WATERFOWL FECES AS A SOURCE OF NUTRIENTS TO A PRAIRIE WETLAND - RESPONSES OF MICROINVERTEBRATES TO EXPERIMENTAL ADDITIONS

We tested the hypothesis that inorganic nutrients released from waterf owl feces would stimulate primary production, thereby affecting microi nvertebrate grazers, by making controlled additions of waterfowl feces to fishless wetland enclosures and measuring the response of plankton ic and phytophilous cladocerans, copepods, and rotifers. Feces were ad ded in two pulses, four weeks apart, to duplicate enclosures at a 'hig h' level (115 g m(-2) wet feces), simulating the total P load (1.6 g m (-2)) applied in an earlier fertilization experiment, and a 'low' leve l (11.5 g m(-2)). Density of microcrustacean grazers in the water colu mn increased in response to both feces additions, although the respons e was more noticeable after the second feces addition. After each addi tion, cladocerans (predominantly Ceriodaphnia dubia) and copepodites i n the water column (and associated with periphyton on acrylic rods in the water column) were most abundant in enclosures with high loading. In contrast, density of microcrustacean grazers associated with macrop hytes (predominantly Chydorus spp. and copepodites) increased in respo nse to the second feces addition only. Microinvertebrate density incre ased only slightly with low feces loading. Community composition showe d similar changes over the season in all enclosures, and differences i n relative abundance were not attributable to treatment effects. Given the small effects produced by nutrient additions that greatly exceed natural loadings, nutrients leaching from waterfowl feces do not appea r to have a significant impact on the foodweb of this wetland.