Understanding and eliminating iron interference in colorimetric nitrate and nitrite analysis

Across many environments, nitrate ( $\mbox{NO}_{3}^-$ ) is an important form of N available for microorganisms and photosynthetic organisms. Accurate $\mbox{NO}_{3}^-$ measurements are important for examining N cycling and retention in terrestrial and aquatic ecosystems, but a common method of $\mbox{NO}_{3}^-$ analysis can underestimate $\mbox{NO}_{3}^-$ concentrations when soluble iron is present (iron > 10 mg L^???1). The basic method is robust, using copperized cadmium to reduce $\mbox{NO}_{3}^-$ and then diazotizing the resulting $\mbox{NO}_{2}^-$ in a two-step process to form an easily measured colored product. We show that iron interference is unique to using an NH₄Cl and ethylenediaminetetraacetic acid (EDTA) buffer. We hypothesize that interference is through iron-catalyzed reduction of the intermediate color product, a diazonium ion. We examine three historical buffers as alternatives to NH₄Cl/EDTA and recommend replacement of EDTA with diethylenetriaminepentaacetic acid, which chelates metals much like EDTA, but unlike EDTA, it does not cause interference in the presence of iron.     

Biannual spawning, rapid larval development and evidence of self-seeding for scleractinian corals at an isolated system of reefs

Some of the most important demographic parameters underlying the resilience of coral communities are determined by their patterns of reproduction. In this study, a variety of methods were used to investigate the patterns of spawning, larval development and dispersal for scleractinian corals at an isolated reef system off northwestern Australia. Two distinct periods of gamete maturation and multi-specific spawning occurred each year, during Spring and Autumn, in contrast to the single season of mass spawning described on most other reefs around Australia. The subsequent rates of embryogenesis and larval development were among the fastest described for corals, with pre-competency periods of approximately 3 days. Within 3 days of spawning, slicks of spawn and current drifters had dispersed up to 5 km, and up to 10 km after 6 days, while the times taken for drifters to travel between adjacent (>240 km) reef systems were similar to or greater than the upper competency periods of most coral larvae. Thus, under these conditions, the entire reef system, and to some extent the reefs within the system, may largely be self-seeded; rates of immigration from other systems are probably insufficient to rapidly increase the recovery of communities within years of a major disturbance. These results have implications for the management of isolated reef systems, highlighting the need to minimize local stressors and maximize community resilience to the increasing scale of disturbance and habitat fragmentation.     

Different motivations for knowledge sharing and hiding: The role of motivating work design

Little research to date has focused on understanding employee motivation to share and hide knowledge. Using self‐determination theory, we tested the premise that knowledge sharing and hiding might be differentially motivated and that work design characteristics might influence the motivation to share knowledge with colleagues. In a panel survey of Australian knowledge workers and in a Chinese knowledge‐intensive organization, we asked knowledge workers, using time‐lagged designs, about perceptions of work design, motivation to share knowledge, and self‐reported knowledge sharing and hiding behaviors. Results, largely replicated across both samples, indicated that cognitive job demands and job autonomy were positively related to future reports of knowledge‐sharing frequency and usefulness via autonomous motivation to share knowledge. Unexpectedly, task interdependence was positively related to the three forms of knowledge hiding (evasive and rationalized hiding, and playing dumb) via external regulation to share knowledge. Implications for the design of jobs that motivate knowledge sharing and demotivate knowledge hiding are discussed.     

Role of sex and breeding status in grooming and total tick load of impala

The lesser mouse lemur (Microcebus murinus) is a prosimian primate which presents evidence of sex ratio bias of offspring that agrees with the direction of bias predicted by the local resource competition model for facultative sex ratio adjustment. That is, females overproduced sons when grouped prior to mating, whereas isolated females exhibited the opposite tendency. In this solitary species, social communication relies heavily on urinary chemical signals. To test the hypothesis that sex biases induced by social factors may be linked to urinary cues, isolated females were exposed (n = 76) or not (control group, n = 16) to urinary cues from other reproductively active females from the beginning of the breeding season (induced by long photoperiod) until oestrus. During that period, females were either continuously (n = 17) or partially (n = 59) exposed to chemosignal stimulation. Females in oestrus were placed in contact with a breeding male and subsequently isolated until they gave birth. All females entered oestrus but the timing of oestrus was significantly delayed by 1 week in urine-exposed females. A general depressive effect of long-term urine exposure on fecundity was demonstrated, involving fewer impregnations, higher abortion frequency and smaller litter sizes. Among females giving birth (n = 55) to a total of 129 young, a significant positive correlation was found between sex ratio bias towards males and the duration of urine exposure. However, the shift in sex ratio at birth depended on the duration of urine stimulation during a sensitive period extending from the beginning of the long photoperiod until the beginning of the follicular phase. In the absence of urinary cues during the sensitive period, females significantly overproduced daughters (32% males of 53 newborn). As urine exposure increased during the sensitive phase, the proportion of males in litters increased from 54% males (n = 50) in partially urine-exposed females to a significant bias towards males (69.2% of 26 newborn) in totally exposed females. The biased sex ratio in response to chemical cues did not show consistent relationships with maternal body weight, parity or litter size. Although the intrinsic mechanisms involved in sex-biased conceptions are not known, chemical cues could interact with the photoperiodic control of gonadotropin secretions. Received: 14 January 1995/Accepted after revision: 26 November 1995     

Sampling household waste at source: lessons learnt in Gaborone.

Municipal solid waste (MSW) quantity and composition analysis is fundamental for the planning of municipal waste management services. The purpose of this paper is to report the results and experiences of sampling household waste at the source of generation in Gaborone, Botswana. The average generation rate, in kg capita(-1) day(-1), and percentages of various components of waste in Gaborone were determined using a statistically designed household sampling survey. The survey covered 47 households with different socio-economic characteristics over 21 days with 893 samples obtained. The results showed that the average waste generation rate for Gaborone was 0.33 kg capita(-1) day(-1). Contrary to common belief, the waste generation rate measured as in weight units was found not be directly related to household income. However, the packaging fractions of plastic and paper measured as volume had a direct relationship with household income. Across all income groups, the putrescible waste fraction constituted the highest proportion of the waste stream at approximately 68%. The main general conclusion is on the importance of practical considerations. As much as statistically designed sampling procedures provide a useful means of estimating the quantity and composition of household waste at source of generation, there are some practical issues that should be carefully considered during sampling to improve the accuracy and relevance of the results.