H34C-01
Humans Transforming the Water Cycle: Community-Based Activities in Hydrologic Synthesis
This paper describes a newly convened effort to design and execute synthesis studies in hydrology. We focus on an emerging view that human activities are affecting strongly the basic character of the water cycle, through a myriad of processes including water abstraction and flow diversion, land cover change, pollution, destruction of aquatic biodiversity, and climate change. A major scientific challenge is to understand how these changes manifest themselves and if they generate synergistic impacts across the different scales. Our primary synthesis goal is to quantify widespread alteration of hydrologic systems over local-to-regional domains focusing on the Northeast corridor of the United States over a 500-yr period (1600 to 2100). This is a region bearing sharp gradients in climate, land and water management and emblematic of pressures on water resources across the nation. This science agenda will be advanced through the activities of a consolidated Working Group (WG), which will study Regional Watersheds, Hydromorphology, and Continental Processes. The effort expands activities first consolidated under CUAHSI, and welcomes several new members who have led major CUAHSI, NSF, National Academy, regional, national, and international community activities. Our WG maintains cross-linked sub-groups on: Regional Earth System Models, Virtual Watershed Simulation, and Hydro-Indicators, organized through an IT framework to provide focus and unity of purpose. A project implementation design will be presented, including research, education, and outreach efforts.
H34C-02 INVITED
Morphodynamics of River Lowlands and Deltas: Combining Historical Maps with Satellite Data
Cartographers have for centuries documented the courses of rivers and their delta's distributary channels. Yet these valuable historical maps have not often been placed into a Global Information System, and verified for their cartographic accuracy. We have obtained between 6 and 15 historical maps (17th – 20th century) for a set of global deltas (Indus, Ganges, Godavari, Krishna, Mahanadi, Brahmani, Yellow, Vistula Danube, Po, Rhone, Niger, Nile, Orinoco, Magdalena, Amazon, and Mississippi). The maps were examined for their registration accuracy, using the location of between 8 and 15 cities or towns. Those maps with RMS errors of less than 5 km had shape files established for the pathways of their rivers and distributary channels. Geolocated Space Shuttle Radar data were binned into 1 m topographic units (? 90 m horizontal footprint) for each river-delta system and used in combination with LANDSAT ETM+ (15-30 m horizontal footprint), as an underlay to each of the historical maps. The satellite data proved useful in verifying the historical courses of these channels, many of which are no longer active. Together the data provide valuable insight to the time dependent dynamics of distributary channel switching and migration, before the heavy anthropogenic footprint of the 20th century (river diversions through barrages, upstream damming of the sediment supply, mitigation of the seasonal flood wave, levee development and stabilization, human-affected delta subsidence, and agricultural infrastructure).
H34C-03 INVITED
Past, Current and Future Trajectories of Watershed Nutrient Sources, Forms and Exports: a Global NEWS Application to the Millennium Ecosystem Assessment Scenarios
Dramatic global increases in anthropogenic nutrient production on land and negative impacts on coastal systems due to export from rivers are extensively documented. Recently, the comprehensive Millennium Ecosystem Assessment (MA) concluded that excessive nutrient loading of ecosystems is one of the major drivers of global ecosystem change. Increased nutrient mobilization is expected to continue for decades in response to economic and population growth. Development of a scientific basis for actions to reverse these trends and sustain riverine and coastal ecosystem health requires quantitative models applicable at regional to global scales, sensitive to changes in watershed anthropogenic forcings, and capable of predicting changes in element ratios and nutrient forms (dissolved vs. particulate, organic vs. inorganic) which have been shown to modulate the impacts of nutrient loading on marine ecosystems. The Global Nutrient Export from Watersheds (NEWS) system of models was designed to meet these requirements and was previously applied to contemporary (1995) forcings. We will present preliminary results from an application to past (1970) and current (2000) conditions, and compare them to four MA future scenarios thru 2050. These scenarios integrate economic, social, and ecosystem processes, and represent plausible futures with contrasting degrees of global cooperation and of sustainability of ecosystem services.
