Kent W. Warnken

Distributions of carbohydrates, including uronic acids, in estuarine waters of Galveston Bay

Abstract The concentrations of carbohydrates, including uronic acids, in dissolved (≤0.45μm) and colloidal (1 kDa—0.45 μm) phases were measured in estuarine waters of Galveston Bay, TX, in order to study their role in heavy metal detoxification. The concentrations of dissolved monosaccharides (MCHO) in Galveston Bay ranged from 13 to 62 μM-C, and those of dissolved polysaccharides (PCHO) ranged from 10 to 42 μM-C. On average, MCHO and PCHO contributed about 11% and 7% to dissolved organic carbon (DOC), respectively. The colloidal carbohydrates (CCHO) in Galveston Bay varied from 7 to 54 μM-C, and accounted for 9% to 24% of the colloidal organic carbon (COC), with an average value of 17%, suggesting that CCHO is abundant in the high molecular weight (HMW) fraction of DOC. The concentration of CCHO is generally significantly higher than that of PCHO. This result is attributed to entrainment of low molecular weight (LMW) carbohydrates into the retentate fraction during ultrafiltration. The concentration of total dissolved uronic acids (DUA) in the same samples varied from 1.0 to 8.3 μM-C, with an average value of 6.1 μM-C, while the colloidal uronic acids (CUA) ranged from 0.8 to 6.4 μM-C, with an average value of 4.8 μM-C. The concentrations of DUA are higher than the previously reported values in coastal waters. Furthermore, CUA represent a dominant component of DUA in Galveston Bay waters. More importantly, significant correlations of PCHO and DUA to dissolved Cu concentrations (≤0.45 μm) were found, suggesting that acid polysaccharides were produced in response to trace metal stressors.

Distribution and partitioning of trace metals (Cd, Cu, Ni, Pb, Zn) in Galveston Bay waters

The distribution of several trace metals has been studied in the surface waters of Galveston Bay, Texas, in order to assess the impact of complexation with organic and reduced sulfur species on the partitioning of trace metals between particulate and aqueous species. The distribution of trace metals in the filter-passing fraction ( Cu>Cd>Zn>Pb>Mn>Fe, while an increasing trend was found in the same sequence for the acid-leachable fractions. The average values of Kd1, the particle-water partition coefficient, expressed as the ratio of weak acid-leachable particulate fractions to the filter-passing fractions, increased in the order Ni<Cu<Cd<Zn<Mn<Pb<Fe. This sequence is consistent with the relative importance of particulate transport of these trace metals from estuaries to coastal oceans. The observed decrease of Kd1 of Cu with increasing concentrations of suspended particulate matter (SPM), also called the “particle concentration effect” (PCE), can be eliminated when the free ionic, rather than the total concentration of Cu in the filter-passing fraction is used for calculating this ratio. A particle concentration effect would be expected if the binding of these trace metals by particles is mediated by solution (i.e., filter-passing) phase ligands. Complexation of Cd, Cu, Ni, Pb, and Zn with reduced sulfur species could be one of the causes for the observed linear correlations between metals and reduced sulfur species in both the filter-passing and filter-retained fractions. Significant correlations between Cu in the weak acid-leachable fraction and chlorophyll a (Chl a) concentrations suggest biological mediation of Cu uptake into the particulate fraction.

