Monitoring nutrients in precipitation inputs and other ecosystem fluxes has advanced our understanding of biogeochemical cycling.  However, uncertainty due to variability or error in observations and models has rarely been reported in ecosystem studies. This makes it difficult to determine rates of change over time or compare results across multiple sites with quantitative confidence.  Failure to address uncertainties can lead to erroneous conclusions, for example in identifying missing sources and sinks. Uncertainty analyses can also help to improve efficiency in ecosystem monitoring efforts, allowing sampling designs to maximize information gained relative to the resources required for data collection and analysis.  In this Synthesis Working Group, we propose to develop and apply approaches to estimating uncertainty in precipitation inputs of nutrients for several LTER sites.