RESUMO
Backwater regions have been formed in the downstream of tributaries since the Three Gorge Reservoir (TGR) was impounded, as the most influential area to the aquatic environment within the reservoir. In order to study the effects and significance of the backwater regions on the nutrient cycling and substance fluxes, dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), dissolved silicon (DSi) were monitored in situ in Caotang tributary backwater region, the adjacent mainstream and Caotang tributaries' upstream every month from August 2012 to July 2013. The results showed that the concentrations of DIN, DIP and DSi in Caotang tributary backwater region were similar to those in the mainstream, and the monthly variation tendency was very consistent with the mainstream Changjiang. DIN, DIP and DSi in the Caotang tributary were mainly originated from the mainstream. The influence of the mainstream water could extend to the upmost of the backwater region due to the good connection and rapid, sufficient water exchange between mainstream and tributary. Nutrients from the mainstream were retained and consumed by primary producers in the tributary during the growing seasons in spring and summer, while released back to the water during late autumn and winter. Nutrient cycling in the tributary could change the seasonal pattern of nutrient transportation. The mainstream nutrient fluxes could receive significant seasonal modification from the large numbers (more than 40) of tributaries within the TGR domain.
RESUMO
The present paper introduces a new method using spectrofluorimetric analysis to determine the concentration of hydrogen peroxide in rainwater. In this method, an oxidation reaction is conducted between o-phenylenediamine (OPDA) and hydrogen peroxide in the buffer medium of NaAc-HAc at pH 4. 48 to form a new product 2,3-diaminophenazine (DAPN). Then the fluorescence intensity of DAPN is measured and 426 and 554 nm are chosen as the excitation and emission wavelengths. Therefore, with the foreknown concentration of input hydrogen peroxide, a series of fluorescence intensities of DAPN are acquired according to a series of different concentration of hydrogen peroxide as input, greatly improving the selectivity and sensibility of the system. A relationship between the input concentration of hydrogen peroxide and the fluorescence intensity of DAPN is then obtained using a linear regression. Results show that fluorescence intensity of DAPN is in proportion to the increase in the concentration of hydrogen peroxide in the range of 9.0 x 10(-7) -3.56 x 10(-5) mol x L(-1) almost linearly. The linear equation is F = 1.15c (micromol x L(-1))+398.6 (r = 0.999 1) and the detection limit is 2.7 x10(-7) mol x L(-1) (n = 11). The relative standard deviation of 11 parallel measurements with the concentration of H2O2 at 7.5 x 10(-6) and 3.0 x 10(-5) mol x L(-1), is 2.2 and 1.0%, respectively. Results from DPD method was used to verify this method. The interference of foreign iron was studied. Compared to the traditional methods, this binary system has a simplified operation and high sensitivity. The proposed method has been successfully applied to determine the concentration of hydrogen peroxide in rainwater.