bluuebunny/crossref_metadata_2025 huggingface dataset:
Three methods to estimate N2O fluxes as impacted by agricultural management
Authors: Burton D. L. , Bergstrom D. W. , Covert J. A. , Wagner-Riddle C. , Beauchamp E. G.
Published: April 2011

This study examines three methods of evaluating N2O flux and accumulation in soil profile over a growing season under three soil management regimes (fallow, fallow with manure addition and cropped to alfalfa). Estimates of N2O flux were made based on measured soil atmosphere concentration gradients in the top 15 cm and compared to flux estimates based on ex situ cores and micro-meteorological measurements made in parallel studies. All methods indicated strong seasonal trends relating to precipitation events. The amounts of N2O accumulating the profile decreased in the order alfalfa < fallow < fallow/manure. The amounts of N2O accumulating in the profile ranged from ambient (0.35 µL L−1) to 490 µL L−1. Diffusion of N2O to the lower profile was shown to provide temporary storage of N2O and thereby provide the opportunity for further reduction to N2 prior to efflux from the surface. In comparing the estimates of surface flux, all three methods were of the same order of magnitude for the fallow site but profile-based estimates were much lower and much higher for fallow/manure and alfalfa sites, respectively. Differences were attributed to the location and timing of carbon addition in each system.

Key words: Nitrous oxide, N2O, flux, measurement, soil, management
Distribution of cadmium in selected soil profiles of Saskatchewan, Canada: Speciation and availability
Authors: Krishnamurti G. S. R. , Huang P. M. , Kozak L. M. , Rostad H. P. W. , Rees K. C. J. Van
Published: April 2011

The distribution of Cd with depth, its particulate-bound speciation and availability index were studied in nine typical soil profiles of Saskatchewan, Canada. In the Ap horizons, Cd was predominantly in the metal-organic complex-bound form, accounting for about 38.8%, on average, of the total Cd present in the soils. The carbonate-bound Cd and the metal-organic complex-bound Cd accounted for 33.5 and 12.9%, respectively, on average, of the total Cd present in the B horizons. In the Ck horizons, Cd was predominantly in the carbonate-bound form, accounting for about 70.9%, on average, of the total Cd present in the soils. The M NH4Cl-extractable Cd of the soils, which is a measure of availability index of soil Cd, generally decreased with depth. Statistical treatment of the M NH4Cl-extractable Cd with different particulate-bound Cd species of various horizons in the soil profiles showed its highest correlation (P = 2.0 × 10−9, n = 42) with the amount of the metal-organic complex-bound Cd species, indicating the importance of the metal-organic complex-bound Cd species in Cd availability to the plants. Key words: Cadmium, soil profile, speciation, availability index, metal-organic complexes
Soil nitrogen and moisture as influenced by composts and inorganic fertilizer rate
Authors: Gagnon B. , Simard R. R. , Goulet M. , Robitaille R. , Rioux R.
Published: April 2011

The addition of compost may mitigate soil degradation and contribute to the soil nutrient supply in spring cereal monoculture. A field study was carried out in eastern Quebec, Canada, to assess the impact of composts from four sources and ammonium nitrate (AN) applied at different rates in spring on soil moisture and inorganic N in spring wheat production (Triticum aestivum L. 'Messier'). The experiment was conducted in 1994 and 1995 on two different soils: a Kamouraska clay (Orthic Humic Gleysol) and a Saint-André sandy loam (Fragic Humo-Ferric Podzol). Composts were applied at rates of 0, 90, 180 and 360 kg total N ha−1. Ammonium nitrate was applied at 0, 45, 90 and 180 kg N ha–1. Treatments in which AN was added to composts were also included. Thirty days after N application, profile soil inorganic N increased linearly with rates of commercial composts and AN but not with farm composts, whereas at harvest, residual soil N was not affected by composts but was increased by AN. The relative contribution of the compost organic fraction was negligible in the first year of application. Soil inorganic N at 30 d after fertilizer applications was significantly related to plant N uptake at harvest (r2 = 0.74), suggesting useful index of compost N availability. Large amounts of compost raised soil moisture content of the sandy loam by 3–5%, particularly under dry climatic conditions. Commercial composts have a small N fertilizer value, whereas composted dairy manure should be considered preferable as a soil amendment. Key words: Dairy manure compost, shrimp wastes, peat moss, wheat
Vector competition analysis: a new approach for evaluating vegetation control methods in young black spruce plantations
Authors: Imo Moses , Timmer Victor R.
Published: April 2011

