Humic substances phosphorus

Organic forms of carbon, nitrogen, sulfur, and phosphorus (typically less than 0.7 pm in diameter) contribute to bulk DOM. Humic substances,... 

A beneficial effect of humic substances on the nutrient uptake and contents of plants has been reported for the major inorganic elements, such as nitrogen, phosphorus, potassium (Mylonas and McCants, 1980), and sulfur (Guminski, 1968). In addition, the uptake and contents of nutrients such as calcium, magnesium (Mylonas and McCants, 1980), sodium (Vaughan and McDonald, 1976) and copper (Rauthan and Schnitzer, 1981) are also enhanced by humic substances. Most of these reports on the effects of HS on the nutrient contents of plants are purely descriptive, and little attempt has been made to elucidate the mechanisms of the action of the humic material. The authors proposed both an indirect and a direct effect of HS on plant nutrition. In the former case HS may, for example, chelate a cation, thus changing... 

Extraction of humic substances has been a useful way of characterizing NOM properties by NEXAFS. In those cases where the element studied also has significant inorganic fractions such as sulfur in submerged soils and sediments, or phosphorus in most mineral soils and sediments, an extract appears to be the only approach to obtain meaningful information about NOM. Often, it was found that the spectra have a lower background and can be more easily analyzed quantitatively... 

Nissenbaum A. (1979) Phosphorus in marine and non-marine humic substances. Geochim. Cosmochim. Acta 43, 1973-1978. 

Nutrient— Any chemical required for life. The most important nutrients that plants obtain from soil are compounds of nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur. Organic matter— Any biomass of plants or animals, living or dead. The most important form of organic matter in soil is dead, occurring as humic substances. 

Francko and Heath (1979) studied the influence of UV radiation on the phosphate complexation properties of dissolved humic substances from Crazy Eddie Bog in the central United States. In this bog, filterable phosphorus compounds were largely associated with humic substances of high apparent molecular weight. These fulvic acid-phosphorus associations resisted hydrolysis by alkaline phosphatase, but released orthophosphate upon irradiation with low doses of UV radiation, " e turnover time of the fulvic acid-phosphorus compounds was calculated to be less than 1 hour at the surface of a lake on a cloudless day. 

Humic substances might sequester organic phosphorus-containing molecules and render phosphate available only through enzymatic hydrolysis. If so, production and release of organophosphorus compounds by the microflora would gradually result in decreased phosphate availability. Biotic equilibrium would be established after increases in alkaline... 

Complexation of metals and trace anions (e.g., phosphate) by humic substances leads to a decrease of toxicity of certain metals toward microorganisms and increases the availability of some metals, but decreases phosphorus resources. At this time, the role of humic substances in reducing the toxicity of trace metals is more clearly understood than the other roles. Adsorption of micropollutants by aquatic humic substances may enhance their toxicity toward microorganisms in many cases. The specific modes of action, however, are mostly unknown. On the other hand, dissolved humic substances may assist in the degradation of organic pollutants. Under environmental conditions, the predominating process is not obvious. 

From a practical standpoint, stream fulvic acids which comprise over 90% of the stream humic substances are not an important food source for aquatic organisms, but all stream humic and fulvic acids are positive influences on biological growth in respect to phosphorus and nitrogen nutrient cycling, trace metal availability, and limiting potential metal toxicity. 

For humic substances which normally are expected to contain small amounts of phosphorus, the molybdenum blue colorimetric method (Ma and Rittner, 1979) is recommended. The blue color provides a high sensitivity, allowing relatively small samples to be used for the determination. 

Usually only a small portion of the sample is water-soluble (chlorides, nitrates, nitrites, sulphates, alkali metals — when unbound in silicates, glycides, fatty acids, humic substances). The extract for the determination of nutrients (nitrogen, phosphorus, potassium, trace elements) is prepared with the use of leaching solutions 1% citric acid, 1% potassium sulphate, 1% hydrochloric acid, calcium lactate, etc. 

X-ray spectra of phosphorus in natural organic molecules. The P NEXAFS spectroscopic studies conducted on isolated humic substances and soil organic molecules indicate that the primary form of P is phosphate and phosphonate (Fig. 24 Myneni and Martinez 1999). When compared to humic substances from soil systems, the fluvial humic substances exhibit phosphonate as one of the important components. However, phosphonate constitutes only a minor fraction of total P in humic substances. Soil samples also exhibit features that correspond to polyphosphate. Another study conducted using NEXAFS spectroscopy at the P absorption edge suggested that marine sediments and humic materials do not exhibit phosphonate and the P NEXAFS spectra of these samples more closely resembled that of hydroxyapatite (Vairavamurthy 1999). 

Magid, j., Tiessen, H. and Condron, L.M. (1996) Dynamics of organic phosphorus in soils under natural and agricultural ecosystems. In Piccolo, A. (ed.) Humic Substances in Terrestrial Ecosystems. Elsevier, Amsterdam, pp. 429-466. 

This chapter reviews the abiotic processes that can lead to the stabilization of organic phosphorus in soils and the aquatic environment. In particular, we examine the role of adsorption to soil minerals, complex-ation reactions, precipitation with polyvalent cations and the incorporation of organic phosphorus into humic substances in stabilizing organic phosphorus. We then discuss the effects of soil solution chemistry on these reactions, as well as the effects of these reactions on the environment. 

The affinity of the organic moiety of phosphorus-containing pesticides with humic substances can lead to their retention in soils and sediments. For example, S4nchez-Martin and Sanchez-Camazano (1991) reported that adsorption of the thio-phosphates methyl parathion and ethyl par-athion by soils is controlled by the organic matter content, while the adsorption of methyl paraoxon and ethyl paraoxon is related to the clay-organic matter complexes. 

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