Seasonal sediment dynamics in a constructed and natural tidal marsh in the northern Gulf of Mexico

Declines in sediment loading, combined with sea-level rise, are a major driver of recent tidal marsh loss. As such, evaluations of sediment dynamics are necessary for assessments of current and future marsh resilience to sea-level rise. While tidal marsh creation is used to offset these losses, few studies have assessed sediment dynamics in these systems; those that have were focused on accumulation at a single time and/or place, without considering the composition of accumulated sediment (i.e., organic vs. inorganic). We compared seasonal sediment dynamics between a natural and nearby 34-year-old constructed tidal marsh in the northern Gulf of Mexico. In July 2021, we set up a series of permanent sampling points along one tidal creek in each marsh and made monthly measurements of sedimentation, surface organic matter accumulation, and surface scour for one year. We found that sedimentation and organic matter accumulation were lower in the constructed marsh, while surface scour did not differ. Additionally, we found that the relationship between distance from the mouth of each tidal creek and sedimentation differed between marshes (positive in natural, negative in constructed), as did organic matter accumulation (no relationship in natural, positive in constructed). Despite this, we found that both marshes followed similar seasonal trends in sediment accumulation (highest in summer, lowest in winter). Our results suggest that considering local sedimentation rates is critical to insuring that adequate sedimentary dynamics develop in restored and created marshes, underscoring the importance of evaluating spatial and temporal variation in sedimentary dynamics to assess restoration outcomes.