GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 158-2
Presentation Time: 9:00 AM-6:30 PM


HASAN, Mejs, Department of Geological Sciences, University of North Carolina, Chapel Hill, Chapel Hill, NC 27599 and BENNINGER, Larry, Department of Geological Sciences, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599,

The effect of storms on water quality in the Chesapeake Bay has been studied in a patchwork way at various sites for short periods of time. We use a relationship between MODIS-Terra red light reflectance and total suspended solid (TSS) concentrations in order to develop a fourteen-year time period of TSS estimates during which effects of storms can be studied. Exponential fits were most appropriate, resulting in viable reflectance-TSS relationships for the four major Lower Western Shore rivers and the Mainstem of the Bay. Other tributaries were less well-disposed for such relationships due to lack of a large range of TSS concentrations, shallow river beds, or low number of data points. Treating the entire Chesapeake as a single entity and modeling a single reflectance-TSS relationship for the entire estuary produced poorer models with less significance compared to treating each channel separately. Over 1000 rain events were studied in the Lower Western Shore between 2000-2014. We did not find conclusive evidence that greater rainfall amounts are accompanied by a corresponding increase in the maximum TSS concentrations within 1 day of the event, nor that post-storm TSS patterns are strongly dependent on land cover. At rainfall events of < 1 inch, maximum TSS within one day of the storm was highly variable, suggesting that factors other than rainfall amount are the main drivers of TSS levels. We did find that high TSS spikes usually require less time than low TSS spikes to return to normal levels. Finally, we found value in the use of prediction intervals around TSS estimates, a statistical procedure not commonly used with satellite-based estimates but which helped ensure our conclusions were based only on rainfall events for which TSS levels changed significantly, and took account of the inherent error involved when relying on satellite estimates.