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Phosphorus enrichment of marsh soils can act as an internal source of nutrients to the water column, continuing to drive existing wetland eutrophic conditions even after external sources have been terminated. The goal of this study were to determine the effects of soil P concentration and flood intolerant vegetation presence on initial (1-10 d) and extended (10-38 d) P release rates from the soils after reflooding. Intact soil cores were collected from P enriched and unenriched areas of the Blue Cypress Marsh in east-central Florida. Initial P release was greater in soils with higher soil total P concentrations and containing vegetation. Soil P enrichment resulted in the final water column P concentrations in the enriched cores to be 50% higher than those in the P unenriched cores. A single drawdown and reflood event led to ~6% of the total soil P released to the water column from the P enriched vegetated treatment compared with a ~1% of total P released from the P enriched non-vegetated treatment. Initial P release rates from the enriched, vegetated treatment were five times greater than the enriched, non-vegetated treatment. Episodic growth of flood intolerant plants under drawdown conditions was shown to be a significant mechanism for nutrient release in ephemerally flooded P enriched wetland systems. Episodic flooding and drying cycles could therefore mobilize P over the long-term from P enriched to P unenriched areas. Abbreviations: BCMCA, Blue cypress marsh conservation area; SRP, soluble reactive P; TDP, total dissolved phosphorus; TP, total phosphorus; TPi, total inorganic P; TPo, total organic P.

Nanoindentation tests have been conducted on five different polyolefins, comprising a high density polyethylene, a low density polyethylene, a linear low density polyethylene, a polypropylene homopolymer and a polypropylene copolymer. The nanoindenter was fitted with a 'Dynamic Stiffness Measurement' (DSM) facility that permits measurement of storage modulus and loss modulus at frequent intervals during an indentation test. The results were quite scattered, especially those for the loss modulus, and methods of processing the data to derive meaningful results were examined and are discussed. The storage modulus measurements were found to give the same stiffness ranking as the monotonic load-displacement data when comparing indentations on the same material. Some correlation was found between the storage modulus and fractional crystallinity. An averaging procedure was developed for the loss modulus values that appeared to give a consistent assessment of the dissipation properties of the different materials. Analysis of the monotonic component of the load-displacement data indicated that the nature of the deformation changed from mainly elastic/viscoelastic to mainly viscoelastic/plastic during the course of the indentation tests. POLYM. ENG. SCI., 46: 1160-1172, 2006. © 2006 Society of Plastics Engineers, INTRODUCTION The traditional method to test the hardness of a material involves loading a hard indenter against the material under scrutiny. If the load is large enough, plastic deformation occurs [...]

Historic phosphorus (P) loading from agricultural areas has been identified as one of the major causes for ecological changes occurring in the Florida Everglades. The restoration plan for the Everglades includes construction of large stormwater treatment areas (STAs) to intercept and treat this relatively high nutrient water down to very low total P (TP) concentrations. One such STA has been in operation for approximately 10 yr and contains both emergent aquatic vegetation (EAV) and submerged aquatic vegetation (SAV) communities. The surface water TP concentrations in areas near the outflow range from 0.02 to 0.05 mg TP [L.sup.-1]. To simulate these areas, we investigated the interaction of vegetation type; EAV or SAV; and hydrology; continuously flooded or periodic drawdown; on the P removal capacity in mesocosms packed with peat soil obtained from STA-1W. The surface water had low TP concentrations with an annual mean = 0.023 mg [L.sup.-1]. For SRP and TP, hydrologic fluctuations alone had no discernable impact on P treatment while vegetation type showed a significant impact. Influent soluble reactive P (SRP) decreased by 49% for the SAV treatments compared with 41% for the EAV treatments, irrespective of hydrology treatment. The reduction of dissolved organic P (DOP) was also higher for the SAV treatment averaging 33% while showing a reduction of 11% for the EAV treatments. There was no significant difference in the treatment efficiency of particulate P (PP) across the treatments. For TP, SAV treatments removed 45% of TP while EAV removed significantly less at 34%. By mass calculations, the EAV required 85% more P for plant growth than was removed from the water column in 1 yr compared with only 47% for the SAV. Therefore, the EAV 'mined' substantially more P from the relatively stable peat soil, translocating it into the detrital pool.