This paper reports on a new graphical analysis technique that facilitates screening alternative strategies for crop management in programs of integrated vegetation management in young forest plantations. The responsiveness of black spruce seedlings to three vegetation management measures (herbicide application, fertilization and seedling nutrient loading) on two contrasting site types (Hardwood [ST 10] and Feathermoss [ST 4]) located in northern Ontario, were compared and evaluated using vector competition analysis. The approach is based on vector diagnosis and regression analysis that compare growth and nutritional interactions between crop and non-crop plants competing for the same growth resources. Response parameters are examined in a bivariate model depicting vectors of changing biomass production or nutrient uptake relative to competition-free treatments. Although herbicide application reduced non-crop vegetation on both sites, it accelerated tree growth and nutrient uptake only in the herb-rich Hardwood site, but had no effect on seedlings in the Feathermoss site. Fertilization stimulated vegetation growth in the competitive Hardwood site causing seedling suppression, but stimulated both tree and non-crop vegetation growth in the Feathermoss site because of weaker competition. Preplant nutrient loading improved seedling growth and nutrition reducing competition of neighboring weeds. Vector competition analysis facilitated interpretation of plant interactive relationships and identification of limiting factors. Advantages over traditional competition indices are that both growth and nutrition parameters, as well as crop and non-crop responses are quantitatively and systematically evaluated, and that simultaneous comparisons simplified screening of the most effective treatments and sites for possible vegetation control. Key words: Competition indices, treatment screening, nutrient loading, fertilization, herbicide
Soil properties and aspen development five years after compaction and forest floor removal
Authors: Stone Douglas M. , Elioff John D.
Published: April 2011

Forest management activities that decrease soil porosity and remove organic matter have been associated with declines in site productivity. In the northern Lake States region, research is in progress in the aspen (Populus tremuloides Michx. and P. grandidentata Michx.) forest type to determine effects of soil compaction and organic matter removal on soil properties and growth of aspen suckers, associated woody species, herbaceous vegetation, and on stand development. Four treatments: (1) total tree harvest (TTH); (2) TTH plus soil compaction (CPT); (3) TTH plus forest floor removal (FFR); and (4) TTH plus CPT + FFR were applied after winter-harvest of a 70-yr-old aspen stand growing on a loamy sand with a site index(age50) of 20.7 m. The CPT treatment significantly increased bulk density and soil strength of the surface 30 cm of soil and neither have recovered during the 5 yr since treatment. The CPT plots had 19.6 thousand (k) suckers ha−1, less than half that of the TTH and FFR treatments; mean diameter (19.4 mm) and height (271 cm) were greatest on the TTH plots. The disturbance treatments (CPT, FFR, and CPT + FFR) each reduced biomass of foliage, stems, and total suckers compared with the TTH treatment. Total aboveground biomass (herbs + shrubs + suckers) was less than half that of TTH plots. There were 5.0 k saplings (suckers >2.5 cm DBH) ha−1 on the TTH plots, but fewer than 1.0 k ha−1 in the other treatments. The disturbance treatments decreased 5-yr growth of potential crop trees, delayed early stand development, and temporarily reduced stockability and site productivity of an aspen ecosystem. Key words: Soil compaction, organic matter removal, site productivity, stand development
Soil nutrient and vegetation response to patch clear-cutting of an aspen forest near Meadow Lake, Saskatchewan
Authors: Maynard Doug G. , MacIsaac Dan A.
Published: April 2011

Alternate silviculture systems, such as small patch clearcuts, may become important in the development of sustainable forest management strategies in aspen forests. A study was initiated in a 64-yr-old trembling aspen (Populus tremuloides Michx.) stand in Meadow Lake Provincial Park, Saskatchewan to determine changes in nutrient dynamics and secondary succession following patch clear-cutting. One hectare replicated patch cuts were logged in the winter of 1993–1994. There was no site preparation following harvest. Annual vegetation, regeneration and soil and plant nutrient data were collected annually, 1 yr prior to, and 3 yr following harvest. Aspen regeneration was 48 375 stems ha−1 2 yr after treatment. Stand (alpha) diversity of the understory was not affected by harvesting, although annual species turnover (beta diversity) increased slightly after harvest. There was an increase in aspen foliar nitrogen (N) for 2 yr following harvest. Soil nutrient concentrations did not differ between patch cut and unharvested plots except total potassium (18% lower in the LFH of the harvested treatments 3 yr after harvesting). Small patch cuts with the litter horizon kept intact may be appropriate for aspen-dominated stands in the boreal mixed wood to minimize ecological disturbance while maintaining aesthetics within a park setting. Key words: Ammonium, aspen regeneration, diversity, nitrate, plant community structure, soil productivity
Forest floor mass and nutrients in two chronosequences of plantations: Jack pine vs. black spruce
Authors: Krause Helmut
Published: April 2011

The purpose of this study was to determine whether change of forest cover had an effect on the development of the organic surface horizons, particularly on those variables that influence nutrient cycling and forest productivity. Jack pine (Pinus banksiana Lamb.) and black spruce (Picea mariana [Mill.] B.S.P.) plantations were selected from among the youngest to oldest (2–16 yr) within a 100 km2 area in southeastern New Brunswick. Natural forests were also included as benchmark sites. The forest floor and tree foliage was sampled and trees measured on 0.05-ha plots. The forest floor samples were used to determine organic mass, nutrient contents and pH. In pine plantations, organic matter accumulated rapidly during the period of exponential tree growth, but leveled off at about 45 Mg ha–1. This was within the range of benchmark sites with mixed conifer-hardwood cover. In spruce plantations, the forest floor mass ranged upward to 77 Mg ha–1. Development was strongly influenced by the nature of the previous forest. Spruce forest floors were on average more acid and had lower nutrient concentrations, particularly N and Ca. The observed differences suggest that nutrients are recycled more rapidly in the pine plantations, partly explaining the superior growth of the latter. Key words: Forest floor, Kalmia angustifolia L., Picea mariana (Mill.) B.S.P., Pinus banksiana Lamb., nutrient cycling, plantation forest
Impact of warm summers on the actual evapotranspiration from spring wheat grown on the eastern Canadian prairies
Authors: Raddatz R. L. , Shaykewich C. F.
Published: April 2011

