Chemical,physical and biological changes associated with chara succession in farm ponds

Four farm ponds in various stages of Chara vulgaris succession -from the initial invasion of the alga to its nearly complete replacement-were followed each week from ice cover to ice cover. Chemical, physical, and biological parameters were analyzed in order to determine differences between ponds and to discover the biological and physicochemical factors associated with succession in Chara vulgaris ponds. The data were analyzed statistically by intraclass (single factor) analysis of variance, the Student's t-test, and stepwise multiple regression analysis.The initial invasion of C. vulgaris appeared to be preceded by a lowering of the nutrient levels of the pond by Zygnematales growth and by the substrate-stabilizing growth of Rhizoclonium sp.Chara-dominated ponds had significantly lower free CO₂, bicarbonate alkalinity, and total hardness readings. Carbonate alkalinity, low phytoplankton productivity, high dissolved O₂, low phosphate, and high Secchi disk readings were also characteristic of ponds in which C. vulgaris was dominant.In ponds where C. vulgaris appeared in the process of being replaced, the physicochemical factors were more closely associated with phytoplankton productivity and diversity and less closely with submerged vegetation species.Succession from C. vulgaris domination to a Najas-Potamogeton community appeared to involve shading of the former by the latter and was accelerated by the smothering effect of decaying debris caused by Gloeotrichia sp.In the final stages of succession, turbid conditions resulting from the lack of substrate-stabilizing vegetation and increased phytoplankton growth appear to have discouraged C. vulgaris growth early in the season.