Carbon, Nitrogen, and Orthophosphate Leaching from Soil under Single- and Mixed-species Landscapes

Abstract

<jats:p>Effective landscape management practices in urban landscapes must include an awareness of nutrient removal from soil caused by leaching, and these practices should be those least damaging to freshwaters. Annual mean dissolved organic carbon (DOC), dissolved organic nitrogen (DON), nitrate-N, ammonium-N, soluble phosphate, and bicarbonate concentrations and fluxes were quantified in leachate from landscapes planted with different urban horticultural types. Plot vegetation consisted of either a single species or mixed species. The experiment was conducted at two sites in Texas with significantly different irrigation water chemistry. At the two sites, plant species had a significant effect on PO<jats:sub>4</jats:sub><jats:sup>3-</jats:sup>-P flux, and irrigation chemistry had a significant effect on all nutrient fluxes. There was an interaction between plant species and irrigation chemistry for PO<jats:sub>4</jats:sub><jats:sup>3-</jats:sup>-P flux (<jats:italic>P</jats:italic> &lt; 0.05) only. The relationship between bicarbonate and DOC flux at sites was stronger and significant (0.92; <jats:italic>P</jats:italic> &lt; 0.05) at the site irrigated with Na-HCO<jats:sub>3</jats:sub> municipal tap water than at the site irrigated with Ca-HCO<jats:sub>3</jats:sub> municipal tap water (<jats:italic>R</jats:italic><jats:sup>2</jats:sup> = 0.76, <jats:italic>P</jats:italic> = 0.05). Type of irrigation water chemistry may result in lower plant water uptake resulting in increased nutrients lost to leachate.</jats:p>

DOC and DON Release and Reactive Soil Pools in Urban and Remnant Soils

“…Our major question of what might be controlling DOC and DON release and RSP in urban and remnant soils was based on our observations of high concentrations of DOC and DON in urban surface waters (Aitkenhead-Peterson et al, 2009;Petrone, 2010) and high DOC and DON leachate or extract fluxes when urban soils were irrigated with sodic versus nonsodic irrigation water (Holgate et al, 2011;Pannkuk et al, 2011;Steele and Aitkenhead-Peterson, 2012a). The expectation was that urban soils would have higher DOC and DON release and RSP relative to remnant soils possibly because of compaction (Pitt et al, 2008) and land management practices such as soil amendment application (gypsum, inorganic fertilizer, and dog feces) (Baker et al, 2001;Groffman et al, 2004).…”

“…Instead, based on our previous work on DOC and DON in urban soils and surface waters (Aitkenhead-Peterson et al, 2009;Holgate et al, 2011;Pannkuk et al, 2011;Steele and Aitkenhead-Peterson, 2012a, b), we used cations (Na + , K + , Mg 2+ , and Ca 2+ ) as a surrogate for irrigation intensity based on the assumption that if the site was well irrigated (as shown by high water-extractable sodium), it would also be highly managed in terms of pesticide and herbicide use, fertilization, soil aeration, and mowing. Municipal tap water used for irrigating urban landscapes in the study region has an average pH of 8.73 ± 0.1, sodium adsorption ratio (SAR) of 34 ± 5, and sodium concentration of 226 ± 4.5 mg L −1 (Table 2).…”

“…No studies have examined DOC and DON release and RSP using the initial mass isotherm method (Nodvin et al, 1986) in urban soils, although several studies have examined waterextractable or leachate soil DOC and DON (Beesley, 2012;Steele and Aitkenhead-Peterson, 2012a;Pannkuk et al, 2011). Our study examined the effect of time since soil disturbance and soil chemistry on DOC and DON release and RSP.…”

“…However, many of these reports only report those chemical and biological constituents that have an Environmental Protection Agency standard for drinking water, although some report secondary contaminants such as sodium because of its implication in high blood pressure in humans. More recent work on urban soils has examined the effect of irrigation water chemistry on DOC and DON leaching from soil under an urban landscape (Holgate et al, 2011;Pannkuk et al, 2011), on extractable soil DOC and DON from soil under turfgrass across Texas (Steele and Aitkenhead-Peterson 2012a), and on DOC and DON leaching from senescent urban vegetation (Steele and AitkenheadPeterson 2012b). All these studies have indicated that irrigation water, particularly water high in sodium, has a negative effect on soil biogeochemical cycling, producing high releases of DOC and DON.…”

Biodegradable dissolved organic carbon in urban and remnant soils in south-central Texas, USA

“…Municipal tap water is typically used for irrigating landscapes in these urban areas and in the study region has naturally high concentrations of sodium, reported at 206 ± 25 mg Na + L − 1 with a sodium adsorption ratio (SAR) of 34 ± 5 (Pannkuk et al, 2011). Irrigation water is considered sodic when its SAR is N 13.…”