New insights into eutrophication management: Importance of temperature and water residence time.

Eutrophication and harmful cyanobacterial blooms threaten water resources all over the world. There is a great controversy about controlling only phosphorus or controlling both nitrogen and phosphorus in the management of lake eutrophication. The primary argument against the dual nutrients control of eutrophication is that nitrogen fixation can compensate the nitrogen deficits. Thus, it is of great necessary to study the factors that can significantly affect the nitrogen fixation. Due to the difference of climate and human influence, the water quality of different lakes (such as water temperature, N:P ratio and water residence time) is also quite different. Numerous studies have reported that the low N:P ratio can intensify the nitrogen fixation capacities. However, the effects of temperature and water residence time on the nitrogen fixation remain unclear. Thus, 30 shallows freshwater lakes in the eastern plain of China were selected to measure dissolved N2 and Ar concentrations through N2: Ar method using a membrane inlet mass spectrometer to quantify the nitrogen fixation capacities and investigate whether the temperature and water residence time have a great impact on nitrogen fixation. The results have shown that the short lake water residence time can severely inhibit the nitrogen fixation capacities through inhibiting the growth of nitrogen-fixing cyanobacteria, changing the N:P ratio and resuspending the solids from sediments. Similarly, lakes with low water temperature also have a low nitrogen fixation capacity, suggesting that controlling nitrogen in such lakes is feasible if the growth of cyanobacteria is limited by nitrogen.

[Changes in Algal Particles and Their Water Quality Effects in the Outflow River of Taihu Lake].

Connected rivers are a common engineering method to ensure the ecological health of urban water. However, for the lakes with serious cyanobacteria blooms, the algal particles are carried by the outflow of the lake and will have a significant impact on water quality. The location at which the Liangxi river meets Meiliang Bay of Lake Taihu was selected to explore the influence of the eutrophic lake on the connected rivers, and high-frequency monitoring was conducted in summer for three consecutive years to analyze the changes in the flux of cyanobacterial bloom particles in rivers and their impact on river water quality. The results show that:① The improvement of the algal cyanobacteria bloom in Meiliang Bay and the operation of the pressure-controlled algae well at the entrance of the river significantly reduced the concentration of chlorophyll a and the flux of algae particles in the Liangxi River. The average value of the concentration of chlorophyll a and the flux of algae particles in the river in summer 2019 were 54.34 µg·L-1 and 84.7 t·d-1, respectively, and significantly lower than those of 2017; ② Water diversion had a significant effect on improving the water quality of the receiving water. Except for DTP, the nitrogen and phosphorus concentrations of the remaining forms of the Liangxi River showed a downward trend from 2017 to 2019, indicating that the water quality of the Liangxi river improved after water transfer; ③ A large amount of cyanobacterial blooms entering the channel significantly increased the particulate nitrogen and phosphorus content of the water. From 2017 to 2019, the nitrogen and phosphorus in the Liangxi River were mainly PN and PP, accounting for 62.5% and 70.8% of TN and TP, respectively; ④ The water quality of the Beijing-Hangzhou Grand Canal and other connected rivers has not been affected by the algal particles in Meiliang Bay. In August 2019, the chlorophyll a content in the canal water decreased by 65% compared with that of June, indicating that cyanobacterial bloom particles have not accumulated in the Grand Canal; ⑤ On the premise that the cyanobacteria bloom in the lake has not been effectively improved, the algae particles carried by the water diversion will have an impact on the water quality and landscape of the local reach connecting the river.

Spatiotemporal dynamics of chlorophyll-a in a large reservoir as derived from Landsat 8 OLI data: understanding its driving and restrictive factors.

Chlorophyll-a (Chla) is an important indicator of water quality and eutrophication status. Monitoring Chla concentration (C Chla ) and understanding the interactions between C Chla and related environmental factors (hydrological and meteorological conditions, nutrients enrichment, etc.) are necessary for assessing and managing water quality and eutrophication. An acceptable Landsat 8 OLI-based empirical algorithm for C Chla has been developed and validated, with a mean absolute percentage error of 14.05% and a root mean square error of 1.10 µg L-1. A time series of remotely estimated C Chla was developed from 2013 to 2015 and examined the relationship of C Chla to inflow rate, rainfall, temperature, and sunshine duration. Spatially, C Chla values in the riverine zone were higher than in the transition and lacustrine zones. Temporally, mean C Chla value were ranked as spring > summer > autumn > winter. A significant positive correlation [Pearson correlation coefficient (r) = 0.88, p < 0.001] was observed between the inflow rate and mean C Chla in the northwest segment of the Xin'anjiang Reservoir. However, no significant relation was observed between mean C Chla and meteorological conditions. Mean (± standard deviation) value for the ratio of total nitrogen concentration to total phosphorus concentration in our in situ dataset is 75.75 ± 55.72. This result supports that phosphorus is the restrictive factor to algal growth in Xin'anjiang Reservoir. In addition, the response of nutrients to Chla has spatial variabilities. Current results show the potential of Landsat 8 OLI data for estimating Chla in slight turbid reservoir and indicate that external pollution loading is an important driving force for the Chla spatiotemporal variability.

Phenolic compounds and antioxidant activity of bulb extracts of six Lilium species native to China.

Lily (Lilium) is used as an important edible and medical plant species with a vague taxonomic classification and a long history in China. Bulbs of six Lilium species (L. regale, L. concolor, L. pumilum, L. leucanthum, L. davidii var. unicolor and L. lancifolium) native to China were investigated with a view to their exploitation as a potential source of natural antioxidants due to their phenolic composition and dietary antioxidant potential. The results showed that all bulb extracts exhibited strong antioxidant activities, which generally correlated positively with the total phenolic contents (r = 0.68 to 0.94), total flavonoid contents (r = 0.51 to 0.89) and total flavanol contents (r = 0.54 to 0.95). High-performance liquid chromatography (HPLC) analysis revealed that rutin and kaempferol were the major phenolic components in the extracts. Hierarchical cluster analysis showed that L. regale belonged to the group with high phenolic content and strong antioxidant power. L. concolor and L. pumilum were arranged in one group characterized by moderate phenolic content and antioxidant capacity, while L. leucanthum, L. davidii var. unicolor and L. lancifolium were clustered in the third group with low phenolic content and weak antioxidant activity. These strongly suggest that lily bulbs may serve as a potential source of natural antioxidant for food and pharmaceutical applications.