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Many inland waters exhibit complete or partial desiccation, or have vanished due to global change, exposing sediments to the atmosphere. Yet, data on carbon dioxide (CO2) emissions from these sediments are too scarce to upscale emissions for global estimates or to understand their fundamental drivers. Here, we present the results of a global survey covering 196 dry inland waters across diverse ecosystem types and climate zones. We show that their CO2 emissions share fundamental drivers and constitute a substantial fraction of the carbon cycled by inland waters. CO2 emissions were consistent across ecosystem types and climate zones, with local characteristics explaining much of the variability. Accounting for such emissions increases global estimates of carbon emissions from inland waters by 6% (~0.12 Pg C y−1). Our results indicate that emissions from dry inland waters represent a significant and likely increasing component of the inland waters carbon cycle.

Many inland waters exhibit complete or partial desiccation, or have vanished due to global change, exposing sediments to the atmosphere. Yet, data on carbon dioxide (CO 2) emissions from these sediments are too scarce to upscale emissions for global estimates or to understand their fundamental drivers. Here, we present the results of a global survey cov- ering 196 dry inland waters across diverse ecosystem types and climate zones. We show that their CO 2 emissions share fundamental drivers and constitute a substantial fraction of the carbon cycled by inland waters. CO2 emissions were consistent across ecosystem types and climate zones, with local characteristics explaining much of the variability. Accounting for such emissions increases global estimates of carbon emissions from inland waters by 6% (~0.12 Pg C y−1). Our results indicate that emissions from dry inland waters represent a significant and likely increasing component of the inland waters carbon cycle. This study was made possible thanks to a large collective effort of a global research network called dryflux (www.ufz.de/dryflux). We would like to thank numerous helpers for their assistance during field work. This research was inspired by GLEON (Global Lake Ecological Observatory Network). This work was supported by the German Research Foundation (DFG, KO1911/6-1 and GR1540/23-1) to P.S.K. and H.P.G., the Spanish Ministry of Science, Innovation and Universities (C-HYDROCHANGE, CGL2017-86788-C3-3-P and CGL2017-86788-C3-2-P) to B.O. and R.M., the Spanish Government (CGL2016-77487-R), the Basque Government (IT951-16), the BBVA Foundation (06417) to D.vS. and A.E., the European Research Council (FP7/2007-2013, ERC grant agreement 336642) to A.L. and R.F.M., CNPq (310033/2017-9) to A.M.A., the Carlsberg Foundation (CF16-0325) to T.R. and A.P., the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO, Veni Grant 86312012) to S.K., the Estonian Ministry of Education and Research (IUT 21-02) and the Estonian Research Council grant (PUT PSG32, PUT1598) to A.L. and E-I.R., the National Research Foundation of Korea (2017R1D1A1B06035179) to J-H.P., German Federal Ministry of Education and Research (BMBF) CLIENT programme (grant: 2WCL1337A) and German Academic Exchange Service (DAAD, grant 57218695) to M.A.F., the Seneca Foundation (20645/ JLI/18) to M.M.S.M. and M.I.A. N.C. was supported by Beatriu de Pinós grant (2016- 00215), A.P. by the Ramón Areces Foundation postgraduate studies programme, R.dC. by the University of Murcia (FPU R-269/2014), E.S.O.J. by the Erasmus+ Programme NON-EU 2017/2018, J.R.P. by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES Finance Code 001). C.M-L. by the French Agency for Biodiversity (ONEMA-AFB, Action 13, ‘Colmatage, échange snappe-rivière et processus biogéochi- miques’), R.M. by the project C-HydroChange, funded by the Spanish Agencia Estatal de Investigación (AEI) and Fondo Europeo de Desarrollo Regional (FEDER) under the contract FEDER-MCIU-AEI/ CGL2017-86788-C3, P.S.K. by a grant for a short‐term scientific mission within the COST Action CA15113 (SMIRES, Science and Management of Intermittent Rivers and Ephemeral Streams, www.smires.eu) and GLEON (student travel grant). In memory of our esteemed colleague and friend Julia Howitt, who passed away after this paper was accepted. She was full of enthusiasm for this work and will be deeply missed by her colleagues around the world. This study was made possible thanks to a large collective effort of a global research network called dryflux (www.ufz.de/dryflux). We would like to thank numerous helpers for their assistance during field work. This research was inspired by GLEON (Global Lake Ecological Observatory Network). This work was supported by the German Research Foundation (DFG, KO1911/6-1 and GR1540/23-1) to P.S.K. and H.P.G., the Spanish Ministry of Science, Innovation and Universities (C-HYDROCHANGE, CGL2017-86788-C3-3-P and CGL2017-86788-C3-2-P) to B.O. and R.M., the Spanish Government (CGL2016-77487-R), the Basque Government (IT951-16), the BBVA Foundation (06417) to D.vS. and A.E., the European Research Council (FP7/2007-2013, ERC grant agreement 336642) to A.L. and R.F.M., CNPq (310033/2017-9) to A.M.A., the Carlsberg Foundation (CF16-0325) to T.R. and A.P., the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO, Veni Grant 86312012) to S.K., the Estonian Ministry of Education and Research (IUT 21-02) and the Estonian Research Council grant (PUT PSG32, PUT1598) to A.L. and E-I.R., the National Research Foundation of Korea (2017R1D1A1B06035179) to J-H.P., German Federal Ministry of Education and Research (BMBF) CLIENT programme (grant: 2WCL1337A) and German Academic Exchange Service (DAAD, grant 57218695) to M.A.F., the Seneca Foundation (20645/ JLI/18) to M.M.S.M. and M.I.A. N.C. was supported by Beatriu de Pinós grant (2016- 00215), A.P. by the Ramón Areces Foundation postgraduate studies programme, R.dC. by the University of Murcia (FPU R-269/2014), E.S.O.J. by the Erasmus+ Programme NON-EU 2017/2018, J.R.P. by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES Finance Code 001). C.M-L. by the French Agency for Biodiversity (ONEMA-AFB, Action 13, ‘Colmatage, échange snappe-rivière et processus biogéochi- miques’), R.M. by the project C-HydroChange, funded by the Spanish Agencia Estatal de Investigación (AEI) and Fondo Europeo de Desarrollo Regional (FEDER) under the contract FEDER-MCIU-AEI/ CGL2017-86788-C3, P.S.K. by a grant for a short‐term scientific mission within the COST Action CA15113 (SMIRES, Science and Management of Intermittent Rivers and Ephemeral Streams, www.smires.eu) and GLEON (student travel grant). In memory of our esteemed colleague and friend Julia Howitt, who passed away after this paper was accepted. She was full of enthusiasm for this work and will be deeply missed by her colleagues around the world.

