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

• Variability in %BDOC of urban soils illustrates complexity of land management.
• Sodic irrigation significantly lowers %BDOC in urban soil.
• Highest urban soil %BDOC in lawns with weeds suggests diversity may increase %BDOC.

Urban streams have been found to have high exports of dissolved organic carbon (DOC) relative to native land use. While wastewater effluent is considered to be a contributor of carbon to streams, it does not wholly account for high concentrations of DOC above which would be expected from the watershed under native vegetation. This study examined biodegradable DOC (BDOC) in urban and remnant soils in order to understand the influence of urbanization on microbial carbon cycling. Average soil BDOC ranged from 24.4 ± 32.7% in a city parks under mixed, warm-season turfgrass to 52.9 ± 38.4% in remnant forests under senesced mixed forest leaf litter. Highest average soil %BDOC was observed in the soils of multi-family homes (61.4 ± 7.7%), which tended to have more weeds and species diversity and were not exposed to sodic irrigation water. Water extractable soil sodium explained 53% of the variability in %BDOC. Urban soils in the study area are generally irrigated using municipal tap water, which is high in sodium. This may lead to a buildup of sodium in the soil, and the noted reduction in %BDOC resulting in a greater availability of DOC for runoff to surface waters.