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Harmful algal blooms: mechanisms, monitoring, and prevention in a rapidly changing world
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Uncovering links between sediment and stoichiometry of nitrogen and phosphorus in water and its role in triggering red tide.
Wednesday 9th @ 1450-1510, Multifunction Hall
Yiyong Zhou* , Chunlei Song
Xiuyun Cao
Presenter Email: zhouyy@ihb.ac.cn |
| Red tide is one of the most serious environmental problems worldwide,however, the key factor driving occurrence of red tides remains unclear. In particular, roles of nutrition, such as nitrogen (N) and phosphorus (P), in triggering red tide are inadequately studied. Xiamen bay and Pingtan area of Fujian coast in China sea was chosen as study regions. Phytoplankton community, concentrations of N and P with different forms and extracellular alkaline phosphatase activities (APA) were analyzed. In the same time, occurrence of extracellular alkaline phosphatase on cell membrane of phytoplankton was detected using enzyme labelled fluorescence(ELF) technique. Additionally, P fractionation and its sorption behaviors were also studied in sediment, together with potential denitrifying activity (PDA). Emphasis was placed on the impact of stoichiometry of N and P on algal growth in relation to couplings between their biogeochemical cyclings in sediment. N appears less representative of a key element limiting algal growth compared to P, as illustrated by a significantly positive relationship between concentrations of chlorophyll-a (chl a) and total P (TP) rather than any N species. P limitation was strengthened by a significantly negative relationship between APA and concentration of soluble reactive phosphorus (SRP). In addition, from the perspective of stoichiometry, N enrichment would further aggravate the deficiency of P. Thus, there existed a significantly positive relationship between APA and rations of N to P (N/P) such as ammonium nitrogen(NH4+-N) to SRP and dissolved inorganic nitrogen (DIN) to SRP. Spatially, the Xiamen bay had significantly higher concentrations of SRP, TP and dissolved TP(DTP) relative to those in Pingtan area that gave a significantly higher concentrations of total N (TN). In parallel, N/P (TN/TP and DTN/DTP) were significantly higher in Pingtan area, where APA was higher and ELF labeling was given by diverse algal species including Prorocentrum sp, a typical red tide causing species, whose density was significantly higher there. Contrastingly, far less ELF labeling was observed in the Xiamen bay. Moreover, trophic states of water were strongly dependent on biogeochemical cyclings of N and P in sediment. In details, iron bond phosphorus in sediment was significantly and positively relative to TP concentration, and negatively relative to TN/TP in water. What is more, it gave a linear increase in the PDA of sediment. Noticeably, comparing to the Xiamen bay, the Pingtan area had significantly lower PDA and equilibrium phosphorus concentration (EPC0) that indicates higher P retention capacity in the sediment. Higher P retention yielded less upward P flux and adversely affected denitrification and nitrogen removal. As a consequence, N concentration increased greatly coupled with a decreased P concentration in terms of higher N/P in water, which exacerbated the negative impact of low P availability to phytoplankton, thereby inducing alkaline phosphatase and triggering blooms of the phytoplankton species with the strong ability to utilize organic P by means of enzymatic hydrolysis. |
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