Study on the concentration, flux, occurrence and retention processes of total phosphorus in Dahuofang reservoir

<p>Dahuofang reservoir (DHFR) is one of the most important drinking water sources in Liaoning province, China. The processes of total phosphorus (TP) concentration, flux and retention rate are very important to the water quality management and drinking water safety for the reservoir. Based on the monitoring data of meteorology, hydrology, water quality and sediment, etc. at the controlled stations of Dahuofang catchment during 1992-2017, The suspended sediment centration(SSC) and TP concentration variation and differences from upper to lower reach of DHFR  during floods in 2010 and 2013 are analyzed and compared respectively. Based  on the  mass balance equation of TP and the related fluxes formula at the different boundaries, the stocking processes in both the overlying water and the active surface sediment layer are solved. The results revealed the TP accumulation variation in the overlying water and the surface sediment layer, together with the controlling mechanism of TP concentration in overlying water under different floods events. Moreover, the results discovered that the combination of flood and dry hydrological rhythms is very important to maintain the dynamic balance of accumulated sediment and TP in the reservoir. The study does not only provide the effective calculation method forthe TP flux, accumulation and retention rate in the large reservoir, but also partly supply a new eyesight on the sediment nutrient control and related continuable management  for large reservoirs in north China.</p>

Methane formation and consumption by sediments in a cross-channel profile of a small river impoundment

Rivers are a natural source of methane (CH4) into the atmosphere and may contribute significantly to total CH4 emissions. Even though the details of sources of CH4 in rivers are not fully understood, weirs have been recognized as a hotspot of CH4 emissions. In this study, we investigated CH4 production and consumption in air-exposed river sediments along a cross-channel transect located upstream of a weir. Stable carbon isotopes were used for determination of individual methanogenic pathways. In order to understand the relationship between physicochemical and biological processes, additional parameters such as organic matter, grain median size, and carbon and nitrogen content were characterized as well. Generally, samples from the surface sediment layer (0-10 cm) had higher CH4 production than sediments from the deeper layer (10-20 cm) during the incubation experiments. Sediments near the bank zones and in the mid-channel were characterized by the highest organic carbon content (6.9 %) as well the highest methanogenic activity (2.5 mmol g-1 DW d-1). The CH4 production was predominated by H2/CO2 dependent methanogenesis in the surface sediment layer (0-10 cm), while the proportion of acetoclastic and hydrogenotrophic methanogenesis in the deeper sediment layer (10-20 cm) was balanced. The CH4 oxidation potential of sediments showed the same spatial pattern as observed for the CH4 production. Our results showed high spatial variability of sediment CH4 production and oxidation in the cross-channel profile upstream of the weir, whereas the highest CH4 dynamics were observed in the littoral zones. This variability was closely linked with the carbon and nitrogen content in the sediment samples.

The concentration, flux and occurrence process of total phosphorus in Dahuofang reservoir and Suggestions for environmental optimal operation

Dahuofang reservoir is one of the most important drinking water sources in Liaoning province, China. Dynamics of total phosphorus (TP) concentration, flux and related retention processes in this reservoir are very important to the water quality management and drinking water safety. Based on the monitoring data of meteorology, hydrology, water quality and sediment from the main stations during 1992-2017, this paper analysed the TP fluxes in the different boundaries and the stocking process in both the overlying water and the active surface sediment layer using the mass balance method. This study revealed the TP accumulation variation in the overlying water and the surface sediment layer and the controlling mechanism of TP concentration in overlying water under different hydrological conditions. The results showed that the combination of flood and dry hydrological rhythms is important to maintain the dynamic balance of TP in the reservoir. Based on these results, to reduce the TP retention rate and accumulated TP in the active surface sediment layer, we put forward suggestions on environmental optimization operations during the early days of large flood and subsequent small flood season by opening the deep flood discharging holes of the reservoir and lowering upstream water level. These results provide an improved understanding and new eyesight of the nutrient control of large reservoirs in the north China.

Utilisation de la scanographie pour l'étude des sédiments : influence des paramètres physiques, chimiques et biologiques sur la mesure des intensités tomographiques

In July 1996, a flash flood resulted in the input of 9 million m3 of sediment toward the Bay of Ha! Ha!, leading to the elimination, partly or totally, of the benthic fauna of the bay. In this study, the CT scanner has been used in a highly perturbed environment, the Bay of Ha! Ha!, to both assess (i) the relationships between the variations of tomographic intensities and the sedimentologic parameters of the sedimentary column and (ii) to quantify the biogenic structures resulting from the activity of benthic organisms. Compaction, CaCO3 contents, and granulometry of sediments are the most important influences on the variation of tomographic intensities. The scanner allowed the study and quantification, in a non destructive way, of the sediment occupation by biogenic structures and, more particularly, allowed to further assess most of the relative importance of the fine fraction of biogenic structures (0.250–1 mm) in the surface sediment layer (0–5 cm). Sediment occupation by biogenic structures reached maximal values at the upper part of the sedimentary column and decreased with depth. If sedimentary reworking leads to an increase in the sediment porosity, destabilization generated by the activity of organisms is balanced by the consolidation of the wall of the biogenic structures. Bioturbation resulting from the activity of benthic organisms into the sediments has a significant role on the sedimentary structure and biogeochemical processes. It is therefore necessary to quantify the volume of sediments occupied by biogenic structures to assess the activity of benthic organisms in the sedimentary column.