A new in situ method showed greater persistence of added soil organic matter in natural than restored wetlands

• Published in: Restoration ecology Vol. 29; no. 7
• Main Authors: Keshta, Amr E., Yarwood, Stephanie A., Baldwin, Andrew H.
• Format: Journal Article
• Language: English
• Published: Malden, USA Wiley Periodicals, Inc 01.09.2021
• Subjects: carbon; decomposition; ecosystem services; hydrology; Phragmites australis; soil organic matter
• ISSN: 1061-2971; 1526-100X
• DOI: 10.1111/rec.13437

One objective of wetland restoration is to promote soil organic matter (SOM) accumulation, but it may take decades for restored wetlands to accumulate SOM to a level similar to natural wetlands. We designed an in situ field SOM microcosm (9 × 51 cm) of known carbon (C) content (hereafter, SOM microcosm) to test retention of SOM in a natural compared to a restored wetland. Homogenized native wetland soil was used to fill SOM microcosms made of three different types of materials varying in opening size for root in‐growth. They were deployed vertically in the soil profiles of a natural wetland (with five habitat types) and a 24‐year‐old restored wetland (with four habitat types). After 2 years, SOM content differed between natural and restored sites in the top 15 cm. In the natural wetland, microcosm C content did not significantly change over the 2‐year period, averaged across habitats and microcosm type, but there was significant loss of soil C in restored wetland SOM microcosms (20 ± 6.7% loss, p < 0.05). The greater loss of SOM generally occurred in microcosms with 3.5‐mm than 1‐mm mesh sizes. Our findings suggest that although plants contribute C to the soil via root production and exudates, they can also have a negative effect on SOM accumulation due to soil aeration that promotes C mineralization. This microcosm approach may be useful in evaluating the persistence of SOM in restored wetlands compared to natural reference sites.