DON Concentrations Research Articles

Seasonal and annual reoccurrence in betaproteobacterial ammonia‐oxidizing bacterial population structure

Microbes exhibit remarkably high genetic diversity compared with plant and animal species. Many phylogenetically diverse but apparently functionally redundant microbial taxa are detectable within a cubic centimetre of mud or a millilitre of water, and the significance of this diversity, in terms of ecosystem function, has been difficult to understand. Thus it is not known whether temporal and spatial differences in microbial community composition are linked to particular environmental factors or might modulate ecosystem response to environmental change. Fifty-three water and sediment samples from upper and lower Chesapeake Bay were analysed in triplicate arrays to determine temporal and spatial patterns and relationships between ammonia-oxidizing bacterial (AOB) communities and environmental variables. Thirty-three water samples (three depths) collected during April, August and October, 2001-2004, from the oligohaline upper region of the Bay were analysed to investigate temporal patterns in archetype distribution. Using a combination of a non-weighted discrimination analysis and principal components analysis of community composition data obtained from functional gene microarrays, it was found that co-varying AOB assemblages reoccurred seasonally in concert with specific environmental conditions, potentially revealing patterns of niche differentiation. Among the most notable patterns were correlations of AOB archetypes with temperature, DON and ammonium concentrations. Different AOB archetypes were more prevalent at certain times of the year, e.g. some were more abundant every autumn and others every spring. This data set documents the successional return to an indigenous community following massive perturbation (hurricane induced flooding) as well as the seasonal reoccurrence of specific lineages, identified by key functional genes, associated with the biogeochemically important process nitrification.

Storm nitrogen dynamics in tile-drain flow in the US Midwest

Storm losses of N via tile-drainage in the US Midwest are a major concern for water quality in the Mississippi River Basin (MRB). This study investigates the impact of precipitation characteristics on NO3−, NH4+ and DON concentrations and fluxes for spring storms in tile-drains in a Midwestern agricultural watershed. Bulk precipitation amount had little impact on solute median concentrations in tile-drains during storms, but clearly impacted Mg2+, K+ and NO3− concentration patterns. For large storms (>6 cm of bulk precipitation), large amounts of macropore flow (43–50% of total tile-drain flow) diluted Mg2+ and NO3− rich groundwater as discharge peaked. This pattern was not observed for NH4+ and DON or for smaller tile-flow generating events ( 80% of N flux during storms, while DON and NH4+ represented only 2–14% and 1–7% of N flux, respectively. This study stresses the non-linear behavior of N losses to tile drains during spring storms in artificially drained landscapes of the US Midwest, at a critical time of the year for N management in the MRB.

Effluent Organic Nitrogen (EON): Bioavailability and Photochemical and Salinity-Mediated Release

The goal of this study was to investigate three potential ways that the soluble organic nitrogen (N) fraction of wastewater treatment plant (WWTP) effluents, termed effluent organic N (EON), could contribute to coastal eutrophication--direct biological removal, photochemical release of labile compounds, and salinity-mediated release of ammonium (NH4+). Effluents from two WWTPs were used in the experiments. For the bioassays, EON was added to water from four salinities (approximately 0 to 30) collected from the James River (VA) in August 2008, and then concentrations of N and phosphorus compounds were measured periodically over 48 h. Bioassay results, based on changes in DON concentrations, indicate that some fraction of the EON was removed and that the degree of EON removal varied between effluents and with salinity. Further, we caution that bioassay results should be interpreted within a broad context of detailed information on chemical characterization. EON from both WWTPs was also photoreactive, with labile NH4+ and dissolved primary amines released during exposure to sunlight. We also present the first data that demonstrate that when EON is exposed to higher salinities, increasing amounts of NH4+ are released, further facilitating EON use as effluent transits from freshwater through estuaries to the coast.

