Summer Experiment Research Articles

Leaf metabolite profile of the Brazilian resurrection plant Barbacenia purpurea Hook. (Velloziaceae) shows two time-dependent responses during desiccation and recovering.

Barbacenia purpurea is a resurrection species endemic to rock outcrops, in Rio de Janeiro, Brazil. It tolerates great temperature variations, which are associated to periods of up to 30 days without precipitation. Using a metabolomic approach, we analyzed, under winter and summer conditions, changes in the leaf metabolite profile (MP) of potted plants of B. purpurea submitted to daily watered and water deficit for at least 20 days and subsequent slow rehydration for 5 days. Leaves were collected at different time points and had their MP analyzed by GC/MS, HPAEC, and UHPLC techniques, allowing the identification of more than 60 different compounds, including organic and amino acids, sugars, and polyols, among others. In the winter experiment, results suggest the presence of two time-dependent responses in B. purpurea under water stress. The first one starts with the increase in the content of caffeoyl-quinic acids, substances with strong antioxidant activity, until the 16th day of water suppression. When RWC reached less than 80 and 70%, in winter and summer respectively, it was observed an increase in polyols and monosaccharides, followed by an increment in the content of RFO, suggesting osmotic adjustment. Amino acids, such as GABA and asparagine, also increased due to 16 days of water suppression. During rehydration, the levels of the mentioned compounds became similar to those found at the beginning of the experiment and when compared to daily watered plants. We conclude that the tolerance of B. purpurea to dehydration involves the perception of water deficit intensity, which seems to result in different strategies to overcome the gradient of water availability imposed along a certain period of stress mainly during winter. Data from summer experiment indicate that the metabolism of B. pupurea was already primed for drought stress. The accumulation of phenolics in summer seemed to be more temperature and irradiance-dependent than on the RWC.

Yield and uranium concentration in two lettuce (Lactuca sativa L.) varieties influenced by soil and irrigation water composition, and season growth

The use of contaminated land or irrigation water for agriculture in the neighborhood of mines as well as the transfer of metals from soils to vegetables and to humans through the food chain is a worldwide concern. This study was conducted to compare the effects on lettuce (Lactuca sativa L. varieties Marady and Romana) grown in different seasons (autumn and summer) when exposed to high and low uranium concentrations, both in irrigation water and soils (total and available fraction), near a former uranium mine. Irrigation with uranium contaminated water (0.94 to 1.14mg/L) together with high concentrations of uranium in the soil available fraction (9.2 to 14.5mg/kg) had negative effects on both lettuce varieties, namely on leaf yield reduction (up to 53% and 87% in autumn and summer experiments, respectively) and increase of uranium concentration in the leaves (up to 2.13 and 5.37mg/kgdryweight) and in the roots (up to 4.64 and 28.2mg/kgdryweight) for Marady and Romana varieties, respectively. The effect on lettuce yield was mainly due to the soil salinity (electrical conductivity up to 6.31mS/cm) as a consequence of water irrigation with high electrical conductivity (1.67 to 1.82mS/cm) and low tolerance of lettuce to the soil salinity. The highest concentration of uranium in the Romana variety was also the result of its growth in a dry season when the frequency and amount of water irrigation was great. The consumption of uranium by an adult, teenager and child, from lettuce that concentrate more this element (234μgU/kg fresh weight) was, respectively, 16.7, 17.7 and 24.4% of the tolerable daily limit intake set by the World Health Organization (0.6mgU/kg body weight daily; WHO, 2005). These values suggest that lettuce had low impact on human uranium intake and should not present a concern for Cunha Baixa inhabitant's health assuming that this vegetable is the only food consumed with high uranium concentrations.

