Seasonal changes in biomass of charophytes in shallow lakes in the northwest of Spain

Seasonal changes in aboveground biomass of submerged macrophytes were recorded in three shallow lakes in northwest Spain from May 1996 to June 1997. The biomass of a monospecific community (Chara globularis) and of several communities with high charophyte coverage (C. globularis-Myriophyllum. alterniflorum, C. globularis-Potamogeton gramineus and Nitella translucens-Potamogeton natans) were studied monthly. The weather and hydrological regime had a strong influence on the seasonal biomass patterns and on between-the-year differences in the biomass of macrophytes. The biomass in the monospecific C. globularis community showed a bimodal pattern, with maximum in mid-July (128 g DW m(-2)) and late autumn (165 g DW m(-2)). Chara overwintered as a green plant and during the subsequent growth period, characterised by high temperature and low rainfall, reached a maximum of 305 g DW m(-2) (June 1997). The highest biomass of C. globularis in the Chara-Myriophyllum community was reached in July (Sentiz: 160 g m(-2), Redos: 204 g m(-2)), while the minimum (Sentiz. 10 g m(-2); Redos: 3 g m(-2)) was recorded in February or March. M. alterniflorum (average biomass: 95 g m(-2)) was a better competitor than C. globularis in Redos lake and appeared to be favoured by the early beginning of the growing season in 1997 and by the later increase in the water level. The biomass of N. translutcens (average biomass: 64 g m(-2)) showed a high stability during the study period, but lacked a well-defined seasonal biomass pattern. R natans had a marked maximum biomass in August (426 g m(-2)). Although the stability of the Potamogeton population was low, shading did not have a significant influence on the development of Nitella biomass. (C) 2002 Elsevier Science B.V. All rights reserved.