How do warm summers (June–July–August) influence the actual evapotranspiration totals from cropped land sown to spring wheat on the eastern Canadian Prairies? The eastern Prairies is a semi-arid region where over 60% of the land is cultivated. Over a third of the cropped land is usually sown to spring wheat. A comparison of mean summer temperatures and modelled evapotranspiration, for the years 1988 to 1996, demonstrated that with the current environmental conditions and farming practices, warm summers have lower actual evapotranspiration totals from spring wheat than cool summers. The average daily actual evapotranspiration rate is generally higher in years with higher mean summer temperatures; however, the crop growth-period is shorter. The net effect is lower total actual evapotranspiration from spring wheat. This suggests that climate warming on the eastern Canadian Prairies, if the current trend continues and all other factors remain equal, will reduce, on average, the total actual evapotranspiration from spring wheat. A reduction in the growth-period actual evapotranspiration from lands sown to spring wheat will likely decrease the total actual evapotranspiration for the entire warm season as growth-period evapotranspiration currently makes up about three-quarters of the seasonal total. However, the magnitude and timing of the reduction is far from certain. The consequence for agriculture may be a reduction in the average spring wheat yield because yield is positively correlated with the actual evapotranspiration total from the crop. Key words: Modelling, crop growth-period, yield, climate warming
The response of soil quality indicators to conservation management
Authors: Bolinder M. A. , Angers D. A. , Gregorich E. G. , Carter M. R.
Published: April 2011

The response of soil quality attributes to management practices across a diverse range of farming systems is key to identifying a robust minimum data set (MDS). The objectives of this study were to compare the response and consistency of different soil organic matter (SOM) attributes to changes in soil management practices in eastern Canadian agroecosystems. Soil samples (0–10 cm) were obtained at sites of several replicated experiments throughout eastern Canada, and 16 paired comparisons were selected to determine the effect of conservation (no-tillage, rotations, organic amendments) versus conventional (fall moldboard plowing, continuous cropping, no organic amendments) management practices. A sensitivity index was calculated for each of the attributes by dividing the values for conservation treatments with their conventionally managed counterparts (i.e., Conservation/Conventional). The index showed that light fraction (LF) N (1.58) and macro-organic matter-N (MOM-N) (1.54) were the most sensitive SOM attributes to conservation management practices. Light fraction-C (LF-C), macro-organic matter-C (MOM-C) and microbial biomass-C (MB-C) also showed high sensitivity to conservation management (1.48, 1.34 and 1.44, respectively). The sensitivity index for carbohydrates, whole soil C and total N were 1.23, 1.16 and 1.17, respectively. However, the Friedman two-way analysis of variance test indicated that the sensitivity of the different attributes to conservation management was site specific. For example, although LF-N was highly ranked, it did not respond as frequently as most of the other attributes. A non-parametric sign test showed that whole soil C and N provided the most consistent response to conservation management. The average sensitivity index was highest for the amendment (1.82) followed by the tillage (1.26) and rotational (1.14) conservation management practices, suggesting that organic amendments had the greatest impact on most of the attributes. These results suggest that for eastern Canadian soils, use of MOM-C and MOM-N, MB-C and whole soil C would provide a useful, easy to measure and robust MDS. Key words: Soil quality indicators, response, conservation management
Clay mineralogy and potassium status of selected soils in the glacial Lake Agassiz region of central Manitoba
Authors: Aide Michael T. , Cwick Gary J. , Cummings Mark F.
Published: April 2011

The clay mineralogy of the soil is important in that it can affect potassium (K) availability, particularly if vermiculite is present. Large areas of Glacial Lake Agassiz in Manitoba contain fine-grained lacustrine sediments that support boreal forest vegetation. The purpose of this investigation was to identify the clay mineralogy of several commonly occurring soils and document its influence on soil fertility, particularly K availability. The soils were classified as either Eluviated Eutric Brunisols or Orthic Eutric Brunisols. X-ray diffraction analysis verified that vermiculite, hydrous mica and kaolinite were the principal clay minerals in these soils. Vermiculite was demonstrated to have hydroxy Al-interlayers and the amount of vermiculite decreased in the deeper soil horizons. Smectite was present in the Btj horizons of the Eluviated Eutric Brunisols, while trace amounts of chlorite were present in every inorganic horizon. Quantity/intensity curves for K and an experimental estimate of the K-fixation potential indicated that the Ae horizons of several Eluviated Eutric Brunisols supported higher K activities in the soil solution and that K-fixation was greater in subsurface horizons. Potassium fixation and the quantity/intensity curves for selected horizons of the Orthic Eutric Brunisols were nearly identical and each showed a reduced intensity to maintain the aqueous activity of K. Key words: Potassium fixation, vermiculite, quantity/intensity
Effects of a polymeric soil conditioner on the early growth of sunflowers
Authors: Rigas F. , Sachini E. , Chatzoudis G. , Kanellopoulos N.
Published: April 2011