Seasonal and hydrologic drivers of dissolved organic matter and nutrients in the upper Kuparuk River, Alaskan Arctic

As the planet warms, widespread changes in Arctic hydrology and biogeochemistry have been documented and these changes are expected to accelerate in the future. Improved understanding of the behavior of water-borne constituents in Arctic rivers with varying hydrologic conditions, including seasonal variations in discharge–concentration relationships, will improve our ability to anticipate future changes in biogeochemical budgets due to changing hydrology. We studied the relationship between seasonal water discharge and dissolved organic carbon and nitrogen (DOC and DON) and nutrient concentrations in the upper Kuparuk River, Arctic Alaska. Fluxes of most constituents were highest during initial snowmelt runoff in spring, indicating that this historically under-studied period contributes significantly to total annual export. In particular, the initial snowmelt period (the stream is completely frozen during the winter) accounted for upwards of 35% of total export of DOC and DON estimated for the entire study period. DOC and DON concentrations were positively correlated with discharge whereas nitrate (NO3 −) and silicate were negatively correlated with discharge throughout the study. However, discharge-specific DOC and DON concentrations (i.e. concentrations compared at the same discharge level) decreased over the summer whereas discharge-specific concentrations of NO3 − and silicate increased. Soluble reactive phosphorus (SRP) and ammonium (NH4 +) were negatively correlated with discharge during the spring thaw, but were less predictable with respect to discharge thereafter. These data provide valuable information on how Arctic watershed biogeochemistry will be affected by future changes in temperature, snowfall, and rainfall in the Arctic. In particular, our results add to a growing body of research showing that nutrient export per unit of stream discharge, particularly NO3 −, is increasing in the Arctic.

A probiotic feed additive containing spores of Bacillus subtilis and B. licheniformis does not prevent absorption and toxic effects of the Fusarium toxin deoxynivalenol in piglets

A 35-day piglet experiment starting from weaning (21 days of age, 7.7 ± 1.1 kg), was performed to examine the effects of feeding a control diet (CTR) and of a Fusarium toxin-contaminated diet (FUS) in the absence (−) or presence (+) of a probiotic additive (2.3 × 10 6 colony-forming units per g diet of a one-to-one ratio of Bacillus subtilis and B. licheniformis) (deoxynivalenol [DON] concentrations of the CTR−, CTR+, FUS− and FUS+ diets were 0.21, 0.20, 2.75 and 2.45 mg/kg, respectively) on performance, blood concentration of DON and on liver function as evaluated by a breath test. Feeding of the FUS diets significantly depressed performance while the probiotic supplement failed to improve performance either when added to the CTR or to the FUS diet. The DON concentrations in the blood of the piglets fed both FUS diets were not significantly different, while the concentration of its degradation metabolite, de-epoxy-DON, was lower than the detection limit. Thus, it can be concluded that the fed probiotic bacteria neither bound nor degraded DON prior to absorption. Taken together, the tested probiotic additive is not suited to prevent the performance depressing effects of DON in piglets.

Spatial and temporal dynamics of stream chemistry in a forested watershed

Abstract. Spatial dynamics of solute chemistry and natural abundance isotopes of nitrate (15N and 18O) were examined in seven locations and at the watershed outlet in 2001 and 2002 in a forest watershed in the Adirondack Mountains of New York State, USA. Temporal dynamics were examined during five discharge periods: winter, snowmelt, spring, summer, and fall, based on discharge levels at the watershed outlet. Solute concentrations were variable across space and time with significant (p≤0.05) interaction effects. Year*period was significant for pH, NH4+, NO3-, total N, DOC, and total Al suggesting that inter-annual variability in discharge levels was more important for these solutes than intra-annual variability. Period*sampling point was significant for pH, Mg2+, Ca2+, sum of base cations, Si, and total Al suggesting that the differences in concentration of these solutes among sampling points were moderated by discharge levels. In general, groundwater sources located in upper watershed controlled stream chemistry at higher elevations with highest pH, Ca2+, sum of base cations, Si, and SO42- concentrations, with higher values in summer, and dilution effects during snowmelt. Two low elevation wetlands had a substantial influence over stream chemistry at those locations contributing lowest NO3- and highest DOC. Snowmelt exhibited among the lowest pH, sum of base cations, and SO42-, and highest NO3-, total N, and total Al; snowmelt appeared to dilute groundwater, and flush stored soil-derived solutes. Summer discharge, composed mainly of groundwater, exhibited the lowest flow, among the highest Mg2+, Ca2+, and lowest DON, DOC, and total Al concentrations. Isotopic analysis indicated that NO3- was microbial with primary source in upper watershed soil, from where it was flushed to stream under high discharge-conditions, or drained to groundwater which became its secondary source when discharge was low. Watershed outlet did not exhibit specific solute levels found at source-areas, but represented solute dynamics in the rest of the watershed well.

