Variations In Nutrient Concentrations Research Articles

Spatial Distribution of Physical and Chemical Properties of Deep Sea Water in Xisha, South China Sea

Deep sea water (DSW) is a globally utilized source of renewable energy and other resources. To understand the characteristics of DSW resources in the South China Sea, in July 2022, the Guangzhou Marine Geological Survey (GMGS) investigated temperature, salinity, pH, dissolved oxygen (DO), inorganic salts (DIN, PO43−-P, and SiO3-Si), heavy metals (Hg, Pb, As, and Cd), trace elements (Cu, Zn, Fe, Mn, Ni, Se, and Mo), and other related indicators. The results of this investigation elucidate the horizontal and vertical changes in the physical and chemical properties of deep sea water in the Xisha Sea. The surface seawater quality in Xisha was found to be excellent and to meet first-class seawater survey standards. However, the concentrations of various nutrient salts in the surface layer were relatively low. As the seawater depth increased, different trace elements and heavy metals exhibited variations, and the concentrations of various nutrients also gradually increased.

Spatial and seasonal variation in zooplankton dynamics in Parangipettai coastal waters Southeast coast of India

The distribution and composition of zooplankton are influenced by a combination of physico-chemical and biological processes, which in turn have effects on the entire ecosystem. In this study, the influence of environmental factors on zooplankton diversity in mangrove-estuarine coastal waters of Parangipettai, southeast coast of India, was investigated. Water samples were collected for a period of four years from January 2014 to December 2017. Totally, 145 species of zooplankton were recorded with highest belonging to the Arthropoda (63.21%) followed by Protozoa (10.53%), Cnidaria (7.95%), Urochordata (6.03%), Chordata (2.92%), Chaetognatha (2.62%), Mollusca (2.42%), Echinodermata (1.14%), Annelida (1.05%), Brachiopoda (1.01%), Ctenophora (0.57%) and Phoronida (0.55%). The findings of cluster, MDS, Factor analysis and CCA showed that variations in nutrient concentration may significantly alter the biotic community of zooplankton species. Furthermore, site score confirmed the effect of environmental conditions on zooplankton distribution. The result of TRIX showed the dry seasons are classified as scarcely eutrophied whereas wet seasons as moderately eutrophied. The findings of this study offer enhanced insight into how physico-chemical factors interact and vary over space and time, which is crucial for evaluating the effects of climate change on ecosystem services mediated by zooplankton.

Evaluation of oil palm (Elaeis guineensis Jacq.) productivity on peatlands based on DRIS analysis of leaf nutrient content in Siak District of Indonesia

Indonesia is the largest producer of oil palm in the world, with Riau Province particularly Siak District being the major contributor. The study focused on oil palm plantations within Siak District, characterized by a tropical rainforest climate of high humidity. The soil type in this area was a peatland with sapric and hemic maturity. The planting material used primarily consists of the DxP Marihat variety, which was planted between 1995-2005, with an average potential fresh fruit bunch productivity of 29.00 tons/ha/year. Variations in nutrient contents in oil palm leaf were observed across each block of the study location. Diagnosis and recommendation integrated system (DRIS) analysis was conducted on found number 17 to determine the key nutrients required to increase oil palm productivity. This method consists of several stages, including norm analysis, DRIS index, nutrient balance index (NBI), optimum leaf nutrient value, and leaf nutrient interval. Data was obtained from 312 leaf nutrient analyses and fresh fruit bunch productivity across 39 blocks for the period between 2015 and 2022. A value of 26.33 tons/ha/year, derived from DRIS norm calculation, indicated the border between high and low productivity blocks. The results showed that the order of macronutrient and micronutrient requirements in high productivity blocks was N>P>K>Ca>Mg and B>Cu>Zn, while in low productivity blocks, it was Ca>Mg>N>K>P and B>Cu>Zn. Regression of DRIS index and leaf nutrient content obtained optimum nutrient values of 2.78%, 0.16%, 1.02%, 0.66%, 0.35%, 29.51 ppm, 3.65 ppm, and 15.37 ppm for N, P, K, Ca, Mg, B, Cu, and Zn, respectively. Therefore, nutrients Ca and B were prioritized to increase the achievement of oil palm fresh fruit bunch productivity.

