Toward a Better Understanding of River and Floodplain Ecosystems II Posters
Presiding: M Delong, Winona State University; J Thorp, University of Kansas
NB33H-01 1330h
Floodplain Vegetation Productivity and Carbon Cycle Dynamics of the Middle Fork Flathead River of Northwest Montana
River floodplains are vital natural features that store floodwaters, improve water quality, provide habitat, and create recreational opportunities. Recent studies have shown that strong interactions among flooding, channel and sediment movement, vegetation, and groundwater create a dynamic shifting habitat mosaic that promotes biodiversity and complex food webs. Multiple physical and environmental processes interact within these systems to influence forest productivity, including water availability, nutrient supply, soil texture, and disturbance history. This study is designed to quantify the role of groundwater depth and meteorology in determining spatial and temporal patterns of net primary productivity (NPP) within the Nyack floodplain of the Middle Fork Flathead River, Northwestern Montana. We examine three intensive field sites composed of mature, mixed deciduous and evergreen conifer forest with varying hydrologic and vegetative characteristics. We use a modified Biome-BGC ecosystem process model with field-collected data (LAI, increment growth cores, groundwater depth, vegetation sap-flow, and local meteorology) to describe the effects of floodplain groundwater dynamics on vegetation community structure, and carbon/nitrogen cycling. Initial results indicate that conifers are more sensitive than deeper-rooted deciduous species to variability in groundwater depth and meteorological conditions. Forest productivity also shows a non-linear response to groundwater depth. Sites with intermediate groundwater depths (0.2-0.5m) allow vegetation to maintain connectivity to groundwater over longer periods during the growing season, are effectively uncoupled from atmospheric constraints on photosynthesis, and generally have greater productivity. Shallow groundwater sites (<0.2m) are less productive due to the indirect effects of reduced soil aerobic decomposition and reduced plant available nitrogen.
NB33H-02 1330h
Floodplain Wetland Dynamics and Development Following Dam Removal on a North Carolina Coastal Plain River
Dam removal is used to experimentally investigate hydrologic, geomorphic and ecological links in streams, particularly floodplain succession and floodplain nutrient retentive capacity (FNRC). Here, FNRC is defined as the ability of the flood plain to attenuate surface water nutrient concentrations during spates. Following dam removal, altered hydraulics will drive upstream channel evolution exposing nutrient-rich sediments for floodplain succession. The dam removal is in progress so particular emphasis will be focused on the fate of interstitial nutrients within the developing floodplain wetland and floodplain community succession. Initial data show interstitial water N and P concentrations 10-20X greater than adjacent surface water. N leaching to the channel from the floodplain has been observed supporting the hypothesis that FNRC will be compromised during early stages of succession. Secondary succession is measured using macrophyte biomass (AFDM) and benthic algae (chl a), and within the rooting-zone using fungal biomass and bacterial productivity. Nutrient data from the floodplain are being collected throughout the successional process (surface water, interstitial and sediment surface). In addition to the field studies, development of FNRC is being simulated using mesocosms within a greenhouse under variable hydrologic conditions in the presence and absence of wetland floodplain vegetation along a biomass gradient.
NB33H-03 1330h
Zooplankton as Potential Indicators of Biotic Condition in Large Rivers
As part of the Environmental Monitoring and Assessment Program (EMAP), supported by the U.S. Environmental Protection Agency, we are examining zooplankton diversity and abundance in three large rivers (Missouri, Ohio, and upper Mississippi). These rivers are particularly interesting because of large differences in their hydrologic patterns, resulting primarily from their different management strategies. Preliminary data from summer 2004 surveys of the Missouri and Ohio rivers reveals high taxonomic diversity of rotifers (32 genera), cladocerans (22 species), and copepods. Rotifers are numerically dominant in all river samples except in the late summer Ohio River samples, where they are occasionally co-dominant with calanoid copepods. Using multivariate analyses, we will present a comparison of zooplankton diversity between rivers, among sites within rivers, and correspondence with 35 physico-chemical properties of the river. These data will be used to develop bioindicators of the current condition of each river in order to support conservation and restoration decisions by management agencies.
NB33H-04 1330h
Benthic Algal Production in two Dryland Rivers
In the highly turbid waterholes of dryland rivers in western Queensland, Australia, low light availability restricts benthic algal production to shallow littoral margins. Despite this limited spatial extent, stable isotope work suggests benthic algae are the major source of energy supporting waterhole food webs during periods of low to no flow. We measured benthic community metabolism using in situ chambers in 30 waterholes across the Cooper Creek and Warrego River catchments. Production was measured twice at each waterhole, once within a couple months of a flood and again after an extended period of no flow. Gross primary production in Cooper Creek was greater than that in the Warrego River, with a mean value of 0.46 g C m-2 day-1 (SE 0.05 g C m-2 day-1) compared to 0.13 g C m-2 day-1 (SE 0.02 g C m-2 day-1). Rates of production were similar for the two Warrego River trips, but increased considerably after the period of no flow in Cooper Creek. Photic zone depths ranged from 10 to 75 cm, and explained a significant portion of the variation in production. Because waterhole production is a function of the benthic surface area within the photic zone, production between floods will be strongly influenced by interactions between water level changes and waterhole morphology.
NB33H-05 1330h
Spatial Heterogeneity of Leaf Litter Decomposition in a Complex Mosaic of Floodplain Habitats
Dynamic floodplains comprise complex mosaics of aquatic, amphibious, and terrestrial habitats that are expected to mediate input, storage and transformation of organic matter. We examined leaf litter breakdown heterogeneity in a complex floodplain ecosystem (Tagliamento, NE Italy), separated the differential effects of microbes and shredding macroinvertebrates on leaf breakdown, and identified key habitats of leaf litter transformation. We employed a leaf-bag approach, using coarse and fine mesh bags, designed to allow or exclude feeding by stream invertebrates. Bags were exposed in eight habitat types, representing the dominant range of floodplain habitats. Breakdown rates varied by an order-of-magnitude, ranging from k = -0.0013 to k = -0.0129 day -1. Results showed that leaf breakdown in coarse mesh bags differed significantly among channels, ponds, and terrestrial habitat types. In fine mesh bags, however, only channels had significantly higher leaf breakdown rates. Leaf decomposition was similar in all terrestrial habitat types despite extensive variability in environmental conditions. Our study emphasizes that floodplain habitats display a remarkable heterogeneity in their ability to process organic matter, whereas lotic and lentic habitats were clearly identified as "hot spots" of leaf litter transformation.
NB33H-06 1330h
A Comparison of Streamside Habitat Assessments and Water Quality Indicators in the Lower Flint River Basin: Do They Agree?
Habitat assessment protocols using factors such as bank stability, riparian land use, and riparian buffer width have been developed by both the USFWS and the EPA. These assessments are standardized, so information about a stream system can be shared among organizations. Both protocols are being used, in conjunction with measurements of water quality parameters such as suspended solids, phosphate, nitrate/nitrite, ammonia, fecal coliform abundance, and caffeine, at sites throughout the Flint River Basin. In agricultural areas without a riparian buffer, increased fertilization could result in elevated nutrient levels in streams. In areas with intact riparian zones, reduced inputs of agricultural runoff are expected. Because the EPA habitat assessment results in a numerical score for each site, this study provides an opportunity to determine whether physical habitat scores correlate with water quality indicators over a gradient of disturbance. Preliminary results do not indicate a relationship between habitat scores and water quality parameters. One possible explanation is that groundwater transport represents a mechanism by which excess nitrogen can bypass the riparian buffer. Therefore, effects of land use on water quality in Coastal Plain streams may not be apparent from streamside assessments.