Spatial and temporal changes to a hydrologically-reconnected coastal wetland: Implications for restoration

Abstract

Mississippi River Delta wetlands were isolated from river influence due to leveeing in the 1900's. Surface water diversions were primarily designed to manage salinity and maintain marsh vegetation by reintroducing Mississippi River water and nutrients into adjacent wetlands.Phosphorus (P) is a major limiting nutrient that can control productivity, but in excess can contribute to wetland eutrophic conditions and water quality degradation. Most wetland soil characterization assessments consider soil total P, however, this parameter alone cannot describe P bioavailability due to difference in organic and inorganic forms. A soil characterization of the Davis Pond diversion was done in 2007, before full-scale operation began, and in 2018 after 11 years of river loading. The top 10 cm of soil from 140 stations each year were analyzed for physiochemical properties and both organic and inorganic P forms. Mineral content is used to delineate areas of river diversion influence and compare P stocks between hydrologically isolated marsh areas and where effective river diversion reconnection took place. The river diversion resulted in a nearly 100% increase in soil mineral content and 58% increase in bulk density. The dominant source of soil P has changed from organic P to inorganic P in 29% of the wetland area, significantly associated with mineral content of the soil. Inorganic P stocks in diversion influenced areas are 9 times higher than those which remained isolated from riverine materials. The study showed that long-term addition of mineral sediments and inorganic P did not lead to deleterious effects in the wetland. This is the first study in the Mississippi River delta

Temporal variability in soil organic matter accretion rates in coastal deltaic wetlands under changing depositional environments

“…The marshes below the depth of 150 cm depth had N sources similar to the core surface with increasing δ 15 N signatures with depth indicating the possibility of the N supply from the river (Spera, 2019). This finding is supported by the increasing mineral matter content below 150 cm depth, which is also indicative of increased river influence (Spera et al., 2020).…”

“…Similarly, TOP increased from the surface (119.22–280.91 mg kg −1 ) to 100–130 cm (282.11–351.11 mg kg −1 ) and then decreased to the lowest value (11.46–96.43 mg kg −1 ) at 170–200 cm depth. Overall, the TOP was greater than TIP down to the depth of 140 cm beyond which the TIP was greater, indicating river sedimentation beyond 150 cm depth (Spera et al., 2020). A similar trend of TOP and TIP has been reported by Sapkota and White (2021) in Barataria Basin, and higher sediment TIP has been linked to increased river influence since the river sediment is over 96% TIP (Mates, 2020).…”

Acceleration of vegetation dynamics in hydrologically connected wetlands caused by dam operation

“…With accelerated global warming and increasing sea levels, approximately 5–20% of coastal wetlands was estimated to disappear by the 2080s (Nicholls, 2004). In Asia, approximately 5000 km 2 of wetlands are lost annually (Mu et al, 2020; Zedler & Kercher, 2005) as a result of various natural and human activities (Hu et al, 2018; Rebelo et al, 2019; Spera et al, 2020). Wetlands area in China has decreased by 26 000 km 2 from 2003 to 2013 due to biological resource exploitation and land use changes (Meng et al, 2017).…”

Assessing Chlorophyll a Spatiotemporal Patterns Combining In Situ Continuous Fluorometry Measurements and Landsat 8/OLI Data across the Barataria Basin (Louisiana, USA)

“…These include the effects of increasing flooding duration, changes in relative elevation and accretion rates in wetlands, and reduction in salinity due to freshwater inputs [31][32][33][34][35]. Because controlled freshwater diversions can also increase N and P loading rates, we also determine the potential impact on phytoplankton biomass at variable spatial scales defined by differences in fertility gradients [35,36]. We hypothesize that the impact of freshwater water diversions on the BB complex plankton biomass reflected in Chl-a values can be accurately and efficiently assessed using a combination of calibrated statistical models and spatially intensive sampling using the continuous flow-thru SWAMMP-R (Spatially explicit WAter Monitoring system to inform Management Priorities and Risks) multiprobe.…”