The role of hillslope hydrology in controlling nutrient loss

Hydrological controls on DOC and N transport at the catchment scale were studied for five storm events from the fall of 2004 through the spring of 2005 in WS10, H.J. Andrews Experimental Forest in the western Cascade Mountains of Oregon. This catchment is devoid of any riparian zone and characterized by hillslopes that issue directly into the stream. This enabled us to compare a trenched hillslope response to the stream response without the influence of riparian zone mixing. DOC and N concentrations and dissolved organic matter (DOM) quality (specific UV-absorbance (SUVA) and C:N of DOM) were investigated at the plot scale, in lateral subsurface flow from the trenched hillslope and stream water at the catchment outlet at the annual and seasonal scale (transition vs. wet period) during baseflow and stormflow conditions. DON was the dominant form of total dissolved nitrogen (TDN) in all sampled solutions, except in transient groundwater, where DIN was the dominant form. Organic horizon leachate and transient groundwater were characterized by high SUVA, and high DOC and total N concentrations, while SUVA and DOC and DON concentrations in lysimeters decreased with depth in the soil profile. This suggests vertical preferential flow without much soil matrix interaction occurred at the site. Deep groundwater (from a spring at the base of the hillslope) was characterized by low SUVA and low DOC and N concentrations. SUVA was always lower in lateral subsurface flow than in stream water at the seasonal scale, even during the wet period when other solutes were similar between lateral subsurface flow and stream water. This suggested mixing of deep groundwater and shallow transient groundwater was different at the hillslope scale compared to the catchment scale. DOC and DON sources were finite (production of DOC and DON from the hillslope soils appeared to be limited) at the seasonal scale since DOC and DON concentrations were significantly lower during the wet period compared to the transition period during stormflow conditions. This was also reflected in the DOC and DON peak and flow weighted storm event concentrations and antecedent soil moisture relationship where drier conditions (less prior flushing) resulted in the highest DOC and DON peak and flow weighted storm event concentrations. Results from this study showed the importance of the hillslope component in DOC and N transport at the catchment scale and underscore the importance of sampling solutes below the root zone (transient groundwater) and the value of using SUVA to fingerprint DOC sources.

Reprint of Dissolved organic carbon and nitrogen in the Western Black Sea

Dissolved organic carbon and nitrogen (DOC and DON) concentrations were measured in the Black Sea during May–June 2001. Sampling was conducted along a Shelf–Gyre transect, and was focused at the suboxic–anoxic interface at the deep stations; hypotheses were tested regarding trends in these variables across the transect and between sub-surface water layers. DOC and DON concentrations were higher (272 μM and 15 μM, respectively) on the Shelf compared to the Gyre (200 μM and 11 μM, respectively), as a result of terrigenous inputs and in situ net production. The bulk DOC:DON ratio was constant with distance and depth (approximately 15–19). DOM concentrations decreased with depth (average anoxic layer concentrations of 123 μM and 6.1 μM for DOC and DON, respectively), in contrast to earlier observations of increasing DOC concentration with depth. The deep Basin (2000 m) DOC concentrations were high compared to deep open ocean values (120 vs 45 μM). We suggest that the high deep DOC is a product of mixing of terrigenous (300 μM) and Aegean Sea (60 μM) DOC, with some in situ decomposition over the 600 year residence time for the deep water mass. High surface concentrations of DOC and DON and high DOC:DON ratios throughout the sampling region indicate the pervasive influence of remnant terrigenous DOM with some net production. The timescales for DOM Shelf–Basin exchange and decomposition could not be estimated due to a lack of geochemical tracer data.

