Effect of phosphorus deficiency on levels of phosphorus compounds in spirodela

When Spirodela plants are transferred to a phosphate-deficient medium, growth slows down immediately, and ceases after 14 days. During this time, inorganic phosphate content falls from 30 to 0.7 μmoles/g fresh weight of tissue, phosphate ester content from 3.5 to 0.6 μmoles/g, phospholipid content from 3.5 to 1.2 μmoles/g, and residual phosphate (mainly RNA) content from 7.5 to 2.0 μmoles/g. Relative proportions of the various phosphate esters, and relative proportions of the various phospholipids, are not markedly affected by phosphate deficiency. Turnover rates of phosphate esters are somewhat higher in phosphate-deficient tissue. In control tissue, inorganic phosphate is present in 2 pools; a metabolic (12%) and a non-metabolic pool (88%). In phosphate-deficient tissues, most of the inorganic phosphate (>90%) is in the metabolic pool. Non-metabolic phosphate is presumably stored in the vacuole, and is not readily accessible to the tissue, so that growth normally occurs at the expense of external phosphate. During deficiency, growth is limited by the rate at which phosphate can be transported through the tonoplast and tissue to the growing point. Growth ceases when the supply of non-metabolic phosphate is exhausted. Metabolic phosphate is presumably located in the cytoplasm: it can not be used for growth. Nor can the plant respond to deficiency by making some phosphorus compounds at the expense of others. In this respect, phosphorus deficiency and nitrogen deficiency are dissimilar.     

Short-term changes in phosphorus storage in an oligotrophic Everglades wetland ecosystem receiving experimental nutrient enrichment

Natural, unenriched Evergladeswetlands are known to be limited by phosphorus(P) and responsive to P enrichment. However,whole-ecosystem evaluations of experimental Padditions are rare in Everglades or otherwetlands. We tested the response of theEverglades wetland ecosystem to continuous,low-level additions of P (0, 5, 15, and30 g L^–1 above ambient) in replicate,100 m flow-through flumes located in unenrichedEverglades National Park. After the first sixmonths of dosing, the concentration andstanding stock of phosphorus increased in thesurface water, periphyton, and flocculentdetrital layer, but not in the soil or macrophytes. Of the ecosystem components measured, total P concentration increased the most in the floating periphyton mat (30 g L^–1: mean = 1916 g P g^–1, control: mean =149 g P g^–1), while the flocculentdetrital layer stored most of the accumulated P(30 g L^–1: mean = 1.732 g P m^–2,control: mean = 0.769 g P m^–2). Significant short-term responsesof P concentration and standing stock wereobserved primarily in the high dose (30 gL^–1 above ambient) treatment. Inaddition, the biomass and estimated P standingstock of aquatic consumers increased in the 30and 5 g L^–1 treatments. Alterationsin P concentration and standing stock occurredonly at the upstream ends of the flumes nearestto the point source of added nutrient. Thetotal amount of P stored by the ecosystemwithin the flume increased with P dosing,although the ecosystem in the flumes retainedonly a small proportion of the P added over thefirst six months. These results indicate thatoligotrophic Everglades wetlands respondrapidly to short-term, low-level P enrichment,and the initial response is most noticeable inthe periphyton and flocculent detrital layer.     

Sulfate control of phosphorus availability in lakes

During summer stratification large amounts of phosphorus (P) accumulate in anoxic bottom waters of many lakes due to release of P from underlying sediments. The availability to phytoplankton of this P is inversely related to the Fe:P ratio in bottom waters. Using data from 51 lakes, we tested the hypothesis that sulfate concentration in lake water may be critical in controlling the Fe:P ratio in anoxic bottom waters. Results showed that Fe:P ratios in bottom waters of lakes were significantly (p<0.001) related to surface water sulfate concentrations. The higher Fe:P ratios in low sulfate systems is due not only to higher iron concentrations in anoxic bottom waters but also to lower P concentrations in anoxic waters. Thus, our results suggest that anthropogenically induced increases in sulfate concentrations of waters (e.g. from fossil fuel burning) may have a double effect on P cycling in lakes. Higher sulfate concentrations can both increase the magnitude of P release from sediments as well as increase the availability of P released from sediments into anoxic bottom waters.     

