RESPONSE OF WOODY SWAMP SEEDLINGS TO FLOODING AND INCREASED WATER TEMPERATURES. I. GROWTH,BIOMASS, AND SURVIVORSHIP

Growth, biomass, and survival of bald cypress (Taxodium distichum [L.] Richard), water tupelo (Nyssa aquatica L.), black willow (Salix nigra Marshall), and button bush (Cephalanthus occidentalis L.) were examined in a 3 times 3 factorial experiment varying water temperatures (AMBIENT, MID, and HIGH [~40 C]) and water levels (DRAINED, SATURATED, and FLOODED). Stem diameter and height, biomass, and survivorship for water tupelo and bald cypress were all reduced by the HIGH/FLOODED treatment. Black willow growth had the greatest variability among nonlethal flooding and temperature treatments, and achieved the greatest biomass of the four species. In the HIGH/FLOODED treatment, however, only 47% of the black willow seedlings survived and stem diameter, height, and biomass of survivors were greatly reduced. Button bush had intermediate variability of growth to the nonlethal treatments as compared to the other study species. Survival of button bush seedlings in the HIGH/FLOODED treatment was high (87%), but root biomass of the survivors was reduced. Interspecific differences in growth, biomass, survivorship, and morphological characteristics existed among these swamp species to experimental conditions. These responses may help explain vegetation patterns in a thermally impacted swamp.     

Seasonal variation in nutrient limitation of microbial biofilms colonizing organic and inorganic substrata in streams

Humans have increased the availability of nutrients including nitrogen and phosphorus worldwide; therefore, understanding how microbes process nutrients is critical for environmental conservation. We examined nutrient limitation of biofilms colonizing inorganic (fritted glass) and organic (cellulose sponge) substrata in spring, summer, and autumn in three streams in Michigan, USA. Biofilms were enriched with nitrate (NO₃ ⁻), phosphate (PO₄ ³⁻), ammonium (NH₄ ⁺), NO₃ ⁻ + PO₄ ³⁻, NH₄ ⁺ + PO₄ ³⁻, or none (control). We quantified biofilm structure and function as chlorophyll a (i.e., primary producer biomass) and community respiration on all substrata. In one stream, we characterized bacterial and fungal communities on cellulose in autumn using clone library sequencing and denaturing gradient gel electrophoresis to determine if community structure was linked to nutrient limitation status. Despite oligotrophic conditions, primary producer biomass was infrequently nutrient limited. In contrast, respiration on organic substrata was frequently limited by N + P combinations. We found no difference between biofilm response to NH₄ ⁺ versus NO₃ ⁻ enrichment, although the response to both N-species was positively related to water column PO₄ ³⁻ concentrations and temperature. Molecular analysis for fungal community composition suggested no relationship to nutrient limitation, but the dominant members of the bacterial community on cellulose were different on NO₃ ⁻, PO₄³, and NO₃ ⁻ + PO₄ ³⁻ treatments relative to control, NH₄ ⁺, and NH₄ ⁺ + PO₄ ³⁻ treatments, which matched patterns for biofilm respiration rates from each treatment. Our results show discrete patterns of nutrient limitation dependent upon substratum type and season, and imply changes in bacterial community structure and function may be linked following nutrient enrichment in streams.     

不同氮处理下速生柳对水体氮的吸收、分配及生理响应

采用水培法,研究了旱柳苗在外源添加不同氮水平(贫氮、中氮、富氮、过氮)的铵态氮(NH+4-N)和硝态氮(NO-3-N)的生长、氮吸收、分配和生理响应。结果表明:一定范围氮浓度的增加能够促进旱柳苗的生长,但过量氮会抑制其生长,且NH+4-N的抑制作用大于NO-3-N;两种氮处理下,旱柳表现出对NH+4-N的吸收偏好,在同一氮水平时,旱柳各部位氮原子百分含量Atom%15N(AT%)、15N吸收量和来自氮源的N%(Ndff%)均为NH+4-N处理大于NO-3-N处理,且随着氮浓度的增加,差异增大,且在旱柳各部位的分布为根﹥茎﹥叶;2种氮素过量和不足均会对旱柳根和叶生理指标产生不同的影响,其中在过氮水平时,NH+4-N和NO-3-N处理下根系活力比对照减少了50.61%和增加了19.53%;在过氮水平时,NH+4-N处理柳树苗根总长、根表面积、根平均直径、根体积和侧根数分别对照下降了30.92%、29.48%、19.44%、27.01%和36.41%,NO-3-N处理柳树苗相应的根系形态指标分别对对照下降了1.66%、5.65%、1.49%、5.06%和25.72%。可见,高浓度NH+4-N对旱柳苗的胁迫影响大于NO-3-N,在应用于水体氮污染修复时可通过改变水体无机氮的比例,削弱其对旱柳的影响,从而提高旱柳对水体氮污染的修复效果。     

