Mechanisms regulating abundance of submerged vegetation in shallow eutrophic lakes

Abstract

Shallow eutrophic lakes tend to be either in a turbid state dominated by phytoplankton or in a clear-water state dominated by submerged macrovegetation. Recent studies suggest that the low water turbidity in the clear-water state is maintained through direct and indirect effects of the submerged vegetation. This study examined what mechanisms may cause a recession of the submerged vegetation in the clear-water state, and thereby a switch to the turbid state. The spatial distribution of submerged vegetation biomass was investigated in two shallow eutrophic lakes in the clear-water state in southern Sweden. Biomass of submerged vegetation was positively correlated with water depth and wave exposure, which also were mutually correlated, suggesting that mechanisms hampering submerged vegetation were strongest at shallow and/or sheltered locations. The growth of Myriophyllum spicatum, planted in the same substrate and at the same water depth, was compared between sheltered and wave exposed sites in two lakes. After 6 weeks the plants were significantly smaller at the sheltered sites, where periphyton production was about 5 times higher than at the exposed sites. Exclosure experiments were conducted to evaluate the effects of waterfowl grazing on macrophyte biomass. Potamogeton pectinatus growth was decreased by grazing, whereas M. spicatum was not affected. The effects were greater at a sheltered than at a wave-exposed site, and also negatively related to distance from the reed belt. These results suggest that competition from epiphytes and waterfowl grazing hamper the development of submerged vegetation at sheltered and/or shallow locations. An increased strength of these mechanisms may cause a recession of submerged vegetation in shallow eutrophic lakes in the clear-water state and thereby a switch to the turbid state.

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

“…3), that is at the point where the resilience of the clearwater state breaks down (the clear-water state ceases to be a basin of attraction). Therefore, herbivory by birds has a synergistic effect with mechanisms that erode the resilience of the clear-water state during eutrophication, in particular shading by phytoplankton and periphyton in the case of freshwater lakes (Weisner et al, 1997;Hilt, 2006;Hidding et al, 2010). For very low nutrient loadings, however, bird impact decreased with increasing nutrient loading.…”

“…It has been hypothesized that the impact of grazing birds on macrophytes varies with the nutrient status of the lake (Perrow et al, 1997;Weisner et al, 1997;Hansson et al, 2010;Bakker & Nolet, 2014). Possible mechanisms for this could be that under eutrophic conditions plants have a higher nutrient content relative to their carbon content, making them more preferred food (Bakker & Nolet, 2014), and that plants have less tolerance to grazing due to increased periphyton growth on the macrophytes (Weisner et al, 1997;Hilt, 2006;Hidding et al, 2010).…”

Allelopathy of Aquatic Autotrophs

“…Members of the genus Myriophyllunz (Haloragaceae) are highly competitive submersed macrophytes (Grace and Wetzel, 1978;Smith and Barko, 1990;Madsen et al, 1991;Weisner et al, 1997). Many studies report their allelopathic activity against algae and cyanobacteria (Fitzgerald, 1969;Planas et al, 198 1;Agami and Waisel, 1985;Saito et al, 1989;Aliotta et al, 1992;Gross et al, 1996;Nakai et al, 2000).…”

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

“…However, with increasing nutrient loading, phytoplankton biomass may increase, creating water turbidity which may result in light limitation and disappearance of submerged macrophytes (Scheffer et al, 1993). However, before the water becomes turbid, there can be direct shading of macrophyte leaves by the accumulation of epiphyton or filamentous algae, which causes macrophyte decline or inhibits their return (Phillips et al, 1978;Weisner et al, 1997;Jones & Sayer, 2003;Roberts et al, 2003;Irfanullah & Moss, 2004;Hilt et al, 2010). Besides the indirect effect of nutrients on macrophyte growth (via light limitation), certain nutrients can be toxic for macrophytes, including ammonium which can be toxic at high concentrations for many macrophyte species (Smolders & Roelofs, 1996), whereas nitrate has been shown to reduce the growth of Chara species (Lambert & Davy, 2011).…”