Simon A. Visser

Ultrastructural localization of N‐acetylglucosamine residues in the cell wall of Gigaspora margarita throughout its life‐cycle

The cell ultrastructure of the VAM fungus Gigaspora margarita was examined, and its N‐acetylglucosamine content and distribution were assessed by means of WGA/ovomucoid‐gold labelling. The various ontogenic stages of the fungus were studied with particular reference to cell walls. The results provide new information on chitin incorporation during spore wall development. A decrease of chitin was observed which was correlated to the structural simplification of the fungus wall throughout its life‐cycle. This suggests an involvement of chitin in specific biological functions such as mechanical resistance and plasticity.

Algal bioassays: their significance in monitoring water quality with respect to nutrients and toxicants

The review focuses on the use of primary producers as a biological tool for evaluating the impact of damage by human activity (eutrophication, toxicity) on the aquatic environment. Studies are discussed following a reductionist approach by using algal bioassays (Selenastrum capricornutum). Variations of algal growth potential (AGP) within watersheds show the impact of human activities such as agriculture and urbanization, on water quality. The study of variation of the AGP in time allowed the investigation of the effect of abiotic (temperature, flow rate) and biotic factors (indigenous primary production) on the concentration of nutrients potentially available to phytoplankton. Seasonal changes of the AGP have further shown the impact of non-point (runoff) or point sources (sewage effluents) on the aquatic system. A staggered relationship was observed between AGP values and chlorophyll a content of indigenous phytoplankton. Values obtained in the laboratory by means of this type of approach would therefore appear to be transferably to natural systems.S. capricornutum was also used to identify toxic characteristics of substances (in pure form or used in formulations) and effluents released into the environment. It was shown that the user of bioassays should use care when evaluating results from tests requiring pretreatment such as storage, autoclaving and filtration. Cautious interpretation is also recommended in order to distinguish between effects of growth-limiting essential elements and the presence of toxic substances.In general it appears from this review that the AGP provides helpful information for a sound management of the aquatic environment.

Potential eutrophication assessment in rivers; relationship between produced and exported loads

In contrast with biological processes in lacustrine environments, the physical characteristics of river waters greatly complicate the relationship between nutrient input and primary productivity.In this paper a new approach to quantify this relationship is developed, linking land use within the watershed to the bioavailability of nutrients in the receiving waters. It estimates by two different ways an enrichment index derived from N/P ratios.A load model links land-use within the watershed area to nutrient export, and allows the estimation of the potential enrichment index from the ratio of calculated annual exports of nitrogen and phosphorus. This index value correlates well with the real enrichment index representing the annual mean value of the corresponding measured ratios in running waters. The latter index can then be related to nutrient availability expressed by chl-a and the algal growth potential.This model, established from 7 sampling stations on the Yamaska-North river, allowed assessment of nutrient bioavailability in the river water as a function of hydrological (low or high water flow) as well as of seasonal (summer or winter) events.