A fields study was conducted to validateconcentrations of zinc in feshwater sediments that are tolerated by benthic macroinvertebrate communities and to determine whether a relationship exists with the acid volatile sulfide (AVS)–simultaneously extracted metal (SEM) model. In both the lake and riverine systems, one sediment type was high in AVS and one low in AVS, which resulted in zinc‐spiked sediments that ranged from low to high SEM to AVS ratios. The colonization trays were sampled seasonally, ranging from 6 to 37 weeks of exposure, and were evaluated using several appropriate benthic indices. Results of the field evaluations at the four test sites confirmed the validity of the AVS‐SEM model, predicting benthic macroinvertebrate effects correctly 92% of the time. In sediments where the SEM to AVS ratio or the AVS and organic (OC)–normalized fractions exceeded 8 and 583 μmol/g of OC, toxicity was observed from the zinc‐spiked sediments. Conversely, when the SEM to AVS ratio or OC‐normalized AVS fractions were less than 2 or 100 μmol/g of OC, no toxicity was observed. In the range of 148 to 154 μmol/g of OC, toxicity varied in two treatments. Total zinc concentrations in sediments showed no relationship to benthic effects. The most impaired benthic community occurred in the high‐gradient stream sediments, which had low OC and AVS concentrations and SEM to AVS ratios of 33 and 44 in the spiked sediments. Five to six benthic metrics were depressed at SEM to AVS ratios of 8.32 and 9.73. The no‐observed‐effect level appeared to be near a SEM to AVS ratio of 2, with slight to no effects between ratios of 2.34 and 2.94. No sites with ratios of less than 2 showed any adverse effects.

Lake Orta (18.2 km2, 1.3 km3, 143 m max. depth) has been severely polluted since industrialisation of its watershed began in 1926, at which time the lake began to receive industrial effluents containing high concentrations of copper and ammonia. Chromium-, nickel-, and zinc-rich effluents from plating factories have also contributed to pollution levels, and pH -levels dropped below 4.0 as a result of the oxidation of ammonia to nitrates. More than 60 papers have documented the evolution of the chemical characteristics of both water and sediment, and the sudden decline of plankton, as well as benthos and fish. As a remedial action the lake was limed from May 1989 to June 1990 with 10,900 tons of CaCO3. The treatment was immediately effective in raising the pH and decreasing the metal concentrations in the water column, and plankton and fish communities quickly rebounded. However, the chemical characteristics of sediments were influenced by the liming to a much lesser extent. Since 900 tons of copper and the same amount of chromium were contained in the top 10 cm of sediment, it appears likely that the sediment could potentially act as a current and future source of these metals to the water column. This observation has resulted in the implementation of a vigorous monitoring regime to track the post-liming recovery of Lake Orta

The paper presents results from seed germination and root elongation tests for the evaluation of Lake Orta sediment contamination. The protocol for this test was developed after a literature survey and careful investigation of the proper conditions for obtaining the germination of commercially available seeds of several plants. Cucumis sativus, Lactuca sativa, and Lepidium sativum were finally chosen and used to detect the phytotoxicity of both liquid and solid phases of Lake Orta sediments. To assess whether exchange at the water – sediment interface could represent a hazard for the environment and the actual bioavailability of the toxicants present into the sediments, the phytotoxicity of samples collected in 1992, 1994, 1996, 1997, and 1998 from selected stations was tested on seeds of three different plant species (Lactuca sativa, Lepidium sativum and Cucumis sativus). The obtained results allow drawing distribution maps of the germination index, which confirm the persistence of toxic effects. However, the lake seems to positively respond to the restoration treatment, since the more contaminated layers of sediments are presently buried under less toxic sediments

ABSTRACT

1985.Geographic patterns of chromosomal variation in populations of the grasshopper (Trimerotropis pallidipennis) from southern Argentina. Can. J. Genet. Cytol. 27: 259-271. Geographic variation has been studied on seven south Argentina populations of Trimerotropis pallidipennis polymorphic with respect to centromere position. Univariate and multivariate statistical analysis were used to assess interpopulation relationships by considering the inversion frequency, the chiasma frequency, and the population distance from the Andes, which is considered to be the hypothetical pathway of migration of this typically North American species to southern latitudes. A cluster analysis indicated strong chromosomal differentiation between the almost monomorphic populations in the Andes' "precordillera" and the highly polymorphic populations in more eastern locations. It also showed that chromosomal similarity between populations could be predicted by geographic proximity. No attempt has been made to relate such a pattern of chromosome variation to ecological data. The lack of any clear relationship with phytogeographic regions or climatic characteristics suggests that microenvironmental factors related to aridity may be important in this case. The presence of inversions within a population has a notable effect on chiasma frequency and position. Chiasmata are suppressed within the inverted region of both inversion heterozygotes and homozygotes. The allelic sequences in the inverted region are thus preserved from recombination and exchanges are limited to terminal regions. Key words: geographic variation, chromosome polymorphism, chiasma frequency, B chromosome, pseudomultiple associations. GONI, B., E. S. DE VAIO, M. BELTRAMI, M. S. LEIRA, M. CRIVEL, F. PANZERA, P. CASTELLANOS et A. BASSO. 1985. Geographic patterns of chromosomal variation in populations of the grasshopper (Trimerotropis pallidipennis) from southern Argentina. Can. J. Genet. Cytol. 27: 259-271.La variation geographique a ete etudiee chez sept populations de Trimerotropis pallidipennis du sud de 1' Argentine, qui sont polymorphes relativement a la position du centromkre. Des analyses statistiques a une ou plusieurs variables ont ete utilisees pour determiner les relations entre populations, en considerant la frequence d'inversions, la frequence de chiasmata et la distance des populations par rappot aux Andes, qui sont considkrees comme le sentier de migration hypothetique de cette espkce typiquement nord-americaine vers les latitudes du sud. Une analyse de groupes a mis en evidence une forte differenciation chromosomique entre les populations presque monomorphes des Andes "precordillkres" et les populations hautement polymorphes localisees plus a l'est. Cette analyse a aussi demontre que la ressemblance des chromosomes pouvait Ztre predite par proximitk gkographique. Ce mode de variation chromosomique n'a en aucune fason kt6 relik aux donnkes Ccologiques. Toutefois, l'absence de relations claires entre les regions phytogeographiques ou les caracteristiques clima...