Search

The unprecedented global increase in the anthropogenic-derived nitrogen (N) input may have profound effects on phosphorus (P) dynamics and may potentially lead to enhanced eutrophication as demonstrated in short-term mesocosm experiments. However, the role of N-influenced P release is less well studied in large-scale ecosystems. To gain more insight into ecosystem effects, we conducted a five-year large-scale experiment in ten ponds (700-1000 m 2 each) with two types of sediments and five targeted total N concentrations (TN) by adding NH 4 Cl fertilizer (0.5, 1, 5, 10, and 25 mg N L -1 ). The results showed that: (ⅰ) The sediment P release increased significantly when TN exceeded 10-25 mg N L -1 . (ⅱ) The most pronounced sediment P release increase occurred in summer and from sediments rich in organic matter (OM Sed ). (ⅲ) TN, algal biomass, fish biomass, non-algal turbidity, sediment pH, and OM Sed were the dominant factors explaining the sediment P release, as suggested by piecewise structural equation modeling. We propose several mechanisms that may have stimulated P release, i.e. high ammonium input causes a stoichiometric N:P imbalance and induce alkaline phosphatase production and dissolved P uptake by phytoplankton, leading to enhanced inorganic P diffusion gradient between sediment and water; higher pelagic fish production induced by the higher phytoplankton production may have led increased sediment P resuspension through disturbance; low oxygen level in the upper sediment caused by nitrification and organic decomposition of the settled phytoplankton and, finally, long-term N application-induced sediment acidification as a net effect of ammonium hydrolysis, nitrification, denitrification; The mechanisms revealed by this study shed new light on the complex processes underlying the N-stimulated sediment P release, with implications also for the strategies used for restoring eutrophicated lakes., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier Ltd.)

Phosphorus (P) release from sediment is a key process affecting the effectiveness of eutrophication mitigation. We hypothesized that high nitrate (NO 3 - ) input may have dual effect on sediment P release: reduce the sediment P release by improving the oxidation of sediment or promote P release by stimulating the growth of phytoplankton and increase the decomposition rates and oxygen consumption at the sediment water interface. To test the effect of different NO 3 - concentrations, we conducted a three-month experiment in 15 cement tanks (1 m 3 ), with five targeted concentrations of NO 3 - : control, 2 mg L -1 , 5 mg L -1 , 10 mg L -1 , and 15 mg L -1 . The results showed that: i) when NO 3 - was maintained at high levels: NO 3 - ≥5-7 mg L -1 (range of median values), there was no effect of NO 3 - on net P release from the sediment, likely because the positive effects of NO 3 - (increasing oxidation) was counteracted by a promotion of phytoplankton growth. ii) after NO 3 - addition was terminated NO 3 - dropped sharply to a low level (NO 3 - ≤0.4 mg L -1 ), followed by a minor P release in the low N treatments but a significant P release in the high N treatments, which likely reflect that the inhibition effect of NO 3 - on P release decreased, while the promotion effects at high NO 3 - concentrations continued. The results thus supported our hypotheses of a dual effect on sediment P release and suggest dose-dependent effect of NO 3 - loading on stimulating P release from the sediment, being clear at high NO 3 - exceeding 5-7 mg L -1 ., Competing Interests: Declaration of Competing Interest No conflict of interests needs to be declared for the manuscript entitled., (Copyright © 2021. Published by Elsevier Ltd.)

