Addition Of Organic Carbon Research Articles

Influence of perennial forages on subsoil organic carbon in a long-term rotation study in Uruguay

Abstract Interest is increasing in Uruguay in management practices that can store carbon in soils, such as the use of perennial forage crops. Previous studies on agricultural soils have focused on organic carbon in surface soil layers. However, due to the ability of perennial forages to develop extensive root systems, the potential exists for these crops to add carbon in the subsoil. A 38-year rotation experiment on a silty clay loam soil in southwestern Uruguay was used to examine the effect of a crop rotation including periods of pasture on total organic carbon (TOC) and particulate (>53 μm) organic carbon (POC) at soil depths of 20–40 and 40–60 cm. Analysis showed the pasture rotation had higher POC concentrations at both depths than an annual crop rotation. This may indicate increased addition of organic carbon in the pasture rotation and signal a future change in TOC and mineral-associated organic carbon levels. Total organic carbon was higher in the rotation including pasture at a P level of 0.14. These results present preliminary observations on the management effects of including perennial forages in rotations on subsoil carbon levels, using a long-term experiment resource to assess very slow changes.

The anammoxosome: an intracytoplasmic compartment in anammox bacteria

Anammox bacteria belong to the phylum Planctomycetes and perform anaerobic ammonium oxidation (anammox); they oxidize ammonium with nitrite as the electron acceptor to yield dinitrogen gas. The anammox reaction takes place inside the anammoxosome: an intracytoplasmic compartment bounded by a single ladderane lipid-containing membrane. The anammox bacteria, first found in a wastewater treatment plant in The Netherlands, have the potential to remove ammonium from wastewater without the addition of organic carbon. Very recently anammox bacteria were also discovered in the Black Sea where they are responsible for 30–50% of the nitrogen consumption. This review will introduce different forms of intracytoplasmic membrane systems found in prokaryotes and discuss the compartmentalization in anammox bacteria and its possible functional relation to catabolism and energy transduction.

Chemical and isotopic evidence for accelerated bacterial sulphate reduction in acid mining lakes after addition of organic carbon: laboratory batch experiments

Acid mine drainage is a widespread environmental problem in Lusatia in the eastern part of Germany, where extensive brown coal and lignite mining was carried out during the last century. As a result of oxidation of pyrite in strip mine dumps of this region, numerous mine drainage lakes have pH values <3 and are characterized by high concentrations of dissolved sulphate and ferrous iron. Using chemical and isotopic techniques, we tested in laboratory bottle experiments the extent to which the addition of degradable organic carbon to acid lake water and sediments could stimulate bacterial (dissimilatory) sulphate reduction. The overall goal was to evaluate whether bacterial sulphate reduction, and subsequent formation of sedimentary sulphide minerals, could generate enough alkalinity to potentially neutralize the acid lakes in Lusatia.Pyruvate, glucose, succinic acid, lactate, ethanol, acetate, and various industrial by-products were added in various concentrations to original lake water and sediments in glass bottles and incubated between 4 and 12 weeks in darkness. The extent of bacterial sulphate reduction was determined by analyzing the concentrations and the isotopic compositions of sulphate in the water column, and the contents and δ34S values of various sedimentary sulphur compounds at the beginning and the end of the experiments. Bacterial sulphate reduction was significantly enhanced after addition of pure substances (lactate, pyruvate, acetate, and ethanol) resulting in elevated pH values (4.5 to 6.0) in the bottle water at the end of the experiments. Cheap industrial by-products (whey, molasses, Pfezi-granules, and Carbokalk) as organic carbon source were also shown to be effective in enhancing bacterial sulphate reduction, thereby increasing the pH value of the bottle water. In general, the addition of selected organic carbon compounds enhanced sufficiently bacterial sulphate reduction and the formation of sedimentary sulphur minerals, generating enough alkalinity for raising the pH of the bottle water to near-neutral values. Further research in enclosures and under field conditions is needed to determine whether this technique constitutes a feasible remediation strategy for the acid lakes in Lusatia.

