Correlating Estimated Nutrient Loading Upstream to In-Stream

Water Quality A First Step Using Midwestern Watersheds

Alison Goss April 28, 2004

Introduction

• Global transformation occurring at a rapid scale – Atmospheric variations– Land use alteration (Ehleringer et al

2001; IPCC 1996; Mooney et al 1998).

• Human activity undoubtedly the driver for many of these conversions

• However, predicting the nature of ecosystem response to complex transformations challenging

Context

• Focus on land use change• Part of a larger endeavor to

establish a link between land use change and ecological integrity

• First step in creating linkage is determination of relationship between NPS loadings output from LTHIA and in-stream water quality

• LTHIA not designed for this analysis– Development of nutrient fate

component

Introduction to LTHIA

http://danpatch.ecn.purdue.edu/~sprawl/LTHIA7/documentation/how%20works.html

Context

LTHIA Output

Nutrient Fate

In-Stream Water Quality Ecologica

l Health

Objective: A first step

• Comparison of LTHIA nutrient loading output with historical in-stream water quality data for two areas in the Midwestern United States with differing depths to bedrock

Hypothesis

• Small depth to bedrock– Less nutrient uptake by soil

microbes– Shorter nutrient pathway– NPS loads will be closer to

surface water quality values

Methods

• Collect land use, soil and WQ data for study sites

• Run LTHIA– Focus on N and P

• Calculate 100% conservation runoff concentration

• Compare to known WQ values• Sensitivity Analysis

Study SitesAve. depth to bedrock 32 meters.

Study SitesAve. depth to bedrock 9 meters.

Calculation of conservation nutrient concentration

• Takes LTHIA output (kg/grid cell) and determines in-stream water quality

• Assumes 100% conservation of nutrients in runoff

3 3

( )*1000000( / )( / ) ( )

( ) /1000( / )

NPSload kg mg kgNPSconc mg L or ppm

Runoff m m L

Actual vs. Modeled Nutrient Loading in streams

Driesbach Smith-Fry Pere Muskegon

Modeled Nitrogen(mg/L) 3.70 4.23 4.25 1.86

Actual Nitrogen (mg/L) 6.33 5.60 0.13 0.19

%Difference 42% 24% 3174% 880%

Modeled Phosphorous (mg/L) 1.07 1.24 1.25 0.47

Actual P (mg/L) 0.45 0.46 0.02 0.05

%Difference 138% 167% 6148% 798%

Modeled TN/TP 3.47 3.41 3.40 3.94

Actual TN/TP 14.12 12.04 6.49 3.62

%Difference 75% 72% 48% 9%

DriesbachSmith-

FryPere Muskegon

Modeled Nitrogen (mg/L) 3.70 4.23 4.25 1.86

Actual Nitrogen (mg/L) 6.33 5.60 0.13 0.19

%Difference 42% 24% 3174% 880%

Modeled Phosphorous (mg/L) 1.07 1.24 1.25 0.47

Actual P (mg/L) 0.45 0.46 0.02 0.05

%Difference 138% 167% 6148% 798%

Modeled TN/TP 3.47 3.41 3.40 3.94

Actual TN/TP 14.12 12.04 6.49 3.62

%Difference 75% 72% 48% 9%

Driesbach Smith-Fry Pere Muskegon

Modeled Nitrogen (mg/L) 3.70 4.23 4.25 1.86

Actual Nitrogen (mg/L) 6.33 5.60 0.13 0.19

%Difference 42% 24% 3174% 880%

Modeled Phosphorous (mg/L) 1.07 1.24 1.25 0.47

Actual P (mg/L) 0.45 0.46 0.02 0.05

%Difference 138% 167% 6148% 798%

Modeled TN/TP 3.47 3.41 3.40 3.94

Actual TN/TP 14.12 12.04 6.49 3.62

%Difference 75% 72% 48% 9%

Sensitivity Analysis

Sensitivity Results

113%

113%

143%

194%

0% 50% 100% 150% 200% 250%

Total Runoff (cm)

Total RunoffVolume (m^3)

Total Nitrogen(kg)

TotalPhosphorous

(kg)

LT

HIA

Ou

tpu

ts

Percent Increase

Conclusions

• LTHIA not a good predictor of downstream surface water quality

• N:P may be closer approximation than individual nutrient values– Consistently within 100% of actual

value– Also could be a fluke

• LTHIA highly sensitive to location of curve number within watershed

References• Ehleringer, J.R., T.E. Cerling, and L.B. Flanagan.

2001. Global changes and the linkages between physiological ecology and ecosystem ecology, p. 115-138. In: M. Press, N. Huntly, and S. Levin (eds.), Ecology: Achievement and Challenge. Blackwell, Oxford.

• Intergovernmental Panel on Climate Change. 1996. Climate Change 1995. The Science of Climate Change. Contribution of working group I to the second assessment report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge.

• Mooney, H.A. 1998. The Globalization of Ecological Thought. Ecology Institute, Oldendorf.