An analysis of total phosphorus transport in river systems

Human activities generate many pollutants from different land uses. These pollutants include nutrients (e.g., phosphorus and nitrogen), toxic substances (e.g., heavy metals and pesticides), and other substances (e.g., chlorides and salts). These materials often enter a river at some upstream point and are transported downstream by the flowing water. Many substances are transported both during storms and during normal river flow and often the major portion of the transport occurs during the storms. This paper considers the quantification of transport primarily during storms. First, the characteristics of storm transport are discussed. Then, a calculation method for estimating the distance of travel for sediment related materials is presented. Third, a technique to estimate the amount of a given chemical passing a point in a stream over a specified period of time is presented. The last part of this paper contains a technique for tracing the movement of substances through a river network. In particular, this procedure yields information as to the source of given pollutants over the entire Storm period. West Virginia University     

Nutritional geometry of calcium and phosphorus nutrition in broiler chicks. The effect of different dietary calcium and phosphorus concentrations and ratios on nutrient digestibility

A total of 600 Ross 308-day-old male broiler chicks were used in a 28 day digestibility study to investigate the interaction between dietary calcium (Ca) and non-phytate phosphorus (nPP) on the digestibility of minerals and amino acids. Diets were formulated to be nutritionally adequate except for Ca and nPP. Fifteen mash diets based on corn and soya bean meal with varying concentrations of Ca (6.4 to 12.0 g/kg) and nPP (2.4 to 7.0 g/kg) were used. Diets were clustered around total densities of Ca and nPP of 12, 13.5 or 15.0 (g/kg) and within each density, a range of five Ca : nPP ratios (1.14 : 1, 1.5 : 1, 2.0 : 1, 2.75 : 1 and 4.0 : 1) were fed. Birds had free access to feed and water throughout the study. At day 28, birds were euthanised for the determination of apparent ileal mineral and amino acid digestibility. Data were modelled in R version 2.15 using a linear mixed-effects model and interrogation of the data was performed by fitting a low order polynomial function. At high Ca concentrations, increasing nPP led to an increase in the apparent digestibility of minerals. Apparent ileal digestibility of phosphorus (P) was enhanced with increasing dietary nPP up to 5.5 g/kg beyond which no improvements were found. Maximal Ca digestibility was found in diets with >8.0 g/kg Ca with concomitant low concentrations of nPP. Diets with a broader Ca : nPP ratio improved the digestibility of Ca but were deleterious to the digestibility of P. In this study, apparent digestibility of amino acids was broadly unaffected by dietary Ca and nPP concentrations. However, interactions between Ca and nPP were observed for the digestibility of glutamine, tyrosine and methionine (all P<0.001). Nitrogen digestibility showed discrete optima around 10.0 and 5.0 g/kg nPP and Na digestibility was maximised around 8 to 9.0 g/kg Ca and 4.5 to 5.4 g/kg nPP. These data show that the ratio of Ca : nPP is more influential to mineral digestibility than the absolute dietary concentration of each macro mineral.     

Do macroconsumers affect insect responses to a natural stream phosphorus gradient?

We assessed the role of macroconsumers (e.g. fishes and shrimps) in affecting the response of insect assemblages to a natural phosphorus gradient formed by six streams with different phosphorus levels (range 12–350 μg/l). We hypothesized that insect responses to the phosphorus gradient would be strongest in the absence of macroconsumers. Within each stream, macroconsumers were allowed access to, or were excluded from, leaf packs using electric `fences'. Macroconsumers did not have significant effects on insects, but there was a significant phosphorus effect. Insect assemblages in high-phosphorus streams had 3–12-fold greater biomass and 3–11-fold greater abundance than assemblages in low-phosphorus streams. We also found that insect responses to phosphorus were more variable when assessed on the natural benthic substrate (e.g. mixed detritus) than in standardized leaf packs. In both substrates, the relationship between insects and phosphorus was not linear: abundance and biomass increased with phosphorus concentration to an asymptote. This suggests that insects were responding to a food resource gradient (e.g. fungi and bacteria). The Michaelis–Menten model provided a good fit for the relationship between insects and phosphorus concentrations, with half-saturation constants ranging from 12 to 60 μg SRP/l. The asymptotic relationship observed between phosphorus and insects suggests that phosphorus saturation occurred above a threshold of ca. 100 μg SRP/l. Our results provide support for the hypothesis that detritus-based food webs are mainly controlled by bottom-up forces.     

