Workshop: Relating Site Specific Insights to Landscape Features for Catchment Scale Management .

Art Gold, Professor, Univ. Rhode Island

Research Coordination Meeting: Strategic Placement and Area-wide Evaluation of

Conservation Zones in Agric. Catchments

IAEA/FAO Vienna, AustriaDecember 17, 2008

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 CanYield Major Differences in Groundwater N Removal in Hydric

Soils at the Same Site

Dosing FieldStudy

Volume of Media (cm3)

16,000 32

Mass (g) 25,000 50

N Removal (μg kg-1 d-1)

50 <2

N Removal Method

Microcosm Study

Conservative Tracers: Mass Balance

Denitrification Gases

Nelson et al., 1995 Groffman et al., 1996

Undisturbed Mesocosms Permit Mass Balance and Process Level Studies

15 cm diam. PVC Core

Extendible Pipe

Hydraulic Jack with press

Back side of pit

Side of pit where core will be extracted

Seasonal High Water Table

Mesocosm Dosing Experiment

Carboy: Groundwater

Br+/5%15NO3

15N 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

Water Table

Introduced plume: 44 kg sample size

2 cm mini-piezometer

1. Pump groundwater2. Amend with 15NO3

-

and Br-

3. Lower DO to ambient levels with gaseous SF6

4. Push (inject) into well5. Incubate6. Pull (pump) from well7. Analyze samples for

15N2 and 15N2O (products of microbialdenitrification)

(Addy et al. 2002, JEQ)

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

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)

N2O production rate 4.26 -0.69 - 16.1 76

High valley-wide variability in point-based N transformation rates

Aspect

N m

iner

aliz

atio

n ra

te,

Nitr

ifica

tion

rate

(kg

N h

a-1 d

-1)

0.0

0.5

1.0

1.5

2.0

N2O

pro

duct

ion

rate

(g N

ha-1

d-1

)

0.0

0.5

1.0

1.5

2.0

N2O productionN facing S facing N facing S facing N facing S facing

a

b**

ab**

N mineralization Nitrification

Landscape attributes (ASPECT) relate to N transformation rates

N mineralization Nitrification

Elevation

N m

iner

aliz

atio

n ra

te,

Nitr

ifica

tion

rate

(kg

N h

a-1 d

-1)

0.0

0.5

1.0

1.5

2.0

N2O

pro

duct

ion

rate

(g N

ha-1

d-1

)

0.0

0.5

1.0

1.5

2.0

N2O productionlow high

a

b***

b***a

a

b***

low high low high

Landscape attributes (ELEVATION) relate to N transformation rates

Dominant species

N m

iner

aliz

atio

n ra

te,

Nitr

ifica

tion

rate

(kg

N h

a-1 d

-1)

0.0

0.5

1.0

1.5

2.0

2.5

N2O

pro

duct

ion

rate

(g N

ha-1

d-1

)

0.0

0.5

1.0

1.5

2.0

RS AB YB SM PB RS AB YB SM PB RS AB YB SM PB

N mineralization Nitrification N2O production

a

abcabc

c*

aab ab

b

c***

Landscape attributes relate (SPECIES) toN transformation rates

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

Denitrifying Bacteria

Surface water storage

Algal matsBiofilms

Woody debris Biofilms

Hyporheic exchangeRunkel USGS

Hyporheic Exchange:

Developed vs Forested Storm Hydrographs

0

50

100

150

200

250

300

350

400

0 2 4 6 8 10 12 14 16

TimeFl

ow R

ate

I. Natural Channel

II. Channel with Incision Due to Increased Runoff

Water Table Stream

• Channel Erosion• Nonfunctional Floodplain• Dry Riparian Soils

Developed

Forested

Intensive Land Use: • Higher flood flows

• Less recharge• Lower Riparian Water Tables

Groffman et al, 2004

Nutrient inputs

Bank Incision

Removal of riparian zone

Stream Degradation

Increased Nitrogen Concentrations

Push Pull Groundwater Denitrification Studies: Low Bank (Unrestored)

High non-connected bank

(Restored)

Low Bank “Connected”to Riparian Water Table

(Restored)

0

50

100

150

200

250

300

June 2003 November 2003 June 2004

Date

Den

itrifi

catio

n R

ate

(μg/

N/k

gso

il/da

y)Unrestored High BankUnrestored Low BankRestored High Un-connected BankRestored Low Connected Bank

Kaushal et al. (2008)

Stream morphology and genesis may provide insight into stream denitrificationThe 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

• 100 lower order Geo-referenced streams

• 6 transects per site

- Hydric soil width

- Presence of seeps

• Compare to SSURGO - Hydric status

- GeomorphicClassification

- Measurements

Water flow

T1 T2 T3

30m

Stream

7.5m 7.5m

Right Bank

Left Bank

T1 T2 T3

SSURGO Riparian Zone Validation StudySoil Survey Geographic Digital Data 1:24,000 vs. Field Data

Riparianecosystem

Surface flow(short-circuiting?)

Stream

Groundwater Seeps: Field Data-Seeps found at 29/34 hydric till sites : Expect reduced groundwater N removalpotential in till-No seeps found at 16/18 hydric outwash sites: Expect groundwater flow through hydric soils with high denitrification potential

Till HydricSoil

% o

f si

tes

>10

m o

f hy

dric

soi

ls>

10m

of

hydr

ic s

oils

& N

O s

eeps

pre

sent

& N

O s

eeps

pre

sent

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

HydricTill

N=34

HydricOutwash

N=18

NonhydricTill

N=17

NonhydricOutwash

N=10

HydricOrganic&AlluviumN=21

SSURGO Validation StudyHydro-geomorphic settings with high potential

for riparian groundwater nitrate removal

30m buffer

Stream flow

T1 T2 T3

Rte 165

SPD

VPD

PD

VPD

PD

SPD

MWD

Right bank

Left bank

Soil Map Units Only Accurate for

Presence/Absence of Hydric Soils

Field Observations:

• Ground-truth map: 3-4 drainage classes

• SSURGO composed of 1 soil map unit

Rte 165

N

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.