Periodic Reporting for period 1 - MetaDryNet (Drying river networks – Understanding and mitigating drought impacts on river ecosystem functioning and biodiversity (MetaDryNet))
Periodo di rendicontazione: 2021-01-01 al 2022-12-31
Rivers are among the world’s most biodiverse ecosystems but also the most threatened by human activities. River networks and their constituent biological communities perform numerous ecosystem functions (e.g. decomposition) that contribute to the recycling of carbon and nutrients. Rivers also provide essential ecosystem services – such as drinking water and climate regulation – that enhance society’s well-being. However, climate change and humans’ increasing water demands are causing river networks to dry, altering river biodiversity, ecosystem functioning (EF) and the provision of key ecosystem services. Although ecological responses to drying have been intensively studied at the local river reach scale, little is known about its impacts at the river network scale, limiting our capacity to predict the far-reaching effects of drying on river biodiversity and EF.
To fill this gap, we used the meta-system approach, which considers rivers as an ensemble of interacting terrestrial-aquatic sub-ecosystems among which organisms (e.g. microorganisms and invertebrates) disperse and resources (e.g. carbon and nutrients) are exchanged and transformed through EF (Fig. 1). In river networks, these fluxes of organisms and resources link small streams to the mainstem (longitudinal dimension) and terrestrial riparian habitats to instream aquatic habitats (horizontal dimension), ultimately linking terrestrial ecosystems to flood plains and oceans. As such, the meta-system approach integrates the multiple-facets of rivers, linking resources, biodiversity and EF across terrestrial-aquatic boundaries.
In this project, we aimed to examine the effects of drying on river-network scale biodiversity and EF and their implication to carbon processing (decomposition) and emissions (CO2). More than 50% of the world’s rivers naturally dry for at least one day per year but climate and anthropogenic changes are exacerbating drying events worldwide. A better understanding of the contribution of drying rivers to carbon cycles will thus inform CO2 emission scenarios and the design of management strategies that best preserve the ecosystem services that rivers provide to our societies.
The overall objectives of this project were to:
(O1) Determine the mechanisms driving the structuring of resource (organic matter), community (invertebrates, bacteria and fungi) and EF (decomposition and CO2 emissions) across aquatic-terrestrial boundaries in river networks fragmented by drying.
(O2) Identify where, when and under which conditions drying leads to mismatches between resource availability and organism activity, affecting carbon processing and meta-ecosystem dynamics.
To fill this gap, we used the meta-system approach, which considers rivers as an ensemble of interacting terrestrial-aquatic sub-ecosystems among which organisms (e.g. microorganisms and invertebrates) disperse and resources (e.g. carbon and nutrients) are exchanged and transformed through EF (Fig. 1). In river networks, these fluxes of organisms and resources link small streams to the mainstem (longitudinal dimension) and terrestrial riparian habitats to instream aquatic habitats (horizontal dimension), ultimately linking terrestrial ecosystems to flood plains and oceans. As such, the meta-system approach integrates the multiple-facets of rivers, linking resources, biodiversity and EF across terrestrial-aquatic boundaries.
In this project, we aimed to examine the effects of drying on river-network scale biodiversity and EF and their implication to carbon processing (decomposition) and emissions (CO2). More than 50% of the world’s rivers naturally dry for at least one day per year but climate and anthropogenic changes are exacerbating drying events worldwide. A better understanding of the contribution of drying rivers to carbon cycles will thus inform CO2 emission scenarios and the design of management strategies that best preserve the ecosystem services that rivers provide to our societies.
The overall objectives of this project were to:
(O1) Determine the mechanisms driving the structuring of resource (organic matter), community (invertebrates, bacteria and fungi) and EF (decomposition and CO2 emissions) across aquatic-terrestrial boundaries in river networks fragmented by drying.
(O2) Identify where, when and under which conditions drying leads to mismatches between resource availability and organism activity, affecting carbon processing and meta-ecosystem dynamics.
Between 2021 and 2022, we carried three field sampling campaigns and two field experiments to examine the effects of drying on the structuring of biodiversity and EF in an intermittent river meta-system: the Albarine (Fig. 2).
To examine how drying affects river-network scale biodiversity and EF, we monitored leaf litter quantity and quality, community composition (invertebrate and microorganisms) leaf litter decomposition and CO2 emissions (with the EU funded DRYvER project (869226) and PhD candidate T. Silverthor) on the riverbed and in the riparian area of 20 river reaches with different hydrological regimes (Fig. 2), across three sampling campaigns, in 2021. Preliminary results indicate that EF slows down and community composition drastically changes with increasing drying frequency and drying reaches upstream, suggesting that upstream fragmentation may affect the EF of downstream ecosystems (Fig. 3). Decomposition instream was also related to decomposition in the riparian area, revealing one of the first network-scale evidence of the relationship between EF across terrestrial-aquatic boundaries.
We also explored the decomposition of organic matter of aquatic origin (i.e. aquatic invertebrate, fish and algae) on dry riverbeds in a field experiment as part of N. Barthélémy MSc thesis. This study indicated that drying may promote transfers of AOM to adjacent terrestrial ecosystems, but effects on recipient terrestrial food-webs still need to be explored. As part of M. Jans MSc thesis, we examined the effects of drying and riparian conditions on the decomposition of leaf litter in a field experiment. This study revealed that leaf decomposition varies depending on where leaves fall, with often equal contribution of invertebrates and microorganisms to decomposition (Fig. 4). Results from DNA metabarcoding analyses will unravel how such preconditioning determines leaf microbial communities across terrestrial-aquatic ecosystems.