The molecular degradation characteristics of three different polyethylenes were determined by deriving chain scission and crosslinking concentrations from gel permeation chromatography molecular weight distributions obtained after 3 weeks and 6 weeks laboratory ultraviolet exposure. Injection-molded bars (3 mm thick) made from a low-density polyethylene (LDPE), a linear low-density polyethylene (LLDPE), and a high-density polyethylene (HDPE) were used and all showed strong depth variations in degradation. Degradation was rapid near the exposed surfaces but very little change occurred in the bar centers, due to oxygen starvation. The most rapid rises in scission and crosslink concentrations were observed with LDPE, for which the concentrations after 6 weeks exposure were approximately double those measured after 3 weeks. With LLDPE and HDPE the scission and crosslink concentrations after 6 weeks exposure were very much greater than twice those after 3 weeks. Scission dominated over crosslinking at all depths and for all materials the scission/crosslink ratio was always ≥3, with a value of ~9 recorded for HDPE near the exposed surface after 6 weeks exposure. POLYM. ENG. SCI., 45:579-587, 2005. © 2005 Society of Plastics Engineers, INTRODUCTION Photooxidation of polyethylenes has been studied intensively over the past three decades [1-4]. This stems from its high volume usage, which makes information regarding its chemical degradation of vital [...]

Test bars (3 mm thick) made from a high-density polyethylene (HDPE), a low-density polyethylene (LDPE), and a linear low-density polyethylene (LLDPE) were injection-molded from virgin polymer and from blends containing recycled photodegraded polymer of the same kind. The molded bars were then subjected to ultraviolet (UV) exposure. Crystallinity measurements were made at different depths from the exposed surface using differential scanning calorimetry. The effects caused by processing and photodegradation were separated by comparing thermograms obtained in the initial DSC run and in a reheating run, respectively. Chemi-crystallization was produced by UV exposure. The results are interpreted in terms of molecular scission and photo-initiated molecular defects. Scission accounts for the observed chemi-crystallization, whereas the molecular defects inhibit crystallization and eventually limit chemi-crystallization. After remelting, crystallization of the photodegraded materials is influenced both by the molecular mass distribution and by the defect content of the material. The changes in crystallization behavior caused by photodegradation are different for the three polyethylenes. The results obtained using blends that included photodegraded recyclate were consistent with this material acting as a pro-degradent. The recyclability of the materials is discussed. POLYM. ENG. SCI., 45:588-595, 2005. © 2005 Society of Plastics Engineers, INTRODUCTION The crystallization of polymers depends on many factors, including the shape and stereoregularity of the repeat unit, the presence of branches and crosslinks, and the molecular chain length in [...]

A study has been made of changes in residual stress distributions caused by weathering in polypropylene and polystyrene. Chemi-crystallization has a major effect in polypropylene and an analysis based on the volumetric changes that occur on crystallization has been developed. Close to the surface, fractional crystallinity changes up to 4% are caused by photodegradation (X-ray measurements by Rabello and White (18)). It is estimated that this would cause a tensile residual stress of [approximately]2MN[m.sup.-2] to form at the surface if there were no preexisting residual stresses; in the case examined here, the effect of this shrinkage stress was to reduce the compressive residual stress to a small value (, INTRODUCTION Residual stresses form in thermoplastic moldings as the result of the temperature gradients present during solidification (1-3). The stresses are normally compressive near the surface of the molding and [...]

Large residual stresses have been generated in injection molded bars by ejecting them prematurely and completing the cooling process by quenching into ice water or liquid nitrogen. The stress distribution formed under these conditions was found to be much closer to parabolic than is the case when the moldings cool conventionally. Limited testing on moldings made in this way indicated significant property enhancement and improved resistance to ultraviolet degradation., INTRODUCTION Residual stresses form in injection moldings as a consequence of the thermal gradients that are present during solidification (1-3). The surface regions of the molding cool and solidify before [...]

Distortion of nylon 6,6 molded bars caused by one-sided absorption of water has been investigated experimentally and the results have been compared with the predictions of an analysis based on data measured on dry bars or bars that were immersed completely in water. Account is taken of swelling, secondary crystallization, variations in Young's modulus, and the original residual stress distribution prior to the absorption of water. The major influences on distortion are (i) swelling and (ii) secondary crystallization. A much smaller effect is caused by the change in the residual stress distribution resulting from the change in the distribution of Young's modulus that develops when water is absorbed. The two major effects normally act in opposite directions, and may sometimes balance out. Differences in distortion obtained when moldings that had different aging histories were exposed to water absorption from one surface only are discussed.