scholarly journals Seasonal variation in marine C:N:P stoichiometry: can the composition of seston explain stable Redfield ratios?

2011 ◽  
Vol 8 (10) ◽  
pp. 2917-2933 ◽  
Author(s):  
H. Frigstad ◽  
T. Andersen ◽  
D. O. Hessen ◽  
L.-J. Naustvoll ◽  
T. M. Johnsen ◽  
...  

Abstract. Seston is suspended particulate organic matter, comprising a mixture of autotrophic, heterotrophic and detrital material. Despite variable proportions of these components, marine seston often exhibits relatively small deviations from the Redfield ratio (C:N:P = 106:16:1). Two time-series from the Norwegian shelf in Skagerrak are used to identify drivers of the seasonal variation in seston elemental ratios. An ordination identified water mass characteristics and bloom dynamics as the most important drivers for determining C:N, while changes in nutrient concentrations and biomass were most important for the C:P and N:P relationships. There is no standardized method for determining the functional composition of seston and the fractions of POC, PON and PP associated with phytoplankton, therefore any such information has to be obtained by indirect means. In this study, a generalized linear model was used to differentiate between the live autotrophic and non-autotrophic sestonic fractions, and for both stations the non-autotrophic fractions dominated with respective annual means of 76 and 55%. This regression model approach builds on assumptions (e.g. constant POC:Chl-a ratio) and the robustness of the estimates were explored with a bootstrap analysis. In addition the autotrophic percentage calculated from the statistical model was compared with estimated phytoplankton carbon, and the two independent estimates of autotrophic percentage were comparable with similar seasonal cycles. The estimated C:nutrient ratios of live autotrophs were, in general, lower than Redfield, while the non-autotrophic C:nutrient ratios were higher than the live autotrophic ratios and above, or close to, the Redfield ratio. This is due to preferential remineralization of nutrients, and the P content mainly governed the difference between the sestonic fractions. Despite the seasonal variability in seston composition and the generally low contribution of autotrophic biomass, the variation observed in the total seston ratios was low compared to the variation found in dissolved and particulate pools. Sestonic C:N:P ratios close to the Redfield ratios should not be used as an indicator of phytoplankton physiological state, but could instead reflect varying contributions of sestonic fractions that sum up to an elemental ratio close to Redfield.

2011 ◽  
Vol 8 (3) ◽  
pp. 6227-6263
Author(s):  
H. Frigstad ◽  
T. Andersen ◽  
D. O. Hessen ◽  
L.-J. Naustvoll ◽  
T. M. Johnsen ◽  
...  

Abstract. Seston is suspended particulate organic matter, comprising a mixture of autotrophic, heterotrophic and detrital material. Despite variable proportions of these components, marine seston often exhibit relatively small deviations from the Redfield ratio (C:N:P = 106:16:1). Two time-series from the Norwegian shelf in Skagerrak are used to identify drivers of the seasonal variation in seston elemental ratios. An ordination identified water mass characteristics and bloom dynamics as the most important drivers for determining C:N, while changes in nutrient concentrations and biomass were most important for the C:P and N:P relationships. A generalized linear model was used to differentiate between the live autotrophic and non-autotrophic sestonic fractions, and for both stations the non-autotrophic fractions dominated with respective annual means of 24 and 45 % live autotrophs. The autotrophic percentage calculated from the statistical model was compared with estimated phytoplankton carbon, and the two independent estimates of autotrophic percentage were comparable with similar seasonal cycles. The estimated C:nutrient ratios of live autotrophs were in general lower than Redfield, while the non-autotrophic C:nutrient ratios were higher than the live autotrophic ratios and above or close to the Redfield ratio. This is due to preferential remineralization of nutrients (especially phosphorus), while carbon gradually builds up in the detritus pool. Despite the seasonal variability in seston composition and the generally low contribution of autotrophic biomass, the variation observed in the total seston ratios was low compared to the variation found in dissolved and particulate pools. This study shows that sestonic Redfield ratios cannot automatically be interpreted as phytoplankton with "balanced growth", but could instead reflect varying contributions of sestonic compartments that sum up to an elemental ratio close to Redfield.