Divvying up the pie: Tissue nutrient content is related to its parasite load.

The nutrient content of host resources can influence the abundance of parasites within an ecosystem, but linking specific nutrients in a host to the abundance of different parasite taxa remains a challenge. Here, we work to forge this link by quantifying the relationship between the nutrient content of specific infection sites and the abundance of multiple parasite taxa within the digestive tract of largemouth bass (Micropterus salmoides) collected from the Mississippi River. To generate a mechanistic understanding of these relationships, we tested four basic predictions: (1) the nutrient content of different host tissues (infection sites) varies within and across hosts, (2) the nutrient content of parasite genera differs from that of their host tissue(s), (3) the nutrient content of parasite genera differ from one another and (4) the nutrient content of host tissues is related to the nutrient content and abundance of parasite genera. We found support for each of these predictions. We found stoichiometric differences between the digestive tissues we examined. We also found that across hosts, intestine and pyloric caeca C:N ratios increased and %N decreased with fish condition factor. Both of the actively feeding parasitic genera we measured had lower C:N ratios compared to both their host tissue and other encysted/non-reproductive genera, suggesting the potential for N limitation of these parasites in the intestines or pyloric caeca of hosts. Consistent with this possibility, we found that the total number of actively feeding parasitic worms in the pyloric caeca increased with that tissue's N:P ratio (but was not related to host condition factor). Our results suggest that parasites encounter significant variation in nutrient content within and across hosts and that this variation may influence the abundance of actively feeding parasites. This work highlights the need for additional empirical comparisons of parasite stoichiometry across tissues and individual hosts.

Nutrient Digestibility of Non-conventional Protein Sources Blend in African Catfish, Clarias gariepinus (Burchell, 1822) Post Juveniles Using Novel Aquafeed Formulation Software

In this study, the growth performance, carcass composition, and apparent digestibility coefficient of African catfish, Clarias gariepinus, were evaluated in relation to different non-conventional protein sources blends diets that were formulated using a novel feed formulation software (FUTA AQUAFEED). Diet 1 served as the control diet, and the other four experimental diets (Diets 2 through 5) included non-conventional protein sources such blood meal, water hyacinth, palm kernel cake, palm beetle meal, blackfly meal, water fern, and Moringa. The gross composition of the experimental feeds exhibited notable variations in nutrient content. The crude protein content in the diets were iso-nitrogenous. Analysis of the composition of the carcass showed that diets varied significantly. Diet 5 had the highest fat content (10.66%), while Diet 3 had the highest crude protein amount (61.57%). Growth performance parameters such as initial and final weights, weight increase, feed conversion ratio (FCR), specific growth rate (SGR), and protein efficiency ratio (PER) exhibited diverse patterns. Diet 5 produced the greatest final weight (324.00 ± 122.94 g) and weight gain (173.32 ± 96.06 g), suggesting that the varied protein blend may have advantages. Dietary differences were seen in the apparent digestibility coefficients of crude protein and lipids. The crude protein digestibility coefficient (90.68%) was best in Diet 3, while the crude lipid digestibility coefficient (92.00%) was highest in Diet 1. In conclusion, the inclusion of unconventional protein sources in the diets of C. gariepinus affects both their growth performance and nutritional makeup. Through the incorporation of alternate protein sources into fish diets, the findings offer insights for improving aquaculture techniques and advancing sustainability.

A comparative analysis of the nutrient and phytochemical richness among different varieties of quinoa in China.

