This paper illustrates the results of an analysis performed on historical data of the main meteorological and water quality variables collected during the last fifty years in the basin of Lake Trasimeno, a shallow lake subjected to important water level fluctuations. The results reveal a significant increase of the annual mean of minimum and maximum air temperature, water temperature and solar radiation, and a significant reduction of precipitation and cloud cover, which have mostly occurred during the last twenty years. The decadal rate of warming observed in the last twenty years for air temperature (0.33 °C decade-1) is consistent with the estimate reported by the IPCC for the land-surface temperature in the Northern Hemisphere, whereas the surface water temperature in Lake Trasimeno shows a more marked increase (0.65 °C decade-1), comparable to that observed in other lakes of Mediterranean areas. On a monthly scale, the most significant variations are observed in late-spring and early summer months for temperature and solar irradiation, and in winter and spring months for rainfall, which result in an appreciable modification of the seasonal progression. The alterations of the thermal and hydrological balance of the lake have caused a progressive lowering of the water level and the emergence of evaporative conditions. As a consequence of the drought, a progressive accumulation of dissolved salts (3.5 106 kg y-1) is observed, which is partially explained by meteoric loading. The analysis also shows that an increase in the total alkalinity has occurred during the main drought phases of the last forty years, which has been shown to be consistent with what expected on the basis of the changes in the ionic composition of the waters. With decreasing water levels, a strong reduction in water transparency has also been observed, which does not appear to be connected with a change in the trophic state of the lake, but rather with the increase of suspended solids from bottom sediments, in agreement with the predictions based on resuspension models in shallow waters. On putting the results into the future scenario of climate change, an accelerating drought and progressive worsening of the water quality can be predicted for Lake Trasimeno in the near future

In this paper, we identified seven ecological network analysis (ENA) metrics that, in our opinion, have high potential to provide useful and practical information for environmental decision-makers and stakeholders. Measurement and quantification of the network indicators requires that an ecosystem level assessment is implemented. The ENA metrics convey the status of the ecological system state variables, and mostly, the flows and relations between the various nodes of the network. The seven metrics are: 1) Average Path Length (APL), 2) Finn Cycling Index (FCI), 3) Mean Trophic level (MTL), 4) Detritivory to Herbivory ratio (D:H), 5) Keystoneness, 6) Structural Information (SI), and 7) Flow-based Information indices. The procedure for calculating each metric is detailed along with a short evaluation of their potential assessment of environmental status.

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.

No abstract

No abstract