In sandy soils water shortage may result in the loss of crops. During prolonged droughts an increase in time to wilting by a few days may diminish yield losses. Soil incorporation of highly water-swelling polymers (hydrogels) to increase time to wilting and to increase biomass production was investigated. The soil conditioner used was a post cross-linked sulphonated polystyrene. The soil used was a sand with sunflowers (Helianthus annuus) grown for 10 wk. The plant parameters examined were emergence time, growth, wilting time and aboveground biomass. Soil parameters included field capacity, wilting point and available water. These parameters were correlated with the polymer content in the soil and the degree of water equilibrium swelling of the polymers. The tests were performed in pots under water deficiency conditions. Second-order factorial designs were applied and the resultant mathematical models proved adequate and reasonable. The presence of soil conditioner resulted in improvements of all parameters investigated. Key words: Arid soils, water economy, soil conditioners, experimental design
Long-term fertilization effects on soil carbon under permanent swards
Authors: Bélanger G. , Richards J. E. , Angers D. A.
Published: April 2011

In a long-term study with four rates each of fertilizer N, P, and K in factorial combination on timothy (Phleum pratense L.), soil C concentration in the 0- to 15-cm layer of an Orthic Dystric Brunisol in New Brunswick ranged from 25 to 37 g C kg−1 after 26 yr, and from 26 to 44 g C kg−1 after 35 yr. Soil C concentration was not related to the wide range of aboveground net productivity resulting from contrasted long-term fertilization treatments. Soil C concentration, however, was negatively correlated to soil pH. Key words:Phleum pratense L., timothy, carbon, fertilization
A portable data collection system for simultaneous cone penetrometer force and volumetric soil water content measurements
Authors: Young G. D. (Joe) , Adams B. A. , Topp G. C.
Published: April 2011

A new mechanism and sensors are described that can improve the quality of soil penetration resistance data. The electric-motor-driven mechanism pushes the cone into the soil at a constant rate. The force measurement is made with a miniature load cell sensor located adjacent to the cone head to reduce errors caused by friction between the soil and penetrometer shaft. A small water-content sensor is located on the shaft just above the load sensor, so that soil volumetric water content measurement is made on the hole walls just after the cone force is measured. The general nature of the electrical performance of the water content sensor was evaluated for different probe geometries by optimizing the portion of the electromagnetic energy passing into the soil compared to that remaining in the probe. Some early field and laboratory test results are shown, which were obtained using a complete prototype instrument. The resolution of each sensor is ±0.03 m3m−3 for water content, ±0.0007 MPa for cone penetration pressure (cone index) and ±0.003 m for depth. Key words: Water content, cone index, soil strength
Interpretation of soil enzyme activities in a comparison of tillage practices along a topographic and textural gradient
Authors: Bergstrom D. W. , Monreal C.M. , Tomlin A. D. , Miller J.J.
Published: April 2011

Assessment of the impacts of soil conservation practices requires measurement of the resulting changes in soil quality at scales inclusive of soil variability comparable to that of typical farms. The objective of this study was to compare changes in six soil enzyme activities (urease, glutaminase, phosphatase, arylsulfatase, β-glucosidase and dehydrogenase) and organic carbon (OC) content resulting from implementation of no-till along a topographic and soil textural gradient. Activities of β-glucosidase, glutaminase, phosphatase and arylsulfatase, and OC content were greater in coarse-textured soils at a lower slope-position than in fine-textured soil at an upper slope-position. Tillage practice influenced activities of urease, glutaminase, β-glucosidase and dehydrogenase but not OC content. The effect of tillage practice on enzyme activities was influenced by sampling depth and slope-position. Phosphatase and arylsulfatase activities of the Ap horizon behaved as indices of soil organic matter (SOM) content along the topographic gradient. Urease and dehydrogenase activities behaved as indices of soil biochemical activity within the Ap horizon. When interpreted in these terms, soil enzyme activities are comparable to other integrative measurements and as such describe system behavior and attributes. Key words: Soil enzyme activity, no-till, topographic position
Comparison of an enclosure drop trap and a visual diving census technique to estimate fish populations in eelgrass habitats
Authors: Bobsien I. C. , Brendelberger H.
Published: April 2011