Microbial cycling of iron and sulfur in sediments of acidic and pH-neutral mining lakes in Lusatia (Brandenburg, Germany)

A vast number of lakes developed in the abandoned opencast lignite mines of Lusatia (East Germany) contain acidic waters (<pH 3) with high concentrations of dissolved iron and sulfate. The elimination of iron and sulfate by microbially mediated reduction processes produces alkalinity, whereas the reoxidation of reduced sulfur compounds consumes alkalinity. In order to determine the influence of environmental factors with the prospect of biological remediation strategies, these processes were investigated in sediments of two acidic and one pH-neutral mining lake. Slightly acidic sediment underlying permanently anoxic waters showed a higher accumulation rate of reduced inorganic sulfur than the pH-neutral sediment (60 v.s. 45 mmol S m−2 a−). Potential Fe(III) reduction measured by the accumulation of Fe(II) during anoxic incubation yielded similar rates in both types of sediments, however, the responses towards the supplementation of Fe(III) and organic carbon were different. Sulfate reduction rates estimated with 35S-radiotracer were much lower in the slightly acidic sediment than in the pH-neutral sediment (156 v.s. 738 mmol SO4 2− m−2 a−1). However, sulfate reduction rates were increased by the addition of organic carbon. Severe limitation of sulfate-reducing bacteria under acidic conditions was also reflected by low most probable numbers (MPN). High MPN of acidophilic iron- and sulfur-oxidizing bacteria in acidic sediments indicated a high reoxidation potential. The results show that potentials for reductive processes are present in acidic sediments and that these are determined mainly by the availability of oxidants and organic matter.

Nitrification and Anammox with Urea as the Energy Source

Urea is present in many ecosystems and can be used as an energy source by chemolithotrophic aerobic ammonia oxidizing bacteria (AOB). Thus the utilization of urea in comparison to ammonia, by AOB as well as anaerobic ammonia oxidizing (Anammox) bacteria was investigated, using enrichments cultures, inoculated with activated sludge, and molecular ecological methods. In batch enrichment cultures grown with ammonia a population established in 2 weeks, which was dominated by halophilic and halotolerant AOB as determined by fluorescence in situ hybridization (FISH) experiments, with the 16S rRNA targeting oligonucleotide probe NEU. In other batch enrichment cultures using urea, the AOB population was assessed by PCR amplification, cloning and phylogenetic analysis of amoA and ribosomal 16S rRNA genes. While only one of the 48 16S rRNA gene clones could be identified as AOB (Nitrosomonas oligotropha), the amoA approach revealed two more AOB, Nitrosomonas europaea and Nitrosomonas nitrosa to be present in the enrichment. FISH analysis of the enrichment with probe NEU and newly designed probes for a specific detection of N. oligotropha and N. nitrosa related organisms, respectively, showed that N. oligotropha-like AOB formed about 50% of the total bacterial population. Also N. nitrosa (about 15% of the total population) and N. europaea (about 5% of the total population) were relatively abundant. Additionally, continuous enrichments were performed under oxygen limitation. When ammonia was the energy source, the community in this reactor consisted of Anammox bacteria and AOB hybridizing with probe NEU. As the substrate was changed to urea, AOB related to N. oligotropha became the dominant AOB in this oxygen limited consortium. This resulted in a direct conversion of urea to dinitrogen gas, without the addition of organic carbon.

Carbon availability controls the growth of detritivores (Lumbricidae) and their effect on nitrogen mineralization.

