Phytoplankton assemblages in North Island lakes of New Zealand: Is trophic state, mixing, or light climate more important?

Abstract

Relationships between phytoplankton assemblages and lake trophic state, mixing regime and light climate were investigated in 40 North Island, New Zealand, lakes. We tested the hypothesis that mixing regime is more important than trophic state or light climate in determining the community composition of phytoplankton assemblages which were represented as presence/ absence of cyanobacteria and diatom genera. Mixing regime, characterised as a function of lake size, more accurately predicted summer phytoplankton composition than indices related to trophic state or light regime. Analysis of similarities indicated distinct differences in phytoplankton assemblages between mixed lakes and those that intermittently or periodically stratify. In mixed lakes, a greater variety of cyanobacteria genera than diatom genera were recorded compared with lakes that stratify stably in summer. Conversely, relatively high numbers of diatom to cyanobacteria genera were found in lakes that stratify compared with mixed lakes. Lakes with different trophic states but similar mixing regimes shared very similar summer phytoplankton assemblages. None of the three variables tested was a good predictor of winter phytoplankton composition. Although phytoplankton biomass may be regulated to a large extent by nutrient status, this study shows that mixing regime plays a more important role in regulating phytoplankton composition than either nutrient status or light climate.

Dynamics of silicon in lakes of the Taupo Volcanic Zone, New Zealand, and implications for diatom growth

“…Observations of phytoplankton species composition in the TVZ lakes (e.g., Vincent et al 1984, Cassie-Cooper 1996, Ryan et al 2006 consistently demonstrate that diatoms dominate during homothermy in winter under conditions of low temperature, low light, high turbulence, and elevated nutrient concentrations. Trolle et al (2011) predicted that a reduced period of winter mixing would occur in a stratified TVZ lake under a future warming climate, together with reductions in the proportion of negatively buoyant diatom populations compared with buoyant cyanoabacteria.…”

“…Diatom populations in many monomictic lakes of the TVZ peak during annual winter mixing (Vincent et al 1984, Ryan et al 2006, coinciding with a period of low temperature and light environments but elevated nutrient concentrations and high turbulence that can maintain cells in suspension (Reynolds 1984, Cassie-Cooper 1996. If nutrients are replete and light is sufficient, then high rates of diatom production may adequately offset losses due to sinking, leading to rapid increases in biomass (Viner and Kemp 1983) or formation of deep chlorophyll maxima composed predominantly of diatoms .…”

Vertical distributions of chlorophyll in deep, warm monomictic lakes

“…Lakes Taupo, Rotoma and Tarawera have low summer mean chlorophyll a (chl a) while values for Lake Rotoiti are relatively high (Table 1), but all are monomictic with winter mixing from late June to early September. The natural seasonal succession of phytoplankton in the four lakes has been documented by Cassie (1978), Vincent (1983), Vincent et al (1984a) and Ryan et al (2006). Diatoms are dominant in winter and spring, while cyanobacteria, chlorophytes and chrysophytes become increasingly abundant in summer and autumn in each of the lakes.…”

“…and Asterionella spp. ; Cassie, 1978), notably at the DCM in Lake Tarawera (Ryan et al, 2006), while Botryococcus sometimes coexists with Aulacoseira granulata in sub-surface samples in Lake Rotoma (Cassie, 1978). Concentrations of NO 3 -N were determined by subtracting NO 2 -N from NO X -N.…”

Are zooplankton invasions in constructed waters facilitated by simple communities?

“…Ryan et al, 2006), or estimated based on either the purpose of the water body (e.g. water reservoirs were assumed to be oligotrophic to mesotrophic) or the surrounding landscape (e.g.…”