Benthic macroinvertebrates as indicators of the water quality in Bulgaria: A case-study in the Iskar river basin

Macroinvertebrates were sampled at 15 locations in the Iskar river basin in Bulgaria for the purpose of water quality assessment. Based on the chemical as well as the biological parameters, it was concluded that the water quality was still good upstream of Sofia, however, despite a huge waste water treatment plant, a strong decrease was observed when the river passed Sofia. Due to self-purification and dilution, a gradual amelioration of the water quality was observed 40 and 80 km downstream of Sofia, however, water quality was still insufficient. The Irish Biotic Index (IBI), which is currently used in Bulgaria for the national monitoring of macroinvertebrates for water quality assessment, does not fulfil the requirements of the European Union Water Framework Directive (WFD). The Multimetric Macroinvertebrate Index Flanders (MMIF), on the contrary, is a WFD compliant method developed for the northern part of Belgium, which is based on (1) the total number of taxa, (2) the number of Ephemeroptera, Plecoptera and Trichoptera taxa, (3) the number of other sensitive taxa, (4) the Shannon–Wiener index and (5) the mean tolerance score. The outcome of this MMIF was strongly correlated with the outcome of the Irish Biotic Index. Therefore, it should be possible to develop a similar multimetric index for macroinvertebrates to evaluate the biological water quality in Bulgaria without much effort.     

Water use efficiency in an arid watershed: a case study

Integrated Water Resource Management (IWRM) becomes increasingly important in arid watersheds, where water resources are scarce and demands are rising under increased population pressure. In this case study, we present the results from the Elqui Valley in Chile, where water resources are shared between agriculture, mining operations, hydropower generation and drinking water for nearby cities. An IWRM model was applied to visualize water resources distribution in the catchment and determine irrigation and water use efficiencies. After calibration with observed surface and groundwater measurements, the model showed large differences in efficiencies between different irrigation sectors. Most notably, irrigation sectors with the highest irrigation security, i.e., higher water rights per hectare, were characterized with lower water use efficiencies. Frequent water deficits were present in sectors downstream of the main reservoir, which was related to limited water rights per hectare, lower irrigation efficiencies and higher water demands due to larger agricultural areas. In subsequent scenario analyses, the model was used to evaluate the impact of improved irrigation and water use efficiencies in these downstream sectors, to confirm an important reduction in water deficits, except for drought years when surface water resources are insufficient. In a third scenario, groundwater resources were allowed to compensate for water deficits, effectively reducing these in most irrigation sectors, especially during droughts. Expansion of the current agricultural area by 37% was evaluated, as a future scenario, and was found to be unsustainable, as aquifer levels are lowered to such levels that make annual recharge insufficient.     

Multimetric Macroinvertebrate Index Flanders (MMIF) for biological assessment of rivers and lakes in Flanders (Belgium)

The European Water Framework Directive requires that member states assess all their surface waters based on a number of biological elements, including macroinvertebrates. Since 1989, the Flemish Environment Agency has been using the Belgian Biotic Index for assessing river water quality based on macroinvertebrates. Throughout the years, the Belgian Biotic Index has proven to be a reliable and robust method providing a good indication of general degradation of river water and habitat quality. Since the Belgian Biotic Index does not meet all the requirements of the Water Framework Directive, a new index, the Multimetric Macroinvertebrate Index Flanders (MMIF) for evaluating rivers and lakes was developed and tested. This index was developed in order to provide a general assessment of ecological deterioration caused by any kind of stressor, such as water pollution and habitat quality degradation. The MMIF is based on macroinvertebrate samples that are taken using the same sampling and identification procedure as the Belgian Biotic Index. The index calculation is a type-specific multimetric system based on five equally weighted metrics, which are taxa richness, number of Ephemeroptera, Plecoptera and Trichoptera taxa, number of other sensitive taxa, the Shannon-Wiener diversity index and the mean tolerance score. The final index value is expressed as an Ecological Quality Ratio ranging from zero for very bad ecological quality to one for very good ecological quality. The MMIF correlates positively with dissolved oxygen and negatively with Kjeldahl nitrogen, total nitrogen, ammonium, nitrite, total phosphorous, orthophosphate and biochemical and chemical oxygen demand. This new index is now being used by the Flemish Environment Agency as a standard method to report about the status of macroinvertebrates in rivers and lakes in Flanders within the context of the European Water Framework Directive.     

