Alessandro Ludovisi

Use of thermodynamic indices as ecological indicators of the development state of lake ecosystems: 2. Exergy and specific exergy indices

Abstract The effectiveness of exergy and specific exergy indices as ecological indicators of the trophic state of lake ecosystems is here tested on a small homogeneous set of shallow lakes which, in spite of their similar nutrient concentrations, morphology and hydrology, show a different trophic state and structure, species composition and abundance. The findings reveal that exergy and specific exergy indices have good negative correlation with phytoplankton biomass and Carlsons trophic state index (TSI) and strong positive correlation to water transparency (the relationship between exergy and eutrophication is clearer if the exergy refers to surface units, rather than volume units) and, hence, that they may be used as ecological indicators of the trophic state of lake ecosystems. The relationship between the responses of the thermodynamic approach and other conventional trophic classification methods (Vollenweiders eutrophication model based on phosphorus loading, the Hillbrich-Ilkowska method and the Vollenweider–OECD classification criterion) previously applied to Lake Trasimeno, was also investigated. The decreasing trend of exergy and specific exergy indices with eutrophication increase appears to be essentially due to the change in species composition and trophic structure, rather than to a different trophic potentiality of the ecosystems investigated. Concerning the identification of the environmental factors responsible for exergy and specific exergy trends, the coherence of the correlation structure between water depth, TSI, exergy and specific exergy indices, suggests that the lakes mean water depth plays a significant role in determining the changes in trophic structure and state (and consequently in exergetic indices) within the set of lakes examined and emphasises the importance of lake morphology in the development and ageing of lake ecosystems.

Use of thermodynamic indices as ecological indicators of the development state of lake ecosystems. 1. Entropy production indices

Abstract The effectiveness of Aokis entropy production indices as ecological indicators of the trophic state is tested here under the changing hydrological conditions of Lake Trasimeno, a shallow freshwater lake in Italy. The analysis leads to a review of Aokis indices and a definition of a new set of eutrophication indices ( c , d , d ′) based on the entropy production per surface unit rather than volume unit, which seem to be good ecological indicators for the trophic state of lake ecosystems. The positive correlation between these indices and the trophic state of a small set of lakes suggests that they are able to take into account the influence of the biological productivity on the whole entropy production of the systems. Moreover, the indices d and d ′ show a good negative linear correlation to the lake mean depth, showing the importance of this morphological parameter in the eutrophication process or succession in lakes. The values of the indices show that Lake Trasimeno exhibits a trophic state consistent with Carlsons TSI indices and with the results previously obtained by the application of Vollenweiders eutrophication model based on phosphorus loading and the Hillbrich–Ilkowska method, but less compliant with the Vollenweider–OECD classification criterion. The study emphasises the importance of a holistic thermodynamic approach in getting new insight into the fundamental mechanisms of the ecological succession of lake ecosystems.

Warming trends of perialpine lakes from homogenised time series of historical satellite and in-situ data

The availability of more than thirty years of historical satellite data is a valuable source which could be used as an alternative to the sparse in-situ data. We developed a new homogenised time series of daily day time Lake Surface Water Temperature (LSWT) over the last thirty years (1986-2015) at a spatial resolution of 1km from thirteen polar orbiting satellites. The new homogenisation procedure implemented in this study corrects for the different acquisition times of the satellites standardizing the derived LSWT to 12:00 UTC. In this study, we developed new time series of LSWT for five large lakes in Italy and evaluated the product with in-situ data from the respective lakes. Furthermore, we estimated the long-term annual and summer trends, the temporal coherence of mean LSWT between the lakes, and studied the intra-annual variations and long-term trends from the newly developed LSWT time series. We found a regional warming trend at a rate of 0.017°Cyr-1 annually and 0.032°Cyr-1 during summer. Mean annual and summer LSWT temporal patterns in these lakes were found to be highly coherent. Amidst the reported rapid warming of lakes globally, it is important to understand the long-term variations of surface temperature at a regional scale. This study contributes a new method to derive long-term accurate LSWT for lakes with sparse in-situ data thereby facilitating understanding of regional level changes in lakes surface temperature.

A Proposed Framework for the Identification of Habitat Utilisation Patterns of Macrophytes in River Po Catchment Basin Lakes (Italy)

The main aim of this study, which is based on cover-abundance values of 20 species of floating-leaved and submersed macrophytes collected in 18 lakes located within the River Po catchment basin (Italy), is to investigate the relationships between lake-scale environmental features (including morphology, hydrology, trophic state and water quality variables) and the changes in species composition and species richness in macrophyte communities. The findings reveal that the main changes in community composition of the pondweed communities, identified by principal component analysis, could be effectively explained by a newly introduced morpho-hydrological parameter (the theoretical laminar water renewal rate – RL) and by the trophic state of the lakes, expressed as Carlson’s trophic state index (TSI). The results of the multivariate analyses performed also show that the grouping of species is strictly related to growth-form traits. In particular, floating-leaved and submerged macrophytes appeared mutually exclusive in dominating different habitat types defined on the basis of the RL–TSI framework. An increasing trend in species richness was also observed in relation to RL. The possibility of using the bivariate RL–TSI framework for the identification of habitat utilisation patterns by single species was also investigated, and cover-abundance prediction maps based on the RL–TSI framework were produced for several macrophyte species. Observations in another system characterised by high spatial heterogeneity for hydrological and trophic conditions, support the predictions in terms of growth-form prevalence, species richness and single species cover-abundance (where available), and also suggest a more refined application of the proposed approach.

The invader mudsnail Potamopyrgus antipodarum in the Tiber River basin (Central Italy).

