Seasonal Losses of Dissolved Organic Carbon and Total Dissolved Solids from Rice Production Systems in Northern California

Abstract

Water quality concerns have arisen related to rice (Oryza sativa L.) field drain water, which has the potential to contribute large amounts of dissolved organic carbon (DOC) and total dissolved solids (TDS) to the Sacramento River. Field-scale losses of DOC or TDS have yet to be quantified. The objectives of this study were to evaluate the seasonal concentrations of DOC and TDS in rice field drain water and irrigation canals, quantify seasonal fluxes and flow-weighted (FW) concentrations of DOC and TDS, and determine the main drivers of DOC and TDS fluxes. Two rice fields with different straw management practices (incorporation vs. burning) were monitored at each of four locations in the Sacramento Valley. Fluxes of DOC ranged from 3.7 to 34.6 kg ha(-1) during the growing season (GS) and from 0 to 202 kg ha(-1) during the winter season (WS). Straw management had a significant interaction effect with season, as the greatest DOC concentrations were observed during winter flooding of straw incorporated fields. Fluxes and concentrations of TDS were not significantly affected by either straw management or season. Total seasonal water flux accounted for 90 and 88% of the variability in DOC flux during the GS and WS, respectively. Peak DOC concentrations occurred at the onset of drainflow; therefore, changes in irrigation management may reduce peak DOC concentrations and thereby DOC losses. However, the timing of peak DOC concentrations from rice fields suggest that rice field drainage water is not the cause of peak DOC concentrations in the Sacramento River.

Controls on dissolved organic carbon composition and export from rice-dominated systems

“…Furthermore, Table 2 Results of LME analyses for DOC concentration and flux, THMFP and THM flux, SUVA DOC concentration patterns were similar among subwatersheds (Online Resource 2) and consistent with patterns measured in the sampling of drainage canals performed by Ruark et al (2010) during the 2006 and 2007 growing seasons. This implies that the 2008 growing season was likely representative of normal conditions.…”

“…The goodness-of-fit parameters of both LME models are presented in Table 2 Biogeochemistry (2012) 108: 447-466 459 into the Sacramento River. All of the watershed scale concentrations are lower than the annual median DOC concentration of 9.5 mg L -1 that was measured over the course of 2 years in California rice field outlets (Ruark et al 2010). The variation in DOC concentration among field and watershed systems highlights the need for research to characterize the response of DOC dynamics to agricultural irrigation activities at multiple scales.…”

“…Rice straw residues are a potentially important DOC source, as Ruark et al (2010) found that the burning of rice straw in the winter, versus the widespread practice of rice straw incorporation into the soil by plowing, significantly lowered DOC concentration and flux in rice field outflow. This is also important to the THMFP of DOC leaving these systems, because vascular plant materials are highly aromatic DOC sources Spencer et al 2009Spencer et al , 2010.…”

Manure and Fertilizer Effects on Carbon Balance and Organic and Inorganic Carbon Losses for an Irrigated Corn Field

“…The water applied during furrow irrigation necessarily exceeds crop evapotranspiration needs (Lehrsch et al, 2005). The excess water can dissolve soil C and transport it to groundwater via deep percolation, and to natural surface waters via surface runoff and return flow (Brye et al, 2001;King et al, 2009;Ruark et al, 2010).…”

“…Similarly, researchers have studied DOC losses in drainage water, tile-drain, and runoff from grassland soils and corn or hay fields, but did not consider other C-budget components (Don and Schulze, 2008;Royer et al, 2007). Other studies have examined the DOC loadings in surface water inflows and runoff for furrow-or flood-irrigated fields, but did not compare untreated soils with manured soils or measure other C inputs and outputs (Poch et al, 2006;King et al, 2009;Lentz and Westermann, 2010;Mailapalli et al, 2010;Ruark et al, 2010;Krupa et al, 2012).…”