Summer Experiment Research Articles

Nucleation in the Karlsruhe plume during the COPS/TRACKS‐Lagrange experiment

AbstractA plume of ultrafine particles was observed downwind of the Karlsruhe city and industrial area during the COPS/TRACKS Lagrangian airborne experiment in summer 2007. These ultrafine particles were identified as nucleation‐generated aerosols from emissions of a coal‐fired power plant and an adjacent refinery, the two main emitters of sulphur dioxide in the area. Modelling the production and growth of aerosols with the COSMO‐ART model required, in agreement with the known emission sources, a strong elevated source of sulphur dioxide to explain the temporal evolution of the particle plume. The power plant at Karlsruhe Rheinhafen emits from a 233 m high chimney. The ultrafine particles produced from these fossil‐fuel‐related sources were the dominant fraction of all ultrafine particles in the rural area of the Kraichgau downwind of Karlsruhe, exceeding all other anthropogenic sources and are suspected of being the major contribution to the number of cloud condensation nuclei (CCN) on a regional scale. Compared to previous investigations on the sulphur chemistry in power‐plant plumes, emissions from this power plant, which is equipped with modern stack‐gas cleaning technology, had a higher yield of nucleation‐mode aerosols as CCN precursors per emitted sulphur dioxide mass. Copyright © 2011 Royal Meteorological Society

Acetate Availability and its Influence on Sustainable Bioremediation of Uranium-Contaminated Groundwater

Field biostimulation experiments at the U.S. Department of Energy's Integrated Field Research Challenge (IFRC) site in Rifle, Colorado, have demonstrated that uranium concentrations in groundwater can be decreased to levels below the U.S. Environmental Protection Agency's (EPA) drinking water standard (0.126 μM). During successive summer experiments – referred to as “Winchester” (2007) and “Big Rusty” (2008) - acetate was added to the aquifer to stimulate the activity of indigenous dissimilatory metal-reducing bacteria capable of reductively immobilizing uranium. The two experiments differed in the length of injection (31 vs. 110 days), the maximum concentration of acetate (5 vs. 30 mM), and the extent to which iron reduction (“Winchester”) or sulfate reduction (“Big Rusty”) was the predominant metabolic process. In both cases, rapid removal of U(VI) from groundwater occurred at calcium concentrations (6 mM) and carbonate alkalinities (8 meq/L) where Ca-UO2-CO3 ternary complexes constitute >90% of uranyl species in groundwater. Complete consumption of acetate and increased alkalinity (>30 meq/L) accompanying the onset of sulfate reduction corresponded to temporary increases in U(VI); however, by increasing acetate concentrations in excess of available sulfate (10 mM), low U(VI) concentrations (0.1–0.05 μM) were achieved for extended periods of time (>140 days). Uniform delivery of acetate during “Big Rusty” was impeded due to decreases in injection well permeability, likely resulting from biomass accumulation and carbonate and sulfide mineral precipitation. Such decreases were not observed during the short-duration “Winchester” experiment. Terminal restriction fragment length polymorphism (TRFLP) analysis of 16S rRNA genes demonstrated that Geobacter sp. and Geobacter-like strains dominated the groundwater community profile during iron reduction, with 13C stable isotope probing (SIP) results confirming these strains were actively utilizing acetate to replicate their genome during the period of optimal U(VI) removal. Gene transcript levels during “Big Rusty” were quantified for Geobacter-specific citrate synthase (gltA), with ongoing transcription during sulfate reduction indicating that members of the Geobacteraceae were still active and likely contributing to U(VI) removal. The persistence of reducible Fe(III) in sediments recovered from an area of prolonged (110-day) sulfate reduction is consistent with this conclusion. These results indicate that acetate availability and its ability to sustain the activity of iron- and uranyl-respiring Geobacter strains during sulfate reduction exerts a primary control on optimized U(VI) removal from groundwater at the Rifle IFRC site over extended time scales (>50 days).

How representative were the meteorological conditions during the COPS field experiment in summer 2007?