H34C-04 INVITED
Microbes, fluvial networks and carbon fluxes from land to the ocean
Metabolism in freshwater ecosystems of terrestrial organic carbon provides a major source of CO2 outgassing to the atmosphere. This contradicts the conventional wisdom that terrestrial organic carbon is recalcitrant and contributes little to the support of aquatic metabolism. We combine recent progress from geophysics, microbial ecology and organic geochemistry to show how the juxtaposition of geophysical opportunity and microbial capacity enhances the net heterotrophy in streams, rivers and estuaries. We identify hydrologic storage and retention zones that extend the residence time of organic carbon during downstream transport and thus provide opportunities for microorganisms to develop as attached biofilms or suspended aggregates, and to metabolize organic carbon for energy and growth. We consider fluvial networks within a meta-ecosystem context to include the acclimation of microbial communities in downstream ecosystems to exploit energy that "escapes" from upstream ecosystems and thereby increases overall energy utilization at the network level. Our interdisciplinary approach emphasises the coupled physical, chemical and microbial processes across various scales that may serve to enhance the predictability of carbon cycling in fluvial ecosystems.
H34C-05
Hydroclimatic controls on eutrophication of lakes in agricultural catchments
The long-term driver of contemporary cultural eutrophication in lakes is generally the supply of phosphorus (P) from agricultural catchments, via manure or fertilizer runoff. However, short-term recycling of P from lake sediment also plays a critical role in sustaining eutrophic conditions after brief high loading rates subside. A comprehensive understanding of the vulnerability of lakes to eutrophication thus requires the synthesis of hydrological, biogeochemical, and limnological data and models across linked land-lake systems. One question such a synthesis may address is the vulnerability of lakes to eutrophication under different climatic conditions. Drawing from global runoff and local P-dynamics data, we develop a lumped model linking dynamics of water column and sediment P to catchments' biogeochemical and hydrological responses across a gradient of mean annual precipitation. Results suggest that climates with an intermediate range of mean annual precipitation are most vulnerable to cultural eutrophication, but only after sufficient time has passed to allow the accumulation of P in the sediments. Vulnerability declines in dryer climates owing to a lack of runoff and P loading, and in wetter climates to increased flushing of P from the lake. The results provide insights for understanding the potential impacts of regional climate change, as well as the vulnerability of regions that are aiming to increase the use of agricultural fertilizer.
H34C-06
Linking hydrology and denitrification kinetics in treatment wetlands
A number of factors control the kinetics of denitrification in natural environments, particularly, in treatment wetlands. In order to understand and, in some sense, optimize nitrogen removal in wetlands we must link hydrological and geochemical processes. Based on a two-dimensional flow model we found that topography and vegetation distribution as well as density of vegetation are crucial reproducing the residence time distribution from a tracer test experiment. The tracer test used simultaneous injection of three labelled isotopes; H2O-3, PO4- 32 and NO3-15. Not only are the reactions constrained by the circulation patterns and water residence time, but there are essential links between vegetation as friction causing objects for the water flow and vegetation as host medium for biofilms in which denitrification can occur. This study has illuminated the importance for the treatment efficiency of the various time-scales involved in the denitrification occurring in wetlands used for treating municipal wastewater. Sampling of bed sediments in Ekeby Wetland, Eskilstuna, Sweden, were used as a basis for laboratory measurements of potential denitrification activity (PDA), evaluation of the Michaelis-Menten kinetics and denaturing gel electrophoreses (DGGE) patterns of nosZ genes, which represent the denitrifying bacterial community structure in various locations. A most essential contribution of the study is to translate such basic microbiological entities into a system response model that considers both water flow and mixing as well as microbiological reactions. The behaviour of this system model was also compared with the tracer test bfreakthrough curves. The structure and placement of vegetation is found to be of utmost importance for the contact between biofilms and nitrate-polluted wastewater and, thus, for the treatment efficiency. Erroneously placed vegetation can cause flow channelling with little utilisation of the entire wetland volume and little availability of the actively denitrifying zones for the wastewater. A statistical analysis reveals that the spatial variation of PDA is more or less linearly related to the nitrogen concentration and the flow residence time from the inlet to a particular location. The linear control on the reaction of the nitrogen concentration implies that the reaction is nitrogen limited, which has consequences for the denitrification kinetics.
