Ecosystems around the globe are being degraded by anthropogenic activity. Coastal ecosystems are considered especially vulnerable given that human populations are concentrated at the coast. Extensive areas of saltmarsh habitat have already been lost to land reclamation, and the continued existence of natural marsh systems is in question.Understanding how saltmarsh plants interact within a changing coastal environment is seen as a vital step in protecting remaining habitat and delivering successful restoration. This thesis
examines patterns of saltmarsh change across Great Britain (GB), and the biological and environmental drivers responsible for change, in order to better understand marsh persistence.
Studies have tended to assess marsh persistence based on their capacity to grow vertically with sea level rise. Long-term horizontal marsh dynamics are often overlooked. Chapter 2 examines 100 years of saltmarsh area change across GB and found that sea level rise and sediment supply determined whether saltmarshes expanded or eroded. All marshes were keeping pace with sea level rise, highlighting the importance of considering horizontal dynamics in long-term marsh change. Identifying the limits on horizontal saltmarsh growth onto tidal flats has been valuable in assessing potential impacts of coastal change on open-coast marsh systems, however little work
has been done on identifying limits of marsh extent within estuaries. Chapter 3 examines saltmarsh extent change between 1948 and 2013 in three sheltered estuaries along western GB, and shows that changes in the position of tidal channels limited marsh extent. Channels periodically migrated across the estuary causing marsh erosion. On the opposite bank, marshes tended to expand, indicating the capacity of marshes to cycle between phases of expansion and erosion retaining a dynamic persistence within estuaries.
Horizontal erosion of saltmarsh creeks causes vegetated marsh debris to accumulate at the creek base. Indications are that these deposits limit further erosion and promote recovery through trapping sediment if they persist. However, biotic and abiotic controls on debris longevity are unclear. Chapter 4 examines monthly creek change over a year and shows that failed bank debris with high root content slow debris erosion rates, thereby promoting sediment
trapping and recovery. Thus, plant growth plays an important role on saltmarsh stability. By investigating marsh change over different spatio-temporal scales, a picture emerges of how biological and environmental drivers collectively influence change in saltmarsh extent. This offers important insight into how management interventions could target the drivers of marsh change at each scale in order to build marsh resilience, and is discussed in chapter 5.