Response of organic phosphorus in lake water to environmental factors: A simulative study

Variations of sediment organic phosphorus and organic carbon during the outbreak and decline of algal blooms in Lake Taihu, China

In this study, sediment organic phosphorus (OP) and organic carbon (OC) in Lake Taihu, China, as well as their relationships, were analyzed during the outbreak and decline of algal blooms (ABs) over a five-month field study. The results showed synchronous temporal changes in the sediment OP and OC contents with the development of ABs. In addition, there was a significant positive correlation between the sediment OP and OC (p < 0.01), suggesting simultaneous deposition and consumption during the ABs outbreak. The sediment OP and OC contents decreased significantly at the early and last stages of the ABs outbreak and increased at the peak of the ABs outbreak and during the ABs decline. These temporal variation patterns suggest that the sediment OC and OP contents did not consistently increase during the ABs outbreak, even though algae are an important source of organic matter in sediments. The depletion or enrichment of OC and OP in sediments may also depend on the scale of the ABs outbreak. The obtained results revealed significant differences in the sediment OC and OP contents between the months (p < 0.05). In addition, OP in the sediments was dominated by orthophosphate diester (phospholipids and DNA-P) and orthophosphate monoester during the ABs outbreak and decline, respectively. The active OC contents and proportions in the sediments in the ABs outbreak were significantly lower than those observed in the ABs decline period, demonstrating the significant impacts of the ABs outbreak and decline on the sediment OC and OP in Lake Taihu.

Improved 31P NMR analysis of phosphorus in highly mineralized lake water using a modified pretreatment procedure with H resin

³¹P Nuclear Magnetic Resonance (³¹P NMR) is an important analytical tool for identifying and quantifying phosphorus-based compounds in aquatic environments. However, the precipitation method typically used for analyzing phosphorus species via ³¹P NMR has limited application. To expand the scope of the method and apply it to highly mineralized rivers and lakes worldwide, we present an optimization technique that employs H resin to assist phosphorus (P) enrichment in highly mineralized lake water. To explore how to reduce analysis interference from salt in highly mineralized water and improve the accuracy of P analysis using ³¹P NMR, we conducted case studies on Lake Hulun and Qing River. This study aimed to increase the efficiency of phosphorus extraction in highly mineralized water samples by using H resin and optimizing key parameters. The optimization procedure included determining the enriched water volume, H resin treatment time, AlCl₃ addition amount, and precipitation time. The final recommended optimization enrichment procedure involves treating 10 L of filtered water sample with 150 g of Milli-Q water-washed H resin for 30 s, adjusting the pH of the treated sample to 6-7, adding 1.6 g of AlCl₃, stirring the mixture, and allowing the solution to settle for 9 h to collect the flocculated precipitate. The precipitate was then extracted with 30 mL of 1 M NaOH +0.05 M DETA extraction solution at 25 °C for 16 h, and the supernatant was separated and lyophilized. The lyophilized sample was redissolved in 1 mL of 1 M NaOH +0.05 M EDTA. This optimized analytical method using ³¹P NMR effectively identified phosphorus species in highly mineralized natural waters and can be applied to other highly mineralized lake waters globally.

Insights into the conversion of dissolved organic phosphorus favors algal bloom, arsenate biotransformation and microcystins release of Microcystis aeruginosa

