Biochar amendments in a California salt marsh restoration reduced denitrification and supported distinct microbial community functions

Accelerated sea level rise, combined with human-induced changes to hydrology and sediment transport pathways poses an existential threat to the survival of coastal wetlands over the next century. To support the preservation of wetlands, restoration and enhancement strategies—such as adding sediment to marsh surfaces to boost their resilience to sea level rise—are being actively tested and monitored. This study aimed to assess how biochar derived from Eucalyptus spp. feedstock influences sediment properties, microbial communities, functional potential, and nitrate reduction pathways in a tidal wetland restoration project. Biochar-amended sediments showed reduced denitrification rates, no detectable DNRA activity, and only subtle changes in sediment properties and microbial nitrogen cycling, with the exception of increased carbon content and higher relative abundance of Cyanobacteria and Truepera, a member of the Deinococcota.  While there was some evidence of increased microbial abu..., Research was conducted at Elkhorn Slough (36.8129°N, -121.7556°), a 12,000-ha estuary tidal estuary in Central California, which was the site of an ambitious 24-ha sediment placement and salt marsh restoration project completed in 2018 (Fig. 1) (termed \"Hester Marsh\"; Fig. 1). During 2017-8, 180,000 m3 of sediment was used to rebuild a low elevation marsh plain, which was diked and drained in the mid-20th century. Sediments included material from Pajaro River floodplains along with upland soils from a nearby regraded hillside. Key restoration goals were to recover lost ecosystem functions such as carbon storage, nutrient sequestration, and denitrification.
Biochar sediment amendments (10% v/v) were incorporated in 2019 in ten sets of paired plots across the mid-marsh platform. Biochar plots (1 x 1 m) received 5000 cm3 of Eucalyptus spp. biochar mixed into the 5-10 cm sediment layer, capped with 5cm of untreated sediment to prevent washout (Fig. 1). Paired (1 x 1 m) plots were disturbed ..., # Biochar in a California salt marsh restoration had modest effects on nitrogen metabolism but supported distinct microbial communities and functions

Dataset DOI: [10.5061/dryad.kprr4xhh8](10.5061/dryad.kprr4xhh8)

## Description of the data and file structure

The following files include processed data associated with 16S amplicon sequence variants (\"asv_table.csv\", \"taxa_rare.csv\", \"asv_rare.csv\", \"refseq.csv\", \"diversity.csv\"), sediment metadata (\"FullSeddata.csv\") and functional annotations (\"Normalized_Data_cleaned.csv\", \"n_met.csv\", \"n_met_paired.csv\", \"ko_new_annotated.csv\", \"path_abun_unstrat.csv\"). Analysis is described by an annotated R script, 16S Ecological Analysis_9June2025.R.

### Files and variables

#### File: FullSeddata.csv

**Description:** This file contains the sediment metadata for the project.

##### Variables

* Sample: The values for this field include Yampah1-5 (the natural marsh), Control 1-10 (the restored marsh), Fresh Biochar 1-5, or Aged Biochar 1-10 (th...,