Seasonal variations in the nitrogen isotopic composition of dissolved nitrate （δ15NO3） were investigated in the surface waters of the Changjiang River estuary in 2009 and 2010. δ15NO3 varied between -4.6‰ and 8.9...Seasonal variations in the nitrogen isotopic composition of dissolved nitrate （δ15NO3） were investigated in the surface waters of the Changjiang River estuary in 2009 and 2010. δ15NO3 varied between -4.6‰ and 8.9%0 with changes in temperature, salinity, dissolved oxygen concentrations, and the composition of the dissolved inorganic nitrogen pool. In February, biological processes decreased because of low temperature, and the mean δ15NO3 near the river mouth was 2.4%0. In May, δ15NO3 was the highest in the surface waters among all seasons. Analysis on the conservative mixing revealed assimilation, and this finding is supported by positive relationship between Chl a and δ15NO3. The fractionation factor of assimilation was estimated to be 2.0‰ by the Rayleigh equation. Nitrification was supported based on the mixing behaviors in November 2010 and the low δ15NO3 values in May and November 2009. The high ammonium concentrations in the adjacent marine area and positive relationships between total organic nitrogen and δ15NO3 in November 2010 indicated that mineralization was taking place.展开更多
Soil is an essential part of the critical zone,and soil-microbe-plant system serves as a key link among lithosphere,biosphere,atmosphere and hydrosphere.As one of the habitats with the richest biodiversity,soil plays ...Soil is an essential part of the critical zone,and soil-microbe-plant system serves as a key link among lithosphere,biosphere,atmosphere and hydrosphere.As one of the habitats with the richest biodiversity,soil plays a critical role in element biogeochemistry on the earth surface(weathered crust).Here we review the soil biological processes that are relevant to mineral weathering,element cycling,and transformation,with an emphasis on rock weathering mediated by soil microbes,plant root and the rhizosphere.展开更多
Concentrations of suspended particle material(SPM), dissolved silicate(DSi), biogenic silica(BSi), phytoliths(plant produced siliceous microscopic structures), and other parameters were analyzed to examine the influen...Concentrations of suspended particle material(SPM), dissolved silicate(DSi), biogenic silica(BSi), phytoliths(plant produced siliceous microscopic structures), and other parameters were analyzed to examine the influence of both natural processes and human activities on silica delivery to the estuary of the Huanghe River(Yellow River). Our results indicate that the concentrations of DSi in the river decreased significantly since 1986. Approximately 34% of dissolved silica was trapped in the basin between 1986 and 2010 due to a reduction of soil erosion. Phytoliths comprised 67.2%–96.3% of BSi, with the smoothing bar type being the dominant form. Concentrations of BSi are significantly higher in the Huanghe River compared to other major rivers throughout the world due to its high sediment yield. We also found that the ratios of BSi/(BSi+DSi) and BSi/SPM were approximately 0.5 and 0.003 at Lijin near the river mouth, indicating that BSi carried in suspension by the Huanghe River was an important component of the rivers silica load. Significant amounts of BSi were also composed of phytoliths in Bohai Sea sediments near the Huanghe River estuary with the smoothing bar form again being the most abundant. The relatively high specific fluxes of BSi in the Huanghe River reflect its high turbidity and high erosion rates in the basin. The high sediment load originating on the Loess Plateau is likely responsible for the higher BSi flux, in agreement with a general trend of increasing BSi flux with increasing sediment flux in global river systems. This study demonstrates that BSi transported by rivers can be composed largely of phytoliths originating from the erosion of topsoils. The flux of phytoliths in river's suspended sediment load may therefore represent a significant contribution to the biogeochemical cycle of silica in coastal waters.展开更多
基金Supported by the National Natural Science Foundation of China(No.41276116)the Fund for Creative Research Groups by NSFC(No.41121064)the National Basic Research Program of China(973 Program)(No.2010CB428706)
文摘Seasonal variations in the nitrogen isotopic composition of dissolved nitrate （δ15NO3） were investigated in the surface waters of the Changjiang River estuary in 2009 and 2010. δ15NO3 varied between -4.6‰ and 8.9%0 with changes in temperature, salinity, dissolved oxygen concentrations, and the composition of the dissolved inorganic nitrogen pool. In February, biological processes decreased because of low temperature, and the mean δ15NO3 near the river mouth was 2.4%0. In May, δ15NO3 was the highest in the surface waters among all seasons. Analysis on the conservative mixing revealed assimilation, and this finding is supported by positive relationship between Chl a and δ15NO3. The fractionation factor of assimilation was estimated to be 2.0‰ by the Rayleigh equation. Nitrification was supported based on the mixing behaviors in November 2010 and the low δ15NO3 values in May and November 2009. The high ammonium concentrations in the adjacent marine area and positive relationships between total organic nitrogen and δ15NO3 in November 2010 indicated that mineralization was taking place.
基金supported by Major Program of National Natural Science Foundation of China(Grant No.41090282)
文摘Soil is an essential part of the critical zone,and soil-microbe-plant system serves as a key link among lithosphere,biosphere,atmosphere and hydrosphere.As one of the habitats with the richest biodiversity,soil plays a critical role in element biogeochemistry on the earth surface(weathered crust).Here we review the soil biological processes that are relevant to mineral weathering,element cycling,and transformation,with an emphasis on rock weathering mediated by soil microbes,plant root and the rhizosphere.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.41106072,41376093,41206064)Natural Science Foundation of Shandong(Grant No.ZR2010DM006)
文摘Concentrations of suspended particle material(SPM), dissolved silicate(DSi), biogenic silica(BSi), phytoliths(plant produced siliceous microscopic structures), and other parameters were analyzed to examine the influence of both natural processes and human activities on silica delivery to the estuary of the Huanghe River(Yellow River). Our results indicate that the concentrations of DSi in the river decreased significantly since 1986. Approximately 34% of dissolved silica was trapped in the basin between 1986 and 2010 due to a reduction of soil erosion. Phytoliths comprised 67.2%–96.3% of BSi, with the smoothing bar type being the dominant form. Concentrations of BSi are significantly higher in the Huanghe River compared to other major rivers throughout the world due to its high sediment yield. We also found that the ratios of BSi/(BSi+DSi) and BSi/SPM were approximately 0.5 and 0.003 at Lijin near the river mouth, indicating that BSi carried in suspension by the Huanghe River was an important component of the rivers silica load. Significant amounts of BSi were also composed of phytoliths in Bohai Sea sediments near the Huanghe River estuary with the smoothing bar form again being the most abundant. The relatively high specific fluxes of BSi in the Huanghe River reflect its high turbidity and high erosion rates in the basin. The high sediment load originating on the Loess Plateau is likely responsible for the higher BSi flux, in agreement with a general trend of increasing BSi flux with increasing sediment flux in global river systems. This study demonstrates that BSi transported by rivers can be composed largely of phytoliths originating from the erosion of topsoils. The flux of phytoliths in river's suspended sediment load may therefore represent a significant contribution to the biogeochemical cycle of silica in coastal waters.
