Abstract
Lake Maggiore underwent a process of eutrophication in the course of the 1960s and 1970s which caused the lake status to change from oligotrophy to meso-eutrophy, sewage phosphorus being the main responsible factor. Starting from the late 1970s the P load has been gradually reduced, so that total phosphorus in-lake concentration is now below 10 µg l-1 at winter mixing, compared to a maximum value of 30 µg l-1 in 1978. Nearly two decades after the start of this reversal in trophic conditions, long-term analyses become fruitful, not least because of a scarcity of published long-term data on lake re-oligotrophication, and consequently of agreed predictions on specific points. This paper presents such an analysis, regarding some phytoplankton characteristics (numbers, biovolume, cell size, chlorophyll a, species richness and composition) and their mutual relations in the time series 1981-1995, as well as recent primary production compared with early observations. Notwithstanding phosphorus reduction, the phytoplankton remained quite stable for many years. Only after 1987, when TP concentration fell to about 15 µg l-1 at mixing, definite changes in species diversity and composition appeared. At the same time, average cell size decreased abruptly and persistently, together with chlorophyll and total biovolume while cell numbers were unchanged or rising. Annual primary production was halved in comparison to a past reference period and the efficiency of the photosynthetic process was apparently enhanced.
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References
American Public Health Association A.P.H.A., 1992. Standard methods for the examination of water and wastewater. 18th Edition. APHA, Washington D.C..
Azam, F., B. C. Cho, D. C. Smith & M. Simon, 1990. Bacterial cycling of matter in the pelagic zone of aquatic ecosystems. In M. M. Tilzer & C. Serruya (eds), Large lakes: ecological structure and function. Springer Verlag, New York 24: 477–488.
Bertoni, R. & C. Callieri, 1993. Organic carbon trend during the oligotrophication of Lago Maggiore. In R. de Bernardi, R. Pagnotta & A. Pugnetti (eds), Strategies for lake ecosystem beyond 2000. Mem. Ist. ital. Idrobiol. 52: 191–205.
Bertoni, R., C. Callieri, G. Morabito, M. L. Pinolini & A. Pugnetti, in press. Quali-quantitative changes in organic carbon production during the oligotrophication of Lake Maggiore, Italy. Verh. int. Ver. Limnol. 26: 300–304.
Calderoni, A., R. de Bernardi & D. Ruggiu, 1993. Osservazioni conclusive. Chimismo delle acque ed evoluzione trofica. In C.N.R. Istituto Italiano di Idrobiologia, Ricerche sull'evoluzione del Lago Maggiore. Aspetti limnologici. Campagna 1992 e Rapporto quinquennale 1988–1992 (ed.), Commissione Internazionale per la protezione delle acque italosvizzere: 111–114.
Calderoni, A., R. Mosello, A. Pranzo & G. Tartari, in press. Chimica lacustre. In C.N.R. Istituto Italiano di Idrobiologia, Ricerche sullevoluzione del Lago Maggiore. Aspetti limnologici. Campagna 1995 (con sintesi degli anni 1993–1994) (ed.), Commissione Internazionale per la protezione delle acque italosvizzere.
Currie, D. J., 1990. Large scale variability and interactions among phytoplankton, bacterioplankton and phosphorus. Limnol. Oceanogr. 35: 1437–1455.
Danish Standards Association (Dansk Standardiseringsråd), 1982. Water Quality – Incubator method for determining the carbon assimilation by plankton algae using 14C technique. Dansk Standard, DS/R 293.
de Bernardi, R., G. Giussani, M. Manca & D. Ruggiu, 1988. Longterm dynamics of plankton communities of Lago Maggiore (Italy). Verh. int. Ver. Limnol. 23: 729–733.
Edmondson, W. T., 1991. The Uses of Ecology. Lake Washington and Beyond. Univ. Washington Press, Seattle, 329 pp.
Harris, G. P., 1986. Phytoplankton Ecology. Chapman and Hall, London, 384 pp.
Harris, G. P., 1994. Pattern, process and prediction in aquatic ecology. A limnological view of some general ecological problems. Freshwat. Biol. 32: 143–160.
Gächter, R., 1972. Die Bestimmung der Tagesraten der planktischen Primärproduktion – Modelle und insitu Messungen. Schweiz. Z. Hydrol. 34: 211–244.