Impacts of excessive dietary phosphorus on zebra mussels

Stoichiometric theory predicts that organisms should experience dietary imbalances not only when nutrients (e.g., phosphorus, P) are limiting relative to carbon (C), but also when nutrients are in excess (i.e., well above somatic demand). Nevertheless, few experiments have elucidated the response of consumers in such low C:P conditions. We assessed the growth, tissue stoichiometry, and nutrient excretion of the invasive primary consumer, zebra mussel (ZM), Dreissena polymorpha, under three dietary C:P conditions (C:P = 20, 45, 380) in the laboratory. The two low C:P conditions represent increasingly common eutrophic systems, while the high C:P treatment is representative of oligotrophic systems. Growth rates and condition were lower when ZMs were fed a low C:P (20 and 45) diet, compared to the C:P = 380 treatment, wherein ZMs grew rapidly and exhibited lower somatic C:P. Furthermore, ZMs in the C:P = 20 and C:P = 45 treatments excreted more ammonia indicative of protein catabolism. These results clearly show that hypereutrophic conditions invoke significant shifts in physiology, growth, and condition of ZMs. Together, these results are consistent with stoichiometric theory that predicts costs associated with the intake of excess dietary P.     

Benthic sediment influence on dissolved phosphorus concentrations in a headwater stream

Phosphate interacts with inorganic sediment particles through sorption reactions in streams. Collectively, this phosphorus (P) buffering mechanism can be an important determinant of soluble reactive P (SRP) concentrations. If sorption reactions control SRP concentrations in a stream, then differences in sediment characteristics may cause spatial differences in SRP concentrations. This prediction was tested by examining sediment-buffering characteristics and spatial variation in SRP among reaches with distinct sediment composition (i.e., fine versus coarse particles) in two tributaries of Boulder Creek, a headwater stream in central Wisconsin. SRP concentrations were significantly lower and algal available P and P sorption capacity were significantly higher in the reach dominated by fine sediments. Although fine particles such as sand had the greatest P sorption capacity, no retention could be attributed to biotic processes, whereas over 50% of P retention in coarse particles such as gravel could be linked to biotic uptake. Equilibrium P concentration (EPC₀) assays from different sediment fractions also indicate that biotic uptake is relatively unimportant in sand particles (EPC_live 10 μg/L: EPC_killed 10 μg/L) but very important in gravel or larger particles (EPC_live 10 μg/L: EPC_killed 80 μg/L). Thus, sediment influence on stream water P concentrations can shift predictably from abiotic sorption in reaches with fine particles to biotic retention in areas dominated by coarse sediments. Consequently, changes in sediment composition due to natural or anthropogenic disturbance have the potential to alter the type and strength of sediment-associated processes determining ambient stream P concentrations.     

Effects of stream phosphorus levels on microbial respiration

SUMMARY 1. We examined microbial respiration among streams in lowland Costa Rica comprising a natural phosphorus gradient (5–350 μg SRP L^?1) resulting from variable inputs of solute‐rich (e.g. P, SO₄ and Cl) groundwater. 2. Microbial respiration rates were determined by measuring oxygen change in situ in nine low‐order streams on three substrate types: mixed leaves collected from the stream bottom, conditioned Ficus leaves and sediments. 3. Respiration rates on both leaf types were positively related to phosphorus and negatively related to N : P ratios. Microbial respiration rates on sediments were not related to any of the variables [i.e. soluble reactive phosphorus (SRP), N‐NO₃ and N : P] measured. 4. Respiration rates on newly colonised Ficus leaves formed an asymptotic curve increasing to a plateau, suggesting that saturation with phosphorus occurred at concentrations <15 μg SRP L^?1. 5. To test the hypothesis that phosphorus was the main solute in solute‐rich water that was driving observed differences in microbial respiration rates, we artificially enriched a small stream with phosphorus and measured changes in respiration before and after enrichment. 6. Experimental phosphorus enrichment produced increases in respiration rates similar in magnitude to those observed in the nine streams forming the natural phosphorus gradient, supporting our hypothesis that phosphorus was the major variable driving interstream differences in microbial respiration rates. Respiration rates were higher in this study than those reported for most other tropical streams and rivers with the exception of those reported for tropical Asian streams. 7. Results indicate that variations in phosphorus concentrations can potentially affect patterns of microbial respiration rates at a landscape level via differential inputs of solute‐rich groundwater into streams.     

