Toward a Better Understanding of River and Floodplain Ecosystems IV
Presiding: M Delong, Winona State University; J Thorp, University of Kansas
NB52D-01 INVITED 10:30h
New Contributions of Remote Sensing and Spatial Data Analysis to Understanding Tropical Floodplain Ecosystems
Extensive floodplains subject to seasonal inundation are found across lowland South America. A few well-studied locations demonstrate how inundation hydrology is a key driver of ecological characteristics of these floodplains. Until recently, the inundation patterns of these vast and often remote floodplains had to be inferred from river stage records. Advances in spaceborne remote sensing and spatial data analysis are now contributing hydrological and geomorphological information of unprecedented detail. This talk highlights examples of remote sensing studies in the Orinoco, Amazon, and Parana/Paraguay river basins that have produced information with direct applications to ecosystem ecology, biogeochemistry, and conservation planning. Remote sensing examples include Landsat, passive microwave emission, synthetic aperture radar, and elevation data from the Shuttle Radar Topography Mission. Spatial data analysis examples include hydrological modeling in GIS and object-oriented image analysis. The growing potential of these tools is just beginning to be exploited to better understand, manage, and protect these ecosystems.
NB52D-02 11:00h
Spatial Heterogeneity in Water Quality across a Restored Floodplain: Implications for Fish and Those Who Care About Them
High resolution spatial monitoring of floodwaters across an experimental floodplain in Central California has revealed patterns in dissolved organic carbon, chlorophyll-a, and nutrients which may have ramifications for local biota and future floodplain restorations. In 2004, seven sites across a 40 ha restored floodplain were monitored before and after 3 major floods. Additionally, in 2005, a multi-parameter sonde with GPS capabilities was used to create a high-resolution water quality map of the floodplain. Floods acted to reset, homogenize, and push productive antecedent waters across the floodplain. Productivity was greatest in shallow areas shortly after storms. As water stagnated on the floodplain deep water areas became more productive with chlorophyll-a levels reaching 17 Μg l-1. Concurrently, vegetated shallow areas released dissolved organic carbon and nutrients and became hypoxic as algae senesced. A parallel fish enclosure study revealed that fish growth was greatest in shallow areas shortly after storms. The fish enclosed in deepwater areas grew faster as shallow water habitat began to decline. Habitat heterogeneity drives water quality variability across the floodplain which in turn influences the local biota, such heterogeneity is important for healthy ecosystem function and should be an integral part of future floodplain restorations.
NB52D-03 11:15h
Hydro-Ecological Modeling of Lower Mississippi River
The Mississippi River is one of largest rivers in the world and has major economic, environmental, ecological, and industrial values not only to Louisiana but also to the entire United States. At present, the Mississippi River Delta area of coastal Louisiana is being deprived of practically all the sediment (about 220 million tons annually) that the river is transporting to the Gulf of Mexico. Therefore, alternative solutions to recover or re-direct portion of this massive amount of valuable sediment to benefit the restoration of Louisiana coastal lands should be carefully investigated. In order for such investigation to be successful, the impact of management and restoration projects on the conditions of the River (supply side) and on the surrounding wetland and water bodies (demand side) should be considered. The objective of this study is to develop a three-dimensional (3D) model for portion of the Lower Mississippi River. The model should provide detailed information on the spatial and temporal patterns of the river's hydrodynamics, salinity, sediment, and water quality parameters. The model will serve as an excellent overall management and analysis tool for the Lower Mississippi River. The model will provide detailed information on the availability of fresh water and sediment for diversion to surrounding wetlands; and determine quantitatively the impact of exiting and planned diversion projects on the dynamics of the river.
NB52D-04 11:30h
Nutrients and chlorophyll a in the Upper Mississippi River System: What can we learn from spatial and temporal patterns?
Variability in time and space is a defining characteristic of large river ecosystems. We investigated temporal and spatial variation in selected nutrients and chlorophyll a concentrations in 5 study reaches of the Upper Mississippi River System (UMRS) using quarterly data collected from 1993 to 2002. We addressed the following questions: 1) Are there consistent differences among aquatic areas (e.g. main channel and off-channel areas (backwaters))? 2) What temporal patterns occur within these aquatic areas? 3) What is the relative importance of spatial and temporal components in the total variance? Chlorophyll a concentrations were generally higher in backwaters than the main channel, whereas dissolved nutrient concentrations were generally lower in backwaters. These differences were most pronounced in summer. Seasonal patterns in nitrate (NO3-) and soluble reactive phosphorus (SRP) showed that minimum [NO3-] coincided with maximum [SRP] in late summer. Seasonal patterns in chlorophyll a concentration varied among study reaches, though minimum concentrations generally occurred in winter. Variance component analysis indicated that temporal components generally explained more variability than did spatial components. The proportion of variability explained by temporal vs. spatial components varied among study reaches. These patterns provide information for understanding chlorophyll a and nutrient dynamics in large river ecosystems.
NB52D-05 11:45h
Spatial Variability of Denitrification and Associated Soil Properties on a Restored and a Natural Floodplain
Floodplains often exhibit high levels of variability in biotic parameters at relatively small spatial scales. Even so, we have limited insight about the structure of this variability. In this study we measured the spatial variation of denitrification rates and determined the scale of spatial autocorrelation and how it differs between a restored and a natural floodplain. Denitrification enzyme activity (DEA, ΜgN2O-N/ kg soil/hr), nitrate, carbon, total nitrogen, and moisture were measured on 116 soil samples collected using a cyclic sampling design to increase sampling efficiency and spatial information. Mean DEA rate was lower on the natural than on the restored floodplain (0.70 vs. 1.85) despite similar ranges (0-5.3 and 0-5.5 respectively), probably due to the increased prevalence of inactive samples (17.2% vs. 2.5%). Furthermore, the CV for DEA was higher in the natural floodplain (137%) than the restored floodplain (60%). The restored floodplain also had a greater range of spatial autocorrelation, suggesting that there was greater spatial structure in denitrification on the restored floodplain. These results contradict conventional wisdom about the homogeneity of restored sites relative to less impacted ones.