Flow paths and phosphorus transfer pathways in two agricultural streams with contrasting flow controls

Abstract

In this paper, we analyse 4 years of data from simultaneous high‐frequency monitoring of streamflow and phosphorus (P) concentration. This was carried out to investigate hydrological flow paths and P transfer pathways from diffuse sources in two intensively farmed river catchments (~10 km2) with contrasting flow controls and dominating flow paths. Catchment scale P loss was viewed on an annual and event flow basis and related to hydrological flow paths. A grassland catchment with mostly poorly drained soils, and a higher Q10:Q90 ratio (60 compared with 24), had three times higher annual P loss than an arable catchment with mostly well‐drained soils (1.04 compared with 0.34 kg TP ha−1) despite the arable catchment having larger areas with high soil P status and more discharge. Neither of the catchments indicated supply limitations. The magnitude of the P losses from the two catchments was not defined by land use, source pressure or discharge volume but rather by more basic rainfall‐to‐runoff partitioning influences that determine proportions of quickflow and slowflow. There were larger differences between the years than between the catchments, and the P loss of the arable catchment appeared more sensitive to climate. The results confirmed the need to manage the quickflow components of runoff to moderate P transfers. Therefore, in order to further reduce diffuse pollution it may be necessary to account for the contrast in hydrological function before or in addition to any of the other factors known to influence P losses from catchments (such as soil P and land use). Schemes designed to attenuate diffuse P after mobilization from soil surfaces can then be targeted (and resourced) more effectively. Copyright © 2014 John Wiley & Sons, Ltd.

Key factors influencing differences in stream water quality across space

“…As a result, the amount of mobilized constituents delivered to the stream can vary with seasonal shifts in flow. 139,150,[154][155][156][157][158] Due to the importance of overland runoff in transporting sediments, particulate nutrients and salts (in urban catchments only) to receiving streams, it is often assumed that these constituents have a positive relationship to river discharge. 114,136,139,159 On the other hand, in rural catchments, salts and dissolved nutrients are typically transported by subsurface flows, and as such they are assumed to have a negative relationship to river discharge, when this discharge is entering the river largely through overland runoff.…”

A data-based predictive model for spatiotemporal variability in stream water quality

“…Water quality conditions can vary across different events as well as at daily, seasonal and inter-annual scales at an individual location (Arheimer and Lidén, 2000;Kirchner et al, 2004;Larned et al, 2004;Pellerin et al, 2012;Saraceno et al, 2009). Water quality conditions also typically differ substantially across locations (Meybeck and Helmer, 1989;Chang, 2008;Varanka et al, 2015;Lintern et al, 2018a). These variabilities in stream water quality are driven by three key mechanisms: (1) the source, which defines the to-D. Guo et al: A data-based predictive model tal amount of constituents available in a catchment; (2) the mobilization, which detaches constituents (both in the particulate and dissolved forms) from their sources via processes such as erosion and biogeochemical processing; and (3) the delivery of mobilized constituents from catchments to receiving waters via multiple hydrologic pathways including surface and subsurface flow (Granger et al, 2010).…”

“…At the same time, temporal shifts in water quality are also influenced by changes in pollutant sources such as land use and land management, including urbanization, agriculture and vegetation clearing (Ren et al, 2003;Smith et al, 2013;Ouyang et al, 2010). In addition, water quality can also vary in time with variations in the mobilization and delivery processes, which are largely driven by the hydroclimatic conditions in a catchment, such as streamflow (Ahearn et al, 2004;Mellander et al, 2015;Sharpley et al, 2002;Zhang and Ball, 2017), the timing and magnitude of rainfall events (Fraser et al, 1999;Miller et al, 2014), and temperature (Bailey and Ahmadi, 2014).…”

Identifying Surface Runoff Pathways for Cost-Effective Mitigation of Pollutant Inputs to Drinking Water Reservoir

“…The transfer of diffuse nutrients from NPS to water bodies is carried out by overland quickflow pathways and belowground slowflow pathways. Overland flow is essential in the relocation of agricultural pollutants [6,7], being the main transport route for phosphorus compounds-dissolved and particulate forms and an important route for nitrogen compounds-organic forms associated with eroded soil and a soluble mineral form [8,9]. Pollutant transport via surface runoff is especially intensified in catchments which are hydrologically sensitive to rainfall (vulnerable to contamination following precipitation events).…”