Optimization of the sucrose and ion concentrations for saikosaponin production in hairy root culture ofBupleurum falcatum

Saikosaponin productivity was examined in aBupleurum falcatum L. BFHR2 hairy root culture in response to changes in the sucrose content (2≈8%), nitrogen content (0≈250 mM NH₄NO₃), phosphate content (0≈12 mM NaH₂PO₄), and the potassium content (0≈87.2 mM KCl) of the culture media. We found that the conditions for maximal saikosaponin production differed from those for optimal root growth. Highest saikosaponin yield was achieved for 8% sucrose, 62 mM NH₄NO₃, 1.2 mM NaH₂PO₄, and 0.5 mM KCl.     

Spatial variability in nutrient concentration and biofilm nutrient limitation in an urban watershed

Nutrient enrichment threatens river ecosystem health in urban watersheds, but the influence of urbanization on spatial variation in nutrient concentrations and nutrient limitation of biofilm activity are infrequently measured simultaneously. In summer 2009, we used synoptic sampling to measure spatial patterns of nitrate (NO₃ ⁻), ammonium (NH₄ ⁺), and soluble reactive phosphorus (SRP) concentration, flux, and instantaneous yield throughout the Bronx River watershed within New York City and adjacent suburbs. We also quantified biofilm response to addition of NO₃ ⁻, phosphate (PO₄ ³⁻), and NO₃ ⁻ + PO₄ ³⁻ on organic and inorganic surfaces in the river mainstem and tributaries. Longitudinal variation in NO₃ ⁻ was low and related to impervious surface cover across sub-watersheds, but spatial variation in NH₄ ⁺ and SRP was higher and unrelated to sub-watershed land-use. Biofilm respiration on organic surfaces was frequently limited by PO₄ ³⁻ or NO₃ ⁻ + PO₄ ³⁻, while primary production on organic and inorganic surfaces was nutrient-limited at just one site. Infrequent NO₃ ⁻ limitation and low spatial variability of NO₃ ⁻ throughout the watershed suggested saturation of biological N demand. For P, both higher biological demand and point-sources contributed to greater spatial variability. Finally, a comparison of our data to synoptic studies of forested, temperate watersheds showed lower spatial variation of N and P in urban watersheds. Reduced spatial variation in nutrients as a result of biological saturation may represent an overlooked effect of urbanization on watershed ecology, and may influence urban stream biota and downstream environments.     

Denitrification and nitrous oxide emissions from riparian forests soils exposed to prolonged nitrogen runoff

Compared to upland forests, riparian forest soils have greater potential to remove nitrate (NO₃) from agricultural runoff through denitrification. It is unclear, however, whether prolonged exposure of riparian soils to nitrogen (N) loading will affect the rate of denitrification and its end products. This research assesses the rate of denitrification and nitrous oxide (N₂O) emissions from riparian forest soils exposed to prolonged nutrient runoff from plant nurseries and compares these to similar forest soils not exposed to nutrient runoff. Nursery runoff also contains high levels of phosphate (PO₄). Since there are conflicting reports on the impact of PO₄ on the activity of denitrifying microbes, the impact of PO₄ on such activity was also investigated. Bulk and intact soil cores were collected from N-exposed and non-exposed forests to determine denitrification and N₂O emission rates, whereas denitrification potential was determined using soil slurries. Compared to the non-amended treatment, denitrification rate increased 2.7- and 3.4-fold when soil cores collected from both N-exposed and non-exposed sites were amended with 30 and 60 μg NO₃-N g⁻¹ soil, respectively. Net N₂O emissions were 1.5 and 1.7 times higher from the N-exposed sites compared to the non-exposed sites at 30 and 60 μg NO₃-N g⁻¹ soil amendment rates, respectively. Similarly, denitrification potential increased 17 times in response to addition of 15 μg NO₃-N g⁻¹ in soil slurries. The addition of PO₄ (5 μg PO₄-P g⁻¹) to soil slurries and intact cores did not affect denitrification rates. These observations suggest that prolonged N loading did not affect the denitrification potential of the riparian forest soils; however, it did result in higher N₂O emissions compared to emission rates from non-exposed forest soils.     

