Phosphorus speciation in surface sediments of a hypertrophic lake,Southwestern China:insights from fractionation and ^(31)P NMR

Phosphorus(P) species in surface sediments from a shallow,hypertrophic lake,Lake Dianchi,China,were investigated by P fractionation and ^(31)P nuclear magnetic resonance(NMR) spectroscopy during a regional algal bloom.In addition,their potential contributions to the overlying water were also evaluated.Labile fractions of P extracted by NH_4C1,bicarbonate dithionite and NaOH ranged from 340.6 to 1,725.8 mg kg^(-1),accounting for20.5%-67.2%of the total P.A two-step extraction method refinement of P recovery was performed before the^(31)P NMR analysis.Recovery rates of sedimentary TP and organic P,by combining EDTA pretreatment and NaOH or mixed reagents,ranged from 31.8%to 69.3%and from19.8%to 51.7%.^(31)P NMR results showed that ortho-P and monoester-P were the most abundant P components in the sediment extractable P of sediments,followed by diester-P and pyro-P.Spatial distribution of the sum of ortho-P,diester-P and pyro-P detected by P NMR corresponded well with the labile P concentration determined by fractionation.Both exhibited a significant positive correlation with the total P in the water column,suggesting that internal loading may be an important source of P for the lake ecosystem.Biogenic P other than ortho-P may contribute to phytoplankton growth,with the relative proportion being 4.4%-18.7%.The release of labile P fractions fueled algal bloom,and the decay of organic matter,following the bloom events,consumed oxygen and elevated the pH value.This co-dependence might lead to a vicious cycle.Transformation mechanisms of various P species remain ambiguous and are worthy of further investigation.

The oxygen isotopic composition of phosphate as an effective tracer for phosphate sources in Hongfeng Lake

In order to characterize the oxygen isotopic composition of internal phosphate and explore the possibility of using these data to identify phosphate sources, we measured oxygen isotopic compositions of phosphate(δ^(18)O_p) in sediment pore water in Hongfeng Lake, a typical deep-water lake in a mountainous area. These data, in combination with δ^(18)O_p in surface water samples and water column samples, were successfully used to identify phosphate sources. The δ^(18)O_p value of sediment pore water ranged from 15.2% to 15.8%, with an average value of 15.5%—the δ^(18)O_p value of internal phosphate. The δ^(18)O_p values decreased gradually through the water column from 19.4% in surface water to 16.4% in deeper water, implying that internal phosphate had more negative δ^(18)O_p values than external phosphate. This finding was substantiated by horizontal variations in δ^(18)O_p values, which decreased with increasing distance from inflowing rivers. All collected evidence suggests that external and internal phosphate have distinctly different isotopic signatures and that these signatures have not been considerably altered by biological mediation in Hongfeng Lake. Therefore, δ^(18)O_p can be used to distinguish phosphate sources. A two-endmember mixing model showed that internal phosphate had an average contribution of 40%, highlighting the influence of internal phosphorus loading on aqueous phosphate and eutrophication. This study illustrates the need to reduce the internal phosphorus load from sediment and provides guidance for nutrient management and in-lake restoration treatment in Hongfeng Lake. The data presented here are limited, but serve to highlight the great potential of δ^(18)O_p as an effective tracer for identifying phosphate sources. Systematic investigations of the oxygen isotopic compositions of external phosphate, internal phosphate, and phosphate through the water column, in combination with in-lake P biogeochemical cycle study, would be desirable in further research.

