bluuebunny/crossref_metadata_2025 huggingface dataset:
"Click, You're It!"
Authors: Kellison Karen , Font George
Published: May 2010

Video games are serious work for today’s students. 93% of the K-12 population plays video games on a regular basis. Educators are now pressed to determine the appropriate integration of this technology into the pedagogy of K-12 classrooms. Research indicates that there are positive effects from playing serious video games, those that aim to teach something. Students are motivated and engaged during such game play. Some speculate that players are using and developing cognitive brain capabilities that have been dormant. The question is whether or not these games, if adequately designed, will teach more than just the skill of playing the game. This chapter takes a look at the evolution of play and games in K-12 education and then seeks to define serious computer games in terms of positive design elements and integration techniques for K-12 classrooms. In conclusion, a research agenda that moves educational gaming forward is explored.
Collaborative Online Roleplay for Adult Learners.
Authors: Pivec Paul , Pivec Maja
Published: May 2010

Game-based learning has gained popularity in schools and has been proposed for adult education, both at Universities and in the corporate training sector. Games are becoming a new form of interactive content and game playing provides an interactive and collaborative platform for learning purposes. Collaborative learning allows participants to produce new ideas as well as to exchange information, simplify problems, and resolve the tasks. Context based collaborative learning method is based on constructivist learning theory and guides the design of the effective learning environments. In this environment the teacher or trainer becomes the active partner, moderator and advisor of the educational process, not just a repository of the information importing his or her own knowledge to a passive learner as in traditional education. Learners bring their prior skills and knowledge to the classroom community. The trainer structures learning situations in which each learner can interact with other learners to develop new knowledge and fashion their own needs and capacities. Knowledge is generated from experience with complex tasks rather than from isolated activities like learning and practicing separately. Skills and knowledge are best acquired within the context. This helps the learners easily to transfer learning from classroom to “real life” and back, or information from one subject to another. Therefore this method requires that the trainer and learners play nontraditional roles such as interaction and collaboration with each other within the educational process. The classroom drops the physical boundaries and becomes a goal-oriented platform dedicated to learning. Online role-play scenario platforms offers an environment where trainers can define their own role-playing scenarios and provide the opportunity for learners to apply factual knowledge and to gain experience through the digital world. Trainers can define new games or adopt and modify sample games without any programming skills. Some platforms provide a variety of communication means within the scenarios; players can communicate with the use of multimedia discussion forums, text and voice chat modules, as well as through multi-user video conferencing. These platforms foster participation in problem-solving, effective communication, teamwork, project management, as well as other soft skills such as responsibility, creativity, micro-entrepreneurship, corporate culture, and cultural awareness. They are designed for use as a supplement to normal in-class teaching and corporate training, but it is also possible to be used independently from a class course. The constructivist design required for successful Game-Based Learning will be discussed and a model is provided to display how Game-Based Learning occurs in a collaborative online environment. This chapter will present example scenarios and highlight resources available to interested teachers and trainers.
"For me it doesn't matter where I put my information"
Authors: Sefyrin Johanna
Published: May 2010

In information technology (IT) design it is essential to develop rich and nuanced understandings of messy design realities. In this chapter Karen Barad’s agential realism is used as an analytical approach in order to obtain such a multifaceted understanding of a local IT design project. The purpose of the paper is to explore entanglements of agency, mutual learning, and gender in a business process analysis. The main argument here is that these issues were inextricably intertwined with each other and with the sociomaterial relations of which they were part. All empirical material used in the chapter was collected with the help of ethnographic methods. Finally the chapter concludes with a discussion about agential realism as an analytical approach.
Challenging Gender Stereotypes Using Virtual Pedagogical Characters
Authors: Gulz Agneta , Haake Magnus
Published: May 2010

This chapter explores motivational and cognitive effects of more neutral or androgynous-looking versus more feminine-looking and masculine-looking virtual characters. A user study is presented, in which 158 students, aged 17-19, encountered four virtual characters that were visually manipulated to represent gender stereotypicality versus androgyny. On the one hand we explored students’ attitudes towards the different characters as seen in how they ranked them as preferred presenters and articulated their arguments for doing so. On the other hand we looked for patterns as to which character(s) influenced female and male students most positively with respect to their attitude towards a university level computer engineering programme. Results from the study are presented and discussed. We conclude by pointing towards future research and potential within the area.
Social Activism in the ‘Blackosphere'
Authors: Kvasny Lynette , Payton Fay Cobb , Hales Kayla D.
Published: May 2010

Using Denning’s model of Internet activism as a sensitizing framework, this chapter describes the manner in which Black bloggers (referred to as the ‘Blackosphere’) express and negotiate their ethnic identity online. We analyze discussions in the Blackosphere in response to the Jena 6 case to illustrate how the Internet has empowered Black people, changed media publicity, and served as a means of collaborative activities that support social activism. It is our hope that this chapter will encourage researchers to explore further how and why historically underserved groups engage in social activism on the Internet, and the various technologies and social practices they use to do so.
Gender Style Differences in Mediated Communication
Authors: Burrell Nancy A. , Mabry Edward A. , Allen Mike
Published: May 2010