Impact of initial soil moisture anomalies on climate mean and extremes over Asia

AbstractThis paper focuses on the impact of soil moisture anomalies on subsequent precipitation and surface air temperature over Asia based on numerical experiments using a regional climate model. Soil moisture anomalies are applied on 1 March, 1 June, and 1 September for the spring, summer, and autumn experiments, respectively, and their impacts on both the climate mean and extremes are examined. Major findings are the following. (1) The land surface memory for soil moisture anomalies is longer in the midlatitudes and shorter in the Tropics, and such memory is enhanced by soil moisture‐precipitation feedback. (2) The wet (dry) initial soil moisture anomalies increase (reduce) the subsequent precipitation amount and reduce (increase) surface temperature. For precipitation, the strongest impacts are found in midlatitude to high‐latitude regions including northwest China, central Asia, southern Siberia; for temperature, the strongest response is found in India and Indochina regions and most of the midlatitude areas in spring, in high‐latitude and midlatitude regions in summer, and in India and eastern China (lower Yellow river basin) in autumn. (3) The impact on mean climate variables can last for 2–3 months over most regions of strong response, and the impact of wet initial soil moisture anomalies tends to be stronger but dissipates faster than the dry initial anomalies. (4) Both the dry and wet initial soil moisture anomalies tend to reinforce severe flood extremes, while other climate extremes respond to initial anomalies in a way similar to the mean climate: wet (dry) initial soil moisture anomalies reduce (amplify) the drought extremes, diminish (reinforce) the hot extremes, and enhance (reduce) the cold extremes over areas of strong soil moisture‐atmosphere coupling.

Climate factors mediate soil respiration dynamics in Mediterranean agricultural environments: an empirical approach

Soil CO2 emissions, the result of soil respiration processes, may be essential in climate change modelling. The complex phenomenon of soil respiration is regulated by a range of mainly climate-related environmental factors. We tested the latest published empirical models in a field experiment in an agricultural soil under Mediterranean conditions. Soil respiration was monitored biweekly with a portable infrared gas analyser, and climate features were monitored for 1 year (2010–11). An additional rewetting assay (watering the soil) was done at the end of the experiment in summer when the soil water content was dry. We tested different approaches to represent the simple effect of climate factors on soil respiration and found Gaussian models to be the best. We also tested the most recent models designed to represent the synergic effects of climate factors, and our modification of the Martin and Bolstad model showed the best coefficient of determination. The results suggest that linear approaches and the use of a fixed Q10 value should be revised to represent climate and soil respiration relations, especially in high-variability environments where soil respiration variability is controlled by soil temperature and moisture interactions, while precipitation pulses induce CO2 emission peaks. Finally, our results showed that the influence of soil temperature and moisture on soil respiration is lower under Mediterranean conditions than in temperate climate types.

Rising plate meters and a capacitance probe estimate the biomass of chicory and plantain monocultures with similar accuracy as for ryegrass-based pasture

Abstract It is useful to gain an estimate of herbage biomass when feed budgeting. However, none of the tools that are available to estimate biomass (e.g., the rising plate meter (RPM) or capacitance probe (CP)) have been tested on popular forage herbs, such as chicory or plantain. We tested the hypothesis that RPM and CP could be used to estimate biomass of first year pure chicory and plantain swards with accuracy at least as great as for ryegrassbased pasture. In two summer experiments at different locations in the Waikato, RPM, CP and uncompressed sward height (SH) readings were taken throughout regrowth within 0.2 m² quadrats in chicory and plantain swards, and ryegrass-based pasture. The herbage was then cut to ground level and oven-dried to estimate biomass. Linear equations relating biomass to mean readings were generated for each method, both within each experiment and as pooled datasets. In ryegrassbased pasture, the correlation coefficients (R²) were 0.73, 0.43 and 0.51 for RPM, CP and SH, respectively. For chicory swards, the pooled correlation coefficients (R²) were 0.73, 0.73 and 0.81 for RPM, CP and SH, respectively, while for plantain swards the R2 were 0.70, 0.59 and 0.68 for RPM, CP and SH, respectively. This led to the conclusion that the RPM was a suitable tool for the estimation of biomass in pure chicory or plantain swards as it had similar accuracy to calibration equations for ryegrass-based pasture. Farmers, at least in the Waikato, can estimate first year chicory or plantain biomass through the summer and autumn period using the following equations: Chicory biomass (kg DM/ha) = 86 × RPM reading + 235, or = 0.64 × CP reading + 437, or = 94 × SH - 190. Plantain biomass (kg DM/ha) = 94 × RPM reading + 455. Keywords: rising plate meter (RPM), capacitance probe (CP), chicory, plantain

