Recent increases of rainfall and flooding from tropical cyclones (TCs) in North Carolina (USA): implications for organic matter and nutrient cycling in coastal watersheds

Abstract

Coastal North Carolina experienced 36 tropical cyclones (TCs), including three floods of historical significance in the past two decades (Hurricanes Floyd-1999, Matthew-2016 and Florence-2018. These events caused catastrophic flooding and major alterations of water quality, fisheries habitat and ecological conditions of the Albemarle-Pamlico Sound (APS), the second largest estuarine complex in the United States. Continuous rainfall records for coastal NC since 1898 reveal a period of unprecedented high precipitation storm events since the late-1990s. Six of seven of the ''wettest'' storm events in this [ 120-year record occurred in the past two decades, identifying a period of elevated precipitation and flooding associated with recent TCs. We examined storm-related freshwater discharge, carbon (C) and nutrient, i.e., nitrogen (N) and phosphorus (P) loadings, and evaluated contributions to total annual inputs in the Neuse River Estuary (NRE), a major sub-estuary of the APS. These contributions were highly significant, accounting for [ 50% of annual loads depending on antecedent conditions and storm-related flooding. Depending on the magnitude of freshwater discharge, the NRE either acted as a ''processor'' to partially assimilate and metabolize the loads or acted as a ''pipeline'' to transport the loads to the APS and coastal Atlantic Ocean. Under base-flow, terrestrial sources dominate riverine carbon. During storm events these carbon sources are enhanced through the inundation and release of carbon from wetlands. These findings show that event-scale discharge plays an important and, at times, predominant

Roles of Nutrient Limitation on Western Lake Erie CyanoHAB Toxin Production

“…This is likely due to larger nutrient loads from the Maumee River than from the Sandusky River, as seen previously in 2007 [ 86 ]. The high nutrient loads were exacerbated by elevated precipitation associated with a very wet winter in 2019 [ 87 ], which will likely continue to be an issue as high precipitation events are predicted to continue in the future [ 88 , 89 , 90 ]. Denitrification and assimilation draw down nitrate to concentrations below the threshold of detection (<0.5 µmol/L) throughout summer and fall in western Lake Erie and Sandusky Bay [ 28 , 91 ], which is a pattern that occurs independent of tributary nutrient loads [ 19 ].…”

A case for addressing the unresolved role of permeable shelf sediments in ocean denitrification

“…layers, deep sediment oxygenation, and the redistribution of organic matter and nutrients (Scavia et al 2002;Osburn et al 2019;Paerl et al 2020). In the last three decades, studies focusing on transport and diagenetic reactions (i.e., physical and chemical processes that alter sediments after deposition) in inner shelf sands suggest they play an underappreciated role in biogeochemical cycling.…”

Decision making in the coastal zone under an uncertain future

“…Storm surges, high river discharge, or waves are caused by extreme weather and occur locally from hours to days 11 . In some regions, tropical cyclones cause coastal flooding 12 . In others, it is the magnitude, coincidence, and relative timing of these drivers which elevates water levels above the normal levels and poses a disproportionately large flood hazard 13 .…”