Authigenic Phosphorus Research Articles

The formation of authigenic phosphorus minerals in cold-seep sediments from the South China Sea: Implications for carbon cycling below the sulfate-methane transition

The formation of authigenic phosphorus (P) minerals near the sulfate-methane transition (SMT) represents an important pathway of P burial in marine sediments. However, our current understanding of the coupling between the formation of authigenic phosphate and carbon and iron (Fe) cycling is insufficient. In this study, a piston core recovered from the Haima cold seeps of the Qiongdongnan basin, northern South China Sea, was used to analyze pore-water parameters and solid-phase Fe and P speciation. Results from a previous study indicate that the current SMT is located at approximately 1 m below the seafloor (mbsf) and a fossil SMT located at approximately 6.5 mbsf. Dissolved phosphate concentrations and solid-phase iron oxide (FeOx) contents are found to decrease with depth, while Fe-bound P (PFe) and authigenic phosphate (PAuth) contents increase with depth in the zone between the current and fossil SMTs where gas hydrate is present, suggesting that vivianite and authigenic apatite formed in this zone. Gas hydrate below the current SMT will dissociate once methane is undersaturated, which could persistently provide dissolved methane to prevent the downward shift of the current SMT where methane is continually consumed. Such a methane-rich environment maintained by gas hydrate may favor the persistent reduction of FeOx and the formation of vivianite. Dissolved phosphate concentrations are high, but decrease rapidly with depth at the fossil SMT. Combined with higher FeOx and PAuth contents and lower PFe contents and lower POrg/total organic carbon (TOC) ratios, these results suggest the formation of authigenic apatite at the fossil SMT. The high dissolved phosphate concentration and low POrg/TOC ratios at the fossil SMT are interpreted to reflect preferential release of P during the degradation of organic matter generated by methanotrophic microorganisms. Overall, our study shows that P speciation in methane-rich sediments provides insight into the formation processes of authigenic P minerals near the SMT and associated carbon and Fe cycling processes.

Isotopic and hydrogeochemical tracking of dissolved nutrient dynamics in the Brahmaputra River System: A source delineation perspective

The Brahmaputra river system (BRS) produces the largest discharge in India, supplying water to more than 62 million inhabitants. The present study aims to quantify the environmental elements that affect the spatio-temporal variation of nutrients in the Brahmaputra river system (BRS). The association of physico-chemical characteristics of floodplain sediments with the distribution pattern of P during wet and dry periods in different depths were also studied. The seasonal variation suggest that the average dissolved inorganic nitrogen and dissolve inorganic phosphorus are found higher in monsoon while the average dissolve silica were higher in post-monsoon. The spatial variation of dissolve inorganic phosphate and nitrate concentration suggests both the nutrient are higher in upstream sites. The DiS concentrations tended to be higher in downstream. In 70% of the sampled tributaries, the average molar ratio for dissolved inorganic nitrogen/dissolved inorganic phosphorous (DIN/DIP) was greater than 16:1, which indicates phosphate limited biological productivity. In contrast, an average molar ratio of dissolved inorganic silica/DIN (DSi/DIN) of 3.8 ± 3.0 favoured diatom growth in those tributaries where DSi/DIN molar ratio was lower than 1, indicating eutrophication. The BRS transported 24.7, 5.93, and 312 × 104 tons/year−1 of DIN, PO4–P and SiO2–Si, respectively. The depth-wise variation of P-fraction during monsoon suggests that the authigenic phosphorus was most abundant followed by Fe-bound, exchangeable, detrital and organic. In the post-monsoon, Fe-bound P was found at a higher concentration followed by authigenic phosphorus. High nutrient concentrations with more δ18O depleted water implied precipitation being the major source of nutrients in the BRS.