Little information is available on influences of the conversion of dissolved organic phosphorus (DOP) to inorganic phosphorus (IP) on algal growth and subsequent behaviors of arsenate (As(V)) in Microcystis aeruginosa (M. aeruginosa). In this study, the influences factors on the conversion of three typical DOP types including adenosine-5-triphosphate disodium salt (ATP), β-glycerophosphate sodium (βP) and D-glucose-6-phosphate disodium salt (GP) were investigated under different extracellular polymeric secretions (EPS) ratios from M. aeruginosa, and As(V) levels. Thus, algal growth, As(V) biotransformation and microcystins (MCs) release of M. aeruginosa were explored in the different converted DOP conditions compared with IP. Results showed that the three DOP to IP without EPS addition became in favor of algal growth during their conversion. Compared with IP, M. aeruginosa growth was thus facilitated in the three converted DOP conditions, subsequently resulting in potential algal bloom particularly at arsenic (As) contaminated water environment. Additionally, DOP after conversion could inhibit As accumulation in M. aeruginosa, thus intracellular As accumulation was lower in the converted DOP conditions than that in IP condition. As(V) biotransformation and MCs release in M. aeruginosa was impacted by different converted DOP with their different types. Specifically, DMA concentrations in media and As(III) ratios in algal cells were promoted in converted βP condition, indicating that the observed dissolved organic compositions from βP conversion could enhance As(V) reduction in M. aeruginosa and then accelerate DMA release. The obtained findings can provide better understanding of cyanobacteria blooms and As biotransformation in different DOP as the main phosphorus source.

The effect of iron oxide types on the photochemical transformation of organic phosphorus in water

Iron oxides play an important role in the transport and transformation of organic phosphorus in aquatic environments. However, the effect of different types of iron oxide on the environmental fate of organic phosphorus has remained unclear. In this study, the photodegradation of the organic phosphorus compound adenosine triphosphate (ATP) via the activity of crystalline (goethite) and amorphous (ferrihydrite) iron oxides was investigated. It was found that ATP was photodegraded by goethite, resulting in the release of dissolved inorganic phosphate under simulated sunlight irradiation. The concentration of ATP on goethite decreased by 75% after 6 h of simulated sunlight irradiation, while the concentration of ATP on ferrihydrite decreased by only 22%. ATR-FTIR spectroscopy revealed that the intensity of the peaks for the P-O and PO stretching vibrations in the goethite-ATP complex decreased significantly more after simulated sunlight irradiation than did those for the ferrihydrite treatment. Combined with the higher TOC/TOC₀ values for the goethite treatment, the results indicate that a more vigorous photochemical reaction took place in the presence of goethite than with ferrihydrite. Reactive oxygen species analysis also showed that hydroxyl and superoxide anion radicals were generated when goethite was exposed to simulated sunlight irradiation, while ferrihydrite did not exhibit this ability. Overall, this study highlights that the type of iron oxide is an important factor in the transformation of organic phosphorus in aquatic environments.

Organic phosphorus regeneration enhanced since eutrophication occurred in the sub-deep reservoir

Lake eutrophication remains a serious environmental problem of global significance, and phosphorus (P) plays a key role in lake eutrophication. Internal P loading, as a result of P release from sediments, is gathering more and more recognition as an important source governing the P availability in these ecosystems. Anoxic condition can promote the release of P associated with Fe oxides, which has already been a consensus. However, it is still unknown whether the anoxic conditions induced by eutrophication act to intensify or weaken the regeneration of organic P (P_org) in sediments. We selected the Hongfeng Reservoir, a typical sub-deep lake, to study the regeneration behaviours of C and P in the sediments buried before and after eutrophication. The results showed that P_org did not significantly increase with the rapid increase in organic C (C_org) since eutrophication occurred. Furthermore, the organic C/P ratio was much higher in sediments buried after eutrophication than in those buried before, which indicated that P_org regeneration had been significantly enhanced since eutrophication occurred. Based on C/P ratios, our estimation suggested that the P_org regeneration and P release from sediment to water approximately enhanced 45.2% ± 8.7% and 34.5% ± 9.8%, respectively. Elevated primary productivity (algae) and the corresponding hypoxic/anoxic condition, both caused by eutrophication, promoted P biogeochemical cycle in the sub-deep reservoir. This study further verifies the significant contribution of regenerated P_org to the internal P load, and highlights the importance of controlling P release from sediments in order to restore clear water ecosystems in sub-deep lakes or reservoirs.