Identifying diffused nitrate sources in a stream in an agricultural field using a dual isotopic approach

Reconstructing historical changes in phosphorus inputs to rivers from point and nonpoint sources in a rapidly developing watershed in eastern China, 1980–2010

“…When significant changes in human activities occur over time, a long-term monitoring dataset should be divided into several multi-year time intervals for separately calibrating the LAM (Bowes et al, 2009a;Chen et al, 2013). Due to the difficulty in acquiring accurate long-term information on wastewater discharge for the large watershed in this study, the 31-yr time series was divided into several time intervals according to changes in the annual average flow-adjusted TP concentration (representing a net influence of human activities on PS and NPS pollution, Basu et al, 2010) and average flow-adjusted Cl − concentrations during the low flow regime (a proxy for the net influence of human activities on PS pollution, Jarvie et al, 2012;Ding et al, 2014). Due to the absence of a significant correlation between flow-adjusted concentrations and year number (p b 0.05) for a time interval, watershed human activities were assumed to have no significant influence on NPS and PS pollution dynamics within a given time period.…”

“…In this study, we adopted a simple method to adjust for this underestimation. First, we assume that the average TP:Cl − ratio from sewage is constant over a given time interval (Neal et al, 2005;Jarvie et al, 2012;Ding et al, 2014). Second, average daily Cl − load during the low flow regime represents the original input load (Cl O ) from sewage (no significant dilution effect and runoff input) (Neal et al, 2005;Jarvie et al, 2012).…”

“…2b). As a conservative indicator for wastewater (Neal et al, 2005;Jarvie et al, 2012;Ding et al, 2014), such an increasing trend for Cl − during the low flow regime (no runoff input and limited dilution effect) implies a significant increase of PS inputs (e.g., industrial, domestic and animal wastewater). Similar to TP concentration, annual flow-adjusted average Cl − concentration during the low flow regime showed no significant trend (p N 0.05) for the time intervals 1980-1984, 1985-1990, 1991-1997, 1998-2002, and 2003-2010 (Fig.…”

“…2) based on changes in the annual flow-adjusted average TP concentrations, as well as Cl − concentration during the low flow regime, offering a more realistic fit to model assumptions. As a conservative indicator for sewage (Jarvie et al, 2012;Ding et al, 2014), information on riverine Cl − concentration is useful to verify long-term changes in estimated PS TP inputs from LAMs, as well as other watershed models. A monthly to bimonthly monitoring interval, which is typical of many monitoring programs (Shrestha et al, 2008;Yu et al, 2010;Chen et al, 2013), may not adequately characterize the high-flow events due to their limited occurrence throughout a given year (Johnes, 2007).…”

Variation in nitrate isotopic signatures in sewage for source apportionment with urbanization: a case study in Beijing, China

“…As with the stable isotope analysis in R language (SIAR) model, which was supposed to produce more precise results about NO 3 − source contributions, its outputs could be further improved by using more narrow ranges of NO 3 − sources provided by original source material (Xue et al 2012). Ding et al (2014) and Zhang et al (2015b) (Xing and Liu 2016;Xu et al 2016). Therefore, seasonal isotope data on various sewage sources could be used as better SIAR input data, and tighter ranges of NO 3 − isotope data may contribute to more precise results from SIAR.…”