Unified concepts for understanding and modelling turnover of dissolved organic matter from freshwaters to the ocean: the UniDOM model

The transport of dissolved organic matter (DOM) across the land-ocean-aquatic continuum (LOAC), from freshwater to the ocean, is an important yet poorly understood component of the global carbon budget. Exploring and quantifying this flux is a significant challenge given the complexities of DOM cycling across these contrasting environments. We developed a new model, UniDOM, that unifies concepts, state variables and parameterisations of DOM turnover across the LOAC. Terrigenous DOM is divided into two pools, T1 (strongly-UV-absorbing) and T2 (non- or weakly-UV-absorbing), that exhibit contrasting responses to microbial consumption, photooxidation and flocculation. Data are presented to show that these pools are amenable to routine measurement based on specific UV absorbance (SUVA). In addition, an autochtonous DOM pool is defined to account for aquatic DOM production. A novel aspect of UniDOM is that rates of photooxidation and microbial turnover are parameterised as an inverse function of DOM age. Model results, which indicate that ~5% of the DOM originating in streams may penetrate into the open ocean, are sensitive to this parameterisation, as well as rates assigned to turnover of freshly produced DOM. The predicted contribution of flocculation to DOM turnover is remarkably low, although a mechanistic representation of this process in UniDOM was considered unachievable because of the complexities involved. Our work highlights the need for ongoing research into the mechanistic understanding and rates of photooxidation, microbial consumption and flocculation of DOM across the different environments of the LOAC, along with the development of models based on unified concepts and parameterisations

Relationships Between Submarine Groundwater Discharge and Coastal Fisheries as a Water-Food Nexus

We introduced the results of investigations conducted in Japan (Yamagata, Fukui, Hiroshima and Oita Prefectures) and discussed the contribution of SGD to the production of fishery resources and their prey (meiobenthic communities). Our recent surveys provided evidence of the contribution of SGD to the production of fishes and their prey. These results strongly support the hypothesis that the contribution of nutrients from SGD to the coastal fishery resources production is much higher than previously suggested. The negative ecological impacts of SGD on meiofaunal abundance were confirmed at the high seepage areas of Kamaiso where the small spatial scale presented strong heterogeneity in SGD environmental conditions. However, the meiofaunal abundance was not low at the low seepage area located slightly apart from the high seepage area. Therefore, the effect of SGD on meiofaunal communities could be limited. However, the environmental heterogeneity significantly enhanced the conservation of the meiofaunal diversity. Thus, SGD determined the property of benthic communities