This study investigates the meteorological conditions in Europe during summer 2007 (June-August) and their representativity compared to climatology, based upon (re-)analysis data from the European Centre for Medium-range Weather Forecasts (ECMWF) for the years 1979-2007. Several parameters have been analyzed locally in the region of the Convective and Orographic Precipitation Study (COPS), e.g., low-tropospheric temperature and humidity and thermodynamic stability, and on the continental scale, e.g., frequency of surface lows and upper-level stratospheric cut-offs, Eady growth rate, and air mass pathways. It has been quantified whether the statistical distributions of these parameters during summer 2007 differ from climatology. It is shown that cyclones were extraordinarily frequent during summer 2007 over the British Isles. At upper levels, they typically went along with quasi-stationary stratospheric cut-offs that supported the transport of relatively cool air masses from the North Atlantic to France and warm air masses from the Mediterranean into Eastern Europe. In the lowest troposphere, the COPS area, situated in between these anomalous airflows, experienced fairly normal temperatures and enhanced humidity values compared to climatology. As a consequence, thermodynamic indices indicate slightly increased potential instability. Consistent with this feature-based analysis, trajectory calculations indicate reduced large-scale advection from Scandinavia and the western North Atlantic, and increased transport from southern France and northern Spain in 2007 compared to the previous almost 30 years. Although warm and humid conditions dominated during the Intense Observation Periods (IOPs) of COPS, the variability of ambient meteorological parameters during IOPs was large. This should be taken into account when interpreting the results from a particular IOP and considering their representativity in a climatological context. It is suggested that a similar approach could also be fruitful for other field experiments and for a feature-based characterization of climatologically extreme seasons like, e.g., the European heat summer 2003.

The effect of reflective coatings on building surface temperatures, indoor environment and energy consumption—An experimental study

This paper presents an experimental study on the impact of reflective coatings on indoor environment and building energy consumption. Three types of coatings were applied on identical buildings and their performance was compared with three sets of experiments in both summer and winter. The first experiment considers the impact of coatings on exterior and interior surface temperatures, indoor air temperatures, globe temperature, thermal stratification and mean radiant temperatures for non-conditioned buildings (free-floating case); the second one focused on the impact of coatings on reduction of electricity consumption in conditioned spaces; in the third experiment, the impact of different envelope material properties equipped with different coatings was investigated. The results showed that, depending on location, season and orientation, exterior and interior surface temperatures can be reduced by up to 20 °C and 4.7 °C respectively using different coatings. The maximum reduction in globe temperature and mean radiant temperature was 2.3 °C and 3.7 °C in that order. For the conditioned case, the annual reduction in electricity consumption for electricity reached 116 kWh. Nevertheless, the penalty in increased heating demand can result in a negative all-year effect in Shanghai, which is characterized by hot summers and cold winters.

Growth and mortality of juvenile white shrimp Litopenaeus setiferus in a marsh pond

Despite the widely held view that certain estuarine habitats are more valuable as nurseries because they provide enhanced growth and reduced mortality, there remain few estimates of growth and mortality rates in support of this paradigm. We conducted field caging experiments and collected weekly nekton samples in shallow open-water habitat in a marsh pond during summer and fall 2007 in Galveston Bay, Texas, USA, to estimate growth and morality rates of juvenile white shrimp Litopenaeus setiferus. Growth rates (mean ± 1 SE) were lower during the summer experiment (0.77 ± 0.05 mm d–1) than the fall (0.91 ± 0.04 mm d–1), and high summer water temperatures may have inhibited shrimp growth. Cohort analysis to derive mortality estimates from 15 weekly sampling trips failed due to extended periods of continuous recruitment, the lack of clearly identifiable cohorts, and high temporal variability in abundance estimates. Catch-curve analysis provided estimates of mean daily instantaneous mortality (Z) during the sampling period of 0.181 for post-larvae and early juveniles 28 mm. The mortality estimates must be interpreted with caution due to potential problems meeting the assumptions of catch-curve analysis. Despite the challenges, comparisons of vital rates among habitats are required to validate long-held paradigms on the functioning of estuarine nurseries and the importance of various coastal habitats in the support of fishery species.

