Depth Distribution and Biomass of Submersed Aquatic Macrophyte Communities in Relation to Secchi Depth

Abstract

Using original data from eight lakes in southern Quebec and literature values from other fakes throughout the world, regression models were developed that allow prediction of the maximum depth of macrophyte colonization (z_c) for angiosperms ((z_c)^0.5 = 1.33 log (D) + 1.40), bryophytes (z_c)−^0.5 = −0.48 log (D) + 0.81), and charophytes (log (z_c) = 0.87 log (D) + 0.31) and the depth of maximum angiosperm biomass (z_b)(z_b^0.5 = 0.54 log (D) + 1.15) from mean summer Secchi depth (D). Irradiance over the growing season at the maximum depth of colonization was about 1800 J/cm² (1 cal/cm² = 0.239 J/cm²) for angiosperms and bryophytes and 1200 J/cm² for charophytes. These values represent, on average, 21 and 11% of the photo-synthetically available radiation incident on the water surface. Changes in maximum angiosperm biomass were, however, not correlated with Secchi depth. This suggests that while the depth distribution of aquatic macrophyte communities is primarily controlled by irradiance, environmental parameters other than irradiance and nutrients are also important in determining maximum angiosperm biomass in individual lakes.