Recycling of internal phosphorus during cyanobacterial growth and decline in a eutrophic lake in China indicated by phosphate oxygen isotopes

Understanding phosphorus recycling in eutrophic lakes is the basis for pollution control. In this study, we analyzed phosphorus fractions, phosphate oxygen isotopes (δ18Op) in iron-bound phosphorus (Fe–P), authigenic phosphorus (Auth-P), detrital phosphorus (Detr-P), and physicochemical indexes at the water–sediment interface to study the recycling of internal phosphorus during the annual cyanobacterial life stage in a eutrophic lake, Lake Chaohu, China. Increased Fe–P in sediments from the cyanobacterial decline to the benthic stage indicated the deposition of newly formed iron-bound phosphorus and the enriched δ18OFe–P indicated that these phosphates were absorbed to ferric oxides derived directly from the cyanobacterial cells (enriched δ18Op). From benthic to the initial growth stage, depletion of δ18OFe–P indicated that these phosphates were derived mainly from the hydrolysis of organic phosphorus (depleted δ18Op). Increased Fe–P in sediments from the initial growth stage to algal blooms indicated a net deposition of phosphorus, and the depletion of δ18OFe–P indicated similar phosphates from the hydrolysis of organic phosphorus. From benthic to the blooms stage, enrichment of δ18OAuth-P suggested phosphates from cyanobacterial remains or transformation of bioavailable phosphorus. Stable Detr-P and δ18ODetr-P in sediments during the cyanobacterial life stage indicated the resistance of Detr-P to biogeochemical alteration. Spatially, δ18OFe–P was more depleted in the western lake than in the middle and eastern lakes, likely due to its high level of Fe–P from domestic sewage, with newly formed Fe–P (enriched δ18OFe–P) only contributing minor proportions. The δ18OAuth-P in the eastern lake was depleted, indicating that the hydrolysis of organic phosphorus served as a phosphate source. Enriched δ18ODetr-P indicated that more phosphates from domestic sewage (enriched δ18Op) contributed to the formation of Detr-P in West Lake Chaohu. The present study provides novel insight into the recycling of internal phosphorus in eutrophic lakes.

Spatial–Temporal Distribution of Phosphorus Fractions and Their Relationship in Water–Sediment Phases in the Tuojiang River, China

Understanding the distribution and transportation of phosphorus is vital for the sustainable development of aquatic environmental protection and ecological security. The spatial–temporal distribution of phosphorus fractions in water–sediment phases in river systems and their relationships remain unclear in Southwest China. In this study, the spatial and temporal distribution of phosphorus fractions in water–sediment phases in the Tuojiang River, a primary tributary of the Yangtze River which plays important roles in the economy and ecology of the region, and the relationships among the different phosphorus fractions were analyzed. These fractions were soluble reactive phosphorus (SRP), dissolved organic phosphorus (DOP), and total particulate phosphorus (PP) fractions in water, and exchangeable phosphorus (Ex-P), organic phosphorus (Or-P), phosphorus bound by Fe oxides (Fe-P), authigenic phosphorus (Ca-P), detrital phosphorus (De-P), and refractory phosphorus (Res-P) fractions in sediment. The SPR and Fe-P were the dominant phosphorus fractions in the water and sediment, respectively. The TP content was greater in the lower reaches than in the middle and upper reaches. The average abundances of most phosphorus fractions in water–sediment phases showed significant seasonal variations. The Fe-P, Org-P, and TP in sediments were released to the water interface, resulting in the increase of phosphorus in the overlying water. Redundancy analysis (RDA) indicated that the physicochemical properties of water and sediment have a certain influence on the spatial–temporal distribution of the phosphorus fractions. Principal component analysis (PCA) revealed that the main phosphorus source was anthropogenic activities. These results provide primary data regarding phosphorus fractions and contribute to understanding phosphorus cycling and controlling phosphorus pollution in the Tuojiang River.

Phosphorus cycling in freshwater lake sediments: Influence of seasonal water level fluctuations

