Decadal-scale Dynamics of Water, Carbon and Nitrogen in a California Chaparral Ecosystem: DAYCENT Modeling Results

Abstract

Abstract. The Mediterranean climate, with its characteristic of dry summers and wet winters, influences the hydrologic and microbial processes that control carbon (C) and nitrogen (N) biogeochemical processes in chaparral ecosystems. These biogeochemical processes in turn determine N cycling under chronic N deposition. In order to examine connections between climate and N dynamics, we quantified decadal-scale water, C and N states and fluxes at annual, monthly and daily time steps for a California chaparral ecosystem in the Sierra Nevada using the DAYCENT model. The daily output simulations of net mineralization, stream flow and stream nitrate (NO 3 À ) export were developed for DAYCENT in order to simulate the N dynamics most appropriate for the abrupt rewetting events characteristic of Mediterranean chaparral ecosystems. Overall, the magnitude of annual modeled net N mineralization, soil and plant biomass C and N, nitrate export and gaseous N emission agreed with those of observations. Gaseous N emission was a major N loss pathway in chaparral ecosystems, in which nitric oxide (NO) is the dominant species. The modeled C and N fluxes of net primary production (NPP), N uptake and N mineralization, NO 3 À export and gaseous N emission showed both high inter-annual and intraannual variability. Our simulations also showed dramatic fire effects on NPP, N uptake, N mineralization and gaseous N emission for three years of postfire. The decease in simulated soil organic C and N storages was not dramatic, but lasted a longer time. For the seasonal pattern, the predicted C and N fluxes were greatest during December to March, and lowest in the summer. The model predictions suggested that an increase in the N deposition rate would increase N losses through gaseous N emission and stream N export in the chaparral ecosystems of the Sierra Nevada due to changes in N saturation status. The model predictions could not capture stream NO 3 À export during most rewetting events suggesting that a dry-rewetting mechanism representing the increase in N mineralization following soil wetting needs to be incorporated into biogeochemical models of semi-arid ecosystems.

Influence of soil moisture on the seasonality of nitric oxide emissions from chaparral soils, Sierra Nevada, California, USA

“…Here, we highlight important implications for NO emissions in chaparral and draw comparisons to previous DAYCENT modeling of NO emissions at our study watershed . (Li et al, 2006). Within our discussion, we elaborate on three important findings: i) ambient NO emissions were highest during the dry season and lowest during the wet season (plant growing season), ii) large NO pulses were only observed during brief periods when dry soils (q < 6%) were wetted, and iii) DAYCENT-modeled seasonal NO emissions patterns for chaparral do not reflect the seasonal variation observed in our field study.…”

“…covering the interspaces between shrubs and the understory. The watershed has not burned since 1960 and therefore represents a mature chaparral ecosystem (Li et al, 2006).…”

“…For chaparral, our understanding of NO seasonal flux patterns stem from a single DAYCENT simulation study that assumes "pipe" control (Li et al, 2006). In the simulation, NO emissions are regulated by nitrification rates driven by soil moisture, and the model predicts greatest fluxes during the wet season.…”

DAYCENT Simulations to Test the Influence of Fire Regime and Fire Suppression on Trace Gas Fluxes and Nitrogen Biogeochemistry of Colorado Forests

“…Between year 1 and 1500, we scheduled regular fires that reflected the fire return intervals at each site ( Table 2). The length of these simulation runs has been found to bring other modeled ecosystems into equilibrium [28]. We examined total soil organic matter pools at each site to verify steady state that we defined as having less than a 5% change in total soil organic matter from year to year.…”

Ecosystem resistance in the face of climate change: a case study from the freshwater marshes of the Florida Everglades

“…DAYCENT has been used to successfully simulate ecosystem responses to changes in climate (Parton et al 1995, Luo et al 2008, Savage et al 2013), and to model gas fluxes (CO 2 , CH 4 , N 2 O, NO x , N 2 ). It has also been used to model C and nutrient dynamics (N, P, S) in shrublands (Li et al 2006), forest (Hartman et al 2007, Parton et al 2010, crops (Del Grosso et al 2002, Stehfest et al 2007, Del Grosso et al 2009, Chang et al 2013, Duval et al 2013, and temperate wetlands and grasslands (Luo et al 2008, Morgan et al 2004, Parton et al 2007. By capturing patterns in soil hydrology, soil thermal regimes, and C dynamics (Chimner et al 2002, Cheng et al 2013, Cheng et al 2014, DAYCENT has been used to effectively model C dynamics in wetland ecosystems, which provides a strong basis for using DAYCENT in Everglades freshwater marsh ecosystems.…”