Activity of soil decomposer microorganisms is generally limited by carbon availability, but factors controlling saprophagous soil animals remain largely unknown. In contrast to microorganisms, animals are unable to exploit mineral nutrient pools. Therefore, it has been suggested that soil animals, and earthworms in particular, are limited by the availability of nitrogen. In contrast to this view, a strong increase in density and biomass of endogeic earthworms in response to labile organic carbon addition has been documented in field experiments. The hypothesis that the growth of endogeic earthworms is primarily limited by carbon availability was tested in a laboratory experiment lasting for 10 weeks. In addition, it was investigated whether the effects of earthworms on microbial activity and nutrient mineralization depend on the availability of carbon resources. We manipulated food availability to the endogeic earthworm species Octolasion tyrtaeum by using two soils with different organic matter content, providing access to different amounts of soil, and adding labile organic carbon (glucose) enriched in (13)C. Glucose addition strongly increased the growth of O. tyrtaeum. From 8 to 17% of the total C in earthworm tissue was assimilated from the glucose added. Soil microbial biomass was not strongly affected by the addition of glucose, though basal respiration was significantly increased and up to 50% of the carbon added as glucose was incorporated into soil organic matter. The impact of earthworms on the mineralization and leaching of nitrogen depended on C availability. As expected, in C-limited soil, the presence of earthworms strongly increased nitrogen leaching. However, when C availability was increased by the addition of glucose, this pattern was reversed, i.e. the presence of O. tyrtaeum decreased nitrogen leaching and its availability to soil microflora. We conclude that irrespective of the total carbon content of soils, O. tyrtaeum was primarily limited by carbon, and that increased carbon availability allowed earthworms to be more effective in mobilizing N. The presence of earthworms increases C limitation of soil microorganisms, due to increased availability of N and P in earthworm casts or a direct depletion of easily available carbon resources by earthworms.

Microbial and nutrient investigations into the use of in situ layers for treatment of tailings effluent.

The release of acidic drainage, containing high concentrations of dissolved metals, is associated with mining districts throughout the world. Remediation of acidic drainage at active and abandoned mines remains a significant challenge. A potential alternative technique to prevent the release of acidic drainage is the addition of labile organic carbon to mine wastes during deposition, creating large in situ treatment systems. Organic carbon can enhance bacterially mediated sulfate reduction and subsequent metal sulfide precipitation, treating metal-contaminated water prior to discharge from the impoundment. Two laboratory column experiments were conducted using simulated mine drainage water. The columns contained tailings derived from the Kidd Creek Metallurgical site in Timmins, Ontario, and reactive materials mixed to a 4:1 volumetric ratio. The average sulfate reduction rate observed in the woodchip column was 0.009 mmol L(-1) day(-1) g(-1) organic matter and in the pulp waste column 0.018 mmol L(-1) day(-1) g(-1) organic matter. Residence times were 14 days in the woodchip column, resulting in the average removal of 500 mg L(-1) (5.2 mmol L(-1)) SO4 and 60 mg L(-1) (1.1 mmol L(-1)) Fe, and 13 days in the pulp waste column, resulting in the average removal of 600 mg L(-1) (6.2 mmol L(-1)) SO4 and the complete removal of 100 mg L(-1) (1.8 mmol L(-1)) Fe. In both columns, sulfate reduction was coupled with an increase in alkalinity and pH and the complete removal of 80 mg L(-1) (1.2 mmol L(-1)) Zn and other metals. Populations of sulfate-reducing bacteria within both columns increased by 3-4 orders of magnitude, and bacterial activity was up to 5 times greater than in the unamended tailings. The woodchip material contained lower concentrations of labile C, N, and P than the pulp waste, possibly accounting for the lower sulfate reduction rates and metal removal capacity observed.

In situ reduction of chromium(VI) in heavily contaminated soils through organic carbon amendment.

