The role of submerged macrophytes in the regulation of internal nitrogen and phosphorus release
Jing Wan (Wuhan University, PR China; Hubei Academy of Environmental Sciences , PR China), Hong Peng, Xu Zhang, Wanshun Zhang* , Xiaomin Chen (Wuhan University, PR China)

Materials and Methods

5ControlV treatment
M treatment(a)Control
V treatment
M treatment(a)204TNs (g/kg)

18TNw (mg/L)

32161412

1051015202530035

5101520253035

Time (d)Time(d)0.32(b)2.0Control
V treatment
M treatment

0.28

ControlV treatment
M treatment

(b)

0.24
1.50.20TPs (g/kg)

In aquatic systems, excessive N and P often leads to rapid production of phytoplankton thus deteriorates thewater quality. Reducing the external N and P loading could not always render a prompt recovery fromeutrophication, as in some cases, N and P stored in sediment as the internal source would become main sources
for eutrophication. Such delayed responses typically stem from the positive feedback between internal N and P
release, which highlights the importance of internal N and P releasing processes at the water-sediment interface.
Sediment is vital in determining the concentration and vertical transport of N and P. Internal cycling
involves the movement of N and P into or out of the sediment as a result of biological, physical and chemical
processes that are affected by factors including temperature, redox conditions, pH, dissolved oxygen, sedimentresuspension and benthic biological community. Nitrogen and phosphorus deposition may be remineralized as
inorganic N and P and released to pore water, which can flux out into overlying water.
Nitrogen and phosphorus can be released from sediment through a variety of mechanisms. Among several
possible processes, N and P release at the water-sediment interface in the regulation of submerged macrophytes isimportant, and further research is needed to clarify how N and P release from sediment affected by submerged
macrophytes. In this study, we aim to have a better understanding of sediment N and P release under the growthof submerged macrophytes.

Results

TPw (mg/L)

Introduction

0.16
0.12

1.0

0.08
0.04

Microcosms and Experimental Design

0.00

0.5

051015202530350Time(d)To have a better understanding of N and P release processes under the growth of submerged macrophytes, Nand P release simulation was conducted in microcosms. Two commonly used submerged macrophytes ineutrophicated water purification in China, V. natans and M. verticillatum, were selected as the experimentalplants. Sediment and overlying water used in the ecological microcosm experiment were collected from Xinghu
Lake in Wuhan University, China (30°31'47″N, 114°21'10″E).
Filling 72 L 1.2-cm-thick glass tanks with 20-cm-thick sediment. Black cloths were wrapped around the glasstanks to exclude light from the tanks’ sides. The collected water was fully mixed and slowly added to the glasstanks until the water depth reached 35 cm, respectively. Leave the microcosms for 48 hours to be stabilized
before planting. Before transplanted into glass tanks, plants of these two submerged macrophytes were washedcarefully with water to remove impurities and then transplanted in glass tanks, separately. The average height ofthese submerged macrophytes was about 20 cm. The ecological microcosm experiment was conducted with andwithout submerged macrophytes. Three treatments were designed which included the control (without planting
submerged macrophytes), V treatment (treatment with V. natans) and M treatment (treatment with M.
verticillatum). Each treatment had three replicates.
To simulate outdoor temperature, the ecological microcosm experiment was conducted under laboratory
conditions without any artificial heat preservation. Glass tanks were placed in the greenhouse of the College ofResources and Environmental Science, Wuhan University, China.

Sample Collection and Analysis

Table 1. The average N and P release rates at the watersediment interface during the ecological microcosm
experiment.
Average release rate

Treatment

VariableControl

RN-2.25

RP-0.26

RN-15.81

RP-1.38

RN-10.02

RP-1.37

M treatment

1015

2025

3035

Time (d)Figure 1. Temporal variations of (a) total nitrogenconcentrations in overlying water (TNw) and (b) total
phosphorus concentrations in overlying water (TPw) during
the ecological microcosm experiment (mean ± SD, n=3).

V treatment5(mg∙m-2∙d-1)

Note: RN-N release rates at the water-sediment interface;
RP-P release rates at the water-sediment interface .

Water samples were collected at intervals of 5 cm, 15 cm and 30 cm at equal volume (10 mL). In order toprevent the sediment disturbance, sediment samples were collected by a sediment core sampler with 2-cmdiameter cross section. The average height of V. natan and M. verticillatum was measured by tape when water andsediment sampled.

Conclusions✓TN and TP concentrations in overlying water and sediment decreased under the effect of V. natans and M. verticillatum. The study revealed that the decreased
release rates of N and P would be presented under the growing of submerged macrophytes.
✓ The RN and RP in all treatments were negative, and the descending order of their absolute values was V treatment, M treatment and control.

Figure 2. Temporal variations of (a) total nitrogen concentrations
in sediment (TNs) and (b) total phosphorus concentrations insediment (TPs) during the ecological microcosm experiment(mean ± SD, n=3).

➢TNw in the control were higher than that in the V andM treatments. TNw in the V treatment at the end of theecological microcosm experiment were lower than thatin the M treatment. TPw in the control fluctuated, andthat in the V and M treatments increased in the first 4
days and then decreased rapidly. TPw were significantly
reduced at the effect of submerged macrophytes.
➢TNs and TPs were significantly influenced by thetreatments (P < 0.05). TNs and TPs were reduced withthe presence of V. natans and M. verticillatum, whose
values were arranged as M treatment < V treatment <control. TNs and TPs in the V and M treatments had agradually decreased trends over time.
➢The absolute values of RN and RP in the V and M
treatments were obviously larger than that in the control,
and arranged in the order of V treatment > M treatment> control. Thus, V. natans and M. verticillatum which
are mainly wetland plants can accelerate the depositionof N and P in overlying water, and have differences incontrolling internal N and P release.

References
Lu, J.; Bunn, S.E.; Burford, M.A. 2018, Science of The Total
Environment.
Diepens, N.J.; Arts, G.H.P.; Focks, A.; Koelmans, A.A. 2014,
Environmental Science & Technology* Corresponding author. Tel.: +86 13971480859, E-mail: wszhang@whu.edu.cn