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1

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PHOSPHORUS ASSIMILATION IN A STREAM SYSTEM OF THE LAKE OKEECHOBEE BASIN (1996)

Reddy, K. R. ; Flaig, E. ; Scinto, L. J. ; [et al.]

Oxford, UK : Blackwell Publishing Ltd

Journal of the American Water Resources Association 32 (1996), S. 0

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ISSN: 1752-1688

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Architecture, Civil Engineering, Surveying , Geography

Notes: : The ability to predict how streams and wetlands retain phosphorus (P) is critical to the management of watersheds that contribute nutrients to adjacent aquatic systems such as lakes. Field and laboratory experiments were conducted to determine the P assimilatory capacity of a stream (Otter Creek) in the Taylor Creek/Nubbin Slough Basin located north of Lake Okeechobee, Florida. Dominant soils in this basin are sandy Spodosols; landuse is primarily dairy farms and beef cattle pastures. Estimates of P assimilation show that sediments assimilate approximately 5 percent of the P load. Phosphorus assimilation rates in the stream were estimated using first-order relationships based on the total P concentration of the water column as a function of distance from the primary source. This method assumes minimal lateral inputs. Stream lengths required for one turnover in P assimilation were estimated to be in the range of 3–16 km. Laboratory studies using intact sediment cores indicated a P assimilation rate of 0.025 m day−1, and equilibrium P concentration of 0.16 ± 0.03 mg L−1 in the water column. Dissolved P concentration gradients in the sediments showed upward flux of P at water column P concentration of 〈0.16 mg L−1. Approximately 56–77 percent of the P assimilated in the above-ground vegetation during active growth was released or translocated within six months of senesence, suggesting short-term storage in above-ground vegetation. Bottom sediments and recalcitrant detrital plant tissue provide for long-term P assimilation in the creek. Although stream sediments have the potential to adsorb P, high flow rate and low contact period between water and sediment limits this process.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1752-1688.1996.tb04061.x

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2

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Mepiquat chloride (PIX)-induced changes in photosynthesis and growth of cotton (1996)

Reddy, A. Ramachandra ; Reddy, K. R. ; Hodges, H. F.

Springer

Plant growth regulation 20 (1996), S. 179-183

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ISSN: 1573-5087

Keywords: cotton ; growth ; mepiquat chloride ; photosynthesis ; PIX ; RuBP carboxylase

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract Mepiquat chloride (N, N-dimethylpiperidinium chloride), well known as PIX, is a potential systemic plant growth regulator. The effects of PIX on plant height, stem elongation, leaf area, net photosynthetic rates, chlorophyll content, sucrose and starch levels, and RuBP carboxylase activity in cotton (Gossypium hirsutum L. cv. DES 119) plants were measured. PIX was sprayed (0, 7.65, 15.3, 30.6 or 61.2 g active ingredient ha−1) on the plants at first square (25 days after emergence) and measurements were made at frequent intervals. Plant height was clearly reduced by PIX. The total length of vegetative branches and fruiting branches was 40% and 50% less than the control. Total leaf area in PIX treated plants was 16% less than the control. Net photosynthetic rates were 25% less in PIX-treated leaves. PIX treated leaves had more chlorophyll content. The activity of RuBP carboxylase was decreased in PIX treated plants. Starch accumulation was noticed in PIX treated leaves while sucrose content was not changed. The data reported here suggest that reduced growth responses induced by PIX results in partial loss of photosynthetic capacity in cotton at least up to 20 days after application of the growth regulator.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00043305

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3

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Influence of redox potential on phosphate-uptake by sediments in two sub-tropical eutrophic lakes (1997)

Olila, O. G. ; Reddy, K. R.

Springer

Hydrobiologia 345 (1997), S. 45-57

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ISSN: 1573-5117

Keywords: P sorphon kinetics ; redox potential (Eh) ; lake sediments ; P fractions ; mineral P equilibria ; eutrophic lakes

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract 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-P ≤ 110 μM) 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.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1002975231341

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4

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Influence of benthic organisms on solute transport in lake sediments (1996)

Rees, K. C. J. ; Reddy, K. R. ; Rao, P. S. C.

Springer

Hydrobiologia 317 (1996), S. 31-40

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ISSN: 1573-5117

Keywords: benthic organism ; diffusion ; mixing ; sediments ; tritium ; transport

