Stephen A. Skrabal

Temporal Variability of Iron Speciation in Coastal Rainwater

Iron occurs in rain as particulateand dissolved Fe and includes both Fe(II) and Fe(III)species. Model calculations and correlation analysisindicate Fe(II)(aq) occurs almost exclusively as thefree ion whereas Fe(III)(aq) occurs as both ironoxalate and Fe(OH)2+(aq) with largevariations over the pH range from 4.0 to 5.0. Complexation with humic-like compounds may also beimportant for Fe(III)(aq); however, the concentrationand structural characteristics of these compounds haveyet to be determined. 112 rain samples were collectedfor iron analysis in Wilmington, North Carolina,between 1 July 1997, and 30 June 1999. Total iron,particulate iron and Fe(III)(aq) were higher inconcentration in summer and spring rain relative towinter and autumn rain. Fe(II)(aq) concentrations, incontrast, did not vary seasonally. Particulate iron,which was approximately half the total rainwater iron,was highest between noon and 6 p.m. (EST), probably dueto more intense regional convection including land-seabreezes during that time. The ratio ofFe(II)(aq)/Fe(III)(aq) was also highest in rainreceived between noon and 6 p.m., which most likelyreflects photochemical reduction of Fe(III)(aq)complexes to form Fe(II)(aq). A conceptual modeldepicting the interplay between iron species, lightintensity and organic ligands in rainwater ispresented.

Distributions of dissolved titanium in porewaters of estuarine and coastal marine sediments

Sediment porewater and water column samples were collected in Chesapeake Bay and the Mid-Atlantic Bight (MAB) and were analyzed for dissolved ( 50 times greater than bottom water (BW) Ti concentrations, with the steepest gradients occurring in muddy sediments of the mid-bay site (0.4–0.5 nM BW vs. 29 nM PW) and shallower gradients in siltier sediments of the lower bay and MAB (0.3–0.5 nM BW vs. 2.7–5.5 nM PW). Porewater Ti concentrations at all sites increased from the sediment–water interface to ∼6–9 cm depth, below which concentrations were relatively constant or decreased slightly to the bottom of the profiles (10–15 cm). The shapes of the profiles suggest the release of Ti from mineral phases or biological detritus in shallow sediments, and adsorption onto or incorporation within mineral phases or organic matter in deeper sediments. Calculated benthic diffusive fluxes of dissolved Ti range from 11–68 nmol m−2 day−1 in fine-grained mid-bay sediments to 1.5–4.2 nmol m−2 day−1 in sediments of the lower bay and MAB. A tentative estimate of the annual benthic flux of Ti in Chesapeake Bay (3.3×104 mol year−1) is comparable to the riverine input of 3.5×104 mol year−1. Experiments using both mud and sand indicated that sediment resuspension only slightly increased the Ti concentrations in overlying waters. These results suggest that benthic fluxes may be a significant source of Ti to estuaries and the ocean.

Stimulation of fecal bacteria in ambient waters by experimental inputs of organic and inorganic phosphorus

Fecal microbial pollution of recreational and shellfishing waters is a major human health and economic issue. Microbial pollution sourced from stormwater runoff is especially widespread, and strongly associated with urbanization. However, non-point source nutrient pollution is also problematic, and may come from sources different from fecal-derived pollution (i.e. fertilization of farm fields, lawns and gardens, and ornamental urban areas). Fecal bacteria require nutrients; thus the impact of such nutrient loading on survival and abundance of fecal coliform bacteria in ambient waters was experimentally investigated in a constructed wetland in coastal North Carolina, USA. A series of nutrient-addition bioassays testing impacts of inorganic and organic nitrogen and phosphorus demonstrated that additions of neither organic nor inorganic nitrogen stimulated fecal coliform bacteria. However, phosphorus additions provided significant stimulation of fecal coliform growth at times; on other occasions such additions did not. Dilution bioassays combined with nutrient additions were subsequently devised to assess potential impacts of microzooplankton grazing on the target fecal bacteria populations. Results demonstrated grazing to be a significant bacterial reduction factor in 63% of tests, potentially obscuring nutrient effects. Thus, combining dilution experiments with nutrient addition bioassays yielded simultaneous information on microzooplankton grazing rates on fecal bacteria, fecal bacterial growth rates, and nutrient limitation. Overall, when tested against a non-amended control, additions of either organic or inorganic phosphorus significantly stimulated fecal coliform bacterial growth on 50% of occasions tested, with organic phosphorus generally providing greater stimulation. The finding of significant phosphorus stimulation of fecal bacteria indicates that extraneous nutrient loading can, at times, augment the impacts of fecal microbial pollution of shellfishing and human contact waters.

