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Vertical stratification in sediments from a young oligotrophic South African impoundment: implications in phosphorus cycling 总被引:2,自引:2,他引:0
Changes at the mud surface in Midmar Dam, following impoundment, were studied by examining vertical profiles of selected parameters in sediment cores. Distinct stratification in organic carbon, pH and exchangeable Al3+ was evident. Phosphate adsorption characteristics in the stratified sediments was quantified using Langmuir adsorption isotherms. The adsorption maxima and bonding energy constants in the surface sediments (0–3 cm) were markedly lower than those below 3 cm, indicating that the surface layers are less efficient at binding phosphate than the deeper layers. Radiotracer experiments indicate that the layers comprising the top 3 cm of sediment predominate in PO4-P exchange with the overlying water. 相似文献
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SUMMARY The major concepts involved in nutrient cycling in wetlands are discussed using phosphorus and nitrogen as examples. The differences in nutrient cycling patterns between hydrologically contrasting wetlands, and the significance of fluctuating water levels in wetlands, are stressed. In South Africa, some research into nutrient cycling in submerged aquatic macrophyte communities has been undertaken, but very little information is available on these processes in wetlands dominated by emergent vegetation forms. Generally, the information available on nutrient cycling processes in South African wetlands is of limited applicability to the assessment of nutrient cycling in whole wetland systems. Therefore, rational wetland management strategies require further research on nutrient cycling. 相似文献
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Isolation columns positioned in approximately 3.5 m of water in Midmar Dam, were enriched with PO4-P and NO3-N, singly and in combination. Increased chlorophyll concentration resulted from all enrichment treatments. Responses showed marked seasonality and varied in intensity and duration. Despite the PO4-P fixing potential of the sediments, SRP concentrations increased markedly at times and possible reasons for this discussed. The marked response to addition of NO3-N alone suggested a flux of phosphorus from the sediment through the water to the algal component. The significance of periphyton within the columns is discussed. 相似文献
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A comparison of nutrient availability measured by chemical analysis and calculated from bioassay yields 总被引:2,自引:1,他引:1
The concentrations of soluble biologically available nitrogen and phosphorus were determined using Selenastrum capricornutum bioassays and compared with analytically measured soluble nitrate (NO3-N) and soluble reactive phosphorus concentrations during enrichment studies in a South African impoundment. The NO3-N analyses consistently underestimated the soluble biologically available nitrogen and the extent of the discrepancy decreased with increasing NO3-N concentration. Biological availability of soluble organic nitrogen during the bioassays is suggested as a reason for the discrepancies. At low soluble reactive phosphorus concentrations the analytical measurements underestimated the soluble biologically available phosphorus while at high soluble reactive phosphorus concentrations the analytical measurements were considerable overestimates of soluble biologically available phosphorus. Possible reasons for the observed trend are discussed. 相似文献
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A. J. Twinch 《Hydrobiologia》1986,135(1-2):23-34
The phosphorus status and distribution of sediments in a hypertrophic water supply reservoir (Hartbeespoort Dam) were investigated, with a view to assessing the role of sediments in counteracting the effects of reduced external phosphorus loading as a restoration measure. In comparison with similar water bodies in South Africa, the sediments in Hartbeespoort Dam contained high levels of both total and potentially mobile phosphorus. The potentially mobile fraction constituted about 60% of the total phosphorus content of the sediments, compared with about 11% in other reservoirs. The excessive eutrophication of Hartbeespoort Dam is clearly reflected in the phosphorus status of the sediments. Sediment distribution in the impoundment was found to be extremely heterogeneous, due to the combined influences of morphometry, hydrology and an imbalance in the nutrient loads entering via rivers at remote points in the water body. It is concluded that sufficient mobile phosphorus has accumulated in the sediments to prolong the response time of the impoundment to phosphorus load reductions. Since phosphorus release from sediments is dependent on dynamic processes not addressed in this study, the extent of the delays in trophic response to load reduction cannot be estimated. 相似文献
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