Iron nutritional status of the phytoplankton assemblage in the Okhotsk Sea during summer

To clarify the iron (Fe) nutritional status of the phytoplankton assemblage in the Okhotsk Sea, we conducted incubation experiments in summer 2006. Replicate surface seawater samples with the natural plankton community were incubated with three treatments: Fe enrichment; addition of the strong Fe chelator siderophore desferriferrioxime B (DFB) which strips Fe from the biologically accessible pool; and as a control, no addition. To prevent macronutrient limitation, we added surplus nutrients to all treatments. At all 4 stations in Sakhalin Bay near the mouth of the Amur River and around the east of Sakhalin Island, net specific growth rate showed no significant difference between the control and +Fe treatment, and was repressed in +DFB treatment both in large- and small-sized phytoplankton. These findings indicate that these waters contain sufficient bioavailable Fe and that the Amur River plume which is transported by the east Sakhalin current is a major source of the Fe. In the Bussol’ Strait, net specific growth rate in the control was significantly higher than +DFB treatment, suggesting a supply of bioavailable Fe through intense vertical mixing at this site. Iron enrichment treatment stimulated the net specific growth rate of large-sized phytoplankton, indicating that Fe still limits the growth for the large-sized phytoplankton assemblage, but not for small-sized phytoplankton, in this area. An index of Fe availability was defined to quantify the degree of ambient Fe availability in each station, and it revealed the spatial variability of ambient Fe availabilities among the sites.

Impacts of transported background ozone on California air quality during the ARCTAS-CARB period – a multi-scale modeling study

Abstract. Multi-scale tracer and full-chemistry simulations with the STEM atmospheric chemistry model are used to analyze the effects of transported background ozone (O3) from the eastern Pacific on California air quality during the ARCTAS-CARB experiment conducted in June, 2008. Previous work has focused on the importance of long-range transport of O3 to North America air quality in springtime. However during this summer experiment the long-range transport of O3 is also shown to be important. Simulated and observed O3 transport patterns from the coast to inland northern California are shown to vary based on meteorological conditions and the O3 profiles over the oceans, which are strongly episodically affected by Asian inflows. Analysis of the correlations of O3 at various altitudes above the coastal site at Trinidad Head and at a downwind surface site in northern California, show that under long-range transport events, high O3 air-masses (O3>60 ppb) at altitudes between about 2 and 4 km can be transported inland and can significantly influence surface O3 20–30 h later. These results show the importance of characterizing the vertical structure of the lateral boundary conditions (LBC) needed in air quality simulations. The importance of the LBC on O3 prediction during this period is further studied through a series of sensitivity studies using different forms of LBC. It is shown that the use of the LBC downscaled from RAQMS global model that assimilated MLS and OMI data improves the model performance. We also show that the predictions can be further improved through the use of LBC based on NASA DC-8 airborne observations during the ARCTAS-CARB experiment. These results indicate the need to develop observational strategies to provide information on the three-dimensional nature of pollutant distributions, in order to improve our capability to predict pollution levels and to better quantify the influence of these Asian inflows on the US west coast air quality.

Detector performance of the ALICE silicon pixel detector

The ALICE Silicon Pixel Detector (SPD) forms the two innermost layers of the ALICE Inner Tracking System (ITS). It consists of two barrel layers of hybrid silicon pixel detectors at radii of 39 and 76 mm. The physics targets of the ALICE experiment require that the material budget of the SPD is kept within ≈ 1 % X 0 per layer. This has set some stringent constraints on the design and construction of the SPD. A unique feature of the ALICE SPD is that it is capable of providing a prompt trigger signal, called Fast-OR, which contributes to the L0 trigger decision. The pixel trigger system allows to apply a set of algorithms for the trigger selection, and its output is sent to the Central Trigger Processor (CTP). The detector has been installed in the experiment in summer 2007. During the first injection tests in June 2008 the SPD was able to record the very first sign of life of the LHC by registering secondary particles from the beam dumped upstream the ALICE experiment. In the following months the SPD has participated in the ALICE cosmic campaign to test the integration with all experimental sub-systems and to acquire data for alignment. Since the LHC start-up in November 2009, the SPD has been recording the LHC activities and in particular the first proton–proton collisions in ALICE.

