[Effects of Algal Blooms and Their Degradation on the Sediment-water Micro-interface].

Effects of algal blooms and their degradation on the sediment-water micro-interface under conditions of disturbance and darkness were investigated. The concentration of chlorophyll a in water was determined via the acetone method, profiles of oxygen near the interface were measured using a microelectrode, and profiles of nutrients and metals in sediments were measured at the millimeter level. The results showed that algal bloom degradation at the sediment-water micro-interface decreased the concentration of oxygen and affected nutrient and metal profiles, at depths over approximately 3 mm. Disturbance played an important role in algal bloom degradation and early diagenesis processes of nutrients, such as C and P, and metals, such as Fe, Ca, Mg, Al, and K. Darkness sped up algal bloom degradation and reduced the influence of disturbance. Under control conditions of no disturbance nor algae, and supplied with enough light, a layer of benthic algae appeared at the sediment surface, whose photosynthesis produced oxygen and greatly changed the microenvironment. This brought about significant differences in the concentrations of nearly all nutrients and metals in the surficial sediment compared with those of other treatments. Correlation analyses showed that the vertical variability of sediment P concentration was most strongly related to sediment Mn, followed by sediment C. The results of this high-resolution research showed that algal bloom degradation had an effect on the sediment-water micro-interface at the millimeter level.

Long-term moderate wind induced sediment resuspension meeting phosphorus demand of phytoplankton in the large shallow eutrophic Lake Taihu.

The objective of this study was to investigate the impact of sediment resuspension and phosphorus (P) release on phytoplankton growth under different kinds of wind-wave disturbance conditions in the large and shallow eutrophic Lake Taihu in China. Short-term strong wind (STSW) conditions, long-term moderate wind (LTMW) conditions, and static/calm conditions were investigated. To address this objective, we (1) monitored changes in surface water P composition during field-based sediment resuspension caused by STSW conditions in Lake Taihu, and also conducted (2) a series of laboratory-based sediment resuspension experiments to simulate LTMW and calm conditions. The results showed that under both strong and moderate wind-wave conditions, suspended solids (SS) and total phosphorus (TP) in the water column increased significantly, but total dissolved phosphorus (TDP) and soluble reactive phosphorus (SRP) remained low throughout the experiments, indicating that the P released from sediments mainly existed in particulate forms. In STSW conditions, alkaline phosphatase activity (APA) and enzymatically hydrolysable phosphorus (EHP) increased rapidly, with the peak value occurring following the peak value of wind speed for 1-2 days, and then rapidly decreased after the wind stopped. Under LTMW conditions, APA and EHP increased steadily, and by the end of the laboratory experiments, APA increased by 11 times and EHP increased by 5 times. Chlorophyll a (Chl-a) in LTMW conditions increased significantly, but remained low under STSW conditions, demonstrating that the former type of sediment P release promoted phytoplankton growth more effectively, and the latter type did not. Despite the fact that STSW conditions resulted in the release of more TP, TP settled to the bottom rapidly with SS after the wind stopped, and did not promote algal growth. Under LTMW conditions, suspended particulate P was hydrolyzed to SRP by phosphatase and promoted algae growth. Algal growth in turn secreted more phosphatase and accelerated particulate P regeneration, which may be the main mechanism of sediment bio-available P release that promotes phytoplankton growth in shallow lakes.

[Effects of wind-induced wave on organic aggregates physical and chemical characteristics in a shallow eutrophic lake (Lake Taihu) in China].

The physical and chemical characteristics were continually monitored during a wind course one time per day, which continued for 10 days, and other water physical and chemical parameters were concomitantly monitored. Organic aggregates (OA) abundance was significantly higher during wind period than calm stage and the maximum of OA abundance, which occurred the same day when wind speed was highest, was 29 times higher than that in the calm stage. Although OA-C, OA-N and OA-P concentration were decreased during wind period, the total C, N and P contend in OA were increased for the increased OA abundance. Additionally, suspended soil (SS), total nitrogen (TN) and total phosphorus (TP) concentration during wind period were significantly higher than that of clam stage, but total dissolved phosphorus (TDP), total dissolved nitrogen (TDN) and soluble reactive phosphorus (SRP) were insignificantly different. During the wind, OA alkaline phosphatase activity (OA-APA) and OA enzymatically hydrolyzable phosphorus (OA-EHP) both increased significantly, which accelerated organic phosphorous mineralization and SRP release. The results indicate that SRP release induced by wind in shallow lakes may comes from suspended matter, especially OA release rather than directly comes from sediment.

[Effects of ecosystem structure on the organic aggregates physical and chemical parameters of Lake Taihu].

The abundance, organic matter content and chemical composition of organic aggregation (OA) were monitored in Lake Taihu in different ecotype sites from January to December in 2007, and other water physical and chemical parameters were concomitantly monitored. The OA abundance was increasing along regional and P-enrichment gradients, and there were significant differences in OA characteristic in different ecotypes. Moreover, wind is one important factor that contributes to OA characteristic in Lake Taihu. OA maybe one potential important nutrient source in lake water for its high enrichment factors of nutrition: the concentrations of P and N in the OA were much higher than that of in the water; more than one third (43.3%) of TP could be attributed to the OA-P, and that number of OA-N is 16.5%.