Lateral and longitudinal patterns within the stygoscape of an alluvial river corridor

In landscape ecology, landscapes are viewed as hierarchically-organized groups of interacting components or zones. This perspective is applied in studies of riverscapes with increasing frequency,particularlyin studies ofchannel habitats and channel-floodplain interactions. Stygoscapes, the subsurface portions of riverscapes, have received less attention. Stygoscapes are composed of three saturated zones beneath and lateral to river channels: the hyporheic, parafluvial and riparian zones. These zones are differentiated on the basis of hydrological, biological and chemical conditions, and the degree of interaction with the channel surface. In this paper, we describe lateral and longitudinal patterns in the shallow (30 cm - 10 m depth) stygoscape of the alluvial Selwyn River, New Zealand. We used abutting hyporheic, parafluvial and riparian zones in large-scale downwelling (losing) and upwelling (gaining) sections of the river mainstem to compare physico-chemical and biological conditions across a broad stygoscape. The stygoscape zones had the same arrangement in both sections: hyporheic zones within the wetted channel, riparian zones furthest from the channel, and parafluvial zones between the hyporheic and riparian zones. Nitrate and dissolved reactive phosphorus concentrations and electrical conductivity were significantly higher, and dissolved organic phosphorus concentrations and pH levels lower, in the gaining section than the losing section. In both sections, ammonium, dissolved reactive phosphorus, and dissolved organic carbon concentrations and pH were higher in the hyporheic zone than the riparian zone. Within the losing section, DON and DOP concentrations were higher in the hyporheic zone than the riparian zone. Physico-chemical conditions were intermediate in the parafluvial zones of both river sections. These among-zone differences suggest that hyporheic zones are sinks for dissolved nutrients, and that effects of hyporheic sinks are greatest in losing river sections with unidirectional flow from the surface to the hyporheic zone. There were large differences among stygoscape zones in invertebrate assemblage composition, and smaller differences between the losing and gaining sections. Invertebrate densities, taxon richness and % insect taxa were higher in hyporheic zones than riparian zones. Invertebrate densities were intermediate in the parafluvial zones, and taxon richness and % insect taxa were similar in parafluvial and riparian zones. The spatial patterns we observed in the Selwyn River suggest that hydrological connectivity between zones, and permeability within zones, are among the most important determinants of chemical and biological dynamics in stygoscapes. Differences in large-scale upwelling and downwelling, and differences in water source (runoff and groundwater) appeared to be of secondary importance.

Stoichiometry of hydrological C, N, and P losses across climate and geology: An environmental matrix approach across New Zealand primary forests

Hydrologic losses can play a key role in regulating ecosystem nutrient balances, particularly in regions where baseline nutrient cycles are not augmented by industrial deposition. We used first‐order streams to integrate hydrologic losses at the watershed scale across unpolluted old‐growth forests in New Zealand. We employed a matrix approach to resolve how stream water concentrations of dissolved organic carbon (DOC), organic and inorganic nitrogen (DON and DIN), and organic and inorganic phosphorus (DOP and DIP) varied as a function of landscape differences in climate and geology. We found stream water total dissolved nitrogen (TDN) to be dominated by organic forms (medians for DON, 81.3%, nitrate‐N, 12.6%, and ammonium‐N, 3.9%). The median stream water DOC:TDN:TDP molar ratio of 1050:21:1 favored C slightly over N and P when compared to typical temperate forest foliage ratios. Using the full set of variables in a multiple regression approach explained approximately half of the variability in DON, DOC, and TDP concentrations. Building on this approach we combined a simplified set of variables with a simple water balance model in a regression designed to predict DON export at larger spatial scales. Incorporating the effects of climate and geologic variables on nutrient exports will greatly aid the development of integrated Earth‐climate biogeochemical models which are able to take into account multiple element dynamics and complex natural landscapes.

Immunochemical assessment of deoxynivalenol tissue distribution following oral exposure in the mouse

Deoxynivalenol (DON or vomitoxin) is a trichothecene mycotoxin commonly found in cereal grains that adversely affects growth and immune function in experimental animals. A competitive enzyme-linked immunosorbent assay (ELISA) was used to monitor the kinetics of distribution and clearance of DON in tissues of young adult B6C3F1 male mice that were orally administered 25 mg/kg bw of the toxin. DON was detectable from 5 min to 24 h in plasma, liver, spleen and brain and from 5 min to 8 h in heart and kidney. The highest DON plasma concentrations were observed within 5–15 min (12 μg/mL) after dosing. There was rapid clearance following two-compartment kinetics ( t 1/2α = 20.4 min, t 1/2β = 11.8 h) with 5% and 2% maximum plasma DON concentrations remaining after 8 and 24 h, respectively. DON distribution and clearance kinetics in other tissues were similar to that of plasma. At 5 min, DON concentrations in μg/g were 19.5 ± 1.9 in liver, 7.6 ± 0.5 in kidney, 7.3 ± 0.8 in spleen, 6.8 ± 0.9 in heart and 0.8 ± 0.1 in the brain. DON recoveries in tissues by ELISA were comparable to a previous study that employed 3H-DON and 25 mg/kg bw DON dose. The ELISA was further applicable to the detection of DON in plasma of mice exposed to the toxin via diet. This approach provides a simple strategy that can be used to answer relevant questions in rodents of how dose, species, age, gender, genetic background and route/duration of exposure impact DON uptake and clearance.

