Abstract
AbstractCatchment nutrient export, especially during high flow events, can influence ecological processes in receiving waters by altering nitrogen (N) and phosphorus (P) concentrations and relative amounts (stoichiometry). Event‐scale N and P export dynamics may be significantly altered by land use/land cover (LULC) and season. Consequently, to manage water resources, it is important to understand how LULC and season interact to influence event N and P export. In situ, high‐frequency spectrophotometers allowed us to continuously and concurrently monitor nitrate (NO3−) and soluble reactive P (SRP) concentrations and therefore examine event‐scale NO3−and SRP export dynamics. Here we analyzed event NO3−and SRP concentration‐discharge hysteresis patterns and yields for >400 events to evaluate how LULC and seasonality influence event NO3−and SRP export dynamics in three low‐order watersheds with different primary LULCs (agricultural, forested, and urban). Differences among event NO3−and SRP hysteresis patterns suggest these nutrients have different source areas and dominant transport pathways that were impacted by both LULC and seasonality. Unexpectedly, we observed similar seasonal patterns in event NO3−:SRP stoichiometry among LULCs, with the most N‐enriched events occurring in spring, and event stoichiometry approaching Redfield N:P ratios in the fall. However, seasonal stoichiometry patterns were driven by unique seasonal NO3−and SRP export patterns at each site. Overall these findings suggest LULC and seasonality interact to alter the timing and magnitude of event NO3−and SRP exports, leading to seasonal patterns in event NO3−to SRP stoichiometry that may influence ecological processes, such as productivity, in receiving waters.
Highlights
High flow events, such as those driven by snowmelt and rain events, are important drivers of dissolved nutrient transport from terrestrial landscapes to stream networks (Dhillon & Inamdar, 2013; Frazar et al, 2019; Inamdar et al, 2006; Janke et al, 2013; Perdrial et al, 2014; Rosenberg & Schroth, 2017; Sharpley et al, 2008)
Overall these findings suggest land use/land cover (LULC) and seasonality interact to alter the timing and magnitude of event NO3− and soluble reactive P (SRP) exports, leading to seasonal patterns in event NO3− to SRP stoichiometry that may influence ecological processes, such as productivity, in receiving waters
An alternate figure depicting data to link hydrobiogeochemical and ecological processes. This approach provided novel insights into how LULC and seasonality drive nutrient export from catchments and how these drivers interact to produce seasonal patterns in stream chemistry that may influence ecological procolored by season instead of site is available in supporting information (Figure S3)
Summary
High flow events, such as those driven by snowmelt and rain events, are important drivers of dissolved nutrient transport from terrestrial landscapes to stream networks (Dhillon & Inamdar, 2013; Frazar et al, 2019; Inamdar et al, 2006; Janke et al, 2013; Perdrial et al, 2014; Rosenberg & Schroth, 2017; Sharpley et al, 2008). Nutrient transport to stream networks can impact ecological processes in receiving waters by altering absolute nutrient concentrations and the relative availability, or stoichiometric ratios, KINCAID ET AL. It is essential to understand how high flow events drive dissolved N and P transport dynamics and resulting N:P ratios. Our understanding of how key drivers of nutrient transport differently influence dissolved N and P transport during high flow events is limited (Frazar et al, 2019; Gächter et al, 2004; Gao et al, 2014; Vanni et al, 2001). A better understanding of these differences will improve our ability to control downstream N and P transport and the resulting stoichiometry of nutrients in receiving waters
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