Water connectivity in hillslope of upland–riparian zone and the implication for stream nitrate-N export during rain events in an agricultural and forested watershed

Abstract

Water connectivity in the hillslopes of the upland-riparian zone has environmental implications for stream nitrate-N (NO 3 --N) export during rain events. This study was conducted to measure the shallow groundwater table over a hillslope with upland, interface, and riparian forest components and measure the stream NO 3 --N concentrations in a 36.6 km 2 agricultural and forested watershed (AFW) in the Shibetsu area of northern Japan from July to November 2009. The groundwater and stream hydrographs at seasonal and rain event scales indicated that the hillslope water connectivity was first established from the riparian forest, and then expanded to the upland after several rain events. The hillslope water connectivity has important implications for NO 3 --N export in the watershed since the NO 3 --N export may primarily be explained by a flushing mechanism. The NO 3 --N export only flushed from riparian forest during the early water connection stage. While in the well water connection stage, the flush of NO 3 --N occurred with the subsurface flow from the upland which had a high shallow groundwater table and displayed higher stream NO 3 --N concentrations. However, lower stream NO 3 --N concentrations occurred during the late water connection stage and indicated that the N source in the upland might be limited due to denitrification and NO 3 --N leaching processes. Nevertheless, it was decided that the hydrology and biogeochemical reactions occurring in the upland controlled the stream NO 3 --N export. A conceptual model was formulated that explained the impacts of the hillslope water connectivity on the watershed stream NO 3 --N export during rain events in early, well, and late water connection stages within the AFW.

Sensitivity of nitrate concentration‐discharge patterns to soil nitrate distribution and drainage properties in the vertical dimension

“…Creed and Band (1998a) emphasize that it is the rate of expansion of the variable source area, not the total variable source area, that regulates the export of nitrates. Other processes or factors including wild fire (Aguilera & Melack, 2018b;Goodridge et al, 2018;Hanan et al, 2016a), macropore flow (Lohse, Sanderman, & Amundson, 2013), shallow groundwater linkage (Jiang et al, 2015), hillslope hydrologic connectivity (Jencso, McGlynn, Gooseff, Bencala, & Wondzell, 2010) and antecedent soil moisture conditions (Macrae, English, Schiff, & Stone, 2010) also contribute to the regulation of nitrate exports.…”

Estudo experimental e de modelagem matemática do escoamento subterrâneo em uma vertente de zona ripária no bioma Cerrado

“…As zonas ripárias, localizadas na interface entre os ecossistemas terrestre e aquático, também são objeto de pesquisa desse ramo da ciência e favorecem a conectividade hidrológica da vertente com o corpo hídrico (Gregory e Ashkenas, 1990;Brutsaert, 2005). A definição do termo conectividade hidrológica, entendida como a transferência de energia e matéria entre duas unidades topográficas, remete aos trabalhos de Haught e van Meerveld (2011), Jiang et al (2015) e Martínez-Carreras et al (2015), como um controle dominante para a formação de escoamento na escala de encosta.…”