Surface waters as a sink and source of atmospheric gas phase ethanol.

This study reports the first ethanol concentrations in fresh and estuarine waters and greatly expands the current data set for coastal ocean waters. Concentrations for 153 individual measurements of 11 freshwater sites ranged from 5 to 598 nM. Concentrations obtained for one estuarine transect ranged from 56 to 77 nM and levels in five coastal ocean depth profiles ranged from 81 to 334 nM. Variability in ethanol concentrations was high and appears to be driven primarily by photochemical and biological processes. 47 gas phase concentrations of ethanol were also obtained during this study to determine the surface water degree of saturation with respect to the atmosphere. Generally fresh and estuarine waters were undersaturated indicating they are not a source and may be a net sink for atmospheric ethanol in this region. Aqueous phase ethanol is likely converted rapidly to acetaldehyde in these aquatic ecosystems creating the undersaturated conditions resulting in this previously unrecognized sink for atmospheric ethanol. Coastal ocean waters may act as either a sink or source of atmospheric ethanol depending on the partial pressure of ethanol in the overlying air mass. Results from this study are significant because they suggest that surface waters may act as an important vector for the uptake of ethanol emitted into the atmosphere including ethanol from biofuel production and usage.

Enhanced detection of the algal toxin PbTx-2 in marine waters by atmospheric pressure chemical ionization mass spectrometry.

RATIONALE Karenia brevis, a marine dinoflagellate, biosynthesizes a unique class of polyether toxins called brevetoxins that produce significant health, environmental and economic impacts in and along coastal waters. Previous application of liquid chromatography/mass spectrometry for detection of the most common brevetoxin, PbTx-2, has relied almost exclusively upon electrospray ionization (ESI). A different ionization source is proposed in this study with improved sensitivity ultimately leading to lower limit of detection compared to (+) ESI. METHODS Brevetoxin standards and samples (PbTx-2) were analyzed by liquid chromatography/mass spectrometry using both (+) atmospheric pressure chemical ionization and (+) electrospray ionization sources. RESULTS LC/MS with (+) APCI exhibited an order of magnitude improvement in the limit of detection (7.7 × 10(-4) pg mass on-column) compared to the same method using (+) ESI (7.5 × 10(-3) pg mass on-column). The calibration sensitivity of (+) APCI (1.3 × 10(3)) was also five times higher than positive mode (+) ESI (0.26 × 10(3)). CONCLUSIONS Positive mode APCI represents a significant improvement in detection and quantification of PbTx-2 by LC/MS allowing for smaller sample sizes compared to previous studies using (+) ESI. This in turn leads to higher throughput of samples during and after bloom events giving stakeholders detailed information on the fate of this potent marine toxin.

Photorelease of microcystin-LR from resuspended sediments

A series of ten photolysis experiments was conducted with sediments exposed to Microcystis sp. blooms to determine if sunlight is capable of mobilizing the biotoxin microcystin-LR (MC-LR) into the water column. There was a net photorelease of MC-LR in irradiated suspensions in all cases relative to dark controls, ranging from 0.4 to 192μgL-1g-1 into the dissolved phase. This should be viewed as a minimum estimate of photorelease due to concurrent photodegradation of dissolved toxin. Dissolved MC-LR concentrations in a sediment suspension increased linearly in the aqueous phase during a six-hour irradiation with simulated sunlight suggesting that longer exposure times produce greater quantities of MC-LR. There was a significant positive correlation between photorelease of toxin and percent organic carbon of the resuspended material, implying that organic-rich sediments yield the greatest photorelease of MC-LR upon exposure to full spectrum sunlight. Samples exposed to photosynthetically active radiation (400nm-700nm) were responsible for less than 2% of the photorelease compared to full spectrum exposures. Model calculations indicate that photochemical processing of bloom impacted sediments could be responsible for as much as 100% of the average standing stock of MC-LR in a freshwater pond located in southeastern North Carolina, where surface water concentrations were also measured. Mass spectrometric analysis revealed a new peak in light exposed flasks that appears to be a photo-induced isomerized product of MC-LR. Photoproduction from resuspended sediments therefore represents a significant but previously unrecognized source of highly toxic MC-LR and photoproducts of unknown toxicity and fate to aquatic ecosystems.