Structure, biomass, production and depth distribution of periphyton onartificial substratum in shallow lakes with contrasting nutrientconcentrations

摘要

To examine how the vertical distribution of periphytic biomass and primary production in the upper 0-1 m of the water column changes along an inter-lake eutrophication gradient, artificial substrata (plastic strips) were introduced into the littoral zones of 13 lakes covering a total phosphorus (TP) summer mean range from 11 to 536 mu g L super(-1). Periphyton was measured in July (after eight weeks) and September (after 15 weeks) at three water depths (0.1, 0.5 and 0.9 m). Periphyton chlorophyll a concentration and dry weight generally increased with time and the communities became more heterotrophic. Mean periphytic biomass was unimodally related to TP, reaching a peak between 60 and 200 mu g L super(-1). The proportion of diatoms in the periphyton decreased from July to September. A taxonomic shift occurred from dominance (by biovolume) of diatoms and cyanobacteria at low TP to dominance of chlorophytes at intermediate TP and of diatoms (Epithemia sp.) in the two most TP-rich lakes. The grazer community in most lakes was dominated by chironomid larvae and the total biomass of grazers increased with periphyton biomass. Community respiration (R), maximum light-saturated photosynthetic rate (P sub(max)), primary production and the biomass of macrograzers associated with periphyton were more closely related to periphyton biomass than to TP. Biomass-specific rates of R, P sub(max) and production declined with increasing biomass. Mean net periphyton production (24 h) was positive in most lakes in July and negative in all lakes in September. Net production was not related to the TP gradient in July, but decreased in September with increasing TP. The results indicate that nutrient concentrations alone are poor predictors of the standing biomass and production of periphyton in shallow lakes. However, because periphyton biomass reaches a peak in the range of phosphorus concentration in which alternative states occur in shallow lakes, recolonisation by submerged macrophytes after nutrient reduction may potentially be suppressed by periphyton growth.