Posições das mudas de alface nas bandejas de poliestireno e efeitos na normalidade e homogeneidade dos erros na produção de plantas

A qualidade de um experimento pode ser descrita por intermédio de estatísticas, sendo o erro experimental um dos parâmetros de avaliação dessa qualidade. O objetivo do trabalho foi verificar a interferência de diferentes posições de mudas de alface em bandeja de poliestireno sobre a normalidade e homogeneidade dos erros em experimentos realizados em estufa plástica e em campo. Foram conduzidos seis experimentos no Departamento de Fitotecnia da Universidade Federal de Santa Maria, sendo três no verão (2006-2007) e três no outono-inverno (2007) com a cultura da alface, cultivar Vera. Os tratamentos foram 12 diferentes posições das mudas na bandeja de produção. As variáveis analisadas na produção de mudas e após o transplante aos ambientes foram a fitomassa fresca e seca da parte aérea e raiz e fitomassa fresca e seca da parte aérea, respectivamente. Foram testadas as normalidade e homogeneidade dos erros sendo comparadas às médias de cada tratamento. Há atendimento da homogeneidade e normalidade dos erros para as fitomassas fresca da parte aérea e de raiz de alface nos experimentos com diferentes posições de mudas na bandeja de produção, nos diferentes ambientes e estações sazonais de cultivo. Para a fitomassa seca da parte aérea não há atendimento da homogeneidade e/ou normalidade dos erros nos experimentos no verão, com produção de mudas e de plantas na estufa plástica. Para a fitomassa seca de raiz não há atendimento da normalidade dos erros no experimento no outono-inverno com produção de mudas.

Population Density and Growth of the Freshwater Mussel Anodonta californiensis in a Flow-Fragmented Stream

ABSTRACT I studied the endemic California floater (Anodonta californiensis) density and growth in pools of a flow-fragmented stream that differed in amount of surface water inflow. Mussel densities, estimated using mark-and-recapture, were lowest in pools having intermittent summer inflows, and in one of those pools a length-frequency histogram of mussel shell lengths was truncated compared to measurements from pools with perennial inflows. In a summer experiment to measure monthly responsiveness of mussel growth to the range of temperature, dissolved oxygen, and pH conditions present in three pools with differing inflows, mean monthly instantaneous growth of caged mussels, based on whole body weight, ranged from 0.22%/day to 0.99% day and was significantly higher in a pool with intermittent inflows than in those with perennial inflows. Mussel shell growth and percentage of dry tissue weight, an indicator of energy stores in mussels, were also highest in the pool with intermittent inflows. Caged mussel growth was compared to un-caged counterparts. Caging did not have a detrimental effect on growth; growth of caged mussels in one pool exceeded by 20% that of un-caged mussels, while growth was nearly identical in another pool. Mussel growth was strongly correlated with water temperature (R2 = 0.67) but was only weakly and non-significantly correlated with other habitat variables. My results suggest that flow-fragmentation is responsible for reduced California floater densities in pools with intermittent inflows in Wenas Creek. However, mussel growth and condition was also highest in a pool with intermittent inflows, suggesting that monitoring growth and condition alone may not sufficiently indicate population responses to habitat change.

Changes in bacterial activity and community composition caused by exposure to a simulated oil spill in microcosm and mesocosm experiments

