Optimum water depth threshold in reed marsh areas ...

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Procedia Environmental Sciences 8 (2011) Procedia Environmental Sciences 13 1846–1852 (2012) 1820 – 1826

Procedia Environmental Sciences www.elsevier.com/locate/procedia

The 18th Biennial Conference of International Society for Ecological Modelling

Optimum water depth threshold in reed marsh areas of the Yellow River Delta, China Y.Y. Huaa, B.S. Cuia, W.J. Hea, Y.L. Liub a

State Key Joint Laboratory of Environmental Simulation and Pollution Control, School of Environment, Beijing Normal University,19 Xinjiekouwai Street, Haidian District, Beijing, 100875, China b Yellow River Delta National Nature Reserve, Dongying Shandong, 257091, China

Abstract Optimum water depth is critical for wetland restoration as it directly influences the distribution, growth and adaptability of wetland vegetation, community structure, and water bird habitat selection. Reed marshes are the main habitats for water birds, especially for the endangered oriental stork Ciconia boyciana in the Yellow River Delta, China. In this study, we determined the optimum water depth threshold based on: (1) the ecological adaptability of the reed Phragimtes australis along the water gradient of the delta and (2) the preferences of C. boyciana for specific habitat characteristics in different seasons, from March to October 2009. The results showed that the optimum water depth thresholds in areas with shallow water and dry land are [0, 5.7] cm and [-1.3, 0] cm in spring, [5, 29.8] cm and [-3.7, 0] cm in summer, and [3.3, 27.5] cm and [-7.7, -3.1] cm in fall, respectively. Our data indicate that future studies should focus on optimum water level and water volume thresholds as practical measures for wetland restoration and protection.

© 2011 Published by Elsevier B.V. Selection and/or peer-review under responsibility of School of © 2011 Published by Elsevier Ltd. Environment, Beijing Normal University. Open access under CC BY-NC-ND license. Keywords: optimum water depth, ecological adaptability, Phragimtes australis, Ciconia boyciana, habitat selection, Yellow River Delta

1. Introduction As the degradation and disappearance of wetlands intensifies, wetland restoration has become a top priority. Water depth (or water level) and its fluctuation are critical parameters in wetland restoration and

* Corresponding author. Tel.: +86-010-58802079; fax: +86-010-58802079 E-mail address: [email protected]

1878-0296 © 2011 Published by Elsevier B.V. Selection and/or peer-review under responsibility of School of Environment, Beijing Normal University. Open access under CC BY-NC-ND license. doi:10.1016/j.proenv.2012.01.175

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protection [1-3] because they directly influence the community structure and distribution, growth and adaptability of wetland vegetation [4-6], which are significant factors affecting water bird habitat selection [7, 8]. Studies have focused on the relationship between vegetation and water depth to determine the optimum threshold for wetland restoration activities [9-12]. However, less emphasis has been given to the influence of seasonal changes on vegetation and water bird habitat preferences. Therefore, there is an urgent need to determine the impact of optimum water depth on both vegetation and water bird adaptation to design improved water restoration strategies. Reed marshes are the main habitats for water birds, especially for the oriental stork, Ciconia boyciana, in the Yellow River Delta, China. Phragimtes australis is the dominant reed species, and its coverage and height, which is affected by water depth, are important factors in C. boyciana habitat selection. Previous studies have shown that the nest positions and habitat types of C. boyciana varied among seasons and were affected by the variation of environmental factors, including water depth, the height and coverage of P. australis, etc [13, 14]. However, fewer studies could provide direct guidance to managers in wetlands restoration and protection activities because of lacks of quantitative water depth threshold. Therefore, there is a need to further study on determination of optimum water depth threshold. The objective of this study is to determine the seasonal optimum water depth threshold based on the integrated analysis of ecological adaptability of P. australis along water depth gradient and the habitat preference of C. boyciana. 2. Materials and methods 2.1. Study area Yellow River Delta is located in the estuary of the Yellow River in Dongying City, Shandong Province (see Fig. 1). It is of temperate continental monsoon climate. The frost–free period, the average annual temperature, average annual precipitation and average annual evaporation are196 days, 12.1℃, 551.6 mm and 1962 mm, respectively. Fertile soil formed from the abundant sediments carried by the Yellow River provides appropriate conditions for the growth of various plant species. However, due to severe salinization and habitat destruction caused by a decrease in the annual runoff of the Yellow River from 1980 to 2002, the vegetation communities have followed reverse succession. With the objective of habitat improvement, an ecological restoration project was implemented by Dawenliu Management Station (37°44'15.78'', 119°03'07'), which is attached to the Yellow River Delta Natural Reserve (YRDNR) (see Fig. 1). The YRDNR restoration project contains two parts: the Wuwanmu Restoration Area (WRA) implemented in 2002 and the Shiwanmu Restoration Area (SRA) implemented in 2006. The study area is located in WRA, covering 5480000 m2. Its dominant vegetation is the water reed P australis, which is also the most favorable habitat for the endangered water bird C. boyciana. The germination, growth and maturity periods for P. australis are in April (i.e., spring), from May to September (i.e., summer) and mid-October (i.e., fall). This distribution is in accordance with the water bird’s activities: migration in spring and fall and breeding/nesting in the summer. 2.2. Data collection and analysis Field monitoring was carried out every month from March to October 2009 in the indicated study area. 9 line transects were set along the water depth gradient (see Fig. 1). Within each line transect, three 1 m × 1 m sampling spots at intervals of 200 m were arranged and the total number of sampling spots is 207. At each sampling spot, we measured water depth and vegetation height by self-braking steel tape rule (Ref), geographic position by GPS (Version: GARMIN eTrex Venture), and the coverage of P. australis. The

