Martina Austoni

Resource ratio and human impact: how diatom assemblages in Lake Maggiore responded to oligotrophication and climatic variability

Diatoms have been often used to track trophic changes from sedimentary records: recent studies demonstrated that these organisms can even be valuable indicators of climatic variability, although it is often difficult to discriminate the role of trophic and climatic drivers. Moving from the hypothesis that oligotrophication and climate affected the composition of the diatom assemblages by changing the resource ratio, we analysed the vernal diatoms succession in Lake Maggiore, between 1984 and 2007, using multivariate techniques (cluster analysis, canonical correspondence analysis, multivariate regression trees), in order to single out the oligotrophication effects from those attributable to climatic variability. Our results point out that Si, TP, temperature and wind emerged as key explanatory variables in species selection, with a stronger link between trophic and climatic drivers after the lake reached a stable oligotrophic status. Peculiar climate-driven events (deep mixing and floods) affected the in-lake Si:P ratio, giving an advantage to diatoms that are excellent P, but poor Si competitors. The classical role of Fragilaria and Tabellaria as early-warning indicators of eutrophication should be reconsidered, taking into account that both can be useful indicators of climate change, when links between their physiological resource needs and environmental data coming from robust limnological investigations can be established.

Could the extreme meteorological events in Lake Maggiore watershed determine a climate-driven eutrophication process?

Lake Maggiore has reached a stable oligotrophic status after a recovery process from mesotrophy that began in the early 1980s. However, the most recent phytoplankton and water chemistry data seem to indicate that various changes are taking place, including a slight increase in TP values, and almost regular blooms have occurred since 2005. Meteoclimatic data collected over the last few decades in the Lake Maggiore watershed highlight an increase in the frequency of extreme rainfall events. Here, for the period 2000–2013, we analyse the relationships between the phytoplankton dynamics and selected extreme precipitation events, in order to evaluate the possible role of rainfall in affecting the nutrient availability and phytoplankton dynamics. Among the algal groups, cyanobacteria showed the strongest relationship with the precipitation pattern, particularly on a short-term temporal scale. Our results support the hypothesis that rainfall may lead to a short-term increase in nutrients that stimulate the growth of phytoplankton and the development of blooms in summer, when epilimnetic waters are usually nutrient depleted. The almost regular cyanobacterial blooms recorded in Lake Maggiore since 2005 can be interpreted as a response to changing precipitation patterns and therefore as a sign of climate-induced eutrophication.

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.

Coupling a bio-accumulator organism and MALDI-TOF MS: an early warning detection system for microcystins in water bodies.

Microcystins produced by freshwater cyanobacteria pose serious threats to human health and are a growing problem in drinking water supplies worldwide. Toxin detection and identification in water reservoirs when cyanobacterial density is still low is a key step to predict harmful algal blooms and to allow the safe use of the resource. For this purpose, developing sensitive and rapid methods of analysis is crucial. Adopting a strategy that couples the use of a filter-feeder organism (Unio elongatulus, Pfeiffer 1825 (Bivalvia: Unionidae)) with matrix-assisted laser desorption ionization—time of flight mass spectrometry (MALDI-TOF MS) technology, effective microcystin detection was achieved. The performances of MALDI-TOF MS, high-liquid-performance chromatography with diode array detector (HPLC-DAD) and enzyme-linked immunosorbent assays (ELISA) test were compared. The results obtained in this study suggest that the exploitation of an efficient bio-accumulator organism, coupled with a rapid and sensitive analytical method, can be a very useful strategy in monitoring programs for early and prompt risk management.