Effects of Lake-Basin Morphological and Hydrological Characteristics on the

Eutrophication of Shallow Lakes in Eastern China

Presenter ： Jian Huang

Advisor ： Xixi Wang

Date ： 11/14/2014

Jian Huang, Qiujin Xu, Beidou Xi, Xixi Wang, 2014. Effects of lake-basin morphological and hydrological characteristics on the eutrophication of shallow lakes in east China. Journal of Great Lakes Research, 40, 666-674.

China Eastern China

Lake area > 1 km2 2,300+ 700+

1/3The Eastern Area

Outline

Introduction

Materials and methods

Results

Discussion

Shallow lakes are easily shifted to a new trophic state1) dimictic nature (Havens et al., 2001)2) high concentration of suspended solids (Vicente et al., 2012)3) lack of long-term, stable thermal stratification (Verbruggen et al., 2011)4) nutrients migrating from sediments into the water (Søndergaard et al., 1992;

2013)

The Characteristics of Shallow Lakes

Introduction

Thus, water quality [e.g., total nitrogen (TN) and total

phosphorus (TP)] of shallow lakes is sensitive to human

activity as well as to climatic and hydrological conditions.

Introduction

Extensive studies have been conducted to better understand mechanisms of algal blooms in shallow, eutrophic lakes.

Study design included long-term observations of climate change (Spears et al., 2012)site-specific experiments (Roessink et al., 2010)analysis of nutrient cycling and trophic dynamics (Kokfelt et al., 2010)model simulation (Mooij et al., 2010)

These studies have taken into account: climate change (Fragoso Jr et al., 2011) external nutrient load (Sas, 1989)in-lake process (Huang et al., 2009)

For a shallow lake, water quality is susceptible not only to climate change and human activity but also to the size of the lake basin and its hydrological characteristics.

Lake Tai

HR

MYR

LT

Lake Hongze

Lake Chao

Lake Poyang

Lake Dongting

Hukou

Yichang

The objective

The objective of this study was to determine the effects of lake

morphology and hydrology on eutrophication for 90 typical shallow

lakes in eastern China.

We hypothesized that eutrophication of shallow lakes is affected both

by lake-basin morphology and hydrology.

Introduction

• Lake morphological factors: mean and maximum water depth (Zmean and Zmax ) and surface water area (SA).

• Hydrological factors: hydrologic connectivity and drainage characteristics

Variable SymbolSample

SizeMinimum Maximum Mean

Primary ProductionChlorophyll-a (μg/L) Chl-a 68 0.54 43.09 13.38Physical parameters pH pH 83 6.81 9.22 7.85Secchi depth (cm) SD 63 11.2 1652 55.2Dissolved oxygen (mg/L) DO 84 6.02 17.39 9.27

Electrical conductivity (μs/cm) EC 76 0.26 3795 406

Chemical parameters Total nitrogen (mg/L) TN 90 0.19 13.54 1.82Total phosphorus (mg/L) TP 90 0.00 0.65 0.16Ammonia nitrogen (mg/L) NH4-N 90 0.05 9.9 0.68Phosphate (mg/L) PO4-P 68 0.00 0.14 0.06Lake morphology Typical surface area (km2) SA 83 1.5 3841 201Mean depth (m) Zmean 78 0.93 8.4 2.42Maximum depth (m) Zmax 75 1.31 23.5 4.44Relative depth Zrel

[1] 76 0.006 0.255 0.066Hydrology Drainage area (km2) DA 28 21 257,000 25,913Recharge coefficient Rc 28 3.70 197.00 30.77Typical water level (m) Z 37 1.42 33.00 13.43Typical volume (108 m3) V 40 0.10 155.42 11.29Retention time (d) tr 16 18 458 120

Data and preprocessing

Data

Data on Chl-a concentration, physicochemical properties , morphology,

and hydrology for the 90 study lakes were obtained from the Chinese

Research Academy of Environmental Sciences (CRAES) for the period

2008 to 2011.

