Mitigating acid sulfate soil development in sediment addition projects through application of sediment amendments

Sediment addition is an increasingly common strategy to promote coastal resilience where sediment is added to salt marsh surfaces to increase elevation and prevent marsh loss. Added sediments are typically dredged materials from marine environments that may become acidic when exposed to air because of their high reduced sulfide levels, known as potential acid sulfate soils (PASS). Low soil pH inhibits plant growth and can delay ecosystem recovery after sediment addition. We used a laboratory soil core experiment to evaluate how a range of amendments altered pH (mulch, crushed shells, pelletized lime, and recycled concrete), and a field study to examine the effects of recycled concrete. We found both shells (7.46 ± 0.22; mean ± std dev) and concrete (laboratory: 8.24 ± 0.32; field: 8.15 ± 0.55) increased pH relative to adding unamended sediment (laboratory: 7.33 ± 0.35; field: 7.21 ± 0.45). Environmental context is likely important for sediment additions and even PASS may not become acidic in flooded, low marsh environments. Under more oxidized conditions, particularly in higher-elevation marsh or when deeper layers of sediment are added, recycled concrete or crushed shells are potential amendments to neutralize acidity. Sediment amendments may also affect other ecosystem responses, including water chemistry and greenhouse gas emissions. We found that concrete amendments lowered ferrous iron concentrations and decreased carbon dioxide emissions compared to adding unamended sediment. Additional testing of amendments under diverse environmental conditions and at field scales would further our understanding of the effectiveness and feasibility of amending soils during sediment additions.

Methods
LabExperimentData

The lab experiment data csv contains the data used for the analysis of a soil core experiment conducted at the Center for Environmental Science and Engineering, Storrs CT in the fall of 2021. The experiment tested the efficacy of recycled concrete, crushed shells, pelletized lime, and mulch as soil amendments to increase pH for sediment addition projects where acid sulfate soils are a concern. The dredge treatment had no added amendment, and acted as a control of sediment amendments, and the control treatment had no added amendment or sediment and acted as a control of sediment addition, and amendments.

There were 42 soil cores total, 7 replicates of each treatment/control.

FieldExperimentData

The field experiment data csv contains the data used for the analysis of a modified bucket experiment installed at Great Meadows Marsh, Stratford CT May 2022-November 2023. The experiment tested the efficacy of crushed recycled concrete as a soil amendment to increase pH for sediment addition projects where acid sulfate soils are a concern. The dredge treatment had no added amendment, and acted as the control.

There were 10 buckets total, 5 of each treatment/control, spaced half a meter apart adjacent to a tidal creek.