Does differential phosphorus processing by plankton influence the ecological state of shallow lakes?

Shallow lakes have a tendency to settle into turbid or clear-water states, the latter having lower concentrations of total phosphorus (TP). However, how P-cycling is affected by and perhaps contributes to maintaining the different states is not well understood, in part because quantifying the processes involved by traditional methods is difficult. To elucidate these processes, we conducted experiments using P-PO as a tracer on samples collected from the unrestored, unvegetated sections of Huizhou West Lake where turbid water prevails as well as the restored, clear-water, macrophyte-rich waters of the lake.

Structure and Measurement Invariance of Ethnic Identity for Native American College Students.

With a specific focus on the Native American population, the current study investigated the structure of ethnic identity, measured by the Multigroup Ethnic Identity Measure, using a bifactor model across Native American ( = 307), Asian ( = 348), and White ( = 549) undergraduate students. We further investigated measurement invariance across ethnic groups that shared the same factor structure. The results indicated that ethnic identity can be modeled by a bifactor structure with a general factor and two group factors, affective pride and exploration, for Native American and Asian respondents but not White respondents.

What free time? A daily study of work recovery and well-being among working students.

Working students face incredible demands on their time and resources, yet little research exists assessing the degree to which they are able to recover from their demands. The current study aimed to determine the extent to which different types of psychological detachment-detachment from work as well as detachment from school-contribute to the well-being of working students, and whether work can serve as an opportunity to recover from school and vice versa. An additional focus of the study was how perceived stress interacts with detachment both from school and from work to impact well-being.

Response to Comment on "An excess of massive stars in the local 30 Doradus starburst".

Farr and Mandel reanalyze our data, finding initial mass function slopes for high-mass stars in 30 Doradus that agree with our results. However, their reanalysis appears to underpredict the observed number of massive stars. Their technique results in more precise slopes than in our work, strengthening our conclusion that there is an excess of massive stars (>30 solar masses) in 30 Doradus.

Representing a large region with few sites: The Quality Index approach for field studies.

Many environmental studies require the characterization of a large geographical region using a range of representative sites amenable to intensive study. A systematic approach to selecting study areas can help ensure that an adequate range of the variables of interest is captured. We present a novel method of selecting study sites representing a larger region, in which the region is divided into subregions, which are characterized with relevant independent variables, and displayed in mathematical variable space.

Herbivorous snails can increase water clarity by stimulating growth of benthic algae.

Eutrophication in shallow lakes is characterized by a switch from benthic to pelagic dominance of primary productivity that leads to turbid water, while benthification is characterized by a shift in primary production from the pelagic zone to the benthos associated with clear water. A 12-week mesocosm experiment tested the hypothesis that the herbivorous snail Bellamya aeruginosa stimulates the growth of pelagic algae through grazing on benthic algae and through accelerating nutrient release from sediment. A tube-microcosm experiment using P-PO as a tracer tested the effects of the snails on the release of sediment phosphorus (P).

Working safely at some times and unsafely at others: A typology and within-person process model of safety-related work behaviors.

Why do individuals choose to work safely in some instances and unsafely in others? Though this inherently within-person question is straightforward, the preponderance of between-person theory and research in the workplace safety literature is not equipped to answer it. Additionally, the limited way in which safety-related behaviors tend to be conceptualized further restricts understanding of why individuals vary in their safety-related actions. We use a goal-focused approach to conceptually address this question of behavioral variability and contribute to workplace safety research in 2 key ways.

The relationship between sleep and work: A meta-analysis.

Sleep has tremendous importance to organizations because of its relationship with employee performance, safety, health, and attitudes. Moreover, sleep is a malleable behavior that may be improved by individual and organizational changes. Despite the consequential and modifiable nature of sleep, little consensus exists regarding its conceptualization, and how the choice of conceptualization may impact relationships with organizational antecedents and outcomes.

Sclerosing rhabdomyosarcoma: presentation of a rare sarcoma mimicking myoepithelial carcinoma of the parotid gland and review of the literature.

Sclerosing rhabdomyosarcoma (SRMS), a recently characterized variant of rhabdomyosarcoma, can pose a significant diagnostic challenge given its rarity and its histological similarity to other malignancies. SRMS is characterized by dense hyalinized or sclerosing collagenous matrix and a pseudovascular pattern of growth. SRMS shares histologic similarities with several mesenchymal tumors including: leiomyosarcoma, osteosarcoma, chondrosarcoma, angiosarcoma, and sclerosing epithelioid fibrosarcoma.

Effects of deposit-feeding tubificid worms and filter-feeding bivalves on benthic-pelagic coupling: implications for the restoration of eutrophic shallow lakes.

