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Between the land and ocean, diverse coastal ecosystems transform, store, and transport material. Across these interfaces, the dynamic exchange of energy and matter is driven by hydrological and hydrodynamic processes such as river and groundwater discharge, tides, waves, and storms. These dynamics regulate ecosystem functions and Earth’s climate, yet global models lack representation of coastal processes and related feedbacks, impeding their predictions of coastal and global responses to change. Here, we assess existing coastal monitoring networks and regional models, existing challenges in these efforts, and recommend a path towards development of global models that more robustly reflect the coastal interface. Coastal systems are hotspots of ecological, geochemical and economic activity, yet their dynamics are not accurately represented in global models. In this Review, Ward and colleagues assess the current state of coastal science and recommend approaches for including the coastal interface in predictive models.

The metabolism of dissolved organic carbon (DOC) along fluvial networks determines what fraction of organic matter is exported to the ocean. Although it is thought fresh rather than older DOC is preferred by bacteria, old DOC can also be highly bioavailable to stream bacterial communities. In strongly seasonal and oligotrophic regions, we argue that groundwater inputs of old DOC may increase the bioavailability of stream organic matter. We sampled 22 streams along a gradient of size (wetted widths from 1 to 60 m) and one groundwater spring in the Kimberley region of northwest Australia to determine how the age and bioavailability of streamwater DOC varied with stream size. Our hypothesis was that stream DOC would become more enriched in 14 C (younger) and less bioavailable as streams increased in size and depleted 14 C-DOC was metabolized by stream microbial communities. We also used fluorescence characterization of DOC, ultraviolet absorbance at 254nm (SUVA 254 ), δ 13 C-DOC and lignin phenol yields to assess how these indicators of DOC character influenced the bioavailability and age of stream DOC. Stream evaporation/inflow ratios ( E / I , used as a proxy for catchment water residence time), determined from changes in stream δ 18 O along the gradient of stream size, were positively related to DOC concentration and carbon-normalized lignin yields, while δ 13 C-DOC became more depleted with increasing E / I . Stream Δ 14 C-DOC varied from −452.1‰ (groundwater) to 48.9‰ and showed progressive enrichment as streams increased in size and accumulated DOC mainly from terrestrial plant material. Older DOC corresponded to higher bioavailability ( R 2 = 0.67, P < 0.01), suggesting that old bioavailable DOC, which has escaped from subterranean food webs utilizing 14 C-depleted carbon, is common to one of the oldest landscapes on earth. Therefore, rapid biotic uptake of old bioavailable DOC originating in groundwater springs and the accumulation of modern, terrestrially derived DOC work in opposite directions affecting DOC dynamics along fluvial networks. We suggest the metabolism of old DOC along fluvial networks provides a biogeochemical link between non-contemporary carbon fixation and modern river productivity.

We present the latest version of the ISBA‐CTRIP land surface system, focusing on the representation of the land carbon cycle. We review the main improvements since the year 2012, mainly added modules for wild fires, carbon leaching through soil and transport of dissolved organic carbon to the ocean, and land cover changes but also improved representation of photosynthesis, respiration, and plant functional types. This version of ISBA‐CTRIP is fully described in terms of land carbon pools, fluxes, and their interactions. Results are compared with the previous version in an off‐line mode forced by observed climate during the historical time period. The two simulations are presented to demonstrate the model performance compared to an ensemble of observed and observation‐derived data sets for gross and net primary productivity, heterotrophic and autotrophic respiration, above and below ground biomass, litter, and soil carbon pools. New developments specific to the new version such as burned area, fire emissions, carbon leaching, and land cover are also validated against observations. The results show clearly that the latest version of ISBA‐CTRIP outperforms the former version and reproduces generally well the observed mean spatial patterns in carbon pools and fluxes, as well as the seasonal cycle of leaf area index. The trends of the global fluxes over the last 50 years agree with other global models and with available estimates. This comparison gives us confidence that the model represents the main processes involved in the terrestrial carbon cycle and can be used to explore future global change projections. Plain Language Summary The land surface exchanges energy, water, and carbon with the atmosphere and partly controls the atmospheric CO2 concentration. It is therefore crucial to represent correctly the carbon cycle on land in models designed to be used in Earth System Models. We present here the improvements made to the representation of the land carbon cycle by the land surface system ISBA‐CTRIP. We improved the representation of several processes using published data, and we added processes that were not represented. The new version of the model performs better than the previous one at representing the carbon fluxes and pools, when compared to a series of observation data sets. This evaluation suggests that we can use ISBA‐CTRIP to explore the changing climate and carbon cycle. Key Points This paper documents the updates to the biogeochemical module of the ISBA‐CTRIP land surface system for use in the CNRM‐ESM 2‐1 Earth system model The newly represented processes are the leaching of carbon and transport of dissolved organic carbon to the ocean, fire with area burned and carbon emissions, and land cover changes The largest improvements in the representation of net primary productivity are due to improved autotrophic respiration

