Improving an existing proxy-based approach for floodplain denitrification assessment to facilitate decision making on restoration

Excess nitrogen (N) from agricultural sources is a major contributor to the water pollution of rivers in Europe. Floodplains are of tremendous importance as they can permanently remove nitrate (NO₃) from the environment by releasing reactive N to the atmosphere in its gaseous forms (N₂O, N₂) during denitrification. However, the quantitative assessment of this ecosystem function is still challenging, particularly on the national level. In this study, we modeled the potential of NO₃-N removal through microbial denitrification in soils of the active floodplains of the river Elbe and river Rhine in Germany. We combined laboratory measurements of soil denitrification potentials with straightforward modelling data, covering the average inundation duration from six study areas, to improve an existing Germany-wide proxy-based approach (PBAe) on NO₃-N retention potential. The PBAe estimates this potential to be 30-150 kg NO₃-N ha^-1 yr^-1. However, with soil pH and Floodplain Status Category identified as essential parameters for the proxies, the improved PBA (PBAi) yields a removal potential of 5-480 kg N ha^-1 yr^-1. To account for these parameters, we applied scaling factors using a bonus-malus system with a base value of 10-120 N ha^-1 yr^-1. Upscaling the determined proxies of the PBAi to the entire active floodplains of the river Elbe and river Rhine results in similarly high NO₃-N retention sums of ~7000 t yr^-1 in spite of very different retention area sizes, strengthening the argument for area availability as the primary objective of restoration efforts. Although PBAs are always subject to uncertainty, the PBAi enables a more differentiated spatial quantification of denitrification because local key controlling parameters are included. Hence, the PBAi is an innovative and robust approach to quantify denitrification in floodplain soils, supporting a better assessment of ecosystem services for decision-making on floodplain restoration.

More losses than gains during one century of plant biodiversity change in Germany

Long-term analyses of biodiversity data highlight a 'biodiversity conservation paradox': biological communities show substantial species turnover over the past century^1,2, but changes in species richness are marginal^1,3-5. Most studies, however, have focused only on the incidence of species, and have not considered changes in local abundance. Here we asked whether analysing changes in the cover of plant species could reveal previously unrecognized patterns of biodiversity change and provide insights into the underlying mechanisms. We compiled and analysed a dataset of 7,738 permanent and semi-permanent vegetation plots from Germany that were surveyed between 2 and 54 times from 1927 to 2020, in total comprising 1,794 species of vascular plants. We found that decrements in cover, averaged across all species and plots, occurred more often than increments; that the number of species that decreased in cover was higher than the number of species that increased; and that decrements were more equally distributed among losers than were gains among winners. Null model simulations confirmed that these trends do not emerge by chance, but are the consequence of species-specific negative effects of environmental changes. In the long run, these trends might result in substantial losses of species at both local and regional scales. Summarizing the changes by decade shows that the inequality in the mean change in species cover of losers and winners diverged as early as the 1960s. We conclude that changes in species cover in communities represent an important but understudied dimension of biodiversity change that should more routinely be considered in time-series analyses.

ReSurveyGermany: Vegetation-plot time-series over the past hundred years in Germany

Vegetation-plot resurvey data are a main source of information on terrestrial biodiversity change, with records reaching back more than one century. Although more and more data from re-sampled plots have been published, there is not yet a comprehensive open-access dataset available for analysis. Here, we compiled and harmonised vegetation-plot resurvey data from Germany covering almost 100 years. We show the distribution of the plot data in space, time and across habitat types of the European Nature Information System (EUNIS). In addition, we include metadata on geographic location, plot size and vegetation structure. The data allow temporal biodiversity change to be assessed at the community scale, reaching back further into the past than most comparable data yet available. They also enable tracking changes in the incidence and distribution of individual species across Germany. In summary, the data come at a level of detail that holds promise for broadening our understanding of the mechanisms and drivers behind plant diversity change over the last century.

Measurement(s)	vegetation-plot resurvey data of vascular plant species
Technology Type(s)	vegetation-plot records
Factor Type(s)	Cover of species in plots
Sample Characteristic - Organism	Vascular plant species
Sample Characteristic - Environment	Terrestrial habitats
Sample Characteristic - Location	Germany