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.

Sequential fractionation of reactive phosphorus in the sediment of a shallow eutrophic lake——Donghu Lake, China

The bioavailability of phosphorus in lake sediment mainly depends on its forms. Therefore, reactive phosphorus (RP) pool of the sediment in a shallow eutrophic lake(Donghu Lake) was determined seasonally and spatially by sequential chemical extraction according to the scheme proposed by Psenner et al. (Psenner, 1985) and its modified version respectively. The ammonium chloride extracted 3%—7% of the total reactive phosphorus (Tot-RP), while the distilled water extracted less(<3%). These two forms of P were significantly higher at the most eutrophic stations(I and IV). The sum of BD-RP(reductant soluble P) and NaOH-RP extracted accounted for 57%—81% of Tot-RP, which could play significant roles in P cycling. The percentages of HCl-extractable RP in the sediments of station III, however, were usually much more than those of other stations, which could reflect the original geochemistrical characteristics and trophic status of the sediments. It was noted that the sediment RP in different fractions varied in different months studied.

Relationship between nutrient pollutants and suspended sediments in upper reaches of Yangtze River

In order to study the relationship between nutrient pollutants and suspended sediments（SS） in the upper reaches of the Yangtze River and two tributaries, water samples were collected from September 1, 2010 to September 30, 2011 at the Zhutuo, Cuntang, Beibei, Wulong, Qingxichang,Wanxian, and Fengjie cross-sections. In the laboratory, the SS concentration and the concentration of SS whose particle size was smaller than0.02 mm were measured. The phosphorus（P）, nitrogen（N）, and permanganate index（CODMn） concentrations in the natural water sample, the settled water sample, and two types of filtered water samples obtained through filter membranes with pore sizes of 0.02 mm and 0.45 mm were monitored synchronously. The results show that there are strong relationships between the P and CODMnconcentrations and the SS concentration. P mainly exists in particulate form, while N mainly exists in dissolved form. SS whose particle size is smaller than 0.02 mm accounts for a high proportion of sediments in the Yangtze River and has a strong effect on water quality. At the seven cross-sections, the amounts of P, N, and CODMnin particulate form in the wet season are higher than in the dry season and the adsorption amounts of P, N, and CODMnper unit mass of sediment are higher in the dry season than in the wet season.

Phosphorus Dynamics in Two Poultry-Litter Amended Soils of Mississippi Under Three Management Systems

An experiment arranged in a randomized complete block design with three replications was conducted on a Lexington soil (fine-silty,mixed,active,thermic,Ultic Hapludalfs) and a Loring soil (fine-silty,mixed,active,thermic,Oxyaquic Fragiudalfs) in Mississippi from September 1997 to September 2000 on 18 runoff plots under natural rainfall condition to study the phosphorus (P) dynamics in poultry litter amended soils under three management systems combining tillage and planting date treatments to identify effective management practices in southern U.S.A.The management systems in the study were:1) tillage in the fall prior to litter application followed by a delayed planting of fall forages (CT-DP);2) tillage followed by immediate planting of the fall forage with subsequent litter application (CT-IP);and 3) no-till with planting prior to litter application (NT-IP).The results indicated that there was significant increase in soil P after 3 years of poultry litter application for both Lexington and Loring soils (P < 0.05).Based on P budget analysis,the majority of P from poultry litter application (> 90%),was accumulated in both soils.In Loring soil,soluble P mass in the runoff was significantly higher from NT-IP than from CT-DP and CT-IP over the entire study period (P < 0.01).For both soils,there were no significant differences in sediment P mass between management systems.For Loring soil,CT-DP and CT-IP were effective management practices to mitigate negative effects due to poultry litter application.

Flow structure and phosphorus adsorption in bed sediment at a 90° channel confluence

The distribution of the phosphorus（P） adsorption in a bed sediment at channel confluences is an important issue for understanding the transport of contaminants in channel networks. In this study, the flow structure and its effect on the P distribution in the bed sediment were investigated in a 90° confluence flume. It is shown that the P adsorption amount in the sediment varies significantly in different hydrodynamic zones. The P adsorption amount is high in the flow separation zone where the horizontal velocity of the flow is very small, and it is low in the maximum velocity zone where the flow velocity reaches a maximum. The low P adsorption amount is observed in the downstream portion of the distorted shear layer, while the P enrichment is found in the upstream portion, as is related to the significant downwelling flow in this zone. Thus, the flow structure, especially, the flow velocity, has a significant effect on the distribution of the P adsorption in the bed sediment at the channel confluences.

Response of organic carbon burial to trophic level changes in a shallow eutrophic lake in SE China

Lakes are an important component of terrestrial carbon cycling. As the trend of eutrophication in many lakes continues, the mechanisms of organic carbon（OC） burial remain unclear. This paper aims to understand the distribution of OC and the effect of trophic level changes on OC burial in Chaohu Lake, a shallow eutrophic lake located in the lower reaches of the Yangtze River, SE China. Two hundred and one surface sediment samples（0–20 cm） and 53 subsurface samples（150–200 cm） from the lake were collected.The OC accumulation rates（OCARs） are relatively low, with an average of 10.01 g/m2/year in the surface sediments. The spatial distribution of the OCARs is similar to that of allochthonous OC. The difference in total phosphate（TP） content between the surface and subsurface sediments（ΔTP） is significantly correlated with the autochthonous OC,suggesting that TP loading is a critical limiting nutrient for the lake＇s primary productivity.It is concluded that allochthonous OC is the dominant source of total OC in surface sediments compared to autochthonous OC. The primary productivity of Lake Chaohu increased due to increasing nutrient loading. However, the autochthonous OC contributed11% of the total OC in the surface sediments. This could be ascribed to strong mineralization in the water column or surface sediments.

Red soil for sediment capping to control the internal nutrient release under flow conditions

Nitrogen （N） and phosphorus （P） released from the sediment to the surface water is a major source of water quality impairment. Therefore, inhibiting sediment nutrient release seems necessary. In this study, red soil （RS） was employed to control the nutrients released from a black-odorous river sediment under flow conditions. The N and P that were released were effectively controlled by RS capping. Continuous-flow incubations showed that the reduction efficiencies of total N （TN）, ammonium （NH4＋-N）, total P （TP） and soluble reactive P （SRP） of the overlying water by RS capping were 77%, 63%, 77% and 92%, respectively, and nitrification and denitrification occurred concurrently in the RS system. An increase in the water velocity coincided with a decrease in the nutrient release rate as a result of intensive water aeration.