Effects of macro elements and nitrogen source on biomass accumulation and bacoside A production from adventitious shoot cultures of <Emphasis Type="Italic">Bacopa monnieri</Emphasis> (L.)

The present work deals with optimization of adventitious shoot culture of Bacopa monnieri for the production of biomass and bacoside A and has investigated the effects of macro elements (NH₄NO_3, KNO_3, CaCl_2, MgSO₄ and KH₂PO₄) and nitrogen source [NH₄ ⁺/NO₃ ⁻] of Murashige and Skoog (Physiol Plant 15:473–497, 1962) medium (MS) on accumulation of biomass and bacoside A content. Optimum number of adventitious shoots (99.33 shoots explant⁻¹), fresh weight (1.841 g) and dry weight (0.150 g) were obtained in the medium with 2.0× strength of NH₄NO₃. The highest production of bacoside A content was also recorded in the medium of 2.0× NH₄NO₃, which produced 17.935 mg g⁻¹ DW. The number of adventitious shoot biomass and bacoside A content were optimum when the NO₃ ⁻ concentration was higher than that of NH₄ ⁺. Maximum number of shoots (70.00 shoots explant⁻¹), biomass (fresh weight 1.137 g and dry weight 0.080 g) and also bacoside A content (27.106 mg g⁻¹ DW) were obtained at NH₄ ⁺/NO₃ ⁻ ratio of 14.38/37.60 mM. Overall, MS medium supplemented with 2.0× NH₄NO₃ is recommended for most efficient bacoside A production.     

Impact of Willow Short Rotation Coppice on Water Quality

Short rotation coppice (SRC) with willow has been grown in Sweden from the late 1980s to produce biomass for energy on agricultural land. This study evaluated the effects of SRC on water quality by determining differences in leaching of nitrogen and phosphorus to groundwater of a number of commercial “old” SRC willow stands in Sweden compared to adjacent arable fields grown with “ordinary” crops. The study was conducted in 16 locations under three vegetation seasons. NO₃–N leaching from willow SRC fields was significantly lower than that from reference fields with cereals. The opposite was observed for PO₄–P; concentrations in the groundwater of SRC were higher compared to reference fields. Sewage sludge applications were not responsible for the elevated PO₄–P leaching under SRC compared to reference crops.     

Nitrogen and phosphorus dynamics in a large river estimated by an in situ Lagrangian tracking approach

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Biofiltering efficiency, uptake and assimilation rates of Ulva clathrata (Roth) J. Agardh (Clorophyceae) cultivated in shrimp aquaculture waste water

