@article{MunjonjiAyisiMudongoetal.2020, author = {Munjonji, Lawrence and Ayisi, Kingsley Kwabena and Mudongo, Edwin I. and Mafeo, Tieho Paulus and Behn, Kai and Mokoka, Malesela Vincent and Linst{\"a}dter, Anja}, title = {Disentangling drought and grazing effects on soil carbon stocks and CO2 fluxes in a semi-arid African Savanna}, series = {Frontiers in Environmental Science}, volume = {8}, journal = {Frontiers in Environmental Science}, publisher = {Frontiers Media}, address = {Lausanne}, issn = {2296-665X}, doi = {10.3389/fenvs.2020.590665}, pages = {14}, year = {2020}, abstract = {Grasslands cover ca. 30\% of the global land surface and provide critical ecosystem services. Among them, carbon storage is one of the most important. However, grasslands are increasingly threatened by drought and overgrazing which might negatively affect soil carbon stocks. Despite this threat, there is a dearth of information on how drought and grazing jointly impact soil carbon stocks and CO2 fluxes in dryland grasslands. With the aid of a large field experiment, we studied the combined effects of a 5-year extreme drought and moderate grazing on soil carbon stocks, CO2 fluxes and soil chemical properties. Extreme drought was induced by reducing ambient rainfall by 66\% using large rainout shelters. We found CO2 fluxes to strongly respond to the 5-year experimental drought. Extreme drought reduced CO2 emission rates by 32\% compared to ambient conditions. CO2 fluxes averaged 5.7 mg m(-2)min(-1) under drought compared to 8.3 mg m(-2) min(-1) under ambient conditions. CO2 fluxes were, however, not influenced by grazing. At the end of the growth period, grazed plots under ambient rainfall had released 16.3 tons of CO2 ha(-1) which was 58\% higher than observed on grazed plots subjected to severe drought. Soil carbon stocks were higher under drought conditions due to slower decomposition rates. Drought resulted in increased concentrations of primary macronutrients (N, P, and K), micronutrients (Zn and Mn) and pH in the top 30 cm of the soil relative to ambient conditions. The results also showed that grazing reduced the concentration of N and P in the topsoil compared to the ungrazed plots. This study provided insights on the soil carbon storage, CO2 emission rates and nutrient dynamics in a semi-arid dryland grassland as influenced by both drought and grazing. Our study also revealed that long-term extreme drought may be favorable in terms of preserving the existing soil carbon stocks through reduced CO2 release. This finding is critical for understanding future soil carbon dynamics in dryland grasslands in the face of climate change.}, language = {en} } @article{BoergensGuentnerDobslawetal.2020, author = {Boergens, Eva and G{\"u}ntner, Andreas and Dobslaw, Henryk and Dahle, Christoph}, title = {Quantifying the Central European droughts in 2018 and 2019 with GRACE Follow-On}, series = {Geophysical research letters : GRL}, volume = {47}, journal = {Geophysical research letters : GRL}, number = {14}, publisher = {American Geophysical Union}, address = {Washington, DC}, issn = {0094-8276}, doi = {10.1029/2020GL087285}, pages = {9}, year = {2020}, abstract = {The GRACE-FO satellites launched in May 2018 are able to quantify the water mass deficit in Central Europe during the two consecutive summer droughts of 2018 and 2019. Relative to the long-term climatology, the water mass deficits were-112 +/- 10.5 Gt in 2018 and-145 +/- 12 Gt in 2019. These deficits are 73\% and 94\% of the mean amplitude of seasonal water storage variations, which is so severe that a recovery cannot be expected within 1 year. The water deficits in 2018 and 2019 are the largest in the whole GRACE and GRACE-FO time span. Globally, the data do not show an offset between the two missions, which proves the successful continuation of GRACE by GRACE-FO and thus the reliability of the observed extreme events in Central Europe. This allows for a joint assessment of the four Central European droughts in 2003, 2015, 2018, and 2019 in terms of total water storage deficits.}, language = {en} } @article{HokeWoodhouseZoccaratoetal.2020, author = {Hoke, Alexa and Woodhouse, Jason Nicholas and Zoccarato, Luca and McCarthy, Valerie and de Eyto, Elvira and Caldero-Pascual, Maria and Geffroy, Ewan and Dillane, Mary and Grossart, Hans-Peter and Jennings, Eleanor}, title = {Impacts of extreme weather events on bacterial community composition of a temperate humic lake}, series = {Water}, volume = {12}, journal = {Water}, number = {10}, publisher = {MDPI}, address = {Basel}, issn = {2073-4441}, doi = {10.3390/w12102757}, pages = {19}, year = {2020}, abstract = {Extreme weather events are projected to increase in frequency and intensity as climate change continues. Heterotrophic bacteria play a critical role in lake ecosystems, yet little research has been done to determine how they are affected by such extremes. The purpose of this study was to use high-throughput sequencing to explore the bacterial community composition of a humic oligotrophic lake on the North Atlantic Irish coast and to assess the impacts on composition dynamics related to extreme weather events. Samples for sequencing were collected from Lough Feeagh on a fortnightly basis from April to November 2018. Filtration was used to separate free-living and particle-associated bacterial communities and amplicon sequencing was performed for the 16S rRNA V4 region. Two named storms, six high discharge events, and one drought period occurred during the sampling period. These events had variable, context-dependent effects on bacterial communities in Lough Feeagh. The particle-associated community was found to be more likely to respond to physical changes, such as mixing, while the free-living population responded to changes in nutrient and carbon concentrations. Generally, however, the high stability of the bacterial community observed in Lough Feeagh suggests that the bacterial community is relatively resilient to extreme weather events.}, language = {en} }