Time evolution of Pb(II) speciation in Pampa soil fractions

Soil pollution by heavy metals, particularly lead, is an important environmental concern; the bioavailability of such pollutants is strongly dependent on their chemical form. Here, the speciation of Pb(II) in soil fractions as a function of time shortly after its incorporation is studied, using a selective sequential extraction method. The sample came from an Argentinean Pampas region and was extensively characterised, including Rietveld analysis of the silt+clay fraction XRD pattern to find the major mineral components. Experiments were run twice, once in the winter and once in the summer. The results show different speciation time profiles in both cases, showing faster changes in winter due to the higher water content. The summer experiment corresponds to an earlier stage in the speciation profile evolution compared with winter. The soluble/exchangeable fraction decreases with time in summer but shows a lower and constant value in the winter. A high proportion is found to be adsorbed onto the stable (aluminosilicates+quartz) mineral fraction. The results strongly suggest that, even at a short time following soil pollution with Pb, a high proportion is adsorbed onto the mineral fraction, with only a low fraction being bioavailable. The most stable (mineral incorporated) form is observed to increase with time. Soil water content appears to be more important than temperature in determining the differences between the two.

Field Experiment of Demand Responsive Load Control in Office Buildings in Summer and Winter: Analysis of Load Reduction Impact and Customers' Acceptance

To explore the possibility of implementation of demand response (DR) program for Japanese commercial buildings, we studied the load impact and customers' acceptance of demand responsive air-conditioning and lighting load control through a field test at two office buildings located in southern Tokyo Metropolitan area, which was conducted in summer and winter of FY2012. The summer experiment results show that, automated DR (ADR) control can shed the load demand during DR hours with some certainty but very likely decreases the subjective working efficiency of workers in the controlled floors. This implies that advanced ADR control techniques having little effect on working efficiency are needed to gain the customers' acceptance and improve the DR value. Pre-cooling might be a promising summer DR technique. The winter experiment results show that, ADR control sheds load with high uncertainty and further research is needed to develop winter DR techniques.

Projected climate change scenario over California by a regional ocean–atmosphere coupled model system

This study examines a future climate change scenario over California in a 10-km coupled regional downscaling system of the Regional Spectral Model for the atmosphere and the Regional Ocean Modeling System for the ocean forced by the global Community Climate System Model version 3.0 (CCSM3). In summer, the coupled and uncoupled downscaled experiments capture the warming trend of surface air temperature, consistent with the driving CCSM3 forcing. However, the surface warming change along the California coast is weaker in the coupled downscaled experiment than it is in the uncoupled downscaling. Atmospheric cooling due to upwelling along the coast commonly appears in both the present and future climates, but the effect of upwelling is not fully compensated for by the projected large-scale warming in the coupled downscaling experiment. The projected change of extreme warm events is quite different between the coupled and uncoupled downscaling experiments, with the former projecting a more moderate change. The projected future change in precipitation is not significantly different between coupled and uncoupled downscaling. Both the coupled and uncoupled downscaling integrations predict increased onshore sea breeze change in summer daytime and reduced offshore land breeze change in summer nighttime along the coast from the Bay area to Point Conception. Compared to the simulation of present climate, the coupled and uncoupled downscaling experiments predict 17.5 % and 27.5 % fewer Catalina eddy hours in future climate respectively.

Biphasic control of Argulus bengalensis Ramakrishna (1951) (Crustacea: Branchiura) with plant derivatives

Efficacy of treatment with some plant parts containing ingredients viz. rotenone, azadirachtin, and nicotine for control of a piscine ectoparasite Argulus bengalensis has been tested in laboratory experiments. Among those plant preparations, tobacco leaf dust (TLD) containing nicotine is found potentially active against the adult parasitic morphs at a lethal concentration of 8ppm which is sublethal and tolerable to the host fish. However, nicotine is not effective on the embryonic life stages of the parasite and thus the gene pool is retained in the form of egg investment. Embryonic development and subsequent hatching of the eggs occurs normally in the post treatment period which results in recurrence of parasitaemia (F1 generation) within 12 to 16days in summer and 15 to 18days in winter in a temperature dependant manner. Considering maturation of F1 generation and subsequent investment of their first clutch of eggs at the age of 21days onwards, one vulnerable time window of 17 to 19days for summer experiment and another of 19 to 21days for winter experiment have been identified. Since the time windows are brief and exist only for three days and those windows overlap at day 19, the day 19 has been targeted for application of a second phase of treatment in both seasons. The study recommends a new approach of biphasic treatment for complete eradication of A. bengalensis infestation.

