Spatial distribution of aquatic macrophytes in the recent reservoir of Ste Croix, Provence, France.

¹ Laboratoire d'Hydrobiologie Marine et Continentale, URA 1355-CNRS, Université de Montpellier II, Place E. Bataillon, F-34095 Montpellier Cedex 5.
² Laboratoire d'hydrobiologie. Universite de Provence, 3, place Victor Hugo - 13331 Marseille Cedex 3.

Abstract

Investigations on horizontal and vertical distribution of aquatic vegetation have been carried out in the regulated lake Sainte Croix from 1985 to 1987. This reservoir, being filled in 1974, has been recently colonized by submersed vegetation. Mac- rophyte data have been collected by using direct observations, echosoundings and grapnel sampling. Two remarkable macroalgae (Tolypella glomerata, Charophyta from temporary water bodies with high alkalinity, and Vaucheria nicholsii, Xanthophyta less known in Europe) and six cosmopolitan phanerogams typical of alkaline waters were recorded in the littoral zone, especially in the bays of Bauduen, Les Salles and Moustiers. Macroalgae reached a maximum growth during spring. Phanerogams developed the most in summer. Myriophyllum spicatum was the dominant species in the whole lake, being associated with Potamogeton crispus in the bay of Moustiers and P nodosus in the bays of Les Salles and Bauduen. Macrophyte depth ranged from 1.9 to 11.3 m. Mean depth was 4.4 m for all the species, varying from 3.5 m (Potamogeton pusillus) to 5.5 m (K nicholsii). The capacity of several predictive models to predict the depth distribution of macrophytes in relation to transparency (Secchi disc) and water level fluctuations is discussed. The best estimation occurs with a model based on mean annual regulation level. Some other environmental parametres, such as nutrient-rich inflows, particularly from sewage supplies, may explain the clustered vegetation communities in some localized stations.