Freshwater lakes experience drastic water level fluctuations because of climate change and human activities. However, the influence of such fluctuations on phosphorus cycling in sediments has rarely been investigated. We conducted a geochemical investigation on the phosphorus cycle in a shallow freshwater lake, Dongting Lake; under the influence of human activities and climate change, its water regime undergoes drastic changes. Irrespective of the permanent inundation zone (PIZ) or seasonal inundation zone (SIZ), the phosphorus cycle in sediments was found to be dominated by the reductive dissolution of iron (Fe) (oxyhydr)oxides, degradation of organic matters, and conversion between authigenic phosphorus (Ca-P) and detrital phosphorus in individual seasons. From winter to summer, with increasing water level, the content of Fe-bound phosphorus and organic phosphorus increase due to the deposition of suspended matter, thus increasing total phosphorus in PIZ. Moreover, the rising water level also reduces the dissolved oxygen content and promotes the reductive dissolution of Fe (oxyhydr)oxides. The mineralization of increased organic matter can release CO2 and reduce pH in the vicinity, which can further result in the acidic dissolution of detrital apatite. In turn, most of the released phosphorus can be adsorbed or co-precipitated with calcium minerals, resulting in the significant increase of Ca-P. The mechanisms of phosphorus transformation in SIZ are similar to those in PIZ, but most of the increased organic matter and total P in a core from SIZ are attributable to the decomposition of plant matter. Therefore, the water level rise not only changes the conservative speciation of phosphorus in sediments to active speciation, but also triggers the release of phosphorus adsorbed to oxides and further increases the risk of phosphorus release from sediments to overlying water. Thus, our findings have major implications for freshwater shallow lakes and their P-driven productivity.

Distribution and speciation of phosphorus in surface sediments of the intertidal zone in the Yellow River Delta

For better understanding the phosphorus (P) cycle, it is essential to distinguish the contents of different P speciation in sediments. In the study, the content of total phosphorus (TP) in the sediments ranged from 88.80 to 227.56 μg·g-1, with an average of 138.42 μg·g-1. The content of inorganic phosphorus (IP) ranged from 84.21 to 224.26 μg·g-1, accounting for 88.74%-98.55% of the TP content, which was the main occurrence form in the intertidal sediments of the Yellow River Delta. the contents of phosphorus fractions in surface sediments were 37.06 to 106.35 μg·g-1 for detrital phosphorus (De-P), 2.99 to 34.39 μg·g-1 for exchangeable phosphorus (Ex-P), 5.27-106.06 μg·g-1 for iron bound phosphorus (Fe-P). On the whole, the existing forms of inorganic phosphorus could be ranked as follows: De-P > Fe-P > Ex-P > authigenic phosphorus (Au-P). The regression analysis between TOC content and various forms of phosphorus showed that TOC content was negatively correlated with De-P.

Distribution of Phosphorus Fractions in Surface Sediments of Minjiang Mainstreams

In recent years, the total phosphorus pollution in Minjiang River was serious, and the surface sediments of the Minjiang River also threatened water quality. To study the spatial distributions of phosphorus in the surface sediments of the Minjiang River, samples of surface sediments were collected upstream (Aba District) and downstream (Yibin District) of the Minjiang River in December, 2016. The sediments were analyzed with the modified sequential extraction method (SEDEX) to obtain six forms of phosphorus, including exchangeable phosphorus (Ex-P), exchangeable organic phosphorus (Org-P), iron-bound phosphorus (Fe-P), authigenic phosphorus (Ca-P), detrital phosphorus (De-P), and refractory phosphorus (Res-P). The results indicated that the contents of total phosphorus (TP) in surface sediments ranged from 522.17 μg ·g-1 to 979.22 μg ·g-1, which were far more than the soil phosphorus background values (700 μg ·g-1). The spatial distribution characteristics of the TP of surface sediments indicated that the TP concentrations in sediments at the Meishan sections (the middle reach of the Minjiang River) were higher than those in the other sections. This was related to the smaller particle size and higher OM contents in sediments in the Meishan sections. The main phosphorus forms in the sediments in the Minjiang River were Ca-P and De-P, with their concentrations accounting for 75% of TP in the sediments. The bio-available phosphorus, which included Ex-P, Org-P, and Fe-P, accounted for 0.31%-29.62% of TP in the sediments of the Minjiang River. The concentrations of bio-available phosphorus in sediments at the Meishan sections and Leshan sections (the middle reach) were highest, indicating that bio-available phosphorus in the surface sediments was high, and its potential environmental impact risks were higher.