The growth, biofiltering efficiency and uptake rates of Ulva clathrata were studied in a series of outdoor tanks, receiving waste water directly from a shrimp (Litopenaeus vannamei) aquaculture pond, under constant aeration and two different water regimes: (1) continuous flow, with 1 volume exchange a day (VE day^-1) and (2) static regime, with 1 VE after 4 days. Water temperature, salinity, pH, dissolved inorganic nitrogen (DIN), phosphate (PO₄), chlorophyll-a (chl-a), total suspended solids (TSS), macroalgal biomass (fresh weight) and tissue nutrient assimilation were monitored over 12 days. Ulva clathrata was highly efficient in removing the main inorganic nutrients from effluent water, stripping 70–82% of the total ammonium nitrogen (TAN) and 50% PO₄ within 15 h. Reductions in control tanks were much lower (Tukey HSD, P < 0.05). After 3 days, the mean uptake rates by the seaweed biomass under continuous flow were 3.09 mg DIN g DW day⁻¹ (383 mg DIN m⁻² day⁻¹) and 0.13 mg PO₄ g DW day⁻¹ (99 mg PO₄ m⁻² day⁻¹), being significantly higher than in the static regime (Tukey HSD, P < 0.05). The chl-a decreased in seaweed tanks, suggesting that U. clathrata inhibited phytoplankton growth. Correlations between the cumulative values of DIN removed from the water and total nitrogen assimilated into the seaweed biomass (r = 0.7 and 0.8, P < 0.05), suggest that nutrient removal by U. clathrata dominated over other processes such as phytoplankton and bacterial assimilation, ammonia volatilization and nutrient precipitation.     

Comparison of Cadmium Effect on Willow and Poplar in Response to Different Cultivation Conditions

Salix alba L. and Populus×euroamericana cv. Robusta cuttings were grown in 10 μM Cd(NO₃)₂ (direct treatment) or in Knop solution and afterwards in Cd(NO₃)₂ (indirect treatment). Cd impact on rooting of directly treated plants and its impact on normally formed roots and shoots of indirectly treated plants were studied. The cumulative length, number and biomass of willow roots, pigment and starch contents, leaf net photosynthetic rate and dry mass/leaf area ratio of willow leaves were positively influenced by indirect treatment. However, indirectly treated poplars were more sensitive to Cd than directly treated ones. Indirect treatment lowered root Cd uptake in willow, Cd accumulation in cuttings of both species and Cd accumulation in poplar shoots. Cd-caused structural changes were similar in both species and in both treatments. Root apices, rhizodermis and cortex were the most seriously damaged root parts. In directly treated willow, the structure of central cylinder (0.5 – 1 cm from apex) remained unchanged in contrast to indirectly treated plants. Formation of cambium close to the apex indicated shortening of root elongation zone of indirectly treated plants. Directly Cd-treated poplar roots exhibited unusual defence activity of root apical meristem and accumulation of darkly stained material around central cylinder. This revised version was published online in July 2006 with corrections to the Cover Date.     

Intercropping <Emphasis Type="Italic">Caragana arborescens</Emphasis> with <Emphasis Type="Italic">Salix miyabeana</Emphasis> to Satisfy Nitrogen Demand and Maximize Growth

Willow shows great promise as a biomass crop and is now used worldwide. However, willow is a nutrient and water demanding plant that often requires the use of nitrogen (N) fertilizer to maximize growth on poor soils. The intercropping of Salix miyabeana with the atmospheric N₂-fixing Caragana arborescens on poor soils of the Canadian Prairies could provide a portion of the N demand of the willow. The main objectives were to: (1) determine the yield potential, N nutrition and water use efficiency (WUE) of willow and Caragana grown in pure and mixed plantations across a range of soil productivity and (2) assess the extent of atmospheric N₂-fixation by the Caragana within the first rotation in central Saskatchewan. We found large differences in willow yields, foliar N and WUE across the sites. The willow yields (1.24 to 15.6 t dry matter ha⁻¹ over 4 years) were low compared to northeastern North American values and reflect the short and dry summers of the region. The yields were positively correlated to foliar N (ranging between 14.3 and 32.4 mg g⁻¹), whereas higher WUE (expressed as δ¹³C) were not positively correlated to water availability but to higher yields. Caragana N₂-fixation (measured using ¹⁵N isotope dilution) was not active at the most productive site but up to 60% of the foliar N was of atmospheric origin at the two other sites. Willow growth increased with Caragana proportions at the least productive site, which is typical of the benefits of N₂-fixing plants on the growth of other plants on poor soils. At the most productive site, Caragana decreased the growth of willow early on due to competition for resources, but willow eventually shaded Caragana to a point of significant canopy decline and dieback. It is therefore more appropriate to intercrop the two species on less productive soils as Caragana is more likely to add N to the system via N₂-fixation and is less likely to be shaded out by willow.     