Quinoa is a nutrient-dense pseudocereal that has garnered global attention for its potential to bolster food security and nutrition. Despite its celebrated status, the detailed nutritional profiles of various quinoa varieties remain poorly understood, which poses a significant barrier to the strategic cultivation and utilization of quinoa's genetic diversity to combat malnutrition. The impetus for this research lies in the urgent need to identify superior quinoa strains that can be tailored to meet specific nutritional requirements and adapt to diverse agro-ecological zones. Our findings reveal substantial variation in nutrient content across different quinoa varieties, highlighting the variety ZLZX-8 as a particularly nutrient-rich strain with the highest levels of protein, fat, essential fatty acids, amino acids, and key minerals such as Mg, K, and Zn. Moreover, ZLZX-8's exceptional antioxidant capacity suggests it may have additional health benefits beyond its macronutrient profile. In contrast, ZLZX-7 stands out for its dietary fiber and phenolic content, which are critical for digestive health and disease prevention, respectively. Meanwhile, ZLZX-5, with its high starch content, could be better suited for energy production in dietary applications. Notably, the study also uncovers a correlation between grain color and nutrient profile, with colored quinoa varieties exhibiting superior fiber, inositol, phenolic content, and antioxidant activity compared to their white counterparts. This work lays the groundwork for an informed selection of quinoa varieties that can enhance dietary quality, support local and global food systems, and contribute to the fight against malnutrition.

Influence of seasons and fish body parts on fatty acid profile and effect of seasons on proximate composition of Anatolian khramulya (Capoeta tinca) and Colchic khramulya (Capoeta sieboldii) captured from the Çekerek Dam in Yozgat, Turkey

Seasonal variations in nutrient content and fatty acid (FA) composition within the dorsal, ventral, caudal and whole muscle tissues of Capoeta sieboldii and Capoeta tinca, which were captured from the Çekerek Dam in Yozgat, Turkey, were investigated. The nutrient and fatty acid compositions of C. sieboldii and C. tinca changed according to the seasons and different body regions. Proximate compositions in these two fish species were 15.78–18.38 % protein, 1.19–2.65 % lipid, 78.42–81.25 % moisture, and 1.02–1.20% ash. The highest levels of saturated FA (SFA) were recorded in both C. sieboldii (26.94 %) and C. tinca (28.32 %) in the autumn, specifically in the ventral region. The highest monounsaturated FA (MUFA) values of C. sieboldii and C. tinca were observed in spring in ventral (31.30 %) and caudal (31.89 %) regions, respectively. The highest polyunsaturated FA (PUFA) values were 30.90 % (ventral) in winter for C. sieboldii and 33.95 % (dorsal) in autumn for C. tinca. The atherogenic index, thrombogenic index, n–6/n–3 FA ratio, and hypocholesterolemic/hypercholesterolemic ratio of C. sieboldii and C. tinca in this study were 0.42–0.67, 0.24–0.37, 0.10–0.34, and 1.34–2.23, respectively. These fish species represent valuable food sources for human health and nutrition.

Synergistic roles of carbon dioxide nanobubbles and biochar for promoting direct CO2 assimilation by plants and optimizing nutrient uptake efficiency

This study investigates the synergistic role of carbon dioxide nanobubbles (CNBs) and biochar (BC) on seed germination, plant growth, and soil quality, employing Solanum lycopersicum (tomato) and Phaseolus vulgaris (beans) as test plant species. CNBs, generated and dispersed in both distilled water (DW) and tap water (TW), exhibited distinct characteristics, with TW-CNBs being larger and more stable (peak values of around 18.17 nm and 299.5 nm, zeta potential (ZP) of −5.91 mV), while DW-CNBs have peak values of around 1.63 nm and 216.1 nm, ZP of −3.23 mV. The results suggest CNBs enhance seed germination by upto 20%. CNBs in BC amended soil further promoted plant height and leaf number. CNBs increased dissolved CO2 levels to 2–24 ppm within 40 min, while BC enriched soil organic carbon from 19.20 to 24.96 ppm in beans and 18.33 to 22.35 ppm in tomatoes. The pH levels decreased from 7.68 to 3.78 for TW-CNBs and from 7.41 to 2.13 for DW-CNBs. Additionally, the electrical conductivity (EC) decreased from 112.1 to 99.6 for TW-CNBs, while it increased from 4.15 to 32.1 for DW-CNBs. Together they significantly increased soil available phosphorus and potassium to 4.03–8.06 and 3.58–7.16 kg ha−1; and 5.67–55.74 and 17.57–43.79 kg ha−1 in bean and tomato, respectively. Variations in nutrient concentrations were observed, with substantial increase in Na (16.27% and 6.58%), Zn (3.39% and 0.46%), and Mg (5.05% and 1.44%) content for beans and tomatoes, respectively. Structural equation model and principal component analysis revealed differences between CNB and BC treated soils, highlighting positive impact on soil quality and plant growth compared to control. Integration of CNBs and BC presents a multifaceted approach to enhance soil quality and promote plant growth, offering promising solutions for sustainable agriculture and environmental management.

