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.     

Competition between isoetids and invading elodeids at different concentrations of aquatic carbon dioxide

1. The growth of submerged macrophytes in softwater lakes is often assumed to be carbon limited. Isoetid species are well adapted to grow at low carbon availability and therefore commonly dominate the submerged macrophyte vegetation in softwater lakes. In many such lakes, however, large‐scale invasions of fast‐growing elodeid species, replacing the isoetid vegetation, have been observed. 2. In a laboratory experiment, we tested how rising aquatic carbon availability, in interaction with different densities of the isoetid Littorella uniflora, affected the growth (and thereby the potential invasion success) of the elodeid Myriophyllum alterniflorum. For this purpose, the growth of M. alterniflorum was determined at a combination of three concentrations of dissolved CO₂ (15, 90, 200 μmol L^?1) and three densities of L. uniflora (0, 553, 1775 plants m^?2). 3. At an ambient CO₂ of 15 μmol L^?1, M. alterniflorum could not sustain itself, whereas at raised CO₂ concentrations, growth became positive and increased with higher CO₂ availability. 4. The presence of L. uniflora, independent of its density, reduced the growth of M. alterniflorum by 50%. Whether this is related to nutrient availability or other factors is not clear. 5. Despite the growth reduction of M. alterniflorum by L. uniflora, at CO₂ ≥90 μmol L^?1, L. uniflora was still overgrown by M. alterniflorum. This may imply that, in field situations, M. alterniflorum can invade softwater systems with relatively high CO₂ availability, even in the presence of dense stands of L. uniflora.     

Bio-availability of phosphorus in sediments of the western Dutch Wadden Sea

The purpose of this study was to make a prognosis of the effects of extended purification of terrestrial waste water, reaching the Wadden Sea by the River Rhine and Lake IJssel, on the phosphate concentration in the western Wadden Sea.The quantities of different phosphorus fractions in intertidal and subtidal sediments of the Marsdiep tidal basin (western Dutch Wadden Sea) were measured. Different methods are applied to determine the amount of phosphorus that can be released from these sediments. The direct bioavailability is determined by inoculating sediment suspensions with a natural mixture of precultured micro-organisms from the sampling area. A second approach is the measurement of the phosphate release under different redox conditions. Sequential extraction of sediment samples with different solvents is also applied. Under the present conditions and compared to the nutrient loads from fresh water (Lake IJssel) and from the North Sea, the phosphorus stored in the sediments of the western Dutch Wadden Sea plays a minor role in the total supply to micro-algae and bacteria. The bulk of the biologically available phosphorus in the sediments originates from the metal-associated fraction. Releasable phosphate may contribute to the local annual primary production to an extent of ca 45 to ca 150 g C m^–2 a^–1. The total amount of phosphorus in the sediment (mainly calcite associated) is twice to 6 times the biologically available amount.     

Evidence for iron‐regulated cyanobacterial predominance in oligotrophic lakes

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Microbial metabolism in surface sediments and its role in the immobilization of phosphorus in oligotrophic lake sediments

Rapid microbial metabolism and a large phosphorus uptake potential were observed in surface sediments of Lake George, New York. This sediment (termed the flocculent layer) also exhibited a phosphorus limited condition and a large reservoir of inorganic phosphorus associated with humic substances. These observations suggest that the empirically observed phosphorus retention in oligotrophic lake sediments may be promoted by a rapid cycling of phosphorus between microflora and its associated organic matter.     

Iron:phosphorus ratio in surface sediment as an indicator of phosphate release from aerobic sediments in shallow lakes

Analysis of Danish lakes showed that both mean winter and mean summer concentrations of lake water total phosphorus in the trophogenic zone correlated negatively with the total iron to total phosphorus ratio (Fe:P) in surface sediments. No correlation was found between the water total phosphorus concentration and either the sediment phosphorus concentration alone or with sediment calcium concentration. The increase in total phosphorus from winter to summer, which is partly a function of net internal P-loading, was lowest in lakes with high Fe:P ratios in the surface sediment.A study of aerobic sediments from fifteen lakes, selected as representative of Danish lakes with respect to the sediment Fe and phosphorus content, showed that the release of soluble reactive phosphorus was negatively correlated with the surface sediment Fe:P ratio. Analysis of phosphate adsorption properties of surface sediment from 12 lakes revealed that the capability of aerobic sediments to buffer phosphate concentration correlated with the Fe:P ratio while the maximum adsorption capacity correlated with total iron. Thus, the Fe:P ratio may provide a measure of free sorption sites for orthophosphate ions on iron hydroxyoxide surfaces.The results indicate that provided the Fe:P ratio is above 15 (by weight) it may be possible to control internal P-loading by keeping the surface sediment oxidized. Since the Fe:P ratio is easy to measure, it may be a useful tool in the management of shallow lakes.     

