Effects of lunar cycles on Artemia density in hypersaline environments

The effects of lunar cycles are known to have an influence, although not yet clear, on the behavior of aquatic organisms. A study was conducted in two different locations (Manaure, Guajira and Chengue, Magdalena, Caribbean coast, Colombia) during July and August, 1997 and November, 1998 to determine the effects of medium term cycles (lunar cycles) on the presence of Artemia franciscana (Crustacea: Anostraca) density. Samples were collected every 4 h from each of 20 fixed stations in a salt production pond during a 24-h sampling period at the peak of the four lunar phases. The data were analyzed using a mixed ANOVA model, setting lunar phases and sampling time intervals as fixed effects, station as the random effect and density as the dependent variable. No significant difference was determined between increasing and decreasing moon. Artemia density was not significantly (P>0.05) higher during new moon compared to full moon. The influence of temperature over Artemia sampling density was clearly noticed, and was a shading factor over the possible effects of any particular lunar phase over Artemia density at any particular sampling time

Nonparametric test performance for trends in water quality with sampling design applications

In this paper four nonparametric tests for monotonic trend detection are compared with respect to their power and accuracy. The importance of comparing powers at equal empirical significance levels rather than nominal levels is stressed. Therefore, an appropriate graphical method is presented. The effect of the sampling frequency is also assessed using Monte Carlo simulations and a trajectory representation that visualizes the dynamics of the trade-off between the type I and type II errors. These methods are applied to compare four nonparametrical tests (seasonal Mann-Kendall, modified seasonal Mann-Kendall, covariance eigenvalue and covariance inversion) under several conditions. It is concluded with respect to the power that it is not worthwhile for the modified seasonal Mann-Kendall test applied to the AR(1) process considered in this paper to increase the sampling frequency from monthly to biweekly for detecting a monotonic trend of 5 percent, 10 percent, or 15 percent of the process variance. Under these conditions the seasonal Mann-Kendall test is highly liberal, while the covariance inversion and the covariance eigenvalue test are conservative. This research is situated in the development of an efficient sampling design for the Flemish water quality monitoring network

High reproducibility of ammonia-oxidizing bacterial communities in parallel sequential batch reactors

Aims: To investigate whether the ammonia-oxidizing bacterial (AOB) communities of replicate nitrifying bioreactors (i) co-evolve or diverge over time and (ii) are stable or dynamic during periods of complete nitrification. Methods and Results: Three sequential batch reactors (SBR) were inoculated with sludge from a municipal wastewater treatment plant, fed with ammonium- enriched tap water and operated in parallel for 134 days. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) demonstrated co-evolvement of the AOB communities over time. During start-up, temporary decreases in nitrification were noticed, and the AOB community rate of change values (Delta(t(week))) were medium to high (12-22%). During the adjacent period of complete nitrification, low AOB community dynamics were observed (Delta(t)(week) < 5%). Further pragmatic processing of the DGGE profiles revealed a high range-weighted richness and a medium functional organization of the AOB communities. Conclusions: After a start-up period, high functional stability and low dynamics of the AOB communities were observed. Deterministic rather than stochastic driving forces led to AOB community co-evolvement in the replicate SBR. Significance and Impact of the Study: Replicates in identical set-ups are reproducible, and pragmatic processing of DGGE patterns is a straightforward tool to score and compare the functionality of the bacterial communities