2021 ◽  
Vol 5 (2) ◽  
pp. 511-532
Author(s):  
Aniefiok Akpaneno ◽  
Matthew Joshua ◽  
K. R. Ekundayo

Solar quiet current (S_q) and Equatorial Electrojet (EEJ) are two current systems which are produced by electric current in the ionosphere.  The enhancement of the horizontal magnetic field is the EEJ. This research is needed for monitoring equatorial geomagnetic current which causes atmospheric instabilities and affects high frequency and satellite communication. This study presents the longitudinal and latitudinal variation of equatorial electrojet signature at stations within the 96°mm and 210°mm African and Asian sectors respectively during quiet condition. Data from eleven observatories were used for this study. The objectives was  to determine the longitudinal and latitudinal geomagnetic field variations during solar quiet conditions, Investigate monthly variation and diurnal transient seasonal variation; Measure the strength of the EEJ at stations within the same longitudinal sectors and find out the factors responsible for the longitudinal and latitudinal variation of EEJ. Horizontal (H) component of geomagnetic field for the year 2008 from Magnetic Data Acquisition System (MAGDAS) network were used for the study. The International Quiet Days (IQDs) were used to identify quiet days. Daily baseline values for each of the geomagnetic element H  were obtained.  The monthly average of the diurnal variation was found. The seasonal variation of dH was found. Results showed that: The longitudinal and latitudinal variation in the dH differs in magnitude from one station to another within the same longitude due to the difference in the influence of the EEJ on them.


2018 ◽  
Vol 56 ◽  
pp. 136-140
Author(s):  
G. S. Sharapa ◽  
O. V. Boyko

Scientific and production experiments were carried out on cows of Ukrainian Black-and-White diary breed (UBAWD) of SE "Seagull" (branch "Lisne") during 2016–2017. The anatomical and physiological state of genital organs of cows was determined by the method of clinical and gynecological research of animals before conducting experiments and during them every 40–50 days. In total 486 cows were kept under control, which were kept in typical rooms with running platforms, but the active motivation of animals was clearly insufficient. Feeding cows according to the recommended standards. The milk yield from the cow in 2017 was 7813 kg. The experiments studied the effect of feeding cows during the dry period, the conditions of retention and some other paratypic factors on the course of the genera and the postnatal period, the duration of the service period and the fertility of cows. In analyzing the research results, personal records and veterinary documentation were used. In conducting experiments, it was found that normal calving was in 89% of cows, and severe and pathological – in 11% of cases. The main diseases in the afterlife period were: detention of the litter – 9.5%, postpartum endometritis – 21.5%, hypofunction of the ovaries – 23.0%, persistent yellow ovarian bodies – 25.6% and others. Normal intervals between stages of excitation of the sexual cycle (18–22 days) were in 63% of cows, and violations of the rhythm of sexual cycle, associated with dysfunction of the ovaries and missed the hunt – 30% of animals. Subunvulation of the genital organs of the cows contributed to the diseases of the limbs, udder and digestive disorders. During 2016–2017, the effect of feeding cows (173 g.) in the dry period on the course of calving, post-autumn period and their fertility was studied. Under the same conditions, keeping cows in the maternity ward and feeding rough and succulent feeds concentrated feeds fed cows of the control group (98 heads) to 1–2 kg daily during the dry period, and experimental (75 heads) – for 18–20 days to calving 2–3 kg. A positive difference was found in favor of cows of the experimental group: there was a more active stage of expulsion of the fetus, less delay of the placenta (by 7%) and endometritis (by 12%), the duration of the postoperative regenerative period decreased by 8.6 days; service period – 19.0 days; fertility from two inseminans was higher by 5.7%. Study of the reproductive capacity of cows at the hotel in different seasons showed that the recovery period was shorter by 11 days in the presence of cows in 3–4 quarters, and the service period – by 23.2 days at hotel in I and IV sq. The average duration of the recovery period was 79.5 days, while the service period was 123.4 days. The longest duration of the joint ventricle was in cows at hotel during the hot summer days of the year. The average fertilization rate from the first insemination of 339 cows was 44.9% with fluctuations in individual groups of milkers from 26.8% to 55.0%. The following indicators were in the number 1 and number 3 (respectively 26.8% and 31.4%). The best fertility rates were in groups № 4, 6 and 7, where there were more cows of the second and third lactation, and the responsible attitude of the milkers to work in organizing cows walks and sexually explicit hunting. When comparing the assessment of the duration of the IP and SP in full-age cows and cows, the first-born, taking into account 225 goals. It was found that these indicators were longer in primitive cows – 20.7 days respectively and 21.9 days in relation to full-age cows. The obtained results are completely consistent with the results obtained by a number of both domestic and foreign researchers. More attention is needed to grow heifers and to prepare newborns for delivery. In 15–17% of cows at and after the hotel, gynecological diseases that occurred in the presence of gastrointestinal diseases, lameness, mastitis and others were diagnosed. This has negatively affected the overall performance of the herd. In studying the duration of HP and SP in healthy and sick cows after calving, it was found that if the SP in healthy cows lasts 73.4 days, then in patients – 116.3 days (the difference was 42.9 days), and the difference in the duration of the joint venture reached 98.7 days. On the basis of the results of the research, it can be concluded that the reproductive function of the cows is influenced by such paratypic factors as feeding animals in the dry period, the temperature factor (time of year), the human factor (the effect of milking on a group of cows), age and physiological state of cows in the hotel and in the afterlife period. When feeding 2–3 kg of bovine feed for cows, together with rough and juicy fodder for 18–20 days prior to calving, the recovery period decreased by 8.6 days and service period – by 19 days, and fertility from two inseminals increased by 5.7%, reaching 85.3%. The smallest duration of the service-period was in the presence of cows in the I and IV quarters year (107.7–117.1 days). In primary cows, the recovery period was longer than that of full-age cows by 20.7 days, and the service period was 21.9 days. In the physiologically healthy cows after calving, the recovery period lasted an average of 73.4 days and service period – 98.7 days, and in patients, after the prescribed treatment – respectively 116.3 days and 197.4 days.