A new experimental setup for studying the formation of phosphate binding iron oxides in marine sediments. Preliminary results

A new laboratory method is introduced to study theformation of phosphate binding iron(III) oxides at theredox boundary in marine sediments. A sediment core isgiven a very well-defined oxic-anoxic interface byplacing a 0.45 µm filter between the sediment andthe overlying water. After a period of 1 months thefilter is covered with a layer of fresh iron oxides,formed by the oxidation of upward diffusing Fe²⁺from the sediment pore water. The formed iron oxidesare investigated by electron probe X-ray microanalysis(EXPMA). With a sediment core from the brackish BalticSea the average molar composition of 788 formedparticles is Fe_1.00±0.13P_0.55±0.06Ca_0.37±0.04 plus unknown amounts of O, H andC. The results show that the particles have a uniformcomposition, and that calcium plays an important rolein the phosphate binding. The laboratory method is auseful supplement to in situ sampling forstudies of iron oxides.     

Regulation of root hair density by phosphorus availability in Arabidopsis thaliana

We characterized the response of root hair density to phosphorus (P) availability in Arabidopsis thaliana. Arabidopsis plants were grown aseptically in growth media with varied phosphorus concentrations, ranging from 1 mmol m⁻³ to 2000 mmol m⁻³ phosphorus. Root hair density (number of root hairs per mm of root length) was analysed starting at 7 d of growth. Root hair density was highly regulated by phosphorus availability, increasing significantly in roots exposed to low-phosphorus availability. The initial root hairs produced by the radicle were not sensitive to phosphorus availability, but began to respond after 9 d of growth. Root hair density was about five times greater in low phosphorus (1 mmol m⁻³) than in high phosphorus (1000 mmol m⁻³) media. Root hair density decreased logarithmically in response to increasing phosphorus concentrations within that range. Root hair density also increased in response to deficiencies of several other nutrients, but not as strongly as to low phosphorus. Indoleacetic acid (IAA), the auxin transport inhibitor 2-(p-chlorophenoxy)-2-methylpropionic acid (CMPA), the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC), and the ethylene synthesis inhibitor amino-oxyacetic acid (AOA) all increased root hair density under high phosphorus but had very little effect under low phosphorus. Low phosphorus significantly changed root anatomy, causing a 9% increase in root diameter, a 31% decrease in the cross-sectional area of individual trichoblasts, a 40% decrease in the cross-sectional area of individual atrichoblasts, and 45% more cortical cells in cross-section. The larger number of cortical cells and smaller epidermal cell size in low phosphorus roots increased the number of trichoblast files from eight to 12. Two-thirds of increased root hair density in low phosphorus roots was caused by increased likelihood of trichoblasts to form hairs, and 33% of the increase was accounted for by changes in low phosphorus root anatomy resulting in an increased number of trichoblast files. These results show that phosphorus availability can fundamentally alter root anatomy, leading to changes in root hair density, which are presumably important for phosphorus acquisition.     

Effect of phosphorus availability on basal root shallowness in common bean

Root gravitropism may be an important element of plant response to phosphorus availability because it determines root foraging in fertile topsoil horizons, and thereby phosphorus acquisition. In this study we seek to test this hypothesis in both two dimensional paper growth pouch and three-dimensional solid media of sand and soil cultures. Five common bean (Phaseolus vulgaris L.) genotypes with contrasting adaptation to low phosphorus availability were evaluated in growth pouches over 6 days of growth, and in sand culture and soil culture over 4 weeks of growth. In all three media, phosphorus availability regulated the gravitropic response of basal roots in a genotype-dependent manner. In pouches, sand, and soil, the phosphorus-inefficient genotype DOR 364 had deeper roots with phosphorus stress, whereas the phosphorus-efficient genotype G19833 responded to phosphorus stress by producing shallower roots. Genotypes were most responsive to phosphorus stress in sand culture, where relative root allocation to the 0–3- and 3–6-cm horizons increased 50% with phosphorus stress, and varied 300% (3–6 cm) to 500% (0–3 cm) among genotypes. Our results indicate that (1) phosphorus availability regulates root gravitropic growth in both paper and solid media, (2) responses observed in young seedlings continue throughout vegetative growth, (3) the response of root gravitropism to phosphorus availability varies among genotypes, and (4) genotypic adaptation to low phosphorus availability is correlated with the ability to allocate roots to shallow soil horizons under phosphorus stress.     