A Note on Tree Deaths during the Current (2001–?) Drought in South-eastern Australia

Tree deaths over large areas during droughts are uncommon. In the semi-arid zone of New South Wales (NSW) such events were last reported during the prolonged droughts of 1895–1903 and 1939–45, though whether caused solely by drought is open to question. Anecdotal and quantitative evidence during the current prolonged drought (2001–?) in NSW's sub-humid zone (where deaths are localised) and semi-arid zone (where deaths are more extensive) suggest that climatic conditions are comparable to, and perhaps more severe than, those of the earlier prolonged droughts. It is suggested that lack of access to deep soil moisture due to inherent shallow rooting, or due to site conditions, is the most likely cause; and that this may be associated with higher than optimal tree densities in cohorts of trees that arose from previous regeneration events during periods of well above average rainfall. A more thorough examination of the extent and severity of this event is warranted.     

Statistical tests for changes in the amplitude, frequency or phase of a sinusoidal variation

The problem considered is that of testing for small changes over time in the properties of a sinusoidal signal contaminated by noise. Two test statistics are proposed. The first is a frequency domain statistic based on the spectrum of the data, while the second is a time domain statistic due to Nyblom. Power studies are used to show that the Nyblom statistic is generally the better. The form of the Nyblom statistic appropriate for phase-change tests also performs well in testing for frequency changes.     

Is there evolution in the infrared Tully–Fisher relation? Comparing two linear regressions

In a recent paper, Puech and co-workers compared K -band Tully–Fisher relations derived for nearby and distant galaxies, respectively. They concluded that the two relations differ, and deduced that there is evolution in the Tully–Fisher relations. The statistical comparison between the two regression lines is re-examined, and it is shown that the statistical test used gives non-significant results. It is argued that better results can be obtained by comparing the 'inverse' Tully–Fisher relations, and it is demonstrated by two different methods that the nearby- and distant-sample relations do indeed differ at a very high significance level. One of the statistical methods described is non-parametric, and can be applied very generally to compare linear regressions from two different samples.     

The numerical determination of the eigenfrequencies of a rotating star

A technique for finding the oscillation spectrum of a rotating star based on the solution of two simultaneous ordinary differential equations is described. Results are presented for someg-modes of the polytrope of index 2. It appears that the functional dependence of frequency on rotational velocity is different for different azimuthal wave numbersm.     

The impact of taphonomic processes on interpreting paleoecologic changes in large lake ecosystems: ostracodes in Lakes Tanganyika and Malawi

Nonmarine ostracodes are often used as proxy indicators for the biotic response to climate as well as anthropogenic changes in large lakes. Their large numbers, small size and sensitivities to environmental conditions make them ideal for assessing how organisms respond to environmental perturbations. However, little is known about the various taphonomic processes related to preserving these organisms in the lacustrine fossil record. Without understanding the amount of time averaging associated with these assemblages, any interpretation of their biodiversity and paleoecology may be problematic.To address these issues, we conducted actualistic experiments to determine transport, time-averaging, and the amount of taphonomic bias in ostracode sub-fossil assemblages. Sand transport experiments revealed significant mixing at all sites at shallower depths and significant mixing on rocky substrates but not sandy ones. Comparisons with ostracode material collected along the experimental transects support this model and demonstrate time averaging in both the sandy and rocky substrates. Preservational models were derived from the experimental data and applied to interpreting the paleobiologic record of ostracodes from piston cores in both Lake Tanganyika and Malawi. The core record reveals assemblages that have undergone significant time-averaging, and in the case of Lake Malawi, preservational degradation. In the core examined from Tanganyika, most assemblages resemble the time-averaged experimental model with respect to species richness, percentage of articulated shells and heavy bias towards adult dead individuals. In the Malawi cores, most of the valves were preserved only as internal molds. The taphonomic signature of these samples resemble the time-averaged assemblages of Tanganyika cores, even though carapaces are not often present.Both the experimental and live/dead valve data suggest significant time-averaging and transport, smearing seasonal-yearly data in some environments involved in using ostracodes to assess biotic changes as a result of climate and or anthropogenically-induced environmental change. Ostracode species richness estimates were impacted by time averaging because transport of dead valve material occurs at high percentages in the shallow depths and on the rocky substrates, suggesting that the ostracode death assemblages in these areas will not reflect living populations. In addition, ecologic models based only upon death assemblages will be less resolved than those based upon live assemblages. A time averaging index was derived using the % dead juveniles ratio, as well as sedimentation rate and information on the population dynamics, if known.