The perpetual increase in California’s population places growing pressure on water supplies within the state. As a result, agricultural and urban areas frequently have conflicting interests and goals surrounding issues of water supply and quality. One such area of active conflict is in the Sacramento-San Joaquin Delta, where agricultural activities are commonly cited as the cause for deterioration of water quality observed as river water transits. As a result, to protect drinking water supplies within the Delta, state and federal planners (CALFED) are considering removal of a significant amount of agricultural land (up to 250,000 acres) from production and converting it to tidal wetlands. Recent preliminary studies, however, have suggested that the changes in water quality may not be due to agricultural activities.¹ The purpose of our studies is to provide a more rigorous examination of this issue and more clearly understand the changes in water quality within the Delta. This information will be useful to agency planners and managers as they make decisions regarding agricultural land retirement as well as water supply and quality in the Delta.

Natural waters contain dissolved organic compounds (DOC) that react to form carcinogenic and teratogenic substances (predominately trihalomethanes (THM)) during the chlorinating disinfection treatment necessary for release as drinking water.² The final concentrations of some of these hazardous compounds are stringently regulated by the US Environmental Protection Agency.³ Delta water is of particular concern because 22 million Californians currently drink water originating in the Sacramento-San Joaquin Delta. Unfortunately, the Delta water contains high levels of bromide and DOC suspected of contributing to the formation of the regulated hazardous compounds found in drinking water. The direct and infrastructure costs of treating this problem are in the billions of dollars prompting state and federal agencies (CALFED) to seek solutions to the problems in the watershed, funded in part by the passage of Proposition 204 in 1996. This problem will only become of greater significance in the decades ahead as the population in California grows and pressure on water resources increases. One solution currently being evaluated is to remove a fraction of agricultural land within the Delta and restore it to wetlands.⁴ This will have an immense economic impact upon the portion of the agricultural community who currently rely on this land. This impact will be felt in terms of lowering productive farming acreage, which will also undoubtedly decrease farm-related jobs, influencing the livelihoods of many farming families.

The Delta is a region of below sea level, peat rich islands maintained in agricultural production by a series of levees and pumps, which capture and return irrigation waters into Delta channels. It is commonly held that agricultural activity on the peat islands releases dissolved organic carbon (DOC) into irrigation return waters which proves to be problematic when Delta waters are later treated for use as drinking water.⁵ However, evidence that agricultural activity is the principle cause of the problem is indirect and inconclusive. (Bergamaschi, in prep).⁸ The studies currently underway in our lab represent a level of chemical scrutiny not yet applied to these issues. We expect the work provide much new information toward understanding the highly complex issues involved in water quality. The work currently underway is designed to address the following questions using a variety of physiochemical measurements diagnostic of the source and chemical composition of DOC in export waters:

1. Is it generally true that addition of DOC agricultural return waters measurably and significantly changes the composition of the DOC in Delta waters in a manner consistent with the observed degradation in water quality?

2. Specifically, is the DOC components present in agricultural return waters a significant contributor of the type of carbon that actually form the hazardous compounds in drinking water?

3. How do the fundamental processes governing the release of DOC from agricultural operations on peat and mineral soils differ? Can these differences provide possible mitigation strategies for DOC?