Influences of fathead minnows and aquatic macrophytes on nutrient partitioning and ecosystem structure in two prairie wetlands

Ecosystem structure and sizes of nutrient pools were compared between two p rairie wetlands with contrasting food-web configurations, one site supporti ng a population of fathead minnows and the other fishless. It was hypothesi zed that the fishless wetland would typify the clear-water state, the wetla nd with fish the turbid-water state, and that macrophytes, epiphyton, and i nvertebrates would be the largest nutrient pools in the fishless site, whil e phytoplankton and fish would be the largest pools in the wetland with fis h. Turbidity, water-column sedimentation rates, and amounts of phosphorus a nd nitrogen in epiphyton, macrophytes, metaphyton, phytoplankton, aquatic i nvertebrates, fathead minnows, seston, interstitial water, and sediment wer e assessed in each wetland. Nutrients were apportioned quite differently in these two wetlands. Major phosphorus and nitrogen pools in the wetland wit h fish were phytoplankton, seston, fathead minnows, and macrophytes, wherea s macrophytes, epiphyton, and aquatic invertebrates were the largest pools in the fishless site. These differences likely reflect direct and indirect influences of fathead minnows and submerged aquatic plants. Our results sup port the hypothesis that low macrophyte abundance and dense populations of fathead minnows favor turbid conditions in deep, semipermanent prairie wetl ands.