Summary1. Changes in the balance between soil carbon storage and release can significantly amplify or attenuate global warming. Although a lot of progress has been made in determining potential drivers of carbon release through large-scale decomposition experiments, climate predictions are still hampered by data limitation at a global scale as a result of high effort and measurement costs of comparative litter decomposition studies. 2. We introduce an innovative, cost-effective, well-standardised method to gather data on decomposition rate and litter stabilisation using commercially available tea bags as standardised test kits. By using two tea types with contrasting decomposability, we can construct a decomposition curve using a single measurement in time. The acquired Tea Bag Index (TBI) consists of two parameters describing decomposition rate (k) and litter stabilisation factor (S).3. The method was tested for its sensitivity and robustness in contrasting ecosystems and biomes, confirming that the TBI is sensitive enough to discriminate between these systems. Within an ecosystem, TBI is responsive to differences in abiotic circumstances such as soil temperature and moisture content. The collected k and S values are in accordance with expectations based on decomposition process literature. They are therefore interpretable within the current knowledge framework. 4. Tea Bag Index is a unique, multifunctional method requiring few resources and minimal prior knowledge. The standardisation and simplicity of the method make it possible to collect comparable, globally distributed data through crowdsourcing. TBI can further provide an excellent decomposition reference and has the potential to increase reliability of soil carbon flux estimates based on extrapolations of decomposition data.

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Soil nitrogen (N) budgets are used in a global, distributed flow-path model with 0.5° × 0.5° resolution, representing denitrification and N 2 O emissions from soils, groundwater and riparian zones for the period 1900–2000 and scenarios for the period 2000–2050 based on the Millennium Ecosystem Assessment. Total agricultural and natural N inputs from N fertilizers, animal manure, biological N 2 fixation and atmospheric N deposition increased from 155 to 345 Tg N yr −1 (Tg = teragram; 1 Tg = 10 12 g) between 1900 and 2000. Depending on the scenario, inputs are estimated to further increase to 408–510 Tg N yr −1 by 2050. In the period 1900–2000, the soil N budget surplus (inputs minus withdrawal by plants) increased from 118 to 202 Tg yr −1 , and this may remain stable or further increase to 275 Tg yr −1 by 2050, depending on the scenario. N 2 production from denitrification increased from 52 to 96 Tg yr −1 between 1900 and 2000, and N 2 O–N emissions from 10 to 12 Tg N yr −1 . The scenarios foresee a further increase to 142 Tg N 2 –N and 16 Tg N 2 O–N yr −1 by 2050. Our results indicate that riparian buffer zones are an important source of N 2 O contributing an estimated 0.9 Tg N 2 O–N yr −1 in 2000. Soils are key sites for denitrification and are much more important than groundwater and riparian zones in controlling the N flow to rivers and the oceans.

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International audienceWe evaluated nitrogen (N) removal efficiency by ri-parian buffers at 14 sites scattered throughout seven European countries subject to a wide range of climatic conditions. The sites also had a wide range of nitrate inputs, soil characteristics, and vegetation types. Dissolved forms of N in groundwater and associated hydrological parameters were measured at all sites; these data were used to calculate nitrate removal by the riparian buffers. Nitrate removal rates (expressed as the difference between the input and output nitrate concentration in relation to the width of the riparian zone) were mainly positive, ranging from 5% m 1 to 30% m 1 , except for a few sites where the values were close to zero. Average N removal rates were similar for herbaceous (4.43% m 1) and forested (4.21% m 1) sites. Nitrogen removal efficiency was not affected by climatic variation between sites, and no significant seasonal pattern was detected. When nitrate inputs were low, a very large range of nitrate removal efficiencies was found both in the forested and in the nonforested sites. However, sites receiving nitrate inputs above 5 mg N L 1 showed an exponential negative decay of nitrate removal efficiency (nitrate removal efficiency 33.6 e 0.11 NO 3 input , r 2 0.33, P 0.001). Hydraulic gradient was also negatively related to nitrate removal (r 0.27, P 0.05) at these sites. On the basis of this intersite comparison, we conclude that the removal of nitrate by biological mechanisms (for example, denitrification, plant uptake) in the riparian areas is related more closely to nitrate load and hydraulic gradient than to climatic parameters

Riparian buffer zones are known to reduce diffuse N pollution of streams by removing and modifying N from agricultural runoff. Denitrification, often identified as the key N removal process, is also considered as a major source of the greenhouse gas nitrous oxide (N2O). The risks of high N2O emissions during nitrate mitigation and the environmental controls of emissions have been examined in relatively few riparian zones and the interactions between controls and emissions are still poorly understood. Our objectives were to assess the rates of N2O emission from riparian buffer zones that receive large loads of nitrate, and to evaluate various factors that are purported to control N emissions. Denitrification, nitrification, and N2O emissions were measured seasonally in grassland and forested buffer zones along first-order streams in The Netherlands. Lateral nitrate loading rates were high, up to 470 g N m(-2) yr(-1). Nitrogen process rates were determined using flux chamber measurements and incubation experiments. Nitrous oxide emissions were found to be significantly higher in the forested (20 kg N ha(-1) yr(-1)) compared with the grassland buffer zone (2-4 kg N ha(-1) yr(-1)), whereas denitrification rates were not significantly different. Higher rates of N2O emissions in the forested buffer zone were associated with higher nitrate concentrations in the ground water. We conclude that N transformation by nitrate-loaded buffer zones results in a significant increase of greenhouse gas emission. Considerable N2O fluxes measured in this study indicate that Intergovernmental Panel on Climate Change methodologies for quantifying indirect N2O emissions have to distinguish between agricultural uplands and riparian buffer zones in landscapes receiving large N inputs.

Abstract. In river basins, soils, groundwater, riparian zones and floodplains, streams, rivers, lakes and reservoirs act as successive filters in which the hydrology, ecology and biogeochemical processing are strongly coupled and together act to retain a significant fraction of the nutrients transported. This paper compares existing river ecology concepts with current approaches to describe river biogeochemistry, and assesses the value of these concepts and approaches for understanding the impacts of interacting global change disturbances on river biogeochemistry. Through merging perspectives, concepts, and modeling techniques, we propose integrated model approaches that encompass both aquatic and terrestrial components in heterogeneous landscapes. In this model framework, existing ecological and biogeochemical concepts are extended with a balanced approach for assessing nutrient and sediment delivery, on the one hand, and nutrient in-stream retention on the other hand.