Toward a Better Understanding of River and Floodplain Ecosystems I
Presiding: M Delong, Winona State University; J Thorp, University of Kansas
NB32F-01 10:30h
Organic Matter Dynamics in a Forested Floodplain of Northwest Spain
The Begonte Atlantic floodplain, a catchment of the Rio Miño in Spain, is unregulated and still retains a native floodplain forest. To study how hydrology and forest characteristics influence organic matter (OM) inputs and processing in aquatic and terrestrial habitats, we measured forest production and nutrients in for three years at four locations along the Begonte floodplain. The study areas differ in forest species composition, flooding frequency and duration. During 2000-2001, a 50-year record rainfall caused frequent flooding. In contrast, no floods occured during 2001-2002. Litterfall, OM (POM and CPOM), and leaf processing were measured in streams and the forest-floor. Total litterfall ranged from 478.44-758.96 gm-2yr-1. Litterfall nitrogen and phosphorous inputs ranged from 6.9-15.2 gNm-2yr-1 and 0.25-0.36 gPm-2yr-1. Alder processing was always faster than oak, with similar rates in the two streams and the oak forest. Lowest processing rates of alder and oak occurred in alder forest. C:N and N:P for litterfall and POM indicate a higher recycling efficiency in the lower-nutrient oak forest compared to the nutrient-rich alder forest. High P content in POM after the wet flooded year, nearly double that measured the driest year, may be a consequence of hydrology and nutrient uptake by forest vegetation.
NB32F-02 10:45h
Effects of Plant Architecture, Bed Position, and Fish Predation on Hydrilla-Dwelling Macroinvertebrates
Hydrilla verticillata invaded south central Louisiana during the 1970s and has become the dominant submerged macrophyte in floodplain habitats of the Atchafalaya River Basin. This plant has had pervasive effects on littoral habitat structure and water quality, and we hypothesized that dense hydrilla stands would also impact vertebrate predation on resident macroinvertebrates, although predation effects would likely be mediated by bed position. During 2003 and 2004 we conducted exclosure experiments in the Basin with artificial substrates to examine variations in hydrilla-dwelling macroinvertebrate communities due to predation, plant architecture, and bed position, and also examined stomach contents of potentially invertivorous fishes associated with these beds. Preliminary results indicate that bed position is more important in determining macroinvertebrate abundance than predation. Diet analyses indicate that the most common fishes either do not feed extensively on macroinvertebrates or are generalist browsers. Although predation by fishes may reduce abundances of specific invertebrate taxa, other factors may also be important in structuring macroinvertebrate communities inhabiting hydrilla beds.
NB32F-03 11:00h
Plant and Invertebrate Community Changes Caused by Flood-Pulsing in a Constructed Riparian Wetland
In 2002, Kent State University constructed a research facility that includes ten independently flooded wetland basins (10 m X 20 m) along a second order creek. We tested the effects of flood-pulsing on the wetland biota by allowing 5 basins (flood-pulse wetlands) to fluctuate with creek water levels to simulate floodplain marshes, and maintaining 5 basins (static wetlands) at constant water levels. We sampled emergent plants and aquatic invertebrates in 2003 and 2004. Abiotic conditions were different between treatments. We collected 83 plant species, and flood pulsing had strong effects on plant communities. Mean species richness and plant cover were higher in static wetlands, and Sorensen's similarity indices between habitat types decreased over time. Plant biomass increased in all wetlands from 2003 to 2004, but mean biomass was not different between treatments. Many dominant plant species were affected by the flood pulsing treatment. Wetland invertebrate communities were diverse (47 taxa), but we detected few responses. Total abundance, species richness, and numbers of most dominant species were not different between treatments. These results indicate that flood-pulsing acted as a stressor on emergent plant communities, but did not strongly impact aquatic macroinvertebrates.
http://www.kent.edu/biology/Research/AquaticEcology/AERF.cfm
NB32F-04 11:15h
Deluge and Deposition: Sediment Accumulation in a Large Midwestern River Following a Catastrophic Flood
Sediment traps were placed at ten locations in the lower Grand River, MI, in April 2004. Morphological, land cover, and land use characteristics of this large, entrenched, sand bottom river were measured to determine variables contributing to the mass and particle size distribution of settleable sediment collected in the traps. Beginning in May, heavy rainfall resulted in water levels rising to five meters over baseflow. Results suggest that the mass of sediment accumulated in the traps may be related to the ratio of baseflow discharge to total channel water carrying capacity. Reaches where baseflow discharge filled a greater proportion of the channel's total capacity had more sediment deposited in the traps (p = 0.013, adj. r2 = .62). These reaches also exhibited a lack of herbaceous riparian vegetation (p = 0.029, adj. r2 = .50), suggesting that a larger proportion of flood discharge escaped the channel and scoured these riparian zones. This riparian scouring also points to overland washload as a major source of settleable sediment. The shape of the river channel also appeared to be a significant variable, with deeper and narrower reaches accruing more sediment than shallower and wider reaches (p = 0.002, adj. r2 = .79). Abstract does not necessarily reflect EPA policy.