Quantifying rates, controls, and spatiotemporal dynamics of water and nitrogen fluxes through the streambed of West Bear Creek, North Carolina, USA

flux;stream;nitrogen;groundwater

Kennedy, Casey David ; Reide Corbett, Committee Member,David DeMaster, Committee Member,Helena Mitasova, Committee Member,David Genereux, Committee Chair,Kennedy, Casey David ; Reide Corbett ; Committee Member ; David DeMaster ; Committee Member ; Helena Mitasova ; Committee Member ; David Genereux ; Committee Chair

University:North Carolina State University

关键词: flux;    stream;    nitrogen;    groundwater;   

Others  :  https://repository.lib.ncsu.edu/bitstream/handle/1840.16/3966/etd.pdf?sequence=1&isAllowed=y

美国|英语

来源: null

【 摘 要 】

This paper presents results on the rates and spatiotemporal dynamics of the coupled water flux (v) and nitrogen (N) fluxes (mainly fNO3 and fDON for nitrate and dissolved organic N) through a streambed in an agricultural watershed in North Carolina.Physical and chemical variables were measured at numerous points in the streambed of a 0.26 km reach:hydraulic conductivity (K) and head gradient (J), and concentrations of NO3- and other N species in the streambed groundwater, from which water (v=KJ) and N fluxes (e.g., fNO3=v[NO3-]) through the streambed were computed, mapped, and integrated in space.The result was a novel set of streambed maps of the linked variables (K, J, v, N concentrations and fluxes), showing their spatial variability and how it varied over a year (based on 7 bimonthly sets of maps).Mean fNO3 during the study year was 154 mmol m-2 day-1;this NO3- flux, together with that of DON (fDON = 17 mmol m-2 day-1) accounted for >99% of the total dissolved N flux through the streambed.Repeat measurements at the same locations on the streambed show significant temporal variability in fNO3, largely controlled by changes in v rather than changes in [NO3-].One of the clearest and most temporally-persistent aspects of spatial variability was lateral variability across the channel from bank to bank.K and v had “center-highâ€patterns (greater values in the center of the channel);this distribution of K (ultimately a reflection of sediment dynamics in the channel) apparently focuses groundwater discharge toward the center of the channel.The opposite “center-lowâ€pattern was found for J, [NO3-], and (to a lesser extent) fNO3. Contrary to suggestions in some prior work, J was not a good index for v. fNO3 was characterized by localized zones of high and low values that changed in size and shape over time but remained in basically the same locations (the same was true of K, J, [NO3-], though less so for v), with 70% of NO3- flux occurring through about 38% of the streambed area.Lateral distributions of the physical hydrologic attributes (K, J, v) were highly symmetrical across the channel, while those of [NO3-] and fNO3 showed higher values on the right than left, likely a reflection of different N use on opposite sides of the stream.These and other results show the streambed-based approach taken here can offer a number of insights not possible with reach mass-balance approaches in which net exchange between a stream reach and surrounding groundwater is calculated using surface water data.