Published research suggests that the total phosphorus ( TP) thresholds for the regime shifts between a clear-water state dominated by submersed macrophytes and a turbid-water state dominated by phytoplankton in shallow lakes vary with forms of lake basins and climates. However, such hypotheses remain untested by direct field evidence. We therefore tested the hypotheses with empirical data from subtropical lakes on the Yangtze floodplain and also from other lakes in temperate to tropical zones., TP thresholds were found to vary little at moderate depths, but to decrease notably when depth exceeds a level of probably 3-4 m, and increase sharply when depth is below a level of around 1-2 m., TP thresholds were found to be nearly equal in shallow lakes (1-2 m

Abstract: Located in the Yunnan–Guizhou Plateau in southwest China, Fuxian Lake covers an area of 211km2, with maximum depth of 155m. It is known to have a unique fauna, including 14 described endemic species. In order to describe the zoobenthic community of the lake more completely, the present study was conducted from August 2002 to August 2003. Altogether 62 benthic taxa, including 22 oligochaetes, 21 molluscs and 18 insects were identified, of which the dominant taxa belonged to Potamothrix, Procladius and Paraprososthenia. The standing stocks of benthos were much higher in the littoral (824ind/m2 in density, 3.72g/m2 in biomass) than in the profundal region (23ind/m2 in density, 0.10g/m2 in biomass). Species richness was greatest in summer and standing stocks were larger in spring and summer than in other seasons. Analyses of functional feeding groups indicated that collector-gatherers and scrapers were predominant in entire lake. Stepwise multiple regression analysis demonstrated that the water depth is the most important factor affecting the distribution of macrozoobenthos. [Copyright &y& Elsevier]

Abstract: Submersed macrophytes in Yangtze lakes have experienced large-scale declines due to the increasing human activities during past decades. To seek the key factor that affects their growth, monthly investigations of submersed macrophytes were conducted in 20 regions of four Yangtze lakes during December, 2001–March, 2003. Analyses based on annual values show that the ratio of Secchi depth to mean depth is the key factor (50% of macrophyte biomass variability among these lakes is statistically explained). Further analyses also demonstrate that the months from March to June are not only the actively growing season for most macrophytes, but the key time the factor acts. Five key-time models yielding higher predictive power (r 2 reaches 0.75, 0.76, 0.77, 0.69 and 0.81) are generated. A comparison between key-time models and traditional synchronic ones indicates that key-time models have higher predictive power. Analyses of transparency thresholds during macrophyte growing season and the limitations of the models are presented. The models and other results may benefit the work concerning submersed macrophyte recovery in Yangtze lakes. [Copyright &y& Elsevier]

Effects of Artificial LED Light on the Growth of Three Submerged Macrophyte Species during the Low-Growth Winter Season: Implications for Macrophyte Restoration in Small Eutrophic Lakes. University of Chinese Academy of Sciences, Beijing 100049, China. 1 Xu C., Wang H.-J., Yu Q., Wang H.-Z., Liang X.-M., Liu M., Jeppesen E. Effects of Artificial LED Light on the Growth of Three Submerged Macrophyte Species during the Low-Growth Winter Season: Implications for Macrophyte Restoration in Small Eutrophic Lakes. [Extracted from the article]

Dolman (2014) argued that our recent finding (Wang et al., 2014) of no marked effect of submerged macrophytes on the chlorophyll a (Chl a) to total phosphorus ( TP) relationship in Yangtze subtropical lakes may not necessarily be valid due to the statistical procedure used to analyse the relationship between these two variables., We agree with Dolman (2014) that a likelihood ratio test could provide an alternative statistical approach to analyse the effect of macrophytes on Chl a versus TP. However, we do not consider it would be appropriate to use the test on only a limited sub-data set corresponding to where TP values overlap for the vegetated and non-vegetated states, as suggested by Dolman (2014)., Besides testing slopes of the log10(Chl a)-log10( TP) relationship, we compared log10(Chl a)/log10( TP) values between vegetated and non-vegetated lakes at a range of overlapping TP concentrations (Wang et al., 2014)., The conclusion drawn by Dolman (2014) from a highly cited work on subtropical lakes in Florida was shown to be invalid. Re-analysis of these lakes demonstrated similar results to those found in Yangtze subtropical lakes. We therefore consider that our original conclusions are valid and that submersed macrophytes in subtropical lakes do not necessarily exert the same strong effects on algal turbidity as in temperate lakes. [ABSTRACT FROM AUTHOR]