This study investigates gender differences in linguistic features of communication styles in the context of mixed public discussion groups in asynchronous, text-based CMC. The study evaluates gendered communication and language styles in situational contexts of CMC. A sample of 3000 messages from 30 Internet discussion groups was content analyzed. Results revealed gender differences in stylistic features used by discussion group participants and partially support the expectation that women’s online communication style is gendered. The data did not reveal an online communication style that significantly discriminated men’s communication. Findings point to the important role of gender enacted through language in the construction of social identity in the context of public discussion groups in CMC. Implications of this investigation and directions for the development of future research on gender in CMC are discussed.
Faculty Development in Instructional Technology in the Context of Learning Styles and Institutional Barriers
Authors: Marinho Robson
Published: May 2010

This chapter describes the within-case analysis of ten faculty members who agreed to share their learning experience and struggles in learning instructional technology. The case focuses on the in-depth description of each participant stressing their unique personal approach and learning styles, describing the main steps experienced and resources utilized by the participants during the learning process. It also highlights one dominant learning characteristic of each participant, which is compared with the participant’s result in the Index of Learning Styles Questionnaire of North Carolina State University, with potential implications for academic administrators in promoting the use of instructional technology by faculty members of diverse profiles. The case also discusses the institutional barriers faced by faculty members while learning how to use instructional technology at a public university in the United States. Three institutional barriers were a major concern for the participants: Time, rewards, and cost. One hundred percent of the participants agreed that providing more time—along with financial and academic rewards—is critical to supporting the learning and implementation of instructional technology.
Mining Education Australia
Authors: Andrews Trish
Published: May 2010

Due to a range of social and economic factors, Australian institutions have struggled to meet the demand for highly trained professionals for the minerals industry in recent years. In order to address this issue, Mining Education Australia, a consortia of four of Australia’s mining schools was established to develop and deliver a common curriculum for mining engineering education.. The use of technology to support the delivery of this common curriculum is integral to the success of this initiative. This chapter outlines the challenges in such collaborations and discusses the range of corporate and open source technologies selected and adopted to overcome these challenges to enable collaborative teaching and learning activities in this trans-national program.
A Framework to Analyze Teaching-Learning Objects (T-LO)
Authors: Nunes Ingrid Kleist Clark , Mallmann Elena Maria
Published: May 2010

The pedagogical mediation in Distance Education (DE) is sustained by hypermediatic didactic materials, which are marked by principles of autonomy, interaction, interactivity, motivation and cooperation. The main thought in this article is to know if the developed Teaching-Learning Objects (T-LO) are potentially meaningful answering these principles. The planning and elaboration of the T-LO are highlighted processes in Brazil. Therefore, the authors present the conceptual singularities of the T-LO; the Instructional Design (ID) processes and the importance of the Instructional Project (IP) elaboration to guarantee a meaningful potentiality of the T-LO. As a research result, the authors center attention on the contribution of a framework (called the T-LO List), which is used to analyze the T-LO developed, implemented, and evaluated in a specific context of a didactic module elaboration. In conclusion, it is important to realize that the usage of a framework to analyze the T-LO can orient theoretical methodological steps of planning, developing, implementing, observing, reflecting, and re-planning, all carried out by multidisciplinary teams.
Chicken TLR21 Is an Innate CpG DNA Receptor Distinct from Mammalian TLR9
Authors: Keestra A. Marijke , de Zoete Marcel R. , Bouwman Lieneke I. , van Putten Jos P. M.
Published: May 2010

TLRs comprise a family of evolutionary conserved sensory receptors that respond to distinct classes of ligands. For one major evolutionary branch of TLRs, the ligands are still largely unknown. Here we report the cloning and function of one member of this group, chicken TLR21 (chTLR21). This TLR is absent in the human species but has homologs in fish and frog and displays similarity with mouse TLR13. Expression of chTLR21 in HEK293 cells resulted in activation of NF-κB in response to unmethylated CpG DNA, typically recognized by mammalian TLR9. Silencing of chTLR21 (but not chTLR4) in chicken macrophages inhibited the response to CpG-DNA (but not to LPS), indicating similar functionality of the endogenous receptor. ChTLR21 responded to human- and murine-specific TLR9 ligands, as well as to bacterial genomic DNA isolated from Salmonella enterica serovar Enteritidis. Confocal microscopy located chTLR21 in the same intracellular compartments as human TLR9. Inhibition of the chTLR21 response by the endosomal maturation inhibitor chloroquine suggested that the receptor is functional in endolysosomes, as known for TLR9. The analogous localization and function of the phylogenetically only distantly related chTLR21 and mammalian TLR9 suggest that during evolution different classes of TLRs have emerged that recognize the same type of ligands.
Green Dot Charter Schools: A Cost-Benefit Analysis of the Proposal to Turn Around Failing High Schools
Authors: Lebow Megan
Published: May 2010

In the current education policy climate, increased pressure has been placed on improving failing high schools that graduate fewer than half of their students. One policy proposal that has gained support proposes replacing these failing schools with successful charter school models. This paper examines the benefits of utilizing the Green Dot charter schools as a “turnaround” model with reference to the costs. If an expanded network of Green Dot charter schools will continue to operate at its current level of effectiveness, then this policy would prove to be cost-beneficial.
Creating an Opportunity Society
Authors: Kooi Kerry
Published: May 2010