In shallow vegetated aquatic habitats exceeding 2 m depth, conventional methods to determine fish abundances are of limited success. In this study, the sampling qualities of 2 methods for investigating the fish community associated with the eelgrass Zostera marina were tested: a newly developed enclosure drop trap (ET) operated from the water surface and a visual diving strip transect technique. The construction and the sampling procedure of the enclosure trap are described in detail. Both sampling procedures were performed simultaneously at the same eelgrass sampling site at depths between 2 and 5 m. The comparison revealed deficiencies in relative catch efficiency for both methods. Limitations with respect to bottom‐dwelling forms are obvious for the ET and with respect to the Syngnathidae and Gasterosteidae for the visual diving census. Abundance estimates of pelagic, schooling species were highly variable with both methods. Correction coefficients for the different behavioral categories of eelgrass fish were calculated. The fish species composition showed good agreement between the 2 methods, but the number of species on each sampling occasion was consistently higher in the ET catches. The length class frequency distributions estimated by the divers corresponded approximately with direct measurements of fish from the ET catches. The methods complemented one another and can be recommended for simultaneous deployment to get accurate quantitative estimates of eelgrass fish populations. The relative capture efficiency of the enclosure trap can be incorporated to improve abundance measurements of small fish in Zostera marina beds without the help of divers.
Intercalibration of four spectrofluorometric protocols for measuring RNA/DNA ratios in larval and juvenile fish
Authors: Caldarone Elaine M. , Clemmesen Catriona M. , Berdalet Elisa , Miller Thomas J. , Folkvord Arild , Holt G. Joan , Olivar M. Pilar , Suthers Iain M.
Published: April 2011

The ratio of tissue RNA to DNA (R/D) is a widely used index of recent growth and nutritional condition in larval and juvenile fish. To date, however, no standard technique for measuring nucleic acids has been adopted. Because methodological details can affect the estimate of R/D, researchers using different analytical protocols have been unable to compare ratios directly. Here, we report on the results of an international interlaboratory calibration of 4 spectrofluorometric protocols to quantify nucleic acids. Replicate sets of 5 tissue samples and 2 standards (common standards) were supplied to each of 5 researchers for analysis with their own methods and standards. Two approaches were evaluated for mitigating the observed differences in values: 1) the use of common nucleic acid standards and 2) standardizing to a common slope ratio (slope of DNA standard curve/slope of RNA standard curve or mDNA/mRNA). Adopting common standards slightly reduced the variability among protocols but did not overcome the problem. When tissue R/Ds were standardized based on a common mDNA/mRNA slope ratio, the variance attributed to analytical protocol decreased dramatically from 57.1% to 3.4%. We recommend that the ratio of the slopes of the standard curves be provided to facilitate intercomparability of R/D results among laboratories using different spectrofluorometric methods for the analysis of nucleic acids in fish.
The accuracy of acoustic Doppler velocimetry measurements in turbulent boundary layer flows over a smooth bed
Authors: Dombroski Daniel E. , Crimaldi John P.
Published: April 2011

An evaluation of acoustic Doppler velocimetry (ADV) in the near‐bed region of turbulent boundary layer flows is presented. Acoustic instruments have large sampling volumes compared with the smallest scales of motion in turbulent flows. This limits the accuracy of the technique, especially when making measurements close to the bed or in flows where large spatial gradients are present. These limitations are quantified by comparing ADV results to laser Doppler velocimetry (LDV) measurements from the same flow, and to direct numerical simulations of similar flows. A SonTek 16 MHz ADVField system was used in the evaluation. Measurements were made in a turbulent boundary layer over a smooth bed in a laboratory flume. The instrument was evaluated in both a fast and slow flow case with free stream velocities similar to those found in many natural environments. Additionally, results from an assessment of ADV sample volume size and position are reported. Mean velocities were within 5% accuracy down to 0.7 cm from the bed for the fast flow case and 1 cm for the slow flow case. ADV‐derived Reynolds stresses matched well with those from LDV to within 1‐2 cm of the bed, however turbulence intensities were found to deviate markedly up to 3‐4 cm from the bed in some cases. In general, errors are largest close to the bed, but extend further away from the bed than reported in previous studies.
An automatically operated system for simulating global change temperature and ultraviolet B radiation increases: application to the study of aquatic ecosystem responses in mesocosm experiments
Authors: Nouguier Jean , Mostajir Behzad , Le Floc'h Emilie , Vidussi Francesca
Published: April 2011

We report on a new, automatically operated system that can provide accurate simulations of the increases in ultraviolet‐B radiation (UVBR: 280‐320 nm) and temperature predicted by climate change scenarios. The system was employed in mesocosms using a factorial design. The originality of this system is that the increases in UVBR and water temperature are proportional to the prevailing ambient levels. In this system, a 20% increase above natural UVBR generated by UV lamps, and a 3°C increase in water temperature generated by submersible heating elements, are both regulated within very short time scales (0.5 s for UVBR and 30 s for water temperature). Thus, the system follows the natural fluctuations that the control mesocosms experience, and so reproduces the high degree of environmental variability that is inherent to aquatic systems. In 2006, eight mesocosms were set up and moored at the Mediterranean platform for Marine Ecosystem Experimental Research (South of France), and 4 treatments were applied in duplicate over a period of 13 d: (i) Control; (ii) a 20% increase in UVBR above ambient UVBR incident at the water surface of the control mesocosms, (iii) a 3°C increase in water temperature above that of control mesocosms, and (iv) a combination of the increased UVBR and temperature. The system proved highly reliable, and therefore represents an adaptable, robust, and accurate tool that can realistically mimic scenarios for temperature and UVBR increases linked to global change to study the effects on aquatic organisms.
Measuring short‐period wind waves in a tidally forced environment with a subsurface pressure gauge
Authors: Jones Nicole L. , Monismith Stephen G.
Published: April 2011

