Importance of horizontal heterogeneity of lake morphometry in modeling algal production and biomass

To explore the importance of the horizontal component of lake morphometry in modeling algal production and biomass, we developed a 2D-approximation of a 3D-model of a radially symmetric, cone-shaped lake and compared it with its 1D-analog, i.e. a flat-bottomed, cylindrical lake of identical mean depth.  The model consists of coupled reaction-diffusion partial differential equations and considers mineral nutrients and light as potentially limiting to algal growth. When compared across a 5-dimensional parameter space covering a wide range in lake area and depth, water clarity, nutrient content and vertical mixing intensity, outcomes from the 2D- and 1D-models at the whole lake scale differ as a rule, the most common deviations being that the 1D-model underestimates the biomass of benthic algae and overestimates the biomass of pelagic algae. Moreover, the horizontally sloping bottom topography produces phenomena that are not possible in 1D, and which depend on other physical properties such as water clarity and lake depth. For example, in shallow, clear lakes pelagic algal biomass decreases and benthic algal biomass increases with lake area, whereas in less transparent and deeper lakes, the opposite can be observed, potentially leading to a switch from benthic to pelagic algal dominance along a gradient of increasing lake size. These findings highlight the importance of considering horizontal heterogeneity in lake ecosystems and emphasize the need for higher dimensional modeling approaches to accurately capture the complex influence of abiotic factors on algal dynamics.

Presentation Preference: Oral

Primary Presenter: Hugo Harlin, Umeå University (hugo.harlin@umu.se)

Authors:

Hugo Harlin, Umeå University  (hugo.harlin@umu.se)

Karl Larsson, Umeå University  (karl.larsson@umu.se)

Sebastian Diehl, Umeå University  (sebastian.diehl@umu.se)