No abstract available.
Microbial cycling of DMSP and DMS in coastalandoligotrophicseawater
Authors: Ledyard Kathleen M. , Dacey John W. H.
Published: May 2010

The rates and concentration dependence of microbial dimethylsulfide (DMS) and dimethylsulfoniopropionate (DMSP) cycling were assessed in Vineyard Sound, Massachusetts, and the Sargasso Sea. Net rates of dissolved DMSP loss, DMS production from DMSP, and DMS consumption were measured at ambient and near‐ambient substrate levels. Turnover times of dissolved DMSP, based on loss rates, were short, usually ranging from 1.5 d to several hours. However, the specific process of DMSP cleavage to form DMS accounted for only a portion of total DMSP turnover. Short‐term variability obscured possible regional or seasonal trends in these data. Dissolved DMSP removal and cleavage exhibited saturable kinetics in spring in Vineyard Sound and in winter in the Sargasso Sea. In fall and spring in the Sargasso Sea, where dissolved DMSP levels ranged from 2 to 9 nM, DMSP cleavage did not saturate at DMSP levels as high as 1 µM. Kinetic parameters of DMSP uptake appeared to increase with proximity to summer, as did the proportion of DMSP uptake resulting in DMS production.
Bacterial utilization of different size classes of dissolved organic matter
Authors: Amon Rainer M. W. , Benner Ronald
Published: May 2010

Bacterial utilization of high‐molecular‐weight (HMW; > 1 kDa) and low‐molecular‐weight (LMW; <1 kDa) dissolved organic C (DOC) was investigated in freshwater and marine systems by measuring dissolved oxygen consumption, bacterial abundance, and bacterial production in size‐fractionated samples. Tangential‐flow ultrafiltration was used to separate HMW and LMW DOC. More than 80% of the DOC in Amazon River samples was recovered in the HMW fraction, whereas most marine DOC (up to 70%) was of LMW. Bacterial growth efficiencies were consistently higher in the LMW fractions (16‐66%) than in the HMW fractions (8‐39%), indicating compositional differences in the two size fractions. In all experiments, measured rates of bacterial growth and respiration in HMW incubations were higher than those in LMW incubations. Carbon‐normalized bacterial DOC utilization rates were 1.4–4‐fold greater in the HMW fractions than in the LMW fractions, and a greater proportion (0.7–22.5%) of HMW DOC was utilized per day than LMW DOC (0.5–6.6%). All bacterial growth and respiration measurements indicated that HMW DOC was utilized to a greater extent than LMW DOC in all environments investigated. The traditional model of DOM degradation, stating that LMW compounds are most bioreactive, does not appear to apply to the bulk of natural DOM. Rather, the data and results from independent studies suggest a new conceptual model whereby the bioreactivity of organic matter decreases along a continuum of size (from large to small) and diagenetic state (from fresh to old). This size‐reactivity continuum model suggests that the bulk of HMW DOM is more bioreactive and less diagenetically altered than the bulk of LMW DOM.
Assimilation and regeneration of trace elements by marine copepods
Authors: Wang Wen‐Xiong , Reinfelder John R. , Lee Byeong‐Gweon , Fisher Nicholas S.
Published: May 2010

Assimilation efficiencies (AE) of five trace elements (Am, Cd, Co, Se, and Zn) and carbon by neritic copepods (Acartia tonsa and Temora longicornis) feeding at different food concentrations and on different food types (diatoms, green algae, flagellates, dinoflagellates, and Fe oxides) were measured with radiotracer techniques. Food concentration had little influence on AEs of C, Cd, Co, and Se within a range of 16‐800 µg C liter‐1. AEs of Am and Zn were highest at low food concentrations (16‐56 µg C liter‐1) but remained relatively constant when food levels exceeded 160 µg C liter‐1. Different algal diets had no major influence on AEs, which generally were in the order Cd > Se > Zn > Co > Am. Metals (Cd, Co, and Zn) were assimilated from Fe oxides with 50% less efficiency than from algal cells. Element regeneration into the dissolved phase was a significant route for the release of ingested elements by copepods and increased with increased food concentration. Element regeneration rates for Cd, Se, and Zn were comparable to the regeneration rates of major nutrients such as P (30–70% daily). Retention half‐times of elements in decomposing fecal pellets ranged from < 1d (Cd) to >10 d (Am). The efficient assimilation and regeneration of Cd, Se, and Zn can significantly lengthen the residence time of these elements in ocean surface waters.
Analysis of a Lake Superior coastal food web with stable isotope techniques
Authors: Keough Janet R. , Sierszen Michael E. , Hagley Cynthia A.
Published: May 2010

