EFFECTS OF SUSPENDED-SOLIDS ON THE ESTABLISHMENT AND GROWTH OF EGERIA-DENSA

To identify levels of suspended solids (SS) in Lake Waahi (Huntly, New Zealand) favourable for the re-establishment of Egeria densa Planchon , shoots were grown in 2 m deep tanks filled with water transported fr om the lake and maintained at selected SS loadings between 5 and 40 g m-3 (predominantly comprised kaolinitic clays). Plant growth was measu red over periods of 44-47 days in spring, summer and autumn. Highest r elative growth rates (RGR) were recorded in summer (maximum 40 mg g-1 day-1). Egeria propagules growing from a depth of 1.85 m showed positi ve growth responses at SS levels up to approximately 2 5 g m-3 (K(d) a lmost-equal-to 1. 7 5 ) in spring and autumn, and approximately 3 5 g M-3 (K(d) almost-equal-to 1.95) in summer. At SS levels up to 15 g m-3 (K(d) = 1.5 m-1), growth was little affected during summer, while dur ing spring and autumn biomass accumulation was reduced to about 60% an d RGR values to about 70% of the maximum seasonal values recorded. Ege ria shoots showed maximum elongation at about 10-20 g m-3 SS (K(d) = 1 .3-1.65). Plant architecture became less branched with increasing SS a nd the number of roots produced decreased. Implications for the establ ishment of Egeria in turbid waters are discussed.