Bioavailability and geochemical speciation of phosphorus in surface sediments of the Southern Caspian Sea

The purpose of this study was to quantify phosphorus bioavailability and various forms of this element in surface sediments of the southern Caspian Sea. To do, sediment samples were collected from different depths in autumn 2015 using a Van Veen Grab. Phosphorus forms were recognized by a sequential extraction procedure (SEDEX). Results revealed that the range of total phosphorus (TP) was between 431ppm and 594ppm with a mean value of 535.25±45.05ppm. Organic phosphorus (OP) ranged from 62 to 99ppm and contributed 14.85±2.21% of total phosphorus in average. The contents of loosely phosphorus, iron-bound phosphorus, authigenic phosphorus and detrital phosphorus varied 35–55ppm, 50–94ppm, 125–189ppm and 152–217ppm, respectively. Generally, inorganic phosphorus (IP) was between 365 and 522ppm which comprised 81.9–88.53% of total phosphorus. Findings showed levels of different phosphorus forms in a descending order: detrital P>Authigenic P>Organic P>Fe-P>Loosely P. Bioavailable phosphorus concentration was between 153ppm and 240ppm and consisted 37.21±3% of total phosphorus. Based on molar ratio of TOC/OP, organic matter obtained from the studied stations suggested a terrestrial origin.

Evolution of the global phosphorus cycle.

The macronutrient phosphorus is thought to limit primary productivity in the oceans on geological timescales. Although there has been a sustained effort to reconstruct the dynamics of the phosphorus cycle over the past 3.5 billion years, it remains uncertain whether phosphorus limitation persisted throughout Earth's history and therefore whether the phosphorus cycle has consistently modulated biospheric productivity and ocean-atmosphere oxygen levels over time. Here we present a compilation of phosphorus abundances in marine sedimentary rocks spanning the past 3.5 billion years. We find evidence for relatively low authigenic phosphorus burial in shallow marine environments until about 800 to 700 million years ago. Our interpretation of the database leads us to propose that limited marginal phosphorus burial before that time was linked to phosphorus biolimitation, resulting in elemental stoichiometries in primary producers that diverged strongly from the Redfield ratio (the atomic ratio of carbon, nitrogen and phosphorus found in phytoplankton). We place our phosphorus record in a quantitative biogeochemical model framework and find that a combination of enhanced phosphorus scavenging in anoxic, iron-rich oceans and a nutrient-based bistability in atmospheric oxygen levels could have resulted in a stable low-oxygen world. The combination of these factors may explain the protracted oxygenation of Earth's surface over the last 3.5 billion years of Earth history. However, our analysis also suggests that a fundamental shift in the phosphorus cycle may have occurred during the late Proterozoic eon (between 800 and 635 million years ago), coincident with a previously inferred shift in marine redox states, severe perturbations to Earth's climate system, and the emergence of animals.

Particle-size distribution and phosphorus forms as a function of hydrological forcing in the Yellow River

Samples were collected monthly from January to December in 2010, and daily observations were made during the water-sediment regulation event in June-July 2010. Sequential extractions were applied to determine the forms of P in different particle-size fractions and to assess the potential bioavailability of particulate phosphorus (PP). The results indicated that exchangeable phosphorus, organic phosphorus, authigenic phosphorus, and refractory phosphorus increased with the decreasing of particulate size; conversely, detrital phosphorus decreased with the decreasing of particulate size. The content of bioavailable particulate phosphorus (BAPP) varied greatly in different sizes of particles. In general, the smaller the particle size, the higher the content of bioavailable phosphorus and its proportion in total phosphorous was found in these particles. Hydrological forcing controlled the variability in the major P phases found in the suspended sediments via changes in the sources and the particle grain-size distribution. The variation of particle sizes can be attributed also to different total suspended sediment (TSS) sources. Water-sediment regulation (WSR) mobilized only particulate matter from the riverbed, while during the rainstorm soil erosion and runoff were the main source. The BAPP fluxes associated with the "truly suspended" fraction was approximately 200 times larger than the dissolved inorganic phosphorus (DIP) flux. Thus, the transfer of fine particles to the open sea is most probably accompanied by BAPP release to the DIP and can support greater primary and secondary production.

