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

Abstract

Although many lake restoration projects have led to decreased nutrient loads and increased water transparency, the establishment or expansion of macrophytes does not immediately follow the improved abiotic conditions and it is often unclear whether vegetation with high macrophyte diversity will return. We provide an overview of the potential bottlenecks for restoration of submerged macrophyte vegetation with a high biodiversity and focus on the biotic factors, including the availability of propagules, herbivory, plant competition and the role of remnant populations. We found that the potential for restoration in many lakes is large when clear water conditions are met, even though the macrophyte community composition of the early 1900s, the start of humaninduced large-scale eutrophication in Northwestern Europe, could not be restored. However, emerging charophytes and species rich vegetation are often lost due to competition with eutrophic species. Disturbances such as herbivory can limit dominance by eutrophic species and improve macrophyte diversity. We conclude that it is imperative to study the role of propagule availability more closely as well as the biotic interactions including herbivory and plant competition. After abiotic conditions are met, these will further determine macrophyte diversity and define what exactly can be restored and what not.

The dispersal capacity of vegetative propagules of riparian fen species

“…Especially because the colonisation of fen banks and ponds by seeds is often hampered, either because the propagule bank does not contain many species (Sarneel, 2010;Bakker et al, 2012) or because germination and establishment are hampered (Sarneel & Soons, 2011).…”

The impact of bird herbivory on macrophytes and the resilience of the clear-water state in shallow lakes: a model study

“…Some studies found that herbivory by birds decreased macrophyte biomass severely, even up to 100% (Sondergaard et al, 1996;Hilt, 2006;Wood et al, 2012;Bakker & Nolet, 2014), while others found that the removed biomass is compensated by macrophyte regrowth (Mitchell & Wass, 1996;Perrow et al, 1997;Hansson et al, 2010). This apparent contradiction may arise from the varying conditions under which these studies have been conducted, such as the macrophyte and the bird species under consideration, or the experimental set-up (Perrow et al, 1997;Bakker et al, 2013). A recent meta-analysis of all available field studies demonstrated that the impact of herbivory by birds on aquatic plants increases with bird biomass density, offering the first proof that birds systematically reduce macrophyte biomass when present at sufficient densities (Wood et al, 2012).…”

The role of charophytes in a Mediterranean pond created for restoration purposes

“…The relationships between charophytes (as submerged macrophytes) and microalgae include a set of known mechanisms, such as competition for inorganic nutrients (Mulderij et al, 2007), allelopathy in both directions (van Donk and van de Bund, 2002;Pflugmacher, 2002), light limitation (Scheffer et al, 1993;Arthaud et al, 2012) and the consequence of shifts in both the size structure and functional roles of the plankton (Bakker et al, 2013), e.g., a decrease in non-edible cyanobacterial filaments (Rojo et al, 2013). Moreover, macrophyte beds offer zooplankton a refuge from fish predation (Burks et al, 2002;Carpenter et al,1985).…”