Release rates and biological availability of phosphorus released from sediments receiving aquaculture wastes

Aquaculture is an increasingly significant user of freshwater resources in Scotland. In 1989, the total fish biomass produced in Scottish freshwater amounted to 7000 t. 50% of this total was reared in floating cage systems situated in lochs (lakes). Both solid (mainly in the form of uneaten feeds and faecal matter) and dissolved byproducts of the production cycle enter the limnetic environment untreated. Much solid waste material accumulates directly on the sediments beneath the cage systems. This leads to a localised enrichment in nutrient elements of the sedimentary environment. The experiments served to quantify rates of total phosphorus (TP) and dissolved reactive phosphorus (DRP) release from undercage and control sites, and to relate such releases to the biological availability of the released P. Results indicate significantly higher levels of NH₄Cl-extractable P in sediments affected by waste deposition from fish cages. TP and DRP release, and greater growth of Chla are obtained from undercage cores compared with control sites. No link between extractable-P content of sediments, or release rate and Chla production was established.     

Resuspension studies in cylindrical microcosms: Effects of stirring velocity on the dynamics of redox sensitive elements in a coastal sediment

Effects of resuspension on the release of dissolved, redox sensitive elements (Fe, Mn) was studied in cylindrical microcosms. Effects from changing water stirring velocity in sediment pools were evaluated through measurements of pore water profiles of dissolved Mn, Fe and redox potential. Mn was a good natural marker to follow such effects. At current velocities below the threshold velocity for resuspension (37 cm s-1), Mn release rates to overlying water were 100 times higher compared to steady-state values. Pulse increases in Mn concentration were the result of convective currents inside flow chambers. These results were strongly supported by measurements of Eh profiles in the sediment pore water. Furthermore, impacts from increasing stirring velocity were found down to 1.9 cm depth below the resuspended layer of sediment.     

Stimulation of root hair elongation in Arabidopsis thaliana by low phosphorus availability

Low phosphorus availability stimulates root hair elongation in many plants, which may have adaptive significance in soil phosphorus acquisition. We investigated the effect of low phosphorus on the elongation of Arabidopsis thaliana root hairs. Arabidopsis thaliana plants were grown in plant culture containing high (1000 mmol m^?3) or low (1 mmol m^?3) phosphorus concentrations, and root hair elongation was analysed by image analysis. After 15d of growth, low-phosphorus plants developed root hairs averaging 0.9 mm in length while high-phosphorus plants of the same age developed root hairs averaging 0.3 mm in length. Increased root hair length in low-phosphorus plants was a result of both increased growth duration and increased growth rate. Root hair length decreased logarithmically in response to increasing phosphorus concentration. Local changes in phosphorus availability influenced root hair growth regardless of the phosphorus status of the plant. Low phosphorus stimulated root hair elongation in the hairless axr2 mutant, exogenously applied IAA stimulated root hair elongation in wild-type high-phosphorus plants and the auxin antagonist CM PA inhibited root hair elongation in low-phosphorus plants. These results indicate that auxin may be involved in the low-phosphorus response in root hairs.     

Phosphorus release from sediments in hardwater eutrophic lakes: the effects of redox-sensitive and -insensitive chemical treatments

1. Phosphorus (P) release from bottom sediments is an important source of nutrient enrichment in many lakes in sedimentary basins, such as those in western Canada. On the Boreal Plain, sediment P release is particularly strong during periods of seasonal anoxia.
2. In this study, the effects of reduction–oxidation (redox)-sensitive and -insensitive chemicals on P release were examined in sediment cores collected from three eutrophic lakes.
3. Contrary to expectations, redox-sensitive treatments were no more effective at lowering total phosphorus (TP) in sediment cores than some redox-insensitive treatments. Redox-sensitive treatments with FeCl₃ and FeCl₃ + O₂ reduced TP to 8 and 6%, respectively, of reference concentrations, whereas redox-insensitive treatments with alum or lime + alum reduced TP to 14% of reference concentrations. Lime and O₂ treatments reduced TP concentrations to 35 and 52% of reference concentrations, respectively.
4. The fraction of P that adsorbed and co-precipitated with iron and aluminium in the sediment cores was low (non-apatite phosphorus fractions < 5%), suggesting that P release was controlled by apatite solubility and bacterial metabolism.     