Benthic-pelagic coupling is a key factor in the dynamics of shallow lakes. A 12-week mesocosm experiment tested the hypothesis that deposit-feeding tubificid worms stimulate the growth of pelagic algae while filter-feeding bivalves promote the growth of benthic algae, using the deposit-feeding tubificid Limnodrilus hoffmeisteri and the filter-feeding bivalve Anodonta woodiana. A tube-microcosm experiment using a (32)P radiotracer tested for differential effects of tubificids and bivalves on the release of sediment phosphorus (P).

Application of fingerprint-based multivariate statistical analyses in source characterization and tracking of contaminated sediment migration in surface water.

This study investigates the suitability of multivariate techniques, including principal component analysis and discriminant function analysis, for analysing polycyclic aromatic hydrocarbon and heavy metal-contaminated aquatic sediment data. We show that multivariate "fingerprint" analysis of relative abundances of contaminants can characterize a contamination source and distinguish contaminated sediments of interest from background contamination. Thereafter, analysis of the unstandardized concentrations among samples contaminated from the same source can identify migration pathways within a study area that is hydraulically complex and has a long contamination history, without reliance on complex hydrodynamic data and modelling techniques.

Using stable isotopes of dissolved oxygen for the determination of gas exchange in the Grand River, Ontario, Canada.

Gas exchange can be a key component of the dissolved oxygen (DO) mass balance in aquatic ecosystems. Quantification of gas transfer rates is essential for the estimation of DO production and consumption rates, and determination of assimilation capacities of systems receiving organic inputs. Currently, the accurate determination of gas transfer rate is a topic of debate in DO modeling, and there are a wide variety of approaches that have been proposed in the literature.

Quantifying quagga mussel veliger abundance and distribution in Copper Basin Reservoir (California) using acoustic backscatter.

Quagga mussels (Dreissena bugensis) have been linked to oligotrophication of lakes, alteration of aquatic food webs, and fouling of infrastructure associated with water supply and power generation, causing potentially billions of dollars in direct and indirect damages. Understanding their abundance and distribution is key in slowing their advance, assessing their potential impacts, and evaluating effectiveness of control strategies. Volume backscatter strength (Sv) measurements at 201- and 430-kHz were compared with quagga mussel veliger and zooplankton abundances determined from samples collected using a Wisconsin closing net from the Copper Basin Reservoir on the Colorado River Aqueduct.

Phytoplankton composition of Euphrates River in Al-Hindiya barrage and Kifil City region of Iraq.

Seasonal variations in phytoplankton abundance and their composition were studied at five stations in the middle region (between Al-Hindiya barrage to Kifil City) of the Euphrates River in Iraq between March, 2004, and February, 2005. A total 151 taxa of phytoplankton were identified, belonging to Bacillariophyceae (98), Chlorophyceae (33), Cyanophyceae (14), Euglenophyceae (2), Xanthophyceae (2), and Dinophyceae (2). The total abundance of phytoplankton cells varied from 136 to 5312 cells l(-1) with maxima in spring and fall.

Culturability and survival of marine, freshwater and clinical Pseudomonas aeruginosa.

Genetic typing of Pseudomonas aeruginosa isolated from the open ocean has revealed that marine strains form unique clusters. To clarify whether this genetic variation reflects differences in pattern of culturability and survival, a marine strain was compared with a freshwater strain and a clinical strain in microcosms with different levels of NaCl (0 to 7% [w/v]), pH (4.0 to 9.

Polymorphic distribution of the ovine prion protein (PrP) gene in scrapie-infected sheep flocks in which embryo transfer was used to circumvent the transmissions of scrapie.

The genetic sequence of the ovine prion protein (PrP) gene between codons 102 and 175 with emphasis on ovine PrP gene codons 136 and 171 was determined, and the polymorphic distribution of the ovine PrP gene in the scrapie-exposed Suffolk embryo donors and offspring from these donors that were transferred to scrapie-free recipient ewes was investigated in this study. The most common genotype was AA(136)QQ(171) (70% and 63% in the donor and offspring flocks, respectively), which is considered a high risk genotype in US Suffolk sheep. Although embryos were collected from scrapie-positive donors and many embryos had the high risk genotype, no scrapie occurred in the resulting offspring.

Maximum growth rate, size and commonness in a community of bactivorous ciliates.

Adaptions which confer competitive ability or resistance to predation are thought to be evolved with a resultant loss in intrinsic rate of increase (r ). Therefore species which are opportunistic should retain high values of r , whereas competitively superior species which employ a strategy of persistance will have low values of r . Whether a ciliate species is slow or fast-growing can be judged by comparison with the empirically derived equation relating growth rate and size given by Fenchel (1968).