Effects of Deoxynivalenol on Cell Cycle and Apoptosis of Human Gastric Carcinoma Cell Line HGC-27 in vitro

Objective To explore the putative effect of deoxynivalenol on cell cycle and apoptosis of human gastric carcinoma cell line HGC-27 in vitro.Methods HGC-27 cells were treated with DON at different concentrations(50、100、1 000、2 000μg/L) for 12,24 and 48 hours,and then cells were harvested for analysis of apoptosis,cell cycle distribution and expression of Bax,Bcl-2 and Caspase-3 with flow cytometric(FCM) and Western Blot methods.Results At relatively higher concentrations(1 000 and 2 000 g/L),DON could affect cell cycle distribution in a time dependent manner.DON treatment for 12 h,the percentages of cells in G0/G1 phases was significantly decreased and that in S phase increased.As the treatment time lasted for 24 h and 48 h,the percentages of cells in G0/G1 phases were significantly increased while that in S phase decreased(P0.05).No significant effects on G2/M phase could be found.The apoptosis rates in all DON treated groups for 12 h,24 h and 48 h were all higher than that in control.Though statistical significance in the difference of apoptosis rate between control and the DON treated groups was not found 12 h after DON treatment but it could be seen 24 and 48 h after DON treatment(P0.05).Significant dose-effect relationships were found between DON concentrations and the apoptosis rates.Western Blot analysis showed bax and caspase-3 expression was up-regulated and bcl-2 expression was down-regulated in DON treated HGC-27 cells in vitro.Conclusion DON could significantly affect the cell cycle distribution of HGC-27 cells in vitro and the effects of DON on cell cycle varied as the concentratrion and treatment time of DON changed.DON treatment could induce apoptosis of HGC-27 cell possibly by up-regulating bax and caspase-3 expression and down-regulating bcl-2 expression.

Response of dissolved organic matter in the forest floor to long-term manipulation of litter and throughfall inputs

Dissolved organic matter (DOM) contributes to organic carbon either stored in mineral soil horizons or exported to the hydrosphere. However, the main controls of DOM dynamics are still under debate. We studied fresh leaf litter and more decomposed organic material as the main sources of DOM exported from the forest floor of a mixed beech/oak forest in Germany. In the field we doubled and excluded aboveground litter input and doubled the input of throughfall. From 1999 to 2005 we measured concentrations and fluxes of dissolved organic C and N (DOC, DON) beneath the Oi and Oe/Oa horizon. DOM composition was traced by UV and fluorescence spectroscopy. In selected DOM samples we analyzed the concentrations of phenols, pentoses and hexoses, and lignin-derived phenols by CuO oxidation. DOC and DON concentrations and fluxes almost doubled instantaneously in both horizons of the forest floor by doubling the litter input and DOC concentrations averaged 82 mg C l−1 in the Oe/Oa horizon. Properties of DOM did not suggest a change of the main DOM source towards fresh litter. In turn, increasing ratios of hexoses to pentoses and a larger content of lignin-derived phenols in the Oe/Oa horizon of the Double litter plots in comparison to the Control plots indicated a priming effect: Addition of fresh litter stimulated microbial activity resulting in increased microbial production of DOM from organic material already stored in Oe/Oa horizons. Exclusion of litter input resulted in an immediate decrease in DOC concentrations and fluxes in the thin Oi horizon. In the Oe/Oa horizon DOC concentrations started to decline in the third year and were significantly smaller than those in the Control after 5 years. Properties of DOM indicated an increased proportion of microbially and throughfall derived compounds after exclusion of litter inputs. Dissolved organic N did not decrease upon litter exclusion. We assume a microbial transformation of mineral N from throughfall and N mineralization to DON. Increased amounts of throughfall resulted in almost equivalently increased DOC fluxes in the Oe/Oa horizon. However, long-term additional throughfall inputs resulted in significantly declining DOC concentrations over time. We conclude that DOM leaving the forest floor derives mainly from decomposed organic material stored in Oe/Oa horizons. Leaching of organic matter from fresh litter is of less importance. Observed effects of litter manipulations strongly depend on time and the stocks of organic matter in forest floor horizons. Long-term experiments are particularly necessary in soils/horizons with large stocks of organic matter and in studies focusing on effects of declined substrate availability. The expected increased primary production upon climate change with subsequently enhanced litter input may result in an increased production of DOM from organic soil horizons.

