Unlocking the potential of ponds and pondscapes as nature-based solutions for climate resilience and beyond: Hundred evidences.

Unlocking the full potential of ponds (small water bodies) and pondscapes (network of ponds) as Nature-based Solutions (NbS) is critical pursuit for enhancing ecosystems and societal resilience to climate change and other societal challenges. Despite scattered initiatives for pond/pondscape creation, restoration and management-each considered here a distinct NbS-there is a significant knowledge gap in utilising ponds/pondscapes as effective NbS. We aimed to assess these NbS in terms of their objectives, outcomes, effectiveness, multifunctionality, delivery of potentially conflicting effects, and the implementation process while considering their Nature's Contributions to People (NCPs, i.e., benefits to society). We compiled data on 183 NbS actions implemented across 93 ponds/pondscapes from 24 countries, predominantly from Europe, via a questionnaire distributed to experienced stakeholders implementing NbS in ponds/pondscapes. One single pond/pondscape may imply more than one NbS action. Two-thirds were in rural areas, and one-third in urban settings. Our analysis revealed that Creation of habitat for biodiversity was a primary delivery objective (targeted NCP) in the implementation of most NbS in ponds/pondscapes, often also combined with other NCPs such as Learning and inspiration, Regulation of water quantity, and Physical and psychological experiences, showcasing their intended multifunctionality. Implemented NbS primarily focused on climate change adaptation (especially Regulation of hazards and extreme events, and water quantity) rather than mitigation, with less emphasis on measures like direct greenhouse gas emissions reduction or enhancing carbon sinks. The costs associated with pond's NbS varied significantly depending on factors such as project scope, objectives, location, socio-economic-cultural system, and specific implementation requirements. The creation of ponds/pondscapes often entailed the highest financial investment, much more than their restoration or their management. In conclusion, our study underscores the multifunctionality of ponds/pondscapes and provides insights about their significant potential as cost-effective NbS for enhancing ecosystem and societal resilience to climate change and biodiversity. It underscores the importance of further research to fully understand and measure the diverse range of NbS they offer, particularly in the context of climate change mitigation. Standardised measurements of the NCP provided by these NbS in ponds/pondscapes are essential for validating managers' claims and exploring their role in addressing climate change.

Diet and food selection by fish larvae in turbid and clear water shallow temperate lakes.

Fish larvae play an important structuring role for their prey and show ontogenetic shifts in diet. Changes in diet differ between species and habitats and may also be affected by turbidity (eutrophication). We investigated the diet (stomach content) and the food selection (ratio of ingested prey and prey availability) of roach and perch larvae in a clear lake and of roach, perch and pikeperch larvae in a turbid lake multiple times during spring to autumn. The diet of the fish larvae changed with size, and for roach and perch larvae between the lakes. Coexisting species of fish larvae had different diets in the two lakes, pointing to resource partitioning; yet, in the clear lake, medium-sized larvae had a high diet overlap, suggesting a competitive relationship at this developmental stage. In the clear lake, roach larvae showed diel differentiation in diet, while perch demonstrated diet shifts between habitats, which probably aided in reducing competition and also evidenced an effect of light on the larval prey capture and/or predator-fish larvae interactions. In the turbid lake, roach and perch larvae did not reveal differences in diet between habitats or time of the day, owing to homogeneity of food items and poor light conditions. However, the diet of pikeperch larvae differed between day and night following daily variations in the abundance of its preferred prey. The roach larvae were highly selective for Bosmina, Daphnia and benthic cladocerans, perch larvae generally consumed what was available, while pikeperch primarily preyed on cyclopoid copepodites. We conclude that turbidity acted as a cover for fish larvae in the turbid lake. Under eutrophication-induced turbidity scenarios the effects of fish larvae on their prey are stronger (i.e., high selectivity for several resources) than that of larvae in clear waters, creating a negative feedback on the path to restore water clarity.

Nutritional stress by means of high C:N ratios in the diet and starvation affects nitrogen isotope ratios and trophic fractionation of omnivorous copepods.

Nutritional stress, from feeding on low-quality diets or starvation, may cause changes in consumers' nitrogen isotope ratios (δ15N = 15N/14N) and trophic fractionation (∆15N = δ15Nconsumer - δ15Nfood source), however, research has shown mixed results in the magnitude and the direction of the change. This is potentially more complex for omnivores whose diets span a wide range of food resources. We conducted seasonal field samplings in Patagonian lakes and analyzed the relationship between seston (SES) quality parameters and the δ15N and ∆15N of an omnivorous copepod, Boeckella gracilipes (Bg). We also performed a 7-day laboratory starvation experiment, an extreme form of nutritional stress, to investigate if lack of food led to changes in δ15NBg values. Our field results showed that increasing values of the seston carbon to nitrogen ratio (C:NSES), chlorophyll a (Chl a), and δ15NSES were related to higher δ15NBg values. C:NSES and Chl a were also positively related to ∆15N; yet, C:NSES alone explained 70% of the variation. C:NSES values correlated with the presence of mixotrophic algae and ciliates that are key food resources for B. gracilipes. In our laboratory starvation experiment, the δ15NBg values increased significantly, pointing to use of internal N sources; yet, the change associated with starvation was less pronounced than that related to C:NSES changes in the field, suggesting depletion of the substrate pool in the former. We found that ∆15N values of omnivorous species consuming a low-quality diet would be higher than that from a conspecific with a high-quality diet; though fasting animals would show intermediate values.