We investigated changes in the quantity and quality of dissolved organic matter (DOM) from rain to stream water in a forested watershed at Yamashiro Experimental Forest (YMS) in southern Kyoto prefecture. The dissolved organic carbon (DOC) concentration and specific UV absorbance at 254 nm (SUVA254) in rainwater increased in the order of bulk rain, throughfall, stemflow, and O layer leachate because of the DOM supply from tree tissue and O layer. Decreases in DOC concentration and SUVA254 with soil depth were not observed in the soil-percolating water. This finding may have been caused by the low free oxide content of the soil and the collection of soil water with a tension-free lysimeter. The DOC concentration was very low in both seepage and stream waters; seasonal variation with a high concentration in summer was observed in the stream water. An increase in K+ concentration in summer was also observed in the stream water; thus, we presumed that DOC seasonal variation was caused by the DOM supply with the accumulated decomposition of litter in the streambed. The significant correlation between DOC concentration and absorbance at 254 nm (UV254) was observed for all sample types of observation target in the watershed; the ratio of DOC concentration to UV254 was different, while the correlation coefficient between DOC concentration and UV254 value differed among sample types in the watershed. We concluded that UV254 which can be measured by simply and easily is a good indicator for estimating DOC concentration in liquid samples in forested watersheds.

China is the global leader in mariculture production. Increasing sequestered marine carbon（also known as blue carbon） via mariculture activities is a promising approach for mitigating climate change and promoting the development of a low-carbon economy. Mariculture blue carbon is also considered an important component of China＇s ＂sea granary＂. In addition to shellfish and macroalgae yields, which represent carbon removed from mariculture environment, blue carbon also includes other important components, which have been largely neglected in the past, such as the carbon transformed by microbes,dissolved organic carbon（mainly referred to as recalcitrant dissolved organic carbon）, and sedimentary particulate carbon. Hence,from different aspects, a comprehensive study on the formation processes and mechanisms of carbon sequestration is of great significance for comprehensively unveiling the carbon sequestration capability in coastal mariculture environment, which will contribute to the sustainable development of the fishery economy and construction of an ecological civilization. Moreover, it may add significant economic benefits to the future carbon-trading market.

Longstanding observations suggest that dissolved materials are lost from fresh litter through leaching, but the role of soil fauna in controlling this process has been poorly documented. In this study, a litterbag experiment employing litterbags with different mesh sizes (3 mm to permit soil fauna access and 0.04 mm to exclude fauna access) was conducted in three habitats (arid valley, ecotone and subalpine forest) with changes in climate and vegetation types to evaluate the effects of soil fauna on the concentrations of dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) during the first year of decomposition. The results showed that the individual density and community abundance of soil fauna greatly varied among these habitats, but Prostigmata, Isotomidae and Oribatida were the dominant soil invertebrates. At the end of the experiment, the mass remaining of foliar litter ranged from 58% for shrub litter to 77% for birch litter, and the DOC and TDN concentrations decreased to 54%–85% and increased to 34%–269%, respectively, when soil fauna were not present. The effects of soil fauna on the concentrations of both DOC and TDN in foliar litter were greater in the subalpine forest (wetter but colder) during the winter and in the arid valley (warmer but drier) during the growing season, and this effect was positively correlated with water content. Moreover, the effects of fauna on DOC and TDN concentrations were greater for high-quality litter and were related to the C/N ratio. These results suggest that water, rather than temperature, dominates how fauna affect the release of dissolved substances from fresh litter.