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collected records from the three sampling spots were averaged to represent the monthly characteristic of each spot. We then averaged the monthly data from March to May, June to August, and September to October 2009 to obtain the seasonal data of spring, summer and fall, respectively. The relationships between the ecological characteristics (height or coverage) and water depth in the different seasons were determined using regression analysis in Microsoft Excel 2010. The optimum water depth thresholds were the intersection of thresholds that determined based on preferences of the height and coverage of P. australis, respectively.

Dawenliu Management Station

Dongying Jinan

Current river Ancient river

37.755

Wuwanmu restoration area 0

Shiwanmu restoration area

240km

37.75

Edge of reserve area Bo ha iS - 3m

ea

37.745

iso b a th

37.74

37.735

37.73

119.02

119.025

119.03

119.035

119.04

Figure 1. Location of the study area and monitoring points

3. Results and discussions 3.1. Growth of P. australis in shallow water Figs. 2, 3 and 4 show the relationship between water depth and either coverage or height of P. australis in shallow water areas in spring, summer and fall, respectively. The coverage of P. australis in shallow water reached their maximum values of 53% in spring, 67% in summer and 62% in fall at a water depth of 0 cm, 14 cm and 11 cm, respectively. The height of P. australis in shallow water reached their maximum values of 86 cm in spring, 140 cm in summer and 157 cm in fall at a water depth of 6 cm, 12 cm and 9 cm, respectively. 120

y = -0.0003x4 + 0.0257x3 - 0.49x2 - 0.1975x + 53.681 R² = 0.7592

60 50 40 30 20 10

4

3

2

y = -0.001x + 0.0701x - 1.6925x + 12.955x + 55.738 2

100

Height（cm）

Coverage（%）

70

R = 0.6724

80 60 40 20

0 0

5

10 15 20 Water depth（cm）

(a)

25

30

0 0

5


(b)

25

30


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Figure 2. The relationship between water depth and (a) coverage or (b) height of P. australis in shallow water areas in the spring season. 100

y = -2E-05x4 + 0.0062x3 - 0.4434x2 + 8.9566x + 9.5015 2

R = 0.5744 Height（cm）

Coverage（%）

80 60 40 20 0 0

10

20

30 40 Water depth（cm）

50

200 180 160 140 120 100 80 60 40 20 0

y = -0.0001x4 + 0.0204x3 - 1.019x2 + 15.799x + 66.194 R² = 0.6825

0

60

10


50

60

(a) (b) Figure 3. The relationship between water depth and (a) coverage or (b) height of P. australis in shallow water areas in the summer season. 90