2013 ◽  
Vol 10 (2) ◽  
pp. 3241-3279
Author(s):  
J. A. Bonachela ◽  
S. D. Allison ◽  
A. C. Martiny ◽  
S. A. Levin

Abstract. The elemental ratios of marine phytoplankton emerge from complex interactions between the biotic and abiotic components of the ocean, and reflect the plastic response of individuals to changes in their environment. The stoichiometry of phytoplankton is, thus, dynamic and dependent on the physiological state of the cell. We present a theoretical model for the dynamics of the carbon, nitrogen and phosphorus contents of a phytoplankton population. By representing the regulatory processes controlling nutrient uptake, and focusing on the relation between nutrient content and protein synthesis, our model qualitatively replicates existing experimental observations for nutrient content and ratios. The population described by our model takes up nutrients in proportions that match the input ratios for a broad range of growth conditions. In addition, there are two zones of single-nutrient limitation separated by a wide zone of co-limitation. Within the co-limitation zone, a single point can be identified where nutrients are supplied in an optimal ratio. The existence of a wide co-limitation zone affects the standard picture for species competing for nitrogen and phosphorus, which shows here a much richer pattern. However, additional comprehensive laboratory experiments are needed to test our predictions. Our model contributes to the understanding of the global cycles of oceanic nitrogen and phosphorus, as well as the elemental ratios of these nutrients in phytoplankton populations.


2014 ◽  
Vol 53 (02) ◽  
pp. 115-120 ◽  
Author(s):  
P. Ryan ◽  
J. E. Hiller ◽  
G. Mnatzaganian

SummaryObjective: Using three risk-adjustment methods we evaluated whether co-morbidity derived from electronic hospital patient data provided significant improvement on age adjustment when predicting major outcomes following an elective total joint replacement (TJR) due to osteoarthritis.Methods: Longitudinal data from 819 elderly men who had had a TJR were integrated with hospital morbidity data (HMD) and mortality records. For each participant, any mor bidity or health-related outcome was retrieved from the linked data in the period 1970 through to 2007 and this enabled us to better account for patient co-morbidities. Co-mor bidities recorded in the HMD in all admissions preceding the index TJR admission were used to construct three risk-adjustment methods, namely Charlson co-morbidity index (CCI), Elixhauser’s adjustment method, and number of co-morbidities. Postoperative outcomes evaluated included length of hospital stay, 90-day readmission, and 1-year and 2-year mortality. These were modelled using Cox proportional hazards regression as a function of age for the baseline models, and as a function of age and each of the risk-adjustment methods. The difference in the statistical performance between the models that included age alone and those that also included the co-morbidity adjustment method was as sessed by measuring the difference in the Harrell’s C estimates between pairs of mod els applied to the same patient data using Bootstrap analysis with 1000 replications.Results: Number of co-morbidities did not provide any significant improvement in model discrimination when added to baseline models observed in all outcomes. CCI significantly improved model discrimination when predicting post-operative mortality but not when length of stay or readmission was modelled. For every one point increase in CCI, postoperative 1- and 2-year mortality increased by 37% and 30%, respectively. Elixhauser’s method outperformed the other two providing significant improvement on age adjustment in all outcomes.Conclusion: The predictive performance of co-morbidity derived from electronic hospital data is outcome and risk-adjustment method specific.