Comparison of iron,manganese, and phosphorus retention in freshwater littoral sediment with growth of Littorella uniflora and benthic microalgae

Sediment columns from an oligotrophic lake were percolatedwith artificial porewater in two 46-day experiments toexamine the effects of Littorella uniflora and benthicmicroalgae on retention of phosphorus (P) by either iron(Fe) or manganese (Mn). Cumulative retention of P, Fe, andMn was 2–5 times higher in sediment with L. uniflora thanin sediment with microalgae, because of higher P uptake andmore efficient Fe and Mn oxidation by L. uniflora than bymicroalgae. Thus 34% and 21%of added P was retained in L. uniflora inhabited sediments asmetal-oxide bound P compared to 11% and2% in microalgae inhabited sediments, inexperiments supplied with Fe and Mn, respectively. Theatomic ratio of Fe/P precipitation was about 1 and forMn/P precipitation it was about 5. These ratios indicateprecipitation of Fe(III)-phosphate (strengite) and metastableMn(IV)-compounds containing phosphate and hydroxide ions invariable amounts. In addition to metal-oxide P precipitation,increased P retention in the vegetated sediment was also causedby the presence of humic acid compounds, which accountedfor about 26% of total retained P.     

Reduced root cortical burden improves growth and grain yield under low phosphorus availability in maize

Root phenes and phene states that reduce the metabolic cost of soil exploration may improve plant growth under low phosphorus availability. We tested the hypothesis that under low phosphorus, reduced living cortical area (LCA) would increase soil exploration, phosphorus capture, biomass, and grain yield. Maize genotypes contrasting in LCA were grown in the field and in greenhouse mesocosms under optimal and suboptimal phosphorus regimes. Percent LCA in nodal roots ranged from 25% to 67%. Plants with 0.2 mm² less LCA under low phosphorus had 75% less root segment respiration, 54% less root phosphorus content, rooted 20 cm deeper, allocated up to four times more roots between 60 and 120 cm depth, had between 20% and 150% more biomass, 35–40% greater leaf phosphorus content, and 60% greater grain yield compared with plants with high LCA. Low‐LCA plants had up to 55% less arbuscular mycorrhizal colonization in axial roots, but this decrease was not correlated with biomass or phosphorus content. The LCA components cortical cell file number and cortical cell size were important for biomass and phosphorus content under low phosphorus. These results are consistent with the hypothesis that root phenes that decrease the metabolic cost of soil exploration are adaptive under phosphorus stress.     

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...     

Influence of redox potential on phosphate-uptake by sediments in two sub-tropical eutrophic lakes

Biogeochemical reactions in shallow eutrophic lakes areaffected bythe changes in redox potential (Eh) as bottom sedimentsundergotemporal resuspension and settling. The stability of varioussediment P fractions and kinetics of P-uptake were evaluatedfortwo sub-tropical lakes (Lake Apopka and Lake Okeechobee,Florida)using sediment suspensions in closed systems maintained atvariousEh levels ranging from –235 to 555 mV. Redox potential hadminimal effect on the stability of NaOH-P (Fe-/Al-bound P plusmoderately resistant organic P) and HCl-P (Ca-/Mg-P) fractionsinLake Apopka sediments. Increases in ortho-P and NH₄Cl-P(loosely-bound P plus labile organic P) concentrations wereobserved in highly reduced (Eh=–225 mV) Apopkasediments.Phosphate solubility diagrams and mineral equilibriacalculationssuggest that P-uptake by Apopka bottom sediments at elevated Pconcentrations (ortho-P110 M) was due toformationof Ca-P compounds and/or co-precipitation of P withCaCO₃. Incontrast, the ortho-P concentrations for Lake Okeechobeebottomsediments increased exponentially with decreasing Eh. Thequantityof NaOH-P fractions for these sediments decreased withdecreasingEh, suggesting the release of Fe- and Mn-bound P intosolution.Phosphate-uptake by Okeechobee bottom sediments (pH 7.5,ambient)followed first order kinetics, yielding a rate constant (k)of 0.51±0.05 h^-1. Unlike that of Apopka, the mudsediments in Lake Okeechobee have strong affinity for P ineitheraerobic or anaerobic conditions. Results suggest that even incalcareous systems, Fe and Al, when present in highconcentrations(as in the case of Lake Okeechobee), are actively involved inregulating P-uptake and geochemistry.     

