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Seasonal variations in the abundance and sinking flux of biogenic silica in Daya Bay, northern South China Sea

Zhao Xiufeng, Yang Weifeng, Ma Haoyang, Li Junjie, Chen Min, Fang Ziming, Zhang Xiao, Zeng Jian, Qiu Yusheng, Zheng Minfang

Oceanologia

2019

No. 61 (2)

239--251

Coastal seas account for > 50% of the biogenic silica (BSi) production in marine environments. However, BSi sinking is poorly understood. Here, seasonal variations in the abundance and sinking flux of BSi were investigated in Daya Bay, in the northern South China Sea. The highest BSi concentrations occurred in summer, averaging 8.04 ± 5.48 μmol L-1 (±SD), followed by autumn (5.51 ± 3.11 μmol L-1) and spring (3.76 ± 3.06 μmol L-1). The lowest BSi concentration of 2.93 ± 1.34 μmol L-1 was observed in winter. Based on234Th/238U disequilibria, the average BSi sinking fluxes were 7.08 ± 8.62, 10.01 ± 13.95, and 8.30 ± 13.06 mmol Si m-2 d-1 in spring, summer, and autumn, respectively. The lowest flux of 4.19 ± 3.98 mmol Si m-2 d-1was measured in winter. Together with nitrogen fluxes, the Si:N sinking ratios were 0.8:1.0, 1.5:1.0, 1.6:1.0, and 1.4:1.0 in spring, summer, autumn, and winter, respectively, indicating that particle sinking induces the faster removal of Si compared to N in Daya Bay.

Rola krzemu w procesie eutrofizacji wód na przykładzie zbiorników Solina i Myczkowce

Koszelnik P.

Rocznik Ochrona Środowiska

2013

Tom 15, cz. 3

2218--2231

This paper reports on studies conducted during 2005–2006 years in the ecosystem of the Solina-Myczkowce mountain complex of mesotrophic reservoirs on the San River, SE Poland. The goal of the present study has been to analyse the functioning of the reservoirs as a dissolved silicon sink especially whether silicon assumes a limiting role where the biological productivity of reservoirs waters is concerned. Silicon is one of the biosphere’s most abundant elements, and one that – in the form of dissolved silica – serves as a very important nutrient playing a major role in the functioning of marine, coastal and inland waters. Investigations indicate that reservoirs are major sinks for the dissolved silica in a river system and that unfavorable changes in water chemistry downstream may ensue where (as is usually the case), the water discharged from a reservoir is poorer in Si than that supplied to it. The noted Si depletion in both the analysed reservoirs influenced growth of non-siliceous algae expressed in terms of chl a. Siliceous algal growth is usually observed there during spring. I suppose that the first chl a maximum in the case of the Solina Reservoir, and the only maximum in the Myczkowce Reservoir, result from the growth of both siliceous and green algae. The next increase in chl a – observed only in the Solina Reservoir – may result from the presence of the cyanobacteria often observed in warm lakes at the end of summer. Their absence from Myczkowce reflects the low temperature of that reservoir’s water, this being supplied from the hypolimnion of the upper one. These observations are confirmed in relationships between mean measured concentrations of Si and mean concentrations of chl a in the euphotic zone of the two reservoirs. Observed summer depletion of the silicate accelerates the growth of phytoplankton exponentially, especially in the case of the upper reservoir.