y = -0.0003x4 + 0.0315x3 - 1.1858x2 + 16.256x - 9.4231 R² = 0.6799

80

Height（cm）

Coverage（%）

70 60 50 40 30 20 10 0 0

10

20 Water depth（cm）

30

40

220 200 180 160 140 120 100 80 60 40 20 0

4

3

2

y = -0.0013x + 0.124x - 3.9074x + 44.749x - 11.882 2

R = 0.7216

0

5

10

15 20 25 Water detph（cm）

30

35

40

(a) (b) Figure 4. The relationship between water depth and (a) coverage or (b) height of P. australis in shallow water areas in the fall season.

3.2. Growth of P. australis in dry land Figs. 5, 6 and 7 show the relationship between water depth and either coverage or height of P. australis in dry land in spring, summer and fall, respectively. The coverage of P. australis in shallow water reached the maximum values of 50% in spring, 65% in summer and 55% in fall, at a water depth of -0.4 cm, -0.8 cm and -5.7 cm, respectively. The height of P. australis in shallow water reached their maximums, and they were 74 cm in spring, 139 cm in summer and 161 cm in fall, at a water depth of -0.3 cm, -0.1 cm and -3.9 cm, respectively. 90 y = -0.0059x 4 - 0.0192x 3 + 0.9936x 2 + 12.435x + 82.556 80 R 2 = 0.6564 70

60 50

60 50

Coverage（%）

40 30 20 10

40 30 20 10

0 -10

-8

-6

-4

Water depth（cm）

-2

H e i g h t （% ）

y = 0.1466x4 + 3.0807x3 + 21.409x2 + 57.281x + 69.118 R² = 0.6809

0

0

-12

-10

-8 -6 -4 W a t e r d e p t h （c m ）

-2

0

(a) (b) Figure 5. The relationship between water depth and (a) coverage or (b) height of P. australis in dry land in the spring season.

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Coverage（%）

y = -0.0391x4 - 1.0416x3 - 7.837x2 - 11.219x + 60.905 80 R² = 0.6856 60 40 20 0 -10

-8

-6 -4 Water depth（cm）

-2

0

-10

-8


200 180 160 140 120 100 80 60 40 20 0

-2

Height（cm）

y = -0.1206x4 - 1.776x3 - 4.8638x2 + 26.602x + 145.07 R² = 0.7573

100

0

(a) (b) Figure 6. The relationship between water depth and (a) coverage or (b) heightof P. australis in dry land in the summer season. y = 0.1161x4 + 2.5607x3 + 16.398x2 + 25.33x + 18.838 R2 = 0.7514

80 70 60 40 30 20 10 0

-12

-10

-8


-2

0

-10

Height (cm)

Coverage (%)

50

y = 0.1791x4 + 2.9198x3 + 8.2491x2 - 24.827x + 67.761 200 R² = 0.6926 180 160 140 120 100 80 60 40 20 0 -8 -6 -4 -2 0 Water depth（cm）

(a) (b) Figure 7. The relationship between water depth and (a) coverage or (b) heightof P. australis in dry land in the fall season.

3.3. Optimum water depth threshold C. boyciana is sensitive to the height and coverage of P. australis and prefers to live in a habitat where the coverage and height of P. australis is higher than 30% and 50 cm, respectively [13, 14]. Accordingly, the optimum water depth thresholds of the Yellow River Delta in spring, summer and fall (Table 1). For the two habitat variables, i.e., coverage and height of P. australis, the optimum water depth thresholds in spring, summer and fall in shallow water and, dry land were [0, 5.7] cm & [-1.3, 0] cm, [5, 29.8] cm & [3.7, 0] cm, and [3.3, 27.5] cm & [-7.7, -3.1] cm, respectively. Table 1. Optimum water depth thresholds for P. australis in shallow water area and dry land in different seasons Seasons

Habitat variables

Preference

Coverage

>30%

Height

>50cm

Coverage

>30%

Spring

Summer Height

>50cm

Coverage

>30%

Height

>50cm

Fall

Optimum water depth threshold (in cm) Shallow water area

[0, 5.7]

Dry land Shallow water area

[-1.3, 0] [0, 16]

