Geomorphological response to system‐scale river rehabilitation I: Sediment supply from a reconnected tributary

Persistence of tidal wetlands under conditions of sea level rise depends on vertical accretion of organic and inorganic matter, which vary in their relative abundance across estuarine gradients. We examined the relative contribution of organic and inorganic matter to vertical soil accretion using lead-210 (210Pb) dating of soil cores collected in tidal wetlands spanning a tidal freshwater to brackish gradient across a Chesapeake Bay subestuary. Only 8 out of the 15 subsites had accretion rates higher than relative sea level rise for the area, with the lowest rates of accretion found in oligohaline marshes in the middle of the subestuary. The mass accumulation of organic and inorganic matter was similar and related (R2 = 0.37). However, owing to its lower density, organic matter contributed 1.5–3 times more toward vertical accretion than inorganic matter. Furthermore, water/porespace associated with organic matter accounted for 82%–94% of the total vertical accretion. These findings demonstrate the key role of organic matter in the persistence of coastal wetlands with low mineral sediment supply, particularly mid-estuary oligohaline marshes.

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Spatiotemporally varying inter-relationships between mainstem riverbed elevation and tributary sediment supply since the last interglacial in the upper Ara River, central Japan

Geomorphology ◽

10.1016/j.geomorph.2021.107697 ◽

2021 ◽

pp. 107697

Author(s):

Takayuki Takahashi ◽

Toshihiko Sugai

Keyword(s):

Sediment Supply ◽

Last Interglacial ◽

Central Japan

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Amplified Impact of Climate Change on Fine-Sediment Delivery to a Subsiding Coast, Humboldt Bay, California

Estuaries and Coasts ◽

10.1007/s12237-021-00938-x ◽

2021 ◽

Author(s):

Jennifer A. Curtis ◽

Lorraine E. Flint ◽

Michelle A. Stern ◽

Jack Lewis ◽

Randy D. Klein

Keyword(s):

Climate Change ◽

Climate Change Impacts ◽

Baseline Period ◽

Climate Impacts ◽

Sediment Supply ◽

Balance Model ◽

Climate Projections ◽

Sediment Delivery ◽

Beneficial Reuse ◽

Coastal Margin

AbstractIn Humboldt Bay, tectonic subsidence exacerbates sea-level rise (SLR). To build surface elevations and to keep pace with SLR, the sediment demand created by subsidence and SLR must be balanced by an adequate sediment supply. This study used an ensemble of plausible future scenarios to predict potential climate change impacts on suspended-sediment discharge (Qss) from fluvial sources. Streamflow was simulated using a deterministic water-balance model, and Qss was computed using statistical sediment-transport models. Changes relative to a baseline period (1981–2010) were used to assess climate impacts. For local basins that discharge directly to the bay, the ensemble means projected increases in Qss of 27% for the mid-century (2040–2069) and 58% for the end-of-century (2070–2099). For the Eel River, a regional sediment source that discharges sediment-laden plumes to the coastal margin, the ensemble means projected increases in Qss of 53% for the mid-century and 99% for the end-of-century. Climate projections of increased precipitation and streamflow produced amplified increases in the regional sediment supply that may partially or wholly mitigate sediment demand caused by the combined effects of subsidence and SLR. This finding has important implications for coastal resiliency. Coastal regions with an increasing sediment supply may be more resilient to SLR. In a broader context, an increasing sediment supply from fluvial sources has global relevance for communities threatened by SLR that are increasingly building resiliency to SLR using sediment-based solutions that include regional sediment management, beneficial reuse strategies, and marsh restoration.

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