Effect of operational and design parameters on removal efficiency of pilot-scale FWS constructed wetlands and comparison with HSF systems

In order to investigate the effect of temperature, hydraulic residence time (HRT), vegetation type, substrate material and wetland shape on the performance of free-water surface (FWS) constructed wetlands treating wastewater, 5 pilot-scale units were constructed and operated continuously from December 2004 until March 2007 in parallel experiments. Four of the units (A, B, C, D) were rectangular in plan view with dimensions 3.40 m in length and 0.85 m in width, and contained substrate material at a thickness of 0.45 m. The fifth unit (E) had a trapezoidal plan view shape, with a width at the inlet of 1.15 m and at the outlet of 0.55 m, while the length and the thickness of the substrate were the same as in the other four. All units operated at a water depth of 0.10 m. Units B–E contained clay substrate and unit A contained sand. The four units with clay were planted as follows: two with cattails (B and E), one with common reeds (C), and one with giant reeds (D). Unit A, containing sand, was planted with cattails. Planting and substrate material combinations were appropriate for comparison of the effect of vegetation and material type on the function of the system. Synthetic wastewater was introduced in the units. During the operation period four HRTs (i.e., 6 days, 8 days, 14 days and 20 days) were used, while wastewater temperatures varied from about 0.0 °C to 29.1 °C. The removal performance of the five constructed wetland units was good, since it reached on the average 77.5%, 67.9%, 60.4%, 53.9%, 56.0% and 51.7% for BOD, COD, TKN, ammonia (NH₄-N), ortho-phosphate (PO₄-P) and total phosphorus (TP), respectively. BOD and phosphorus removal efficiencies showed dependence on temperature in most units. The 14-day HRT was found adequate for acceptable removal of organic matter, nitrogen and phosphorus for most temperatures. A 20-day HRT is recommended for acceptable removal of BOD and PO₄-P in the cold season. The unit with the trapezoidal plan view shape showed the best performance, with mean removals of 80.1%, 73.5%, 70.4%, 68.6%, 64.7% and 63.5% for BOD, COD, TKN, NH₄-N, PO₄-P and TP, respectively. The cattail was found statistically more efficient than the other two plants in COD and PO₄-P removal. The unit that contained the clay substrate was found statistically more efficient in phosphorus removal than the unit containing sand. HSF CW units were found more efficient than FWS units in removal of most pollutant.     

Variation in the uptake of Arsenic, Cadmium, Lead, and Zinc by different species of willows Salix spp. grown in contaminated soils

The experiment assessed the variability of in seven clones of willow plants of high biomass production (Salix smithiana S-218, Salix smithiana S-150, Salix viminalis S-519, Salix alba S-464, Salix ’Pyramidalis’ S-141, Salix dasyclados S-406, Salix rubens S-391). They were planted in a pots for three vegetation periods in three soils differing in the total content of risk elements. Comparing the calculated relative decrease of total metal contents in soils, the phytoextraction potential of willows was obtained for cadmium (Cd) and zinc (Zn), moderately contaminated Cambisol and uncontaminated Chernozem, where aboveground biomass removed about 30% Cd and 5% Zn of the total element content, respectively. The clones showed variability in removing Cd and Zn, depending on soil type and contamination level: S. smithiana (S-150) and S. rubens (S-391) demonstrated the highest phytoextraction effect for Cd and Zn. For lead (Pb) and arsenic (As), the ability to accumulate the aboveground biomass of willows was found to be negligible in both soils. The results confirmed that willow plants show promising results for several elements, mainly for mobile ones like cadmium and zinc in moderate levels of contamination. The differences in accumulation among the clones seemed to be affected more by the properties of clones, not by the soil element concentrations or soil properties. However, confirmation and verification of the results in field conditions as well as more detailed investigation of the mechanisms of cadmium uptake in rhizosphere of willow plants will be determined by further research.     

Ecological indicators of nutrient enrichment, freshwater wetlands, Midwestern United States (U.S.)