Chromium has become an important soil contaminant at many sites, and facilitating in situ reduction of toxic Cr(VI) to nontoxic Cr(III) is becoming an attractive remediation strategy. Acceleration of Cr(VI) reduction in soils by addition of organic carbon was tested in columns pretreated with solutions containing 1000 and 10 000 mg L(-1) Cr(VI) to evaluate potential in situ remediation of highly contaminated soils. Solutions containing 0,800, or 4000 mg L(-1) organic carbon in the form of tryptic soy broth or lactate were diffused into the Cr(VI)-contaminated soils. Changes in Cr oxidation state were monitored through periodic micro-XANES analyses of soil columns. Effective first-order reduction rate constants ranged from 1.4 x 10(-8) to 1.5 x 10(-7) s(-1), with higher values obtained for lower levels of initial Cr(VI) and higher levels of organic carbon. Comparisons with sterile soils showed that microbially dependent processes were largely responsible for Cr(VI) reduction, except in the soils initially exposed to 10 000 mg L(-1) Cr(VI) solutions that receive little (800 mg L(-1)) or no organic carbon. However, the microbial populations (< or = 2.1 x 10(5) g(-1)) in the viable soils are probably too low for direct enzymatic Cr(VI) reduction to be important. Thus, synergistic effects sustained in whole soil systems may have accounted for most of the observed reduction. These results show that acceleration of in situ Cr(VI) reduction with addition of organic carbon is possible in even heavily contaminated soils and suggest that microbially dependent reduction pathways can be dominant.

Adsorption, complexation, and phytoavailability of copper as influenced by organic manure

Copper (Cu) is bound strongly to clay minerals and organic matter in soils, and forms both insoluble and soluble organic complexes with organic carbon. In this experiment, the effect of five manure composts (biosolid, farmyard manure, spent mushroom, pig manure, and poultry manure) on the adsorption and complexation of Cu in a mineral soil (Manawatu sandy soil, Palmerston North, New Zealand) low in organic matter content was examined. The effect of biosolid on the uptake of Cu from the soil, treated with various levels of Cu (0-400 mg/kg soil), was examined by using mustard (Brassica juncea L.) plants. The redistribution of the added Cu in soil was evaluated by a chemical fractionation scheme. Addition of manure compost increased the adsorption and complexation of Cu by the soil. At the same level of total organic carbon addition, a significant difference was found in the extent of Cu adsorption among the manure-amended soils. However, less difference was found in the amount of Cu complexed among the manure-amended soils. A significant inverse relationship was found between the extent of Cu adsorption and the dissolved organic carbon (DOC) in the manure-amended samples, indicating that DOC formed soluble complexes with Cu. Increasing addition of Cu increased Cu concentration in plants, resulting in decreased plant growth at high levels of Cu (i.e., phytotoxicity). Addition of biosolid was found to be effective in reducing the phytotoxicity of Cu at high levels of Cu addition. Significant relationships were found between dry matter yield and total Cu or free Cu2+ concentration in soil solution. Addition of biosolid decreased the concentration of the soluble and exchangeable Cu fraction but increased the concentration of the organic-bound Cu fraction in soil.

P limitation of respiration in the Sargasso Sea and uncoupling of bacteria from P regeneration in size-fractionation experiments

Community respiration rates were measured in unfiltered seawater collected in the upper 75 m of the water column along a transect in the Sargasso Sea and at the Bermuda Atlantic Time-series Study (BATS) station (31° 50' 00 N; 64° 10' 00 W) during a cruise in June and July 2001. Community respiration rates in the upper 75 m of the water column averaged 1.1 ± 0.4 µM O2 d -1 and exhibited significant spatial and temporal variability. Concurrent determination of the heterotrophic and autotrophic community revealed no relationship between community respiration and the abun- dance of any of the major metabolic groups. Addition of inorganic nutrients (NO3 and PO4) and organic carbon (glucose) indicated that community respiration was P-limited in the surface mixed layer. Size-fractionation experiments indicated that the abundance of heterotrophic bacteria in the <0.6 µm fraction was ~80% of the abundance in unfiltered seawater, but respiration rates in the <0.6 µm size fraction accounted for only 23% of community respiration. Addition of P to the <0.6 µm size fraction increased respiration rates ~2-fold, indicating bacterial respiration was P-limited. It appears that the uncoupling of bacteria from nutrient regeneration in size fractionation experiments resulted in a reduction of bacterial metabolism in the P-limited surface waters of the Sargasso Sea.