Diel patterns of oceanic dimethylsulfide (DMS) cycling: Microbial and physical drivers

AbstractDimethylsulfide (DMS) is a biogenic gas with potential climatic effects, and its marine emission depends on the interplay between microbial activity and physical forcing in the oceanic upper mixed layer. We investigated the diel cycling patterns of DMS and its precursor dimethylsulfoniopropionate (DMSP) in four experiments (28 to 48 h long) performed in mesotrophic to ultraoligotrophic Mediterranean and Sargasso Sea waters. Samples taken every 4 or 6 h were analyzed for dimethylated sulfur pools and incubated to measure DMS and DMSP cycling rates, as well as primary and bacterial production. In all four experiments, DMS budgets showed pronounced day versus night variability. In the three summer experiments, gross community DMS production (GPDMS) increased by twofold to threefold from nighttime to daytime, peaking 0–4 h after solar noon. This excess GPDMS was balanced by higher photochemical and microbial sinks during the day, effectively buffering DMS concentrations. In the only winter experiment, GPDMS exhibited opposed temporal dynamics and peaked at nighttime in parallel to total DMSP consumption. Community DMSP to DMS conversion yields were generally <10% throughout the winter experiment and at night in summer, and increased to >15% (even >50%) during the day in summer, presumably due to phytoplankton radiative stress. Our data suggest that (1) diel variability should be taken into account in process studies, diagnostic, and prognostic models of DMS cycling and (2) the community DMS yield is a key variable that defines characteristic DMS cycling regimes.

Fine particulate organic matter transport dynamics in a small Coastal Plain stream: influence of hydrology and channel morphology

Fine particulate organic matter (FPOM) represents a major component of stream organic matter budgets, and its dynamics greatly affect the productivity and metabolism of a stream community. FPOM transport dynamics has been well documented in high-gradient streams with rocky substrates, but information from low-gradient, sandy-bottom streams has been lacking. We estimated FPOM retention patterns in Payne Creek, a 2nd order Coastal Plain stream (USA), under naturally varying hydraulic conditions (discharge and velocity). Corn pollen, as an FPOM analogue, was released along with a conservative solute tracer and the particle retention coefficient (k p) was calculated by fitting the ratio of total pollen remaining in the water column against the longitudinal transport distance to an exponential decay model. Pollen k p (n = 4) ranged from 0.034 to 0.214 /m, and particle transport distance (S p) ranged from 4.7 to 29.7 m. The S p measured in Payne Creek was in the lowest range of previously reported values, and such rapid particle retention was attributed to the low channel slope and slow current velocity. S p was significantly correlated to water velocity and the channel friction factor, but not to discharge (Q). Two summer experiments conducted in contiguous stream segments resulted in the shortest (4.7 m) and longest (29.7 m) S p, despite the similar Q. This was attributed to the segment-scale channel alterations that occurred during the previous winter, which led to very different hydraulic conditions in the two stream segments. In Payne Creek, seasonal changes in hydrology and segment-scale variation in channel morphology were the main factors controlling FPOM transport and retention.

Effects of low temperature storage and sucrose pulsing on the vase life of Lilium cv. Brindisi inflorescences

Lilium cv. Brindisi inflorescences were stored at 2.5°C for 5, 10, 15 or 20d, comparing dry storage with storage of the stem ends in water. Prior to storage, inflorescences were treated with 20 or 100gL−1 sucrose in water, for 20h at 20°C. After storage the inflorescences were individually placed in water at 20°C. The floral buds were still closed at the end of cold storage. In experiments carried out in summer, the time to bud opening was hastened by storage at 2.5°C in water, more so after a longer period of cold storage. The time to tepal senescence after cold storage in water decreased with the time of storage. The time to tepal abscission was about 1 day longer than the time to tepal senescence. Repeat experiments in late fall and winter additionally showed early leaf yellowing after cold storage. Compared to the experiments in summer, more desiccated floral buds were found in the fall. Pulse treatment with 100gL−1sucrose prior to cold storage reduced the number of desiccated buds. However, leaf yellowing was aggravated by the 100gL−1 sucrose pulse treatment. Compared to cold storage in water, dry storage at 2.5°C further hastened the time to bud opening and also further hastened tepal senescence and abscission. Dry storage also produced more buds that desiccated or opened poorly. Sucrose treatment (100gL−1) alleviated the effects of dry storage on tepal senescence and bud desiccation. The data showed that lily cv. Brindisi inflorescences are prone to chilling injury, but can be stored, depending on the treatment, for 5–10d, during most of the year.

