Riparian Land-Use and Rehabilitation: Impact on Organic Matter Input and Soil Respiration

Abstract

Rehabilitated riparian zones in agricultural landscapes enhance environmental integrity and provide environmental services such as carbon (C) sequestration. This study quantified differences in organic matter input, soil biochemical characteristics, and soil respiration in a 25-year-old rehabilitated (RH), grass (GRS), and undisturbed natural forest (UNF) riparian zone. Input from herbaceous vegetation was significantly greater (P < 0.05) in the GRS riparian zone, whereas autumnal litterfall was significantly greater (P < 0.05) in the RH riparian zone. Soil bulk density was significantly greater (P < 0.05) in the RH riparian zone, but its soil chemical characteristics were significantly lower. Soil respiration rates were lowest (P < 0.05) in the UNF (106 C m(-2) h(-1)), followed by the RH (169 mg C m(-2) h(-1)) and GRS (194 C m(-2) h(-1)) riparian zones. Soil respiration rates were significantly different (P < 0.05) among seasons, and were significantly correlated with soil moisture (P < 0.05) and soil temperature (P < 0.05) in all riparian zones. Soil potential microbial activity indicated a significantly different (P < 0.05) response of the microbial metabolic diversity in the RH compared to the GRS and UNF riparian zones, and principle component analysis showed a distinct difference in microbial activity among the riparian land-use systems. Rehabilitating degraded riparian zones with trees rather than GRS is a more effective approach to the long-term mitigation of CO2. Therefore, the protection of existing natural/undisturbed riparian forests in agricultural landscapes is equally important as their rehabilitation with trees, given their higher levels of soil organic C and lower soil respiration rates.

Spatial and Temporal Variation in Soil Nitrous Oxide Emissions from a Rehabilitated and Undisturbed Riparian Forest

“…Differences in soil moisture between RH and UNF treatments were also observed in a previous study at the same site by Oelbermann et al (2015). They attributed this difference to a greater soil organic matter content and age of the UNF treatment (Oelbermann et al, 2015). Xiong et al (2015) also found that soil moisture naturally varies within and among riparian zones, where differences with distance from the stream, or differences between up-and downstream locations, are commonly observed and which were also detected in the present study.…”

“…Differences in soil moisture between RH and UNF treatments were also observed in a previous study at the same site by Oelbermann et al (2015). They attributed this difference to a greater soil organic matter content and age of the UNF treatment (Oelbermann et al, 2015).…”

“…A significantly greater TN content in the UNF treatment was also the result of age differences between the two riparian forests. For example, in 2010, Oelbermann et al (2015) reported a TN content of 3.50 g N kg −1 in the RH treatment, and 5 yr later, results from our study found that TN increased to 4.96 g N kg −1 , representing a gain of 42%. Bush (2008) determined that after 20 yr of rehabilitation, soil TN was still accumulating in a rehabilitated riparian forest along the San Antonio River in Texas.…”

“…For example, the RH treatment had greater light penetration because of the younger age of this forest, which led to a lower soil moisture compared with the UNF. Additionally, N uptake by trees in the RH treatment was 51% greater than in the UNF treatment (Oelbermann et al, 2015), causing similar N 2 O‐N emissions between the two sites, despite their age difference (Omonode et al, 2017). This is because N uptake and N requirement, to support the production of new foliage, is greater in younger than in mature riparian forests (Emmett et al, 1994).…”

“…Studies on greenhouse gas emissions from riparian zones in agricultural landscapes remain limited (Vidon and Serchan, 2016). The majority of these studies focused on carbon dioxide (CO 2 ) (Tufekcioglu et al, 2001; Oelbermann et al, 2015), whereas existing studies on N 2 O emissions have centered on grass buffers (Kim et al, 2009; Shrestha et al, 2009). To date, we know little about N 2 O emissions from rehabilitated riparian forests, making it difficult to assess if the C sink in rehabilitated riparian zones can offset N 2 O emissions (Merbold et al, 2013).…”