1. Temperature and oxygen are recognised as the main drivers of altitudinal limits of species distributions. However, the two factors are linked, and both decrease with altitude, why their effects are difficult to disentangle. 2. This was experimentally addressed using aquatic macroinvertebrates; larvae of Andesiops (Ephemeroptera), Claudioperla, (Plecoptera), Scirtes (Coleoptera) and Anomalocosmoecus (Trichoptera), and the amphipod Hyalella in an Ecuadorian glacier-fed stream (4100-4500ma.s.l.). The following were performed: (i) quantitative benthic sampling at three sites to determine altitudinal patterns in population densities, (ii) transplants of the five taxa upstream of their natural altitudinal limit to test the short-term (14days) effect on survival, and (iii) in situ experiments of locomotory activity as a proxy for animal response to relatively small differences in temperature (5 degrees C vs. 10 degrees C) and oxygen saturation (55% vs. 62%). 3. The transplant experiment reduced survival to a varying degree among taxa, but Claudioperla survived well at a site where it did not naturally occur. In the in situ experiment, Scirtes and Hyalella decreased their activity at lower oxygen saturation, whereas Andesiops and Anomalocosmoecus did so at a low temperature. The decrease in activity from a high to a low temperature and oxygen for the five taxa was significantly correlated with their mortality in the transplant experiment. 4. Together the present experiments indicate that even relatively small differences in temperature and oxygen may produce effects explaining ecological patterns, and depending on the taxon, either water temperature or oxygen saturation, without clear interacting effects, are important drivers of altitudinal limits.