Vegetation and soil indicators of nutrient condition were evaluated in 30 wetlands, 10 each in 3 Nutrient Ecoregions (NE) (VI-Corn Belt and Northern Great Plains, VII-Mostly Glaciated Dairy Region, IX-Temperate Forested Plains and Hills) of the Midwestern United States (U.S.) to identify robust indicators for assessment of wetland nutrient enrichment and eutrophication. Nutrient condition was characterized by surface water inorganic N (NH₄-N, NO₃-N) and P (PO₄-P) concentrations measured seasonally for 1 year, plant available and total soil N and P, and aboveground biomass, leaf N and P and species composition of emergent vegetation measured at the end of the growing season. Aboveground biomass, nutrient uptake and species composition were positively related to surface water NH₄-N (N) but not to PO₄-P or NO₃-N. Aboveground biomass and biomass of aggressive species, Typha spp. plus Phalaris arundinacea, increased asymptotically with surface water N whereas leaf P, senesced leaf N and senesced leaf P increased linearly with N. And, species richness declined with surface water N. Soil total P was positively related to surface water PO₄-P but it was the only soil indicator related to wetland nutrient condition. Individual regressions for each NE generally were superior to a single regression for all NEs. In NE VI (Corn Belt), few indicators were related to surface water N because of the high degree of anthropogenic disturbance (85% of the landscape is cleared) as compared to NEs VII and IX (24–53% cleared). Of the indicators evaluated, stem height (r² = 0.42 for all NEs, r² = 0.56 for NE VII + IX) and percent biomass of aggressive species, Typha spp. plus Phalaris, (r² = 0.46 for all NEs, r² = 0.54 for NE VII + IX), were the best predictors of wetland nutrient enrichment. Vegetation-based indicators are a promising tool for assessment of wetland nutrient condition but they may not be effective in NEs where landscape disturbance is intense and widespread.     

In situ nutrient monitoring: A tool for capturing nutrient variability and the antecedent conditions that support algal blooms

While increased nutrient concentrations and eutrophication are recognized to be among the causative factors contributing to algal blooms, including harmful algal blooms (HABs), relationships between nutrient fluxes and specific blooms are often not well defined or understood. In an attempt to better decipher these relationships, we employed in situ nutrient monitors to collect time-series data to document variability ranging from hourly to monthly, including rain events and the resulting response of phytoplankton biomass. Multiple deployments are reported here, all conducted in tributaries of Chesapeake Bay. The suite of nutrients that were monitored varied with deployment; examples given here include nitrate + nitrite (NO₃⁻ + NO₂⁻), ammonium (NH₄⁺), phosphate (PO₄³⁻), and urea. Common features in the data included highly varying concentrations on time-scales of a few hours related to tidal oscillations, and longer-term responses on the scale of days related to rainfall events. Increases following rainfall events for all nutrients generally tended to be many fold, up to an order of magnitude, higher than pre-rainfall concentrations. However, the time scale of response to rainfall for individual nutrients varied. Ephemeral increases in PO₄³⁻ and urea typically were contemporaneous with rain events, and were also followed by longer-term sustained increases relative to pre-rainfall levels. Increases in NO₃⁻ + NO₂⁻ and NH₄⁺ lagged rainfall events by a period of several days and generally lasted for several days. These dynamics generally would be missed by traditional manual sampling. Algal responses tended to follow the increases in nitrogen, underscoring nitrogen limitation in these systems even when ambient concentrations were not depleted.     

Evaluation of leaf analysis as a guide to nitrogen and phosphorus fertilization of potato (Solanum tuberosum L.)

