AOBPreview published online on June 2, 2009
Annals of Botany, doi:10.1093/aob/mcp138
Convective gas flow development and the maximum depths achieved by helophyte vegetation in lakes
National Institute of Water and Atmospheric Research, PO Box 8602, Christchurch, New Zealand
* For correspondence. Present address: Department of Biological Sciences, Plant Biology, University of Aarhus, Ole Worms Allé, Building 1135, DK-8000 Århus C, Denmark. E-mail: brian.sorrell{at}biology.au.dk
Received: 3 February 2009 Returned for revision: 19 March 2009 Accepted: 23 April 2009
Background and Aims: Convective gas flow in helophytes (emergent aquatic plants) is thought to be an important adaptation for the ability to colonize deep water. In this study, the maximum depths achieved by seven helophytes were compared in 17 lakes differing in nutrient enrichment, light attenuation, shoreline exposure and sediment characteristics to establish the importance of convective flow for their ability to form the deepest helophyte vegetation in different environments.
Methods: Convective gas flow development was compared amongst the seven species, and species were allocated to ‘flow absent’, ‘low flow’ and ‘high flow’ categories. Regression tree analysis and quantile regression analysis were used to determine the roles of flow category, lake water quality, light attenuation and shoreline exposure on maximum helophyte depths.
Key Results: Two ‘flow absent’ species were restricted to very shallow water in all lakes and their depths were not affected by any environmental parameters. Three ‘low flow’ and two ‘high flow’ species had wide depth ranges, but ‘high flow’ species formed the deepest vegetation far more frequently than ‘low flow’ species. The ‘low flow’ species formed the deepest vegetation most commonly in oligotrophic lakes where oxygen demands in sediments were low, especially on exposed shorelines. The ‘high flow’ species were almost always those forming the deepest vegetation in eutrophic lakes, with Eleocharis sphacelata predominant when light attenuation was low, and Typha orientalis when light attenuation was high. Depths achieved by all five species with convective flow were limited by shoreline exposure, but T. orientalis was the least exposure-sensitive species.
Conclusions: Development of convective flow appears to be essential for dominance of helophyte species in >0·5 m depth, especially under eutrophic conditions. Exposure, sediment characteristics and light attenuation frequently constrain them to a shallower depth than their flow capacity permits.
Key words: Aeration, convective flow, exposure, helophytes, lakes, lakeshore vegetation, light attenuation, redox, regression tree, sediment motion, trophic state, waves
Present address: Aquatic Research Solutions Ltd, Cambridge, New Zealand.