Keeley Claire Martinez , Anne Liston, Tina Hammel, Steven Sesma, Helen Fillmore, Steven Sadro

Long-term datasets are invaluable resources for understanding broad-level temporal patterns in ecosystems. For over two decades, UC Davis and Lake County Water Resources Department have collaborated on a long-term monitoring project of Clear Lake sediment nutrient concentrations, in an effort to better understand nutrient cycling in Clear Lake. When the need for a new total phosphorus digestion method arose, it was paramount to develop a method that was both more efficient and safer than the previous method while maintaining continuity with the long-term dataset through the calculation of a conversion factor. This white paper details the development and validation of a new total phosphorous digestion method for sediment samples, as well as the calculation of a conversion factor. Our major findings are:
1. The historic and new methods were highly correlated but significantly different.
2. A regression analysis model provided a robust method to convert data between both methods.
3. Both methods produce consistent and acceptable recoveries using a standard reference material.