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 59:169-183 (2010) - DOI: https://doi.org/10.3354/ame01380 Changes in bacterial activity and community composition caused by exposure to a simulated oil spill in microcosm and mesocosm experiments Itziar Lekunberri1,*, Alejandra Calvo-Díaz2, Eva Teira3, Xosé Anxelu G. Morán2, Francesc Peters1, Mar Nieto-Cid4,5, Oscar Espinoza-González4, Isabel G. Teixeira4, Josep M. Gasol1,** 1Departament de Biologia Marina i Oceanografia, Institut de Ciències del Mar-CSIC, 08003 Barcelona, Catalunya, Spain 2Instituto Español de Oceanografía-Xixón, 33212 Xixón, Spain 3Departamento de Ecoloxía e Bioloxía Animal, Universidade de Vigo, 36310 Vigo, Spain 4Instituto de Investigaciones Marinas-CSIC, Eduardo Cabello s/n, 36208 Vigo, Spain 5Present address: Woods Hole Oceanographic Institution, Watson Building 115, Woods Hole, Massachusetts 02543, USA Corresponding authors. *Email: itzileku@hotmail.com;**Email: pepgasol@icm.csic.es ABSTRACT: We studied the effects of the Prestige oil spill on Ría de Vigo bacterial abundance, production and community structure by using mesocosms (ca. 3500 l) filled with water from the center of the Ría, to which we added a realistic concentration of polycyclic aromatic hydrocarbons (PAHs; initial concentrations of approximately 20 to 30 µg l–1 chrysene equivalents) at each of the 4 periods of the seasonal cycle: spring bloom, summer stratification, autumn upwelling and winter. We followed the changes in bacterial activity by leucine and thymidine incorporation, and the changes in bacterial assemblage structure by 16S rDNA DGGE. In addition, simultaneously with the winter mesocosm experiment, we ran microcosms with fuel additions equivalent to 0.5, 1, 2 and 4× the treatment imposed on the mesocosms in the seasonal experiments. Bacterial community structure was also analyzed by CARD-FISH. We detected significant effects of the PAHs on bacterial community structure (increased number of bands) and production only in the summer experiment. In the microcosm experiments, we found similar effects to those in the mesocosms at PAH concentrations of ca. 20 to 40 µg l–1, and clear detrimental effects on phytoplankton at concentrations of ca. 80 µg l–1, with large development of Gammaproteobacteria. Our results indicate that an oil spill of the Prestige’s magnitude will have effects on the microbial resident community only at certain times of the year, while at higher PAH concentrations the effects might be more evident. For most of the year, the resident Ría de Vigo microbial communities appear to be accustomed to PAH concentrations such as those used in these experiments. KEY WORDS: PAHs · Bacterioplankton · Production · Bacterial community structure · Mesocosms · Prestige oil Full text in pdf format PreviousNextCite this article as: Lekunberri I, Calvo-Díaz A, Teira E, Morán XAG and others (2010) Changes in bacterial activity and community composition caused by exposure to a simulated oil spill in microcosm and mesocosm experiments. Aquat Microb Ecol 59:169-183. https://doi.org/10.3354/ame01380 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 59, No. 2. Online publication date: April 08, 2010 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2010 Inter-Research.

Removal of humic substances using solar irradiation followed by granular activated carbon adsorption

This study proposed a new method using freely available sunlight and granular activated carbon (GAC) adsorption for enhanced removal of humic substances (HS). Experiments were carried out under natural sunlight conditions in winter and summer. A parabolic solar collector (PC) was applied to concentrate solar energy. HS were characterized by UV254 absorbance, dissolved organic carbon (DOC) concentration and molecular weight (MW). As a result of solar irradiation, decreases of DOC up to 14% in winter and 58% in summer were observed. A comparison of adsorption isotherms and chromatograms of the irradiated and non-irradiated HS confirmed that smaller molecules formed during solar irradiation were preferentially adsorbed by GAC. A dramatic MW change upon solar irradiation was observed in HS irradiation in PC in summer experiment and almost no UV254 detected components were remaining in solution after adsorption (GAC dose 400 mg/L), as measured with high performance size exclusion chromatography (HPSEC). The combined solar irradiation-GAC adsorption method proved to be effective in enhancing HS removal by GAC with no additional energy and chemicals consumption.

