Effects of storm flow samplings on the evaluation of inorganic nitrogen and sulfate budgets in a small forested watershed

Abstract

Abstract:To investigate the effects of storm flow samplings on the evaluation of DIN and SO 4 2 budgets, we conducted storm flow samplings and discrete interval (weekly) samplings of stream water, throughfall, and stemflow. This investigation lasted for three years and took place in a small forested watershed in western Japan. Annual exports were calculated by the sum of the load (L total )-sum of the discharge (Q total ) relationships obtained by storm flow samplings. These were then compared to calculated ones that were based on LQ relationships obtained by discrete interval sampling. The results of discrete interval sampling showed that the relationships of DIN or SO 4 2 concentration to the discharge amount found in stream water differed from those of storm flow sampling. This was especially notable in years with higher annual precipitation and subsequent higher annual discharges. Also, exports of DIN and SO 4 2 during storm flow periods accounted for 83% and 78% of annual exports on 3-year averages, respectively. These results confirmed that storm flow samplings are essential for estimating annual exports of DIN and SO 4 2 . Annual exports that were calculated based on just discrete interval sampling (46% and 17%, respectively) overestimated DIN and SO 4 2 from discrete interval and storm flow samplings on a 3-year average. These overestimates were pronounced in years of higher discharge, and critically affected the rates of net-retention or export of DIN and SO 4 2 . The relationship of smaller input than output of DIN was reversed if storm flow sampling was included.

Determining storm sampling requirements for improving precision of annual load estimates of nutrients from a small forested watershed

“…The nutrient loads during the storm flow periods were calculated using the ∑L-∑Q equation derived from the concentration and discharge data obtained during storm events (Chiwa et al 2010a;Ebise 1984;Ebise and Goda 1985;Ide et al 2009). The ∑L-∑Q equation calculates the cumulative nutrient load per storm event and is expressed as follows:…”

“…Therefore, the ratio of nutrient loads during storm flow periods to the annual nutrient load is generally high in forested watersheds in Japan (Chiwa et al 2010a;Ide et al 2008a;Komai et al 2003;Takeda 2002c). Since the concentration of nutrients drastically changes with stream discharge during storm flow periods, it is essential to consider changes in their levels to enable adequate estimation of the annual nutrient load.…”

“…To improve the prediction accuracy of the load estimates, a regression equation of the cumulative load versus cumulative stream discharge (∑L-∑Q) relationship, i.e. a ∑L-∑Q equation has been proposed (Chiwa et al 2010a;Ebise 1984;Ebise and Goda 1985;Ide et al 2008a). The prediction accuracy of the ∑L-∑Q equation should be higher than those of the C-Q or L-Q equations because the ∑L-∑Q equation reduces the effects of hysteresis loops in the C-Q relationships on the load estimates during storm flow periods (Chiwa et al 2010a).…”

Effects of hydrologic conditions on SWAT model performance and parameter sensitivity for a small, mixed land use catchment in New Zealand

“…monthly) are often used to calibrate water quality models, but these are unlikely to fully represent the range of hydrologic conditions in a catchment (Bieroza et al, 2014). In particular, water quality data collected during storm flow periods are rarely available for SWAT calibration, thus prohibiting opportunities to investigate how parameter sensitivity varies under conditions which can contribute disproportionately to nutrient or sediment transport, particularly in lower-order catchments (Chiwa et al, 2010;. Failure to fully consider storm flow processes could therefore result in overestimation of model performance.…”

<sup>17</sup>O excess traces atmospheric nitrate in paleo-groundwater of the Saharan desert

“…Periodic infiltration events enhanced the leaching of accumulated NO − 3 from plant and soil surfaces and also from below the near-surface and rooting zone. Accordingly, the NO − 3 -enriched solutions migrated downward through the vadose zone to the water table and correspondingly high NO − 3 concentrations occur in the recharging groundwater (see also Edmunds and Gaye, 1997, Tyler et al, 1997, Hartsough et al, 2001, Walvoord et al, 2003and Chiwa et al, 2010.…”