Food‐web components of a Lake Superior coastal wetland and adjacent offshore waters were examined with stable isotope ratiotechniques for carbon and nitrogen. We found distinct carbon isotope ratio signatures for organisms collected in the wetland and from offshore. Both food‐web groups seemed to be based on carbon fixed by phytoplankton. Compared to offshore organisms, the wetland food web was depleted in 13C. We found the nitrogen isotope ratio signatures to be enriched in 15N by ~3‰ at each succeeding trophic level in both wetland and lake samples. No evidence of a direct energy link between the abundant macrophyte biomass in the wetland and the fisheries food web was found. The carbon ratio of rainbow smelt (Osmerus mordax) and walleye (Stizostedion vitreum) exhibited a shift from a wetland signature in young‐of‐the‐year to an offshore signature in juveniles and adults. Yellow perch (Perca flavescens) young‐of‐the‐year exhibited a planktivorous δ15N signature, while adults were enriched in 15N. Both examples illustrate the utility of stable isotope ratio techniques in confirming feeding shifts associated with growth and habitat change.
Water circulation and coastal trapping of brackish water in a tropical mangrove‐dominated bay in Kenya
Authors: Kitheka Johnson U.
Published: May 2010

Water circulation patterns in a tropical mangrove‐fringed bay with seagrass and coral reef are driven by tides that generate strong reversing tidal currents. The wind, which has an onshore component, generates a net clockwise‐rotating eddy. The dominant tidally driven water circulation pattern, coupled with the effects of onshore wind and alongshore current generated by wave breaking, promotes the coastal trapping of turbid brackish water and its inherent nutrient content. This brackish water inundates the mangrove swamp and seagrass beds but not the coral reef ecosystem. Weak stratification prevails during the wet season in the upper parts of Kidogoweni Creek as a result of freshwater influx from rivers. In the dry season, well‐mixed homogeneous water is found in most regions of the bay. A small zone of hypersaline water (salinity reaching 38 PSU) is found in the upper region of the mangrove‐dominated creeks during the dry season. The connection between the mangrove swamp, with its wide salinity variations, and seagrass beds is apparently through river plumes and tidal effects. The link between seagrass beds and coral reefs is mainly through tidal influences.
Assimilation of trace elements and carbon by the mussel Mytilus edulis: Effects of food composition
Authors: Wang Wen‐Xiong , Fisher Nicholas S.
Published: May 2010

Assimilation efficiency (AE) is an important physiological parameter in determining trace element influx from food sources into aquatic animals. We used radiotracer techniques to examine the influence of diet [seven species of algae (two diatoms, two chlorophytes, a prasinophyte, and two dinoflagellates) and glass beads] on the assimilation of seven trace elements (Ag, Am, Cd, Co, Cr, Se, Zn) and C in the mussel Mytilus edulis. Trace element assimilation was related to C assimilation and cytoplasmic distribution in the algae and to gut passage time in the mussels. Mussels displayed different C AEs for the different algal diets; the chlorophytes, which had highly refractory cell walls, were the least digestible food. Assimilation of Cd, Se, and Zn was directly correlated with C assimilation; for Am, Ag, and Cr, no relationship with C assimilation was apparent. For each species except the chlorophytes, AEs of all elements significantly correlated with their cytoplasmic distribution within each algal cell. Among all species, AEs of Am, Co, and Se also increased with elemental penetration into the cytoplasm; however, this relationship was not statistically significant for Ag, Cd, or Zn. With the exception of Cr, AEs of elements increased with gut passage time, implying more efficient digestion‐absorption when the element was retained longer in the digestive tract. In waters containing large mussel populations, unassimilated particle‐reactive elements should be removed from suspension and enriched in biodeposits in sediments, whereas assimilated metals should be enriched in mussel tissues.
An appraisal of the Allen paradox in a New Zealand trout stream
Authors: Huryn Alexander D.
Published: May 2010

Studies of invertebrate production in trout streams have often shown prey production to be insufficient to support trout production while simultaneously providing a reasonable surplus of prey (Allen paradox). The Allen paradox was explained by analyzing a comprehensive production budget for a trout stream in New Zealand. Budget compartments included primary production, production by brown trout and surficial and hyporheic macroinvertebrates, input of terrestrial invertebrates, and cannibalism by trout. Ecological efficiencies from the literature were used to estimate food demands. Although much of the food demand by trout was apparently derived from surficial macroinvertebrates, a balanced budget was obtained only when all other prey sources were included. The budget indicated that surplus production by benthic macroinvertebrates was nil. However, given the uncertainty of budget statistics, surpluses as high as ~10–20% would probably not be detected. Secondary production by primary consumers required only ~20% of total primary production, indicating strong top‐down control of herbivory by trout. Results from this study, other recent studies showing strong effects of trout on stream food webs, and the long tradition of the Allen paradox suggest that in productive streams (>100 kg wet mass trout ha−1 yr−1) trout may consume most (>80%) benthic prey production.
Physiological ecology of a species of the filamentous green alga Mougeotia under acidic conditions: Light and temperature effects on photosynthesis and respiration
Authors: Graham James M. , Arancibia‐Avila Patricia , Graham Linda E.
Published: May 2010