Role of macrofauna functional traits and density in biogeochemical fluxes and bioturbation

The importance of different functional traits of macrobenthos in benthic processes of the Southern Bight of the North Sea was investigated to estimate the effects of density declines and species loss on benthic ecosystem functioning. Two laboratory experiments were performed: before (winter, temperature = 10°C) and after (summer, temperature = 18°C) sedimentation of the spring phytoplankton bloom. Single species treatments of key species (Abra alba, Lanice conchilega and Nephtys sp.) with different functional traits were added to microcosms at 3 density levels (natural, lower, lowest) to account for possible density declines. Sediment-water exchanges of oxygen and nutrients, denitrification and bioturbation were measured. In absence of fauna, benthic minerali- sation in the summer experiment was 2.0 times higher than in winter. Fauna stimulated microbial respiration more in summer (up to 100% in L. conchilega treatments) than in winter (negligible fauna effect). As chlorophyll a concentrations were similar in both seasons, the stronger fluxes in summer must be explained by a higher macrobenthic activity owing to the elevated temperature and better condition of the animals. Stimulation of mineralisation by the 3 species in the microcosms was different, and behaviour-related. Owing to its irrigation activity, the tube dweller L. conchilega had more pronounced influences on benthic respiration, nutrient release and denitrification than did the biodiffusers, A. alba and Nephtys sp. A. alba appeared to be a more effective bioturbator than Nephtys sp. Processes such as benthic respiration, nutrient fluxes, denitrification and bioturbation seem to be related to animal densities and therefore decreases in densities can possibly have impli- cations for ecosystem functioning.

Nutritional and management methods to decrease nitrogen losses from beef feedlots1

Nitrogen losses from open beef feedlots are a concern. Methods that decrease volatilization losses will lead to greater manure N, which is likely to be beneficial in open lot beef operations. Twelve or more pens were dedicated to N research whereby N intake, retention, and excretion were quantified and a mass balance conducted using manure, runoff, soil balance, and loss quantities. The objective was to decrease N volatilization losses or increase manure N or both. Dietary CP affects N excretion and N volatilization losses. Four experiments across 2 yr compared industry average CP (13%) to diets that were phase-fed to not exceed protein requirements (12.1 to 10.9%). Phase-fed cattle excreted 12 to 21% less N (P < 0.01), and N volatilization losses were reduced 15 to 33% (P < 0.01). In 2 other experiments, phase-fed diets were formulated to recycle undegradable intake protein. Steer G:F was similar (P = 0.18) or improved (P = 0.09), whereas N excretion and N volatilization losses tended to be reduced (P < 0.11) and N in manure was not affected (P > 0.35) compared with cattle fed 13% CP. Feeding less protein did not affect manure N, indicating manure N from open lots is related to other factors. A series of experiments evaluated increasing OM on the pen surface to increase N in manure. Feeding less digestible diets using fiber increased manure N (P < 0.01) and decreased (P < 0.10) N volatilization losses in 2 experiments conducted from November to May, but did not affect (P > 0.30) manure N or volatilization losses during 2 summer experiments. Adding bedding (i.e., OM) increased manure N in the winter as well. Another method evaluated was increasing pen cleaning frequency, which decreased N volatilization losses by 19 to 44% and increased manure N by 26 to 41% across 3 experiments. Other methods, such as acidifying manure by manipulating dietary cation anion difference, clinoptilite zeolite clay addition, and feeding different amounts of by-products had variable impacts on N volatilization losses. No treatments markedly affected runoff N, which is <5% of excreted N. Dietary protein affects N volatilization losses but not manure N. Other factors, such as OM on the pen surface, affect manure N. Cleaning manure frequently, which decreases exposure of manure N to air, decreases volatilization losses. Treatments should be evaluated across seasons due to seasonal effects.

Effects of temperature, season and locality on wasting disease in the keystone predatory sea star Pisaster ochraceus

This study investigates wasting disease in the northeast Pacific keystone predatory sea star Pisaster ochraceus on the outer west coast of Vancouver Island (British Columbia, Canada). To quantify the effects of temperature, season and locality on the vulnerability of P. ochraceus to wasting disease, we conducted surveys and experiments in early and late summer. To test the prediction that a small increase in temperature would result in heightened infection intensities, we housed sea stars at different temperatures in the laboratory and caged sea stars subtidally at 2 depths. Prevalence and infection intensity were always higher in warm temperature treatments and did not differ between the sexes or with increasing size. Disease effects also varied with season and locality. Specimens held in aquaria displayed significantly higher disease prevalence and infection intensity in June versus August. Furthermore, sea stars from a sheltered inlet showed markedly higher prevalence of the disease in late summer, while wave-exposed sites had consistently low disease prevalence. Seasonal changes in reproductive potential, host condition and/or physiological acclimation, as well as differences in environmental regime among localities, may impact the dynamics of wasting disease. These results demonstrate that small increases in temperature could drive mass mortalities of Pisaster due to wasting disease, with vulnerability possibly reaching a peak in spring and in populations from sheltered localities. This is the most northern report of wasting disease in the class Asteroidea on the west coast of North America.

