Hydrological and hydrochemical dynamics

The terms hydrological and hydrochemical dynamics imply the motion of water and associated solutes under the influence of external forces and mass exchanges. They are also suggestive of process operations and of energy exchange within a defined systems framework. This chapter examines such concepts from two distinct but complementary perspectives. The first section examines in greater detail the fundamental dependency of upland water quality on dynamic hydrological pathways, chemical budgets and catchment characteristics. Here emphasis is placed on micro- to mesoscale processes, and on the role of heterogeneity within basins. The second section considers the aggregate effect of multiple headwater systems routed and mixed via the channel network and the significance of channel-floodplain interactions. This will underline the importance of considering macroscale controls versus anthropogenic impacts from both a spatial and temporal perspective. Throughout the discussion a twofold division into headwater streams and large rivers provides a useful vehicle for examining the significance of scale and connectivity.