Personality and Information Gathering in Free-Ranging Great Tits

One aspect of animal personality that has been well described in captivity, but received only little attention in studies in the wild, is that personality types may vary in their behavioural flexibility towards environmental changes. A fundamental factor underlying such differences is believed to be the degree to which individual behavior is guided by environmental stimuli. We tested this hypothesis in the wild using free-ranging great tits. Personality variation was quantified using exploratory behaviour in a novel environment, which has previously been shown to be repeatable and correlated with other behaviours in this and other populations of the same species. By temporarily removing food at feeding stations we examined whether birds with different personality differed in returning to visit empty feeders as this may provide information on how birds continue to sample their environment after a sudden change in conditions. In two summer experiments, we found that fast-exploring juveniles visited empty feeders less often compared to slow-exploring juveniles. In winter, sampling behaviour was sex dependent but not related to personality. In both seasons, we found that birds who sampled empty feeders more often were more likely to rediscover food after we again re-baited the feeding stations, but there was no effect of personality. Our results show that personality types may indeed differ in ways of collecting environmental information, which is consistent with the view of personalities as different styles of coping with environmental changes. The adaptive value of these alternative behavioural tactics, however, needs to be further explored.

Temporal shifts in top‐down vs. bottom‐up control of epiphytic algae in a seagrass ecosystem

In coastal marine food webs, small invertebrate herbivores (mesograzers) have long been hypothesized to occupy an important position facilitating dominance of habitat-forming macrophytes by grazing competitively superior epiphytic algae. Because of the difficulty of manipulating mesograzers in the field, however, their impacts on community organization have rarely been rigorously documented. Understanding mesograzer impacts has taken on increased urgency in seagrass systems due to declines in seagrasses globally, caused in part by widespread eutrophication favoring seagrass overgrowth by faster-growing algae. Using cage-free field experiments in two seasons (fall and summer), we present experimental confirmation that mesograzer reduction and nutrients can promote blooms of epiphytic algae growing on eelgrass (Zostera marina). In this study, nutrient additions increased epiphytes only in the fall following natural decline of mesograzers. In the summer, experimental mesograzer reduction stimulated a 447% increase in epiphytes, appearing to exacerbate seasonal dieback of eelgrass. Using structural equation modeling, we illuminate the temporal dynamics of complex interactions between macrophytes, mesograzers, and epiphytes in the summer experiment. An unexpected result emerged from investigating the interaction network: drift macroalgae indirectly reduced epiphytes by providing structure for mesograzers, suggesting that the net effect of macroalgae on seagrass depends on macroalgal density. Our results show that mesograzers can control proliferation of epiphytic algae, that top-down and bottom-up forcing are temporally variable, and that the presence of macroalgae can strengthen top-down control of epiphytic algae, potentially contributing to eelgrass persistence.

Modeling Gas Transport in the Shallow Subsurface in Maguelone Field Experiment

In this paper, TOUGH2/EOS7CA model is used to simulate the shallow injection-monitoring experiment carried out at Maguelone, France, during 2012 and 2013. The ultimate objective of the work is to improve our understanding of gas transport in the shallow subsurface as well as to develop and validate the model to monitor it. This work represents first results towards modelling the nitrogen and CO2 injection experiments carried out. The pressure data from the first injection experiments in summer 2012 is used as basis for comparison. Work is presently going on to incorporate the experimental data into the numerical simulation further.

