Vertical distributions of chlorophyll in deep, warm monomictic lakes
The factors affecting vertical distributions of chlorophyll fluorescence were examined in four temperate, warm monomictic lakes. Each of the lakes (maximum depth >80 m) was sampled over 2 years at intervals from monthly to seasonal. Profiles were taken of chlorophyll fluorescence (as a proxy for algal biomass), temperature and irradiance, as well as integrated samples from the surface mixed layer for chlorophyll a (chl a) and nutrient concentrations in each lake. Depth profiles of chlorophyll fluorescence were also made along transects of the longest axis of each lake. Chlorophyll fluorescence maxima occurred at depths closely correlated with euphotic depth (r 2 = 0.67, P < 0.01), which varied with nutrient status of the lakes. While seasonal thermal density stratification is a prerequisite for the existence of a deep chlorophyll maximum (DCM), our study provides evidence that the depth of light penetration largely dictates the DCM depth during stratification. Reduction in water clarity through eutrophication can cause a shift in phytoplankton distributions from a DCM in spring or summer to a surface chlorophyll maximum within the surface mixed layer when the depth of the euphotic zone (z eu) is consistently shallower than the depth of the surface mixed layer (z SML). Trophic status has a key role in determining vertical distributions of chlorophyll in the four lakes, but does not appear to disrupt the annual cycle of maximum chlorophyll in winter.
KeywordsPhytoplankton Deep chlorophyll maximum Rotorua lakes Fluorescence Non-photochemical quenching
This study was funded through the Foundation of Research, Science and Technology (Contract UOWX0505) and the University of Waikato Lakes Chair supported by Environment Bay of Plenty. KO’B’s participation in this project was supported by research Grants from the School of Engineering, University of Queensland. We acknowledge the assistance of Dennis Trolle in discussions on this manuscript, and George Ganf, Warwick Vincent and Emanuel Boss for reviews.
- Arar EJ, Collins JB (1992) In vitro determination of chlorophyll-a and pheophytin-a in marine and freshwater algae by fluorescence. Method 445.0, National Exposure Laboratory, Office of Research and Development, US Environmental Protection Agency, Washington DCGoogle Scholar
- Bayley SE, Creed IF, Sass GZ, Wong AS (2007) Frequent regime shifts in shallow lakes on the Boreal Plain: Alternative “unstable” states? Limnol Oceanogr 52:2002–2012Google Scholar
- Carpenter SR (2003) Regime shifts in lake ecosystems: pattern and variation: excellence in ecology series, vol 15. Ecology Institute, OlendorfGoogle Scholar
- Hamilton DP (2005) Land use impacts on nutrient export in the Central Volcanic Plateau, North Island. N Z J For 49:27–31Google Scholar
- Huisman J, Thi NNP, Karl DM, Sommeijer B (2006) Reduced mixing generates oscillations and chaos in the oceanic deep chlorophyll maximum. Nature 439:322–325Google Scholar
- Reynolds CS (1997) Vegetation processes in the pelagic: a model for ecosystem theory: excellence in ecology series, vol 9. Ecology Institute, OlendorfGoogle Scholar
- Ryan EF, Hamilton DP, Hall JA, Cassie-Cooper UV (2005) Lake phytoplankton composition and biomass along horizontal and vertical gradients. Verh Int Ver Limnol 29:1033–1036Google Scholar
- Sherman BS, Webster IT, Jones GT, Oliver RL (1998) Transitions between Aulacoseira and Anabaena dominance in a turbid river weir pool. Limnol Oceanogr 43:1902–1915Google Scholar
- Steele JH (1964) A study of production in the Gulf of Mexico. J Mar Res 22:211–222Google Scholar
- Viner AW, White E (1987) Phytoplankton growth. In: Viner AB (ed) Inland waters of New Zealand. Department of Scientific Information and Research Bulletin No. 241, Wellington, pp 191–224Google Scholar