The ability of a current meter equipped with a standard pressure sensor to estimate the wave spectra of underdeveloped, fetch‐limited waves (peak period ~2 s) in a tidally forced, estuarine environment was investigated. Instruments of this type were placed at four heights throughout the 2.5 m water column, and data were recorded synchronously with a co‐located capacitance wave gauge. Linear wave theory was found to adequately describe the wave field in the lower frequency portion of the spectra (<0.6 Hz). The capacitance wave gauge data revealed that the equilibrium range of the spectrum could be modeled as ƒ−4. Large variability in the noise floor of the identical pressure gauges was found. The optimal cutoff frequency (beyond which the ƒ−4 model was applied) was defined as the location where the pressure spectra was 12 times the noise floor but was at least 1.1 times the peak frequency. Using these criteria, the pressure sensors measured root‐mean‐squared wave heights and mean wave periods with an uncertainty of 0.035 m and 0.13 s, respectively (95% confidence level). Applying a point measurement of the current in the transformation of the pressure spectra was found to be as reliable as applying a vertically averaged current. Using the criteria found to best estimate the wave spectra, an expression that determines the ability of a pressure sensor to measure the wave field of interest was developed. This expression enables the user to specify the wind velocity and peak wave frequency at a site and determine the maximum depth below the water surface at which the pressure gauge can be placed.
Isotope disequilibrium and mass spectrometric studies of inorganic carbon acquisition by phytoplankton
Authors: Rost Björn , Kranz Sven A. , Richter Klaus‐Uwe , Tortell Philippe D.
Published: April 2011

Given the need to assess potential effects of rising atmospheric CO2 on aquatic primary productivity, many studies have investigated the physiological mechanisms of inorganic carbon acquisition by a variety of phytoplankton species. Membrane inlet mass spectrometry (MIMS) has become the preferred methodological approach for laboratory experiments, whereas the 14C disequilibrium method has proven to be particularly useful for field studies. In the present investigation, we explicitly compare results of carbon acquisition measurements obtained with both of these approaches. Testing a range of phytoplankton species from different taxa, we show that both methods provide nearly identical results on the contribution of HCO3− and CO2 relative to net carbon fixation. In contrast, although both approaches yielded highly reproducible estimates for extracellular carbonic anhydrase activity, the results differed significantly between the two methods. By directly comparing these two leading methods, we provide experimental confirmation of key assumptions used for data interpretation and discuss possible effects of assay conditions. Our analysis highlights the individual strengths and weaknesses of different approaches.
Oxygen depletion and benthic mortalities: the first in situ experimental approach to documenting an elusive phenomenon
Authors: Stachowitsch Michael , Riedel Bettina , Zuschin Martin , Machan Rudolf
Published: April 2011

Oxygen depletion events and anoxia are a key threat to shallow marine coastal seas worldwide. The mortalities they trigger, however, are difficult to document in full. We developed an underwater device to experimentally induce hypoxia and anoxia on the seafloor. The EAGU (Experimental Anoxia Generating Unit) combines a time‐lapse camera and flashes with an array of sensors and a datalogger. The unit was successfully deployed in 24 m depth in the Northern Adriatic Sea for 3 to 5 d and yielded detailed information on the behavior and sequence of mortality of macrobenthic organisms — both epi‐ and infauna — under decreasing oxygen and increasing H2S concentrations. This unit, designed as a chamber with an instrument lid, also can be deployed in an open configuration to document low dissolved oxygen (DO) events. The equipment can provide data for a catalog of behavioral patterns, define indicator species, help reconstruct past mortalities, and better gauge the stability and status of benthic communities.
HPLC determination of phytoplankton and microphytobenthos pigments: comparing resolution and sensitivity of a C18 and a C8 method
Authors: Mendes Carlos R. , Cartaxana Paulo , Brotas Vanda
Published: April 2011

The effectiveness of two HPLC methods (a monomeric C18 column with a high ion strength solvent gradient and a monomeric C8 column with a pyridine‐containing mobile phase) in the separation, identification, and quantification of pigments are compared, using phytoplankton, microphytobenthos, and algal cultures. Although the two studied methods showed good analytical resolution, the C18 method presents a higher discrimination for several carotenoid pigments. On the other hand, the C8 method allows the separation of chlorophylls c1, c2, and Mg‐2, 4‐divinyl phaeoporphyrin a5 monomethyl ester as well as the pair chlorophyll a/divinyl Chl a. The C18 method had a shorter elution program and a lower solvent flow rate, making it cheaper and faster than the C8 method. Furthermore, the C18 method showed significantly lower detection and quantification limits, a particularly important advantage for pigments present in trace amounts in both phytoplankton and microphytobenthic samples. Differences in the sensitivity of the two studied methods were due mainly to differences in flow rate, with significantly higher peak areas for slower flow rates. No method is ideal for all pigments and sample types and the choice of method should be made in accordance with the objective of each study, taking into consideration the advantages and disadvantages identified for each method.
Effects of long‐term sample storage on the detection of bacterial cells using fluorescence in situ hybridization
Authors: Keats Kimberley F. , Rivkin Richard B. , Hale Michelle S. , Schneider David C.
Published: April 2011

