Rivers are dynamic components of the terrestrial carbon cycle and provide important functions in ecosystem processes. Although rivers act as conveyers of carbon to the oceans, rivers also retain carbon within riparian ecosystems along floodplains, with potential for long‐term (> 102 years) storage. Research in ecosystem processing emphasizes the importance of organic carbon (OC) in river systems, and estimates of OC fluxes in terrestrial freshwater systems indicate that a significant portion of terrestrial carbon is stored within river networks. Studies have examined soil OC on floodplains, but research that examines the potential mechanistic controls on OC storage in riparian ecosystems and floodplains is more limited. We emphasize three primary OC reservoirs within fluvial systems: (1) standing riparian biomass; (2) dead biomass as large wood (LW) in the stream and on the floodplain; (3) OC on and beneath the floodplain surface, including litter, humus, and soil organic carbon (SOC). This review focuses on studies that have framed research questions and results in the context of OC retention, accumulation and storage within the three primary pools along riparian ecosystems. In this paper, we (i) discuss the various reservoirs for OC storage in riparian ecosystems, (ii) discuss physical conditions that facilitate carbon retention and storage in riparian ecosystems, (iii) provide a synthesis of published OC storage in riparian ecosystems, (iv) present a conceptual model of the conditions that favor OC storage in riparian ecosystems, (v) briefly discuss human impacts on OC storage in riparian ecosystems, and (vi) highlight current knowledge gaps. Copyright © 2015 John Wiley & Sons, Ltd.

Among the least studied ecosystem services of mangroves is their value as global carbon (C) stocks. This is significant as mangroves are subject to rapid rates of deforestation and therefore could be significant sources of atmospheric emissions. Mangroves could be key ecosystems in strategies addressing the mitigation of climate change though reduced deforestation. We quantified ecosystem C stocks at the seaward, interior, and upland edges of mangroves in the Republic of Palau and Yap, Federated States of Micronesia. The relatively high aboveground biomass coupled with carbon-rich soils resulted in the presence of large ecosystem carbon stocks compared to other tropical forests. Ecosystem C storage at the Palau site ranged from 479 Mg/ha in the seaward zone to 1,068 Mg/ha in the landward zone; in the Yap site C storage ranged from 853 to 1,385 Mg/ha along this gradient. Soils contained~70% of the ecosystem C stocks. The elevation range of mangroves was <146 cm, suggesting that projected sea-level rise can influence a large portion of existing stands. Declines in ecosystem carbon stocks will be pronounced if mangroves are replaced by communities adapted to greater inundation such as seagrass communities, where C pools were ≤7% of that of mangroves (48 Mg C/ha).

Published research emphasizes rapid downstream export of terrestrial carbon from mountainous headwater rivers, but little work focuses on mechanisms that create carbon storage along these rivers, or on the volume of carbon storage. Here we estimate organic carbon stored in diverse valley types of headwater rivers in Rocky Mountain National Park, CO, USA. We show that low-gradient, broad valley bottoms with old-growth forest or active beaver colonies store the great majority of above-and below-ground carbon. These laterally unconfined valley segments constitute o25% of total river length, but store B75% of the carbon. Floodplain sediment and coarse wood dominate carbon storage. Our estimates of riverine carbon storage represent a previously undocumented but important carbon sink. Our results indicate that: not all mountainous rivers rapidly export carbon; not all valley segments are equally important in carbon storage; and historical changes in riverine complexity have likely reduced carbon storage.

Despite the numerous values of riparian areas and the recognition of fire as a critical natural disturbance, few studies have investigated the behavior, properties, and influence of natural fire in riparian areas of the western USA. Riparian areas frequently differ from adjacent uplands in vegetative composition and structure, geomorphology, hydrology, microclimate, and fuel characteristics. These features may contribute to different fire environments, fire regimes, and fire properties (frequency, severity, behavior, and extent) in riparian areas relative to uplands. In certain forested riparian areas, fire frequency has generally been lower, and fire severity has been more moderate than in adjacent uplands, but in other areas, fires have appeared to burn riparian areas with comparable frequency. Impacts of land use and management may strongly influence fire properties and regimes in riparian areas. Fire suppression, livestock grazing, logging, damming and flow regulation, agricultural diversions, channel modifications, and introduction of invasive species have led to shifts in plant species composition, structure and distribution of fuel loads, and changes in microclimate and areal extent of riparian areas. Cumulative impacts of human alterations are likely to exert the most pronounced influence on fire behavior during periods of drought and under conditions of extreme fire weather. Riparian plant species possess adaptations to fluvial disturbances that facilitate survival and reestablishment following fires, thus contributing to the rapid recovery of many streamside habitats. Given the critical resource values of riparian zones, additional data are needed to understand interactions between fire and riparian ecosystems, and how riparian zones affect spatial and temporal patterns of fires at the landscape scale. An improved understanding of fire ecology and effects in riparian areas is needed to prescribe ecologically sound rehabilitation projects following fire.