Summary Recently matured leaf samples were collected, at 45, 60 and 75 days after planting, from potato (Solanum tuberosum L.) plants of cultivar Kufri sindhuri grown with varying levels of nitrogen (0, 60, 120, 180 and 240 kg N/ha) and phosphorus (0, 60, 120 and 180 kg P₂O₅/ha) on loam soil at Pantnagar. They were separated into petiole, midrib and leaf-lets and analysed for NO₃-N content. Petiole samples were also analysed for PO₄-P content. Nitrogen application increased the NO₃-N content of all the leaf components. P application increased the PO₄-P content in petiole. NO₃-N content and PO₄-P content in leaf tissues were positively correlated with final tuber yield. The association of NO₃-N content of petiole with the final tuber yield was very consistant. Hence this proved to be the best indicator tissue for reflecting the nitrogen status of the plant, particularly at 45 days after planting. NO₃-N content of midrib, at this stage, was also a good indication of nitrogen nutrition status of the plant. PO₄-P content of petiole at 45 days after planting was a good indication of nutritional status of plant with respect to phosphorus. The critical concentration of NO₃-N in petioles of 45 days old plants was in the range of 9100–9600 ppm. The corresponding range for midrib was 3000 to 3900 ppm. The critical concentration of PO₄-P for petioles of 45 days old plants was 2250 ppm.Publication No 796 under journal series of the G.B. Pant University of Agriculture and Technology, Experiment Station, Pantnagar.Junior Agronomist, Indian Institute of Horticultural Research, Bangalore-6, India.Junior Agronomist, Indian Institute of Horticultural Research, Bangalore-6, India.     

Nitrate and phosphate ion removal from water by Phormidium laminosum immobilized on hollow fibres in a photobioreactor

Removal of nitrate and phosphate ions from water, by using the thermophilic cyanobacterium Phormidium laminosum, immobilized on cellulose hollow fibres in the tubular photobioreactor at 43 °C, was studied by continuously supplying dilute growth medium for 7 days and then secondarily treated sewage (STS) for 12 days. The concentrations of NO⁻ ₃ and PO³⁻ ₄ in the effluent from the dilute growth medium decreased from 5.0 mg N/l to 3.1 mg N/l, and from 0.75 mg P/l to 0.05 mg P/l respectively, after a residence time of 12 h. The concentrations of NO⁻ ₃ and PO³⁻ ₄ in the effluent from STS decreased from 11.7 mg N/l to 2.0 mg N/l, and from 6.62 mg P/l to 0.02 mg P/l respectively, after a residence time of 48 h. The removal rates of nitrogenous␣and phosphate ions from STS were 0.24 and 0.11 mmol day⁻¹ l reactor⁻¹ respectively, under the same conditions. Although, among nitrogenous ions, nitrate and ammonium ions were efficiently removed by P.␣laminosum, the nitrite ion was released into the effluent when STS was used as influent. Treatment of water with thermophilic P. laminosum immobilized on hollow fibres thus appears to be an appropriate means for the removal of inorganic nitrogen and phosphorus from treated wastewater. Received: 15 August 1997 / Received last revision: 18 November 1997 / Accepted: 29 November 1997     

Soil CO2 effluxes,temporal and spatial variations,and root respiration in shrub willow biomass crops fields along a 19‐year chronosequence as affected by regrowth and removal treatments

In shrub willow biomass crop (SWBC) production systems, the soil CO₂ efflux (F_c) component in the carbon cycle remains poorly understood. This study assesses (i) differences of F_c rates among the 5‐, 12‐, 14‐, and 19‐year‐old SWBCs with two treatments: continuous production (regrowth) willow fields that were harvested and allowed to regrow, and willow fields that were harvested, killed, and then stools and roots were ground into the soil (removal); (ii) temporal and spatial variations of F_c rates; (iii) root respiration contributions to total F_c; and (iv) climatic variables affecting F_c. During the growing season (May to September), F_c rates showed no statistically significant differences across different ages (P = 0.664), and between treatments (P = 0.351); however, there was an interaction between age and treatment (P = 0.001). Similarly, during the dormant season (October to April), F_c rates revealed no statistically significant differences across different ages (P = 0.305) and treatment interaction with age (P = 0.097). F_c rates differed significantly (P < 0.001) among different times of the day and times of the year. F_c rates, between 00 and 1059 h, between 1100 and 1659 h, and between 1700 and 2400 h displayed consistency from May to November; however, F_c rates in these three time intervals showed significant differences (P < 0.0001). In December, F_c rates remained constant over 24 h. F_c rates demonstrated higher temporal and spatial variations among willow age classes than between regrowth and removal treatments. Temporal and spatial variations of F_c were higher during the dormant season than during the growing season. The proportion of root respiration to total F_c ranged from 18 to 33% across age classes. F_c rates showed strong association with soil and air temperatures, and relative humidity.