Workshop: Relating Site Specific Insights to Landscape Features for Catchment Scale Management . Research Coordination Meeting: Strategic Placement and Area-wide Evaluation of Conservation Zones in Agric. Catchments IAEA/FAO Vienna, Austria December 17, 2008 Art Gold, Professor, Univ. Rhode Island
Motivations For Scaling • Inherent conceptual interest in scaling • Interest in a micro-scale process that is relevant at large scales, e.g. N gas fluxes • Need to solve a specific problem at a large scale, e.g. nitrate delivery to coastal waters, that is regulated by micro-scale processes
Overview: Relating Landscape Features to Site Process for Catchment Management • Site Scale – Does our sample size capture the controlling processes – the hot spot issue at the micro level? – Does our sampling design capture transformation rates at the scale of single landscape feature? • Landscape Scale – What “map” attributes relate to landscape features that control or reflect hot spots of transformations? – Is the mapping scale suitable to capture critical processing at the landscape scale?
Sample Size Question: Do microcosms for soil and aquifer biogeochemistry capture site processes? R. L. Smith, USGS
In situ Nitrate Dosing Experiment Explore Biogeochemistry on Larger Sample Volumes
Scale of Site Measurements Can Yield Major Differences in Groundwater N Removal in Hydric Soils at the Same Site Microcosm Dosing Field Study Study Volume of Media 16,000 32 (cm 3 ) Mass (g) 25,000 50 N Removal 50 < 2 ( μ g kg -1 d -1 ) Conservative Denitrification N Removal Method Tracers: Mass Gases Balance Nelson et al., 1995 Groffman et al., 1996
Undisturbed Mesocosms Permit Mass Balance and Process Level Studies Seasonal High Water Table 15 cm Back side diam. Side of pit of pit PVC Core where core will be extracted Extendible Pipe Hydraulic Jack with press
Mesocosm Dosing Experiment Carboy: Groundwater Br+/5% 15 NO 3
15 N Mesocosm Experiments: Carbon rich microsites (1-5% by volume) in hydric cores generated the denitrification and N removal
Push-Pull Method: In Situ Denitrification Capacity Push Pull 1. Pump groundwater - Amend with 15 NO 3 2. and Br - 3. Lower DO to ambient levels with gaseous SF 6 Water Table 4. Push (inject) into well 5. Incubate 6. Pull (pump) from well 7. Analyze samples for 15 N 2 and 15 N 2 O (products of microbial denitrification) Introduced plume: 44 kg (Addy et al. 2002, JEQ) sample size 2 cm mini-piezometer
Question: Does our sampling design capture transformations at the scale of a single landscape feature? • Hubbard Brook “valley-wide” study (Schwarz, Venterea, Lovett, Groffman) • Are there intra-valley patterns of N transformations that must be considered for scaling up to regional/catchment scale gas flux study? • Can map attributes (elevation, aspect, geology, soils, vegetation) explain variation and permit scaling from point samples?
Sampling Scheme: Hubbard Brook Watershed, NSF Long Term Ecological Research Site 1.5 km
High valley-wide variability in point-based N transformation rates Mean Range CV (kg N ha -1 d -1 ) % N mineralization rate 1.18 0.25 - 2.33 44 Nitrification rate 0.61 -0.01 - 1.53 71 (g N ha -1 d -1 ) N 2 O production rate 4.26 -0.69 - 16.1 76
Landscape attributes (ASPECT) relate to N transformation rates Aspect 2.0 2.0 N 2 O produ ction rate (g N h a -1 d -1 ) Nitrification rate (kg N h a -1 d -1 ) b** 1.5 1.5 N m in era lization rate, a 1.0 1.0 b** a 0.5 0.5 0.0 0.0 N facing S facing N facing S facing N facing S facing N 2 O production N mineralization Nitrification
Landscape attributes (ELEVATION) relate to N transformation rates Elevation 2.0 2.0 N 2 O produ ction rate (g N h a -1 d -1 ) Nitrification rate (kg N h a -1 d -1 ) b*** 1.5 1.5 N min eralization rate, a 1.0 1.0 b*** b*** a 0.5 a 0.5 0.0 0.0 low high low high low high N mineralization N 2 O production Nitrification
Landscape attributes relate (SPECIES) to N transformation rates Dominant species 2.5 2.0 N 2 O produ ction rate (g N ha -1 d -1 ) Nitrification rate (kg N ha -1 d -1 ) 2.0 c*** 1.5 N min eralization rate, 1.5 c* 1.0 c 1.0 abcab b ab ab 0.5 a a 0.5 0.0 0.0 RS AB YB SM PB RS AB YB SM PB RS AB YB SM PB N mineralization N 2 O production Nitrification
