Six man-made wetlands (0.02 ha each) and pen-reared broods of American black ducks (Anas rubripes) were used to assess the effects of reduced pH on the quality of fish- free, palustrine habitat for brood rearing. Acid treatment was assigned randomly among newly constructed wetlands during April through June 1984-85, to simulate depressed pH from snowmelt and spring rain. Sampling of chlorophyll epiphytic growth, zooplankton and macroinvertebrates confirmed reduced productivity of acidified (pH 5.0) versus control (pH 6.8) wetlands. Primary productivity was particularly reduced in acidified wetlands in early spring as indicated by high water transparency and low chlorophyll a concentrations. Chlrophyll a concentrations showed treatment (p = 0.01) and date (p = 0.05) effects, but no interaction, and dry weight of epiphytic growth was lower (p = 0.03) in acidified versus control wetlands. Numbers of zooplankton were similar in experimental wetlands, although controls generally exceeded acidified wetlands in abundance; only a single treatment effect for cladocerans (p = 0.1) was detected. Sweep net samples yielded greater numbers (p = 0.03), taxa (p = 0.01) and biomass (p = 0.07) of macroinvertebrates in control wetlands with gastropods, pelecypods and leeches notably reduced by acidification. Placement of 18 broods (female with four 10-day-old ducklings) for 10-day trials on experimental wetlands revealed limited growth, altered behaviour and marked reduction in survival of ducklings on acidified wetlands. An inadequate number of invertebrates is indicated as the cause for poor duckling productivity on acidified wetlands