Effects of Organic Amendments on the Reduction and Phytoavailability of Chromate in Mineral Soil

In this study, seven organic amendments (biosolid compost, farm yard manure, fish manure, horse manure, spent mushroom, pig manure, and poultry manure) were investigated for their effects on the reduction of hexavalent chromium [chromate, Cr(VI)] in a mineral soil (Manawatu sandy soil) low in organic matter content. Addition of organic amendments enhanced the rate of reduction of Cr(VI) to Cr(III) in the soil. At the same level of total organic carbon addition, there was a significant difference in the extent of Cr(VI) reduction among the soils treated with organic amendments. There was, however, a significant positive linear relationship between the extent of Cr(VI) reduction and the amount of dissolved organic carbon in the soil. The effect of biosolid compost on the uptake of Cr(VI) from the soil, treated with various levels of Cr(VI) (0–1200 mg Cr kg−1 soil), was examined with mustard (Brassica juncea L.) plants. Increasing addition of Cr(VI) increased Cr concentration in plants, resulting in decreased plant growth (i.e., phytotoxicity). Addition of the biosolid compost was effective in reducing the phytotoxicity of Cr(VI). The redistribution of Cr(VI) in various soil components was evaluated by a sequential fractionation scheme. In the unamended soil, the concentration of Cr was higher in the organic-bound, oxide-bound, and residual fractions than in the soluble and exchangeable fractions. Addition of organic amendments also decreased the concentration of the soluble and exchangeable fractions but especially increased the organic-bound fraction in soil.

Effects of organic amendments on the reduction and phytoavailability of chromate in mineral soil.

In this study, seven organic amendments (biosolid compost, farm yard manure, fish manure, horse manure, spent mushroom, pig manure, and poultry manure) were investigated for their effects on the reduction of hexavalent chromium [chromate, Cr(VI)] in a mineral soil (Manawatu sandy soil) low in organic matter content. Addition of organic amendments enhanced the rate of reduction of Cr(VI) to Cr(III) in the soil. At the same level of total organic carbon addition, there was a significant difference in the extent of Cr(VI) reduction among the soils treated with organic amendments. There was, however, a significant positive linear relationship between the extent of Cr(VI) reduction and the amount of dissolved organic carbon in the soil. The effect of biosolid compost on the uptake of Cr(VI) from the soil, treated with various levels of Cr(VI) (0-1200 mg Cr kg(-1) soil), was examined with mustard (Brassica juncea L.) plants. Increasing addition of Cr(VI) increased Cr concentration in plants, resulting in decreased plant growth (i.e., phytotoxicity). Addition of the biosolid compost was effective in reducing the phytotoxicity of Cr(VI). The redistribution of Cr(VI) in various soil components was evaluated by a sequential fractionation scheme. In the unamended soil, the concentration of Cr was higher in the organic-bound, oxide-bound, and residual fractions than in the soluble and exchangeable fractions. Addition of organic amendments also decreased the concentration of the soluble and exchangeable fractions but especially increased the organic-bound fraction in soil.

A comparison of organic and inorganic carbon controls over biological denitrification in aquaria

In aquaria and rearing tanks, nitrate accumulation as a result of organic matter degradation is inevitable and has two major negative side effects: direct toxicity to organisms, specially invertebrates, and the introduction of a reducing environment by oxygen consumption. The aim of this study was to compare two alternate methods of removing nitrogen compounds from closed systems, autotrophic columnar denitrification (ACD) and heterotrophic columnar denitrification (HCD) by following end product concentrations as reaction progressed. A pilot plant consisting of two series of 50 dm 3 recirculating flow systems (each in triplicate) was used to test both methods. Absence of pH control was also useful in autotrophic denitrification systems in order to follow effects over reaction rates and pathways. Concentrations of NO 3 −, NO 2 − and NH 4 + were followed throughout the experiment, as well as pH, temperature and salinity. Under different flow conditions results show that higher nitrate reduction rates were possible in the autotrophic systems (35.1±4.7 μM/day without pH control until reversal of the process and 20.6±7.3 μ M/day after reestablishment of pH control) in comparison with heterotrophic ( 9.9±1.3 μ M/day). However, pH control through calcium bicarbonate addition was found to be crucial in maintaining constant levels of total denitrification in ACD systems, just as it was necessary to closely maintain organic carbon addition to HCD systems.