IntroductionThe biogeochemical processes underlying carbon cycling in Arctic coastal systems are rapidly evolving due to intensified ice loss. (Aim) This study examined the distinct contributions of dissolved organic carbon (DOC) and particulate carbon from sea ice in Kongsfjorden, Svalbard (Methods) focusing on the optical characteristics of coloured dissolved organic matter (CDOM) to trace its fate.ResultsOur results reveal that sea ice melt delivers a complex mixture: specific types of CDOM and a dominant load of total particulate carbon (TPC) that was identified as being primarily particulate inorganic carbon (PIC). The fate of the dissolved fraction was clearly traced by Gaussian decomposition.DiscussionSea ice delivered nitrogen-rich organic components, creating spatial hotspots of aCDOM275 at the innermost site and of aCDOM330 at the outermost site, with a strong correlation with CO2. At the surface, photodegradation breaks down high-molecular-weight (HMW) (low S275–295) dissolved organic matter (DOM) into low-molecular-weight (LMW) fractions (high S275–295). Below the surface, microbial degradation further transforms this organic carbon, promoting remineralisation processes and releasing dissolved inorganic carbon (DIC) and CO2. Higher N:P and Si:P ratios and nutrients in these layers indicated enrichment by meltwater (sea ice/glacial) and microbial organic matter (OM) degradation, supported by shifts in CDOM spectral properties (SR, S275–295, and S350–400) and higher CO2. In contrast, the PIC-dominated TPC pool was decoupled from these biological transformations. Given the accelerating rate of Arctic warming, the impacts of sea ice and glacial melting on carbon dynamics in fjords like Kongsfjorden are likely to intensify, with potential positive feedback in the Arctic.

Global changes and human disturbances can strongly affect the quantity of aboveground litter entering soils, which could result in substantial cascading effects on soil biogeochemical processes in forests. Despite extensive reports, it is unclear how the variations in litter depth affect soil carbon and nitrogen cycling. The responses of soil carbon and nitrogen to the variability of litter inputs were examined in a coniferous–broadleaf mixed forest of Central China. The litter input manipulation included five treatments: no litter input, natural litter, double litter, triple litter, and quadruple litter. Multifold litter additions decreased soil temperature but did not affect soil moisture after 2.5 years. Reductions in soil pH under litter additions were larger than increases under no litter input. Litter quantity did not affect soil total organic carbon, whereas litter addition stimulated soil dissolved organic carbon more strongly than no litter input suppressed it. The triggering priming effect of litter manipulation on soil respiration requires a substantial litter quantity, and the impacts of a slight litter change on soil respiration are negligible. Litter quantity did not impact soil total nitrogen, and only strong litter fluctuations changed the content of soil available nitrogen (nitrate nitrogen and ammonium nitrogen). Litter addition enhanced soil microbial biomass carbon and nitrogen more strongly than no litter input. Our results imply that the impacts of multifold litter inputs on soil carbon and nitrogen are different with a single litter treatment. These findings suggest that variability in aboveground litter inputs resulting from environmental change and human disturbances have great potential to change soil carbon and nitrogen in forest ecosystems. The variability of aboveground litter inputs needs to be taken into account to predict the responses of terrestrial soil carbon and nitrogen cycling to environmental changes and forest management.

Straw return improves soil carbon pool and dissolved organic matter (DOM) characteristics in black soil. Optimal straw return rate is the key to promoting straw return practices in farmland in Northeast China. The experiment was conducted at the Science and Technology Park of China Grain Storage and Northern Corporation in NenJiang, Heilongjiang Province, straw return at 0 kg hm −2 , 3000 kg hm −2 , 4500 kg hm −2 , and 9000 kg hm −2 . In the seventh year of the experiment, we used three-dimensional excitation-emission matrices combined with Parallel Factor analysis to characterize the fluorescence characteristics of DOM of black soils. The results showed substantial improvement in soil physical characteristics and soil organic matter (SOM) following straw return, SOM content rises in proportion to the amount of straw returned, and a significant positive correlation coefficient between water-holding capacity (WHC) ( p  < 0.001, r = 0.82) and dissolved organic matter (DOC) ( p  < 0.01, r = 0.77). Moreover, straw return significantly increased the richness of three fluorescent components, namely fulvic acid (UV and visible fulvic acids), humic-like acid, and protein-like (short and long-wavelength tryptophan). The fluorescence intensities of these components were lower in straw treatments than in no straw return. The fluorescence intensities of fulvic and humic acids showed decreasing and increasing trends, respectively, with increasing straw return amount. The fluorescence spectroscopy data of DOC demonstrated the key role of high straw return amounts in enhancing substantially the metabolic activity of soil microorganisms. Overall, straw-returning practices improve soil fertility and can be beneficial for black soil farmlands, with the optimal return rate observed at 4500 kg hm −2 .