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Under the Paris Agreement, Parties must track the implementation and achievement of their nationally determined contributions (NDCs). In many cases, NDC targets are expressed as a greenhouse gas (GHG) emissions level and their implementation and achievement is tracked through national GHG inventories. To achieve their targets, it is thus essential for countries that the effects of mitigation measures are visible in their inventories. Inventory visibility is understood as the degree to which a change in GHG emissions or removals resulting from mitigation actions is reflected in GHG inventories. Inventory visibility can be assessed by identifying which emission sources and gases are affected by a mitigation action, determining the minimum inventory methods required for reflecting the related emission reduction, and identifying the completeness of and methods used by the current GHG inventory. In addition, it is useful to identify potential differences with the quantification approaches used under carbon market mechanisms. Inventory visibility is found to be generally high for measures that reduce CO2 emissions from fossil fuel combustion, while in parts of the industrial processes sector and in the forestry sector there is a higher risk that emission reductions are not visible. An analysis of the portfolio of Clean Development Mechanism projects shows that for most projects this risk is low; only 8% of the carbon credit supply potential is assessed to have a medium risk and 5% is assessed to have a high risk. However, as future carbon market mechanisms under Article 6 of the Paris Agreement may need to tap more into project types with medium to higher risk of non-visibility, national GHG inventory systems may need to be strengthened to assure visibility of mitigation projects. [ABSTRACT FROM AUTHOR]

Eutrophication of various lakes on the Swiss Plateau was targeted in the 1980s by reducing external nutrient loading and installing aeration/oxygenation systems. For five eutrophic lakes, three of which have been artificially oxygenated and aerated for almost 20 yr, phosphorus (P) balances were established using input, water-column inventory, export via the outlet, and sediment core data. To separate the effects of aeration/oxygenation from the effects of P-input reduction, two measures of P retention were determined--the ratio of net sedimentation to input and the ratio of net sedimentation to gross sedimentation. A comparison among the five lakes shows that, presently, P retention does not differ significantly between lakes with aeration/oxygenation and lakes with an anoxic hypolimnion, whereas retention at times of maximum P concentrations in the 1970s and 1980s was significantly lower compared with retention in today's moderately eutrophic lakes. This is in agreement with the finding that net sedimentation in all lakes remained relatively constant between 280 and 950 kg k[m.sup-2], independent of their P concentration. It is shown that constant net sedimentation is likely to prevail as long as P concentrations remain above a critical value of around 40 mg [m.sup-3]. Constant net sedimentation indicates that permanent deposition of P is limited by the sediment's binding capacity. Oxic conditions in the hypolimnion do not necessarily increase this capacity because redox-dependent P species may still be released within the anoxic bulk sediment and diffuse back into the water column. To characterize the P retention capacity of anoxic sediments, we suggest that the P burial rate be determined from dated sediment cores rather than from input/output balances.

Nutrient transfer from soils to surface waters is associated with large, hydrologically induced fluctuations. Consequently, stream-based estimation of long-term changes in nutrient leaching is masked by variations of stream discharge. Using high-resolution discharge and soluble reactive phosphorus (SRP) data from three small catchments (up to 42 km2), SRP loads are calculated by applying two different rating curves. Monte Carlo simulations are carried out to determine monitoring strategies for optimizing the number of water samples, their distribution between periods of low and high discharge, and the duration of composite sample collection. Trends in SRP load are isolated from natural variations by applying the discharge time series of 1 year each to annually changing rating curves. By applying this approach to various monitoring data sets, collected over the past 15 years, downward trends in SRP leaching of up to −3% yr−1 are detected. We describe how to determine the number of annual samples required to detect trends in nutrient load, depending on monitoring duration, available resources, and the magnitude of the expected trend. [ABSTRACT FROM AUTHOR]