The overarching aim of this thesis is to expand the knowledge base on the dynamics of total dissolved solids, with special focus on the most widespread nutrients in agricultural systems (N, and to a lesser extent P). To this end, (1) the exports of dissolved solids and their dynamics in a watershed network have been quantified, considering different agrosystems of the region of Navarre (Spain). Recognizing the influence of these compounds on different water bodies, and with the aim of shedding more light on the black box watershed approach in water quality, (2) the relatively recent concept of overland flow connectivity has been assessed through an Overland Flow Connectivity index. This index is based on broadly adopted overland flow connectivity indices, and implemented at two rainfed winter cereal watersheds (Latxaga and La Tejería). Regarding nutrients, and focusing on nitrate and phosphate dynamics, (3) these two watersheds have been characterized in terms of concentration and exports of nitrate and phosphate, for a range of temporal scales, with insights on the controlling factors of these processes. Finally, (4) the nutrient controlling factors previously identified have been quantified considering different possible scenarios. The AnnAGNPS model capacity has been evaluated for dissolved nitrogen exports at the two rainfed winter cereal watersheds.