Effects of benthic algae on release of soluble reactive phosphorus from sediments: a radioisotope tracing study

To evaluate the effect of benthic algae on soluble reactive phosphorus（SRP） release from sediments in shallow lakes, experiments on SRP release with and without benthic algae in sediment cores and an experiment on SRP uptake by benthic algae were conducted using the radioisotope（32P） tracing method. The dissolved oxygen（DO） concentration in sediment cores was also investigated. The results show that benthic algae effectively reduce the release of SRP from sediments to overlying water. The uptake of SRP by benthic algae, which is the direct way in which benthic algae affect the SRP release from sediments, is low in filtered water and increases with the SRP concentration. However, in the experiment, the increased uptake rate lasted for a short time（in one hour）, and after that it returned to a low rate. Benthic algae make the DO concentration and the oxic layer thickness increased, which can indirectly reduce the SRP release from sediments. These findings indicate that benthic algae can reduce the SRP release from sediments in both direct and indirect ways. It seems that the indirect way also plays an important role in reducing the SRP release from sediments.

Sediment pollution characteristics and in situ control in a deep drinking water reservoir

Sediment pollution characteristics, in situ sediment release potential, and in situ inhibition of sediment release were investigated in a drinking water reservoir. Results showed that organic carbon（OC）, total nitrogen（TN）, and total phosphorus（TP） in sediments increased from the reservoir mouth to the main reservoir. Fraction analysis indicated that nitrogen in ion exchangeable form and Na OH-extractable P（Fe/Al-P） accounted for 43% and 26% of TN and TP in sediments of the main reservoir. The Risk Assessment Code for metal elements showed that Fe and Mn posed high to very high risk. The results of the in situ reactor experiment in the main reservoir showed the same trends as those observed in the natural state of the reservoir in 2011 and 2012; the maximum concentrations of total OC, TN, TP, Fe,and Mn reached 4.42 mg/L, 3.33 mg/L, 0.22 mg/L, 2.56 mg/L, and 0.61 mg/L, respectively. An in situ sediment release inhibition technology, the water-lifting aerator, was utilized in the reservoir. The results of operating the water-lifting aerator indicated that sediment release was successfully inhibited and that OC, TN, TP, Fe, and Mn in surface sediment could be reduced by 13.25%, 15.23%, 14.10%, 5.32%, and 3.94%, respectively.

Effect of intermittent aeration mode on nitrogen concentration in the water column and sediment pore water of aquaculture ponds

Nitrogen in pond sediments is a major water quality concern and can impact the productivity of aquaculture.Dissolved oxygen is an important factor for improving water quality and boosting fish growth in aquaculture ponds,and plays an important role in the conversion of ammonium-nitrogen(NH4-N)to nitrite-nitrogen(NO2--N)and eventually nitrate-nitrogen(NO3--N).A central goal of the study was to identify the best aeration method and strategy for improving water quality in aquaculture ponds.We conducted an experiment with six tanks,each with a different aeration mode to simulate the behavior of aquaculture ponds.The results show that a 36 hr aeration interval(Tc=36 hr:36 hr)and no aeration resulted in high concentrations of NH4-N in the water column.Using a 12 hr interval time(Tc=12 hr:12 hr)resulted in higher NO2--N and NO3--N concentrations than any other aeration mode.Results from an 8 hr interval time(Tc=8 hr:8 hr)and 24 hr interval time(Tc=24 hr:24 hr)were comparable with those of continuous aeration,and had the benefit of being in use for only half of the time,consequently reducing energy consumption.

Can the narrowing of the Lower Yellow River by regulation result in non-siltation and even channel scouring？

This study considered whether the narrowing of the upper （broad and wandering） reaches of the Lower Yellow River could result in a reduction in sedimentation and even an increase in channel erosion in both the upper and the lower （narrow and meandering） reaches. Analysis of field data and numerical modeling results both justify the proposal to narrow the channel. A positive correlation was found between channel eroded-area and the channel width. Therefore narrowing under conditions of low flow will reduce the amount of erosion in the reach, which, in turn, will reduce the amount of sediment transported into the lower channel. This will reduce the amount of siltation in the lower reaches of the river. However, narrowing under conditions of high flow with a low concentration of sediment will reduce both the extent of flood attenuation along the narrowed channel and the amount of lateral channel bank collapse, which results in increased flows and less sedimentation in the lower channel, leading to increased erosion. When flows with a high concentration of sediment are released from the Xiaolangdi Reservoir, both the lower narrow channel and the upper channel can transport a large amount of the sediment load. It is concluded that the narrowing of the upper broad channel will result in a reduction in sedimentation, or even in channel erosion, in both the upper and the lower channels if the reservoir is operated such that the volume of sediment added during low flows is balanced by the volume eroded during high flows with a low concentration of sediment.