Spatial Variability in Sedimentation, Carbon Sequestration, and Nutrient Accumulation in an Alluvial Floodplain Forest

Abstract

We measured soil properties, vertical accretion, and nutrient (organic C, N, and P) accumulation across a range of habitats to evaluate spatial variability of soil properties and processes of alluvial floodplain wetlands of the Altamaha River, Georgia, USA. The habitats vary in elevation and distance from the river channel, creating differences in the depth and duration of inundation. Habitats closer to the river had lower bulk density and higher total P than habitats further removed.137 Cs and 210 Pb accretion rates were also greater at sites closer to the channel. Mineral sediment deposition and nutrient accumulation were greater in sloughs closer to the channel and lower in elevation relative to other habitats. We found distance to be a significant predictor of mineral soil properties across the floodplain. Bulk density increased whereas TP and silt content decreased with distance from the river channel.137 Cs accretion, P accumulation, and mineral sediment deposition also decreased with distance from the main channel. Elevation was not a significant predictor of soil properties or processes measured. Long-term (100 year) sediment accumulation rates based on 210 Pb were significantly higher than 50-year rate of sedimentation based on 137 Cs, perhaps as the result of greater land clearing for agriculture and lack of best management practices in the southeastern USA prior to 1950. Distance from the main channel is the driving force behind the spatial variability of soil properties and processes measured; however, slough habitats closest to the channel and lowest in elevation relative to other habitats maintain distinct vegetation patterns and are hotspots for N, P, and sediment accumulation. Characterization of soil properties and processes of alluvial floodplain forests and other wetlands should take into consideration microtopographic and spatial variation across the wetland.

Land Cover Changes (1963–2010) and Their Environmental Factors in the Upper Danube Floodplain

“…Higher sites in the floodplain are much drier than lower sites because they are farther from the groundwater table. Distance to river is a significant factor for the spatial variability in the depth and duration of inundation, soil properties, nutrient accumulation and other ecological processes in the floodplain [99]. Bürgi and Turner [100] detected different land cover changes in various soil conditions: agricultural land changed into forest as a result of agricultural abandonment on shallow soils; arable land changed into grassland due to the decline of farming intensity on more sandy and deeper soils; fertile grassland sites on silty soils were transformed into arable land owing to agricultural intensification.…”

From the headwaters to the sea: The role of riparian, alluvial, and tidal wetlands to filter nutrients and ameliorate eutrophication

“…Wetlands, transitional between terrestrial and aquatic ecosystems, trap sediment, filter nutrients, nitrogen (N) and phosphorus (P), and sequester carbon (C). Their ability to remove sediment and nutrients depends, in part, on their proximity to the source material (Phillips, 1989), including adjacent uplands, their degree of connectivity to aquatic ecosystems such as rivers and estuaries, flood duration, distance from the main channel, vegetation type, and other factors (Bannister et al, 2015; Craft & Casey, 2000; Job & Sieben, 2022; Lisenby et al, 2019; Noe et al, 2022; Woznicki et al, 2020). Riparian wetlands are known for their ability to intercept sediment and P from adjacent uplands, especially runoff from agricultural land (Fennessy & Craft, 2011; Graziano et al, 2022; Stutter et al, 2021).…”

“…Over geologic time, headwater regions serve as a net source of material whereas areas near the mouth of rivers and estuaries, and ultimately the sea, are sinks for these materials. Along the way downstream, wetlands store N and P as they are buried by mineral sediment and by deposition of nutrient‐rich litter that is incorporated into the soil (Bannister et al, 2015; Noe & Hupp, 2005). To date, most studies of wetland nutrient retention have focused on individual wetland types such as riparian (Hoffmann et al, 2011) or alluvial (Noe et al, 2022), or tidal wetlands (Cornwell et al, 2021), eschewing measurements of the variation of these processes along the length of the waterway.…”