Trends in surface elevation and accretion in a retrograding delta in coastal Mississippi, USA from 2012–2016

Abstract

The Grand Bay estuary is in the north-central Gulf of Mexico and lacks riverine sediment input for marsh elevation maintenance. This study quantified trends in surface elevation change and accretion along an elevation gradient within the estuary. Elevation change rates were compared to short (13.71 mm/yr; 95% CI: -2.38–29.81), medium (6.97 mm/yr; 95% CI: 3.31–10.64), and long-range (3.50 mm/yr; 95% CI: 2.88–4.11) water level rise (WLR) rates for the region. Elevation change rates ranged from 0.54 mm/yr (95% CI: -0.63–1.72) to 5.45 mm/yr (95% CI: 4.27–6.62) and accretion rates ranged from 0.82 mm/yr (95% CI: -0.16–1.80) to 3.89 mm/yr (95% CI: 2.90–4.89) among marsh zones. Only the elevation change rate at a Juncus roemerianus marsh located high in the tidal frame was lower than long- (P < 0.001) and medium-range WLR rates (P < 0.01). The elevation change rate at a lower elevation J. roemerianus marsh was higher than the long-range WLR rate (P < 0.05). No marsh zones had elevation change rates that were significantly different from short-range WLR. These results suggest that J. roemerianus marshes higher in the tidal frame are the most vulnerable to increases in sea level. Lower elevation marshes had higher rates of elevation change driven by sediment accretion and biogenic inputs. Other local research suggests that shoreline erosion is a threat to marsh persistence but provides elevation capital to interior marshes. Marsh migration is a potential solution for marsh persistence in this relatively undeveloped area of the Gulf Coast.