Late onsets of tropical cyclones in the decaying years of super El Niño events

The 2015/2016 El Nino event reached the threshold of super El Nino event,and was comparable to the super events in 1982/1983 and 1997/1998.Interestingly,the tropical cyclones(TCs)were found to have very late onsets in the decaying years of the super El Nino events.This study discusses the causes of late TC onsets related with atmospheric circulation,disturbance sources and trigger mechanisms.The analysis shows that the western North Pacific subtropical high(WNPSH)from January–June during the decaying years of the super El Nino events were stronger than the climatic mean,which resulted in a relatively stable atmospheric state by inhibiting deep convection.As a disturbance source,the April–June intertropical convergence zone(ITCZ)during the decaying years of the super El Nino events were significantly weaker than its climatic mean.The cross-equatorial flow and monsoon trough,as important TC generation triggers,were weaker from April–June during the decaying years of the super El Nino events,which further reduced the probability of TC generation.As for the late TC onsets,the role of atmospheric circulation anomalies(i.e.,subtropical-high,the ITCZ,cross-equatorial flow,and monsoon trough)were more important.The cross-equatorial flow may take as predictor of TC onsets in the decaying years of the super El Nino events.

An efficient wear-leveling-aware multi-grained allocator for persistent memory file systems

Persistent memory(PM)file systems have been developed to achieve high performance by exploiting the advanced features of PMs,including nonvolatility,byte addressability,and dynamic random access memory(DRAM)like performance.Unfortunately,these PMs suffer from limited write endurance.Existing space management strategies of PM file systems can induce a severely unbalanced wear problem,which can damage the underlying PMs quickly.In this paper,we propose a Wear-leveling-aware Multi-grained Allocator,called WMAlloc,to achieve the wear leveling of PMs while improving the performance of file systems.WMAlloc adopts multiple min-heaps to manage the unused space of PMs.Each heap represents an allocation granularity.Then,WMAlloc allocates less-worn blocks from the corresponding min-heap for allocation requests.Moreover,to avoid recursive split and inefficient heap locations in WMAlloc,we further propose a bitmap-based multi-heap tree(BMT)to enhance WMAlloc,namely,WMAlloc-BMT.We implement WMAlloc and WMAlloc-BMT in the Linux kernel based on NOVA,a typical PM file system.Experimental results show that,compared with the original NOVA and dynamic wear-aware range management(DWARM),which is the state-of-the-art wear-leveling-aware allocator of PM file systems,WMAlloc can,respectively,achieve 4.11×and 1.81×maximum write number reduction and 1.02×and 1.64×performance with four workloads on average.Furthermore,WMAlloc-BMT outperforms WMAlloc with 1.08×performance and achieves 1.17×maximum write number reduction with four workloads on average.

Phosphorus speciation in the sediment profile of Lake Erhai, southwestern China: Fractionation and ^(31)P NMR

The distribution characteristics of phosphorus （P） forms in the sediment profile of Lake Erhai, in southwestern China has been investigated by sequential extraction and 31p nuclear magnetic resonance spectroscopy （NMR） of NaOH extracts to understand P dynamics and its potential contribution to lake eutrophication. Contents of P fractions varied in the order of NH4C1 extracted P （NH4C1- P） 〈 bicarbonate-dithionite extracted P （BD-P） 〈 HC1-P, Residual-P 〈 NaOH extracted P （NaOH-P）. The highly available NH4C1-P represented less than 1% of total P （TP）. BD-P and NaOH extracted reactive P （NaOH-rP） averaged 39%, while the ratio of Fe/P was higher than 15, indicating low P release from the sediments under permanent oxic condition. The less bio-available HC1-P, NaOH extracted nonreactive P （NaOH-nrP） and residual-P contributed 61% of TP. Regression analysis revealed that BD-P, NaOH-rP and HC1-P were positively correlated with the contents of Fe and Mn, A1 and Fe, and Ca, respectively. The investigation of P compound groups in NaOH extracts by 31p NMR showed that ortho-P and monoester-P were the largest two constituents of the P pool, followed by diester-P, phosphonate and pyro-P. A comparison of vertical variations of P groups in the sediment profile suggested that these compounds were involved in the P recycling to different extents in Lake Erhai. In particular, the lake exhibits high potential for labile P release from the surface sediments, which should be taken into consideration even after the outsourced P runoff ceased.