Longitudinal assessment of the effect of concentration on stream N uptake rates in an urbanizing watershed

We examined the effect of concentration on nitrogen uptake patterns for a suburban stream in Maryland and addressed the question: How does NO3 − uptake change as a function of concentration and how do uptake patterns compare with those found for NH4 +? We applied a longitudinal (stream channel corridor) approach in a forested stream section and conducted short-term nutrient addition experiments in late summer 2004. In the downstream direction, NO3 − concentrations decreased because of residential development in headwaters and downstream dilution; NH4 + concentrations slightly increased. The uptake patterns for NO3 − were very different from NH4 +. While NH4 + had a typical negative relationship between first-order uptake rate constant (K c ) and stream size, NO3 − had a reverse pattern. We found differences for other metrics, including uptake velocity (V f ) and areal uptake rate (U). We attributed these differences to a stream size effect, a concentration effect and a biological uptake capacity effect. For NO3 − these combined effects produced a downstream increase in K c , V f and U; for NH4 + they produced a downstream decrease in K c and V f , and a not well defined pattern for U. We attributed a downstream increase in NO3 − uptake capacity to an increase in hyporheic exchange and a likely increase in carbon availability. We also found that K c and V f were indirectly related with concentration. Similar evidence of ‘nutrient saturation’ has been reported in other recent studies. Our results suggest that higher-order uptake models might be warranted when scaling NO3 − uptake across watersheds that are subject to increased nitrogen loading.

Use of acoustic frequency shifts for monitoring oceanographic processes in shallow water.

Waveguide invariant theory is used to calculate the frequency shifts of the acoustic intensity spectral levels caused by environmental variability in shallow water. In winter conditions, long-term acoustic monitoring of tide and slope water intrusions has been demonstrated using measured frequency shifts of the acoustic intensity spectral levels [Turgut et al., J. Acoust. Soc. Am. 121, 2534–2541 (2007)]. Acoustic frequency shifts caused by other oceanographic processes such as background internal waves and solitary internal waves are also investigated. Additional broadband acoustic data from several summer experiments indicate the feasibility of extracting background internal wave parameters as well as internal solitary wave parameters when they propagate almost perpendicular to the acoustic propagation path. [This work was supported by the ONR.]

Diazinon reduction and partitioning between water, sediment and vegetation in stormwater runoff mitigation through rice fields

Contamination of surface waters by pesticides is a concern in the United States and around the world. Innovative mitigation strategies are needed to remediate this potential environmental contaminant. One potential solution is to divert pesticide-laden drainage or surface water through agricultural rice fields. With a hydroperiod, hydrosoil and hydrophyte (rice), these systems serve essentially as a type of constructed wetland. In both summer and fall experiments, diazinon-amended water was diverted through two rice ponds at the University of Mississippi Field Station. Likewise, a non-vegetated control pond was amended with diazinon-laden water. Water, sediment and plant samples were taken spatially and temporally to determine the distribution of diazinon within systems. Outflow diazinon concentrations decreased significantly (P < 0.05) from inflow in both vegetated ponds for both preharvest and post-harvest experiments. Although sorption to rice plants was minimal in the overall mass distribution of diazinon (1-3%), temporal data indicated that diazinon concentrations reached the outflow sediment of the non-vegetated control twice as fast as in either vegetated (rice) system. In both vegetated systems, sediment diazinon concentrations decreased (77 and 100%) from inflow to outflow, while a decrease of <2% was noted in the non-vegetated control. Diversion of pesticide-contaminated water through rice fields demonstrated potential as a low-cost, environmentally efficient mitigation practice. Studies on these systems are continuing to evaluate the optimal chemical retention time for rice field mitigation, as well as diazinon transfer to rice grain seeds that may be used as a food source.

