Climate and hydrology are relevant control factors determining the timing and amount of nutrientlosses from land to downstream aquatic systems, in particular of phosphorus(P) from agricultural lands. The main objective of the study was to evaluatethe differences in P export patterns and the performance of alternativemonitoring strategies in streams under contrasting climate-driven flowregimes. We compared a set of paired streams draining lowlandmicro-catchments under temperate climate and stable discharge conditions(Denmark) and under sub-tropical climate and flashy conditions (Uruguay). Weapplied two alternative nutrient sampling programs (high-frequency compositesampling and low-frequency instantaneous-grab sampling) and estimated thecontribution derived from point and diffuse sources fitting a sourceapportionment model. We expected to detect a pattern of higher total andparticulate phosphorus export from diffuse sources in streams in Uruguaystreams, mostly as a consequence of higher variability in flow regime (higherflashiness). Contrarily, we found a higher contribution of dissolved P inflashy streams. We did not find a notably poorer performance of thelow-frequency sampling program to estimate P exports in flashy streamscompared to the less variable streams. We also found signs of interactionbetween climate/hydrology and land use intensity, in particular in thepresence of point sources of P, leading to a bias towards underestimation ofP in hydrologically stable streams and overestimation of P in flashy streams.Based on our findings, we suggest that the evaluation and use of moreaccurate monitoring methods, such as automatized flow-proportional watersamplers and automatized bankside analyzers, should be prioritized wheneverlogistically possible. However, it seems particularly relevant in currentlyflashy systems and also in systems where climate change predictions suggestan increase in stream flashiness.
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