2010 ◽  
Vol 67 (11) ◽  
pp. 1721-1729 ◽  
Author(s):  
Jari Syväranta ◽  
Milla Rautio

We found considerable seasonal, latitudinal, and taxonomic differences in zooplankton lipid content and concurrent δ13C values of zooplankton. We collected cladoceran as well as cyclopoid and calanoid copepod zooplankton from boreal and subarctic lakes throughout a year, allowing us to study zooplankton likely subjected to different isotopic fractionation processes and with highly variable lipid contents. Considerable seasonal variation was observed in the difference between bulk and lipid-extracted zooplankton δ13C values, indicating that seasonally changing lipid content introduced notable variation in zooplankton δ13C values. The difference between bulk and lipid-extracted material was most amplified in lipid-rich subarctic zooplankton in winter, δ13C difference being >5 units. Significant differences were also observed among zooplankton taxa, with copepods showing a greater lipid impact on δ13C than cladocerans. Published lipid correction models failed to produce satisfying fits to our data, and considerable variation was left even after recalibrating the model parameters. This was likely due to taxonomic differences in lipid effects on δ13C values. We therefore produced separate mass balance-based lipid correction models for cladocerans and also cyclopoid and calanoid copepods. We conclude that arithmetic lipid correction models perform well with zooplankton samples, but taxonomic differences need to be considered.


1995 ◽  
Vol 31 (1) ◽  
pp. 1-11 ◽  
Author(s):  
A. Buerkert ◽  
P. R. Lawrence ◽  
J. H. Williams ◽  
H. Marschner

SummaryA simple hand-held reflectometer was used to estimate the shoot dry matter of pearl millet (Pennisetum glaucum), groundnut (Arachis hypogaea), cowpea (Vigna unguiculata), weeds and grass swards non-destructively. While the instrument was able to predict shoot dry matter well for single, standing millet and cowpea plants and proved useful for a growth analysis of millet, its reliability was unsatisfactory for groundnut. For millet, the slope of two separate regressions between the difference of reflectance ratios and shoot dry matter, taken 10 days apart, was almost identical. This suggests a possible simplification in future crop growth models. The usefulness of the instrument for estimating dry matter in natural species mixtures such as weeds and grasses depended on the homogeneity of the mixture and the uniformity of their physiological state.Medición de la biomasa utilizando la reflexión


Author(s):  
L. R. Fisher ◽  
S. K. Kon ◽  
S. Y. Thompson

SummaryResults are given for measurements of fat, vitamin A and carotenoids in groups of Meganyctiphanes norvegica, Thysanoessa raschii, Crangon allmani, C. vulgaris, Nephrops norvegicus and eyes of Homarus vulgaris, collected at regular intervals for a year or longer.In both species of euphausiids vitamin A was consistently present mainly in the ester form and concentrated chiefly in the eyes. More than half the total astaxanthin was in the eyes. No other carotenoids were detected.Astaxanthin and vitamin A were accumulated by the euphausiids more rapidly during the spring and autumn-feeding periods associated with diatom outbursts than at other seasons. There was a delay in Thysanoessa raschii, but not in Meganyctiphanes norvegica, between resumption of more rapid growth during spring and autumn and increase in concentration of vitamin A and astaxanthin. The difference was possibly due to differences in diet of the two species in relation to the seasonal biological composition of the plankton.In the euphausiids, concentrations of vitamin A and astaxanthin were much higher in larvae and in adults over 30 mm long of M. norvegica, and in larvae and adults over 15 mm of Thysanoessa raschii, than in mature adults of Meganyctiphanes norvegica of 20–30 mm and Thysanoessa raschii of 13–15 mm, respectively. An inverse relationship between fat and vitamin A concentration was noted in both species throughout the year.In Crangon spp. and Nephrops norvegicus there was no evidence of any seasonal variation of either vitamin A or carotenoids. Differences in the carotenoid metabolism of the two species of Crangon are discussed.


Nukleonika ◽  
2020 ◽  
Vol 65 (2) ◽  
pp. 153-157
Author(s):  
Iveta Smetanová ◽  
Karol Holý ◽  
Ľubica Luhová ◽  
Kristian Csicsay ◽  
Dagmar Haviarová ◽  
...  

AbstractThe continuous monitoring of 222Rn activity concentration, CO2 concentration, and microclimatologic parameters (internal air temperature and relative humidity) in the Važecká Cave (Northern Slovakia) is being carried out at three monitoring stations, namely, Gallery, Lake Hall, and Entrance Hall. Radon activity concentration and CO2 concentration exhibited a clear annual variation. The daily average of radon concentration ranged 1300–27 700 Bq/m3 at the Lake Hall station and 3600–42 200 Bq/m3 at the Gallery station. Radon reached its maximum in the summer months, from June to September. The annual maximum of CO2 concentration is registered approximately one month later than radon maximum. The annual variation of radon and CO2 is controlled by the seasonal change of ventilation regime associated with the seasonal variation of the difference between the temperature measured inside the cave and the atmospheric temperature.


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