Conclusions from valley-wide study • There are coherent patterns of N cycling across the landscape of the Hubbard Brook valley • These patterns can be related to map attributes and permit scaling up for catchment or regional gas flux estimates
Stream N Cycling Is Quite Variable Question: Can we use landscape attributes to relate stream morphology to N removal? Hypotheses • Stream denitrification is stimulated by hydrologic “connectivity” with riparian system • Stream morphology reflects potential connectivity • Appropriate stream restoration increases rates of hyporheic denitrification Kausal et al., 2008
Possible Denitrification Pathways In Stream Ecosystems Woody debris Denitrifying Bacteria Algal mats Biofilms Biofilms Hyporheic Exchange: Surface water storage Hyporheic exchange Runkel USGS
Intensive Land Use: I. Natural Channel • Higher flood flows • Less recharge • Lower Riparian Water Tables Stream Water Table Developed vs Forested Storm Hydrographs Developed 400 350 300 Flow Rate 250 II. Channel with Incision 200 Forested 150 Due to Increased Runoff 100 50 0 0 2 4 6 8 10 12 14 16 Time • Channel Erosion • Nonfunctional Floodplain • Dry Riparian Soils Groffman et al, 2004
Stream Nutrient inputs Degradation Removal of riparian zone Bank Incision Increased Nitrogen Concentrations
Push Pull Groundwater Denitrification Studies: Low Bank (Unrestored)
High non-connected (Restored) bank
Low Bank “Connected” to Riparian Water Table (Restored)
300 Denitrification Rate ( μ g/N/kg Unrestored High Bank Unrestored Low Bank 250 Restored High Un-connected Bank Restored Low Connected Bank 200 soil/day) 150 100 50 0 June 2003 November 2003 June 2004 Date Kaushal et al. (2008)
Stream morphology and genesis may provide insight into stream denitrification The Rosgen Classification System
Question: Is the mapping scale suitable to capture critical processing at the landscape scale? Example: Geospatial data to identify high N removal riparian zones • Can we identify narrow bands of hydric riparian soils? – 10 m of hydric soil width = substantial nitrate sink – 10 m < 0.02” at 1:24,000 scale • Can we identify map features that reflect riparian flow paths? – Riparian Groundwater flow > > denitrification than Surface Flow
SSURGO Riparian Zone Validation Study Soil Survey Geographic Digital Data 1:24,000 vs. Field Data T1 T2 T3 • 100 lower order Geo- referenced streams Right 30m Bank • 6 transects per site 7.5m 7.5m - Hydric soil width Water flow Stream - Presence of seeps T1 T2 Left Bank T3 • Compare to SSURGO - Hydric status - Geomorphic Classification - Measurements
Groundwater Seeps: Field Data - Seeps found at 29/34 hydric till sites : Expect reduced groundwater N removal potential in till - No seeps found at 16/18 hydric outwash sites : Expect groundwater flow through hydric soils with high denitrification potential Surface flow (short-circuiting?) Riparian Stream ecosystem Till Hydric Soil
SSURGO Validation Study Hydro-geomorphic settings with high potential for riparian groundwater nitrate removal 90.0 80.0 70.0 > 10m of hydric soils > 10m of hydric soils & NO seeps present & NO seeps present 60.0 50.0 % of sites 40.0 30.0 20.0 10.0 0.0 Hydric Hydric Hydric Nonhydric Nonhydric Organic& Till Outwash Till Outwash Alluvium N= 34 N= 18 N= 17 N= 10 N= 21
Soil Map Units Only Rte 165 N Accurate for Right bank Presence/Absence 30m buffer T1 T2 T3 of Hydric Soils SPD Field Observations: • Ground-truth map: 3-4 PD drainage classes • VPD SSURGO composed of 1 soil map unit VPD Stream flow PD Rte 165 SPD MWD Left bank
Summary • Great value in hypothesis based research relating landscape attributes (soils, morphology, topopgrahy, plant community) to biogeochemical cycling. • Geospatial analyses can serve to “scale- up” site specific studies on wetland, riparian and stream functions at the catchment scale.
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