Response to Comments by Liu et al. 2021 to 'Springs drive downstream nitrate export form artificially-drained agricultural headwater catchments' by Goeller et al., 2019

摘要

We thank Liu et al. (2021) for highlighting some important aspects of our study, Goeller et al. (2019) "Springs drive downstream nitrate export form artificially-drained agricultural headwater catchments." Below we respond to two main points focussing on: 1) the monitoring methods and the potential underestimation of tile drain contributions to downstream nitrate fluxes, and 2) the potential misinterpretation of sources of variability in downstream nitrate fluxes reported. Overall, we agree with Liu et al. (2021) that a better understanding of the sources and variability of nitrate fluxes, including uncertainty of these estimates as influenced by monitoring or attenuation, is needed to spatially target and evaluate diffuse pollution management actions, particularly in waterways with artificial drainage. A key challenge that our field study sought to address was to answer these questions across the landscape and at farm-scale for nine small subcatchments receiving multiple load inputs from upstream, groundwater, and tributary surface and subsurface drains. Typically, such studies have been done on single or a small number of agricultural fields or pastures and waterways, potentially missing important insights available from a comparative approach. We therefore welcome the interdisciplinary discussion around how to implement emerging technologies such as high-frequency, in-situ nitrate sensors paired with discrete sampling methods to help fill critical data gaps in waterway monitoring programmes at larger scales. High frequency sampling at the scale we worked on would certainly reduce the uncertainty being debated, and we are hopeful that the technological and financial resources will be available to do that.