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Understanding and managing against phosphorus (P) transfer from agricultural soils to receiving waters is a multidisciplinary task in which the role of hydrology is particularly difficult to simplify. We review current knowledge to define the spatial and temporal controls on P transfer from agricultural soils via the various hydrological pathways. Rainfall intensity and duration and the interval between rainfall events are key temporal variables which influence the discharge (and hence P load) to receiving waters. In terms of understanding mechanisms, we postulate that levels of hydrological activity may be nominally classified at two levels. Level 1 activity occurs during light or little rainfall for a high proportion of time; in contrast, level 2 activity occurs less frequently but is more energetic and has a large capacity for P transfer over a small time period. The range of potential hydrological pathways of P transfer creates confusion because terminology varies. Often, process terms such as leaching or generic terms such as drainage are confused with hydrological pathways per se. Here we define the spatial variation in the hydrological pathways responsible for P transfer at two scales-soil profile and slope/fieldwhich subsequently can help the understanding of P transfers into the wider catchment, where problems occur. Our aim is to provide a simplified basis for classifying the otherwise complex hydrochemical regimes which result in P transfer.

Ammonia is a reactive pollutant emitted primarily by agricultural sources near ground level in the rural environment. The consequence of these factors is that, in addition to the effects of long-range pollutant transport, ammonia has major effects at a local scale, with emission and receptor areas often closely located in the rural landscape. There is a substantial local spatial variability that needs to be considered in effects assessments, while variations in local deposition may affect the amount of ammonia available for impacts further afield. The wide-ranging UK programme ADEPT (Ammonia Distribution and Effects ProjecT) has addressed these issues through a combination of measurement and modelling activities concerning the distribution of emissions, atmospheric transport, deposition and effects assessment. The results are illustrated here by summarizing the findings of a joint experiment at Burrington Moor, Devon, and wider modelling contrasting the variability at a field scale with 5 km resolution estimates for the UK. The fraction of emitted NH3 deposited locally is shown to depend critically on the downwind land-cover, with fluxes being dependent on interactions with the ammonia compensation point. This will restrict deposition back to agricultural land, but may mean that non-conservation woodlands could be of benefit to recapture a significant fraction of emissions. The generalized models demonstrate the high spatial variability of ammonia impacts, with a case study being used to show the consequences at a field scale. In source regions substantial variability occurs at sub-1 km levels and this will have major consequences for the emission reduction targets needed to protect ecosystems.