Characterizing spatial structure of sediment E. coli populations to inform sampling design

Escherichia coli can persist in streambed sediments and influence water quality monitoring programs through their resuspension into overlying waters. This study examined the spatial patterns in E. coli concentration and population structure within streambed morphological features during baseflow and following stormflow to inform sampling strategies for representative characterization of E. coli populations within a stream reach. E. coli concentrations in bed sediments were significantly different (p?=?0.002) among monitoring sites during baseflow, and significant interactive effects (p?=?0.002) occurred among monitoring sites and morphological features following stormflow. Least absolute shrinkage and selection operator (LASSO) regression revealed that water velocity and effective particle size (D ₁₀) explained E. coli concentration during baseflow, whereas sediment organic carbon, water velocity and median particle diameter (D ₅₀) were important explanatory variables following stormflow. Principle Coordinate Analysis illustrated the site-scale differences in sediment E. coli populations between disconnected stream segments. Also, E. coli populations were similar among depositional features within a reach, but differed in relation to high velocity features (e.g., riffles). Canonical correspondence analysis resolved that E. coli population structure was primarily explained by spatial (26.9–31.7 %) over environmental variables (9.2–13.1 %). Spatial autocorrelation existed among monitoring sites and morphological features for both sampling events, and gradients in mean particle diameter and water velocity influenced E. coli population structure for the baseflow and stormflow sampling events, respectively. Representative characterization of streambed E. coli requires sampling of depositional and high velocity environments to accommodate strain selectivity among these features owing to sediment and water velocity heterogeneity.     

Effect of algal bloom deposition on sediment respiration and fluxes

Using sediment cores collected in November 1989 from Aarhus Bight, Denmark, the fluxes of O₂, CO₂ (total CO₂), NH ₄ ⁺ , NO ₃ ^– +NO ₂ ^– and DON (dissolved organic nitrogen) across the sediment-water interface were followed for 20 d in an experimental continous flow system. On day 7, phytoplankton was added to the sediment surface, to see the result of simulated algal bloom sedimentation. Benthic O₂ consumption and CO₂ efflux, 38 to 41 mmol O₂ m^-2 d^-1 and 25 to 30 mmol CO₂ m^-2 d^-1, respectively, immediately increased by 39% and 100% after the algal addition, but gradually declined to the orginal level. Fluxes of NH ₄ ⁺ (1.0 to 1.2 mmol m^-2 d^-1) and DON (0.3 to 0.9 mmol m^-2 d^-1) increased due to the organic substrate addition. NH ₄ ⁺ and NO ₃ ^– flux changed direction, becoming an efflux and influx, respectively, for a few days and a large amount of DON (max. rate 4.0 mmol m^-2 d^-1) was immediately produced either by bacterial hydrolytic activity or from autolysis of the algae. DON was the most significant nitrogen component in pore water and in terms of N-flux from sediment. A temporary stimulation of anaerobic respiration processes (sulfate reduction and denitrification) and a decrease in nitrification were indicated. After the effect of the organic addition had declined, the fluxes gradually reverted to the original rates. The halflife of the added algal material, of which 20 to 30% was very labile, was estimated to be 2 to 3 wk.     

Prenatal diagnosis by in situ hybridization on uncultured amniocytes: Reduced sensitivity and potential risk of misdiagnosis in blood-stained samples

Maternal cell contamination was assessed in 18 macroscopically blood-stained amniotic fluid samples from male fetuses. The samples were analysed by double-target fluorescent in situ hybridization (ISH) with Y and X chromosome-specific probes. The only sample with an aberrant karyotype (47, XY, +18) was also analysed by hybridization with a chromosome 18-specific probe. An interpretation of extensive maternal cell contamination was made in two samples, one of which was the sample with trisomy 18. ISH with the chromosome 18-specific probe on this latter sample showed that the sensitivity of the ISH method for chromosome enumeration of uncultured amniotic fluid samples may be reduced in bloodstained samples. It was calculated that by using ISH for chromosome enumeration of the two extensively contaminated samples, a case of trisomy 21 might have been overlooked in both samples, while a case of trisomy 18 might only have been overlooked in one of the samples. It is concluded that ISH should not be used for chromosome enumeration of uncultured amniotic fluid samples that are macroscopically blood-stained without further technical developments.     

