Suchergebnisse

This report summarizes the finding of the InHabit project on the importance of atmospheric nitrogen deposition in affecting the chemical composition of lake water and in eventually altering the biological communities living in them. Previous deliverables (I2d5, Id26 and I2d7) have shown that; 1. in both regions studied in the InHabit project (Piedmont and Sardinia), atmospheric deposition of nitrogen compounds is relevant; 2. the flux of nitrogen from the atmosphere to the ecosystem is markedly larger in Piedmont than in Sardinia; 3. models of the dynamic behavior of nitrogen in forested catchments indicates that Piedmon soils are mainly N-saturated, so that nitrogen carried by atmospheric deposition can be released form forest soil to the surface water; 4. in Sardinia, soil are less saturated, but a part of the deposited nitrogen is still carried to surface water; 5. trend analysis of deposition and stream water revealed that nitrogen deposition is stable or slightly decreasing in recent years, both in atmospheric deposition and in stream water; 6. the importance relative importance of N deposition is relevant for sites in or close to reference conditions; 7. the relationships between environmental variables and organisms belonging to the four biotic communities used to define the lake's ecological quality, according to provisions of the Italian legislation (D.Lgs. 260, November 2010) and the European Water Framework 2000/60 differ depending on the biological quality element considered; 8. phytoplankton community shows the clearer responses: according to the result of multivariate analysis, total nitrogen and ammonium nitrogen are among the most significant factors explaining the relationships among phytoplankton orders, species and environmental variables. In particular, cyanobacteria increased considerably with increasing availability of ammonium nitrogen. Conversely, high concentrations of this compound suppress the development of diatoms. On the basis of those results, which are summarized in this deliverable, we focused on the effect of different levels of nitrogen in lakes with low phosphorus concentration, slightly affected by direct trophic pressure and close to the reference conditions. The comparison between two lakes in Piedmont with low P concentration and high N concentration with two reservoirs in Sardinia with low levels of both nutrients shows that the formers are dominated by diatoms and the latter by dynophytes. Two reservoirs in Piedmont with high N levels are also dominated by diatoms. In spite of the small number of lakes studied, it seems that dynophytes are more fitted to low N lakes, probably because of their ability to use an heterotrophic metabolism, while lakes in reference conditions are generally considered to be dominated by oligotrophic diatoms, Our findings call for deeper studies on reference conditions in the Mediterranean ecoregion, because they suggest that lakes not affected by direct trophic pressure, i.e. reference lakes, may host different diatom communities depending on the amount of nitrogen deposition they receive.

This report presents an analysis of the relationships between environmental variables and organisms belonging to the four biotic communities used to define the lake's ecological quality, according to provisions of the Italian legislation (D.Lgs. 260, November 2010) and the European Water Framework 2000/6. The data analyzed were collected during the sampling surveys carried out within InHabit Project in 13 water bodies, 7 in Piedmont and 6 in Sardinia respectively. In particular, the aim of the study was to evaluate the possible effects of nitrogen on biotic communities. Phytoplankton community shown the clearer responses: according to the result of multivariate analysis, total nitrogen and ammonium nitrogen are among the most significant factors explaining the relationships among phytoplankton orders, species and environmental variables. In particular, cyanobacteria increased considerably with increasing availability of ammonium nitrogen. Conversely, high concentrations of this compound suppress the development of diatoms. Other algal groups show a nonlinear response with respect to nitrogen, with a possible limitation under low levels of nitrogen and an inhibition at higher levels. A comparative analysis, carried out to evaluate the response to the gradient of total phosphorus, shows that this nutrient is not as selective as nitrogen in controlling the structure of the algal assemblage in different environmental conditions. Other biotic communities did not show a clear relationship with nitrogen, but they rather responded to the trophic gradient as a whole: responses by macroinvertebrates seem, especially in the analysis of functional groups, complex and difficult to discriminate, highlighting a possible shifting of the food web towards the presence of large carnivores at high trophic status. Regarding the fish, the results show that nitrogen alone does not seem to be an important controlling factor for the fish communities. However together with the phosphorus, is one of the main elements controlling both biomass and size of the fish fauna, as well as the presence of tolerant, omnivorous or benthofagous species. In conclusion, the results of our analysis highlight the need for a greater emphasis on nitrogen inputs, which, especially in cases of nitrogen carried by atmospheric deposition, may even affect lake ecosystems relatively distant from direct impacts of human activities, thus altering the structure of biotic communities. ; A partire dai dati raccolti con le campagne di campionamento effettuate nell?ambito del progetto InHabit, questo documento presenta un?analisi delle relazioni tra le variabili ambientali e gli organismi appartenenti alle quattro comunit? biotiche utilizzate per la definizione della qualit? ecologica degli ambienti lacustri, secondo quanto previsto dal D.Lgs. 260 del novembre 2010, che recepisce la Direttiva Europea sulle Acque 2000/60. I campionamenti sono stati condotti in 13 ambienti lacustri, 7 in Piemonte e 6 in Sardegna. In particolare, lo scopo del lavoro ? stato valutare i possibili effetti sulla comunit? biotiche di concentrazioni variabili dei composti azotati inclusi tra le variabili considerate. La comunit? che mostra le risposte pi? chiare ? quella fitoplanctonica: come risulta dall?analisi multivariata, sia azoto ammoniacale che azoto totale compaiono tra le variabili significative per spiegare l?ordinamento di ordini e specie fitoplanctoniche. Tra questi, sono soprattutto i cianobatteri che aumentano sensibilmente all?aumentare della disponibilit? di azoto ammonicale. Al contrario, elevate concentrazioni di questo composto deprimono lo sviluppo delle diatomee. Altri gruppi algali mostrano una risposta non lineare rispetto ai composti azotati, con una possibile limitazione a bassi livelli di azoto ed una inibizione a livelli troppo elevati. L?analisi della risposta rispetto al gradiente di fosforo totale, mostra che questo nutriente non ? selettivo come l?azoto nel controllare la struttura delle associazioni algali in diverse condizioni ambientali. Le altre comunit? non hanno mostrato una relazione evidente con i composti azotati, ma, piuttosto, con il gradiente trofico complessivo: le risposte evidenziate dalla fauna macroinvertebrata, sembrano, soprattutto nell?analisi dei gruppi funzionali, complesse e difficili da discriminare, evidenziando un possibile spostamento degli equilibri della rete trofica verso i carnivori in presenza di elevati livelli trofici. Relativamente alla fauna ittica, i risultati mostrano che da solo l?azoto non sembra essere un fattore di controllo importante per la comunit? ittiche. Tuttavia insieme al fosforo, ? uno degli elementi principali a cui si associano positivamente la biomassa e le dimensioni della fauna ittica, nonch? la presenza di specie tolleranti, onnivore o bentofaghe. In conclusione, i risultati della nostra analisi, sottolineano ulteriormente la necessit? di porre una maggiore attenzione agli apporti di azoto, che, soprattutto nei casi di azoto veicolato da deposizioni atmosferiche, potrebbero interessare anche ecosistemi lacustri relativamente distanti da impatti diretti delle attivit? antropiche, alterandone la struttura delle comunit? biotiche.