One Year Monitoring of Ecological Interaction of Silurus glanis in a Novel Invaded Oligotrophic Deep Lake (Lake Maggiore)

The European catfish (Silurus glanis) was introduced in Italy during the last century for aquaculture purposes, and now it is well-established. S. glanis is an invasive species and a top predator that can deplete prey supply in the surrounding habitat, leading to changes in the aquatic food web. Consequently, its presence is considered a threat to native fish populations. Its presence in the Lake Maggiore (Northern Italy) is recent and there is a lack of knowledge about its ability to completely exploit this new ecosystem throughout the year. This study corroborated the ability of European catfish to exploit both pelagic and littoral habitats, promoting trophic interactions in both habitats. Over 2019, multiple sampling approaches have been applied by collecting S. glanis and analysing its stomach contents with the aim of inferring interactions with the freshwater community. Its diet was mainly based on crayfish (Orconectes limosus), followed by six prey fish and the genus Corbicula; two fish species (Padogobius bonelli and Salaria fluviatilis) were added to the list of known prey fish. Notably and alarmingly for the early potential top-down pressure towards all trophic levels, young individuals were proved to also feed on fish and crayfish. S. glanis showed the ability to hunt at deep depths (>60 m) and a high growth rate, despite Lake Maggiore being oligotrophic.

Temporal changes in nutrients in a deep oligomictic lake: the role of external loads versus internal processes

The impact of climate change on stratification and mixing patterns has important effects on nutrient availability and plankton dynamics in deep lakes. We demonstrate this in a long-term study of Lake Maggiore, a deep oligomictic lake located in the subalpine lake district in Northern Italy. Studies on physical, chemical and biological features of the lake have been performed continuously since the 1980s. The lake recovered from eutrophication in response to a reduction of catchment nutrient loads and reached a stable oligotrophic status by the end of the 1990s, with average total phosphorus concentrations in the water column around 10 µg L-1. However, both reactive and total phosphorus have slightly increased since 2010, leading to a shift in the lake trophic state towards mesotrophy. The increase in phosphorus has been limited to the hypolimnetic layers, concentrations being fairly stable or decreasing in the epilimnion. Reactive silica also progressively increased in the hypolimnion, while nitrate and total nitrogen concentrations have steadily decreased in both deep and surface layers, especially in the summer period. These changes were assessed in relation to catchment loads, atmospheric deposition and climate-related variations in stratification and mixing patterns and in nutrient retention. Long-term changes in primary production, represented by chlorophyll levels, and biovolume of the main algal groups were also considered. During the eutrophication period and until the 1990s, in-lake phosphorus concentrations were tightly related to external loads; successively, phosphorus and its vertical distribution up the water column became more controlled by internal processes, in particular by stratification and mixing regime. An increase of thermal stability and a reduced frequency and intensity of deep mixing events has fostered oxygen depletion and phosphorus and silica accumulation in the hypolimnion. Another consequence of reduced deep mixing events, has been a reduction in nutrient replenishment of the upper layers at spring mixing. External loads are still the main driver of change for nitrogen compounds: the decrease in the atmospheric load of nitrogen that occurred in the Lake Maggiore area over the last decade, as an effect of reduced nitrogen emissions, has caused decreasing concentration of inorganic nitrogen in the lake. However, the phytoplankton community changes observed might also play a role in nitrogen dynamics, particularly in the nitrate minima observed during summer in recent years.

An archive for the history of limnology at Verbania Pallanza in the Italian Lake District

Since 2010, work has been underway to curate and catalogue the historical documentation archive of the Verbania Pallanza section of the CNR Institute for Research on Waters, located on the shores of Lake Maggiore in the Italian Lake District. This laboratory was established during the first decade of the 1900s with the work of Marco De Marchi, and research activities intensified from 1938 onwards with the foundation of the Italian Institute of Hydrobiology. The curation of the archives dating from these earliest times to the present has been done with professional archivist technicians from the Archival Superintendence and in collaboration with researchers from the Institute. The archived documents include those from the first phase of the organization of the Institute, as well as those derived from scientific and administrative activities and exchanges with the Ministry of Education. The documents also cover activities at a second section of the Institute, located in an ancient historical residence in Varenna, on the shores of Lake Como. The archive has a photographic section, which includes a series of photographic glass plates, digitized to allow for current use, containing photos of the Institute's environments and laboratories at different times through its history. A third section of the archive consists of around 50 interviews with aquatic scientists on topics relating to research projects carried out in the past. A further section concerns the recording of about 150 seminars on environmental research carried out in the institute between 2015 and 2020. The main research topics considered concern physical, chemical and biological limnology, with particular attention to Lake Maggiore, Lake Orta (severely polluted due to industrial waste), and high-altitude lakes in the Alps. The Institute also houses a library dedicated to environmental issues and some miscellaneous papers by the most important scholars of freshwater science in Italy, with publications starting from the second half of the nineteenth century. Other collections of archival interest are a museum of field and laboratory instruments, and a collection of biological samples, mainly plankton, collected in various Italian lakes.

