so exposed patches of fine sediment are the principal source of bedload material. Consequently, discharge events not considered as disturbances in geomorphic terms may initiate frequent episodes of so‐called ‘catastrophic drift’ from patches of stream bed.     

Nitrate removal from three different effluents using large-scale denitrification beds

Simple technologies that remove nitrate from effluents and other point discharges need to be developed to reduce pollution of receiving waters. Denitrification beds are lined containers filled with organic carbon (typically wood chip or coarse sawdust) and are a technology that is proving promising. Water containing NO₃^? (treated effluent or agricultural drainage) is passed through the bed and the wood chips act as an energy source for denitrifying bacteria that convert NO₃^? to N gases. There are few data on the efficiency of NO₃ removal in large-scale beds. We report here NO₃^? removal results from three large denitrification beds with volumes of 83, 294, and 1320 m³ treating dairy shed effluent, treated domestic effluent and glasshouse effluent, respectively. Nitrate was nearly completely removed from the dairy shed effluent (annual load of 31 kg N) and domestic effluent (annual load 365 kg N). In these beds, NO₃^? removal, presumably by denitrification, was limited by NO₃^? concentration. However, the bed treating glasshouse effluent was overwhelmed by very high NO₃^? concentration (about 250 g N m^?3) and high flow rates (about 150 m³ d^?1) but still reduced NO₃^? concentration to about 150 g N m^?3. For this bed, long-term NO₃^? removal was between 5 and 10 g N m^?3 of bed material when NO₃^? was non-limiting and was similar to rates reported for other smaller denitrification beds. As expected, organic N, ammonium and phosphorus were not removed from any of the effluents following passage through the beds. Our results suggest that denitrification beds are a relatively inexpensive system to construct and operate, and are suitable for final treatment of a range of NO₃^?-laden effluents.     

Effects of retention site on breakdown of organic matter in a mountain stream

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Stoichiometry and estimates of nutrient standing stocks of larval salamanders in Appalachian headwater streams

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Studies on Chironomidae in experimental recirculating stream systems. II. The growth, development and production of a spring generation of Orthocladius (Euorthodadius) calvus Pinder

SUMMARY.

• 1 Orthodadius (Euorthodadius) calvus Pinder. similar to Orthocladius (Euorthodadius) thienemanni Kieffer. colonized a new gravel substratum in two recirculating stream channels. A maximum population density of 68.621 m^-2 was attained after only 16 days. This had fallen to a negligible density by the thirty-third day.
• 2 Some recruitment occurred over most of the study period (April-May 1981) and no single sharply defined cohort was evident. There was a large range of body lengths within each instar. and considerable overlap between instars. The population density estimates for instars I and II were low compared with instars III and IV.
• 3 The relationship between instantaneous growth rate (g) and geometric mean length indicated that growth was best described by a Gompertz curve. Growth rate decreased with increasing length from a value of about 40% length day^-1 at 2 mm body length to about 5% length day^-1 at 9 mm.
• 4 Growth rates for individual larvae, kept in culture, were very variable with maximum rates close to the values determined from the field data. Mean duration of larval life was 16 days.
• 5 Estimates of production for the study period ranged from 13.5 g dry wt m^-2 (Channel III, size-frequency method) to 34.2 g dry wt m^-2 (Channel II, Allen's graphical method, values corrected for non-linear growth).
• 6 Gut contents were estimated to represent about 55% of the total weight therefore production values should be reduced by this amount.