Issue |
Annls Limnol.
Volume 19, Number 3, 1983
|
|
---|---|---|
Page(s) | 229 - 234 | |
DOI | https://doi.org/10.1051/limn/1983027 | |
Published online | 15 August 2009 |
Assessment of the trophic state of a water body
Evaluation de l'état trophique d'un plan d'eau
Department of Physical and Natural Sciences. Commission of the European Communities. J.R.C. 21020 ISPRA (VARESE) ITALY
The difference in point of view between the limnologist and the public on the trophic level of a water body is discussed in relation to actions promoted by administrators. Numerical and probabilistic classification, models, "trophic indices" and biological indicators for assessing the trophic degree of lakes are briefly illustrated. The contribution of the OECD's "Eutrophication programme" (1971-1979) to the assessment of the trophic degree of lakes is relevant. In agreement with Vollenweider's model, this programme adopted as a guide-line the relationship between phosphorus load from the watershed and the phosphorus concentration in the lake water and between this concentration and that of phytoplankton, expressed as chlorophyll concentration. These relationships are statistically significant but a certain number of lakes deviate from them. These deviations and their causes are considered ; for example, nutrient release from sediments, short hydrological relention time, high mineral turbidity, excessive development of macrophytes, non available forms of phosphorus, high predation pressure by zooplankton. The opportunity to take into consideration the influence of toxic pollutants in eutrophicated water bodies is emphasized. To compare the trophic degree of lakes laying at different latitudes, the pattern of solar radiation and temperature should be considered, in addition to nutrient loading. As a case study to show the difficulties involved in assessing the trophic degree of a lake and identifying the causes of its evolution the results from a study carried out from 1969 to 1980 on the small alpine lake Monate (Northern Italy) are discussed.
Résumé
La perception du niveau trophique d'un plan d'eau par les limnologistes et par le public est discutée par rapport aux actions engagées par les administrations. Les critères d'évaluation du niveau trophique des lacs - classifications, modèles, indices trophiques, indicateurs biologiques - sont brièvement illustrés. En accord avec le modèle de Vollenweider, le "Programme Eutrophisation" de l'O.C.D.E. (1971-1979) a adopté comme fondement les relations entre la charge de phosphore, les concentrations de cet élément dans l'eau et la biomasse de phyto exprimée en concentration de chlorophylle. Ces relations sont statistiquement significatives, mais un certain nombre de lacs font exception. Ces exceptions et leur cause (p. ex relargage du phosphore par les sédiments, faible temps de rétention hydraulique, forte turbidité minérale, développement excessif de macrophytes, biodisponibilité du phosphore, forte pression prédatrice du zooplancton) sont évoquées. Le rayonnement solaire et la température doivent également être pris en considération pour comparer le niveau trophique de lacs sous différentes latitudes. Les difficultés rencontrées pour évaluer le degré de trophie d'un lac et identifier les causes de son évolution sont illustrées par des résultats d'une étude conduite en 1969 et en 1980 sur un petit lac alpin du nord de l'Italie, le lac Monate.
© Masson, 1983
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.