Microwave-assisted digestion of organoarsenic compounds for the determination of total arsenic in aqueous, biological, and sediment samples using flow injection hydride generation electrothermal atomic absorption spectrometry

A microwave assisted wet digestion method for organoarsenic compounds and subsequent determination of total arsenic in aqueous, biological and sediment samples by means of flow injection hydride generation electrothermal atomic absorption spectrometry (FI-HG-ETAAS) is described. Sodium persulfate, sodium fluoride and nitric acid serve as digestion reagents, which allow a quantitative transformation of organoarsenic compounds to hydride forming species in a commercial microwave sample preparation system. The maximum operating pressures of the applied tetrafluorometoxil (TFM) liners are 75 bar (high pressure vessels) and 30 bar (medium pressure vessels), corresponding to maximum solution temperatures of 300 and 260 °C. For the investigated samples, digestion temperatures of 210–230 °C (medium pressure vessels) and 240–280 °C (high pressure vessels) were obtained. In medium pressure vessels, arsenic recovery from aqueous testing solutions of dimethylarsinic acid (DMA), phenylarsonic acid (PAA) and tetraphenylarsonium chloride (TPA) at initial concentrations of 100 and 10 μg l −1 is complete, even in the presence of an excess of organic carbon (potassium hydrogen phthalate, 2000 mg l −1) or fatty acids (linolenic acid 70%; linoleic acid ≈20–25%; Oleic acid ≈3%, 900–4500 mg l −1). Arsenic recovery from aqueous arsenobetaine (ASB) solutions with the same initial concentrations is also complete if high pressure vessels and a higher concentration of fluoride ions are used, whereas the addition of organic carbon (potassium hydrogen phthalate, 2000 mg l −1, fatty acids, 900–4500 mg l −1) leads to a decrease in arsenic recovery of about 2–5%. In all cases, residual carbon contents are close to the limit of detection for the applied analytical method (15 mg l −1). Results of arsenic analysis in reference standard materials revealed a significant dependence on the material’s nature (sediment samples, plant materials and seafood samples). Sediment samples and plant materials show recoveries for arsenic around 100% after a single-step digestion in medium pressure TFM liners. Seafood (fish/lobster/mussel samples) usually require either the use of high pressure vessels or a second digestion step, if medium pressure vessels are used.

Factors regulating nitrification in aquatic sediments: effects of organic carbon, nitrogen availability, and pH

We investigated the response in nitrification to organic carbon (C) availability, the interactive effects of the C: nitrogen (N) ratio and organic N availability, and differing pH in sediments from several streams in the upper midwestern United States. In addition, we surveyed 36 streams to assess variability in sediment nitrification rates. Labile dissolved organic carbon (DOC) additions of 30 mg C·L–1 (as acetate) to stream sediments reduced nitrification rates (P &lt; 0.003), but lower concentration additions or dilution of ambient DOC concentration had no effect on nitrification. C:N and organic N availability strongly interacted to affect nitrification (P &lt; 0.0001), with N availability increasing nitrification most at lower C:N. Nitrification was also strongly influenced by pH (P &lt; 0.002), with maximum rates occurring at pH 7.5. A multiple regression model developed from the stream survey consisted of five variables (stream temperature, pH, conductivity, DOC concentration, and total extractable NH4+) and explained 60% of the variation observed in nitrification. Our results suggest that nitrification is regulated by several variables, with NH4+ availability and pH being the most important. Organic C is likely important at regulating nitrification only under high environmental C:N conditions and if most available C is relatively labile.