Períodos de interferência de plantas daninhas na cultura do girassol

Objetivou-se neste trabalho determinar os períodos de interferência de plantas daninhas na cultura do girassol. Foram realizados dois experimentos com o girassol híbrido Helio 250, sendo um conduzido no verão e o outro, no inverno. Para ambos, o delineamento experimental utilizado foi em blocos casualizados, com quatro repetições, e cada unidade experimental foi constituída de cinco linhas de plantas com 6,0 m de comprimento, espaçadas por 0,7 m. No experimento de verão foram avaliados oito períodos de convivência e controle de plantas daninhas: 10, 20, 30, 40, 50, 60, 70 e 88 dias após a emergência (dae). No experimento de inverno, os períodos foram: 7, 14, 21, 28, 38, 48, 58 e 82 dae. Avaliaram-se a massa da matéria seca e a área foliar das plantas de girassol, produtividade, massa de mil aquênios e massa da matéria seca de plantas daninhas. Estimaram-se os períodos anteriores à interferência (PAI), períodos críticos de prevenção à interferência (PCPI) e períodos totais de prevenção à interferência (PTPI). Considerando-se a produtividade de aquênios no verão, o PAI foi de 16 dae da cultura, o PTPI, de 39 dae e o PCPI abrangeu 23 dias do ciclo da cultura. No inverno, o PAI foi de 12 dae, o PTPI estendeu-se até os 34 dae, resultando em um PCPI de 22 dias.

Comparative stress responses to short transport and related events in Hereford and Brahman steers1

Three summer experiments compared responses to transportation-related events in 2- to 4-yr-old Brahman (Bos indicus) and Hereford (B. taurus) steers. In Exp. 1, steers were hauled round-trip (4 h) or fasted in holding pens. Transport transiently increased (P < 0.01) plasma cortisol and glucose concentrations, decreased (P < 0.05) plasma triglyceride concentrations, and increased total leukocyte counts. Blood constituents were not altered for steers fasting in holding pens. Treatment-day BW shrink was greater (P < 0.01) in transported steers than penned steers. Blood constituent responses were unaffected (P < 0.05) by subspecies. Hereford experienced greater (P < 0.05) transport-day BW shrink than Brahman across treatments. Steers in Exp. 2 were hauled to a new farm for a 1-wk relocation period or hauled round-trip an equal time (0.67 h) and returned to the home station. Both treatments similarly experienced transport-day BW shrink and increased (P < 0.01) plasma cortisol and glucose. Subspecies did not affect (P < 0.05) blood constituent responses to transport. Hereford experienced greater (P < 0.05) transport-day shrink than Brahman. Relocation did not elicit (P < 0.05) changes in blood profiles beyond the day of transport. In Exp. 3, steers were loaded and unloaded without transport, transported round-trip (1 h), or fasted in a holding pen for 3 h. Cortisol increased (P < 0.01) after transport and after loading/unloading. Leukocytes and glucose increased (P < 0.01) after the 1 h transport. Steers transported experienced greater treatment-day BW shrink than those fasted or loaded and unloaded (P < 0.01; -3.13 vs. -1.36 and -0.35 ± 0.76%, respectively). The subspecies did not vary (P < 0.05) for blood constituent responses or shrink in Exp. 3. Animal responses were not evident 24 h after treatments in each experiment. In summary, transport caused stress, but Brahman steers were not more sensitive than Herefords. Hereford steers were susceptible to greater transport BW shrink than Brahman under the summer conditions.

Duration of Flumioxazin-Based Weed Control in Container-Grown Nursery Crops

Flumioxazin is used in nursery production and landscape maintenance industries. In these situations, weed control provided by flumioxazin often lasts longer than that reported in soil. Our objective was to quantify flumioxazin longevity under conditions found in nursery production. Pots were filled with 6 : 1 (v/v) pine bark : sand mixture. This nonsoil media is typical of what is used for nursery crop production. Pots were treated with flumioxazin at either 0.28 or 0.42 kg ai ha−1, and subsequently sown with either hairy bittercress (two winter experiments) or spotted spurge (two summer experiments) at weekly intervals. Weed seed germination, emergence, and seedling establishment in the treated pots was compared with nontreated control and used as a proxy for herbicide activity. Flumioxazin provided approximately 7 wk of complete (100%) hairy bittercress control regardless of rate. However, a rate effect was evident in only one of the two experiments conducted with hairy bittercress. In both experiments with hairy bittercress, marginal and highly variable activity was still evident at 18 wk after treatment. Flumioxazin at 0.28 and 0.42 kg ha−1provided 2- and 4-wk complete spotted spurge control, respectively. No spotted spurge control was evident after about 8 wk. Subjecting this less-variable data to nonlinear regression revealed that the time required for 50% reduction in flumioxazin activity was approximately 5.5 and 6.6 wk for the two rates, respectively. A column leaching study revealed that flumioxazin activity remained localized near the surface (0 to 4 cm). Therefore the dissipation observed was likely the result of in situ degradation and not displacement. The high organic matter content of the nonsoil media contributes to the observed persistence of flumioxazin activity.