Spoiled for Choice during Cold Season? Habitat Use and Potential Impacts of the Invasive Silurus glanis L. in a Deep, Large, and Oligotrophic Lake (Lake Maggiore, North Italy)

The ecological features of invasive alien species are crucial for their effective management. However, they are often lacking in newly invaded ecosystems. This is the case of the European catfish Silurus glanis L. in Lake Maggiore, where the species is present since 1990, but no scientific information is available on its ecology. To start filling this knowledge gap, 236 catfish (67 cm to 150 cm of total length) were collected, measured, and dissected for stomach content analyses from three localities and in two habitats (littoral vs. pelagic) in late autumn/early winter. The NPUE and BPUE (individuals (N) and biomass (B, in grams) per unit effort (m2), respectively) of catfish were generally higher in littoral (NPUE > 0.01; BPUE > 96) than in pelagic habitats (NPUE < 0.009; BPUE < 114), but the catfish had, on average, larger sizes in pelagic habitats. Overall, 581 individual prey items were recorded, belonging to 12 taxa. Pelagic catfish specialized their diet exclusively on three prey fish (coregonids, shad, and roach), whilst the diet of littoral catfish was more variable and dominated by crayfish, perch, and roach. These results highlighted for the first time the interaction of larger catfish with the lake’s pelagic food web, and thus possible consequences are discussed, including the potential contrasting role S. glanis may have for the lake’s fishery.

Spoiled for Choice during Cold Season? Habitat Use and Potential Impacts of the Invasive Silurus glanis L. in a Deep, Large and Oligotrophic Lake (Lake Maggiore, North Italy)

Ecological information of invasive alien species are crucial for their effective management. How-ever, they are often lacking in newly invaded ecosystems. This is the case of the European catfish Silurus glanis L. in Lake Maggiore where the species is present since 1990 but no scientific infor-mation are available on its ecology. To start filling this knowledge gap, 236 catfish (67 cm to 150 cm of total length) were collected, measured, and dissected for stomach content analyses from three localities and in two habitats (littoral vs. pelagic) in late autumn/early winter. NPUE and BPUE (individuals and biomass (g) per unit effort (m2)) of catfish was generally higher in littoral (NPUE &gt; 0.01; BPUE &gt; 96) than pelagic habitats (NPUE &lt; 0.009; BPUE &lt; 114) but catfish had, on average, larger sizes in pelagic habitats. Overall, 581 individual prey items were recorded belonging to12 taxa. Pelagic catfish specialized their diet exclusively on three prey fish (coregonids, shad and roach) whilst the diet of littoral catfish was more variable, and was dominated by crayfish, perch, and roach. These results highlighted for the first time the interaction of larger catfish with the lake&rsquo;s pelagic food web, and thus possible consequences are discussed, including the potential contrasting role S. glanis may have for the lake&rsquo;s fishery.

Transparent Exopolymer Particles (TEP), phytoplankton and picocyanobacteria a littoral-to-pelagic depth-gradient in a large subalpine lake

Transparent Exopolymer Particles (TEP) play an important role in the organic carbon cycle of many aquatic systems but the production and distribution of TEP have been studied mainly in the marine environment, neglecting the large oligotrophic lakes. We selected Lake Maggiore, one of the most important freshwater reserve in Northern Italy, to study the horizontal and vertical distribution of TEP and of its possible drivers. Samplings along a transect in the Borromeo basin were performed in May, July and September 2019. Total Organic Carbon (TOC), TEP, chlorophyll-a (Chl) of different algal groups, picocyanobacteria, bacteria and eukaryotes counting, were measured at six stations and five depths. Our study showed that TEP exhibited a clear vertical heterogeneity from surface to the bottom related to the autotrophic microorganisms that are the main source of TEP and are prevalent in the euphotic zone of the lake. On the other hand, TEP was fairly evenly distributed along the horizontal transect from littoral to pelagic zone, although patches were present in spring, when TEP concentrations were low. In contrast to TEP, TOC and to a lesser extent Chl and bacteria showed horizontal heterogeneity, in some months. In Lake Maggiore TEP indeed was an important fraction of Total Organic Carbon (TOC), making up to 54% of TOC (in carbon units: 910 µg C L-1) and it was significantly correlated with Chl. The highest TEP concentration (1.44 mg GX eq L-1) was measured in September 2019, in coincidence with an episode of superficial foam appearance. Considering the biomass as Chl concentrations, the algal group mostly related to TEP was that of brown algae, particularly diatoms; but considering the numbers, the picocyanobacteria and bacteria were more significantly correlated to TEP. The presence of pennate diatoms in May and July, with their TEP-related chlorophyll, did not produce TEP in as high concentration as that observed in September in the presence of centric diatoms and of very high numbers of picocyanobacteria and bacteria.