Dry land

[-3.75, 0]

Shallow water area

[5, 29.8]

Dry land

[-4.8, 0]

Shallow water area

[0, 32.5]

Dry land

[-3.7, 0]

Shallow water area Dry land Shallow water area Dry land

[3.3, 27.5] [-8.1, -3.1] [2.5, 37.5] [-7.7, 0 ]


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4. Conclusions There have been some positive effects of the restoration projects in the YRDNR. However, they have been ineffective in controlling the water depth distribution amongst seasons in different areas of the reserve, specifically, between shallow water and dry land regions. The optimum water depth thresholds determined by the integrated analysis of ecological adaptability of P. australis along water depth gradient and the seasonal habitat preferences of C. boyciana reveal that… This will provide significant guidance for conservation ecologists to establish the foundation for "Ecological Water Requirements", which is a critical factor to maintain the wetland ecological system. Overall, our results indicate that future studies should focus on optimum water level and water volume thresholds as practical measures for wetland restoration and protection. Acknowledgements This study was financially supported by grants from the National Natural Science Foundation (No. 41071330) and the Scientific Research Foundation of Beijing Normal University (No. 2009SD-24). We would like to acknowledge Yueliang Liu, Shuyu Zhu and Kai Shan from the Yellow River Delta Management Bureau for their help in historical data compilation and fieldwork. References [1] Watt SCL, Garcı´a-Berthou E, Vilar L. The influence of water level and salinity on plant assemblages of a seasonally flooded Mediterranean wetland. Plant Ecology 2007; 189: 71-85. [2] Alexander ML, Woodford MP, Hotchkiss SC. Freshwater macrophyte communities in lakes of variable landscape position and development in northern Wisconsin, U.S.A. Aquatic Botany 2008; 88: 77-86. [3] Li HL, Zhi YB, Lei GC et al. Plant growth reproduction characters and biomass allocation in response to water level gradient in the clonal plant Spartina anglica. Acta Ecological Sinica 2009; 29(7): 3525-3531. [4] Jackson MB, Colmer TD. Response and Adaptation by Plants to Flooding Stress. Annals of Botany 2005, 96(4): 501–505. [5] Sim LL, Davis JA, Chambers JM. Ecological regime shifts in salinised wetland systems. II. Factors affecting the dominance of benthic microbial communities. Hydrobiologia 2006; 573(1): 109–131. [6] Laitinen J, Rehell S, Oksanen J. Community and species responses to water level fluctuations with reference to soil layers in different habitats of mid-boreal mire complexes. Plant Ecology 2008; 194(1): 17–36. [7] Robertson D, Massenbauer T. Applying hydrological thresholds to wetland management for waterbirds, using bathymetric surveys and GIS. In Zerger A, Argent R M (eds), MODSIM 2005 International Congress on Modelling and Simulation; 2005, p. 2407-13. [8] Francois B, Alan DA. Monitoring waterbird abundance in wetlands: The importance of controlling results for variation in water depth. Ecological Modelling 2008; 216: 402-8. [9] PagterM, Bragato C, Brix H. Tolerance and physiological responses of Phragm ites australis to water deficit. Aquatic Botany, 2005; 81: 285- 99. [10] Saltmarsh A, Mauchamp A, Rambal S. Contrasted effects ofwater limitation on leaf functions and growth of two emergent co2occurring p lant species, Cladium m ariscus and Phragm ites australis. Aquatic Botany, 2006; 84: 191- 8. [11] Sharma P, Asaeda T, Kalibbala M, et al.. Morphology, growth and carbohydrate storage of the plant Typhaangustifolia at different water depths. Chemistry and Ecology 2008a; 24: 133-45. [12] Sharma P, Asaeda T, Fujino T. Effect of water depth on the rhizome dynamics of Typhaangustifolia. Wetlands Ecology and Management 2008b; 16: 43-9.

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[13] Xue WW. Breeding ecology and habitat selection of Oriental White Stork (Ciconia boyciana) in Yellow River Delta. Anhui University, 2010. [14] Duan YB. Behavior and habitat selection of Oriental White Stork in breeding season in the Yellow River Estuary Nature Reserve, 2010.