Effects of Sediments Phosphorus Inactivation on the Life Strategies of Myriophyllum spicatum: Implications for Lake Restoration

Zhenmei Lin,Guolong Yu,Baohua Guan,Yishu Fu,Chen Zhong,Zhengwen Liu,Jinlei Yu

doi:10.3390/w13152112

Abstract

Eutrophication often results in the loss of submerged vegetation in shallow lakes and turns the lake to be a turbid state. Recovery of submerged macrophytes is the key in the restoration of shallow eutrophic lakes to create a clear water state. However, internal loading control was considered as the critical process for the recovery of submerged macrophytes in shallow lakes after the external nutrient reduction. Phoslock® (Lanthanum modified bentonite) is a useful passivation material in controlling the internal loadings (release of phosphorus from the sediments), which was applied to restore the eutrophic lakes. However, the effects of Phoslock® on the growth and life strategies of submerged macrophytes are less focused so far. In the present study, we studied the responses in the growth and morphological characteristics of Myriophyllum spicatum to the addition of Phoslock® to the sediments. Our results showed that the addition of Phoslock® significantly decreased the contents of bioavailable forms of phosphorus in the sediments, such as redox-sensitive phosphorus bound to Fe and Mn compounds (BD–P), phosphorus bound to aluminum (Al–P) and organic phosphorus (Org–P). However, the concentration of the non-bioavailable forms of phosphorus in the sediments, such as calcium bound phosphorus (Ca–P), increased significantly in the Phoslock® treatments compared with the controls. At the end of the experiments, the total biomass, aboveground biomass and relative growth rate (RGR) of M. spicatum decreased significantly in the Phoslock® mesocosms compared with the controls. In contrast, the wet root biomass, root–shoot biomass ratio, root numbers and root length of M. spicatum were significantly higher in the Phoslock® treatments than that in the controls. Our results indicated that the growth of M. spicatum was suppressed by the addition of Phoslock®, and thus the biomass was decreased; however, the increase of root biomass might be beneficial to the inhibition of phosphorus release and resuspension of sediments and to the restoration of the lake ecosystem.

Highlights

Introduction conditions of the Creative CommonsThere are two alternative states of equilibrium in shallow lakes, the turbid states dominated by high biomass of phytoplankton and the clear-water state dominated by high coverage of submerged macrophytes [1,2,3]
This may be due to the rich nutrients in the sediments, which can support the high biomass of phytoplankton and induce a low light availability suppressing the growth of submerged macrophytes [19,20,21,22]
We found that the addition of Phoslock® to the sediment reduced the concentration of bioavailable forms of phosphorus in the sediments

Summary

Introduction

Introduction conditions of the Creative CommonsThere are two alternative states of equilibrium in shallow lakes, the turbid states dominated by high biomass of phytoplankton and the clear-water state dominated by high coverage of submerged macrophytes [1,2,3]. The recovery of submerged macrophyte communities has become crucial in stabilizing a clear-water state of shallow lakes [12,13,14]. The natural recovery of the submerged macrophytes community shows a delayed response to the external loading reductions [17,18,19]. This may be due to the rich nutrients in the sediments (internal loading), which can support the high biomass of phytoplankton and induce a low light availability suppressing the growth of submerged macrophytes [19,20,21,22]. In the last two decades, transplantation of submerged macrophytes was conducted to enhance the establishment of submerged macrophyte communities in subtropical and tropical shallow lakes, especially in China [12,23,24,25]

Methods

Discussion

Conclusion