INHABIT project

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Home Themes & Results Nutrients (I2) Lakes results - Group of actions I2

Results within actions group I2 for lakes

Lakes - Importance of atmospheric deposition of pollutants

Some pollutants can be emitted into the atmosphere outside the basin of the lake and be carried by atmospheric deposition within the basin itself. These are for examples nitrogen oxides (from traffic and industrial combustions at high temperature), ammonium (from agriculture and livestock, and in part from traffic) and volatile persistent organic micropollutants (POPs). The importance of the atmospheric inputs of nitrogen is particularly evident when the agricultural activities in the catchment are negligible and local pollution sources are controlled.



Lakes - Contribution of atmospheric nitrogen compounds in reference sites

The atmospheric transport of pollutants affects the general framework proposed by the Water Framework Directive, which considers the pathway of pollutants in the river basin only through the waterways. On the contrary, nitrogen, like other volatile pollutants can reach water bodies through atmospheric deposition, even from sources located outside the catchment areas .
The depositions of nitrogen affecting the regions investigated during the project INHABIT were evaluated using the results of the EMEP models (European Monitoring and Evaluation Programme) , resulting from the International Cooperative Programs for the evaluation of the transport of air pollutants, and through the results of analyzes of atmospheric deposition mainly collected in forest sites.
We compared the amount of nitrogen coming to the lakes from point and diffuse sources, through direct deposition on the surface of the lake and through the deposition in the catchment area, taking into account the processes affecting different nitrogen compounds (mineralization, nitrification, denitrification), and microbial and plant uptake.
Results show that the contribution from atmospheric deposition is negligible when direct contributions of nitrogen are strongly present. However, in lakes less affected by local sources, such as Lake Mergozzo, the atmospheric contribution can reach 95 % of the total input of nitrogen to the lake. These results are particularly important for those biological quality elements that can respond directly to an increased concentration of nitrogen: this should be taken into account in the definition of reference conditions; lake considered as a "reference" for the small direct human impact, may in fact be far from reference conditions because of the amount of nitrogen deposition, consequently altering the estimates of the ecological quality ratios.
These results are presented in detail in deliverable I2d6.



Lakes - Response of biological parameters to the concentration of nitrogen

The data collected in the field under the INHABIT project were used to analyze the relationships between environmental variables of the waterbodies and the four biotic communities used for the definition of the ecological quality of lacustrine environments indicated in Annex 5 to the Water Framework Directive.
Sampling was performed in 13 waterbodies, 7 in Piedmont and 6 in Sardinia, to assess the possible effects on biotic communities of varying concentrations of nitrogen compounds.
Phytoplankton was the biological element showing the clearer response. In multivariate analysis , both total nitrogen and ammonium were among the most significant variables in the ordination of phytoplankton taxa: cyanobacteria increased significantly with increasing availability of ammonium. In contrast, low concentration of this compound leads to a better development of diatoms.
Other algal groups show non-linear response to nitrogen levels, with a possible limitation at low levels and an inhibition at higher levels. Compared to total phosphorus, this latter nutrient is not so selective as nitrogen in controlling the structure of algal associations in different environmental conditions.
Other biological elements are not clearly related to nitrogen compounds, but to the overall trophic gradient: for macroinvertebrate fauna, the analysis of functional groups indicates a possible shift towards carnivores in the presence of higher nutrient levels, while for fishes the results show that nitrogen alone does not seem to be a controlling factor, while together with phosphorous it is one of the main elements influencing fish biomass and size, as well as the presence of tolerant species.
These results are presented in detail in deliverable I2d7.



Lakes - Differences in phytoplankton in sites unaffected by direct human pressures , but with different inputs of atmospheric nitrogen

In the INHABIT project, we evaluated the importance of atmospheric deposition of nitrogen compounds for the chemical composition of lake waters and for the composition of biological assemblages.
In the first part of the project we found that in the two investigated regions (Piedmont and Sardinia), the atmospheric deposition of nitrogen compounds is relevant: nitrogen flow from the atmosphere to aquatic and terrestrial ecosystems, however, is much greater in Piedmont than in Sardinia.
Models of nitrogen behavior in forest soils identified a high nitrogen saturation in soils in Piedmont, which leads to a marked release of nitrogen compounds from forest soils to surface water. The level of saturation in Sardinia is smaller, but a significant part of atmospheric nitrogen still reaches surface water.
As the relative importance of atmospheric nitrogen is particularly relevant for sites close to reference conditions, we focused on the effect of different levels of nitrogen in lakes with low content of phosphorus, which are not affected by local pressures and are classified as reference sites or are in ecological conditions similar to reference conditions.
In comparing two natural lakes in Piedmont, low in phosphorus and rich in nitrogen, with two reservoirs in Sardinia lacking of both nutrients, the former were dominated by diatoms, and the latter by dinophytes. In order to verify that the difference was not related to hydromorphological alterations related to the presence of the dam, we also examined oligotrophic reservoirs in Piedmont (also with relatively high levels of N) that were also dominated by diatoms.
Despite the small number of lakes considered, it seems that dinophytes are better adapted to nitrogen-poor environments, probably due to their ability to adopt a heterotrophic metabolism.
These results highlight the need to better define the reference conditions, especially in the Mediterranean areas, suggesting that different lakes, affected by similar trophic pressures, can be dominated by different algal communities, depending on the atmospheric load of nitrogen.
These results are presented in detail in deliverable I2d8.