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Introducció a l’estudi limnològic de la llacuna del Ter vell (Baix Empordà) = Introduction to the limnology of Ter Veil lagoon (Baix Emporda , Catalonia, Spain)

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Ter Vell is a small (0.8 Ha) and shallow (usually less than 1 m deep) lagoon locatedin one of the ancient Ter River mouths. A one year (biweekly samples) study wascarried out in 1984 to describe some limnological characteristics of the lagoon.Conductivity varied between 1 and 39 mS/cm. It was 1-3 mS/cm higher in theSouth basin (closer to the sea) than in the North one. Maximum values were observedin autumn-winter and minimum ones in summer. Phosphorus concentrations were most ofthe year over 4 u.g-at P-PO;-/I. The highest concentrations (50 ^Lg-at/I) were observed insummer. Phosphorus concentrations from October to May were positively correlated to conductivity,while those from May to September were not. Oxydized dissolved inorganic nitrogenwas very low all the year round (less than 4 pg-at/I).Phytoplankton assemblages were between 104 and 4.105 cells per ml mostly becauseNannochloris sp., which was overwhelming during all the year. Accompanying species wereMonoraphidium sp. pl., Actinastrum hantzschii, Dictyiosphaerium pulchellurn, Cyclotella kutzingiana,Lepocinclis ovum and Ochromonas sp. pl. during summer, and Dunaliella sp., Hemiselmisrufescens, Pseudopedinella pyriformis, Katodinium rotundatum and Oxyrrhis marinaduring winter. The amount of chlorophyll a per cell was always very low (between 0,1and 2 pg per cell). During summer the most abundant zooplankters were Brachionus sp. pl.,Moina micrura, and Acanthocyclops g. vernalis. During the cold months Notholca squamula,Synchaeta sp., and Epiphanes brachionus were the most abundant. Maximum abundanceschanged from 2,000 individuals/I in summer to 600 individuals/I in winter.Ter Vell is an eutrophic lagoon with marked differences between chemical and biologicalcharacteristics of different periods of the year. Two main periods can be distinguishedrelated to temperature. External factors, mainly freshwater and sea water inflows,also control the differences observed

Institut d’Estudis Catalans. Institució Catalana d’Història Natural