Processing of atmospheric nitrogen by clouds above a forest environment

Dissolved inorganic ions (NH4+, Ca2+, Mg2+, K+, H+, NO3−, and SO42−) and organic nitrogen (DON) were measured in cloud water samples collected over the northern lower peninsula of Michigan. Within a given cloud field, several altitudes were sampled to examine changes in concentration and speciation with altitude. Several samples were analyzed for bacterial content and activity. Convective cumulus (cumulus congestus) were more concentrated than fair weather cumulus (cumulus humilis) for all major ions and DON, with the cloudy air DON concentrations in convective cumulus being twice as large as for fair weather cumulus, and for all other ions, the droplets were 4–6 times more concentrated. The molar average distribution of nitrogen in the cloud water was 43 (±10, 1σ)% ammonium, 39 (±7)% nitrate and 18 (±11)% DON. High concentrations of bacteria were observed in the clouds with an average concentration of 2.9 × 105 (±1.0 × 105, 1σ) bacteria m−3 of cloudy air but which contributed less than 1% of the nitrogen in the cloud water. In addition, nitrifying bacteria were identified, indicating bacterial processing of nitrogen in the cloud water may occur. Air mass origin and altitude influence observed cloud water concentrations, with the exception of DON. The correlation of ammonium and sulfate, and calcium and nitrate suggest that ammonium sulfate and calcium nitrate aerosol may be important sources of these ions.

Soil and Plant Nitrogen Pools as Related to Plant Diversity in an Experimental Grassland

Increasing plant species richness decreases soil NO 3 - concentrations in experimental plant mixtures, but the role of particular plant functional groups has remained unclear. Most analyses have focused on particular times of the year or were restricted to NO 3 - . We tested whether plant species richness or particular plant functional groups affect the size of plant-available N pools in soil (KCl-extractable NO 3 - , dissolved inorganic N and organic N [DON] and total dissolved N [TDN] in soil solution) and N concentrations and pools in aboveground biomass. Furthermore, we assessed seasonal variations in the effects of plant species richness and plant functional groups. The experimental grassland site had 86 plots with different combinations of numbers of species (1, 2, 4, 8, 16, and 60) and numbers of functional groups (1, 2, 3, and 4, being grasses, small nonlegume herbs, tall nonlegume herbs, and legumes). In the second year after establishment, increasing species richness reduced soil NO 3 - concentrations (ANOVA, 11% of sum of squares [SS]). The presence of legumes correlated positively with soil NO 3 - concentrations (17% of SS). The presence of grasses significantly decreased soil NO 3 - concentrations (11% of SS). Seasonality had no influence on the relationships between NO 3 - concentrations and species richness. Volume-weighted mean DON and TDN concentrations in soil solution correlated negatively with species richness. Nitrogen pools in plant mixture biomass correlated positively with species diversity (14% of SS), indicating that total N uptake increased with increasing diversity. We conclude that both diversity (either in species or functional groups) and functional composition of grassland mixtures are significant controls of soil and plant N pools. Plant communities with more diverse mixtures are liable to use limiting resources such as N more effectively.