Although the New Zealand mudsnail Potamopyrgus antipodarum has been observed in Italy since 1961, no investigations have gone beyond recording its presence. In this study, populations from three Italian watercourses with different environmental features were comparatively analysed with a view to shedding light on the relationships between habitat type and reproduction. At the study sites, populations were exclusively composed of females. Ultra‐structural details showed that egg growth takes place through the accumulation of stored materials, which are essentially constituted by translucent vesicles (lipids) and by electron‐dense granules with a darker rim (proteins), the latter deriving from the confluence of smaller granules of the same type. The egg surface displays numerous microvilli, which interdigitate with those emerging from both adjacent eggs and bordering cells. Our comparative analysis shows that the populations differ slightly in fecundity, whereas the number of brooded embryos/female markedly decreases, in parallel with the mean density, in running‐water habitats lacking aquatic vegetation. Statistical analysis confirms that P. antipodarum positively selects biological substrates, such as beds of Vaucheria sp. and even, on occasion, dead leaves and wood floating on the water surface. The results suggest that biological substrates constitute one of the key factors favouring the massive spread of P. antipodarum in watercourses.

Study of seasonal variations of glutathione and detoxification enzymes in Lophopus crystallinus Pallas (Bryozoa) from Lake Piediluco (Umbria, Italy)

Abstract Lophopus crystallinus, a freshwater bryozoan, was collected monthly from Lake Piediluco (Umbria, Italy) to study variation of the biochemical responses to seasonal progress. Temperature seemed very important in conditioning the presence of the species: in fact, water temperature of over 20° C seemed to be out of its tolerance range. Seasonal variations of total glutathione, glutathione‐dependent enzymes (glutathione‐S‐transferases, glutathione peroxidases, glutathione reductase, glyoxalase I and gly‐oxalase II) and catalase were studied. The results suggest the existence of an annual cyclic path for glutathione‐dependent enzyme activities. The progress of this biochemical pattern could be considered a useful tool for characterising seasonal variations in the metabolic status of these organisms.

Plankton dynamics across the freshwater, transitional and marine research sites of the LTER-Italy Network: patterns, fluctuations, drivers

A first synoptic and trans-domain overview of plankton dynamics was conducted across the aquatic sites belonging to the Italian Long-Term Ecological Research Network (LTER-Italy). Based on published studies, checked and complemented with unpublished information, we investigated phytoplankton and zooplankton annual dynamics and long-term changes across domains: from the large subalpine lakes to mountain lakes and artificial lakes, from lagoons to marine coastal ecosystems. This study permitted identifying common and unique environmental drivers and ecological functional processes controlling seasonal and long-term temporal course. The most relevant patterns of plankton seasonal succession were revealed, showing that the driving factors were nutrient availability, stratification regime, and freshwater inflow. Phytoplankton and mesozooplankton displayed a wide interannual variability at most sites. Unidirectional or linear long-term trends were rarely detected but all sites were impacted across the years by at least one, but in many case several major stressor(s): nutrient inputs, meteo-climatic variability at the local and regional scale, and direct human activities at specific sites. Different climatic and anthropic forcings frequently co-occurred, whereby the responses of plankton communities were the result of this environmental complexity. Overall, the LTER investigations are providing an unparalleled framework of knowledge to evaluate changes in the aquatic pelagic systems and management options.

A geographic distribution data set of biodiversity in Italian freshwaters

We present a data set on the biodiversity of Italian freshwaters, including lakeshores and riverbanks of natural (N=379: springs, streams and lakes) and artificial (N=11: fountains) sites. The data set belongs partly to the Italian Long Term Ecological Research network (LTER-Italy) and partly to LifeWatch, the European e-Science infrastructure for biodiversity and ecosystem research. The data included cover a time period corresponding to the last fifty years (1962-2014). They span a large number of taxa from prokaryotes and unicellular eukaryotes to vertebrates and plants, including taxa linked to the aquatic habitat in at least part of their life cycles (like immature stages of insects, amphibians, birds and vascular plants). The data set consists of 6463 occurrence data and distribution records for 1738 species. The complete data set is available in csv file format via the LifeWatch Service Centre.

Beyond the mean: A comparison of trace- and macroelement correlation profiles of two lacustrine populations of the crayfish Procambarus clarkii

In invertebrate biomonitors of chemical pollution, emphasis has been generally given to mean accumulation patterns and how they reflect varying environmental levels of contamination. Intra-population variability, and how it relates with individual phenotypic traits, has received less attention. Here, a set of analytes including trace elements (B, Ba, Cd, Cr, Cu, Fe, Li, Mn, Ni, Pb, Sr, V, and Zn), macroelements (C, Ca, K, Mg, N, Na), and carbon and nitrogen stable isotopes (δ13C and δ15N) was measured in two populations of the crayfish Procambarus clarkii from Lake Trasimeno and Lake Bolsena (Central Italy). The influence of location, sex, body size, and condition factor was assessed; in addition, the analyte correlation profiles of the two populations were compared to verify their congruence. In general, significant inter-lake differences were observed in the concentration of both trace- and macroelements in crayfish tissues, generally mirroring the local chemistry of water and of benthic non-living matrices (sediment and plant detritus). Crayfish CN isotopic signatures excluded the occurrence of inter-lake variations in their omnivorous trophic habits. Correlation profiles varied considerably between the two populations in the nature and strength of bivariate relationships. However, Mantel tests and procrustean analyses indicated a general, significant congruence; C, N, and, to a lesser extent K, Li, Ni, Pb, and δ13C showed the highest procrustean residuals, suggesting that their associations with other analytes may be partially influenced by inter-population differences in growing phases. Our study indicates that the local geochemistry of the lacustrine environment influences the elemental fingerprint of Procambarus clarkii; the considerable inter-individual variability in the concentration of analytes, however, does not significantly reflect on their association, thus corroborating its effectiveness as an indicator species.