养分和水添加对弃耕草地土壤无机磷组分的影响

合理的养分和水分管理措施是提高退化草地生产力和生物多样性的有效途径,但养分和水添加对弃耕草地土壤无机磷组分的影响研究较少.本文依托内蒙古多伦县2005年建立的养分(N∶ 10 g·m-2·a-1、P∶ 10g·m-2·a-1)和水分(植物生长季增水180 mm)添加田间试验,研究了表土(0～10 cm)无机磷组分及有效...     

Plant based phosphorus recovery from wastewater via algae and macrophytes

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Highlights? Algal ponds and macrophyte wetlands in widespread use for wastewater treatment. ? Harvested algae/macrophytes require <1/10 of the area compared to terrestrial crops for phosphorus uptake. ? Luxury uptake could be used to increase the phosphorus content of the biomass. ? Multiple opportunities exist (e.g. offshore cultivation) but are still in their infancy. ? Phosphorus recovery via plants has potential to become an important future solution.     

Allocation trade-off between root and mycorrhizal surface defines nitrogen and phosphorus relations in 13 grassland species

Plant and Soil - In oligotrophic ecosystems efficient nutrient uptake mechanisms, like extensive root systems or the association with belowground symbionts (e.g. arbuscular mycorrhizal fungi, AMF),...     

A key role of aluminium in phosphorus availability,food web structure,and plankton dynamics in strongly acidified lakes

We studied extracellular acid phosphatase activity (AcPA) of planktonic microorganisms, aluminium (Al) speciation, and phosphorus (P) cycling in three atmospherically acidified (pH of 4.5–5.1) mountain forest lakes: ?ertovo jezero (CT), Prá?ilské jezero (PR), and Ple?né jezero (PL) in the Bohemian Forest (?umava, Böhmerwald). Microorganisms dominated pelagic food webs of the lakes and crustacean zooplankton were important only in PR, with the lowest Al concentrations (193 µg L^?1) due to 3–4 times lower terrestrial input. The lakes differed substantially in Al speciation, i.e., in the proportion of ionic and particulate forms, with the highest proportion of ionic Al in the most acid CT (pH = 4.5). The P concentration in the inlet of PL (mean: 22.9 µg L^?1) was about five times higher than in CT and PR (3.9 and 5.1 µg L^?1, respectively). Average total biomass of planktonic microorganisms in PL (593 µg C L^?1) was, however, only ～2-times higher than in CT and PR (235 and 272 µg C L^?1, respectively). Enormous AcPA (means: 2.17–6.82 µmol L^?1 h^?1) and high planktonic C : P ratios suggested severe P limitation of the plankton in all lakes. Comparing 1998 and 2003 seasons, we observed changes in water composition (pH and Al speciation) leading to a significant increase in phytoplankton biomass in the lakes. The increase in the seston C : P ratio during the same time, however, indicates a progressive P deficiency of the lakes. The terrestrial Al inputs, together with in-lake processes controlling the formation of particulate Al, reduced P availability for planktonic microorganisms and were responsible for the differences in AcPA. At pH < 5, moreover, ionic Al forms caused inhibition of extracellular phosphatases. We postulate that both particulate and ionic Al forms affect P availability (i.e., inhibition of extracellular phosphatases and inactivation of P), specifically shape the plankton composition in the lakes and affect plankton recovery from the acid stress.     

氮磷添加对内蒙古温带草原植物功能群氮含量的影响

植物功能群氮含量既是理解氮沉降对生物多样性影响的关键指标,也是生产力过程模型模拟的重要参数,极易受氮素可利用性的影响和磷元素的限制。基于内蒙古温带草原4年氮磷添加试验(N10、N40、P5、P10及其交互,数字代表添加剂量,单位为g m^-2 a^-1),分析氮磷添加对植物群落及三种植物功能群(禾本科、灌木和杂类草)氮含量的影响。结果表明:(1)氮添加显著增加了群落及各功能群的氮含量,同一处理水平下禾本科(N10)和灌木(N10和N40)的氮含量显著高于杂类草,同一功能群不同氮添加剂量间无显著差异;(2)磷添加对群落和三种功能群的氮含量无显著影响;(3)与单独氮添加相比,氮磷同时添加显著增加了群落、禾本科和杂类草氮含量,且高剂量氮磷添加的促进作用更大;(4)与单独氮添加相比,氮磷同时添加显著增加群落和三种功能群磷含量而降低氮磷比,相同处理水平下禾本科和杂类草磷含量增加幅度最大。本研究将为草原生态系统管理和应对全球变化提供科学依据。     

