| Title | Lake Orta chemical status 25 years after liming: Problems solved and emerging critical issues |
| Abstract | Lake Orta, located in Piedmont, northwestern Italy, has been severely affected by industrial pollution since the 1930s. A successful liming intervention, performed in 1988-1990, returned pH levels in the lake to neutrality, and accelerated the reduction of aqueous trace metal concentrations. In this paper, we present an update knowledge of the chemical status of Lake Orta, focusing on the data collected from 1990 to 2014. In this period we sampled the lake at its deepest point (Qualba station), on a monthly (1990-2000) or seasonal (since 2001) basis. Samples were collected at nine depths through the water column, and analyzed for pH, conductivity, alkalinity, major ions, nutrients, and trace metals. Collectively, these data allowed us to evaluate the long-term response of the lake to the restoration treatment, with particular regard to its acid-base status; they also provided insights into emerging or potential critical issues, including eutrophication and re-suspension of trace metals that still linger in the lake. Furthermore, the evaluation of the present chemical condition of the lake is a precondition for any successive restoration measure, such as fish introduction. The recent data confirmed the lake's water quality has recovered, i.e. returned to a pre-pollution chemical state. Lake water values of pH and concentrations of ammonium, sulphate and base cations have stabilized. Alkalinity and nitrate concentrations are also expected to reach stable level in the next few years. Levels of nitrate, reactive silica, and phosphorus compounds are now regulated by algal uptake, providing indirect evidence of a partial biological recovery. For instance, both the inter-annual average decline and the reappearance of a seasonal signal in silica confirmed the presence of a stable diatom community. The lake is presently oligotrophic, and concentrations of both N and P compounds are steady and low throughout the year. However, a monthly check of nutrient levels of the lake and inflowing waters is recommended. The monitoring of base chemical variables, major ions and trace metals should be maintained to assess the overall status of the ecosystem in response to various drivers, including climate change. |
| Source | Journal of limnology (Testo stamp.) 75, pp. 93–106 |
| Keywords | Acidification recovery; long-term trends; monitoring; trace metals; nutrients; LTER |
| Journal | Journal of limnology (Testo stamp.) |
| Editor | Istituto per lo Studio degli Ecosistemi., Verbania Pallanza, Italia |
| Year | 2016 |
| Type | Articolo in rivista |
| DOI | 10.4081/jlimnol.2016.1320 |
| Authors | Rogora M.; Kamburska L.; Mosello R.; Tartari G. |
| Text | 381413 2016 10.4081/jlimnol.2016.1320 Scopus 2 s2.0 84964911244 Acidification recovery; long term trends; monitoring; trace metals; nutrients; LTER Lake Orta chemical status 25 years after liming Problems solved and emerging critical issues Rogora M.; Kamburska L.; Mosello R.; Tartari G. National Research Council, Institute of Ecosystem Study, Largo Tonolli 50, Verbania Pallanza, 28922, , Italy Lake Orta, located in Piedmont, northwestern Italy, has been severely affected by industrial pollution since the 1930s. A successful liming intervention, performed in 1988 1990, returned pH levels in the lake to neutrality, and accelerated the reduction of aqueous trace metal concentrations. In this paper, we present an update knowledge of the chemical status of Lake Orta, focusing on the data collected from 1990 to 2014. In this period we sampled the lake at its deepest point Qualba station , on a monthly 1990 2000 or seasonal since 2001 basis. Samples were collected at nine depths through the water column, and analyzed for pH, conductivity, alkalinity, major ions, nutrients, and trace metals. Collectively, these data allowed us to evaluate the long term response of the lake to the restoration treatment, with particular regard to its acid base status; they also provided insights into emerging or potential critical issues, including eutrophication and re suspension of trace metals that still linger in the lake. Furthermore, the evaluation of the present chemical condition of the lake is a precondition for any successive restoration measure, such as fish introduction. The recent data confirmed the lake s water quality has recovered, i.e. returned to a pre pollution chemical state. Lake water values of pH and concentrations of ammonium, sulphate and base cations have stabilized. Alkalinity and nitrate concentrations are also expected to reach stable level in the next few years. Levels of nitrate, reactive silica, and phosphorus compounds are now regulated by algal uptake, providing indirect evidence of a partial biological recovery. For instance, both the inter annual average decline and the reappearance of a seasonal signal in silica confirmed the presence of a stable diatom community. The lake is presently oligotrophic, and concentrations of both N and P compounds are steady and low throughout the year. However, a monthly check of nutrient levels of the lake and inflowing waters is recommended. The monitoring of base chemical variables, major ions and trace metals should be maintained to assess the overall status of the ecosystem in response to various drivers, including climate change. 75 Published version http //www.scopus.com/record/display.url eid=2 s2.0 84964911244 origin=inward Acidification recovery; long term trends; monitoring; trace metals; nutrients; LTER pdf 1320 6629 3 PB.pdf Articolo in rivista Istituto per lo Studio degli Ecosistemi. 1129 5767 Journal of limnology Testo stamp. Journal of limnology Testo stamp. J. limnol. Testo stamp. Journal of limnology. Testo stamp. lyudmilatodorova.kamburska KAMBURSKA LYUDMILA TODOROVA michela.rogora ROGORA MICHELA rosario.mosello MOSELLO ROSARIO gabriele.tartari TARTARI GABRIELE |