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Increased inputs of nutrients into the waters of Lake Okeechobee has raised concern that the lake is becoming hypereutrophic. One aspect in understanding the overall cycling and dynamics of the nutrients in the system is the effect of benthic organisms on solute transport. Various diffusional models have been used to approximate the effect of benthic organisms on solute transport within sediments using diffusion coefficient values which represent the pooled contributions of molecular diffusion (D s ) and enhanced solute mixing due to macrobenthos activity (D i ). The objective of this study was to investigate the impact of benthic activity on solute transport by measuringD s (i.e., no benthic activity) and an apparent-dispersion or mixing coefficientD m (i.e., with benthic activity) for the four major sediment types of Lake Okeechobee, Florida using a reservoir technique. This method involved monitoring the depletion of a conservative tracer (tritiated water) from the overlying water (reservoir) resulting from transport into sediments using disturbed sediments repacked in cores (3.2 cm diam.) and undisturbed cores (3.2 to 12 cm diam.) obtained from the lake. Additional estimates ofD m andD s were also obtained by measuring tracer concentration profiles in the sediment cores at the end of a specified diffusion period. Molecular diffusion coefficients (D s ) measured forrepacked cores of sand, littoral, mud and peat sediments ranged from 0.90 to 1.29 cm2 d−1, and estimates ofD s were slightly higher in undisturbed cores without benthic organisms.D m values for undisturbed cores of mud, sand and littoral sediments having macrobenthic populations ranged from 2.09 to 24.78 cm2 d−1; values that were 1.6 to 15 times higher than those in sediments without benthic activity. Undisturbed cores of varying diameter from mud sediments had similar estimates ofD m for tritium; however, the undisturbed cores with larger diameters from littoral sediments yielded larger estimates ofD m , reflecting the heterogeneity of benthic population densities and activity. Therefore,D s estimates may not adequately represent transport processes for mud, sand and littoral sediments of Lake Okeechobee; hence careful consideration should be given to the role of benthic organisms in the overall transport of solutes across the sediment-water interface.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00013723

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5

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Forms and distribution of inorganic phosphorus in sediments of two shallow eutrophic lakes in Florida (1995)

Olila, O. G. ; Reddy, K. R. ; Harris, W. G.

Springer

Hydrobiologia 302 (1995), S. 147-161

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ISSN: 1573-5117

Keywords: phosphorus ; chemical fractionation ; synthetic P compounds ; minerals ; sediments ; eutrophic lakes

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Phosphorus (P) reactivity and bioavailability in lake sediments may be determined by different forms of P and their distribution. Reactive and nonreactive P pools in two shallow subtropical lake sediments (Lake Apopka and Lake Okeechobee) were determined by sequential chemical extraction using 1 M NH4Cl (pH 7.0), 0.1 M NaOH, and 0.5 M HCl, reportedly representing loosely-bound P, Fe- and Al-bound P, and Ca- and Mg-bound P respectively. The sequential P fractionation was tested using pure P compounds and selected P minerals. The scheme effectively separated Fe- and Al-P from Ca-P fractions in an FePO4-AlPO4-Ca3(PO4)2 mixture. Readily available P, defined as the sum of water-soluble P and NH4Cl-extractable P, in the unconsolidated gyttja (UCG) layer (surface 0–30 cm) of Lake Apopka sediments accounted for 10.1 to 23.7% of total P (TP). This sediment P fraction constitutes a large reservoir which may act as a source of P to the overlying water. In subsurface marl layers (134–148 cm depth) of Lake Apopka, NH4Cl-P constituted 〈I% of TP whereas Ca-Mg-bound P and highly resistant P (residual P) accounted for 35 and 64% of TP respectively. Results suggest that 1 M NH4Cl (pH 7.0) and 0.5 M HCl, reported to dissolve carbonate-bound P and Ca-Mg-bound P, respectively, may not be extracting distinct pools of P. Lake Okeechobee mud sediments had low concentrations of readily available P (2% of TP) and were dominated by Ca-Mg-bound P (HCl-P≥58% of TP). Sediments in the littoral and peat areas of Lake Okeechobee, however, had high concentrations of readily available P (9.7 and 17.4% of TP respectively); hence, these sediments may play an important role in internal P cycling. The NaOH-P (Fe-Al-P) concentrations for Lake Okeechobee sediments were strongly correlated with amorphous and poorly-crystalline Fe (p〈 0.01), suggesting that some P reactions in these sediments may be sensitive to changes in physico-chemical conditions such as redox potential and sediment resuspension.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00027039

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6

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Electrokinetic remediation of metal contaminated glacial tills (1997)

Reddy, K. R. ; Shirani, A. B.

Springer

Geotechnical and geological engineering 15 (1997), S. 3-29

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ISSN: 1573-1529

Keywords: Soil ; glacial till ; contamination ; metals ; electrokinetics ; remediation

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences

Notes: Summary This paper presents the results of an experimental investigation which studied the feasibility of using the electrokinetic process to remediate contaminated clays of glacial origin, otherwise known as glacial tills. An overview of the electrokinetic phenomena, as well as previously performed laboratory and field investigations, is first presented. The methodology of the electrokinetic experiments which were conducted to investigate the removal of metals from a glacial till is then described. A total of 16 experiments were conducted using glacial till samples obtained from a project site near Chicago. Sodium and calcium were used as the surrogate cationic metallic contaminants. These experiments demonstrated that ion transport during the electrokinetic process occurs due to both electro-osmosis and electromigration, but that due to electromigration is significantly higher than that due to electro-osmosis. Unlike other clays such as kaolinite, the glacial till used for this investigation possessed high buffering capacity because of its high carbonate content which prevented the acid front migration from the anode to the cathode during the electrokinetic process. The ion removal efficiency of the electrokinetic process was found to increase when: (1) the voltage gradient applied to the soil was increased, (2) the initial concentration of the contaminants was increased, and (3) the duration of the treatment process was increased. The ion removal efficiency was also greater for smaller ions which possess less ionic charge and when the ions existed independently in the soil as compared to when they coexisted. This investigation suggests that the electrokinetic process has significant potential for remediating glacial tills contaminated with metals. However, the properties of Na and Ca are not representative of contaminants, such as heavy metals, so further investigations are needed.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00881236

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