Geochemical discrimination of bulk organic matter in surface sediments of the Cross River estuary system and adjacent shelf, South East Nigeria (West Africa)

Distribution, sources, and decomposition of soil organic matter along a salinity gradient in estuarine wetlands characterized by C:N ratio, δ13C‐δ15N, and lignin biomarker

“…In contrast, the proportions of terrestrial OC appeared negative values in Site 1 of the most upstream position (Figure 5). This may be attributed to the pollution of non‐point sources (i.e., domestic and industrial wastewater, agricultural runoffs), which are all possible sources of anthropogenic organic C (Barros et al., 2010; Dan et al., 2019). The δ 13 C values in our study are comparable to those observed in the Yangtze River estuary (−24.5‰ to −21.2‰; Zhang et al., 2007), Pearl River estuary (−27.0‰ to −20.8‰; Yu et al., 2010), Colville River delta (−27.2‰ to −21.9‰; Zhang et al., 2015), the Amazon region (−27‰ to −24‰; Ramaswamy et al., 2008), and Bohai Sea near the Yellow River Estuary (−23.9 to −20.8‰; Liu et al., 2015).…”

“…Consistently, the losses of 15 N‐depleted inorganic N (i.e., nitrate) by plant's uptake decreased from habitats I to III, allowing the remaining residuals enriched in 15 N in soils. In addition, the degree of SOM decomposition dropped from landward to seaward (Dan et al., 2019). The values of δ 15 N in tidal flat (i.e., habitat IV) increased with soil depth, which may be related to (a) the N sources are possibly derived from marine algae and phytoplankton (Li et al., 2016); and (b) differences that existed in N components with depth by intensified tidal action.…”

“…The proportion of terrestrial OC ( f , in %) in soils or sediments of estuarine wetlands was calculated using a two end‐member stable isotope mass balance equation:where is the of marine end‐member, being an average of −20.9‰; is the terrestrial end‐member, with an average of −27‰ (Dan et al., 2019); and is the measured of the samples.…”

“…where δ 13 C marine is the δ 13 C of marine end-member, being an average of −20.9‰; δ 13 C terrestrial is the terrestrial end-member, with an average of −27‰ (Dan et al, 2019); and δ 13 C org is the measured δ 13 C of the samples. to 33.1% and overall increased with soil depth (Table S1).…”

“…In contrast, the proportions of terrestrial OC appeared negative values in Site 1 of the most upstream position ( Figure 5). This may be attributed to the pollution of non-point sources (i.e., domestic and industrial wastewater, agricultural runoffs), which are all possible sources of anthropogenic organic C (Barros et al, 2010;Dan et al, 2019). Ramaswamy et al, 2008), and Bohai Sea near the Yellow River Estuary (−23.9 to −20.8‰; Liu et al, 2015).…”