Dynamics of natural populations of the dertitivorous mudsnail Potamopyrgus antipodarum (Gray) (Hydrobiidae) in two interconnected Lakes differing in trophic state

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Table 1 Selected characteristics of the two lakes

	Meso-oligotrophic lake	Eutrophic lake
Year created	1960	1967
Surface area (ha)	70	20
Max. depth (m)	30	25
Range 1% light depth (m)	7–11	3–7.5
Range P.PO₄ (μg.1^-1)	0–2	8–304
Range total P (μg.1^-1)	3.5–17	151–365
Range N.NO₃ (μg.1^-1)	130–350	30–1,400
Max. primary phytoplankton prod. (mg C.m^-2.day^-1)	500	8,125
Ca²⁺(mg.1^-1)	61	75
Conductivity (μS.cm^-2)	355	550
pH*	8.2	7.9

Nutrient concentrations at 0.5 m depth. For references see Dorgelo and Gorter (1984).
*taken from Swain et al. (1987).