Vivianite is a major sink for phosphorus in methanogenic coastal surface sediments

Studies of authigenic phosphorus (P) minerals in marine sediments typically focus on authigenic carbonate fluorapatite, which is considered to be the major sink for P in marine sediments and can easily be semi-quantitatively extracted with the SEDEX sequential extraction method. The role of other potentially important authigenic P phases, such as the reduced iron (Fe) phosphate mineral vivianite (Fe(II)3(PO4)*8H2O) has so far largely been ignored in marine systems. This is, in part, likely due to the fact that the SEDEX method does not distinguish between vivianite and P associated with Fe-oxides. Here, we show that vivianite can be quantified in marine sediments by combining the SEDEX method with microscopic and spectroscopic techniques such as micro X-ray fluorescence (μXRF) elemental mapping of resin-embedded sediments, as well as scanning electron microscope–energy dispersive spectroscopy (SEM–EDS) and powder X-ray diffraction (XRD). We further demonstrate that resin embedding of vertically intact sediment sub-cores enables the use of synchrotron-based microanalysis (X-ray absorption near-edge structure (XANES) spectroscopy) to differentiate between different P burial phases in aquatic sediments. Our results reveal that vivianite represents a major burial sink for P below a shallow sulfate/methane transition zone in Bothnian Sea sediments, accounting for 40–50% of total P burial. We further show that anaerobic oxidation of methane (AOM) drives a sink-switching from Fe-oxide bound P to vivianite by driving the release of both phosphate (AOM with sulfate and Fe-oxides) and ferrous Fe (AOM with Fe-oxides) to the pore water allowing supersaturation with respect to vivianite to be reached. The vivianite in the sediment contains significant amounts of manganese (∼4–8wt.%), similar to vivianite obtained from freshwater sediments. Our results indicate that methane dynamics play a key role in providing conditions that allow for vivianite authigenesis in coastal surface sediments. We suggest that vivianite may act as an important burial sink for P in brackish coastal environments worldwide.

Study on different forms and phosphorus distribution in the coastal surface sediments of Southern Caspian Sea by using UV–Vis spectrophotometery

This paper presents distribution of phosphorus (total P, organic and inorganic P) in the southern of Caspian Sea sediments where collected from four sampling stations in the summer 2009. Several forms of the phosphorus in sediment were separated and extracted according to sequential extraction method. Then extracted phosphorus in each fraction was determined by UV–Vis spectrophotometery. Five forms of phosphorus were studied (i) loosely sorbed phosphorus, (ii) ferric-iron-bound phosphorus, (iii) authigenic phosphorus, (iv) detrital phosphorus, and (v) organic phosphorus. The total P contents were ranged from 124.5 to 328.2μgg−1. It was found that more than 98% of the total P is inorganic phosphorus (IP). Among the four forms of IP, loosely bound P, P–Fe, P–detrital and P–authigenic distribution ranges were 2.70–17.31%, 10.00–44.79%, 0.40–1.70% and 48.35–83.48%, respectively. Result also showed that the most abundant forms of phosphorus were authigenic phosphorus. Relative abundances of other forms of phosphorus follow the order: P–Fe>loosely bound-P>organic P>detrital P.

Strong gradient of benthic biogeochemical processes along a macrotidal temperate estuary: focus on P and Si cycles

This study aims to investigate the role of spatial and temporal physical, biological and biogeochemical gradients on sediment biogeochemistry along a macrotidal and Si-rich estuary. Scanning and biogeochemical analyses were performed in the inner, mid and outer Aulne Estuary (France) at four seasons. The inner estuary shows high diagenetic activity linked to fluid mud dynamics and river loads. The highest authigenic phosphorus (Aut-P) concentrations ever found in the literature are observed in the inner estuary (18 μmol g−1 PS sediment). This is explained by a combination of favorable factors, i.e. the high organic matter and nutrient loads, the reductive conditions, the freshwater properties (low pH, OH−, sulfate and Mg2+ concentrations), the increase of particle residence time by the upward convergence of particles due to residual currents, and allochthonous riverine Aut-P. We suggest that the high Si(OH)4 concentrations (>400 μM) may even increase Aut-P precipitation through the increase of Fe–P formation in these low salinity conditions. In the mid estuary, erosion–deposition dynamics dominate in point bars and lead to the succession of poor and rich organic and authigenic phosphorus layers, recording thus the seasonality of matter loads and its seasonal translocation from the inner estuary. In the outer estuary, deposition rates are high and constant and biogeochemical properties are characteristic of marine environments. The precipitation of Aut-P from free phosphate (PO4 3−) is lower than in the inner estuary and might be limited by higher Mg2+ concentrations in saline waters. This study highlights that small macrotidal estuaries, and especially their freshwater sediments, may constitute an important phosphorus sink through the precipitation of Aut-P. This precipitation could even be enhanced in fresh or brackish environments, thus increasing long term phosphorus storage and altering benthic fluxes of PO4 3− to the pelagic ecosystem.