One of the earliest and most reliable indications of acid precipitation affecting freshwater systems is the development of littoral blooms of the filamentous green alga Mougeotia (Zygnematales, Charophyceae). Field observations of depth distribution and seasonal abundance in Little Rock Lake, an experimentally acidified seepage lake in north‐central Wisconsin, suggest that Mougeotia might prefer warmer temperatures and carry out net photosynthesis at fairly low light levels. To test these hypotheses, we measured net photosynthesis and respiration at 56 combinations of irradiance and temperature in a controlled environment facility. Optimum conditions were 25°C and 300‐2,300 µmol quanta m−2 s− 1. Over this range, net photosynthesis averaged 40.4 mg O2 g−1 h−1. Respiration rates increased with both temperature and prior irradiance. Light‐enhanced respiration rates were significantly greater than dark respiration rates following irradiance ≥ 164 µmol quanta m−2 s−1. Mougeotia's photosynthetic response to temperature and irradiance explains aspects of its growth and distribution in acidified lakes but it does not by itself explain the magnitude of this alga's growth at low pH.
Effects of pH and selected metals on growth of the filamentous green alga Mougeotia under acidic conditions
Authors: Graham James M. , Arancibia‐Avila Patricia , Graham Linda E.
Published: May 2010

When acid precipitation impacts freshwater systems, littoral blooms of the filamentous green alga Mougeotia (Zygnematales, Charophyceae) frequently develop. Field observations of its development in Little Rock Lake, an experimentally acidified seepage lake in north‐central Wisconsin, indicated that the species of Mougeotia present there may have an optimum pH for growth of ~5.2. Because a number of metals increase in concentration in acidified waters, we also proposed that this species of Mougeotia may be particularly tolerant of metals. To test these hypotheses, we grew Mougeotia from Little Rock Lake in culture at eight levels of pH (3 through 10) and measured net photosynthesis and respiration at each level. We also grew this isolate over a range of Zn concentrations from 10 to 2,400 µg liter−1 and Al concentrations from 10 to 3,600 µg liter−1. Little Rock Lake Mougeotia grew over a broad range of pH levels from 3 to 9 with an optimum at 8, in contrast to our expectation. Mougeotia, however, was tolerant to levels of Zn and Al considerably higher than the elevated levels to which it had been exposed in the acidified basin of the lake. Mougeotia may grow luxuriously in acidified waters because of an efficient uptake of CO2 and dissolved organic C and a lack of grazing pressure.
Sedimentary geolipid records of historical changes in the watersheds and productivities of Lakes Ontario and Erie
Authors: Bourbonniere Richard A. , Meyers Philip A.
Published: May 2010

The organic matter contents of sediments de posited in Lakes Erie and Ontario contribute to the record of changes in the lake watersheds and aquatic ecosystems which have resulted from European settlement and cultural eutrophication of these systems over the past two centuries. Compositions of n‐alkanes and n‐alkanoic acids extracted from lake sediments track the clearing of the original natural forests and the appearance of agriculture in the watershed areas beginning about 1820. Aquatic productivity increased as runoff of soil nutrients increased. Cultural eutrophication in the 1950s is recorded in increases in organic C and in n‐C17 alkane concentrations. Diagenetic effects overprint source changes as shorter chain length and unsaturated lipid components are preferentially removed from the sedimentary record.
Production of strong, extracellular Cu chelators by marine cyanobacteria in response to Cu stress
Authors: Moffett James W. , Brand Larry E.
Published: May 2010

Copper speciation in the upper marine water column is dominated by strong ligands thought to be of recent biological origin. Cultures of the marine cyanobacteria Synechococcus spp., a ubiquitous and important group of phytoplankton highly sensitive to Cu toxicity, were previously shown to produce chelators comparable in strength to those detected in the water column. Here we show that cultures of Synechococcus exposed to toxic concentrations of Cu produce an extracellular ligand with a binding constant comparable to constants for ligands found in the water column. Coordination of Cu by this compound decreases the concentration of free cupric ion (the toxic form) in the culture media to levels that do not inhibit growth. A tight linear correlation between chelator and Cu concentration suggests that production of this substance may be regulated by the concentration of free Cu in the media in a feedback mechanism. Similarly, the concentrations of Cu and Cu‐binding ligands in the water column are often closely related. These results suggest that cyanobacteria modify Cu chemistry in seawater, creating conditions more favorable for growth.
Seasonal nitrogen fixation dynamics in a marine microbial mat: Potential roles of cyanobacteria and microheterotrophs
Authors: Paerl Hans W. , Fitzpatrick Matthew , Bebout Brad M.
Published: May 2010

Diel rates of nitrogen (N2) fixation (acetylene reduction) and primary production (14CO2 fixation) were examined seasonally on a North Carolina Atlantic coastal, intertidal, benthic microbial mat community dominated by the filamentous, nonheterocystous cyanobacterial genera Microcoleus and Lyngbya. Highest hourly and daily rates of N2 and CO2 fixation were observed during spring through fall. During this period, an inverse temporal relationship was noted between these processes, with CO2 fixation closely tracking irradiance and N2 fixation rates remaining low during daylight and becoming maximal at night. Under the influence of the photosynthetic (PS 2) inhibitor 3‐(3,4 dichlorophenyl)‐1,1 dimethylurea (DCMU), daytime N2 fixation was enhanced, indicating in situ O2 inhibition of N2 fixation. The most pronounced DCMU stimulation of daytime N2 fixation was in spring‐fall. Both N2 and CO2 fixation rates were lower in winter. Winter patterns of diel N2 fixation were the reverse of those in summer, with maximum rates at midday. The reversal was related to seasonal changes in daily and hourly photosynthetic rates, leading to differential O2 suppression of N2 fixation. Seasonal changes in cyanobacterial community composition and bacterial diazotrophy may have played additional roles in determining diel rates and patterns of N2 fixation and mat production. Results indicate a more important role for bacteria in the dynamics of mat N2 fixation than has been previously recognized.
Isotopic fractionation of ammonium and nitrate during uptake by Skeletonema costatum: Implications for δ15N dynamics under bloom conditions
Authors: Pennock Jonathan R. , Velinsky David J. , Ludlam John M. , Sharp Jonathan H. , Fogel Marilyn L.
Published: May 2010

