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Phosphorus Fractions (phosphorus + fraction)
Selected AbstractsSediment phosphorus characteristics in the clearwater state of Lake Mogan, TurkeyLAKES & RESERVOIRS: RESEARCH AND MANAGEMENT, Issue 3 2008Serap Pulatsü Abstract This study examined the vertical distributions of total phosphorus (TP) and phosphorus fractions, and the iron and organic matter, in the littoral sediment in a macrophyte-dominated, clearwater state in Lake Mogan between September 2005 and August 2006. Benthic macroinvertebrates and total bacteria in the sediment also were determined. No clear seasonal or depth-related (0,20 cm) patterns were found in sediment concentrations for the measured parameters. The phosphorus release was quantitatively very low, and a negative phosphorus release (,0.132 µg m,2 day,1) was measured during the summer months. The TP concentrations of the sediment samples ranged between 675.00 and 1463.80 µg g,1 dry weight (DW), and the trophic level of the lake was eutrophic. On average, inorganic phosphorus fractions comprised the largest fraction (63%), while organic-bound phosphorus (Org , P) constituted 37% of the TP in Lake Mogan. The most important phosphorus-immobilizing factors are high iron content (14 200,47 750 µg g,1 DW), the sediment's clay content (47.80,51.80%), and an abundance of macrophytes at the sampling station. The low abundance of benthic macroinvertebrates (510,850 individuals m,2), which depend on sediments with high iron and low organic matter (5.42,13.30%), played a role in the sediment phosphorus retention. Although bacterial abundance in the surficial sediment appeared to be positively correlated to temperature, the overlying water did not experience anoxic conditions, supporting a state in which bacteria were able to retain phosphorus in their cell structures. Long-term changes in the sediments of Lake Mogan must be monitored lake. In order to optimize the management of the lake, and to determine the longevity of a clearwater state following management measures and continued external phosphorus loading, long-term changes in the sediments of Lake Morgan must be monitored. [source] Sources and bioavailability of phosphorus fractions in freshwaters: a British perspectiveBIOLOGICAL REVIEWS, Issue 1 2001C. S. REYNOLDS ABSTRACT This paper seeks a perspective on the forms of phosphorus which promote aquatic eutrophication, with the particular quest of establishing their sources. A short background traces the development of understanding of nutrient enrichment and the suppositions about the relative contributions of agriculture, sewage and detergent residues. Most aquatic systems, and their primary producers, are naturally deficient in biologically-available phosphorus. Aquatic plants have evolved very efficient phosphorus uptake mechanisms. The biomass responses to an increase in the supply of phosphorus are stoichiometrically predictable. The most bioavailable forms of phosphorus are in solution, as orthophosphate ions, or are readily soluble or elutable from loose combinations. Ready bioavailability coincides well with what is measurable as molybdate-reactive (MRP) or soluble-reactive phosphorus (SRP). Most other forms, including phosphates of the alkaline earth metals, aluminium and iron are scarcely available at all. Orthophosphate ions sorbed to metal oxides and hydroxides are normally not biologically available either, except through weak dissociation (,desorption'). The production of alkaline phosphatase provides organisms with an additional mechanism for accelerating the sequestration of phosphate from organic compounds. Bioavailable phosphate is liberated when redox- or alkali-sensitive metal hydroxides dissolve but these processes are minor contributors to the biological responses to nutrient enrichment. Most of the familiar eutrophication is attributable to the widespread application of secondary sewage treatment methods to the wastes emanating from a burgeoning and increasingly urbanised human population. The use of polyphosphate-based detergents, now in decline, has contributed to the problem. In aquatic systems, the additional phosphorus raises the biological supportive capacity, sometimes to the capacity of the next limiting factor (carbon, light, hydraulic retention or of another nutrient). At high orthophosphate loadings, the straight stoichiometric yield relationship between biomass yield and phosphorus availability is lost. Movements of phosphorus and its recycling within aquatic systems do not prevent the slow gravitation of phosphorus to the bottom substrata. The phosphorus retentivity of sediments depends upon their chemical composition. While oxide-hydroxide binding capacity in the surface sediments persists, they act as a sink for phosphorus and a control on further cycling. Iron-rich and clay-rich sediments perform best in these conditions; calcareous sediments least so. Eutrophication may lead to the exhaustion of sediment P-binding capacity. Non-sorbed phosphate is readily recyclable if primary producers have access to it. Recycling is most rapid in shallow waters (where sediment disturbance, by flow, by wind action and through bioturbation, is frequent) and least in deep ventilated sediments. The contributions of phosphorus from catchments are assessed. The slow rate of weathering of (mostly apatitic) minerals, the role of chemical binding in soils and the incorporation and retentivity by forested terrestrial ecosystems each contribute to the minimisation of phosphorus leakage to drainage waters. Palaeolimnological and experimental evidence confirms that clearance of land and ploughing its surface weakens the phosphorus retentivity of catchments. The phosphorus transferred from arable land to drainage remains dominated by sorbed fractions which are scarcely bioavailable. Some forms of intensive market gardening or concentrated stock rearing may mobilise phosphates to drainage but it is deduced that drainage from agricultural land is not commonly a major source of readily bioavailable phosphorus in water. Careful budgeting of the phosphates in run-off from over-fertilised soils may nevertheless show that a proportionately small loss of bioavailable phosphorus can still be highly significant in promoting aquatic plant production. The bioavailable-phosphorus (BAP) load achieving the OECD threshold of lake eutrophy (35 mg P m,3) is calculated to be equivalent to a terrestrial loss rate of approximately 17.5 kg BAP km,2 year,1), or only 1,2% of a typical fertiliser application. The output is shown to be comparable with the P yield from secondary treatment of the sewage produced by a resident population of 30,44 persons km,2. With tertiary treatment, the equivalence is with approximately 200 persons km,2. [source] Labile Phosphorus in Soils of Forest Fallows and Primary Forest in the Bragantina Region, BrazilBIOTROPICA, Issue 1 2003Jacqueline Frizano ABSTRACT We used the Hedley sequential extraction procedure to measure nine different organic inorganic soil phosphorus fractions in forest soil of the Bragantina region of Para, Brazil. We compared the labile fractions (resin-extractable P + HCO3-extractable inorganic and organic P) in Oxisols from three secondary forests (10, 20, and 40 years old) and a primary forest. These stands were located in an area that has supported shifting agriculture for approximately a century. After agricultural use, total P and labile P in soils of young secondary forests are diminished compared to the amounts presents in the primary forest soil. Within each stand, organic carbon content was a good predictor of labile organic and inorganic P, consistent with the large body of research indicating that mineralization of organic matter is important to plant nutrition in tropical ecosystems. During the reorganization of P pools during forest development, the pool of labile organic P (HCO3-extractable) diminishes more than the other labile fractions, suggesting that it is directly or indirectly an important source of P for the regrowing forest vegetation. Across the four age classes of forest, the soil reservoir of labile P was equal to or greater than the total amount of P in the vegetation. If labile P measured by this method adequately represents P available to plants in the short term (as suggested by the current consensus), we would conclude that plant-available P is reasonable abundant, and that the effects of agriculture on available P pools are detectable but not sufficient to compromise forest regrowth in this area. [source] | ||||||||||