Comparing Stream Discharge, Dissolved Organic Carbon, and

Selected MODIS Indices in Freshwater Basins

Wade Shaver and Dr. Wil Wollheim

Research and Discover

University of New Hampshire

Summer 2009

Background• Dissolved Organic Carbon (DOC) is an important water quality parameter because:

• It creates disinfection by-products in water treatment facilities, which are carcinogenic, and it is responsible for the transport and fate of toxic, heavy metals such as mercury. (Aiken and Reddy, 2002; Dittman et al., 2009; Singer, 1999)

• It can help explain anomalies in the terrestrial carbon budget, and provide insight into climate change phenomena. (Striegl et al. 2005, Worral and Burt 2007, Freeman et al. 2001, Fahey et al. 2005)

Background• Proposal submitted to NASA with an objective to “Quantify DOC quantity and quality across season and flow conditions … by coupling terrestrial and aquatic remote sensing information, models, and field measurements.”

• Preliminary findings showed that the Moderate Resolution Imaging Spectroradiometer (MODIS) Enhanced Vegetation Index (EVI) had a good relationship with temporal DOC variability in the Ipswich River Basin in Massachusetts.

Purpose

To explore using remote sensing tools as a means for predicting temporal DOC variability in freshwater basins.

Methods• Water quality data from the United States Geological Survey (USGS) National Water Quality Assessment (NAWQA) program was obtained.

• Site Selection Criteria:• Small Receiving Basins (< 600km2)• Continuous, Long-term DOC and Discharge Data

• MODIS data was collected for each site’s receiving basin and evaluated along with the temporal variability in DOC and discharge.

• The MODIS indices were chosen based on theirconnections with terrestrial DOC and include:

• Normalized Difference Vegetation Index (NDVI)• Enhanced Vegetation Index (EVI)• Daily Photosynthesis (PSN)• Leaf Area Index (LAI)

• Coefficients of determination (r2) and correlation coefficients (r) were calculated for relationships between DOC vs. Discharge and DOC vs. MODIS.

Site Locations

OH PA

NY

MA

VT

NH

WV

CT

NJ

ME

VA

NC

MDDE

RI

Atlantic Ocean

Lake Ontario

N

Ipswich Site

Study Sites

ResultsDischarge Correlated Site Discharge Poorly Correlated Site

ResultsAs the DOC vs. Q correlation coefficient increases, the DOC vs. MODIS correlation coefficient decreases. (Significance < 1% for all indices)

ResultsData Unaltered DOC Outlier Removed/MODIS Shifted Ahead One Month

Results

(For All Sites: 30<n<160)

Site DOC vs Q DOC vs Q r DOC vs NDVI r DOC vs EVI r DOC vs PSN r DOC vs LAI r1119375 no effect 0 0.431 0.37 0.374 0.3361124000 diluting -0.212 0.55 0.471 0.411 0.491125100 diluting -0.397 0.515 0.429 0.41 0.491184490 concentrating 0.462 0.141 0.155 0.126 0.1181192500 no effect -0.077 0.428 0.484 0.345 0.4091196222 concentrating 0.507 0.247 0.1 0.207 0.1381203000 concentrating 0.322 0.378 0.35 0.239 0.2971208049 diluting -0.416 0.647 0.633 0.473 0.6431485500 concentrating 0.374 0.421 0.485 0.445 0.4581487000 concentrating 0.831 0.232 0.161 0.322 0.2051491000 concentrating 0.801 0.1 0.105 0.089 02097464 concentrating 0.572 -0.032 0 0.032 -0.071Ipswich no effect 0.1 0.471 0.469 0.411 0.352

Correlation Coefficients between DOC vs. Discharge and DOC vs. MODIS

Conclusions• MODIS indices used in this study were found to account for significant variations in DOC in some basins.

• As the DOC vs. discharge correlation increases the DOC vs. MODIS correlation decreases, but only if the discharge effect is concentrating.

• Sites with diluting discharge effects have the best MODIS correlations.

• When there is a good DOC vs. MODIS relationship, the MODIS index seems to rise and fall shortly before the DOC measurements, indicating a “lag time.”

• When MODIS indices have the best correlation coefficients with DOC variability they are the NDVI and EVI.

Future Work• In order to better examine DOC vs. MODIS correlations regression trees should be developed (eg. Xiao et al., 2008) to account for things such as land cover, wetlands, discharge events, droughts, etc.

• Other sites outside of the USGS NAWQA program should be investigated in the same manner. (In progress)

• Field measurements in smaller headwater basins should be established to ensure a terrestrial signal is being obtained to compare to terrestrial MODIS products. (In progress)

• Other MODIS indices like Gross Primary Production (GPP) and Land Surface Water Index (LSWI) should be considered.

Acknowledgements

UNH EOS Staff

Ben CurranStanley Glidden

George HurttRichard LammersMichael Routhier

ReferencesWater quality data obtained from USGS NAWQA web site: http://water.usgs.gov/nawqa/MODIS data obtained from: http://daac.ornl.gov/MODIS/

Aiken, G. and M. Reddy (2002). Interactions of mercury with dissolved organic carbon in the Florida Everglades. U.S. Dept. of Interior Fact Sheet. USGS.

Dittman, J. A., J. B. Shanley, C. T. Driscoll, G. R. Aiken, A. T. Chalmers and J. E. Towse (2009). Ultraviolet absorbance as a proxy for total dissolved mercury in streams. Environmental Pollution, 157: 1953-1956.

Fahey, T. J., T. G. Siccama, C. T. Driscoll, G. E. Likens, J. Campbell, C. E. Johnson, J. J. Battles, J. D. Aber, J. J. Cole, M. C. Fisk, P. M. Groffman, S. P. Hamburg, R. T. Holmes, P. A. Schwarz, and R. D. Yanai (2005), The biogeochemistry of carbon at Hubbard Brook, Biogeochemistry, 75, 109-176.

Freeman C., C.D. Evans, D.T. Monteith, B. Reynolds, and N. Fenner (2001). Export of organic carbon from peat soils. Nature, 412: 785.

Singer, P. C. (1999). Humic substances as precursors for potentially harmful disinfection by-products. Water Science Technology, 40: 25-30.

Striegl, R., G.R. Aiken, M. Dornblaser, P. Raymond, and K. Wickland (2005). A decrease in discharge-normalized DOC export by the Yukon River during summer and autumn. Geophysical Research Letters, 32: L21413, doi:10.1029/2005GL024413.

Worrall, F., and T. P. Burt (2007), Flux of dissolved organic carbon from UK rivers, Global Biogeochemical Cycles, 21.

Xiao, J. et al. (2008), Estimation of net ecosystem carbon exchange for the conterminous United States by combining MODIS and AmeriFlux data. Agricultural and Forest Meteorology, 148, 1827-1847.