Nanoplanktonic diatom rapidly alters sinking velocity via regulating lipid content and composition in response to changing nutrient concentrations

Diatom sinking plays a crucial role in the global carbon cycle, accounting for approximately 40% of marine particulate organic carbon export. While oceanic models typically represent diatoms as microphytoplankton (> 20 μm), it is important to recognize that many diatoms fall into the categories of nanophytoplankton (2-20 μm) and picophytoplankton (< 2 μm). These smaller diatoms have also been found to significantly contribute to carbon export. However, our understanding of their sinking behavior and buoyancy regulation mechanisms remains limited. In this study, we investigate the sinking behavior of a nanoplanktonic diatom, Phaeodactylum tricornutum (P. tricornutum), which exhibits rapid changes in sinking behavior in response to varying nutrient concentrations. Our results demonstrate that a higher sinking rate is observed under phosphate limitation and depletion. Notably, in phosphate depletion, the sinking rate of P. tricornutum was 0.79 ± 0.03 m d-1, nearly three times that of the previously reported sinking rates for Skeletonema costatum, Ditylum brightwellii, and Chaetoceros gracile. Furthermore, during the first 6 h of phosphate spike, the sinking rate of P. tricornutum remained consistently high. After 12 h of phosphate spike, the sinking rate decreased to match that of the phosphate repletion phase, only to increase again over the next 12 hours due to phosphate depletion. This rapid sinking behavior contributes to carbon export and potentially allows diatoms to exploit nutrient-rich patches when encountering increased nutrient concentrations. We also observed a significant positive correlation (P< 0.001) between sinking rate and lipid content (R = 0.91) during the phosphate depletion and spike experiment. It appears that P. tricornutum regulates its sinking rate by increasing intracellular lipid content, particularly digalactosyldiacylglycerol, hexosyl ceramide, monogalactosyldiacylglycerol, and triglycerides. Additionally, P. tricornutum replaces phospholipids with more dense membrane sulfolipids, such as sulfoquinovosyldiacylglycerol under phosphate shortage. These findings shed light on the intricate relationship between nutrient availability, sinking behavior, and lipid composition in diatoms, providing insights into their adaptive strategies for carbon export and nutrient utilization.

Fodder beet: know what you are feeding for a nutritionally balanced diet for dairy cattle

Fodder beet’s (FB) high soluble sugar and low crude protein content provide environmental benefits but also nutritional challenges, making it a unique crop in New Zealand dairy systems. Knowledge of dietary nutrient content is important to inform both mineralsupplementation and type of supplementary feed to offer. This will help ensure nutritional requirements for dairy cows are met, maximising the likelihood of positive outcomes for animal health and production. A database containing 694 samples of FB leaf andbulb tissue was compiled from monitor farm data, research projects, and cultivar evaluation trials with the objective of determining the variability in nutritional content. Descriptive statistics were used to highlight the range and variability in FB leaf and bulb nutritional composition between regions and cultivars. Our results reinforce that FB bulbs (which usually make up 70- 90% of the crop DM) are typically low in crude protein, fibre, phosphorus, calcium, and sulphur, but are high in soluble sugars. The variation in nutrient content between cultivars, and within cultivars both between and within regions shown in this study highlights the importance of paddock-specific feed analyses, and the limitations of textbook values, particularly whole crop values which do not differentiate between bulb and the more nutritionally valuable leaf.

