Habitat-specific metabolism and nutrient limitation within an oligotrophic Patagonian lake

In this study, we quantify the differences in gross primary production (GPP), respiration (R), and algal nutrient limitation (nitrogen and phosphorus) in the littoral and pelagic habitats of an oligotrophic Patagonian lake (southern South America). We used submerged high frequency sensors that measure light, temperature, and dissolved oxygen and wind data to calculate GPP and R in both lake habitats. In addition, we carry out nutrient enrichment bioassays with nitrate, ammonium, and phosphate to determine which nutrient(s) limit algal growth in each lake habitat. On average, the productivity rate was 7.2 times higher at the epi-littoral (32.0 to 5.3 mmol O2 m-2 d-1) relative to the epi-pelagic (4.1 to 1.3 mmol O2 m-2 d-1). Algal growth in the littoral habitat was limited by nitrate and ammonium, while the pelagic habitat was co-limited by nitrogen (nitrate or ammonium) and phosphorus. Our work demonstrates that the littoral habitat of a Patagonian oligotrophic lake is more productive than the pelagic habitat and that the nutrients limiting algal growth in both habitats are different. These results underscore habitat variations and their significance in shaping the lake's trophic dynamics for the first time in the southern hemisphere.