Sediment-water exchange of Mn, Fe, Ni and Zn in Galveston Bay, Texas

In-situ benthic flux studies were conducted at three stations in Upper Galveston Bay twice during March 1996 to directly measure release rates of dissolved Mn, Fe, Ni and Zn from the sediments. Results showed reproducible increases with time in both replicate light and light–dark benthic chambers, resulting in average fluxes of −1200±780, −17±12, −1.6±0.6 and −2.4±0.79 μmol m−2 day−1 for Mn, Fe, Ni and Zn, respectively. Sediment cores collected during 1994–1996 showed that surficial pore water concentrations were elevated compared to overlying water column concentrations, suggesting diffusive release from the sediments. Diffusive flux estimates of Mn and Zn agreed in direction with chamber fluxes measured on the same date, but only accounted for 5–38% of the measured flux. Diffusive fluxes of Fe agreed with measured fluxes at the near Trinity River station but overestimated actual release in the mid and outer Trinity Bay regions, possibly due to inaccurate determination of the Fe pore water gradients or rapid oxidation processes in the overlying water at these stations. In general, measured fluxes of Mn and Ni were higher in the mid Trinity Bay region and suggested a mechanism for the elevated trace metal concentrations previously reported for this region of Galveston Bay. However, the fluxes of Fe were highest in close proximity to the Trinity River, supporting the elevated Fe concentrations measured in this region during this and other studies, and decreased towards middle and outer Trinity Bay. Trace metal turnover times were between 0.1 and 1.2 days for Mn, between 1.3 and 4.6 days for Fe, and between 27 and 100 days for Ni and 12–20 days Zn, and were considerably shorter than the average Trinity Bay water residence time (1.5 years) for this period. Comparing area averaged benthic inputs to Trinity River inputs shows the sediments to be a significant source of trace metals to Galveston Bay. However, while benthic inputs of trace metals were measured, water column concentrations remained low despite rapid turnover times for Mn and Fe, suggesting removal of these metals from the water column after release from the sediments.

Trace metal composition of colloidal organic material in marine environments

Abstract Marine colloidal material (1 kDa–0.2 μm) was isolated by cross-flow ultrafiltration followed by diafiltration and freeze-drying from surface waters of the Gulf of Mexico and the Middle Atlantic Bight (MAB), as well as from estuarine waters of Galveston Bay. Elemental characterization of isolated colloidal material included organic carbon (OC) and selected trace metal (Cu, Pb, Zn, Cd, Co, Ni, Cr, Be, Fe, Al, Mn, V, Ba, and Ti) determinations. It was found that levels of these metals in marine colloids ranged from 120 μg/g. Most metals (Cu, Pb, Zn, Ni, Al, Mn, V, and Ti) had an average concentration >1 μg/g while concentrations of Cd, Co and Be were usually Ni, Cr, Zn>Mn>Co>Pb, Cd, which is similar to the Irving–Williams order except for Mn, suggesting that the interaction of metals with marine colloids is determined by the affinity of metals for specific organic ligands.

Performance optimization of a commercially available iminodiacetate resin for the determination of Mn, Ni, Cu, Cd and pb by on-line preconcentration inductively coupled plasma-mass spectrometry

The on-line preconcentration performance characteristics of a commercially available iminodiacetate resin (Toyopearl AF-Chelate 650M) were investigated. The method was optimized for several parameters, including buffer pH, rinsing of matrix salts from the resin, elution acid type and strength, and the nebulizer gas flow rate. An ammonium chloride buffer with a pH of 8.80 was mixed with the sample on-line prior to loading. This pH was found to be optimal for Mn, Cu, Cd and Pb, whereas a pH of ≥9.2 was optimal for Ni analysis. Column rinse experiments showed that both buffer and water reduce Na concentrations to <100 μM in the rinse solution within 3 min. It was also determined that using 1 M HNO3 acid for column elution yielded higher intensities for Mn, Ni, Cu and Pb, while 1 M HCl yielded higher count rates for Cd. The change from the optimization solution, with a 0.2% HNO3 acid concentration, to the 10% elution acid required a reduction in the nebulizer gas flow rate of 0.05 l min−1 in order to obtain reduced blank intensity ratios. Calibrations performed using standard solutions (1 ml) with concentrations ranging from 0 to 10 pg ml−1 (ppt) resulted in regression coefficients of 0.990–0.998. Method detection limits of 1.1, 0.08, 0.47, 0.06 and 0.16 pg ml−1 for Mn, Ni, Cu, Cd and Pb, respectively, were obtained. Accuracy was demonstrated by results from runs of the certified standard reference materials (SRMs), CASS-4, a newly available coastal seawater reference standard and NASS-4, an open ocean seawater reference material.