Isotopic fractionation of ammonium (NH4+) and nitrate (NO3−) during uptake by phytoplankton was examined in batch culture experiments with the diatom Skeletonema costatum under nitrogen‐enriched conditions (5–100 µM). The fractionation factor (ε) for NO3− uptake by Skeletonema was −9.0±0.7‰ and was concentration‐independent. For NH4+, ε was more variable and dependent on ambient NH4+ concentration. For NH4+ concentration ranges of 100‐50, 50‐20, and 20‐5 µM, ε was −24.6±5.5, −27.2±1.6, and −7.8±3.0‰. In these cultures, isotopic fractionation by phytoplankton caused variations in δ15N of up to 50‰ for NH4+, 12‰ for NO3−, and 25% for particulate N. Similar variability in the δ15N of both dissolved inorganic and particulate organic N pools should be expected during phytoplankton blooms in nature. As a result, phytoplankton‐mediated isotopic variability must be considered when isotopic data are used to examine biogeochemical and physical processing of organic matter in marine ecosystems, particularly when biosynthesis and loss processes are decoupled in either space or time during bloom conditions.
Mesocosm tracer studies. 2. The fate of primary production and the role of consumers in the pelagic carbon cycle of a mesotrophic lake
Authors: Lyche Anne , Andersen Tom , Christoffersen Kirsten , Hessen Dag O. , Berger Hansen Paul H. , Klysner Annette
Published: May 2010

The fate of primary production in the pelagic food web in mesotrophic Svinsjøen, southeastern Norway, was studied in a 10‐d mesocosm experiment with 14C addition. Specific assimilation rates for all the main compartments in the system were estimated by applying tracer models and further combined to construct a balanced C budget by means of mathematical inverse methods. The specific carbon assimilation rates for the phytoplankton and bacteria were 0.24 and 0.49 d−1, respectively, and 70% of the bacterial production was fueled by phytoplankton exudates. The C budget shows that roughly half of the gross primary production was lost as exudates and 10% was respired. Only 20% of phytoplankton net production was assimilated by consumers. The rest of the net primary production was lost as dissolved and particulate detritus or by sedimentation. Of the net bacterial production, a third accumulated as bacterial biomass, a third was assimilated by bacterivores, and a third was lost as detritus. The coupling between the microbial loop and the classical grazer food web was insignificant, probably due to low Daphnia biomass. The microbial food web thus acted as a sink rather than as a source of C to the higher consumers. Altogether, <2% of gross primary production was incorporated into consumer biomass.
Digestion and alteration of the biochemical constituents of a diatom (Thalassiosira weisflogii) ingested by an herbivorous zooplankton (Calanus pacificus)
Authors: Cowie Gregory L. , Hedges John I.
Published: May 2010

A laboratory experiment was conducted in which 14C‐labeled diatoms (Thalassisora weissflogii) were fed to an herbivorous copepod zooplankton (Calanus pacificus). Digestion efficiencies, as defined by changes in concentration relative to biogenic silica from the diet to fecal pellets, were calculated for 14C, organic carbon, nitrogen, and chlorophyll‐type pigments as well as proteins (as amino acids) and polysaccharides (as aldoses).

The majority of organic material ingested (≥65% of all components except pigments, 30%) was digested. Digestion efficiencies were similar to reactivity patterns observed in previous studies of the same organisms (total N > organic C > total chlorophyll‐type pigments). Polysaccharides and particularly amino acids were clearly important nutrients for copepods. However, together with chlorophyll‐type pigments, these biochemicals accounted for only 57% of organic C in the diatom and only 35% in fecal pellets. Although lipids represented some fraction of the uncharacterized materials, an important, relatively stable diatom component remained unidentified and apparently was concentrated in the fecal pellets.