土壤胶体磷活化迁移的影响因素及分析技术

胶体在土壤磷素迁移中起重要作用.土壤胶体磷活化迁移对土壤磷库的变化和周围水环境质量产生影响.本文介绍了土壤胶体磷研究的相关进展,探讨了土壤理化性质、施肥、降雨、土壤改良剂等因素对胶体磷在土壤赋存迁移中的影响,分析了流场分离、电镜能谱、同步辐射X光近边吸收结构光谱和核磁共振等技术在胶体磷研究中的应用,以及降低胶体磷流失的方法,以期为胶体磷在土壤中赋存变化和迁移机制的研究提供重要信息.
     

Characterizing bioavailable phosphorus concentrations in an agricultural stream during hydrologic and streambed disturbances

In freshwater ecosystems, phosphorus (P) is often considered a growth-limiting nutrient. The use of fertilizers on agricultural fields has led to runoff-driven increases in P availability in streams, and the subsequent eutrophication of downstream ecosystems. Isolated storms and periodic streambed dredging are examples of two common disturbances that contribute dissolved and particulate P to agricultural streams, which can be quantified as soluble reactive P (SRP) using the molybdate-blue method on filtered water samples, or total P (TP) measured using digestions on unfiltered water reflecting all forms of P. While SRP is often considered an approximation of bioavailable P (BAP), research has shown that this is not always the case. Current methods used to estimate BAP do not account for the role of biology (e.g., NaOH extractions) or require specialized platforms (e.g., algal bioassays). Here, in addition to routine analysis of SRP and TP, we used a novel yeast-based bioassay with unfiltered sample water to estimate BAP concentrations during two storms (top 80% and?>?95% flow quantiles), and downstream of a reach where management-associated dredging disturbed the streambed. We found that the BAP concentrations were often greater than SRP, suggesting that SRP is not fully representative of P bioavailability. The SRP concentrations were similarly elevated during the two storms, but remained consistently low during streambed disturbance. In contrast, turbidity and TP were elevated during all events. The BAP concentrations were significantly related to turbidity during all disturbance events, but with TP only during storms. The novel yeast assay suggests that BAP export can exceed SRP, particularly when streams are not in equilibrium, such as the rising limb of storms or during active dredging.

     

Carbon : nitrogen : phosphorus ratios influence biofilm formation by Enterobacter cloacae and Citrobacter freundii

AIMS: To test the effects of C : N : P ratio modification of a well-known nutrient medium formulation, the Endo formulation on biofilm formation by Enterobacter cloacae Ecl and Citrobacter freundii Cf1 in both single-species and binary species biofilms. METHODS AND RESULTS: The C : N : P atom : atom ratio of a well-known nutrient medium formulation, the Endo formulation, that has been applied in fermentative biohydrogen studies, was modified to include two different C concentrations, one containing 17.65 g l(-1) and the other 8.84 g l(-1) sucrose, each containing four different C : N : P ratios, two at higher C : N : P ratios (334 : 84 : 16.8 and 334 : 84 : 3) and two at lower C : N : P ratios (334 : 28 : 5.6 and 334 : 28 : 1). Attached cells were enumerated after dislodging the biofilms that had formed on granular activated carbon (GAC). The modified medium containing 17.65 g l(-1) sucrose and having a C : N : P ratio of 334 : 28 : 5.6 resulted in significantly (P < 0.05) higher counts of attached cells for both single-species biofilms at 7.73 log(10) CFU g(-1) GAC and 9.3 log(10)CFU g(-1) GAC for Ent. cloacae Ecl and Cit. freundii Cf1, respectively, and binary species biofilms at 8.2 log(10) CFU g(-1) GAC and 6.34 log(10) CFU g(-1) GAC for Ent. cloacae Ecl and Cit. freundii Cf1, respectively. Scanning electron micrographs showed qualitative evidence that the 334 : 28 : 5.6 ratio encouraged more complex and extensive biofilm growth for both single-species and binary species biofilms. CONCLUSIONS: The differences in the attachment numbers between the different ratios were found not to be a result of the individual actions of the bacterial isolates involved but rather because of the effects of the various C : N : P ratios. The 334 : 28 : 5.6 ratio showed significantly (P < 0.05) higher counts of attached cells for both single-species and binary species biofilms. SIGNIFICANCE AND IMPACT OF THE STUDY: This study indicates that C : N : P ratios should be a key consideration with regard to maximizing biofilm formation in shake flask and fluidized bed bioreactor studies as well as understanding fundamental factors affecting biofilm growth in natural environments.     