Gaedke, U.& A. Schweizer, 1993. The first decade of oligotrophication in Lake Constance. I. The response of phytoplankton biomass and cell size. Oecologia 93: 268–275.
Lee, S. & J. A. Fuhrman, 1987. Relationships between biovolume and biomass of naturally derived marine bacterioplankton. Appl. Envir. Microbiol. 53: 1298–1303.
Manca, M., A. Calderoni & R. Mosello, 1992. Limnological research in Lago Maggiore: studies on hydrochemistry and plankton. Mem. Ist. ital. Idrobiol. 50: 171–200.
Mosello, R.& D. Ruggiu, 1985. Nutrient load, trophic conditions and restoration prospects of Lake Maggiore. Int. Revue ges. Hydrobiol. 70: 63–75.
Platt, T., 1971. The annual production of phytoplankton in St. Margaret's Bay, Nova Scotia. J. Cons. Explor. Mer 33: 324–333.
Reynolds, C. S., 1988. Functional morphology and the adaptive strategies of freshwater phytoplankton. In C. D. Sandgren (ed.), Growth and Reproductive Strategies of Freshwater Phytoplankton. Cambridge University Press, Cambridge: 388–433.
Ruggiu, D., 1989. Indagini sul fitoplancton. In Relazione conclusiva delle indagini limnologiche relative al Lago Maggiore. Commissione internazionale per la protezione delle acque italosvizzere. Rapporto quinquennale 1983–1987: 65–77.
Ruggiu, D., 1993. Osservazioni conclusive. Considerazioni generali sull'evoluzione a lungo termine dei popolamenti planctonici. Fitoplancton. In C.N.R. Istituto Italiano di Idrobiologia, Ricerche sull'evoluzione del Lago Maggiore. Aspetti limnologici. Campagna 1992 e Rapporto quinquennale 1988–1992 (ed), Commissione Internazionale per la protezione delle acque italosvizzere: 115–116.
Ruggiu, D. & C. Saraceni, 1977. Fitoplancton, clorofilla e produzione primaria nel Lago Maggiore durante gli anni 1972–1973. Mem. Ist. ital. Idrobiol. 34: 57–78.
Ruggiu, D. & P. Panzani, 1988. Indagini sul fitoplancton. In: C.N.R. Istituto Italiano di Idrobiologia, Ricerche sull'evoluzione del Lago Maggiore. Aspetti limnologici. Programma quinquennale 1983–1987. (Campagna 1986) (ed.), Commissione Internazionale per la protezione delle acque italosvizzere: 65–71.
Ruggiu, D., P. Panzani & A. Candido, 1982. Indagini sul fitoplancton. In C.N.R. Istituto Italiano di Idrobiologia, Ricerche su studi e ricerche condotti nel bacino de Lago Maggiore. (Campagna 1981) (ed.), Commissione Internazionale per la protezione delle acque italosvizzere: 189–217.
Sas, H. (ed.), 1989. Lake restoration by reduction of nutrient loading: Expectations, Experiences, Extrapolations. AcademiaVerlag Richarz, St. Augustin, 497 pp.
Sommer, U., U. Gaedke & A. Schweizer, 1993. The first decade of oligotrophication in Lake Constance. II. The response of phytoplankton taxonomic composition. Oecologia 93: 276–284.
Tilzer, M. M., U. Gaedke, A. Schweizer, B. Beese & T. Wieser, 1991. Interannual variability of phytoplankton productivity and related parameters in Lake Constance: no response to decreased phosphorus loading? J. Plankton Res. 13: 755–777.
Willén, E., 1987. Phytoplankton and Reversed Eutrophication in Lake Mälaren, Central Sweden, 1965–1983. Br. phycol. J. 22: 193–208.
Willén, E., 1992. Longterm changes in the phytoplankton of large lakes in response to changes in nutrient loading. Nord. J. Bot. 12: 575–587.
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Ruggiu, D., Morabito, G., Panzani, P. et al. Trends and relations among basic phytoplankton characteristics in the course of the long-term oligotrophication of Lake Maggiore (Italy). Hydrobiologia 369, 243–257 (1998). https://doi.org/10.1023/A:1017058112298
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DOI: https://doi.org/10.1023/A:1017058112298