Individual amino acids and especially aldoses were digested to differing degrees, apparently due to preferential digestion of intracellular materials with concomitant preservation of cell‐wall polymers in the fecal pellets. Overall, egested materials were dramatically altered in composition relative to the diet. Digestion efficiencies for all components were similar in magnitude and pattern to reactivities observed in temperate coastal sites in which diatoms and copepods are important contributors to plankton populations and sinking particle fluxes.
Chemical enhancement of CO2 exchange in natural waters
Authors: Wanninkhof Rik , Knox Molly
Published: May 2010

Exchange of CO2 under low turbulence conditions and high pH can be enhanced by hydration reactions of CO2 with hydroxide ions and water molecules in the boundary layer. A series of field experiments was performed on several lakes, including alkaline closed‐basin lakes, using enclosures (helmets) to study the enhancement process in nature. In addition, the enhancement of CO2 exchange was studied in laboratory experiments with freshwater and seawater. The results of the experiments are compared with published theoretical calculations. Within the experimental uncertainties and shortcomings of the chemical enhancement models, reasonable agreement was observed between experimental and theoretical results for seawater. The experiments indicate, in accordance with theory, that chemical enhancement has a minor effect on air‐sea gas exchange of CO2 under average oceanic turbulence conditions. However, for the equatorial CO2 source regions, with high temperatures and low winds, the calculated CO2 enhancement amounts to 4–8% of the total exchange. The observations on lakes show poorer agreement with models, which is attributed to experimental uncertainty and poor characterization of the chemistry of the lake waters. The experiments show that chemical enhancement of CO2 is ubiquitous for the alkaline closed‐basin lakes with enhancements of up to a factor of three.
Interannual variability of a salt‐marsh ecosystem
Authors: Teal John M. , Howes Brian L.
Published: May 2010

Data from Great Sippewissett Salt Marsh are used to gauge the extent of change of Spartina alterniflora marsh during periods of several to 22 yr. Our data all relate to plant production: from aboveground, maximum plant biomass measured over the entire period; from belowground, live root and rhizome biomass measured in 1974 and 1983, CO2 evolution from the sediments for 7 yr, and pore‐water concentrations of dissolved sulfide for 6 yr. All the measures indicated a relatively low degree of interannual change in salt‐marsh areas vegetated by tall‐ and short‐form S. alterniflora. The similarity in both plant and biogeochemical parameters between years is likely related to the regular, high‐frequency tidal flooding of grass stands. These interannual comparisons of each quantified parameter support the contention that measurements made in any single year can be applied to other years with suitable precautions to account for seasonal cycles. Our data also illustrate the importance of long time series for establishing sound correlations in environmental data.
Determinants of temporal coherence in the satellite‐derived 1987–1994 ice breakup dates of lakes on the Laurentian Shield
Authors: Wynne Randolph H. , Magnuson John J. , Clayton Murray K. , Lillesand Thomas M. , Rodman Daniel C.
Published: May 2010

Remotely sensed ice breakup dates for 62 lakes on the Laurentian Shield were analyzed to preliminarily assess determinants of the mean breakup date and to identify determinants of temporal coherence of lake‐ice breakup. Correlations between mean breakup date and the explanatory variables (surface area, maximum depth, surface area: maximum depth ratio, latitude, longitude, and elevation) revealed that only latitude (r = 0.96) and surface area (r = 0.45) were significant at ≤ 0.05. Latitude and surface area were significantly correlated (r = 0.42).

The temporal coherence of breakup dates between each pair of lakes was calculated by taking the product‐moment correlation between their 8‐yr time series (1987–1994) of breakup dates. There is a general lack of strong temporal coherence between lakes, implying that no lake in this study area is representative of the entire region. The significant (P ≤ 0.05) correlates of the temporal coherence of breakup dates were difference in mean breakup date (‒0.49) and difference in latitude (r = ‒0.51), themselves significantly correlated (r = 0.89). The differences in surface area, maximum depth, surface area: maximum depth ratio, longitude, and elevation were not significant. The general lack of strong temporal coherence between lakes and the significant correlation between coherence and mean breakup date are further confirmation that breakup dates for different lakes may be reflections of (and indicators for) different periods of meteorological forcing.
Climate change and northern prairie wetlands: Simulations of long‐term dynamics
Authors: Poiani Karen A. , Johnson W. Carter , Swanson George A. , Winter Tom C.
Published: May 2010

A mathematical model (WETSIM 2.0) was used to simulate wetland hydrology and vegetation dynamics over a 32‐yr period (1961–1992) in a North Dakota prairie wetland. A hydrology component of the model calculated changes in water storage based on precipitation, evapotranspiration, snowpack, surface runoff, and subsurface inflow. A spatially explicit vegetation component in the model calculated changes in distribution of vegetative cover and open water, depending on water depth, seasonality, and existing type of vegetation.

The model reproduced four known dry periods and one extremely wet period during the three decades. One simulated dry period in the early 1980s did not actually occur. Simulated water levels compared favorably with continuous observed water levels outside the calibration period (1990–1992). Changes in vegetative cover were realistic except for years when simulated water levels were significantly different than actual levels. These generally positive results support the use of the model for exploring the effects of possible climate changes on wetland resources.
Changes in climate and hydrochemical responses in a high‐elevation catchment in the Rocky Mountains, USA
Authors: Williams Mark W. , Losleben Mark , Caine Nel , Greenland David
Published: May 2010