Trace metal analysis of natural waters by ICP-MS with on-line preconcentration and ultrasonic nebulization

Concentrations of Mn, Ni, Cu, Zn and Pb in natural waters were measured by inductively coupled plasma mass spectrometry (ICP-MS) with on-line preconcentration using Toyopearl TSK-immobilized 8-hydroxyquinoline resin columns and ultrasonic nebulization. Trace metal concentrations, quantified after analyzing calibration standards, were measured in 3 mL samples in under 15 min with better than 5% precision. Method detection limits were 0.26, 0.86, 1.5, 10 and 0.44 ng L –1 for Mn, Ni, Cu, Zn and Pb, respectively. The accuracy of the method was demonstrated by results from runs of certified reference materials SLRS-3 and CASS-3, which have very different ionic strengths. This on-line system was successfully applied to measure water column trace metal concentrations in Galveston Bay, Texas, and the results compared favorably with those obtained using state-of-the-art off-line preconcentration techniques.

Benthic Exchange of Nutrients in Galveston Bay, Texas

Nutrient regeneration rates were determined at three sites increasing in distance from the Trinity River, the main freshwater input source, to Galveston Bay, Texas, from 1994 through 1996. Diffusive fluxes generally agreed in direction with directly measured benthic fluxes but underestimated the exchange of nutrients across the sediment-water interface. While the fluxes of ammonium and phosphate were directed from the sediment into the overlying waters, the fluxes of silicate and chloride changed in both magnitude and direction in response to changing Trinity River flow conditions. Oxygen fluxes showed benthic production during both summer 1995 and winter 1996, while light-dark deployments showed production-consumption, respectively. Benthic inputs of nutrients were higher at either the middle or outer Trinity Bay regions, most likely due to a higher quality and quantity of the autochthonous organic matter deposited. This feature is consistent with and gives evidence for previously observed non-conservative mixing behaviors reported for nutrients in this region of Galveston Bay. Calculated turnover times, between 7 to 135 d for phosphate, 4 to 56 d for silicate, and 0.3 to 10 d for ammonium were significantly shorter than the average Trinity Bay water residence time of 1.5 yr for the period September 1995 through October 1996. During periods of decreased Trinity River flow and increased residence times, benthic inputs of ammonium and phosphate were 1 to 2 orders of magnitude greater than Trinity River inputs and were the dominant input source of these nutrients to Trinity Bay. The sediments, a sink for silicate when overlying water column concentrations of silicate were elevated, became a source of silicate to the overlying waters of Trinity Bay under reduced flow, high salinity conditions.

Chapter 16 Theory and applications of DGT measurements in soils and sediments

Publisher Summary This chapter sets out the developing theoretical basis for the use of diffusive gradients in thin-films (DGT) in soils and sediments and appraises the key applications that have advanced understanding of chemical interactions occurring in these complex media. When DGT is deployed in soils or sediments, a steady-state condition is never truly reached. Thus, time-dependent models are required to quantify the contribution of diffusional supply and release from the solid-phase to the accumulated mass of solute. The DGT-induced fluxes in soils and sediments (DIFS) model provides a numerical simulation of the interaction between the DGT device and its deployment medium. The model assumes that all pore spaces are filled with solution, which restricts its use to sediments and soils with moisture content at or above field capacity. Initial calculations, based on a finite difference approach, considered two-dimensional diffusion and release processes in the soil perpendicular to the plane of the DGT device.

Chapter 11 In situ monitoring and dynamic speciation measurements in solution using DGT

Publisher Summary Diffusive gradients in thin-films (DGT) has been deployed in situ in a wide range of natural waters, including fresh-waters, such as soft Canadian shield lakes, coastal sea-water, and open ocean sea-water. This chapter focuses on its further development and applications in aqueous systems that include its use for speciation measurements and kinetic tools; for bioavailability studies; and for routine environmental monitoring. DGT has been used to measure a wide range of analytes in natural waters simply by varying the binding agent used within the resin-gel layer. While DGT is simple to use and the interpretation in terms of concentration is straightforward in most cases, the exceptions are being increasingly explored. The exact dependence of the DGT measurement on ionic strength and diffusive layer thickness has increased the detailed understanding of the processes involved. DGTs capability to discriminate solution species, based on their diffusion coefficients in the diffusion layer, has been explored in the laboratory and successfully applied to fresh-waters. This rigorous foundation has provided a better appreciation of what DGT measures when it is used as an in situ passive sampler for monitoring purposes.