Assessing the micro-phytoplankton response to nitrate in Comau Fjord (42°S) in Patagonia (Chile), using a microcosms approach

Anthropogenic (aquaculture) changes in environment nutrient concentrations may affect phytoplankton (biomass and taxa composition) in marine coastal waters off the Chilean Patagonia. The effects of adding nitrate (NO₃(-)) to natural phytoplankton assemblages were evaluated considering biomass, cell abundance, and taxonomic composition. Microcosm experiments were performed in the spring, summer, and winter in the Comau Fjord located in Subantarctic Patagonia. At the end of the experiments, NO₃(-) decreased rapidly and was undetectable in treatments, indicating a strong NO₃(-) deficiency associated with an exponential increase in Chl-a concentrations, particulate organic nitrogen, and carbon in these treatments. Moreover, given the depleted nitrate concentrations of the spring and summer experiments, the micro-phytoplankton taxa structure shifted from mixed diatom and dinoflagellate assemblages (Ceratium spp., Dinophysis spp., Coscinodiscus sp., Rhizosolenia pungens) to assemblages dominated by blooms of the classic chain-forming diatoms found in temperate and cold waters such as Chaetoceros spp., Skeletonema spp., and Thalassiosira spp. Thus, nitrogen sources (i.e., nitrate, ammonia) may influence phytoplankton abundance and biomass accumulation dynamics in the northern section of Patagonia. It also emphasizes the importance of diatom taxa in regards to the short-term response of phytoplankton to changing environmental nutrient conditions due to natural (decreasing freshwater stream flow) and anthropogenic (aquaculture) events. This situation may be one of the future scenarios in the Patagonian fjords, thus stressing the needs for active environmental monitoring and impact assessment.

Particle size distribution of nitrated and oxygenated polycyclic aromatic hydrocarbons (NPAHs and OPAHs) on traffic and suburban sites of a European megacity: Paris (France)

Abstract. The size distribution of particulate nitrated and oxygenated polycyclic aromatic hydrocarbons (NPAHs and OPAHs) was determined during two field campaigns at a traffic site in summer 2010 and at a suburban site during the MEGAPOLI (Megacities: Emissions, urban, regional and Global Atmospheric POLlution and climate effects, and Integrated tools for assessment and mitigation) experiment in summer 2009. Both, OPAHs and NPAHs were strongly associated (&gt;85%) to fine particles (Dp&lt; 2.5 μm) increasing the interest of their study on a sanitary point of view. Results showed really different NPAH and OPAH particle size distributions between both sites. At traffic site, clearly bimodal (notably for NPAHs) particle size distributions (Dp = 0.14 and 1.4 μm) were observed, while the particle size distributions were more scattered at the suburban site, especially for OPAHs. Bimodal particle size distribution observed at traffic site for the NPAH could be assigned to the vehicle emissions and the particle resuspension. Broadest distribution observed at the suburban site could be attributed to the mass transfer of compounds by volatilization/sorption processes during the transport of particles in the atmosphere. Results also showed that the combination of the study of particle size distributions applied to marker compounds (primary: 1-nitropyrene; secondary: 2-nitrofluoranthene) and to NPAH or OPAH chemical profiles bring some indications on their primary and/or secondary origin. Indeed, 1,4-anthraquinone seemed only primary emitted by vehicles while 7-nitrobenz[a]anthracene, benz[a]antracen7,12-dione and benzo[b]fluorenone seemed secondarily formed in the atmosphere.