We also worked in collaboration with M. Talluto and G. Singer (University of Innsbruck) to develop a mechanistic model to test our theoretical framework and assess the effects of different configurations of drying and fragmentation on resource and organism dynamics in simulated river-networks.
As of February 2023, results from this project have been published in two peer-reviewed publications and at least four more publications are in the making. We also presented project advances and results at three international conferences. The project was also featured in the Horizon Magazine: “big-lessons-about-biodiversity-loss-from-a-little-french-river”. In both 2021 and 2022, as part of the Science Days: “Fête de la Science” we designed and delivered outreach activities for six different schools, to raise awareness on the causes and effects of drying in our rivers.
To examine how drying affects river-network scale biodiversity and EF, we monitored leaf litter quantity and quality, community composition (invertebrate and microorganisms) leaf litter decomposition and CO2 emissions (with the EU funded DRYvER project (869226) and PhD candidate T. Silverthor) on the riverbed and in the riparian area of 20 river reaches with different hydrological regimes (Fig. 2), across three sampling campaigns, in 2021. Preliminary results indicate that EF slows down and community composition drastically changes with increasing drying frequency and drying reaches upstream, suggesting that upstream fragmentation may affect the EF of downstream ecosystems (Fig. 3). Decomposition instream was also related to decomposition in the riparian area, revealing one of the first network-scale evidence of the relationship between EF across terrestrial-aquatic boundaries.
We also explored the decomposition of organic matter of aquatic origin (i.e. aquatic invertebrate, fish and algae) on dry riverbeds in a field experiment as part of N. Barthélémy MSc thesis. This study indicated that drying may promote transfers of AOM to adjacent terrestrial ecosystems, but effects on recipient terrestrial food-webs still need to be explored. As part of M. Jans MSc thesis, we examined the effects of drying and riparian conditions on the decomposition of leaf litter in a field experiment. This study revealed that leaf decomposition varies depending on where leaves fall, with often equal contribution of invertebrates and microorganisms to decomposition (Fig. 4). Results from DNA metabarcoding analyses will unravel how such preconditioning determines leaf microbial communities across terrestrial-aquatic ecosystems.
We also worked in collaboration with M. Talluto and G. Singer (University of Innsbruck) to develop a mechanistic model to test our theoretical framework and assess the effects of different configurations of drying and fragmentation on resource and organism dynamics in simulated river-networks.
As of February 2023, results from this project have been published in two peer-reviewed publications and at least four more publications are in the making. We also presented project advances and results at three international conferences. The project was also featured in the Horizon Magazine: “big-lessons-about-biodiversity-loss-from-a-little-french-river”. In both 2021 and 2022, as part of the Science Days: “Fête de la Science” we designed and delivered outreach activities for six different schools, to raise awareness on the causes and effects of drying in our rivers.
As dry rivers are the norm rather than the exception, and predicted to become more and more common, this research is of high scientific and societal priority, guiding environmental adaptation to climate change. Our preliminary results highlight the key impact of fragmentation by drying on river meta-ecosystems and particularly on network-scale organic matter and carbon cycling. Drying, by promoting the accumulation of unprocessed leaf litter, modifies the timing and quantity of organic matter transported to recipient ecosystems (e.g. lakes, flood plains and oceans). Such mismatches in the transfer of carbon across ecosystems may have far-reaching implications for global biogeochemical cycles and the food-webs that depend on these resources.
Project's results will be used to estimate the carbon processing rate, emissions and storage of an entire river network, including a diversity of aquatic and terrestrial habitats, constituting one of the first such estimate which will also inform CO2 emission scenarios. Results from our mechanistic model will also help us better pinpoint the mechanisms driving responses to network fragmentation by drying, allowing us to identify tipping points after which network scale biodiversity and EF may collapse. Using climate change scenarios, we will also be able to predict how biodiversity and carbon processing may change in the future, in response to changes in drying extent and duration.
Future analyses exploring how microbial community – EF linkages are affected by drying will allow us to identify the conditions under which communities may perform ecosystem functions sub-optimally, thereby altering the carbon cycling. By helping to identify when, where, and under which conditions the links between biodiversity and EF may be altered, our findings will inform the design of adaptive management that preserve the ecosystem services that rivers provide to our societies.
Project's results will be used to estimate the carbon processing rate, emissions and storage of an entire river network, including a diversity of aquatic and terrestrial habitats, constituting one of the first such estimate which will also inform CO2 emission scenarios. Results from our mechanistic model will also help us better pinpoint the mechanisms driving responses to network fragmentation by drying, allowing us to identify tipping points after which network scale biodiversity and EF may collapse. Using climate change scenarios, we will also be able to predict how biodiversity and carbon processing may change in the future, in response to changes in drying extent and duration.
Future analyses exploring how microbial community – EF linkages are affected by drying will allow us to identify the conditions under which communities may perform ecosystem functions sub-optimally, thereby altering the carbon cycling. By helping to identify when, where, and under which conditions the links between biodiversity and EF may be altered, our findings will inform the design of adaptive management that preserve the ecosystem services that rivers provide to our societies.