Ecological dynamics of two remote alpine lakes during ice-free season

Abstract

We studied hydrochemistry and plankton dynamics in two remote alpine lakes: lake Nivolet <em>superiore</em> (2530 m asl) and lake Trebecchi <em>superiore</em> (2729 m asl) in the Gran Paradiso National Park (Western Italian Alps) in summer 2009. The aim of this study was to enhance the understanding of natural ecological dynamics in the pelagic habitat of alpine lakes by enlarging the number of biotic and abiotic variables usually considered to this end and by increasing the frequency of samplings, generally low in remote lakes. During the eight samplings performed in 2009, chemical and physical variables were measured both in situ and in the laboratory. We also followed the dynamics of all the compartments of the naturally simplified trophic chain of the two lakes from pico-prokaryotes to phytoplankton and zooplankton. Our results confirm the oligotrophic, close-to-pristine state of lake Nivolet and lake Trebecchi as they are not affected by hydromorphological alterations, they are naturally fishless and are not sensitive to acidification risk and acidity pulses. On the other hand, the two lakes have distinct abiotic conditions due to their glacial origin and to the lithological composition of their watersheds. We found some differences in the spatial variation of pico-prokaryotes, phytoplankton and zooplankton due to the different mixing regimes and maximum depth of the two lakes. Conversely, temporal patterns were similar in both lakes, related to ecological interactions and to changes in the abiotic conditions. The rapid succession of events in extreme ecosystems, such as the alpine lakes studied here, confirm the predominant role of external environmental factors (<em>e.g.</em> the duration of the ice-free season) and of ecological interactions among different trophic compartments. This research underlines the importance of seasonal niche partitioning among organisms with different size

Ecological impact of transhumance on the trophic state of alpine lakes in Gran Paradiso National Park

“…On the other hand, the concentrations of TN and NO 3 are mainly related to nitrogen atmospheric deposition and are driven by the NO − 3 dynamics (which accounts for 62.2% of the total nitrogen content), even if livestock is an additive source of nitrogen compounds (Ohio State University, 2006). In Northern Italy, nitrogen load due to atmospheric deposition can reach values as high as 15 kg·ha −1 ·y −1 (Rogora et al, 2006), while in this study it was 14.4 kg N·ha −1 ·y −1 (estimated value in 2009 at the sampling station of La Thuile, about 30 km NW of the Gran Paradiso National Park; Tiberti et al, 2013). The TN concentration and the relative proportion of different nitrogen compounds are controlled both by atmospheric N deposition rates, and by catchment features (Marchetto et al, 1994).…”

Ciliate community structure and interactions within the planktonic food web in two alpine lakes of contrasting transparency

“…The copepod C. abyssorum tatricus and rotifers such as P. dolichoptera and Keratella spp. are commonly found in Alpine lakes (Table S3; Tartarotti et al, 1999;Obertegger, Flaim & Sommaruga, 2008;Tiberti et al, 2013). Beside algae, ciliates are also in their food spectrum (Arndt, 1993;Wickham, 1995;Weisse & Frahm, 2002).…”

Recovery of high mountain Alpine lakes after the eradication of introduced brook trout Salvelinus fontinalis using non-chemical methods

“…Amphibians, littoral macroinvertebrates, pelagic zooplankton, chlorophyll-a, nutrient content, and water transparency were used as indicators of the recovery process. Samples and surveys were repeated (from 1 to 8 times per year) in all the study lakes at different times during the ice-free period to account for the strong seasonality governing alpine lakes (Tiberti et al 2013).…”

“…-DAY: an integer variable indicating the number of days elapsed from the 1st of June and accounting for the strong seasonal variations (Tiberti et al 2013).…”