Novel insights into molecular composition of organic phosphorus in lake sediments

Recognizing the variation of DNA-P during and after the algal bloom in lake Hulun

Eutrophication has spread from shallow lakes in temperature zones to lakes in cold regions as a result of a continuous warm climate and human activities. Little proof for the importance of dissolved organic phosphorus (DOP) in contributing to phosphorus cycling and algae growth has been generated for aquatic ecosystems, particularly in cold eutrophic lakes. In this study, a comprehensive in situ study was conducted in overlying water, suspended particulate matter, and sediment during and after algal bloom (in July and September, respectively) in Lake Hulun. Multiple methods of 31P NMR, enzymatic hydrolysis, and UV-visible technologies were combined to detect phosphorus occurrence, bioavailability, and molecular structure from a novel angle. The 31P NMR analysis results showed that DNA-P is mainly stored in the dissolved phase and has not been detected in suspended particulate matter or sediment. Enzymatic hydrolysis was used to determine the bioavailability of DOP, which revealed that in July and September, respectively, 85% and 79% of DOP were hydrolyzable. UV-visible analysis represented that the degree of humification and molecular weight of DOP were high during the algal bloom, but these values considerably dropped following the algal bloom. The large amount of DNA-P present in the overlying water is the main reason for the high degree of humification and high molecular weight of the water body. Besides, Lake Hulun's DNA-P remains highly bioavailable during algal blooms, despite its high degree of humification and molecular weight. These findings can serve as a theoretical basis for understanding the migration and transformation of DOP, as well as the persistence of algal blooms in eutrophic lakes located in cold regions.

Effects of different chemical agents on changes in sediment phosphorus composition and the response of sediment microbial community

Controlling the release of sediment phosphorus (P) using chemical agents is a promising method for controlling internal P in eutrophic lakes. However, mineral P formation and changes in the organic P composition after sediment amendment with P-inactivation agents remain poorly understood. Furthermore, little is known about the changes in the sediment microbial community composition after remediation. Here, various ratios of poly aluminum chloride (PAC) and lanthanum-modified bentonite (LMB) were added to nutrient-rich sediments and incubated. Sequential P extraction, solution/solid-state ³¹P nuclear magnetic resonance (NMR), and microbial analyses were periodically performed on the inactivated sediments. The results indicate that PAC and LMB effectively reduced sediment iron-bound P and organic P, respectively, markedly increasing the content of aluminum- and calcium-bound P in the sediment, respectively. Solid-state ³¹P NMR results confirmed the formation of rhabdophane (LaPO₄. nH₂O) in the LMB-amended sediment. Solution ³¹P NMR results showed that PAC preferentially reduced the organic P fractions of pyrophosphate, whereas LMB efficiently reduced the organic P fractions of orthophosphate, monoesters, and diesters in the sediment. Compared with the control sediment, PAC addition can cause short-term negative effects on sediment microbes at high doses, whereas LMB addition can increase bacterial diversity or richness in the sediment. These results provide a deeper understanding of the differences between PAC and LMB in internal sediment P control.

How phoD-harboring functional microbial populations trigger the release risk of phosphorus in water sediment system of Shijiuhu Lake, China after experiencing the transseasonal shift

