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Forcing, Feedbacks, and Coupling

How does the aggregate water balance of a watershed reflect the integrated effect of nonlinear interactions among runoff, vegetation dynamics, mountain block groundwater dynamics, urbanization and water use dynamics?

Prior work in the Great Salt Lake Basin (Shun and Duffy, 1999) has suggested that low frequency components in runoff and Great Salt Lake volume time series are related to modulation of the climate forcing through mountain block groundwater dynamics.

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Reconstructed "noise-free" Precipitation-Temperature-Runoff (P-T-R) phase-plane plot (1950-1990) at three elevations across the Wasatch Front, the watershed for the Great Salt Lake. High elevation P-T-R dominated by annual cycle and orographic forcing. Intermediate elevation reflect translation and intermediate time scales from upland storage as well as transmission losses and recharge from losing streams across the mountain front. Low elevation P-T-R exhibits low- frequency oscillations (decadal time scales) where climate signals are amplified by upwelling groundwater discharge to streams from deep basin sediments.
Source:  Lall and Duffy (2004)

What are the relative roles played by long and short-term climate variability and land use change due to population and economic growth in the region in driving the system dynamics?

The Great Salt Lake serves as a natural integrator for the observation of these dynamics in the forms of lake volume fluctuations and sediment and solute accumulations. Sediments in the Great Salt Lake hold a wealth of historical information and can provide valuable information regarding anthropogenic and natural changes that have occurred within the basin over a variety of time scales. As part of the Great Salt Lake Basins NAWQA Study, the USGS is studying the sediments of the Great Salt Lake for this very purpose.

The following figures illustrate that polycyclic aromatic hydrocarbons (PAHs), which are a large class of chemicals that are suspected to be carcinogenic, are formed through the incomplete combustion of hydrocarbons including coal, oil, gasoline, and wood, and are indicative of the effects of urbanization, have increased with population growth over the past 60 years. In addition, lead concentrations increased after about 1842, coincident with mining and smelter activities in the region, and continued to increase as the use of leaded gasoline became popular. Lead concentrations have decreased markedly since their peak in the mid 1980s since mining and smelting have declined and leaded gasoline is no longer in popular use.

PAHs have increased as the population of Salt Lake County has grown, as evidenced by an increase of these compounds with time in the sediment of Farmington Bay. Lead concentration in sediment core from Farmington Bay indicates increasing inputs after about 1842, coinciding with the mining and smelter activities in the region.
Source:  USGS (2004)

References

Duffy, C. J. and U. Lall, (2001), "The Great Basin as a Natural Laboratory for the Conjoint Dynamics of Water, Earth, Biota and Climate Mass Fluxes," Eos. Trans. AGU, 82(47): Fall Meet. Suppl., Abstract H42A-0338.

Shun, T. and C. J. Duffy, (1999), "Low-Frequency Oscillations in Precipitation, Temperature, and Runoff on a West Facing Mountain Front: A Hydrogeologic Interpretation," Water Resources Research, 35(1): 191-202, doi:10.1029/98WR02818.

USGS. 2004. Water Quality in the Great Salt Lake Basins Utah, Idaho, and Wyoming 1998-2001. National Water-Quality Assessment Program. Circular 1236.

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