Shoreline vegetation distribution in relation to wave exposure and bay characteristics in a tropical great lake, Lake Victoria

Abstract

Abstract:We investigated the presumption that wind-wave exposure is a major regulator of vegetation distribution within lakes. Along a 675-km stretch of shore in northern Lake Victoria (Uganda), the pattern of vegetation distribution in relation to shoreline features, and the variation of shoreline swamp area along a gradient of wave exposure were examined. The ability of wave exposure, when combined with bay morphometric characteristics, to predict the lakeward limit of vegetation distribution was assessed. Data were collected through a shoreline survey and from maps. Maximum effective fetch, computed from topographic maps, was used as a surrogate for wave exposure. Our results reinforce and amplify the notion that wave exposure is an important regulator of the within-lake distribution of vegetation. We found shoreline plants to either occupy stretches of shore shielded by coastal islands or hidden by convolutions of the lake margin. The area of shoreline swamps declined exponentially with increasing wave exposure. Of the coastal characteristics examined, bay area had the strongest influence on the lakeward expansion of vegetation. Wave exposure acting together with bay area, accounted for 64.4% of the variance in the limit of lakeward vegetation advancement.

Morphometric and biotic variables as potential predictors ofLudwigia sedoides(Humb. & Bonpl.) Hara in a large Amazonian reservoir

“…Therefore, extensive colonization of L. sedoides is expected to occur in littoral areas that are stable and shallow, with low declivity. Fetch (i.e., wind-wave exposure; Azza et al, 2007) was another important variable in explaining the distribution of L. sedoides in Lajeado reservoir. Negative relationships between fetch and macrophyte distribution have been commonly reported, including several species of different life forms (Strand and Weisner, 1996;Rea et al, 1998;Riis and Hawes, 2003;Schutten et al, 2004;Bini and Thomaz, 2005;Azza et al, 2007).…”

“…Fetch (i.e., wind-wave exposure; Azza et al, 2007) was another important variable in explaining the distribution of L. sedoides in Lajeado reservoir. Negative relationships between fetch and macrophyte distribution have been commonly reported, including several species of different life forms (Strand and Weisner, 1996;Rea et al, 1998;Riis and Hawes, 2003;Schutten et al, 2004;Bini and Thomaz, 2005;Azza et al, 2007). Disturbance is mainly mechanical, damaging plants and impairing colonization and development (Schutten et al, 2004;Pierini and Thomaz, 2009).…”

“…The fetch was calculated to evaluate the exposure to wind action, not corrected for wind direction. The calculation was based on Azza et al (2007), but the first vertical line was defined perpendicular to the shore (90x), since the wind direction is variable in Lajeado reservoir. The slope was calculated using three equidistant (2.5 m intervals) measures of depth, taken in each side of the plot (perpendicular to the shore, 6 values in total).…”

Multiple effects of land-use changes impede the colonization of open water in fen ponds

“…The expansion of helophytes that root in the bottom is frequently found to be limited to shallow water (<1–1.5 m), either by light limitation, disturbance from waves, as a consequence of the anoxic environment, or through a combination of these factors (e.g. Mäkelä et al 2004; Azza et al 2006, 2007; Jackson 2006). Based on our study, we cannot specify which of these factors mainly cause the lack of colonization at greater water depths.…”

Post‐dispersal probability of germination and establishment on the shorelines of slow‐flowing or stagnant water bodies

“…They are formed in shallow waters during mesotrophic succession and consist of a meshwork of floating roots and rhizomes (Verhoeven & Bobbink ; Azza et al. ). In Dutch fens, species that colonize open water and induce the formation of such floating mats have become rare (Verhoeven & Bobbink ; Sarneel et al.…”