EBF CF SDF AM

Str

eam

DO

C (

mg/

L)

0

1

2

3

4

5

6a a a

b(a)

S1 S2 S3

SO

C (

g/kg

)

0.0.2.4.6.8

1.01.21.41.61.8

EBFCFSDFAM

(b)

a a

a

b

a ab

c

aabb

c

Water 5cm Soil depth

Tem

pera

ture

()

℃

0

5

10

15

20(c)

b

aa

b b

aa

b

Jun Aug Oct Dec Feb Apr

Str

eam

DO

C (

mg/

L)

0

2

4

6

8

10

12

14

EBFCFSDFAM

(a)

Jun Aug Oct Dec Feb Apr

Str

aem

nitr

ate

(mg/

L)

0.0

.2

.4

.6

.8(b)

Stream nitrate of the antecedent two months (mg/L)0.0 .2 .4 .6 .8 1.0 1.2

Str

eam

DO

C (

mg/

L)

0

2

4

6

8

10

12

14

EBFCFSDFAM

r2=0.270**(c)

Altitude (m)

500 1000 1500 2000 2500

Str

eam

DO

C (

mg/

L)

3.0

3.5

4.0

4.5

5.0

5.5

6.0

r2=0.423*

(a)

SOC (g/kg)0.0 .2 .4 .6 .8 1.0 1.2 1.4 1.6 1.8

0-10 cm10-25 cm25-40 cm

(b)

r2=0.475*

Temperature ( )℃9 10 11 12 13 14 15 16 17

Water temperatureSoil temperature

r2=0.334*

r2=0.477*

(c)

Table 1 Mean annual precipitation (mm).

Altitudinal gradient of dissolved organic carbon in Altitudinal gradient of dissolved organic carbon in headwater streams of the Wuyi Mountains in Chinaheadwater streams of the Wuyi Mountains in China

Question

Wei Huang1, Honghua Ruan1 ＊ , Xiaoming Zou1, 2, William H. McDowell3, Jiashe Wang4, Liguang Li1

1 Faculty of Forest Resources and Environmental Science, Nanjing Forestry University, China; 2Institute for Tropical Ecosystem Studies, University of Puerto Rico, USA; 3 Department of Natural Resources and the Environment, University of New Hampshire, USA; 4 Administrative Bureau of Wuyishan National Nature Reserve, China.

Dissolved organic carbon (DOC) in stream water is positively correlated with soil organic carbon (SOC) at regional scales in which climate and vegetation are relatively invariant.

• Does this correlation hold when variations of temperature, precipitation and vegetation are large across altitudinal gradient?

Objective

• To examine the altitudinal patterns of headwater stream DOC concentrations along an altitudinal gradient in the Wuyi Mountains of China.

• To investigate the relationship between headwater stream DOC concentrations and SOC contents along an altitudinal gradient.

• To find the environmental factors that can be used to predicted headwater stream DOC concentrations.

Site description and experimental design

Fig. 1 Map of headwater streams in the Wuyi Mountain National Nature Reserve of southeastern China (WNR, Wuyi Mountain National Nature Reserve; FJ, Fujian Province; JX, Jiangxi Province.).

Wuyi Mountain National Nature Reserve, with distinct vertical zones of vegetation along the altitudinal gradient, is located in the subtropical monsoon region of China.

Result

Subtropical evergreen broadleaf forest (EBF)

Coniferous forest (CF)

Subalpine dwarf forest (SDF)

Alpine meadow (AM)

1700 2000 2200 3100

Fig. 2 Annual mean values in headwater stream (a) DOC concentrations, (b) SOC contents, and (C) temperature (S1: 0-10 cm soil layer; S2: 10-25 cm soil layer; S3: 25-40 cm soil layer). Significant differences between the means are marked with different letters.

Fig. 3 Correlations between annual mean headwater stream DOC concentrations and (a) altitude, (b) SOC contents, and (C) temperature (n=12; * indicated significant level at 0.05).

• Positive correlations were found between stream DOC concentrations and temperature.

Stream DOC concentrations peaked in February at the end of the dry season and were lowest in August at the end of the rainy season. Seasonal variation of stream DOC concentrations correlated positively with stream water nitrate concentrations in the antecedent two months.

Fig. 4 Seasonal variations of (a) headwater stream DOC, (b) nitrate, and (c) correlation between headwater stream DOC concentrations and stream nitrate concentrations of the antecedent two months (n=72; ** indicated significant level at 0.01).

☼ Conclusion ☼• Concentrations of DOC in headwater streams are not solely controlled by SOC contents. Factors influencing the decomposition of SOC, such as temperature, as well as the dilution of stream DOC source by precipitation, can also play an important role in determining DOC concentrations in headwater streams along an altitudinal gradient that across vegetation types.

• Annual mean values in headwater stream DOC can be largely predicted by temperature alone across the altitudinal gradient, and seasonal variation in stream DOC levels can be predicted by stream nitrate concentrations two months in advance.

Nanjing Forestry University Nanjing Forestry University *Corresponding author; e-mail: honghuaruan@gmail.com

• Annual mean concentration of stream DOC exhibited a decreasing pattern with increasing altitude .

• In contrast, annual mean contents of SOC showed an increasing trend with altitude. Contents of SOC correlated negatively with stream DOC along the altitudinal gradient .