We used equatorial glacier-fed streams as a model system to investigate the relationships between flow fluctuation and benthic fauna at different temporal scales. Water level was measured at 30 min intervals over 29 months (942 d) and benthic macroinvertebrates were sampled 14 times over the study period. We performed wavelet analyses on water-level time series to identify temporal scales at which significant flow variation occurs, and calculated three indices: intensity, frequency and temporal clustering of the diurnal flow variation for periods from 2 d to 50 d. We determined the effect of temporal scaling (length of the periods considered) on relationships between benthic community dissimilarity (using Sorensen index) and differences in flow indices among the 14 sampling dates. Temporal scaling affected flow-variation frequency and temporal clustering and their subsequent relationships with benthic community dissimilarity. A time scale of 15 d before benthic sampling was relevant to the assessment of flow-biota relationships. Community dissimilarity significantly increased with increasing difference in flow-fluctuation intensity. This dissimilarity was associated with a decrease in the density of dominant taxa and a taxa turnover along the temporal gradient in flow-fluctuation intensity. Although flow fluctuations are frequent and highly predictable in equatorial glacier-fed streams, macroinvertebrate communities exhibited a temporal variability in taxon assemblage, which was linked to the intensity of flow fluctuation. We explain these patterns by downstream displacement during high flow events and upstream displacement during low flow periods, thereby highlighting the need of considering temporal scaling effects on benthic fauna to understand the ecological dynamics of lotic systems.

The downstream pattern in benthic macroinvertebrate assemblages along glacier-fed streams is a result of decreasing glacial influence on environmental conditions. However, meltwater run-off shows temporal variation, reflected in differences in, for example, temperature, conductivity and turbidity. Consequently, depending on their run-off patterns, comparable environmental conditions may occur at different distances along glacier-fed streams. Our aim was to assess whether short-term variations in glacial run-off were reflected by changes in longitudinal distribution patterns of macroinvertebrates along a glacier-fed stream in the Ecuadorian Andes. We measured environmental parameters, obtained continuous gauging data, measured macroinvertebrate drift rate with an hourly resolution during glacial floods and sampled benthic macroinvertebrates c. 3-monthly for 30months at three sites at varying distances (0.1-4.3km) from the glacier. For each sampling date, we fitted logarithmic equations to plots of taxon richness versus distance from the glacier, calculated similarity in assemblage composition between sites and calculated weighted averages of mid-points of taxon distributions. These data were analysed in relation to mean maximum flow over the 45days prior to sampling. Mean conductivity and temperature increased while turbidity decreased downstream. During glacial afternoon floods, conductivity decreased while temperature and turbidity increased. High flow moved maximal taxon richness downstream (reduced the slopes from logarithmic fits), while low flow made assemblages more downstream like (higher similarity with downstream assemblages). No significant relationships were found between weighted average distributions and flow. Drift rate (ind.h(-1)) increased by an order of magnitude at the onset of afternoon floods, and the taxa that contributed most to total drift were those whose benthic densities were most reduced by increases in flow. Our study provides hints as to how biological distribution patterns in glacier-fed streams might be affected by more permanent changes in run-off caused by glacial shrinkage. This study predicts a multidirectional shift in altitudinal/longitudinal species ranges, with a potential downward shift in species ranges as a consequence of global change.

1. As glacier shrinkage is accelerating due to climate change, it is important to understand the effect of changes in glacier runoff on downstream aquatic communities. The overall goal of this study was to test the relevance of recently developed wavelet-based metrics of flow variations caused by glacial melting cycles to deepen our knowledge about the relationship between glacial influence and aquatic biodiversity. 2. In an equatorial glacierised catchment, we selected 15 stream sites covering a gradient of direct contribution from glacial runoff. At each site, we recorded water level time series for 10 months and sampled benthic macroinvertebrates. Wavelet analyses on the water level time series were used to calculate three indices: glacial flood intensity, frequency and temporal clustering. We then examined how these three indices were related to macroinvertebrate community composition using generalised additive models. 3. While macroinvertebrate density decreased significantly with glacial flood intensity, we found a significant hump-shaped relationship between local taxon richness and glacial flood intensity, a pattern that was not produced simply by overlapping broad taxon distributions from either end of the environmental gradient. These results suggest that glacial meltwater contribution creates local peaks in macroinvertebrate richness and enhances regional diversity in the catchment. 4. The significant relationships between faunal metrics and the new glacial influence indices suggest the latter are valuable for assessing the effects of altered meltwater contributions on aquatic communities of glacier-fed rivers. Relationships differed depending on the feature of the glacial disturbance considered (glacial flood intensity, frequency, temporal clustering). We anticipate that these distinctions may help disentangle the mechanisms driving aquatic biodiversity in glacierised catchments, especially in terms of identifying resistance and/or resilience as key processes in glacial macroinvertebrate communities.