Lag Times as Indicators of Hydrological Mechanisms Responsible for NO3-N Flushing in a Forested Headwater Catchment

Abstract

Understanding the temporal variability of the nutrient transport from catchments is essential for planning nutrient loss reduction measures related to land use and climate change. Moreover, observations and analysis of nutrient dynamics in streams draining undisturbed catchments are known to represent a reference point by which human-influenced catchments can be compared. In this paper, temporal dynamics of nitrate-nitrogen (NO3-N) flux are investigated on an event basis by analysing observed lag times between data series. More specifically, we studied lag times between the centres of mass of six hydrological and biogeochemical variables, namely discharge, soil moisture at three depths, NO3-N flux, and the precipitation hyetograph centre of mass. Data obtained by high-frequency measurements (20 min time step) from 29 events were analysed. Linear regression and multiple linear regression (MLR) were used to identify relationships between lag times of the above-mentioned processes. We found that discharge lag time (LAGQ) and NO3-N flux lag time (LAGN) are highly correlated indicating similar temporal response to rainfall. Moreover, relatively high correlation between LAGN and soil moisture lag times was also detected. The MLR model showed that the most descriptive variable for both LAGN and LAGQ is amount of precipitation. For LAGN, the change of the soil moisture in the upper two layers was also significant, suggesting that the lag times indicate the primarily role of the forest soils as the main source of the NO3-N flux, whereas the precipitation amount and the runoff formation through the forest soils are the main controlling mechanisms.

Nitrate Nitrogen (NO3-N) Export Regimes Based on High-frequency Measurements in the Kuzlovec Stream Catchment

“…Na porečju je bila v okviru projekta SedAlp (2012SedAlp ( -2015 nameščena merska oprema za spremljanje količine, trajanja in lastnosti padavin, iznosa sedimentov in hidroloških razmer (Bezak et al, 2013). V letih 2018 in 2019 smo mersko mrežo posodobili z opremo za časovno zvezno spremljanje koncentracij NO3-N in vlažnosti tal (Sapač et al, 2020). V prispevku smo uporabili podatke meritev iz obdobja april 2018-april 2020.…”

“…Osenčeni dogodki so iz obdobja vegetacije, ostali dogodki pa iz obdobja mirovanja. Ne glede na to, da z vidika režimov iznosa snovi s porečja sezonskost ni bila eksplicitno zaznana, pa je študija časov zakasnitve pretoka in iznosa snovi (Sapač et al, 2020) pokazala, da so časi zakasnitve v obdobju vegetacije oziroma v spomladanskopoletnem obdobju krajši kot v obdobju mirovanja oziroma jesensko-zimskem obdobju. Slednje potrjuje domnevo o vplivu sezonske raznolikosti padavin na oblikovanje hidrogramov odtoka in posledično na časovno dinamiko koncentracij NO3-N v vodotoku.…”

Hydrochemical dynamics of stream following rainfall events at agricultural catchments in New Zealand

“…Numerous investigations have focused on the hydrologic response of catchments to particular rainfall occurrence, such as those by Pavlin et al (2021), Saffarpour et al (2016), andDetty &McGuire (2010), or have reported on the impact of rainfall characteristics on runoff quantity and quality, as seen in studies by Sapač et al (2020), Lintern et al (2018), andMacrae et al (2010). However, there are existing knowledge gaps regarding the relationships between hydrological responses, various rainfall events, and the reasons for variations in nutrient loads, particularly in pastoral catchments that contribute to lake inflows (Levine et al, 2021;Abell et al, 2013;Menneer et al, 2004).…”