Effects of Submerged Vegetation on Water Clarity Across Climates

Abstract

A positive feedback between submerged vegetation and water clarity forms the backbone of the alternative state theory in shallow lakes. The water clearing effect of aquatic vegetation may be caused by different physical, chemical, and biological mechanisms and has been studied mainly in temperate lakes. Recent work suggests differences in biotic interactions between (sub)tropical and cooler lakes might result in a less pronounced clearing effect in the (sub)tropics. To assess whether the effect of submerged vegetation changes with climate, we sampled 83 lakes over a gradient ranging from the tundra to the tropics in South America. Judged from a comparison of water clarity inside and outside vegetation beds, the vegetation appeared to have a similar positive effect on the water clarity across all climatic regions studied. However, the local clearing effect of vegetation decreased steeply with the contribution of humic substances to the underwater light attenuation. Looking at turbidity on a whole-lake scale, results were more difficult to interpret. Although lakes with abundant vegetation (>30%) were generally clear, sparsely vegetated lakes differed widely in clarity. Overall, the effect of vegetation on water clarity in our lakes appears to be smaller than that found in various Northern hemisphere studies. This might be explained by differences in fish communities and their relation to vegetation. For instance, unlike in Northern hemisphere studies, we find no clear relation between vegetation coverage and fish abundance or their diet preference. High densities of omnivorous fish and coinciding low grazing pressures on phytoplankton in the (sub)tropics may, furthermore, weaken the effect of vegetation on water clarity.

Restoring macrophyte diversity in shallow temperate lakes: biotic versus abiotic constraints

“…Several studies have reported enhanced water clarity above charophyte vegetation (Scheffer et al, 1994;Hargeby et al, 2007), although this clearing effect is not limited to charophytes (Kosten et al, 2009b). Charophytes can attain high biomass and form dense stands (Blindow, 1992b;Van Nes et al, 2002;Bakker et al, 2010), which may improve the trapping of sediment.…”

Macrophyte effects on algal turbidity in subtropical versus temperate lakes: a reply to Dolman (2014)

“…Re-analysing the data from Canfield Jr et al (1984) cited by Dolman (2014) and suggesting a strong effect of macrophytes in subtropical lakes, we found no significant contribution of submersed macrophytes to increasing the coefficient of determination of Chl a -TP regression and the ratio differed slightly (P = 0.74) between vegetated and non-vegetated lakes with overlapping TP ranges. In conclusion, the only four relevant works on subtropical lakes we could find in literature (Bachmann et al, 2002 andKosten et al, 2009 being the other two) all suggest weaker effects of macrophytes on algal turbidity than in temperate lakes.…”

Effect of a size-selective biomanipulation on nutrient release by gizzard shad in Florida (USA) lakes

“…Thus the influence of fish on nutrient cycles could be greater during warmer seasons and at warmer latitudes. However, biomanipulations may actually be less effective at warmer latitudes because of the longer growing season, increased omnivory and increased risk of algal blooms (Jeppesen et al, 2007, Kosten et al, 2009, which may offset the gains made by fish reductions. Clearly, more research on biomanipulation efforts in tropical and subtropical systems is needed (Jeppesen et al, 2007).…”