Soil C sequestration has been proposed as a tool for addressing climate change. However, models used to predict soil C sequestration do not account for C saturation and functional differences among soil C pools. In this study, we examined differences in soil C pool content of a forest soil in Pennsylvania following 20 yr of detrital manipulation (i.e., control, no roots, no leaf litter, no inputs, double leaf litter). Detrital input treatments had a highly significant (ANOVA, F = 10.6, p < 0.0001) effect on soil C in the 0‐ to 5‐cm soil depth. However, soil C pools responded differently to the different treatments: the intra‐microaggregate silt + clay, intra‐microaggregate particulate organic matter (POM), and silt + clay within large macroaggregates in plots receiving no detrital inputs had significantly lower C concentrations (1.1, 2.5, and 0.4 g C kg−1 soil, respectively) than the control, double‐leaf‐litter, and no‐roots plots. Carbon in coarse POM within small macroaggregates was significantly lower in double‐leaf‐litter (4.5 g C kg−1 soil) and no‐leaf‐litter plots (6.6 g C kg−1 soil) than all other treatments (15.3–28 g C kg−1 soil). The intra‐microaggregate fractions in double‐leaf‐litter plots had greater C concentrations than in the control plots; along with moderate C concentrations in all bulk soil samples, this suggests that the soil is not yet approaching C saturation. This study reinforces the use of microaggregates within large macroaggregates as a diagnostic fraction for changes in soil C content and demonstrates that altering the organic matter source and quantity significantly affects soil C sequestration dynamics. Consideration of these factors will enable improved assessment of soil C sequestration capacity and management.

Agricultural irrigation leachate is often the largest source for aquifer recharge in semi-arid groundwater basins, but contamination from fertilizers and other agro-chemicals may degrade the quality of groundwater. Affected communities are frequently economically disadvantaged, and water supply alternatives may be too costly. This study aimed to demonstrate that, when addressing these issues, environmental sustainability and market profitability are not incompatible. We investigated the viability of two low impact crops, alfalfa and vineyards, and new recharge basins as an alternative land use in recharge buffer zones around affected communities using an integrated hydrologic, socio-geographic, and economic analysis. In the southern Central Valley, California, study area, alfalfa and vineyards currently constitute 30% of all buffer zone cropland. Economic analyses of alternative land use scenarios indicate a wide range of revenue outcomes. Sector output gains and potential cost saving through land use conversion and resulting flood control result in gains of at least $2.3 billion, as compared to costs of $0.3 to $0.7 billion for treatment options over a 20 year period. Buffer zones would maintain the economic integrity of the region and concur with prevailing OPEN ACCESSWater 2015, 7 13 policy options. Thus, managed agricultural recharge buffer zones are a potentially attractive option for communities facing financial constraint and needing to diversify their portfolio of policy and infrastructure approaches to meet drinking water quality objectives.