Testate amoebae are informative bioindicators of critically high ammonia deposition on peatlands

The global nitrogen cycle has been majorly disrupted by anthropogenic activity. While nitrogen emissions in the UK and Ireland are declining, ammonia (NH₃) remains a significant exception. NH₃ emissions are mostly agriculturally sourced and deposited on nearby habitats at high rates in both countries. Peatlands are globally important wetlands that are vulnerable to NH₃ deposition. Essential peatland restoration risks being diminished by excessive NH₃ deposition, leading to the loss of valuable ecosystem services. This study investigates testate amoebae (indicators of contemporary and historic peatland conditions) as bioindicators of seasonal NH₃ deposition on six peatlands across Northern Ireland, UK. Sphagnum, an NH₃-sensitive bryophyte, was sampled adjacent to NH₃ monitoring sites once per season for a year. When NH₃ deposition was critically high, multivariate analysis demonstrates a link between NH₃ and testate amoebae assemblage change. Similarly, at high NH₃ deposition sites, testate amoebae taxa diversity is observed to be significantly reduced in springtime, when it is expected to be highest. Although, in response to high NH₃ deposition large algivorous taxa do not proliferate as was anticipated, and mixotrophic taxa abundance decreases could not be linked primarily to NH₃. This research demonstrates the continued potential of testate amoebae as highly informative peatland bioindicators.