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Distributed ecohydrological modeling: the potential for water resources management

Distributed ecohydrological modeling: the potential for water resources management. Larry Band, UNC Christina Tague, SDSU. Characteristics of watersheds regulating biogeochemical cycling and export. In situ cycling of carbon and nutrients

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Distributed ecohydrological modeling: the potential for water resources management

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  1. Distributed ecohydrological modeling: the potential for water resources management Larry Band, UNC Christina Tague, SDSU

  2. Characteristics of watersheds regulating biogeochemical cycling and export • In situ cycling of carbon and nutrients • Ecosystem Processes: deposition/fixation, assimilation, uptake, decomposition, mineralization, nitrification, immobilization, denitrification, and all that…. • Transport within hydrologic flowpaths • Hydrologic Processes: overland flow, shallow throughflow, groundwater flow,…. • Distribution of net source/sink strength along flowpaths

  3. Plot based ecosystem models • water, carbon, nutrient flux computed in 1-d • long time step (one day to one month) • long time domain (decades to centuries) incorporating long term feedbacks to ecosystem state • typically run without consideration of spatial heterogeneity • no incorporation of spatial dependency along flowpaths

  4. Dynamic BGC

  5. Nitrogen saturation hypothesis: • Definition: Terrestrial ecosystems have a maximum rate of nitrogen uptake determined by the net ecosystem productivity and other (plot) N sinks, input exceeding this rate may leach to ... • Streamwater chemistry diagnostics: • ecosystem saturation stage diagnosed by streamwater chemistry, particularly in growing season • Based on plot paradigm: assumes leaching below rooting zone is contributed directly to streams

  6. Watershed model: • e.g. HSPF - works well for discharge based on land use • also typically fix nutrient loading from land surface classes • lumped models cannot address downslope divergence (variable nutrient source/sink strength along flowpaths) • adjust for BMPs with reduction factor • no feedback to ecosystem processes controlling source quality

  7. Baltimore Ecosystem Study: Urban LTER Oregon Ridge

  8. Infrastructure impacts on flowpaths

  9. Characteristics of watersheds regulating biogeochemical cycling and export:anthropogenic alteration • direct addition or abstraction of material • irrigation, fertilization, spills • wastewater treatment and disposal • alteration of hydrologic flowpaths • impermeable surfaces • street drainage • storm and sanitary sewers • vegetation management

  10. RIPARIAN ZONES • Critical interface between terrestrial and aquatic components of a watershed. • Demonstrated ability to prevent pollutant movement from upland land uses into streams. • Most work on groundwater nitrate, in agricultural watersheds.

  11. Denitrification NO3- NO2-  NO  N2O  N2 - Anaerobic - Heterotrophic (requires organic C) • Expect high rates in wetland soils. • Key component of the water quality maintenance function of riparian zones.

  12. Model and data flow structure

  13. RHESSys Object Hierarchy

  14. Basin/hillslope/patch hierarchy

  15. Major carbon flux processes: patch level • Photosynthesis: Farquhar algorithm combining conductance and enzymatic limitations • Stomatal physiology: Conductance uses Jarvis method f(temp, LWP, PAR, VPD) • Respiration: Organ (foliage, root, stem) specific rates (massC/massC) modified by temperature Q10 • Allocation: Root, stem, foliar allocation of net photosynthate determined by Waring/Landsberg function on water, nutrient stress, and carbon supply • Litter decomposition: litter/soil moisture, T, quality determines rates from different soil pools

  16. Daily carbon flux (g.m-2day-1): Upland plot, Pond Branch

  17. Nitrate export from Pond Branch: Note large increase in concentrations during summer - partially derived from riparian zones

  18. Denitrification rates during summer and winter for hillslope 1

  19. NO3 export concentrations as f(hydrology) • riparian patches typically near saturation, anaerobic, active denitrifying zones • significant reduction of [NO3] from upslope • low decomposition, accumulates carbon, nutrient rich material • during dry-downs riparian patches • may disconnect from uplands, WFPS drops • become aerobic, strongly nitrify • flip from sink to source of NO3 • note: growing season NO3 export not related to catchment nitrogen saturation

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