Fluorescence in situ hybridization (FISH) is widely used to characterize bacterial community structure. However, a major limitation of the FISH technique is that the effectiveness of target cell detection varies widely over ecosystem types and with differences in methodology. Samples collected at sea often are stored for weeks or months before analysis using FISH, therefore quantifying the effects of storage on the detection of bacterial cells is crucial for comparing studies of bacterial community structure from diverse regions and ecosystems. Presented are the results of a 12‐month time‐course study during which replicate seawater samples were prepared, stored frozen, and hybridized after 0, 1.5, 3, 6, and 12 months to determine the effects of long‐term sample storage on hybridization efficiency and the characterization of community structure. The time‐dependent slope of the probe for Bacteria, but not the Cytophaga‐Flavobacteria cluster or the α‐ and γ‐Proteobacteria, was significantly different from zero, with a 6.3% change in target cell detection per year. This change in detection was small and within the typical error reported for bacterial counting. We conclude that during this 12‐month time‐course study there was a minimal effect of long‐term storage on the detection of bacterial cells using FISH.
A high‐throughput method to measure photosynthesis‐irradiance curves of phytoplankton
Authors: Johnson Zackary I. , Sheldon Tamara L.
Published: April 2011

Photosynthesis‐irradiance (P‐E) curves are an important tool used to characterize the physiology of phytoplankton. In most marine environments, low biomass and photosynthetic rates make the carbon‐14 tracer technique, used in conjunction with photosynthetrons to create the light gradient, the method of choice to measure P‐E curves. However, conventional photosynthetrons are bulky and require large chilled‐water recirculators to maintain temperature. In addition, setting the light levels is difficult. Here we describe a new type of photosynthetron, the microphotosynthetron, which avoids these problems. The microphotosynthetron is based on the standard 96‐well plate format and allows precise light control using tunable light‐emitting diodes (LEDs). Temperature is regulated using a Peltier device. Using monotypic cultures of several phytoplankton strains grown at different light levels and mixed field populations from different sampling sites and depths, we evaluated the utility of the microphotosynthetron by comparing the measured P‐E curves to curves from standard photosynthetrons. The microphotosynthetron P‐E curves were identical in initial slope (α) (P > 0.1) and light‐saturated photosynthesis (Pmax) (P > 0.1) to P‐E curves measured using conventional photosynthetrons. In addition, because the microphotosynthetron is based on a standard 96‐well plate format, set‐up and processing is greatly expedited in comparison to the conventional photosynthetron technique. Although the microphotosynthetron utilizes smaller sample volumes (200 µL) and therefore might not be suitable for highly heterogeneous samples, it has numerous advantages over the conventional protocol. We recommend the microphotosynthetron approach to measure P‐E curves as a method for the rapid screening of photophysiological properties of phytoplankton, in particular, monotypic cultures.
Fractionation of sediment phosphorus revisited. I: Fractionation steps and their biogeochemical basis
Authors: Lukkari Kaarina , Hartikainen Helinä , Leivuori Mirja
Published: April 2011

The aim of this work was to assess the validity of a phosphorus fractionation procedure, introduced by Psenner and co‐workers and modified by Jensen and Thamdrup, in chemical characterization of sediment P. In this procedure, P is separated into 6 pools: loosely bound (and pore water) P, redox‐sensitive P (bound to iron and manganese), P bound to oxides of aluminum and nonreducible Fe, calcium‐bound P, and mobile and immobile pools of organic P. The procedure was slightly modified further, and every step of the work is described in detail. Reproducibility of the method and variation within the extracts obtained at each step were investigated with a commercial reference material. The validity of the results considered against the theoretical basis of the P fractionation procedure was evaluated in terms of the elemental composition of the separate extracts. The results showed good reproducibility of the method; variation in amounts of the different P forms in the separate extractions was small (coefficient of variation <15%). In addition, the analysis of selected elements extracted along with P were reliable enough to deduce the origin of the various P forms. The analytical results for P and the other elements were in accordance with the general theoretical basis of the fractionation procedure. Despite some shortcomings, the tested procedure, in combination with the laboratory practices and analytical methods described, gives reliable and valuable results for distinguishing between potentially mobile and immobile P in sediment.
Automated high resolution ectoenzyme measurements: instrument development and deployment in three trophic regimes
Authors: Gaas Brian M. , Ammerman James W.
Published: April 2011