Lake morphology (SA, Zmean and Zrel) and hydrologic characteristics

were chosen as the independent variables, while Chl-a and nutrient

concentrations (TN and TP) were chosen as dependent variables.

Materials and methods -- classified

Mean depth (Zmean): very shallow = Zmean ≤ 2 m, shallow = Zmean > 2 m)

Surface area (SA): small = SA ≤ 25 km2, large = SA > 25 km2

Relative depth (Zrel)computed as suggested by Köiv et al. (2011),

where Zmax is the maximum water depth.

Morphology

Relative depth

Materials and methods -- classified

Lake Tai

HR

MYR

LT

Lake Hongze

Lake Chao

Lake Poyang

Lake Dongting

Hukou

Yichang

Three groups : middle Yangtze River, Lake Tai and Huaihe River

basins. 30 lakes are hydraulically connected to the river and 60 isolated

from the river.

Hydrology

• Mean depth Zmean was found to negatively affect TN (Fig.b) and TP (Fig.c) concentrations (p-value < 0.03),

• but it had no significant influence on Chl-a (Fig.a) growth (p-value = 0.44).

Results I - Effects of mean depth (Zmean)

R² = 0.0089

0 5

10 15 20 25 30 35 40 45 50

0 1 2 3 4 5 6 7 8 9

Chl

-a C

once

ntra

tion

(µg

L-1

)

Zmean (m)

(a)

R² = 0.1069

0

1

2

3

4

5

6

0 1 2 3 4 5 6 7 8 9

TN

Con

cent

ratio

n (m

g L

-1)

Zmean (m)

(b)

R² = 0.1025

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 1 2 3 4 5 6 7 8 9

TP

Con

cent

ratio

n (m

g L

-1)

Zmean (m)

(c)

Results II- Effects of mean depth (Zmean) and surface area (SA)

Small Large Small Large

0

10

20

30

40

50

DEPTH CLASSAREA CLASS

shallow

Chl

-a C

once

ntra

tion

(μg

L-1)

Very shallowSmall Large Small Large

0

1

2

3

4

5

6

DEPTH CLASSAREA CLASS

shallow

TN

Con

cent

ratio

n (m

g L

-1)

Very shallowSmall Large Small Large

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

DEPTH CLASSAREA CLASS

shallow

TP

Con

cent

ratio

n (m

g L-1

)

Very shallow

(a) (b) (c)

Zmean ≤ 2m, very shallow Zmean > 2m, shallow

SA ≤ 25 km2, small

SA > 25 km2, large

SA ≤ 25 km2, small

SA > 25 km2, large

Chl-a (ug L-1) Fig.a 9 10 20 8

TN (mg L-1) Fig.b 1.2 1.8 0.9 1.1

TP (mg L-1) Fig.c 0.09 0.15 0.05 0.05

• Chl-a (a) tended to increase with increase of Zrel for the lakes with SA ≤ 25 km2, while it tended to decrease with increase of Zrel for the lakes with SA > 25 km2.

• Concentrations of both TN (b) and TP (c) decreased with increase of Zrel regardless of SA.

Results III- Effects of relative depth Zrel

0.05 0.10 0.15 0.20 0.25-5

0

5

10

15

20

25

30

35

40

45

Chl

-a C

once

ntra

tion (μ

g L-1

)

Area = 25km＜ 2 Area 25km＞ 2

0.00 0.02 0.04 0.06 0.08 0.10-5

0

5

10

15

20

25

30

35

40

45

ZrelZrel

0.05 0.10 0.15 0.20 0.25-1

0

1

2

3

4

5

6

TN

Con

cent

ratio

n (m

g L-1

)

Area = 25km＜ 2

0.00 0.02 0.04 0.06 0.08 0.10-1

0

1

2

3

4

5

6

ZrelZrel

Area 25km＞ 2

0.05 0.10 0.15 0.20 0.25-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

TP

Con

cent

ratio

n (m

g L

-1)

Area = 25km＜ 2

0.00 0.02 0.04 0.06 0.08 0.10-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

ZrelZrel

Area 25km＞ 2

(a) (b)

(c)

(1) The TN and TP concentrations were lower in the (Middle Yangtze River) MYR lakes than in the (Lower Yangtze River) LT and (Huaihe River) HR lakes.