H34C-07
Regional hydrologic synthesis using a system model for watersheds: a new integrative tool to advance knowledge and predictability of hydrologic systems
The new integrative tool based on a cyber model of landscapes is developed to address the behavior of hydrologic systems. This cyber model of landscapes in spatial organization consists of the following subsystems: atmosphere, hydrosphere, lithosphere, pedosphere, biosphere and antroposphere. Using watershed (catchment, basin) as a unit of the landscape in three-dimensional format and combining it with the cyber model subsystems provides the opportunity to address the issues of hydrologic structure and similarity. Derived from the cyber model the system model architecture using watershed units can provide the quantification of hydro-climate characteristics (stream runoff, ground-water levels, precipitation, air temperature) as well as classification of hydrologic units derived from landscape components (climate, soil, vegetation, topography, and geology). This approach uses a multi-level system architecture for landscapes in which the watershed as a subsystem is analyzed from the global to continental to regional and finally to a local scales to quantify hydro- climatic characteristics. The hydrologic units in this tool are represented by a set of watersheds that are quantified by linkages to landscape components using statistical tools. Regional analysis based on such a system model for watersheds was completed at different scales for the conterminous US, the Great Lakes Region and the territory of Minnesota. Regional hydrologic synthesis was used to map stream flow as well as recharge/discharge in Minnesota, East Central Minnesota and the Twin Cities Metropolitan area. The analysis for Minnesota is based on the quantification of stream runoff attributes and their association with landscape components defined as the geology, hydrogeology, the stream network system, relief, soils, vegetation and atmosphere characteristic (climate). The analysis of stream runoff components (annual, seasonal and monthly minimal) includes three phases: (1) system analysis of the geosphere, i.e. Earth landscape systems in three-dimensional format, (2) hierarchical subdivision of landscape components features and (3) spatial- temporal mapping of stream runoff. The investigation proceeds from a global to a regional or basin level and then to a local level, with the greater detail available at the lower levels adding refinement to the description of the natural landscapes. The spatio-temporal structure of annual, seasonal, monthly and minimal monthly runoff and its linkage to landscape components was achieved by using multidimensional statistics tools.
H34C-08
Interdisciplinary synthesis - a catalyst or a stumbling block for advancing predictability?
Most hydrologists will agree that synthesis is needed for both solving numerous real world problems and for advancing the science. However, it is also true that a clever choice of limited system boundaries has always been the hallmark of scientific progress as it allows to isolate problems one can understand with the data and concepts at hand. Operational challenges in conducting interdisciplinary research projects include communication, lack of leadership and difficulties with integrating sub-projects, and also issues with breadth versus depth of enquiry - the further you spread it, the shallower it gets. The main scientific challenge in interdisciplinary synthesis is how to represent complex interacting dynamic systems including feedbacks between system components. This talk will discuss examples taken from real time flood forecasting and flood estimation where process understanding and process representations from the atmospheric sciences, geomorphology and hydrology are merged. In the examples, feedbacks between different scales will be analysed with a focus on interactions and emergent properties: feedbacks between event and long term scales (storm runoff and landform evolution); and feedbacks between local and regional scales (local runoff generation and regional water balance). It is argued that one of the keys to advancing predictability in an interdisciplinary setting is - similar to the disciplinary case - a prudent choice of system boundaries. Similarly important is the willingness of individuals to move outside their "comfort zone", to represent processes they would not usually attempt to represent in a quantitative way.