Soil nutrient levels regulate the effect of soil microplastic contamination on microbial element metabolism and carbon use efficiency

Microplastics (MPs) are emerging environmental contaminants in soil ecosystems that disrupt the soil carbon (C) pool. Therefore, the response of microbial metabolism to MP-contaminated soil is crucial for soil-C stabilization. We undertook factorial experiments in a greenhouse with three types of soil microplastics with three levels of soil nutrients and undertook soil physiochemical analyses after 60 days. The present study revealed how the presence of degradable polylactic acid (PLA) and non-degradable polyethylene (PE) MPs affects soil microbial nutrient limitation and C use efficiency (CUE) at varying nutrient concentrations. The presence of PLA in soil with low nutrient levels led to a significant increase (29%) in the activities of nitrogen (N)-acquiring enzymes. In contrast, the presence of MPs had no effect on C- and N-acquiring enzymes. The occurrence of PE caused a 41% reduction in microbial C limitation in high-nutrient soils, and microbial nutrient metabolism was limited by the occurrence of MPs in soils amended with nutrients. A strong positive correlation between microbial C and nutrient limitation in the soil indicates that addressing C limitation followed by amendment of soil with MPs could potentially intensify microbial N limitation in soils with varying nutrients. In comparison, the microbial CUE increased by 10% with the application of degradable MPs (PLA) to soils with a low nutrient status. These findings highlight the significant influence of both degradable PLA and non-degradable PE MPs on soil microbial processes and C dynamics. In conclusion, PLA enhances metabolic efficiency in nutrient-rich soils, potentially aiding C utilization, whereas PE reduces microbial C limitation, offering promise for soil C sequestration strategies. Our findings underscore the importance of considering MPs in soil ecosystem studies and in broader sustainability efforts.

Nutrient retention in a small reservoir under changed variability of inflow nutrient concentration

ABSTRACT Within freshwater networks, lakes and reservoirs are reactors that modify nutrient dynamics. Their functioning is based on an interplay of hydrological and biogeochemical processes, rendering them vulnerable to climate change. Future changes in catchment characteristics are likely to alter the timing and magnitude of nutrient concentrations in discharge. This study investigated the impact of changing variability of nutrient concentrations on lake and reservoir dynamics. We examined intraannual nutrient retention and analyzed the role of reservoirs in reconfiguring the variability of nutrients. Utilizing the 1D lake model GOTM-WET, we simulated nutrient processing in a mesotrophic reservoir. Further, we performed scenario simulations by modifying the variability of inflow nitrogen and phosphorus concentrations. Our findings indicate that the reservoir removed ∼4% and ∼12% of total nitrogen (TN) and total phosphorus (TP), respectively. Particulate fractions were retained efficiently, but there was a net export of dissolved organic fractions. Regarding mixing and stratification periods, however, we observed net nitrogen export during stratification in certain years. During stratification, outflow concentration variability remained relatively unchanged for TN and TP compared to inflow concentrations. Conversely, phosphate and nitrate concentration variability increased in the outflow because of in-lake assimilation and the influence of hydrological events. With increasing inflow concentration variability during stratification, there was decreased removal of TN and TP by the reservoir, but increased variability of concentration. By evaluating the lake's capacity to attenuate variability of nutrient inflows under altered conditions, there are opportunities to improve monitoring of nutrient export and evaluate the potential impact of nutrient peaks on downstream drinking water resources and ecosystems.

Interkingdom network analyses reveal microalgae and protostomes as keystone taxa involved in nutrient cycling in large freshwater lake sediment.

Few studies have explored the role of interkingdom interactions between bacteria and microeukaryotes in nutrient cycling in lake ecosystems. We conducted sediment sampling from 40 locations covering Hongze Lake and analyzed their chemical properties. Intra- and interkingdom networks were constructed using 16S and 18S rRNA gene amplicon sequencing. Microeukaryotic intranetworks were more complex in spring than in autumn, while no clear variation in the complexity of bacterial intranetworks was found between autumn and spring. Larger and more complex bacterial-microeukaryotic bipartite networks emerged in spring than in autumn, correlated with lower carbon, nitrogen, and phosphorus levels in spring, likely resulting in intense microbial competition. Bacteria and microeukaryotes played different topological roles in interkingdom networks, with microeukaryotes contributing to the networks' greater complexity. Seven keystone modules were identified in spring and autumn nutrient cycling. Importantly, keystone taxa in these modules belonged to photoautotrophic microalgae or predatory protostomes, indicating that these organisms are key drivers in lake sediment nutrient cycling. Our results suggested that nutrient content variation in autumn and spring changes interkingdom networks' topological structure between bacteria and microeukaryotes. Microalgae and protostomes are essential in freshwater lake nutrient cycling and may be targeted to modulate nutrient cycling in large freshwater ecosystems.