A system-dynamic model on the competitive growth between Potamogeton malaianus Miq. and Spirogyra sp.

A system-dynamic model has been built to evaluate the competition between submerged macrophytes Potamogeton malaianus Miq. (PM) and filamentous green algae Spirogyra sp. (SP). The data background is based on a spring–summer and an autumn–winter experiment carried out in artificial field ponds. The experiments had the aim to acquire a knowledge base necessary to a successful restoration of submerged macrophyte vegetation in Lake Taihu, China by use of P. malaianus Miq. The model mainly focuses on variations in water volume; biomass dynamics of P. malaianus Miq., Spirogyra sp. and zoobenthos; nutrients cycling between water column, P. malaianus Miq., Spirogyra sp., zoobenthos, detritus and sediment. Sixteen state variables are included in the model: biomass of P. malaianus Miq., Spirogyra sp. and zoobenthos; nitrogen in sediments, detritus, in P. malaianus Miq., in Spirogyra sp. and zoobenthos; total dissolved nitrogen; phosphorus in sediments, detritus, in P. malaianus Miq., in Spirogyra sp. and in zoobenthos; total dissolved phosphorus, and water volume of the experiment pond. The calibration and validation of the model show a good accordance with the results of the spring–summer experiment and the autumn–winter experiment. Model outputs show that higher temperature, shading effect and improper nutrients would result in a decrease in biomass of P. malaianus Miq. The most crucial factor having a negative effect on the growth of P. malaianus Miq. is Spirogyra sp., which entangles the stems and leaves of P. malaianus Miq. In order to successfully restore the vegetation of P. malaianus Miq., Spirogyra sp. should be suppressed in the early phase.

Impacts of aerosol chemical composition on microphysics and precipitation in deep convection

Aerosols affect precipitation by modifying cloud properties such as cloud droplet number concentration (CDNC). Aerosol effects on CDNC depend on aerosol properties such as number concentration, size spectrum, and chemical composition. This study focuses on the effects of aerosol chemical composition on CDNC and, thereby, precipitation in a mesoscale cloud ensemble (MCE) driven by deep convective clouds. The MCE was observed during the 1997 department of energy's Atmospheric Radiation Measurement (ARM) summer experiment. Double-moment microphysics with explicit nucleation parameterization, able to take into account those three properties of aerosols, is used to investigate the effects of aerosol chemical composition on CDNC and precipitation. The effects of aerosol chemical compositions are investigated for both soluble and insoluble substances in aerosol particles. The effects of soluble substances are examined by varying mass fractions of two representative soluble components of aerosols in the continental air mass: sulfate and organics. The increase in organics with decreasing sulfate lowers critical supersaturation ( S c) and leads to higher CDNC. Higher CDNC results in smaller autoconversion of cloud liquid to rain. This provides more abundant cloud liquid as a source of evaporative cooling, leading to more intense downdrafts, low-level convergence, and updrafts. The resultant stronger updrafts produce more condensation and thus precipitation, as compared to the case of 100% sulfate aerosols. The conventional assumption of sulfate aerosol as a surrogate for the whole aerosol mass can be inapplicable for the case with the strong sources of organics. The less precipitation is simulated when an insoluble substance replaces organics as compared to when it replaces sulfate. When the effects of organics on the surface tension of droplet and solution term in the Köhler curve are deactivated by the insoluble substance, S c is raised more than when the effects of sulfate on the solution term are deactivated by the insoluble substance. This leads to lower CDNC and, thus, larger autoconversion of cloud liquid to rain, providing less abundant cloud liquid as a source of evaporative cooling. The resultant less evaporative cooling produces less intense downdrafts, weaker low-level convergence, updrafts, condensation and, thereby, less precipitation in the case where organics is replaced by the insoluble substance than in the case where sulfate is replaced by the insoluble substance. The variation of precipitation caused by the change in the mass fraction between the soluble and insoluble substances is larger than that caused by the change in the mass fraction between the soluble substances.