Effect of Drought Conditions on Plankton Community and on Nutrient Availability in an Oligotrophic High Mountain Lake

Figures & data

Table 1 Data compiled in previous studies in La Caldera Lake. TP: total phosphorus, DIN: dissolved inorganic nitrogen, TN: total nitrogen, DIN∶TP (mass ratio), Phy: phytoplankton abundance, B: bacterial abundance, HNF: heterotrophic nanoflagellates abundance, Zoo: zooplankton abundance.

Figure 1 Lake thermal response to 24-hour variations in meteorological conditions during the ice-free period in La Caldera (from June to October of 2005 and 2006). Solid line: temperature registered by a thermistor placed at surface, broken line: temperature registered by a thermistor placed at the bottom. p-values corresponding to differences between surface and bottom temperatures are shown for each year.

Figure 2 Mean water column concentrations of nutrients. (a) Total phosphorus (TP; µg L⁻¹) and soluble reactive phosphorus (SRP; µg L⁻¹); (b) total nitrogen (TN; mg L⁻¹) and dissolved inorganic nitrogen (DIN; mg L⁻¹); and (c) Nitrogen∶Phosphorus mass ratio in summer of 2005 and 2006. Broken line in (c) indicates zones of nutrient limitation for the DIN∶TP from Morris and Lewis (1988). Above the line, DIN∶TP values indicate P-limitation and below the line indicate N-limitation. Significant differences at p < 0.05 between years are indicated with letters. Error bars represent ± standard deviation (SD) of the mean.

Figure 3 Within-year and year-to-year variations in the abundance (a, c) and biovolume (b, c) of bacteria (abundance: 10⁹ cell mL⁻¹; biovolume: 10⁹ µm³ L⁻¹), phytoplankton (abundance: 10⁷ cell mL⁻¹; biovolume: 10⁹ µm³ L⁻¹), HNF (abundance: 10⁷ cell mL⁻¹; biovolume: 10⁸ µm³ L⁻¹), ciliates (abundance: 10³ cell mL⁻¹; biovolume: 10⁸ µm³ L⁻¹), and zooplankton (abundance: ind L⁻¹; biovolume: 10⁸ µm³ L⁻¹) in La Caldera in summers of 2005 and 2006. Significant differences at p < 0.05 between years are indicated with letters. Error bars represent standard deviation (SD).

Table 2 Chlorophyll a concentrations (Chl-a, µg L⁻¹) and Autotrophic:Heterotrophic ratio (A∶H).

Figure 4 Inter-annual variability of (a) maximum depth, (b) accumulated annual rainfall of La Caldera, and (c) relationship between maximum depth and accumulated annual rainfall during the last 20 years. Vertical arrows in (a) and (b) indicate the occurrence of severe droughts (1995, 1999, and 2005), and broken lines in (b) indicate the mean values ± standard deviation of annual precipitation of 1985–2006 period. Data of accumulated annual rainfall were obtained from CETURSA Sierra Nevada, S.A. (management company of Sierra Nevada ski resort).

Figure 5 Winter North Atlantic Oscillation (NAO) index for each period. Boxes  =  standard errors. Whiskers  =  min.−max.

Figure 6 Long-term evolution of (a) DIN∶TP mass ratio; TP, DIN, and TN concentrations (µg L⁻¹) and (b) bacteria (× 10⁵ cell mL⁻¹), phytoplankton (× 10³ cell mL⁻¹), zooplankton (ind L⁻¹), and HNF abundances (× 10² cell mL⁻¹). Error bars represent ± standard deviation (SD) of the mean. Period I: maximum depth > 10 m; Period II: maximum depth ranging from 4 to 10 m, Period III: maximum depth < 4 m. Significant differences at p < 0.05 between periods are indicated with letters.

Figure 7 Scatterplots between DLTM_depth and DLTM for each water quality parameter (TP, TN, Phytoplankton, Zooplankton, Bacteria, and HNF). Solid regression lines are shown for significant relationships while dashed lines are shown for non-significant relationships.

Morris, D. P. and W. M. Lewis . 1988. Phytoplankton nutrient limitation in Colorado mountain lakes. Freshwater Biology 20:315–327.

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