Nutrient condition modulates the antibiotic tolerance of Pseudomonas aeruginosa

The variation in nutrient content across diverse environments has a significant impact on the survival and metabolism of microorganisms. In this study, we examined the influence of nutrients on the antibiotic tolerance of the PAO1 strain of Pseudomonas aeruginosa. Our findings indicate that under nutrient-rich conditions, this strain exhibited relatively high tolerance to ceftazidime, chloramphenicol, and tetracycline, but not aminoglycosides and fluoroquinolones. Transcriptome analysis revealed that genes associated with antibiotic tolerance were expressed more efficiently in nutrient-rich media, including ribosomal protein genes and multidrug efflux pump genes, which conferred higher tetracycline tolerance to the strain. Furthermore, the genes responsible for translation, biosynthesis, and oxidative phosphorylation were suppressed when nutrients were limited, resulting in decreased metabolic activity and lower sensitivity to ciprofloxacin. Artificial interference with ATP synthesis utilizing arsenate confirmed that the curtailment of energy provision bolstered the observed tolerance to ciprofloxacin. In general, our results indicate that this strain of P. aeruginosa tends to activate its intrinsic resistance mechanisms in nutrient-rich environments, thereby enhancing resistance to certain antibiotics. Conversely, in nutrient-limited environments, the strain is more likely to enter a dormant state, which enables it to tolerate antibiotics to which it would otherwise be sensitive. These findings further suggest that antibiotics released in environments with varying eutrophication levels may have divergent effects on the development of bacterial antibiotic resistance.

Concentrations of macro and microelement in Brazilian white cheeses: Evaluating sample preparation procedures and estimation of dietary intake

Two sample preparation procedures, microwave-assisted and closed digestion block, were developed to establish the nutritional content of white cheeses. A two-level full factorial design was performed to optimize the decomposition parameters. Under optimum conditions, both procedures led to low dissolved carbon content (< 11% w.w-1) employing 2 mol. L-1 HNO3. Nevertheless, the closed block presented smaller analytical throughput with approximately 11 digested samples h-1 against 20 samples h-1 for MW. Both procedures showed accuracy for Ca, K, P, Na, and Zn and precision with RSD < 10%. The limits of detection ranged from 2.2 (P) to 16 μg g-1 (Ca) (microwave) and 0.8 (K) to 14 μg g-1 (Na) (closed block). The validated procedures were employed to analyze buffalo mozzarella, minas frescal, Ricotta, Coalho, and cottage cheeses. Based on the nutritional analysis, the type of cheese influenced the variation in nutrient content. Furthermore, for all types of cheese, a discrepancy (p < 0.05) was observed between concentrations for at least one analyte, confirming the lack of uniformity in nutritional composition. The recommended daily intake evaluation demonstrated that all samples of buffalo mozzarella and minas frescal cheese analyzed could be considered sources of Ca and P.

Nutrient transport in surface runoff and sediment yield on macroplots and zero-order catchments under no-tillage

