A mobile pool of contaminated sediment in the Penobscot Estuary, Maine, USA.

The natural recovery of estuaries from contamination is largely determined by the timescale over which contaminated sediment is exported or buried and replaced by cleaner sediment that enters from the watershed or the ocean. That timescale depends on the size of the "pool" of contaminated sediment that resides in the estuary. The larger the pool, the longer the recovery timescale for a given rate of sediment input. A field study was undertaken as part of a study of mercury contamination in the Penobscot estuary to assess the mechanisms affecting the transport and fate of contaminated sediment. Based on measurements of water properties, currents and sediment transport and seabed samples analyzed for sediment properties and contaminant concentrations, a "mobile pool" of contaminated sediment with relatively uniform geochemical characteristics along a 20-km reach of the estuary was identified. This pool of sediment is mobilized seasonally by resuspension and trapping processes associated with salinity fronts that vary in location with discharge conditions. Sediment is transported down-estuary during high discharge and up-estuary during low discharge, with seasonal, bi-directional transport of sediment in the estuary significantly exceeding the annual input of new sediment from the watershed. This continual, bi-directional transport leads to homogenization of the chemical properties of the mobile sediment, including contaminant concentrations. The large mass of mobile sediment relative to the input of sediment from the watershed helps explain the long recovery timescale of contaminants in the Penobscot estuary.

Broadband acoustic quantification of stratified turbulence.

High-frequency broadband acoustic scattering techniques have enabled the remote, high-resolution imaging and quantification of highly salt-stratified turbulence in an estuary. Turbulent salinity spectra in the stratified shear layer have been measured acoustically and by in situ turbulence sensors. The acoustic frequencies used span 120-600 kHz, which, for the highly stratified and dynamic estuarine environment, correspond to wavenumbers in the viscous-convective subrange (500-2500 m(-1)). The acoustically measured spectral levels are in close agreement with spectral levels measured with closely co-located micro-conductivity probes. The acoustically measured spectral shapes allow discrimination between scattering dominated by turbulent salinity microstructure and suspended sediments or swim-bladdered fish, the two primary sources of scattering observed in the estuary in addition to turbulent salinity microstructure. The direct comparison of salinity spectra inferred acoustically and by the in situ turbulence sensors provides a test of both the acoustic scattering model and the quantitative skill of acoustical remote sensing of turbulence dissipation in a strongly sheared and salt-stratified estuary.

Advances in estuarine physics.

Recent advances in our understanding of estuarine circulation and salinity structure are reviewed. We focus on well- and partially mixed systems that are long relative to the tidal excursion. Dynamics of the coupled system of width- and tidally averaged momentum and salt equations are now better understood owing to the development of simple numerical solution techniques. These have led to a greater appreciation of the key role played by the time dependency of the length of the salt intrusion. Improved realism in simplified tidally averaged physics has been driven by simultaneous advances in our understanding of the detailed dynamics within the tidal cycle and across irregular channel cross-sections. The complex interactions of turbulence, stratification, and advection are now understood well enough to motivate a new generation of physically plausible mixing parameterizations for the tidally averaged equations.

Plume tracking and dilution of effluent from the Boston sewage outfall.

Field surveys were conducted on the Boston sewage outfall plume to test and certify the outfall's initial dilution in the near field and to investigate its dispersion in the far field. Rhodamine WT dye was added to the effluent at the treatment plant at a constant concentration over a 6-h period and tracked offshore over three days. During the near-field surveys, the current was flowing closely parallel to the diffuser, resulting in the wastefield spreading laterally as a dynamic density current at a rate that was closely predicted by theoretical equations. The plume was submerged by the oceanic density stratification, with a minimum initial dilution of about 102 within a few tens of meters from the diffuser. The initial dilution and the other near-field characteristics were in good agreement with predictions of mathematical models and with the physical model study on which the diffuser design was based. After a travel time of 24h, the dye patch was still intact and oceanographic mixing and dispersion had increased dilution by a factor of about two to more than 200:1. After 48h, the plume had broken into large patches, and most dilutions considerably exceeded 400 with an average dilution of order 1000. For the approximately 52h that the dye patch was followed in the far field, mixing was due to lateral diffusion; vertical mixing was negligible. This slow vertical mixing is due to the stable density stratification in the water column. The outfall is performing as designed. The field surveys provided a strong confirmation of the ability of small-scale laboratory model studies to replicate and predict the near-field characteristics of ocean wastewater outfalls. They also increase the confidence that mathematical models can be used to reliably estimate initial dilution under other effluent flows, oceanographic conditions, and stratification regimes.

The Temporal Response of the Length of a Partially Stratified Estuary to Changes in River Flow and Tidal Amplitude.