Excessive phosphorus (P) enrichment is the critical cause of eutrophication in the lake water. Organic P (P_o) mineralization processes induced by alkaline phosphatase (APase) regulated by phoD-encoding microorganisms in the lake ecosystems was still ambiguous due to the transseasonal shift of water temperatures and depths. Different P pools in the water and sediments of Shijiuhu Lake at varied seasons were measured using chemical extraction methods and solution ³¹P NMR. The alkaline phosphatase activity (APA) in the sediments were assessed together with enzyme kinetic parameters. The abundances and compositions of microbial communities encoding functional gene phoD were also obtained using high-throughput sequencing. The results showed that P_o concentrations remarkably increased from winter toward spring when having higher water depths due to the terrigenous input and biomass deposition. Noteworthy elevation in the PO₄³- concentration was observed in the interstitial water during the spring, particularly at around 5 cm sediment depth with value reaching as high as 0.43 mg/L. The degradation and mineralization of momoesters and diesters with higher concentrations in the sediments of spring aggravated the PO₄³- load in the interstitial water. Higher APA reaching 91.6 μg/(g·h) in spring was responsible for the mineralization of P_o. Remarkably upwards increasing of absolute abundance of phoD-encoding gene in spring reaching up to 2.6 times of that in winter facilitated the generation of APA in spring. Cobetia and Calothrix followed by Aquabacterium and Mitsuaria were the most abundant phoD-encoding genera with relative abundance > 4%. Weakly positive correlation between dominant bacterial genera and APA and P fractions suggested that low-abundance genera was also involved in the APA generation and P_o hydrolysis. These results indicate that spring with high water temperature and depth facilitate the mineralization of P_o in the sediment and increase of labile PO₄^3- load in the water, further provide valuable information for the management of eutrophic lakes.

Dissolved Organic Phosphorus Removal in Secondary Effluent by Ferrate (VI): Performance and Mechanism

Dissolved organic phosphorus (DOP), which is recalcitrant in municipal wastewater treatment, accounts for 26-81% of dissolved total phosphorus in the effluent. More importantly, the majority of DOP could be bioavailable, potentially threatening the aquatic environment through eutrophication. This study aimed to develop a ferrate (VI)-based advanced treatment to effectively destruct and remove DOP from secondary effluent and use deoxyribonucleic acid (DNA) and adenosine-5'-triphosphate (ATP) as DOP model compounds to explore the relevant mechanisms. The results showed that ferrate (VI) treatment could efficiently destruct and remove 75% of the DOP in secondary effluent from an activated sludge-adopted municipal wastewater treatment plant, under normal operating conditions. Moreover, the coexistence of nitrate, ammonia, and alkalinity barely affected the effectiveness, while the presence of phosphate significantly inhibited DOP removal. The mechanistic study revealed that ferrate (VI)-induced particle adsorption was the dominant way to achieve DOP reduction, rather than oxidating DOP to phosphate and forming precipitation afterward. Meanwhile, DOP molecules could be effectively decomposed into smaller ones by ferrate (VI) oxidation. This study clearly demonstrated that ferrate (VI) treatment could achieve a promising DOP removal from secondary effluent for mitigating the risk of eutrophication in receiving water bodies.

Cognizing and characterizing the organic phosphorus in lake sediments: Advances and challenges

Organic phosphorus (OP) is one of the main forms of phosphorus in lake ecosystems. Mounting evidence has shown that sediment OP has become a major but underestimated issue in addressing lake eutrophication and algal bloom. However, a holistic view of sediment OP remains missing. This review aims to provide an overview of progress on the studies of OP in lake sediments, focusing on the contribution of OP to internal P loading, its potential role in algal bloom, and the migration and transformation. In addition, this work systematically summarized current methods for characterizing OP content, chemical fraction, composition, bioavailability, and assessment of OP release in sediment, with the pros and cons of each method being discussed. In the end, this work pointed out following efforts needed to deepen the understanding of sediment OP, namely: (1) In-depth literature review from a global perspective regarding the contribution of sediment OP to internal P loading with further summary about its pattern of distribution, accumulation and historical changes; (2) better mathematical models for describing drivers and the linkages between the biological pump of algal bloom and the replenishment of sediment OP; (3) fully accounting the composition and molecular size of OP for better understanding its transformation process and mechanism; ; (4) developing direct, high-sensitivity and combined techniques to improve the precision for identifying OP in sediments; (5) establishing the response of OP molecular properties and chemical reactivity to OP biodegradability and designing a comprehensive and accurate composite index to deepen the understanding for the bioavailability of OP; and (6) integrating fundamental processes of OP in current models to better describe the release and exchange of P in sediment-water interface (SWI). This work is expected to provide critical information about OP properties and deliver perspectives of novel characterization methods.