Coastal aquaculture regulates phosphorus cycling in estuarine wetlands: Mobilization, kinetic resupply, and source-sink process

Research methods for seawater intrusion in China and recommendations for novel radium-radon technologies

Seawater intrusion has been a globally significant environmental issue. This paper comprehensively reviews and highlights the research methods of seawater intrusion in China, recommending the potential application of novel radioactive radium-radon isotopes. Geochemical and geophysical techniques have been extensively utilized in studying seawater intrusion in China, including methods such as hydrochemical analysis, groundwater level observations, geophysical survey techniques, and isotope tracing. The former three methodologies boast a lengthier historical application in seawater intrusion field, while the radium-radon tools in isotope tracing, as newcomers, can specifically indicate crucial scientific questions such as seawater intrusion rates, salt groundwater age, water-rock reactions, and preferential flow dynamics. However, it is imperative to acknowledge the limitations inherent in the utilization of radium-radon tools within the realm of seawater intrusion research, as with any other methodologies. Strategic integration of radium-radon tools with other methodologies will propel advancements in the investigation of seawater intrusion in China. While the primary focus is on research methods in China, insights gained from novel radium-radon tools could have broader value for seawater intrusion research and coastal management globally.

Coastal degradation regulates the availability and diffusion kinetics of phosphorus at the sediment-water interface: Mechanisms and environmental implications

Coastal wetlands have experienced considerable loss and degradation globally. However, how coastal degradation regulates sediment phosphorus (P) transformation and its underlying mechanisms remain largely unknown in subtropical coastal ecosystems. This study conducted seasonal field measurements using high-resolution diffusive gradient in thin films (DGT) and dialysis (Peeper) techniques, as well as a DGT-induced fluxes in sediments (DIFS) model, to evaluate the mobilization and diffusion of P along a degradation gradient ranging from pristine wetlands to moderately and severely degraded sites. We observed that sediment P is diminished by coastal degradation, and severely degraded sites exhibit a decline in the concentration of available P, despite the presence of distinct seasonal patterns. High-resolution data based on DGT/Peeper analysis revealed that labile P and soluble reactive P (SRP) concentrations varied from 0.0006 mg L-1 to 0.084 mg L-1 (mean 0.0147 mg L-1) and from 0.0128 mg L-1 to 0.1677 mg L-1 (mean 0.0536 mg L-1), respectively. Coastal degradation had a substantial impact on increasing SRP and labile P concentrations, particularly at severely degraded sites. Although severely degraded wetlands appeared to be P sinks (negative P flux at these sites), we did also observe positive diffusive flux in October, indicating that coastal degradation may accelerate the diffusion and remobilization of sediment P into overlying water. The simulations of the DIFS model provided compelling proof of the high resupply capacity of sediment P at severely degraded sites, as supported by the increased R and k-1 values but decreased Tc values. Taken together, these results suggest coastal degradation reduces the sediment P pool, primarily attributed to the strong remobilization of P from the sediment to porewater and overlying water by enhancing the resupply capability and diffusion kinetics. This acceleration induces nutrient loss which adversely impacts the water quality of the surrounding ecosystem. To reduce the adverse effects of coastal degradation, it is essential to adopt a combination of conservation, restoration, and management efforts designed to mitigate the risk of internal P loading and release, and ultimately maintain a regional nutrient balance.