The significance of aquatic lateral carbon (C) export in mangrove ecosystems highlights the extensive contribution of aquatic pathways to the net ecosystem carbon budget. However, few studies have investigated lateral fluxes of dissolved organic carbon (DOC) and inorganic carbon (DIC), partly due to methodological difficulty. Therefore, we evaluated area-based lateral C fluxes in a small mangrove estuary that only had one exit for water exchange to the coast. We sampled water from the mouth of the creek and integrated discharge and consecutive concentration of mangrove-derived C (ΔC). Then, we estimated the area-normalized C fluxes based on the inundated mangrove area. DIC and DOC concentrations at the river mouth increased during ebb tide during both summer and winter. We quantified the ΔC in the estuary using a two-component conservative mixing model of freshwater and seawater. DIC and DOC proportions of ΔC concentrations at the river mouth during ebb tide was between 34% and 56% in the winter and 26% and 42% in the summer, respectively. DIC and DOC fluxes from the estuary were estimated to be 1.36 g C m⁻² d⁻¹ and 0.20 g C m⁻² d⁻¹ in the winter and 3.35 g C m⁻² d⁻¹ and 0.86 g C m⁻² d⁻¹ in the summer, respectively. Based on our method, daily fluxes are mangrove area-based DIC and DOC lateral exports that can be directly incorporated into the mangrove carbon budget.

Dissolved iron (dFe) in boreal rivers may play an important role in primary production in high-latitude oceans. However, iron behavior in soils and dFe discharge mechanism from soil to the rivers are poorly understood. To better understand iron dynamics on the watershed scale, we observed the seasonal changes in dFe and Dissolved Organic Carbon (DOC) concentrations in the river as well as dFe concentration in soil pore waters in permafrost watershed from May to October. During snowmelt season, high dFe production (1.38–4.70 mg L${}^{-1}$) was observed in surface soil pore waters. Correspondingly, riverine dFe and DOC concentrations increased to 1.10 mg L${}^{-1}$ and 32.3 mg L${}^{-1}$, and both were the highest in the year. After spring floods, riverine dFe and DOC concentrations decreased to 0.15 mg L${}^{-1}$ and 7.62 mg L${}^{-1}$, and dFe concentration in surface soil pore waters also decreased to 0.20–1.28 mg L${}^{-1}$. In late July, riverine dFe and DOC concentrations increased to 0.33 mg L${}^{-1}$ and 23.6 mg L${}^{-1}$ in response to heavy rainfall. In August and September, considerable increases in dFe concentrations (2.00–6.90 mg L${}^{-1}$) were observed in subsurface soil pore waters, probably because infiltrated rainwater developed reducing conditions. This dFe production was confirmed widely in permafrost wetlands in valley areas. Overall, permafrost wetlands in valley areas are hotspots of dFe production and greatly contribute to dFe and DOC discharge to rivers, especially during snowmelt and rainy seasons.

River water temperature serves as a critical indicator of numerous biological and chemical processes essential for ecosystem support and water quality maintenance. River temperatures are expected to rise due to the increasing impact of climate change, causing potential adverse consequences. Hence, a thorough understanding of the drivers influencing river temperature is imperative. Physically or process-based models are suitable for enriching our understanding of the mechanisms regulating river temperature. In this study, we collected articles on river water temperature and modeling and classified them according to their modeling type and energy components. We reviewed the physically based models to determine the relative proportions of various energy fluxes that affect the temperature of river water. The results indicated that despite its importance, groundwater flux has not been given as much consideration as the other fluxes, particularly for small rivers. We also reviewed the semi-distributed Soil and Water Assessment Tool (SWAT) model, which has been applied to the computation of stream temperature and found that some modifications made to the model primarily used the equilibrium temperature approach, whereas only a few studies considered the groundwater flux. Our findings highlight the need for further improvements in modeling techniques, with special emphasis on improving the representation of subsurface fluxes, particularly groundwater, for the better management of ecosystem preservation and water quality.