Relationship between C addition and storage in a Vertisol under soybean-wheat cropping system in sub-tropical central India

Kinetic relationship between addition of organic carbon (through unharvested crop biomass and externally applied farmyard manure) and storage in a Vertisol (Typic Haplustert) was studied in a seven-year soybean-wheat rotation experiment. We investigated 16 treatments comprised of combinations of four annual rates of farmyard manure (0, 4, 8 and 16 t ha—1 on dry weight basis) and four annual rates of fertilizer N (0, 72.5, 145, and 230 kg N ha—1). Average annual contribution of C input from soybean was 21.65% and from wheat was 32.32% of the harvestable above ground biomass. Net increases in the contents of soil organic C (Corg) at 0—15 and 15—30 cm depth were observed in all treatments. The annual rate of Corg enrichments ranged from 85 to 739 kg C ha—1 at 0—15 cm and 54 to 149 kg C ha—1 at 15—30 cm soil depth. The observed annual rate of change in Corg (δCs/δt, kg C ha—1 yr—1) at 0-30 cm was positively correlated with the gross annual C input (A, kg C ha—1 yr—1) to the 0—30 cm soil horizon, as described by a linear equation (δCs/δt = 0.1806 × A — 160.34; r = 0.978, P < 0.01). This indicates that 18.06% of the annual gross C input was incorporated in soil organic matter.

Effect of organic carbon (peat) on moisture retention of peat:mineral mixes

Quantification of the effects of organic carbon (OC) addition to reclaimed soils is an important reclamation issue. Such effects on soil texture, field capacity (FC), wilting point (PWP) and water-holding capacity (WHC), all expressed both on a gravimetric and volumetric basis, were quantified using both in situ soil samples and laboratory-prepared peat:mineral mixes. Soil samples were collected from both natural and reclaimed areas within the Oil Sands region of Alberta; peat was obtained from the same area. Organic carbon was determined for laboratory-created mixtures and expressed as volume ratios; for the in situ samples it was expressed as % OC. Bulk density, an important factor in the effects of OC on water retention, was measured in situ.Water retention parameters of in situ samples on a gravimetric basis were significantly related to % OC, but those on a volume basis were not. Trends in volumetric WHC for in situ, coarse-textured samples were similar to those for gravimeteric WHC, due to similar bulk densities ranging from 1.30 to 1.40 Mg m–3. However, for in situ peaty soils, trends in volumetric water retention did not mimic those expressed on a gravimetric basis due to low and irregular bulk densities. For laboratory-constructed peat:mineral mixes, FC and WHC were significantly impacted by % OC, however, PWP was not. The addition of peat material resulted in minor textural changes for sand and loamy sand; hence, the change in texture could not be responsible for the increases in WHC as the result of peat additions. The results for sandy loam were variable. Key words: Bulk density, field capacity, reclamation, water-holding capacity

Effects of organic carbon, organic nitrogen, inorganic nutrients, and iron additions on the growth of phytoplankton and bacteria during a brown tide bloom

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 209:19-34 (2001) - doi:10.3354/meps209019 Effects of organic carbon, organic nitrogen, inorganic nutrients, and iron additions on the growth of phytoplankton and bacteria during a brown tide bloom Christopher J. Gobler*, Sergio A. Sañudo-Wilhelmy Marine Sciences Research Center, SUNY at Stony Brook, Stony Brook, New York 11794-5000, USA *Present address: Natural Science Division, Southampton College of Long Island University, Southampton, New York 11968, USA. E-mail: cgobler@southampton.liu.edu ABSTRACT: Although nutrient inputs are the most commonly cited cause of brown tide blooms of Aureococcus anophagefferens on Long Island, New York, there is no consensus as to which nutrient(s) stimulates A. anophagefferens growth in the field. To evaluate the ability of dissolved organic carbon (DOC as glucose), dissolved organic nitrogen (DON as urea), nitrate, phosphate and iron to enhance A. anophagefferens growth during blooms, 10 nutrient enrichment experiments were conducted over the course of a brown-tide bloom during May, June and July of 1998 in West Neck Bay (WNB), Long Island, USA, using whole bay water. During the experiments, A. anophagefferens densities ranged from 1 × 104 to 5 x 105 cells ml-1, representing between 2 and 90% of algal biomass. Brown tide growth changed as a function of ambient nutrient levels during experiments, as the bloom shifted from organic carbon to N-limitation when nitrate levels in WNB decreased from elevated (2 to 20 µM) to low (<0.5 µM) levels. Contrary to current hypotheses that organic nitrogen fuels A. anophagefferens bloom formation and inorganic nitrogen can repress it, brown tide growth in response to equimolar nitrate and urea additions was nearly identical during experiments. Additions of nitrate or urea either had no effect or significantly decreased the relative abundance of the brown tide among the algal community during experiments. In contrast, augmentation of A. anophagefferens growth and decreases in non-brown-tide phytoplankton (NBTP) growth during organic carbon (glucose) additions resulted in significant increases in the relative abundance of brown tide among phytoplankton. Simultaneous enhancement of bacterial growth by glucose additions indicated a possible A. anophagefferens-NBTP-bacterial interaction by which monospecific brown tides may be initiated. Therefore, it is hypothesized that processes introducing copious amounts of labile DOC during A. anophagefferens blooms, such as leakage or remineralization of NBTP blooms, could promote monospecific brown tides. KEY WORDS: Brown tide · Harmful algal blooms · Bacteria · Phytoplankton · Nutrients · Organic carbon · Iron Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 209. Online publication date: January 05, 2001 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2001 Inter-Research.

