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Assessing the Consequences of Land Use Change in the Upper Potomac

Robert H. Gardnerwith

Jason Julian, Andrew J. Elmore,Todd R. Lookingbill, Marcella Suarez-Rubio

Appalachian LaboratoryUniversity of Maryland Center for Environmental Science

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The Appalachian Laboratory

To “… determine the effects of natural and human-induced changes on organisms, landscapes, and biogeochemical and hydrological cycles.”

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Outline

1. Importance of land-use and land-cover

(LULC) change in the Potomac River

Basin

2. The challenge of determining effects

3. An integrated approach for prediction

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1. Importance of LULC change• LULC is accelerating and is global in extent• Directly linked with declines in

– Biodiversity– Water quality and availability– Ecosystem productivity (especially

economically important species)• LULC may also

– Accelerate climate change– Enhance the spread of disease (new

pandemics)

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• Basin: 38,000 km2

• Mainstem:617 km (170 km tidal)

• 6 physiographic provinces

• Climate boundary

The Potomac River Basin

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Key attributes of the PRB• Located in one of most rapidly

urbanizing areas in the US– 5.3 million people w/n basin– Coal mining affects Appalachians– Agriculture in Ridge and Valley– Piedmont and Coastal Plain continue

to be urbanized• The 617 km river main stem has

relatively unregulated flows

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History of LULC change• Not glaciated – but glacial runoff produced

coastal plain & Chesapeake Bay• Frontier stage – (17th century)

– natural resource use, local deforestation• Agricultural Expansion – (18th century)

– Pops of 380,000– 20-30% of forests cleared– Sediment accumulation in Bay affect

navigation

http://www.chesapeakebay.net/history.htm

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More history• Industrialization – (late 18th century)

– Urban corridor formed– Population of 2.5 million, raw sewerage

in Bay– Railroads consume 15-20 million acres

of Eastern Deciduous Forest• Population expansion – (19th century)

– Beginning of environmental legislation and control (Clean Air Act, etc.)

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Effects of LULC within the Potomac• Hardened surfaces result in buried streams

with increased throughput– Nutrient retention declines, export

increases• Population growth increases water demands

– From Upper Potomac to Lower• Ecosystem recovery from wide variety of

disturbances remains unknown• New invasives impact terrestrial and aquatic

habitats

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The problem of buried streams

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The gradient of population density

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Lower Potomac >> Upper Potomac

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Low-flow correlated with high demand

Lookingbill et al., in press

Low flow frequency Low flow demand

112 year record shows 13% of years have extremely low flows

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Invasive organisms are here to stay– Gypsy moth– Hemlock wooly adelgid– Chestnut blight

• New (potential)– Emerald ash borer has been found in MD– Sirex noctilio – wasp (horntail) kills pines– Sudden oak death– Asian long horned beetle (in MD)

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Potomac River Ecosystem has not been adequately studied

River ISI References

Columbia 3,263Mississippi 2,921Colorado 2,195Hudson 1,193Missouri 826Potomac 309

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2. Determining effectsLandscapes are composed of many

“elements” including …– roads– agricultural “units”– forests of diverse types and ages– urban & suburban development

And diverse economic conditions

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We know that the spatial arrangement of “elements” is critical

• Riparian buffers effectively reduce sediment and nutrient export

• While development selectively removes headwaters ecosystems*

• No single sub-watershed is representative of the Potomac

• Small critical areas (wetlands) are most effective nutrient and sediment filters

*Elmore and Kaushal, 2008

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Effects of LULC are not additive

• If linear then effects of change are additive– we can extrapolate using mean value(s) – landscape assessment can be produced

by simple summation (spread sheet)– or by sampling extremes (boundaries)

and interpolating for each set of unique conditions

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“Many challenges remain in extending our understanding of how hydrologic processes within small catchments scale to larger river basins.”

