Abstract
The restoration of riparian zones has been an important issue in many regions for the recovery of ecosystem functions. The objective of this study was to assess soil aggradation in a 7-year established riparian switchgrass buffer (SGB) and in a non-buffered riparian zone with an annual row crop (ARC). We measured the aggregate size distribution and stability of macroaggregates, aggregate-associated soil organic carbon, soil organic matter fractions and the chemical composition of light particulate organic matter to monitor soil aggregation in a riparian soil following the conversion of agricultural row crops to switchgrass filters. Aggregate size fractions were separated by wet sieving using the aggregate size-stability protocol. The proportion of soil and total organic C was quantified for each aggregate size class. Soil organic matter fractions were isolated by size and density into light particulate organic matter and heavy particulate organic matter and mineral fraction organic matter. The categorization of aggregates by size and water stability (slaking resistance) showed a significantly larger (p < 0.001) proportion of water-unstable large macroaggregates (>2000 µm) under SGB (34%) compared to that under ARC (29%), while the proportion of water-unstable small macroaggregates (250–2000 µm) was significantly higher under ARC (14%) than under SGB (10%). Our results showed that the amounts of light and heavy particulate organic matter did not change in the short-term (7 years) after SGB establishment. It appears that the lower soil stabilization and soil organic C storage under SGB is related to (i) the large number of coarse roots; (ii) lower inputs of light and heavy particulate organic matter; (iii) no changes in the alkyl-C/O-alkyl-C ratio over time; and (iv) light particulate organic matter with a high C/N ratio.
Highlights
Riparian zones have important geomorphic and hydrologic roles and support high levels of biological productivity
Analysis of water-stable aggregates showed that the proportion of soil present as water-stable large macroaggregates (>2000 μm) changed no more under switchgrass buffer (SGB) (4.65%) than it did under annual row crop (ARC)
Seven years after the conversion of the ARC to SGB, there was no apparent difference between the formation of new stable large and small macroaggregates
Summary
Riparian zones have important geomorphic and hydrologic roles and support high levels of biological productivity. They have a disproportionate ecological role in the landscape considering their narrow extent, which makes them a good example of small natural features. Reforestation of riparian zones is increasingly practiced in many regions for purposes of biodiversity conservation, bank stabilization, and improvement in water quality. This occurs in spite of the actual benefits of reforestation for recovering underlying soil properties, and its functions remain poorly understood [4]
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