A commercial flow‐injection analysis (FIA) unit was adapted for rapid, automated measurements of ectoenzyme activity. Seawater was injected with a small amount of the substrate 6,8‐difluoro‐4‐methylumbelliferyl phosphate or L‐leucine‐7‐amido‐4‐methylcoumarin, the hydrolysis products of which were measured fluorometrically in a flow cell. The FIA system was run using sequential injection stopped‐flow analysis, allowing activities to be calculated directly from the rate of substrate hydrolysis. The FIA unit sampled autonomously, with the exception of running standard curves and creating new killed controls. The FIA unit was deployed in three environmentally distinct locations — the hypereutrophic Louisiana shelf (July 2004), the oligotrophic Sargasso Sea (February–March 2005), and the eutrophic Hudson River estuary (April 2005). Both phosphatase (Louisiana shelf and Sargasso Sea cruises) and peptidase (Hudson estuary cruise) activities were detectable by the FIA unit. Good correlations were observed between activities measured by the FIA unit and a fluorescence microplate reader. Incubation times ranged from 5–20 min with sampling rates of one sample every 11–26 min. Differences in incubation time, mixing coil length, and detector settings altered the dilution of standards and substrates but did not affect the detection limit of fluorescence. High resolution contour maps and time‐series measurements of ectoenzyme activities in eddies, localized upwellings and downwellings, blooms, and river plumes may be used to understand and predict biogeochemical changes in these and other aquatic environments.
Development and field assessment of a quantitative PCR for the detection and enumeration of the noxious bloom‐former Anabaena planktonica
Authors: Rueckert Andreas , Wood Susanna A. , Cary S. Craig
Published: April 2011

Anabaena planktonica is a harmful, bloom‐forming freshwater cyanobacterium, which has arrived recently in New Zealand. In the short time since its incursion (<10 yr), A. planktonica has spread rapidly throughout lakes in the North Island. To date, the identification and enumeration of A. planktonica has been undertaken using light microscopy. There is an urgent demand for a highly sensitive and specific quantitative detection method that can be combined with a high sample processing capability in order to increase sampling frequency. In this study, we sequenced 36 cyanobacterial 16S rRNA genes (partial), complete intergenic transcribed spacers (ITS), and 23S rRNA genes (partial) of fresh‐water cyanobacteria found in New Zealand. The sequences were used to develop an A. planktonica specific TaqMan QPCR assay targeting the long ITS1‐L and the 5′ terminus of the 23S rRNA gene. The QPCR method was linear (R2 = 0.999) over seven orders of magnitude with a lower end sensitivity of approximately five A. planktonica cells in the presence of exogenous DNA. The quantitative PCR (QPCR) method was used to assess the spatial distribution and seasonal population dynamics of A. planktonica from the Lower Karori Reservoir (Wellington, New Zealand) over a five‐month period. The QPCR results were compared directly to microscopic cell counts and found to correlate significantly (95% confidence level) under both bloom and non‐bloom conditions. The current QPCR assay will be an invaluable tool for routine monitoring programs and in research investigating environmental factors that regulate the population dynamics and the blooming of A. planktonica.
Toward a transport‐based analysis of nutrient spiraling and uptake in streams
Authors: Runkel Robert L.
Published: April 2011

Nutrient addition experiments are designed to study the cycling of nutrients in stream ecosystems where hydrologic and nonhydrologic processes determine nutrient fate. Because of the importance of hydrologic processes in stream ecosystems, a conceptual model known as nutrient spiraling is frequently employed. A central part of the nutrient spiraling approach is the determination of uptake length (Sw), the average distance traveled by dissolved nutrients in the water column before uptake. Although the nutrient spiraling concept has been an invaluable tool in stream ecology, the current practice of estimating uptake length from steady‐state nutrient data using linear regression (called here the “Sw approach”) presents a number of limitations. These limitations are identified by comparing the exponential Sw equation with analytical solutions of a stream solute transport model. This comparison indicates that (1) Sw is an aggregate measure of uptake that does not distinguish between main channel and storage zone processes, (2) Sw is an integrated measure of numerous hydrologic and nonhydrologic processes—this process integration may lead to difficulties in interpretation when comparing estimates of Sw, and (3) estimates of uptake velocity and areal uptake rate (vf and U) based on Sw are not independent of system hydrology. Given these findings, a transport‐based approach to nutrient spiraling is presented for steady‐state and time‐series data sets. The transport‐based approach for time‐series data sets is suggested for future research on nutrient uptake as it provides a number of benefits, including the ability to (1) separately quantify main channel and storage zone uptake, (2) quantify specific hydrologic and nonhydrologic processes using various model parameters (process separation), (3) estimate uptake velocities and areal uptake rates that are independent of hydrologic effects, and (4) use shortterm, non‐plateau nutrient additions such that the effects of regeneration and mineralization are minimized. In summary, the transport‐based, time‐series approach provides a means of estimating traditional measures of nutrient uptake (Sw, vf , U) while providing additional information on the location and magnitude of uptake (main channel versus storage zone). Application of the transport‐based approach to time‐series data from Green Creek, Antarctica, indicates that the bulk of nitrate uptake (~74% to 100%) occurred within the main channel where benthic uptake by algal mats is a likely process. Substantial uptake (~26%) also occurred in the storage zone of one reach, where uptake is attributed to the microbial community.