施磷对川西北高寒草地土壤磷形态及有效性的影响

以川西北高寒草地为研究对象,采用随机区组设计,设置0、10、20、30、40、50、60 g/m²的过磷酸钙(P₂O₅,16%)施肥试验,分析土壤不同形态磷含量和有效磷(Olsen-P)含量变化特征,探究施磷对川西北高寒草地土壤磷形态及有效磷的影响。结果表明：(1)随施磷量增加,土壤总磷(TP)含量先增加后趋于平稳而Olsen-P含量减少。高水平(50、60 g/m²)施磷下氢氧化钠有机磷(NaOH-Po)及残留磷(Residual-P)是高寒草地主要的磷素累积形态,其含量显著高于不施磷处理;(2)树脂交换态磷(Resin-Pi)、碳酸氢钠无机磷(NaHCO₃-Pi)、碳酸氢钠有机磷(NaHCO₃-Po)和氢氧化钠无机磷(NaOH-Pi)含量随施磷量增加整体呈先增加后降低趋势,表层土壤30 g/m²磷肥用量下其值均为最高,分别为21.54、22.94、65.86、64.48 mg/kg。酸溶性无机磷(HCl-Pi)随施磷量增加整体呈下...     

Particulate and dissolved phosphorus forms in freshwater: composition and analysis

In recent research, particulate and dissolved phosphorus components have been separated and characterized on the basis of their physical and chemical properties and partly by their origins.Classical operationally defined monitoring variables (dissolved reactive phosphorus, dissolved unreactive phosphorus and particulate phosphorus) are not congruent with known specific physical or chemical components of phosphorus in natural waters or with their bioavailability.Physical isolation of true particles, colloids and molecules of various sizes is possible at present although it is not recommended for routine use.Chemical characterization of particulate phosphorus is performed mainly by sediment extraction procedures (specialized for inorganic species) and — to a lesser degree — by cell extraction procedures (specialized for organic compounds). The extraction procedures are similar and physical preseparation or alternative procedures (e.g. enzymatic assays) are essential.Smaller colloids and dissolved compounds are physically separated by column chromatography and are often chemically characterized by degradation on the addition of specific enzymes.     

Seasonal changes in inorganic and organic phosphorus in the soil of a riparian forest

This study addresses the temporal distribution of forms of phosphorus in the soil of a temporarily flooded riparian forest of the valley of the river Garonne (Southwest of France). A sequential extraction for forms of phosphorus of increasing chemical stability was used. During the study period (13 months), the forest was flooded a few days during March and May. In winter, resin-Pi concentration was high (26 g g^–1) in comparison to spring values (<9 g g^–1). NaHCO₃-Po, NaHCO₃-Pi or NaOH-Pi concentrations increased during winter (up to 74, 124 and 78 g g^–1 respectively) and decreased significantly during spring (32, 44 and 32 g g^–1 respectively). This pattern was attributed to simultaneous mineralization and plant uptake during the growing season and to the flood events (erosional processes and P-release). During summer and fall, resin-Pi concentration increased significantly (up to 26 g g^–1 in October). NaHCO₃-Po concentrations remained low during spring and summer (<33 g g^–1), and increased significantly in fall (>45 g g^–1 NaHCO₃-Pi or NaOH-Pi increased in late spring or summer (90 g g^–1 and 68 g g^–1 respectively). Increasing concentrations of the labile forms during late spring or summer were ascribed to the warm temperature and soil dryness that limited plant growth. HCl-Pi increased regularly after the floods (174 g g^–1 before the flood events to 254 g g^–1 after the floods). Residual P presented a similar pattern i.e. 214 g g^–1 and 279 g g^–1 respectively before and after the flood events. This pattern was attributed to a progressive incorporation of flood deposits to the soil.