Automated high frequency monitoring of Lake Maggiore through in situ sensors: system design, field test and data quality control

A high frequency monitoring (HFM) system for the deep subalpine lakes Maggiore, Lugano and Como is under development within the EU INTERREG project SIMILE. The HFM system is designed to i) describe often neglected but potentially relevant processes occurring on short time scale; ii) become a cost-effective source of environmental data; and iii) strengthen the coordinated management of water resources in the subalpine lake district. In this project framework, a first HFM station (LM1) consisting of a monitoring buoy was placed in Lake Maggiore. LM1 represents a pilot experience within the project, aimed at providing the practical know-how needed for the development of the whole HFM system. To increase replicability and transferability, LM1 was developed in-house, and conceived as a low-cost modular system. LM1 is presently equipped with solar panels, a weather station, and sensors for water temperature, pH, dissolved oxygen, conductivity, and chlorophyll-a. In this study, we describe the main features of LM1 (hardware and software) and the adopted Quality Assurance/Quality Control (QA/QC) procedures. To this end, we provide examples from a test period, i.e., the first 9-months of functioning of LM1. A description of the software selected as data management software for the HFM system (IstSOS) is also provided. Data gathered during the study period provided clear evidence that coupling HFM and discrete sampling for QA/QC controls is necessary to produce accurate data and to detect and correct errors, mainly because of sensor fouling and calibration drift. These results also provide essential information to develop further the HFM system and shared protocols adapted to the local environmental (i.e., large subalpine lakes) and technical (expertise availability) context. Next challenge is making HFM not only a source of previously unaffordable information, but also a cost-effective tool for environmental monitoring.

Phytochemical Profile and Antioxidant Properties of Italian Green Tea, a New High Quality Niche Product

The hot beverage commonly known as tea results from the infusion of dried leaves of the plant Camellia sinensis (L.) O. Kuntze. Ranking second only to water for its consumption worldwide, it has always been appreciated since antiquity for its aroma, taste characteristics, and beneficial effects on human health. There are many different processed tea types, including green tea, a non-fermented tea which, due to oxidation prevention maintains the structure of the bioactive compounds, especially polyphenols; these bioactive compounds show a number of benefits for the human health. The main producers of tea are China and India, followed by Kenya, Sri Lanka, Turkey, and Vietnam, however recently new countries are entering the market, with quality niche productions, among which also Italy. The present research aimed to assess the bioactive compounds (polyphenols) and the antioxidant activity of two green teas (the “Camellia d’Oro” tea—TCO, and the “Compagnia del Lago” tea—TCL) produced in Italy, in the Lake Maggiore district, where nurserymen have recently started to cultivate C. sinensis. In this area the cultivation of acidophilic plants as ornamentals has been known since around 1820. Due to the crisis of the floricultural sector, producers have been trying to diversify their product in order to increase their competitiveness, starting to cultivate Italian tea. Their antioxidant activity was assessed, finding a similar or higher antioxidant capacity than in other green teas, as reported in literature. TCO showed a higher antioxidant activity (42,758.86 mmol Fe2+ kg−1; 532.37 µmol TE g−1 DW; 881.08 µmol TE g−1 DW) and phenolic content (14,918.91 mg GAE 100 g−1 DW) than TCL (25,796.61 mmol Fe2+ kg−1; 302.35 µmol TE g−1 DW; 623.44 µmol TE g−1 DW; 8540.42 mg GAE 100 g−1 DW). Through HPLC, a total of thirteen phenolic compounds were identified quantitatively, including catechins, benzoic acids, cinnamic acids, and flavonols, in TCO while only 9 in TCL, and mainly in lower amounts. Albeit with differences, both teas were found to be of quality proving that Italy could have the possibility to grow profitably C. sinensis.

Between Medicine and Faith

The monastery of Saint Catherine of Sasso was built overhanging the eastern shore of Lake Maggiore in the municipality of Leggiuno (VA). In particular, our paper concerns the relics housed in the Sacellum of the church of St. Caterina. According to the tradition, the first Sacellum dedicated to the saint was built before the 16th century over a medieval hermit’s refuge. The chronicle, the Historieta, remembers that, in the 12th century, a merchant of Arolo, Alberto Besozzi, survived the lake crossing shipwreck and made a vow to St. Catherine of Alexandria. He decided to retreat in prayer in a cave on that part of the coast. The Sacellum, now incorporated in the monastery complex (at the bottom of the central nave of the church), preserved human remains of Blessed Alberto in the past. We present the important role that the Sacellum and the relics have played not only for the faith, but also for the devotion of pilgrims and local people. In this context, this monument is related to the sense of religiosity and spirituality that pervaded medieval life, where every form of prayer is to be materialized in the physicality of a tangible creation.