A continuous climate record since 1951 at Niwot Ridge in the Colorado Front Range shows a decline in mean annual temperature, an increase in annual precipitation amount, and a decrease in mean daily solar radiation for the summer months. The increase in precipitation amount explains about half of the 200% increase in annual wet deposition of NO3‒ to Niwot Ridge over the last decade. Differences in climate parameters between 1994 and 1995 (increased snow depth and decreased net energy flux to the snowpack) resulted in a 4–5‐fold increase in the magnitude of solute release from the snowpack in the form of an ionic pulse. In turn, the high chemical loading of strong acid anions in the seasonal snowpack and release of these solutes from the seasonal snowpack in the form of an ionic pulse is causing episodic acidification (ANC < 0 µeq liter‒1) in headwater catchments at present deposition levels. Small changes in climate parameters may cause large changes in the hydrochemistry of alpine streams. The changes in climate at Niwot Ridge are not in synchrony with lowland warming in the Great Plains to the east and serve as a reminder that climate in alpine areas is driven by local conditions and may be asynchronous with regional and global climate trends.
The influence of landscape position on lake chemical responses to drought in northern Wisconsin
Authors: Webster Katherine E. , Kratz Timothy K. , Bowser Carl J. , Magnuson John J. , Rose William J.
Published: May 2010

Climatic shifts to drier conditions during drought alter the hydrologic pathways of water and solute flow to aquatic ecosystems. We examined differences in drought‐induced trends in the semiconservative cations, Ca+Mg, in seven northern Wisconsin lakes. These spanned the range of hydrologic settings in the region, including hydraulically mounded, groundwater flowthrough, and groundwater‐discharge lakes. Parallel increases in concentration across the seven lakes during drought were attributable to evapoconcentration. However, we observed divergent trends for mass, which better reflects altered solute flux by accounting for changes in lake volume. Ca+Mg mass increased in three groundwater‐dominated lakes as precipitation inputs were low and groundwater discharging from longer flowpaths became proportionately more important. In contrast, decreases in Ca+Mg mass for two precipitation‐dominated lakes reflected diminished inputs of solute‐rich groundwater. Landscape position, defined by the spatial position of a lake within a hydrologic flow system, accounted for the divergence in chemical responses to drought.
Effects of climate change on hypoxia in coastal waters: A doubled CO2 scenario for the northern Gulf of Mexico
Authors: Justić Dubravko , Rabalais Nancy N. , Turner R. Eugene
Published: May 2010

Projections of general circulation models suggest that freshwater discharge from the Mississippi River to the coastal ocean will increase 20% if atmospheric CO2 concentration doubles. This result is likely to affect water column stability, surface productivity, and global oxygen cycling in the northern Gulf of Mexico, which is the site of the largest (up to 16,500 km2) and most severe hypoxic zone (<2 mg O2 liter‒1) in the western Atlantic Ocean. We use a coupled physical‐biological two‐box model to investigate potential effects of climate change on seasonal oxygen cycling and hypoxia in river‐dominated coastal waters. The model was developed and calibrated using comprehensive environmental data sets collected on the Mississippi River and in the northern Gulf of Mexico between 1985 and 1993. The relative magnitude of changes in river runoff and severity of hypoxia during the 1993 Mississippi River flooding provide an excellent data set for model verification. Model simulations for a doubled CO2 climate predict a 30–60% decrease in summertime subpycnoclinal oxygen content, relative to a 1985–1992 average. Under those conditions, the hypoxic zone in the northern Gulf of Mexico will expand and encompass an area greater than that of summer 1993.
Effects of ultraviolet radiation on periphyton in an alpine lake
Authors: Vinebrooke Rolf D. , Leavitt Peter R.
Published: May 2010

Many alpine lakes have low concentrations of ultraviolet (UV) radiation‐absorbing dissolved organic matter, yet receive higher UV radiation flux than low‐elevation lakes. We tested whether ambient UV radiation affected periphyton development in a small alpine lake in Banff National Park, Canada. After 30 d, total periphytic biomass and chlorophyll accrual on artificial substrates were enhanced ∼100% (t‐test, P < 0.05) by removal of UV radiation (<400 nm). The inhibitory effect of UV radiation was species‐specific, significantly suppressing (Bonferroni‐adjusted t‐test, P < 0.05) Achnanthes minutissima Kützing but not other colonists. Although taxa apparently differed in their sensitivity to UV radiation, periphyton communities remained dominated by early successional taxa, especially A. minutissima (75% of total biovolume). In contrast, natural epilithic communities were dominated by cyanobacteria (Anabaena subcylindrica Borge, Calothrix sp.). These findings suggest that ambient UV radiation at alpine sites can suppress periphyton development by inhibiting littoral diatom production during the short ice‐free season (July–September).
Zooplankton egg banks as biotic reservoirs in changing environments
Authors: Hairston Nelson G.
Published: May 2010

The long‐lived diapausing eggs of zooplankton constitute an ecological and evolutionary reservoir that can impact the rate and direction of population, community, and ecosystem response to environmental change. Viable diapausing eggs are often extremely abundant and can survive in aquatic sediments for decades or longer. As the mean environment changes, the frequency of extreme conditions will likely increase, and species with prolonged diapause will be able to survive extreme years of no recruitment, whereas species lacking an egg bank will not. An altered environment may change which species have poor recruitment and even, through effects on thermal diapause cues, which species produce an egg bank. The interaction between environmental variation and generation overlap (produced by prolonged diapause) results in the maintenance of biotic diversity (both species richness and genetic variation), which forms the foundation for response to future environmental change.