No-till farming is widely used in grain production in Brazil. However, the lack of runoff control and the low phytomass input are major causes of soil degradation. In addition, surface runoff transports chemical elements, including carbon and nutrients, in dissolved and particulate forms impacting water quality. Given this scenario, this study sought to evaluate the influence of phytomass amount, chiseling, and terracing on nutrient loss (NH4+, NO3− + NO2−, total N, P, K, Ca, Mg, Cu, and Zn) associated with surface runoff, suspended sediments, and to quantify their presence in sediment deposits at the end of the monitoring unit. This study was based on hydrological monitoring in four macroplots and two paired zero-order catchments during rainfall events. The macroplots reproduce use or absence of chiseling with lower or higher phytomass input, and the catchments, presence or absence of terraces. Nutrient concentrations were determined in surface runoff and sediment. In surface runoff, the highest median values of NH4+, NO3− + NO2−, total N, P, K, Ca, Mg, Cu and Zn concentrations in the catchments were 0.9,1.0, 1.5, 0.1, 3.1, 3.9, 1.1, 0.0, and 0.01 mg/L, and in the macroplots 1.0, 1.2, 2.1, 0.2, 3.4, 5.3, 1.7, 0.0, and 0.02 mg/L. In the suspended sediments, the highest median values of P, K, Ca, and Mg concentrations in suspended sediment in the catchments were 0.6, 6.7, 3.4, and 0.8 g kg−1 and in the macroplots 0.6, 6.1, 1.9 and 0.7 g kg−1. Our findings revealed a wide variation in nutrient concentrations in runoff and sediments regardless of the management practices. Nevertheless, the dissolved fraction of surface runoff controls the loss of nutrients during high-magnitude rainfall events. The effects of the increased phytomass and the presence of terraces, affect nutrient losses due to runoff control.

Seasonal and vertical variations of nutrient cycling in the world’s deepest blue hole

Nutrient cycling in anoxic seawaters is essential to marine ecosystem health and sustainability, yet it remains poorly understood. In this work, we analyzed dissolved inorganic nutrients as well as hydrochemical parameters in the Yongle Blue Hole (YBH) of the South China Sea in October 2019, which is the world’s deepest blue hole and is characterized by anoxia below the depth of 100 m. Nutrient data collected in two sampling campaigns in 2017 were also incorporated to examine the seasonal and vertical variations of nutrient cycling across steep redox gradients in the YBH. In response to the changes in redox conditions in different seasons, nutrients in the YBH showed significant seasonal variations. The nitrate maximum rose from a depth of 90 m in March 2017 to 60-80 m in October 2019, while the primary nitrite maximum concentration decreased from 0.5 μmol/L to 0.1 μmol/L. In October 2019, the nitrite decreased to below the detection limit at about 100 m, while in March 2017, it was 140 m. The regeneration of phosphate and silicate both started from around 40 m in October 2019 and from 80 m in March 2017. Silicate shows non-conservative adding behaviors relative to phosphate and DIN, and phosphate shows a similar but weaker adding behavior relative to DIN. The nutrient ratios also varied seasonally, especially for N/P, which fluctuated greatly on the surface at 80 m, while Si/N and Si/P fluctuated above 50 m. At the oxic-anoxic interface, extreme values of nutrient ratios were observed, and below 150 m, the N/P, Si/N, and Si/P were kept constant at about 17, 1.5, and 26, respectively. Seasonal and vertical variations of nutrient concentrations and ratios in the YBH reflect the impact of redox conditions on nutrient cycling in anoxic seawaters, especially during the transition from oxic to anoxic zone. And the high-resolution distributions of nutrients and hydrochemical parameters are helpful to better understand the nutrient cycling processes in highly dynamic coastal environments that are suffering deoxygenation.

Effects of rainfall and land use on nutrient responses in rivers in the Brazilian semiarid region.

This paper investigated whether rainfall promotes dilution or increase in nutrient concentrations and which land use indicators are the main predictors of nutrients in intermittent rivers in a large Brazilian semiarid region. The total phosphorus (TP) and total inorganic nitrogen (TIN) were monitored between 2013 and 2018 at 92 river water quality monitoring sites. The monthly rainfall (Rn) was obtained from 575 rain gauges. Pearson's correlation (R) between Rn and nutrient concentration was performed. The correlation patterns were also analysed based on land use data: urban area (%), agricultural field area (%), demographic density (inhabitants/km2), sewer system coverage (%), and reservoir density (reservoir/km2). Backward stepwise regression was performed to identify predictors of nutrient concentrations. The results revealed a marginal effect of rainfall on nutrients when the effects of urbanisation outweigh all other aspects. However, in regions with greater accumulated rainfall and lower reservoir density, the rainfall was related to a linear increase in nutrient concentrations (R > 0.8). Contrastingly, in the basins with less accumulated rainfall and greater inter-basin hydrological disconnection, there was a linear reduction in nutrient concentration (R < - 0.5). In the backward stepwise regression, sewer system coverage and Rn had the greatest influence for TP, and the urban area was the strongest predictor for TIN. Importantly, our results demonstrated that in semiarid rivers in densely populated regions, there is no single pattern of variability in nutrient concentration, on a wide scale of assessment. Therefore, adaptative and decentralised management can be more effective in improving water quality in these regions.

