Factors controlling nitrogen release from two forested catchments with contrasting hydrochemical responses

Abstract

Abstract:Quantifying biogeochemical cycles of nitrogen (N) and the associated fluxes to surface waters remains challenging, given the need to deal with spatial and temporal variability and to characterize complex and heterogeneous landscapes. We focused our study on catchments S14 and S15 located in the Adirondack Mountains of New York, USA, which have similar topographic and hydrologic characteristics but contrasting stream nitrate (NO 3 ) concentrations. We characterized the mechanisms by which NO 3 reaches the streams during hydrological events in these catchments, aiming to reconcile our field data with our conceptual model of factors that regulate nutrient exports from forested catchments. Combined hydrometric, chemical and isotopic (υ 18 O-H 2 O) data showed that the relative contributions of both soil and ground water sources were similar between the two catchments. Temporal patterns of stream chemistry were markedly different between S14 and S15, however, because the water sources in the two catchments have different solute concentrations. During late summer/fall, the largest source of NO 3 in S14 was till groundwater, whereas shallow soil was the largest NO 3 source in S15. NO 3 concentrations in surface water decreased in S14, whereas they increased in S15 because an increasing proportion of stream flow was derived from shallow soil sources. During snowmelt, the largest sources of NO 3 were in the near-surface soil in both catchments. Concentrations of NO 3 increased as stream discharge increased and usually peaked before peak discharge, when shallow soil water sources made the largest contribution to stream discharge. The timing of peaks in stream NO 3 concentrations was affected by antecedent moisture conditions. By elucidating the factors that affect sources and transport of N, including differences in the soil nutrient cycling and hydrological characteristics of S14 and S15, this study contributes to the overall conceptualization of NO 3 release from temperate forested catchments.

Dynamics of storm-driven suspended sediments in a headwater catchment described by multivariable modeling

“…In contrast, 2008 was the wettest year in terms of annual precipitation depth (946 mm), which also resulted in a greater amount of quickflow. 24_hr R stands for the cumulative total runoff over 24 h prior to the start of an event; Pint is the maximum precipitation intensity per 30 min; SSC_max is the peak suspended sediment concentration; QF cumul is the cumulative runoff via quickflow; Q_base is the baseflow discharge prior to a rainfall-runoff event; P total is the total precipitation depth per event; API 7 and API 14 are the antecedent precipitation indices for 7 and 14 days prior to the start of an event; Prec 5 d is the cumulative precipitation depth over 5 days prior to an event; Temp 5 d is the mean air temperature over 5 days prior to the start of an event 2.4 Antecedent hydro-meteorological conditions Several researchers used the antecedent precipitation index to describe antecedent moisture conditions prior to a runoff event (e.g., Christopher et al 2008). In this paper, the antecedent precipitation index (API) was calculated for 7 and 14 days prior to the start of an event as:…”

“…Under dry conditions, the water storage capacity of a catchment is higher than under wet conditions when the surface and subsurface storage may be saturated. Antecedent moisture conditions actively control water flow paths (Christopher et al 2008) and responsiveness of a catchment to precipitation (Buttle et al 2001;James and Roulet 2009;Macrae et al 2010). Antecedent moisture status of soils also determines the magnitude and the direction of the discharge (Q)-suspended sediment concentration (SSC) hysteresis loops (Butturini et al 2006;Ide et al 2008;NadalRomero et al 2008).…”

Spatial and temporal dynamics of stream chemistry in a forested watershed

“…Previous studies in this watershed increased our understanding of the regulation of solute fluxes during high-discharge hydrologic events. Snowmelt and storm activity, for example, flush NO − 3 to stream from sites of nitrification in upland soils (Ohrui et al, 1999;McHale et al, 2002;Inamdar et al, 2004;Piatek et al, 2005;Mitchell et al, 2006;Christopher et al, 2008). During these events, groundwater table rises to the upper soil horizons and establishes connectivity with the stream channel (Inamdar et al, 2004;Christopher et al, 2006).…”

“…1). One of them, located at elevation of about 650 m (S14), exhibits unusually high NO − 3 concentrations throughout the year and is fed by deep groundwater (McHale et al, 2002;Christopher et al, 2006Christopher et al, , 2008. At low elevations, another tributary forms an extensive conifer wetland (S11) before it resumes channelized flow into an open grassy field.…”

Avaliação biogeoquímica de águas fluviais com ênfase no comportamento dos compostos de nitrogênio e fósforo total para diagnoses provenientes do sistema aquático Bacia do Rio Doce, no Espírito Santo

“…Os ciclos de N e P são complexos devido ao fato de haver muitas e diferentes espécies quí-micas envolvidas (Goller et al 2006). Além disso, eles são influenciados por fatores físico-químicos naturais e atividades antrópicas como o uso de fertilizantes e queima de combustíveis fósseis (Vitousek et al 1997, Christopher et al 2008.…”