Mechanisms of Organic Matter Export in Estuaries with Contrasting Carbon Sources

Abstract

Modifications in land use and climate will result in shifts in the magnitude and composition of organic matter (OM) transported from wetlands to coastal waters, but differentiation between riverine and wetland OM sources in coastal areas remains a challenge. Here, we evaluate particulate and dissolved OM export dynamics in two representative estuary geomorphologies—Apalachicola Bay (AP) and Barataria Bay (BB), characterized primarily by blackwater river inputs and high particle abundance, respectively. The magnitude and composition of OM exported from each estuary was evaluated based on seasonal measurements of surface water dissolved organic carbon (DOC), particulate organic carbon (POC), particulate nitrogen, the stable isotopic composition of DOC and POC, dissolved and particulate lignin phenols, and carbon‐normalized dissolved lignin‐phenol yields. Data and discriminant analyses support the initial hypothesis; AP is dominated by a more terrestrial source of OM due to importance of fluvial dissolved OM inputs, while BB is a more particle‐rich and wetland carbon‐dominated system. Total lignin export (sum of mean dissolved and mean particulate) was higher in BB (5.73 ± 2.50 × 105 kg/year) than in AP (4.21 ± 2.35 × 105 kg/year). Particulate lignin export from BB was greater than the export of dissolved lignin at either BB or AP, suggesting coastal marsh erosion may be driving this comparatively large export of particulate lignin. These data have important implications for the stability of stored OM in coastal habitats, particularly since such habitats in this region are highly vulnerable due to relative sea level rise.

Quantifying Drivers of Methane Hydrobiogeochemistry in a Tidal River Floodplain System

“…Filtered samples (0.2 µm) were analyzed for DOC and TDN using a Shimadzu TOC-L system equipped with a total nitrogen module at the PNNL Marine and Coastal Research Laboratory [33] and in the Bianchi Lab at the University of Florida [36]. Headspace gas measurements and analyses followed the procedure in [34].…”

Environmental Flow Requirements of Estuaries: Providing Resilience to Current and Future Climate and Direct Anthropogenic Changes

“…Western coastlines of North and South America and parts of the eastern coastline of the United States are less affected by sea level rise (Church et al, 2013). Sea level rise alters the geomorphological structure and physicochemical characteristics of estuaries (Kimmerer and Weaver, 2013;Arellano et al, 2019;Khojasteh et al, 2021). Seawater is likely to intrude further inland, particularly where elevation gradients are low and where there are reductions in freshwater flows (Payne et al, 2019;Khojasteh et al, 2021).…”

“…The importance of marine-derived organic matter, nutrients and sediments relative to catchment inputs may affect biogeochemical activity, impacting estuarine organisms and food webs as river water is typically more nutrient-rich than seawater (Statham, 2012). Sea level rise associated tidal incursion may cause erosion and act with decreasing freshwater inputs to reduce intertidal habitat (Whitfield et al, 2012;Arellano et al, 2019). The collective impacts of reductions in rainfall, increased frequency of drought (#9 Figure 3) and freshwater extraction and diversion (#10 Figure 3), together with greater saline intrusion, impact species distributions and can affect drinking water availability (Kingsford et al, 2011;Romañach et al, 2019;Wang and Hong, 2021).…”

Sources, Composition, and Export of Particulate Organic Matter Across British Estuaries

“…Spatial and temporal variability in POC concentrations can be very high, driven by changes in the physicochemical and hydrological conditions, as well as variations in land cover (Duan & Bianchi, 2006). High‐rainfall events often cause soil erosion, transporting terrigenous material into estuaries (Abril et al., 2002; Arellano et al., 2019; Hope et al., 1997; Ye et al., 2017). In situ growth of autochthonous planktonic organisms, as well as marine POC transported into estuaries, may increase POC concentrations, but will reduce the proportion of terrigenous POC (TPOC) within estuaries (He et al., 2014; Liénart et al., 2017).…”