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.

Response of dissolved organic matter (DOM) and microbial community to submerged macrophytes restoration in lakes: A review.

Microorganisms play a crucial role in the biogeochemical processes of Dissolved Organic Matter (DOM), and the properties of DOM also significantly influence changes in microbial community characteristics. This interdependent relationship is vital for the flow of matter and energy within aquatic ecosystems. The presence, growth state, and community characteristics of submerged macrophytes determine the susceptibility of lakes to eutrophication, and restoring a healthy submerged macrophyte community is an effective way to address this issue. However, the transition from eutrophic lakes dominated by planktic algae to medium or low trophic lakes dominated by submerged macrophytes involves significant changes. Changes in aquatic vegetation have greatly affected the source, composition, and bioavailability of DOM. The adsorption and fixation functions of submerged macrophytes determine the migration and storage of DOM and other substances from water to sediment. Submerged macrophytes regulate the characteristics and distribution of microbial communities by controlling the distribution of carbon sources and nutrients in the lake. They further affect the characteristics of the microbial community in the lake environment through their unique epiphytic microorganisms. The unique process of submerged macrophyte recession or restoration can alter the DOM-microbial interaction pattern in lakes through its dual effects on DOM and microbial commu-----nities, ultimately changing the stability of carbon and mineralization pathways in lakes, such as the release of methane and other greenhouse gases. This review provides a fresh perspective on the dynamic changes of DOM and the role of the microbiome in the future of lake ecosystems.

Rapid shifts in pond sediment microbiota in response to high ambient temperature in a water-sediment microcosm.

Unlike the extensive research on the response of soil microorganisms to high ambient temperature (HTA), the response of sediment microorganisms to HTA remains unclear. Understanding the response of sediment microorganisms to HTA is important to forecast their impacts on ecosystems and climate warming under projected climate change scenarios. Against the background of climate warming and frequent high ambient temperatures in summer, we conducted a laboratory incubation experiment to clarify the unique assembly characteristics of pond sediment bacterial communities at different temperatures (4, 10, 15, 25, 30 and 35 °C). The results showed that the structure and function of the microbial community in pond sediments at 35 °C were different from those under other temperatures; the microbial community structure at 35 °C had the most large modules and an average module size. Temperature and dissolved oxygen influenced the microbial community network modularity. The CO2 emission rates of pond sediments at 35 °C were significantly higher than those at other temperatures. At 35 °C, heterogeneous selection was the most important assembly process. Additionally, warming altered the microbial network structure and ecosystem functioning but not the microbial diversity or community composition, which may be related to horizontal gene transfer. Revealing the rapid response of pond sediment microorganisms to HTA is important for identifying their role in nutrient cycling and assessing the ecological impacts of climate warming and high ambient temperatures on inland water sediments.

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.

The effects of climate warming on microbe-mediated mechanisms of sediment carbon emission.

Due to significant differences in biotic and abiotic properties of soils compared to those of sediments, the predicted underlying microbe-mediated mechanisms of soil carbon emissions in response to warming may not be applicable for estimating similar emissions from inland water sediments. We addressed this issue by incubating different types of sediments, (including lake, small river, and pond sediments) collected from 36 sites across the Yangtze River basin, under short-term experimental warming to explore the effects of climate warming on sediment carbon emission and the underlying microbe-mediated mechanisms. Our results indicated that under climate warming CO2 emissions were affected more than CH4 emissions, and that pond sediments may yield a greater relative contribution of CO2 to total carbon emissions than lake and river sediments. Warming-induced CO2 and CH4 increases involve different microbe-mediated mechanisms; Warming-induced sediment CO2 emissions were predicted to be directly positively driven by microbial community network modularity, which was significantly negatively affected by the quality and quantity of organic carbon and warming-induced variations in dissolved oxygen, Conversely, warming-induced sediment CH4 emissions were predicted to be directly positively driven by microbial community network complexity, which was significantly negatively affected by warming-induced variations in pH. Our findings suggest that biotic and abiotic drivers for sediment CO2 and CH4 emissions in response to climate warming should be considered separately when predicting sediment organic carbon decomposition dynamics resulting from climate change.

Biotic and abiotic controls on sediment carbon dioxide and methane fluxes under short-term experimental warming.

Due to the differences in biotic and abiotic factors between soil and sediments, the predicted linkages between biotic and abiotic factors and soil carbon dioxide (CO2) and methane (CH4) fluxes under warming may not be suitable for sediments. Additionally, the combination of biotic and abiotic factors which determines sediment temperature-dependent CO2 and CH4 fluxes remains unresolved. To address this issue, different types of sediments (including lake, small river and pond sediments) collected from 30 sites across the Yangtze River Basin were incubated under short-term experimental warming. During the incubating phase, the sediment temperature-dependent CO2 and CH4 fluxes as well as the accompanying biotic factors (organic carbon and microbial community) and abiotic factors (pH and dissolved oxygen (DO)) were determined and analyzed synthetically. Our results indicated that sediment CO2 fluxes were more sensitive than CH4 fluxes to warming, which might lead to a relatively large CO2 contribution to total greenhouse gas emissions in a warming climate. Additionally, temperature-dependent CO2 fluxes in pond sediments were more sensitive than those in lake sediments. Random forest analysis indicated that DO greatly affected the variation in the sediment temperature-dependent CO2 fluxes, whereas Methanococcales primarily predicted the CH4 fluxes under warming. DO also highly affected the variation in the temperature sensitivity of CH4 fluxes, whereas pH mostly predicted the temperature sensitivity of CO2 fluxes. Our findings suggest that biotic and abiotic factors, especially DO, pH and the composition of methanogens, coregulate CO2 and CH4 emissions in response to climate warming. Therefore, biotic and abiotic factors should be considered in the models for predication and investigation of sediment organic carbon dynamics under climate change.