(2) The lakes in the lower Yangtze River basin had the highest Chl-a concentrations.

(3) The HR lakes had higher TN and TP concentrations, but it had lower Chl-a concentrations.

Results IV- Effects of lake-river hydraulic connectivity

Lake Tai

HR

MYR

LT

Lake Hongze

Lake Chao

Lake Poyang

Lake Dongting

Hukou

Yichang

Lower TN, TP

Highest Chl-aHigher TN, TP

• As expected, the mean depth, surface area, and electrical conductivity (EC) in the lakes hydrologically connected with rivers were higher than in the isolated lakes,

• while the concentrations of TN, TP, and Chl-a in the lakes isolated from the river were higher than the lakes hydrologically connected with rivers.

Results V - Effects of lake-river hydrologic connectivity

Connected with River(s)?

Numberof Lakes

SA(km2)

Zmean(km2)

EC(μs/cm)

DO(mg/L)

TN(mg/L)

NH4-N(mg/L)

TPmg/L

Chl-a(μg/L)

Connected 30 367 2.56 2778 9.00 1.66 0.49 0.14 12.06

Isolated 60 107 2.33 883 9.41 2.14 0.88 0.18 13.92

• TN and TP were found to decrease with increase of Zmean.

Discussion – lake morphology

Such negative relationships between nutrient levels and water depth are consistent with our common knowledge.

• Chl-a concentration in the lakes with SA >25 km2 and Zmean < 2 m significantly differed from those in the lakes with SA > 25 km2 and Zmean > 2 m.

Thus, Chl-a increase is affected not only by temperature, nutrient concentrations, and light intensity, but it also depends on Zmean and SA because these two variables control the extent of energy needed for vertical mixing and hence the rate of recycling nutrients into the trophogenic production zone (Kolding and Zwieten, 2006).

• Chl-a concentration increased as Zrel increased in the lakes with SA ≤ 25 km2 but the concentration decreased as Zrel increased in the lakes with SA > 25 km2.

Relative depth has widely been used as a surrogate of morphology in assessing limnological characteristics of lakes.

• Both TN and TP were lower in the MYR lakes than in the LT and HR lakes.

Discussion - Drainage characteristics

• The water quality of the lakes hydraulically connected with rivers was better than that the isolated lakes.

Since 1949, the middle and lower Yangtze River basins have lost one-third of their original lake areas to agriculture (Yin and Li, 2001), while many lakes that used to be naturally connected with rivers have become either isolated or dam-controlled.

Lake Dongting Lake Poyang Lake Chao Lake Tai

Connected with River(s)?

Connected Connected Isolated Isolated

Retention time (d) 18 30 210 310

Location Middle Middle Lower Lower

• Compared with well-studied shallow lakes in North America (e.g., Saginaw Bay of Lake Michigan, Lake Erie, and Lake St. Clair the Lakes in the US) and in Europe (azLake Balaton in Europe), our Chinese study lakes have much higher concentrations of TP, TN, and Chl-a.

Discussion - Comparison with other selected shallow lakes

The average TP and TN concentrations in our study lakes are about 3 to 5 times higher than those in Saginaw Bay (Dolan et al., 1978; Dyle, 2012), Lake Erie (Herdendorf and Rockwell, 1983; LEW, 2013), Lake St. Clair (MCM, 2013), and Lake Balaton (EuLakes, 2011; Pintér et al., 2008).

In terms of observed historical trends, from a long-term

perspective, concentrations of TN, TP, and Chl-a all tend

to decrease.

Thank you