Quantifying plant pigments and live diatoms in aphotic sediments of Scandinavian coastal waters confirms a major route in the pelagic–benthic coupling

The fate of pelagic diatoms in marine coastal aphotic sediments was investigated from sediment profiles in western Scandinavian waters. We used three independent methods to estimate pigment pools in the sediment: (1) fluorometry, (2) high-performance liquid chromatography and (3) pigments estimated from germinable diatom cells, using the dilution extinction method. A strong positive relationship with an intercept close to zero was observed between fucoxanthin, a marker of diatoms, and chlorophyll a. The fucoxanthin/chl a ratio was on average 1.05, which was similar to monocultures of dominating diatom taxa, indicating that sedimentary chl a was to a large extent of diatom origin. Chl a and fucoxanthin correlated significantly and positively with, and where within the same order of magnitude as, corresponding substances predicted from live diatom cell numbers obtained with the dilution extinction method. This indicates that a major part of surficial sediment chl a was bound in live cells of pelagic diatoms. There was a consistent change in viable cells with sediment depth and with timing of dominating taxa, with the non-spore-forming Skeletonema costatum dominating in the surface sediment in March and May, while the spore forming Chaetoceros spp. dominated deep in the sediment and during periods outside of the spring bloom (February and August). This indicates that chl a is bound in several different cell pools with different degradation rates, depending on diatom taxonomy. Thus, diatoms originating predominantly from the spring bloom may provide an important direct link in the pelagic–benthic coupling in this area.     

Sorption, degradation and mobility of ptaquiloside, a carcinogenic Bracken (Pteridium sp.) constituent, in the soil environment

Ptaquiloside (PTA) is a carcinogenic norsesquiterpene glucoside produced by Bracken in amounts up to at least 500 mg m(-2). The toxin is transferred from Bracken to the underlying soil from where it may leach to surface and groundwater's impairing the quality of drinking water. The objectives of the present study were to characterize the solubility, degradation and retention of PTA in soils in order to evaluate the risk for groundwater contamination. PTA was isolated from Bracken. The logarithmic octanol-water and ethyl acetate-water partitioning coefficients for PTA were -0.63 and -0.88, respectively, in agreement with the high water solubility of the compound. PTA hydrolysed rapidly in aqueous solution at pH 4 or lower, but was stable above pH 4. Incubation of PTA with 10 different soils at 25 degrees C showed three different first order degradation patterns: (i) rapid degradation observed for acid sandy soils with half life's ranging between 8 and 30 h decreasing with the soil content of organic matter, (ii) slow degradation in less acid sandy soils with half-lives of several days, and (iii) fast initial degradation with a concurrent solid phase-water partitioning reaction observed for non-acid, mostly clayey soils. The presence of clay silicates appears to retard the degradation of PTA, possibly through sorption. Degradation at 4 degrees C was generally of type (iii) and degradation rates were up to 800 times lower than at 25 degrees C. Sorption isotherms for the same set of soils were almost linear and generally showed very low sorption affinity with distribution coefficients in the range 0.01-0.22 l kg(-1) at a solution concentration of 1 mg l(-1) except for the most acid soil; Freundlich affinity coefficients increased linearly with clay and organic matter contents. Negligible sorption was also observed in column studies where PTA and a non-sorbing tracer showed almost coincident break-through. Leaching of PTA to the aqueous environment will be most extensive on sandy soils, having pH >4 and poor in organic matter which are exposed to high precipitation rates during cold seasons.     