The problem of scale

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0

0.2

0.4

0.6

0.8

1

1.2

0 10 20 30 40

Impervious Land Cover (%)

Bro

ok T

rout

Den

sity

(#/m

2 )

AbsentPresent

Critical thresholds: Brook trout density and impervious cover

Stranko et al. 2008

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Disturbance induces time lags• Disturbances are not simple transient

events?– History of change is important

• We may not be able to predict the future from the past

• Forest harvesting has altered age and species distribution of flora– Decline (possibly permanent declines)

in oak and pine abundance

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Gypsy Moth Defoliation and Annual Nitrate-N Export

1980 1985 1990 19950

20

40

60

80

100

0.0

1.0

2.0

3.0

4.0

5.0

Water Year

% o

f for

este

d ar

ea

kg/h

adefoliation

nitrate-N export

White Oak Run, Virginia

Eshleman et al. 2005

Significant effects on nutrient cycling

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AMD

Permanent effects of coal mining

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3. An integrated, predictive approach

Understanding -> predictionBut this requires:• Spatial and temporal characterization of

weather patterns• Determination of trends in land use change• A process-based representation considers

interactive effects of multiple changes• Estimation of unknowns and uncertainties

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Interactive effects are important?• Flood potential – is a combined effect of

LULC and climate change• Denitrification – depends on the location

of critical habitat placement– Sources and sinks– Effectiveness of restoration

• Meeting water quality demands – A moving target: growth, development,

LULC and climate change

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SLEUTH: a model of land-use change

• USGS sponsored development– Slope, Land use, Exclusion, Urban

extent, Transportation, Hillshade – Clark (1998)

• Being explored and widely used w/n Chesapeake Watershed

• A pattern-based model – Uses a fine-scale, gridded landscape– Projects urban growth

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Historical records are necessary

• Required GIS layers– Urban growth (3-4 layers)– Roads (2 layers)– Exclusion (1 layer) – protected lands– Hillshade (1 layer)– Slope (1 layer)– Land use (1 layer) – current

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Empirical (best fit) of 5 growth parameters govern probability of urbanization• Spontaneous dispersion – formation of

new urban locations• Growth (increase in size) of new urban

locations• Growth of old (established) locations• Road gravity – increased growth rates

near roads• Slope resistance – decreased growth

with increasing slopeDietzel (2007)

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Calibration first

• Brute force calibration (inefficient)– Parameters varied over broad range– Monte Carlo techniques applied– Subset (“best fit”) determined by

spatial comparison to history of change

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Prediction requires

• Current land use maps for initialization– Urban extent– Transportation network– Exclusion layer

• Future scenarios performed by varying– Exclusion layer (e.g., streams, etc.)

•And exclusion “rules”– Constraints on transportation network

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Baltimore-Washington projections (Jantz et al. 2003)

• Three scenarios for piedmont & coastal plain of Maryland and Northern Virginia

• Variable exclusion layers developed– By state and land use type

• Scenarios:A. Current trendsB. Managed growthC. Ecological preservation

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ResultsChange (km2 / y)

Scenario Urban Forest Agriculture

A. Current trends

110 -43 -51B. Managed

growth41 -15 -15

C. Ecological preservation

28 -10 -9

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Summary• Moderate “exclusions” have large effects

on patterns of LULC change• Population trends continue to drive

change• Model improvements always desirable

– Local policies not yet implemented• Linkage of land use projections with

ecosystem models urgently needed– Water, nutrients, sediments as a

function of land-use change– Biotic effects of land-use change

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Our efforts for the Potomac

• We have spent ~1 year on data acquisition, verification

• Calibration has been performed• Simulations begun on development

scenarios in the Upper Potomac– Focus on effects of habitat change on

bird community (Ph.D. thesis)

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Next steps

• This summer– Plans for a workshop at Appalachian Lab

•Include relevant parties using SLEUTH w/n Chesapeake

•Share “mutual” resources (data layers)•Apply uniform methods for calibration

and prediction – for cross-comparisons•Shared effort – data enhancement,

model improvement

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Special thanks Sujay KaushalWalter BoyntonTom FisherLarry SanfordJeff CornwellBill DennisonClair Jantz