Development of deltaic and estuarine wetlands under decadal and long-term climate variations

SCHÜRCH MARK; BÄCHTIGER MARCEL ; KUMBIER KRISTIAN; GARCIA-RODRIGUEZ FELIPE ; CARRETERO SILVINA; SCHNACK ENRIQUE; VAFEIDIS ATHANASIOS

Congreso; International Conference Deltas in Times of Climate Change II; 2014

Coastal wetland areas all around the world are under increasing pressure by global climate change and accelerated sea-level rise (SLR). The morphological development of coastal wetlands generally depends on the local tidal range and sediment availability as well as the occurrence of storm events. In estuaries, tidal range and sediment availability significantly vary from the inner to the outer estuary and exhibit decadal and long-term variations. The riverine sediment discharge and the occurrence of strong and extreme storm events determine both variables to a large extent.In the present study, we investigate how decadal and long-term variations in river discharge and storm activity affect the morphological development of the marshes in the Rio de la Plata. River discharge of the major rivers flowing into the Rio de la Plata is influenced by intense human modifications and changes in climatic variables (primarily precipitation) in the river catchment. The El Niño Southern Oscillation (ENSO) thereby has a major impact on the discharge regimes and introduces a large decadal variability on sediment availability for the marshes around the Rio de la Plata. Our hypothesis is that these variations are particularly important for the development of the marshes in the inner estuary that are located in the Paraná delta, which is subject to annual progradation rates of approximately 70 m/yr. In contrast, marsh development in the outer estuary is assumed to be primarily controlled by variations in storm activity. Using radioisotope analysis, we assess the long-term vertical accretion rates and explore how decadal variability of river discharge and storm activity affects the adaptive capacity of coastal marshes to long-term accelerated SLR. Data from 15 sites around the estuary are used to study the relative importance of variations in river discharge and storm activity on vertical accretion rates. Preliminary results indicate a large spatial variability in the marsh morphology along the estuary. Storm-induced waves appear to play a significant role in the development of the outer marshes on the Uruguayan side, while the availability of fine-grained sediments seems to be more important for the marshes in the inner estuary and along the Argentinean coast. Combined with the assessment of spatial variations of the governing hydrological and hydrodynamic drivers for estuarine marsh development, this study contributes to a better understanding of how decadal variations of environmental drivers impacts the long-term ability of estuarine marshes to persist under future climate conditions.