to test the hypothesis that water-level changes in Great Lake coastal wetlands influence nutrient cycling and also food resources for fish and wildlife by affecting plant litter decomposition rates and communities of detritivorous invertebrates.

This project will help determine how short-term water-level fluctuations from seiches affect macroinvertebrate populations and detritus decomposition, which influence other important wetland processes such as plant productivity, algal blooms, and food resources for gamefish and wildlife (e.g., shorebirds, waterfowl). Current strategies to manage Great Lake coastal marshes often include constructing dikes to minimize damage from storms and carp, but this also eliminates effects of seiches in these wetlands. The information from these projects will be useful to wetland managers to determine potential effects of diking on nutrient cycling and invertebrate food resources for fish and wildlife. Potential users of these data are wildlife management agencies such as the U.S. Fish and Wildlife Service, State Fish and Game management agencies, and private waterfowl hunting clubs. These studies will also provide preliminary data in support of a larger proposal to test effects of water-level fluctuations on ecosystem processes in Great Lake coastal wetlands.

I will test this hypothesis in two ways. First, I will determine biomass and diversity of macroinvertebrate assemblages in areas that are permanently flooded and those that are dewatered during seiche events. For this, I will use Ekman dredge samplers to collect invertebrates in > 1-m, 0.5-m, and 0.1-m water depths in the Crane Creek Estuary marsh (Ottawa National Wildlife Refuge, Lucas Co., OH) that is open to Lake Erie and fluctuates with lake water-level changes. This will characterize invertebrates that are associated with habitats with permanent flooding, intermittent dewatering, and frequent dewatering, respectively. Second, I will test how fluctuating water levels affect cattail litter decomposition rates using plant litter bag experiments. For this, I will place preweighed cattail samples in permanently flooded, intermittently dewatered, and adjacent non-flooded sites in this coastal marsh. I will collect litter bags throughout the summer and determine changes in biomass and nutrient content (phosphorous, nitrogen) of cattail litter. Biomass and diversity of macroinvertebrates feeding on plant litter will also be determined and compared among these habitats.

This study compared leaf litter decomposition and aquatic macroinvertebrate communities among different microhabitats in Crane Creek Marsh, a Lake Erie coastal wetland. Mesh litter bags with Nymphaea odorata leaves were placed along a non-flooded transect and three different water depths (10 cm, 40 cm, and 70 cm below the water surface). Daily water levels in this marsh fluctuated a mean 15 cm each day due to wind driven changes (e.g. seiches), and seasonal changes were over 45 cm. Therefore, habitats ranged from terrestrial to intermittently flooded to permanently flooded. Litter bags were collected in each transect from 11 July 2000 to 4 September 2000, and dry weight, percent organic matter, percent nitrogen, and percent carbon were measured in the litter. Invertebrate samples were collected at the same time and identified to the lowest taxonomic group.

As expected decomposition was slowest in the non-flooded transect and fastest at the 10 cm transect (intermittently flooded habitat). Dissolved oxygen levels were highest in the 10 cm transect, suggesting that environmental conditions were most favorable in this habitat for microbial growth. Nymphaea litter decayed surprisingly quickly in all flooded transects, and decay rates in this study (k day^-1= 0.07-0.08) were higher than previously reported for Nymphaceae litter in freshwater habitats. These data show that leaf breakdown can be extremely high in shallow zone in coastal wetlands, perhaps due to mechanical fragmentation or microbial decomposition.

Invertebrate colonization of leaf litter was different among transects, with the highest diversity and population numbers in the 10 cm transect. Detritivores numbers were also highest in the 10 cm transect and lowest in the terrestrial transect. These results indicate that leaf litter quality promoted the highest invertebrate productivity in shallow habitats in this coastal wetland.