Toward a Better Understanding of River and Floodplain Ecosystems III
Presiding: M Delong, Winona State University; J Thorp, University of Kansas
NB51E-01 INVITED 08:30h
A Model of Biocomplexity in River Networks - Part I: General Theory
We are proposing an integrated, heuristic model of lotic biocomplexity that encompasses spatiotemporal scales from headwaters to large rivers and from main channels to floodplains. Our hope is that this model will provide a foundation for understanding both broad, often discontinuous patterns along longitudinal and lateral dimensions of river networks and local ecological patterns across various temporal and smaller spatial scales. The model represents a conceptual marriage of eco-geomorphology with a terrestrial landscape model describing hierarchical patch dynamics (HPD). Contrasting with a common view of rivers as continuous, longitudinal gradients in physical conditions, our model portrays rivers as downstream arrays of large hydrogeomorphic patches formed by catchment geomorphology and climate. Unique "functional process zones" (FPZs) will be formed within individual types of hydrogeomorphic patches because of physiochemical habitat differences affecting ecosystem structure and function. Our conceptual model blends our perspectives on biocomplexity with aspects of aquatic models proposed from 1980-2004. In Part I of our oral presentation, we will give an overview of this biocomplexity model and discuss how it varies from our perspectives on the ecology of lotic ecosystems.
NB51E-02 INVITED 09:00h
A Model of Biocomplexity in River Networks - Part II: Tenets and Predictions
We are proposing a model of lotic biocomplexity encompassing spatiotemporal scales from headwaters to large rivers and from main channels to floodplains. Part I of our presentation in the symposium discusses the general theory and predicted changes along longitudinal gradients in the river network. In Part II, we use the foundation of this theory to make predictions for the ecological behavior of the river ecosystem. These predictions are designed to stimulate research tests of these hypotheses and to obtain data allowing the continuing refinement of the overall model. Fourteen principles or model tenets are included which describe the functioning of epigean portions of lotic ecosystems on ecological time scales; they are focused more on the riverscape than the entire riverine landscape. These 14 tenets predict how patterns of individual species distributions, community regulation, lotic ecosystem processes, and floodplain interactions will vary over spatiotemporal scales, especially as they relate to the functional process zones formed by hydrogeomorphic patches. We make no claim to originality for all these tenets. Some of these ideas are well supported in the scientific literature, others may be acceptable to the scientific community but currently lack empirical support, and some may be very speculative and possibly controversial.
NB51E-03 INVITED 09:15h
A Continua or a Series of Patches - the Downstream Morphology of a Large Dryland River System
There is no abstract associated with this presentation.
NB51E-04 INVITED 09:30h
Influence of Flow Regime on the Food web of a Dryland River System
Australian dryland rivers are among the most variable and unpredictable in the world in terms of their flow regimes. Although renowned for their spectacular floods over vast floodplains, rivers exist for much of the time as discrete waterholes, which are important refugia for aquatic biota. During these dry spells, aquatic food webs in waterholes are clearly supported by algal production, despite the high natural turbidity and significant terrestrial carbon inputs. However, the relative importance of pelagic and benthic sources is less clear. Although fish rarely have stable isotope signatures consistent with a phytoplankton diet, gut contents analysis suggests that zooplankton can be a significant component of diets. Planktonic sources of carbon appear to be important during and immediately after flood events, where aquatic production on inundated floodplains provides an immense food resource. As waterholes become isolated post-flood, we predict that benthic sources of production become increasingly important as algae develop along the relatively stable shoreline. More frequent flow pulses connect waterholes and enhance their physical persistence, but may disrupt the formation of these productive algal mats. We propose that the relative importance of benthic and pelagic algal production to dryland river food webs varies in response to recent flow history.
NB51E-05 INVITED 09:45h
The Importance of Flow, Thermal, and Resource Pulses for Floodplain Processes
In floodplains, flow, temperature, and resource pulses interact in complex ways and maintain biodiversity and biological productivity in these systems. We investigated the driving force of multiple pulses (i.e. flow, temperature, resource) on ecosystem processes in semi-natural floodplains in Central Europe (Val Roseg, Tagliamento, Danube). We used imaging techniques to quantify thermal patch dynamics over diel cycles and inundation patterns at the landscape scale. In the proglacial Val Roseg floodplain, surface temperature exhibited a complex spatiotemporal pattern, with values from -5° C to 30° C over a diel cycle. Furthermore, we studied the differential effects of alternating drying and wetting cycles on leaf litter decomposition and sediment respiration. Based on these data, we identified key habitats of ecosystem processes at the floodplain scale. Locations of organic matter input, storage, and processing were spatially separated. In the Tagliamento, standing stock of CPOM, for example, was up to 800g/m2 on vegetated islands but less than 20g/m2 in channels. Decomposition rate, however, was k = 0.0129 in channels compared to k = 0.0013 on islands. Finally, by overlaying different pulses, we identified "windows of ecological opportunity"; i.e., crucial time periods when conditions were most favourable to foster ecosystem processes and therefore to control floodplain biota.
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