Iron and manganese shuttles control the formation of authigenic phosphorus minerals in the euxinic basins of the Baltic Sea

Microanalysis of epoxy resin-embedded sediments is used to demonstrate the presence of authigenic iron (Fe) (II) phosphates and manganese (Mn)-calcium (Ca)-carbonate-phosphates in the deep euxinic basins of the Baltic Sea. These minerals constitute major burial phases of phosphorus (P) in this area, elevating the total P burial rate above that expected for a euxinic depositional environment. Particle shuttles of Fe and Mn oxides into the deep euxinic basins act as drivers for P-bearing mineral authigenesis. While Fe(II) phosphates are formed continuously in the upper sediments following the sulfidization of Fe-oxyhydroxides and release of associated P, Mn-Ca-carbonate-phosphates are formed intermittently following inflow events of oxygenated North Sea water into the deep basins. The mechanism of Fe(II) phosphate formation differs from previously reported occurrences of vivianite formation in marine sediments, by occurring within, rather than below, the sulfate-methane transition zone. The spatial distribution of both authigenic phases in Baltic sediments varies in accordance with the periodic expansion of anoxia on centennial to millennial timescales. The results highlight the potential importance of authigenic P-bearing minerals other than carbonate fluorapatite for total P burial in euxinic basins.

Processes controlling forms of phosphorus in surficial sediments from the eastern Arabian Sea impinged by varying bottom water oxygenation conditions

Abstract The surficial sediments from the upper continental slope of the eastern Arabian Sea, impinged by the oxygen minimum zone (OMZ, 150–1200 m water depth), show varying concentrations of the biogenic element phosphorus (P, 0.1–0.2%) in the northern and southern areas even though total organic carbon concentrations are relatively constant (TOC, 2–5%; Prakash Babu et al., 1999). To understand this discordance, 17 surface sediment samples from shelf, slope and deep sea of the eastern Arabian Sea were investigated using a five-step sequential extraction scheme to delineate the process responsible for P enrichment in OMZ. High fractions of organic phosphorus (Porg 10–26%), biogenic phosphorus (Pbio 36–48%), relatively low molar Corg/Porg ratios (322–447), and Corg/Preactive ratios close to Redfield Ratio in OMZ sediments of the SE Arabian Sea suggest accumulation under high surface production and low residence time of labile forms of P due to high sedimentation rates. Despite higher productivity in surface waters, low fractions of Porg (8–13%; less than deep-sea sediments of the study area 12–13%), Pbio (25–33%), relatively high molar Corg/Porg ratios (341–508), and Corg/Preactive ratios less than Redfield Ratio in OMZ sediments from the NE Arabian Sea may indicate a higher degree of regeneration and diagenetic transformation of labile forms of P to other phases. Authigenic phosphorus (Paut) fraction varies by a factor of 2–8 in sediments from the OMZ when compared to well-oxygenated deep-sea sediments of the study area. While the Ptotal remains constant, significant P transformation seems to occur in NE Arabian Sea, which is suggested by high Paut fraction (∼50%) compared to low Paut fraction (10–39%) in the SE Arabian Sea sediments. Supply rates of phosphorus, variable rates of P dissolution under varying dissolved oxygen contents in the bottom waters, and early diagenetic transformation of P within the sediments seem to influence P geochemistry in sediments overlain by the OMZ in the eastern Arabian Sea.

Interpretation of past climatic changes around Tsokar Lake, Ladakh for the last 33 ka on the basis of chemical data

Environmental changes during Late Quaternary for Tsokar Lake, Ladakh, J & K have been inferred based on the variations of K, Na, Mg, Fe and Mn, organic and mineral matter and authigenic phosphorus contents in sediments and 14C dates. The climatic conditions around Tsokar Lake, Ladakh has been deduced as dry arid immediately prior to 31·4 ka and alternated from dry arid to brief amelioration of climate till the beginning of Holocene The climate amelioration of Tsokar Lake around 16.8 ka correlates with the end of Philipi interstadial around 16 ka in Greece. The climatic amelioration around the last 10 ka also correlates with the infilling of lake basin of Rajasthan and Southern Ethiopia.