Seasonal variation of phosphorus limitation of bacterial growth in a small lake

A series of bioassay experiments were performed from spring to autumn in a small dimictic lake (Deep Pond, Massachusetts) to examine the potential for bacterial growth limitation by organic carbon (glucose), inorganic nutrients (ammonium or phosphate), or both. The experiments demonstrated that phosphorus was the primary element limiting bacterial growth in Deep Pond during a large part of the summer. Significant increases (relative to controls) in bacterial cell volumes, protein production rates, and abundances were observed during 24‐h incubations for samples amended with phosphate alone. Organic carbon was near colimitation for most of the samples, however, and dramatic increases in bacterial abundance and rates of protein production were obtained only when both substances (phosphate and glucose) were added together. There was no evidence for nitrogen limitation of bacterial growth during the study. Temperature was not an important determinant for bacterial production rates above 12°C, but below 12°C temperature acted to mute the effect of nutrient and organic carbon additions on production rates. Bacterial growth was not significantly increased by the addition of any combination of glucose, ammonium, or phosphate below 12°C. A significant, albeit complex, effect of the microbial community on the bacterial response to nutrient/carbon enrichment was apparent in the samples. Substrate/nutrient supply and biomass removal by bacterivores both appeared to play a role in the outcome of the experiments.

Regulation of nitrification in aquatic sediments by organic carbon

Nitrification, the microbial conversion of ammonium to nitrate, is an important transformation in the aquatic nitrogen cycle, but the factors regulating nitrification rates in freshwater ecosystems are poorly understood. We investigated the effects of organic carbon quantity and quality on nitrification rates in stream sediments. First, we hypothesized that when environmental C: N ratios are high, heterotrophic bacteria are subject to N limitation and will outcompete nitrifying bacteria for available NH4+, thereby reducing nitrification rates. In laboratory experiments, organic carbon amendments (30 mg C L−1, as glucose) to stream sediments completely inhibited nitrification with or without addition of NH4+ (P &lt; 0.0001), whereas amendment with NH4+ only (0.75 mg N L−1) increased nitrification by 40% compared with unamended controls (P &lt; 0.0001). Carbon amendments also increased microbial respiration rates over controls by 4–6 times. Therefore, organic carbon additions significantly decreased nitrification rates but increased total microbial activity. Second, we hypothesized that carbon of high quality would have a stronger negative effect on nitrification than would carbon of low quality. To stream sediments, we added organic carbon as either glucose (higher quality) or sugar maple leaf extract (lower quality). Nitrification rates were reduced by the addition of either organic carbon source but were more severely inhibited by glucose (P = 0.001). Our results suggest that organic carbon is an important regulator of nitrification rates and is of key importance in understanding N dynamics in freshwater ecosystems.