The temporal response of the length of a partially-mixed estuary to changes in freshwater discharge, Qf , and tidal amplitude, UT , is studied using a 108 day time series collected along the length of the Hudson River estuary in the spring and summer of 2004 and a long-term (13.4 year) record of Qf , UT , and near-surface salinity. When Qf was moderately high, the tidally-averaged length of the estuary, L5, here defined as the distance from the mouth to the up-estuary location where the vertically-averaged salinity is five psu, fluctuated by more than 47 km over the spring-neap cycle, ranging from 28 km to >75 km. During low flow periods, L5 varied very little over the spring-neap cycle and approached a steady length. The response is quantified and compared to predictions of a linearized model derived from the global estuarine salt balance. The model is forced by fluctuations in Qf and UT relative to average discharge, Qo, and tidal amplitude, UTo, and predicts the linear response time scale, τ, and the steady-state length, Lo, for average forcing. Two vertical mixing schemes are considered, in which a) mixing is proportional to UT and b) dependence of mixing on stratification is also parameterized. Based on least-squares fits between L5 and estuary length predicted by the model, estimated τ varied by an order of magnitude from a period of high average discharge (Qo = 750 m3s-1, τ = 4.2 days) to a period of low discharge (Qo = 170 m3s-1, τ = 40.4 days). Over the range of observed discharge, Lo ∝ Qo-0.30±0.03, consistent with the theoretical scaling for an estuary whose landward salt flux is driven by vertical estuarine exchange circulation. Estimated τ was proportional to the discharge advection time scale (LoA/Qo, where A is the cross-sectional area of the estuary). However, τ was three to four times larger than the theoretical prediction. The model with stratification dependent mixing predicted variations in L5 with higher skill than the model with mixing proportional to UT . This model provides insight into the time dependent response of a partially-stratified estuary to changes in forcing and explains the strong dependence of the amplitude of the spring-neap response on freshwater discharge. However, the utility of the linear model is limited because it assumes a uniform channel and because the underlying dynamics are nonlinear and the forcing, Qf and UT , can undergo large amplitude variations. River discharge, in particular, can vary by over an order of magnitude over timescales comparable to or shorter than the response timescale of the estuary.

Initiation of apoptosis by photodynamic therapy using a novel positively charged and water-soluble near infra-red photosensitizer and white light irradiation.

Our aim was to investigate the photophysical and photodynamic properties of a new, water-soluble positively charged and chemically stable photosensitizer: tetrahydroporphyrin tetratosylat (THPTS). Absorption, fluorescence and (1)H NMR spectra and the intracellular distribution of THPTS were measured. The apoptosis in choroidal melanoma cells was measured using cell death detection ELISA and caspase-8 activity assay. THPTS-PDT efficiency was studied in Balb/c mice bearing C26 colon carcinoma. Subcutaneously located tumors were irradiated with a white light source at a fluence rate of 100 mW/cm(2). THPTS was administrated 3 h before illumination. The tumoricidal effect was examined 24 h after THPTS-PDT by vital staining with 0.4-ml 1% Evans blue solution, intraperitoneally injected to each mouse. THPTS showed a strong absorption band at 760 nm. Its purity, measured by (1)H NMR, is better than 99%. At 24-h incubation period, CLSM revealed THPTS fluorescence in mitochondria and cell nucleus. THPTS possesses no toxic effect in preincubated CM cells without irradiation, and THPTS-PDT causes efficient apoptosis. THPTS-PDT using white light irradiation at a dose of 480 J/cm(2) caused necrosis with a depth of 8 mm in subcutaneously located C26 colon carcinoma in Balb/c-mice. In accordance with the present results, the THPTS seems to be of interest for further in vivo investigations with broad-band white light sources.

Possibilities for controlling a PHB accumulation process using various analytical methods.

Poly-beta-hydroxybutyrate (PHB) and other polyesters can be produced by various species of bacteria. Of the possible carbon sources, methane could prove to be one of the most suitable substrates for the manufacture of PHB. The methanotrophic strain Methylocystis sp. GB 25 DSM 7674 was applied in order to accumulate PHB in a rapid, non-sterile process. Cultivation was performed in two stages: a continuous growth phase (dilution rate 0.17 h(-1)) and a PHB accumulation phase under deficiency conditions of an essential nutrient (e.g. phosphorus) in batch culture. The PHB content of the biomass was as high as 51%; efficiency was the highest during the first 5 h of the product formation process. The PHB produced is of very high quality, having a high molecular mass of up to 2.5 x 10(6) Da. In order to monitor and control the process, a rapid analysis method based upon turbidimetry in the visible range (438 nm) was applied. Moreover, the PHB content of the biomass was determined using an FT-IR-spectroscopic method with ATR sampling and multivariate calibration. We achieved a value of 1.4% as the best standard error of cross validation. The nitrogen content of the PHB final product (a product quality parameter) was estimated by spectroscopic method in the visible range.

A comparative characterization of dissolved organic matter by means of original aqueous samples and isolated humic substances.

The aim of our study is to test the use of less time-consuming spectroscopic methods applied on original water samples in order to obtain information about DOM composition without any sample preparation. These results were directly compared with results from a conventional isolation and characterization procedure of dissolved humic substances (fulvic acids--FA) isolated from the same water sample. FAs were characterized by UV-, fluorescence-, FTIR spectroscopy and elemental composition. UV absorbance and fluorescence behavior of FAs and original water samples follow the same pattern. A lower UV absorbance and a lower humification index (derived from the synchronous fluorescence spectra) of about 15% is typical for water samples compared to the FAs. We computed linear relationships between properties of the original water sample (UV-, synchronous fluorescence spectra) and the isolated FA (IR absorption, C/N ratio). The application of synchronous fluorescence and UV spectroscopy of aqueous samples has been proved to result in similar information about DOM composition as the characterization of isolated humic substances concerning the content of aromatic structures and the degree of humification.

Characterization of yeast strains of the genera candida, Hansenula, Kluyveromyces, Pichia, Rhodotorula, and Saccharomyces by mixed-dye fluorometry.

An analytical method in which we used the selective adsorption of several fluorophores by yeast cells is described. The suitability of using binary mixtures of 1-pyrene butyric acid, 3,6-dimethylamino acridine, 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid, and rhodamine B isothiocyanate for the characterization and identification of microorganisms was tested with 98 yeast strains belonging to the genera Candida, Hansenula, Kluyveromyces, Pichia, Rhodotorula, and Saccharomyces. The application of multivariate statistical methods and pattern recognition methods to the allocation of the yeast strains into genus-species-strain structures and to a comparison of fluorescence data sets for differentiation and identification purposes showed the usefulness of the method.