Can We Manage Nonpoint‐Source Pollution Using Nutrient Concentrations during Seasonal Baseflow?

Abstract

Core Ideas Nutrient concentrations in streams are positively correlated during baseflow and runoff conditions. High nutrient concentrations at baseflow suggest high nutrient loads from nonpoint sources. Manage nonpoint sources by targeting subwatersheds with elevated nutrient concentrations during baseflow. Focusing on baseflow conditions frees up resources to monitor water quality more broadly across watersheds. Nationwide, a substantial amount of resources has been targeted toward improving water quality, particularly focused on nonpoint‐source pollution. This study was conducted to evaluate the relationship between nutrient concentrations observed during baseflow and runoff conditions from 56 sites across five watersheds in Arkansas. Baseflow and stormflow concentrations for each site were summarized using geometric mean and then evaluated for directional association. A significant, positive correlation was found for NO3–N, total N, soluble reactive P, and total P, indicating that sites with high baseflow concentrations also had elevated runoff concentrations. Those landscape factors that influence nutrient concentrations in streams also likely result in increased runoff, suggesting that high baseflow concentrations may reflect elevated loads from the watershed. The results highlight that it may be possible to collect water‐quality data during baseflow to help define where to target nonpoint‐source pollution best management practices within a watershed.

Inexpensive spot sampling provides unexpectedly effective indicators of watershed nitrogen status

“…The SERC and CBNTN data sets both support the conclusion that spot measurements are very good predictors of flow‐weighted average concentration for materials transported in dissolved form, but much less effective for estimating flow‐weighted average concentrations of materials that bind to particles. This is consistent with other reports of much higher correlations for nitrogen than phosphorus when comparing spot samples to composite samples (Schleppi et al 2006 a , b ) or baseflow spot samples to storm samples (McCarty and Haggard 2016). Table 2 also supports ranking nitrogen> phosphorus > sediment in order of predictability as reported for a variety of modeling approaches (Weller et al 2003, Brakebill et al 2010, Preston et al 2011, Boomer et al 2013).…”

“…6), we support its more widespread application in nitrogen assessment and management. McCarty and Haggard (2016) made a similar recommendation. They argued for a revolution in allocating water quality monitoring resources by using spot sampling of baseflow to assess nitrogen and phosphorus pollution and to target management actions, thus freeing resources to examine water quality at finer spatial scales and to provide a more complete information on spatial variability in water quality across watersheds.…”

“…6) should be tempered when considering phosphorus or other materials transported mainly on particles. McCarty and Haggard (2016) suggested using baseflow sampling for assessing other materials, such as phosphorus. We did find statistically significant correlations between spot measurements of phosphorus and flow‐weighted average levels in composite measurements, but those relationships have much lower explanatory power ( R 2 < 42%) than the relationships for nitrate and total nitrogen ( R 2 > 82%; Table 2).…”

Nutrient Concentrations in Big Creek Correlate to Regional Watershed Land Use

“…Base‐flow conditions in Big Creek were classified from hydrograph inspection when flow had not increased or decreased within 3 d of sample collection. McCarty and Haggard (2016) suggested that stream nutrient concentrations under base flow can be used to identify nonpoint sources and target remedial measures in Boston Mountains and Ozark Highland watersheds.…”

Water Chemistry During Baseflow Helps Inform Watershed Management: A Case Study of the Lake Wister Watershed, Oklahoma

“…A variety of techniques have been used to identify priority locations for BMP implementation to improve water quality, including qualitative indices [e.g., P Index, (Lemunyon and Gilbert 1993; Sharpley et al 2001)] and watershed modeling (Pai et al 2011). Recent work suggests that water quality monitoring during baseflow conditions can be used to prioritize subwatersheds for BMP implementation (McCarty and Haggard 2016). The premise is that stream water quality during baseflow conditions reflects the influence of NPS pollution across the watershed.…”