Dissolved organic carbon and nitrogen in the Western Black Sea

Dissolved organic carbon and nitrogen (DOC and DON) concentrations were measured in the Black Sea during May–June 2001. Sampling was conducted along a Shelf–Gyre transect, and was focused at the suboxic–anoxic interface at the deep stations; hypotheses were tested regarding trends in these variables across the transect and between sub-surface water layers. DOC and DON concentrations were higher (272 μM and 15 μM, respectively) on the Shelf compared to the Gyre (200 μM and 11 μM, respectively), as a result of terrigenous inputs and in situ net production. The bulk DOC:DON ratio was constant with distance and depth (approximately 15–19). DOM concentrations decreased with depth (average anoxic layer concentrations of 123 μM and 6.1 μM for DOC and DON, respectively), in contrast to earlier observations of increasing DOC concentration with depth. The deep Basin (2000 m) DOC concentrations were high compared to deep open ocean values (120 vs 45 μM). We suggest that the high deep DOC is a product of mixing of terrigenous (300 μM) and Aegean Sea (60 μM) DOC, with some in situ decomposition over the 600 year residence time for the deep water mass. High surface concentrations of DOC and DON and high DOC:DON ratios throughout the sampling region indicate the pervasive influence of remnant terrigenous DOM with some net production. The timescales for DOM Shelf–Basin exchange and decomposition could not be estimated due to a lack of geochemical tracer data.

Comparison of ochratoxin A and deoxynivalenol in organically and conventionally produced beers sold on the Belgian market

Beer was chosen as a cereal-derived and homogeneous product for a comparison of organic and conventional production methods in terms of mycotoxin contamination levels. Ochratoxin A (OTA, a storage mycotoxin) and deoxynivalenol (DON, a field mycotoxin) were assessed by HPLC in organically and conventionally produced beers sold in Belgium. Immunoaffinity column (OchraTest® and DONPrep®) purification was used prior to HPLC analysis. For in-house validation, recovery experiments, carried out with the spiked beers in the ranges of 50–200 ng OTA l−1 and 20–100 µg DON l−1, led to the overall averages of 91% (RSD = 10%, n = 9) and 93% (RSD = 5%, n = 27), respectively. Organic beers collected during 2003–2004 were more frequently OTA-contaminated (95%, n = 40) than their conventional counterparts (50%, n = 40). Conventional beers were OTA-contaminated at a mean concentration of 25 ng l−1 (range: 19–198 ng l−1), while organic beers contained a mean level of 182 ng l−1 (range: 18–1134 ng l−1). High OTA contamination above the limit of 200 ng l−1 (up to 1134 ng l−1) occasionally occurred in organically produced beers. A complementary survey performed with the same brands in 2005 did not confirm this accidental presence of excessive OTA loads (range: 3–67 ng l−1 for 10 conventional beers and 19–158 ng l−1 for 10 organic beers). Establishing a maximum of 3 µg OTA kg−1 in malt, the application of the regulation EC No. 466/2001 (entered in force before the last sampling) may be related to the observed improvement. The overall incidence of DON was 67 and 80% in conventional and organic beers, respectively. DON concentrations ranged from 2 to 22 µg DON l−1 (mean = 6 µg DON l−1) in conventional beers, while organic beers ranged from 2 to 14 µg DON l−1 (mean=4 µg DON l−1). Thus, DON in beers does not appear to be a major matter of concern. From the statistical tests, it was concluded that the variation between different batches was significant (P < 0.0001), in contrast to that observed between different brands, showing a lack of homogeneity in the raw materials. This occurs either in organically or in conventionally produced materials. Considering these results, an optimized frequency of controls according to European Regulations EC No 466/2001 and EC No 856/2005 should be recommended to reject the irregular batches.

Ecosystem response to 15 years of chronic nitrogen additions at the Harvard Forest LTER, Massachusetts, USA

Humans have altered the global and regional cycles of nitrogen more than any other element. Alteration of N cycling patterns and processes in forests is one potentially negative outcome of accelerated N deposition worldwide. To assess potential impacts of N deposition on temperate forests, a series of chronic nitrogen additions in two contrasting forest types (red pine plantation and mixed hardwood stand) were designed as a core experiment of the Harvard Forest (HF) Long-term Ecological Research (LTER) program. This paper describes the chronic N experimental study site in detail and presents the long-term baseline measurements established at the beginning of treatments in 1988. Results reported here continue or accelerate trends presented in previous papers. Losses of inorganic N remain high in the high N plots (higher in pines than hardwoods) and low N plots in the pine stand also have measurable DIN losses. Foliar and fine root N concentrations are elevated significantly. Mortality of red pine reached 56% by 2002 in the pine high N plot, and biomass accumulation has stopped altogether. The high N hardwood stand shows increased ANPP, but excess N availability and a severe drought in 1995 contributed to mortality of 72% of red maple trees by 2002. Species importance and litterfall patterns were altered in several plots after 1995. Roots, foliage and wood have diminished as net sinks for added N, re-emphasizing the role of soils in N retention. Two mechanisms for large net retention of added N were suggested in a review paper in 1998. Of these, abiotic immobilization is supported by a growing set of papers, while assimilation and re-exudation by mycorrhizae is suggested by increased DON concentrations.

