Concentration‐discharge relationships derived from a larger regional dataset as a tool for watershed management

Abstract

Concentration‐discharge (C‐Q) relationships have been widely used to assess the hydrochemical processes that control solute fluxes from streams. Here, using a large regional dataset we assessed long‐term C‐Q relationships for total phosphorus (TP), soluble reactive phosphorus (SRP), total Kjeldahl nitrogen (TKN), and nitrate (NO3) for 63 streams in Ontario, Canada, to better understand seasonal regional behavior of nutrients. We used C‐Q plots, Kruskal‐Wallis tests, and breakpoint analysis to characterize overall regional nutrient C‐Q relationships and assess seasonal effects, anthropogenic impacts, and differences between “rising” and “falling” hydrograph limbs to gain an understanding of the dominant processes controlling overall C‐Q relationships. We found that all nutrient concentrations were higher on average in catchments with greater levels of anthropogenic disturbance (agricultural and urban land use). TP, SRP, and TKN showed similar C‐Q dynamics, with nearly flat or gently sloping C‐Q relationships up to a discharge threshold after which C‐Q slopes substantially increased during the rising limb. These thresholds were seasonally variable, with summer and winter thresholds occurring at lower flows compared with autumn and greater variability during snowmelt. These patterns suggest that seasonal strategies to reduce high flows, such as creating riparian wetlands or reservoirs, in conjunction with reducing related nutrient transport during high flows would be the most effective way to mitigate elevated in‐stream concentrations and event export. Elevated rising limb concentrations suggest that nutrients accumulate in upland parts of the catchment during drier periods and that these are released during rain events. NO3 C‐Q patterns tended to be different from the other nutrients and were further complicated by anthropogenic land use, with greater reductions on the falling limb in more disturbed catchments during certain seasons. There were few significant NO3 hydrograph limb differences, indicating that there was likely to be no dominant hysteretic pattern across our study region due to variability in hysteresis from catchment to catchment. This suggests that this nutrient may be difficult to successfully manage at the regional scale.

Improving the understanding of N transport in rural catchments under Atlantic climate conditions from analysis of the concentration-discharge relationship derived from a high frequency data set

“…The above findings contrast with the general interpretations presented in several previous studies carried out in rural catchments (e.g., Bowes et al, 2015;Rose et al, 2018;D'Amario et al, 2021), which described exclusively NO3 dilution processes linked to dilution of NO3 concentrations in groundwater by surface runoff. However, in the study catchment, the dilution responses (with anticlockwise rotation (ΔC ≤ 0%)) were only observed in certain runoff events recorded just after other events (Δt < 1day).…”

“…In the case of the Corbeira catchment, the TKN response was almost concurrent with discharge, so TKN may come from the eroded soil material delivered to the stream primarily by surface runoff, in a similar way to suspended sediment matter and particulate phosphorus (Rodríguez-Blanco et al, 2013;. This is in accordance with findings from (D'Amario et al, 2021), who reported a dominance of clockwise patterns for TKN in Canadian catchments consisting of different types of land use due to the surface runoff of eroded soil particles. Although the dominant pattern for TKN concentrations is clockwise, some events showed anticlockwise trajectories.…”

“…This traditional sampling method can provide valuable information to identify sites that are under pressure due to anthropogenic activities, also to observe long-term trends in relation to land use, but cannot provide knowledge on nutrient dynamics under contrasting hydrological conditions, which is essential to develop suitable management programs to restore or maintain water quality (Bieroza et al, 2018). Therefore, there is an increasing interest in high-frequency water quality monitoring over the long term, which can be used to investigate nutrient behaviors, as this type of monitoring enables a broad range of nutrient concentrations in response to discharge to be captured (Bieroza et al, 2018;D'Amario et al, 2021).…”

Catchment concentration–discharge relationships across temporal scales: A review

“…Power law 1 <5 years of weekly to monthly grab samples (F. R. Hall, 1971) Discrete 2 30 years of low frequency grab sample data (e.g., 5-7Â per year; Godsey et al, 2009 3 >2 years of 15-min sensor data (Koenig et al, 2017;Speir et al, 2021) Break-point analysis 1 >3 years of daily concentrations (Meybeck & Moatar, 2012) Discrete 2 Long-term (10-30 years) of weekly to monthly data (Moatar et al, 2017;Underwood et al, 2017) 3 Hourly stormflow samples from 44 events across >10 years (L. A. Rose et al, 2018) 4 >1 year of daily mean sensor data (Marinos et al, 2020;Speir et al, 2021) 5 >10 years of grab sample data (D'Amario et al, 2021) 6 7 years of weekly to monthly gaseous carbon concentrations (G omez-Gener et al, 2021) Long-term data analysis (≥10 years)…”

Role of Lakes, Flood, and Low Flow Events in Modifying Catchment‐Scale DOC:TN:TP Stoichiometry and Export

“…For example, flooding of forested areas can increase N and P release, while decreasing TN:TP ratios in reservoirs (Talbot et al., 2021). In forested landscapes, nutrient and DOC concentrations may decrease with stream discharge, due to a limited pool of readily mobilizable solutes (Basu et al., 2010; D’Amario et al., 2021; Fasching et al., 2018; Moatar et al., 2017), especially during snowmelt in northern landscapes influencing N export to streams (Sebestyen et al., 2009).…”