Continental shelves are a highly productive part of the oceans, playing a key role for both marine life and human activities. We know that they can easily be affected by a changing climate. They are also a particularly challenging system in marine trace element chemistry. The shelves are very strong sources for trace elements due to river runoff, dry deposition, submarine groundwater discharge (SGD), pore water fluxes, redox and salinity gradients, bioirrigation, and many other processes. These source terms, some of them extremely variable in space and time, are encountered by nearly equally strong and variable sink terms, like bioproductivity, precipitation reactions or fishing, just to name a few. The net flux is therefore a difference of two very large and variable terms, resulting in large uncertainties. In addition, discussing and quantifying individual parts of this budget is often problematic due to slightly different uses of terminology: is advective pore water flux the same as SGD? What are point sources, what are diffuse sources (and where does SGD stand here)? Where do you draw a boundary between suspended particle transport and sediment transport? This talk will aim to highlight a few of the main sources and sinks, uncertainties in their determination and challenges, as well as identifying areas where a closer look at definitions might help to improve our understanding of fluxes across the continental shelf.