Nutrient limitation, organic matter cycling, and plankton dynamics during an Aureococcus anophagefferens bloom

We evaluated plankton dynamics and the role of nutrients (organic and inorganic) during an intense (>1.5 × 10 6 cells ml -1 ) and sustained (>4 mo) brown tide bloom of the pelagophyte Aureococcus anophagefferens during the summer of 2000 in Great South Bay (GSB), New York, USA. During the study, light and dissolved inorganic nitrogen (DIN) levels were low (mean 1% light depth = 2 m, mean DIN = 0.7 µM), while dissolved organic carbon and nitrogen levels were high (mean = 600 and 45 µM, respectively). Co-occurring with the A. anophagefferens bloom was a consortium of other small phytoplankton: 60 ± 19% of chlorophyll present during the bloom was 10 6 cells ml -1 following the peak of the brown tide. Although the growth of non-brown-tide phytoplankton, such as picocyanobacteria, was consistently enhanced by nitrate and urea additions (during 100% of experiments conducted, n = 18), the net population growth of A. anophagefferens was not stimulated by N-enrichment in 60% of the experiments. During bloom initiation, decreases in DOC, DON, and DOP concentrations in GSB were similar to concurrent calculated increases in cellular C, N, and P of the burgeoning A. anophagefferens population, suggesting direct or indirect utilization of compounds within these pools by brown tide and associated microbes. In contrast, levels of DOM rose sharply when A. anophagefferens densities decreased and picocyanobacteria became the dominant phototrophs. These results illustrate a dichotomy in the algal communities of estuaries which host brown tides: often nitrogen-replete A. anophagefferens populations which are associated with DOM degradation and non-brown-tide phytoplankton populations such as picocyanobacteria which are consistently nitrogen-limited and associated with water column accumulation of DOM.

The biology and chemistry of land fast ice in the White Sea, Russia?A comparison of winter and spring conditions

Various abiotic and biotic parameters, including phytoplankton distribution, were studied to investigate seasonal changes within the fast-ice cover in Chupa Inlet, a freshwater-influenced Arctic-like fjord in Kandalaksha Bay (White Sea). Sea ice and under-ice water were collected along transects in the inlet in February and April 2002. Ice-texture analysis, salinity and δ18O values indicated that the complete ice sheet had transformed within 2 months. This resulted from an upward growth of snow ice and subsequent melting at the underside of the ice, which makes a comparison between the two sampling periods difficult in terms of defining temporal developments within the ice. Nutrients, DOC and DON concentrations in the under-ice water were typical for Russian Arctic rivers. Concentrations of nitrate, silicate and DOC in the ice were lower, which is attributed to a loss as the ice forms. The concentrations were also modified by biological activity. In February, there was a strong correspondence between the distribution of biological parameters, including particulate and dissolved organic carbon and nitrogen (POC and PON, DOC and DON) and inorganic nutrients (nitrate, nitrite, phosphate and silicate), which was not the case in April. The correlation between both DOC and DON with ammonium indicates heterotrophic activity within the winter ice collected in February. Sea-ice organisms were distributed throughout the ice, and several assemblages were found in surface layers of the ice. In April, a more "typical" distribution of biomass in the ice was measured, with low values in the upper part and high algal concentrations in the lower sections of the ice, characteristic of a spring ice-algal bloom. In contrast to the February sampling, there was evidence that the ice-algal assemblage in April was nitrogen-limited, with total inorganic nitrogen concentrations being <1 µm and a mean inorganic nitrogen to phosphorus ratio of 2.8. The ice assemblages were dominated by diatoms (in particular, Nitzschia spp.). There were temporal shifts in the assemblage composition: in February, diatoms accounted for 40% and in April for >98% of all organisms counted.