Potentials of baobab in food systems

The current study aims to review the prospects for baobab domestication and cultivation, nutrient variability, food applications, industrial value and future potentials of the African baobab. The variations in nutrient content of baobab as seen in several studies could have arisen from differences in provenance the sample was obtained, age of the parent plant, as well as differences in soil and climate. Regardless, baobab is a rich source of nutrients, bioactives and functional polysaccharides, representing a huge market potential for food industries. It has garnered widespread interest as a functional ingredient for preventive health care and disease management. Due to approvals given by the United States Food and Drug Administration (FDA) and the European Commission (EC), baobab fruit pulp has gained widespread popularity as a novel food ingredient. In addition, baobab fruit pulp offered as a dietary supplement has been used in its naturally dehydrated form or processed into pills. There are huge information gaps on processing and safety of baobab seed oil, use of baobab seeds and leaf powder - a rich source of mucilage, in food systems. An industrially significant product from baobab are the functional polysaccharides which are a rapidly advancing application. Baobab plant parts, fruit pulp, kernels, whole seeds, funicles, leaves, empty fruit shells and roots all inclusive, are of significant value for their key role in nutrition and health, food security and economic welfare of the rural communities in regions where the trees are originally found. Both traditional and novel applications of the various parts of the baobab tree have been explored in this paper. These include use in edible products like gruels, jams, yoghurt, wines, juice etc. Application of extrusion processing as an economical means of value addition to baobab commodities has been reviewed, especially relating to the classification of baobab as a neglected and underutilized species (NUS).

Geochemical responses of scleractinian corals to nutrient stress

The impact of changing nutrient conditions on scleractinian coral-based geochemical proxies is poorly understood, despite the nutrient balance in many coral reefs being disturbed by anthropogenic activity. Here, the geochemical responses of tropical corals Acropora polystoma and Porites lichen to nutrient enrichment and depletion are examined following growth under cultured conditions, to assess the impact of nutrients on traditional geochemical proxies for both temperature and the coral internal carbonate system. The corals were exposed to four different nutrient treatments over a period of 140 days: (1) a replete treatment with optimal levels of nitrate (∼4.5 μM) and phosphate (∼0.6 μM), (2) a nutrient depleted treatment with negligible nitrate and phosphate, (3) a treatment with high nitrate (∼73 μM) and negligible phosphate, and (4) a treatment with high phosphate (∼5.7 μM) and negligible nitrate. Results suggest nutrients play a hitherto under-appreciated role in coral skeleton elemental (Li/Ca, B/Ca, Mg/Ca, Sr/Ca, Li/Mg) and isotopic (δ11B) composition, with the internal carbonate chemistry also impacted. For example, Mg/Ca and Sr/Ca are lower, and Li/Mg higher, in the nutrient imbalanced and deplete treatments compared to the replete treatment for both species. Disruption to the carbonate system in corals cultured under imbalanced nutrient conditions is best explained by a decrease in dissolved inorganic carbon flux to the extracellular calcifying medium. Variations in nutrient concentration — or nutrient imbalance — can have dramatic consequences on both reconstructed sea surface temperatures and ocean or calcification pH, with reconstructed temperatures varying from −7°C to +52 °C, and δ11B-derived pH by up to 0.13 pH units. The impact from anthropogenically-induced nutrient disturbances should therefore be considered when generating temporal records of environments using coral skeletal archives.