Inter‐ and intra‐annual variability in the phytoplankton community of a high mountain lake: the influence of external (atmospheric) and internal (recycled) sources of phosphorus

Abstract

1. The inter‐ and intra‐annual changes in the biomass, elemental (carbon (C), nitrogen (N) and phosphorus (P)) and taxonomical composition of the phytoplankton in a high mountain lake in Spain were studied during 3 years with different physical (fluctuating hydrological regime) and chemical conditions. The importance of internal and external sources of P to the phytoplankton was estimated as the amount of P supplied via zooplankton recycling (internal) or through ice‐melting and atmospheric deposition (external). 2. Inter‐annual differences in phytoplankton biomass were associated with temperature and total dissolved phosphorus. In 1995, phytoplankton biomass was positively correlated with total dissolved phosphorus. In contrast, the negative relationship between zooplankton and seston biomass (direct predatory effects) and the positive relationship between zooplankton P excretion and phytoplankton biomass in 1997 (indirect P‐recycling effects), reinforces the primary role of zooplankton in regulating the total biomass of phytoplankton but, at the same time, encouraging its growth via P‐recycling. 3. Year‐to‐year variations in seston C : P and N : P ratios exceeded intra‐annual variations. The C : P and N : P ratios were high in 1995, indicating strong P limitation. In contrast, in 1996 and 1997, these ratios were low during ice‐out (C : P < 100 and N : P < 10) and increased markedly as the season progressed. Atmospheric P load to the lake was responsible for the decline in C : P and N : P ratios. 4. Intra‐annual variations in zooplankton stoichiometry were more pronounced than the overall differences between 1995 and 1996. Thus, the zooplankton N : P ratio ranged from 6.9 to 40.1 (mean 21.4) in 1995, and from 10.4 to 42.2 (mean 24.9) in 1996. The zooplankton N : P ratio tended to be low after ice‐out, when the zooplankton community was dominated by copepod nauplii, and high towards mid‐ and late‐season, when these were replaced by copepodites and adults. 5. In 1995, the minimum demands for P of phytoplankton were satisfied by ice‐melting, atmospheric loading and zooplankton recycling over 100%. In order of importance, atmospheric inputs (> 1000%), zooplankton recycling (9–542%), and ice‐melting processes (0.37–5.16%) satisfied the minimum demand for P of phytoplankton during 1996 and 1997. Although the effect of external forces was rather sporadic and unpredictable in comparison with biologically driven recycle processes, both may affect phytoplankton structure and elemental composition. 6. We identified three conceptual models representing the seasonal phosphorus flux among the major compartments of the pelagic zone. While ice‐melting processes dominated the nutrient flow at the thaw, biologically driven processes such as zooplankton recycling became relevant as the season and zooplankton ontogeny progressed. The stochastic nature of P inputs associated with atmospheric events can promote rapid transitional changes between a community limited by internal recycling and one regulated by external load. 7. The elem...

The interaction of phytoplankton and bacteria in a high mountain lake: Importance of the spectral composition of solar radiation

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“…There are no visible inlets or outlets, and the drainage basin area : lake surface area ratio was 7.3 in both years (Villar-Argaiz et al 2001). Inputs of allochthonous organic C are negligible and largely restricted to the ice-melting period.…”

“…The balance between new and regenerated production tends to shift toward regeneration as the season progresses. Macrophytes, littoral vegetation, and fish are absent, and the pelagic community is relatively simple (Carrillo et al 1996a;Reche et al 1996;Medina-Sán-chez et al 1999;Villar-Argaiz et al 2001, 2002.…”

Roles of phosphorus and ultraviolet radiation in the strength of phytoplankton‐zooplankton coupling in a Mediterranean high mountain lake

“…Our results also match observations of phytoplankton blooms after strong occurrences of atmospheric P inputs in these lakes, which did not translate into higher zooplankton accrual (see fig. 6 in Villar-Argaiz et al 2001). Hence, the combination of greater atmospheric depositions (favoring phytoplankton development) and high UV irradiance (constraining zooplankton growth) in Mediterranean high mountain lakes would not positively affect the development of herbivores, consequently weakening PZC.…”

Response of the Phytoplankton Community in an Alpine Lake to Drought Conditions: Colorado Rocky Mountain Front Range, U.S.A

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