Sedimentary losses of phosphorus in some natural and artificial Iowa lakes

Phosphorus sedimentation in four natural and four artificial Iowa lakes was measured by using sediment traps to determine if sedimentary phosphorus losses were greater in artificial lakes than in natural lakes and the limnological factors influencing phosphorus loss rates. Mean phosphorus sedimentation rates ranged from 13.3 to 218 mg · m^–2 day^–1. Although phosphorus sedimentation rates for the natural lakes as a group did not differ significantly from the rates for artificial lakes, there were significant differences among individual lakes. Phosphorus sedimentation rates also varied significantly during different seasons at different locations within a lake and at different depths within a location. Despite the variance, phosphorus sedimentation rates were strongly correlated with inorganic sediment concentrations and inorganic matter sedimentation rates, thus suggesting that inorganic sediments influence phosphorus sedimentation rates. When Iowa data were combined with data from published studies, mean sedimentation rates were directly correlated with mean chlorophyll a concentrations of the lakes. These data strongly suggest that sedimentation rates as measured by sediment traps are strongly influenced by the trophic status of a lake. Though sedimentation rates were higher in the more productive lakes, it is suggested that these rates represent only gross sedimentation rates rather than net sedimentation rates because of resuspension and resedimentation of bottom sediments.     

Particle size,percent organic carbon,phosphorus, mineralogy,and deposition of sediments in Ham's and Arbuckle lakes

Several sediment parameters were examined in a 40 ha lake with a maximum depth of 9 m and in a 950 ha lake, 26 m deep, from May through October, 1977. Particle size was finer at the deeper stations than at the shallower stations in both lakes. Sediments of the shallow stations generally had a more even grain size distribution. Variation in percent organic carbon and phosphorus among stations of different depths was not significant. However, temporal variation of phosphorus was significant as values increased during summer. Kaolinite was the dominant clay particle in both lakes, but the sediments also included quartz, mica, montmorillonite, and a montmorillonite-vermiculite interlayer. Sedimentation rate was inversely related to depth in the larger lake, while variation among stations in the smaller lake was slight.Research supported with funds from the Office of Water Research and Technology and the Bureau of Reclamation     

Genotypic variation of rice in phosphorus acquisition from iron phosphate: Contributions of root morphology and phosphorus uptake kinetics

To elucidate the contributions of rice root morphology and phosphorus uptake kinetics to P uptake by rice from iron phosphate, a sand culture experiment with either sufficient P supply (control treatment, 10 mg P/l as NaH₂PO₄) or Fe-P as the only source of P (40 mg P/pot as FePO₄ × 4H₂O) and a solution culture experiment supplied with either sufficient P (10 mg P/l) or deficient P (0.5 mg P/l) were conducted. Eight rice cultivars, which differed in P uptake from Fe-P, were investigated. Plant P uptake, root morphology, and P uptake kinetics were determined. There were significant (P < 0.05) genotypic variations in both plant dry weight and P uptake per plant among eight rice (Oryza sativa L.) cultivars when supplied with Fe-P as the P source. The Fe-P treatment significantly (P < 0.05) decreased plant dry weight, P uptake per plant, and P concentration in plant dry matter of all cultivars in comparison with the control plants. In Fe-P treated plants, significant (P < 0.05) genotypic variation was shown in root morphology, including root length, surface area, volume, and number of lateral roots. The P uptake per plant from Fe-P by rice was significantly (P < 0.05) correlated with root surface area and root volume as well as with the number of lateral roots, suggesting that the ability of rice to absorb P from Fe-P was closely related to root morphology. Low P supply in solution significantly increased the I _max (P < 0.05), but significantly decreased the K _M (P < 0.05) for P absorption by all rice cultivars. We supposed that kinetic characteristics of root P uptake could not account for the ability of rice to absorb P from Fe-P. Published in Russian in Fiziologiya Rastenii, 2007, Vol. 54, No. 2, pp. 260–266. The text was submitted by the authors in English.