Cláudia Pascoal

Freshwater microbial communities sustain ecosystem functions and services, with aquatic fungi playing a key role in organic matter decomposition and nutrient transfer. However, the combined effects of multiple stressors on stream fungal biodiversity and functioning remain poorly understood. This study examines how land‐use and climate‐driven stressors influence fungal biodiversity and key ecosystem functions. We conducted a two‐year survey across 62 Iberian stream sites, assessing the combined effects of six stressors—organic matter and inorganic nutrient enrichment, oxygen depletion, thermal and drying stresses and riparian degradation—along with hydrology. We evaluated multiple facets of fungal biodiversity (taxonomic and functional diversity, and community composition) and proxies of two key functions: organic matter decomposition and fungal biomass accrual. Responses were analysed across two stream compartments: the water column versus streambed sediments. Organic matter enrichment enhanced fungal biodiversity and functioning, whereas thermal and drying stresses and riparian degradation had negative effects. The streambed sediment compartment buffered the adverse effects of thermal and drying stresses when compared to the water column compartment, thereby conferring resistance to microbial communities and enhancing the resilience of stream ecosystems to global stressors. Our findings underscore the strong influence of multiple stressors on fungal biodiversity and functioning, which are expected to intensify under climate change. Our findings reinforce previous evidence indicating that additive responses are most frequently observed in field studies, in contrast to experimental studies, where antagonistic responses predominate. Collectively, our results indicate that safeguarding conditions that support fungal biodiversity and ecosystem functions is essential to maintaining vital ecosystem services in the face of global change.

The increasing human population growth raises water demand, while global change brings additional challenges, such as higher temperatures, nutrient enrichment and altered precipitation patterns. These shifts can lead to stream flow interruptions and eutrophication, which can affect biodiversity and disrupt stream ecosystem functioning. Aquatic fungi are key players in freshwater ecosystems, mainly due to their role in organic matter decomposition, nutrient cycling and energy transfer to higher trophic levels. Despite their importance, little is known about how aquatic fungal communities recover from environmental stress. This study aims to investigate the role of fungal diversity (species richness and identity) in the recovery of aquatic fungal communities following drying events, both alone and in combination with other abiotic stressors. We used a microcosm approach to simulate drying events and assess the recovery of aquatic fungal communities under four stress scenarios. Microcosms were exposed to increased temperature and/or nutrient levels throughout the entire experiment, including colonisation, drying and recovery phases. This resulted in four treatments: drying alone, drying with increased temperature, drying with increased nutrient levels and drying with both increased temperatures and nutrients. We also tested whether the presence of other fungal species affected recovery dynamics. Fungal species exhibited different recovery capabilities, suggesting species‐specific tolerance to a range of stress conditions. Across all treatments, overall recovery measured by their reproductive ability was delayed under abiotic stress. This delay indicates potential shifts in community composition, which could impair ecosystem functioning and reduce the potential for natural recovery. Our results showed that abiotic stress not only slows fungal recovery but also alters community dynamics, potentially reducing ecological stability. Moreover, the presence of certain fungal species facilitated the recovery of others, emphasising the role of fungal interactions in enhancing community resilience. This study is among the first to highlight the importance of aquatic fungal biodiversity and species complementarity in buffering freshwater ecosystems against abiotic stress. By demonstrating that higher fungal diversity enhances recovery and supports ecosystem functioning under stress, it reinforces the importance of biodiversity conservation and the management of freshwater ecosystems in a changing world.

Invasive species have been drivers of biodiversity loss and functional changes in aquatic ecosystems, including in protected areas. Therefore, monitoring population invasion dynamics and biological traits is fundamental to better understand their ecological and economic impacts and for management actions development. We followed signal crayfish (Pacifastacus leniusculus) invasion in Rabaçal River upper reach at Montesinho Natural Park, Portugal. We collected information on the spread and biological traits (abundance, size, weight, physical condition, sex ratio, and aggressiveness) to assess differences between invasion core and front areas and among years. Signal crayfish population remained restricted since first reports in 2013 in the invasion core until 2017. After 2019, signal crayfish population has been spreading downstream, decreasing abundance at invasion core but increasing at invasion front. Significant higher number of crayfish with claw loss indicate potential higher signs of aggressiveness in the invasion front. Results also demonstrate a significant dominance of females although sex ratio is closer to 1:1 at the invasion front. Overall, results indicate signal crayfish is spreading and increasing their abundance at Rabaçal River highlighting the need for immediate management actions to hold dispersion and mitigate possible impacts.

Streams are significant contributors of greenhouse gases (GHG) to the atmosphere, and the increasing number of stressors degrading freshwaters may exacerbate this process, posing a threat to climatic stability. However, it is unclear whether the influence of multiple stressors on GHG concentrations in streams results from increases of in‐situ metabolism (i.e., local processes) or from changes in upstream and terrestrial GHG production (i.e., distal processes). Here, we hypothesize that the mechanisms controlling multiple stressor effects vary between carbon dioxide (CO₂) and methane (CH₄), with the latter being more influenced by changes in local stream metabolism, and the former mainly responding to distal processes. To test this hypothesis, we measured stream metabolism and the concentrations of CO₂ (pCO₂) and CH₄ (pCH₄) in 50 stream sites that encompass gradients of nutrient enrichment, oxygen depletion, thermal stress, riparian degradation and discharge. Our results indicate that these stressors had additive effects on stream metabolism and GHG concentrations, with stressor interactions explaining limited variance. Nutrient enrichment was associated with higher stream heterotrophy and pCO₂, whereas pCH₄ increased with oxygen depletion and water temperature. Discharge was positively linked to primary production, respiration and heterotrophy but correlated negatively with pCO₂. Our models indicate that CO₂‐equivalent concentrations can more than double in streams that experience high nutrient enrichment and oxygen depletion, compared to those with oligotrophic and oxic conditions. Structural equation models revealed that the effects of nutrient enrichment and discharge on pCO₂ were related to distal processes rather than local metabolism. In contrast, pCH₄ responses to nutrient enrichment, discharge and temperature were related to both local metabolism and distal processes. Collectively, our study illustrates potential climatic feedbacks resulting from freshwater degradation and provides insight into the processes mediating stressor impacts on the production of GHG in streams.

Water pollution from unsustainable agricultural practices is a global problem that undermines human health and economic development. Sustainable agricultural practices have been considered to maintain global food production without compromising water quality and ecosystem health. However, the effectiveness of sustainable agricultural practices in reducing sediments and nutrient export and the combination of practices that will best achieve water quality objectives is still under-explored. In this study, we assess the effectiveness of sustainable agricultural practices in reducing sediments and nutrients export to rivers and determine the combination of practices that would allow the highest reductions of sediments and nutrients, using the Soil and Water Assessment Tool (SWAT) in a Portuguese river basin highly affected by agricultural pollution. SWAT was calibrated and validated for river discharge, sediments, phosphorous, and nitrate loads at the outlet of the basin, with a good agreement between simulated and observed values. The effects of filter strips, fertilizer incorporation, and conservation tillage were analyzed considering both individual and combined effects. Our study shows that sustainable agricultural practices can substantially reduce sediments and nutrients export from a river basin, with the highest average combined depletion of sediments, phosphorus, and nitrate export (25%) achieved when fertilizer incorporation, conservation tillage, and filter strips were implemented simultaneously. Additional studies exploring the effect of sustainable agricultural practices across a range of climate and watershed characteristics, as well as their capacity to deal with challenges related to climate change, will further improve our understanding of the effectiveness of sustainable agricultural practices.