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Assessment of the trophic state of three inner basins in Cataluña (Foix, Besòs y Llobregat) through the aquatic vegetation: Application of a trophic index (IVAM-FBL)

Abstract:

During April, 2005 a survey of the macroscopic aquatic vegetation was carried out in the basins of the Foix, Llobregat, and Besòs rivers with a total of 68 sampling stations. The main objective was to assess the trophic status of those basins by means of a Spanish macrophyte index called IVAM (Macroscopic Aquatic Vegetation Index). Forty-four taxa were identified: 8 genera of Cyanophyta, 5 of Rodophyta, 2 of Xantophyceae, 3 of Bacillariophyceae, 15 of Clorophyta, 8 of Spermatophyta, 1 lichen, and 2 bryophytes (mosses and liverworts). The Llobregat basin was the most diverse (37 taxa), followed by Besòs (33) and Foix (25). The most common taxa were Cladophora, Vaucheria, Oedogonium, Apium, Rorippa and Oscillatoria, along with mosses. Phanerogams were scarce, with Ranunculus, Zannichellia, and Potamogeton as the most common genera. The taxa with the highest IVAM score corresponding to good water quality (tolerance value, vt = 8) were, although scarce, Ranunculus, Cymbella, Rivularia, Nostoc, Tolypothrix, Chroococcus, and Lemanea, which indicate oligotrophic conditions. In good quality waters, although slightly eutrophic (mesotrophic waters vt = 6), the most frequent taxa were Chara, Monostroma, and Hildenbrandia, along with liverworts and one lichen. According to the trophic qualifications provided by the IVAM index, 38.2 % of sites had a good trophic status (classes I and II) while 61.8 % of sites had an altered status. The IVAM response to nutrient concentration (phosphate, ammonium, nitrite, and nitrate) was always significant and a high correlation between IVAM and phosphate concentration (r = 0.71, p < 0.001) can be highlighted, with a value higher than those reached by other diatom and macrophyte indices that use a species-level taxonomic resolution. This supports the advantage of using the IVAM index in the trophic status assessment of rivers since it is not necessary to reach a taxonomic species level to obtain a good response to this kind of disturbance. © Asociación Ibérica de Limnología.