Occurrence of the carcinogenic Bracken constituent ptaquiloside in fronds,topsoils and organic soil layers in Denmark

Bracken (Pteridium aquilinum (L.) Kuhn) is a common fern found on all continents except Antarctica. It is under suspicion of causing cancer among people who utilizes it as food. The main carcinogenic compound is thought to be the water-soluble compound ptaquiloside. Ptaquiloside-uptake may occur not only through food, but also via drinking water as ptaquiloside might leach from plant material. The purpose of the study was to identify environmental parameters that correlate with the ptaquiloside-content in fronds, and to quantify the amount of ptaquiloside in the soil environment. The ptaquiloside-content in fronds, Oi/Oe-, and Oa/A-horizons was quantified at end of the growth season at 20 sites in Denmark. The fronds had ptaquiloside-contents between 108 and 3795 microgg(-1). The Oi/Oe-horizons had contents between 0.09 and 7.70 microgg(-1), while Oa/A-horizons had contents between 0.01 and 0.09 microgg(-1). The ptaquiloside-content in the standing biomass, which could be transferred to the soil by the end of the growing season, ranged between 10 and 260 mgm(-2), with nine sites having ptaquiloside loads over 100 mgm(-2). The carbon-content in the O-horizon, the precipitation, the amount of Bracken-litter, the turnover rate and the size of Bracken-stands determined the ptaquiloside-content in the soil materials while the content in fronds was found to be a function of the frond-height and the light-exposure in the ecosystem.     

Assessment of the importance of sorption for steroid estrogens removal during activated sludge treatment

Distribution coefficients (K(d)) between water and activated sludge particles (f(oc)=27.7+/-0.1%) were measured for the steroid estrogens (SE), estrone (E1), 17beta-estradiol (E2) and 17alpha-ethinylestradiol (EE2) in batch experiments. Experimental concentration levels ranged from environmentally realistic low ng/l to the high microg/l. In this range K(d)s were independent of their water concentration. The experimentally obtained K(d)s (with 95% confidence intervals) were 402+/-126 l/kg, 476+/-192 l/kg and 584+/-136 l/kg for E1, E2 and EE2, respectively. K(d)s were used to estimate the fraction of the total SE concentration that is expected to be sorbed in the activated sludge treatment tanks of a typical STP assuming equilibrium conditions. Assuming a suspended solids concentration of 4 g/l dissolved solids (ds), it was estimated that 61+/-9%, 66+/-13% and 70+/-6% of the total concentration of E1, E2 and EE2, respectively, would be sorbed during activated sludge treatment. The fraction of the SEs that was expected to be sorbed to suspended sludge particles in the effluents from a typical Danish STP was estimated to be only 0.20+/-0.06%, 0.24+/-0.10% and 0.29+/-0.07% of the total concentration of E1, E2 and EE2, respectively, at a suspended solids concentration of 5 mg/lds. For a typical STP the removal of steroid estrogens with excess sludge was estimated to be only 1.5-1.8% of the total loading if equilibrium conditions exists. Sorption is therefore not important for the fate of SEs in STPs compared to biodegradation.     

Patterns in species composition of rocky shore communities in sub-arctic fjords of eastern Iceland

Quantitative data on plants and animals from 20 transects of the eulittoral zone in 8 fjords of sub-arctic east Iceland were analysed by a number of classification and ordination techniques. Field work was carried out during two periods of spring tides in June and July 1987. The study was restricted to gently sloping stable bedrock, but transects were otherwise randomly chosen. Species composition was strongly influenced by the relative position of the transects along the length of the fjords. Species richness increased from heads towards mouths. Increased temperature fluctuations towards inner parts of fjords are suggested as an explanation for these patterns, while salinity is unlikely to be a critical factor. The analyses also indicate that degree of exposure, as measured both by a physically derived index and by a simple biological index, is an important factor in structuring these eulittoral communities, although affecting species richness only slightly, if at all. Classification of transects results in a number of community types which, however, are not well defined. A classification based on the presence/absence of three canopy-forming fucoids yields groups of transects differing in species composition and in degree of exposure. The rocky eulittoral communities of the fjords of eastern Iceland resemble those of northern Norway, but differ in that several key species of the latter communities are missing, probably largely due to the isolation of Iceland.