114 L
. Zou et al. J. Exp. Mar. Biol. Ecol. 249 2000 111 –121 Table 1
Methods of chemical analysis for nutrient species, including precision and detection limits mM Species
Methods Detection
Precision limits
Nitrate Cd–Cu reduction
0.05 1.2
Nitrite Azo dye complex
0.02 0.5
Ammonium Indophenol blue complex
0.15 3.7
Orthophosphate Phosphomolybdate complex
0.03 0.6
Silicate Silicomolybdic complex
0.05 0.5
were prepared in the laboratory and stored at 48C. The unchelated FeCl solution was
3
freshly mixed with Milli-Q water in situ prior to experimentation. All containers and tubing for storing and dispensing were made of polyethylene or natural rubber, soaked
with 20 HCl for 24 h, washed by distilled water and then Milli-Q water. The following incubations were carried out for 24 h in the same manner as in the rain experiment.
In all experiments, control samples were prepared. After incubation, samples were filtered immediately through 0.45-mm pore-size filters and frozen until analysis.
2.5. Nutrient analysis All experimental containers e.g. incubation bottles were rinsed in 10 HCl for 24 h
and then rinsed thoroughly with DDW before use. Nitrate, nitrite, ammonium, orthophosphate and dissolved silicate were analyzed by classic colorimetric methods
Parsons et al., 1987. Detection and precision of the analyses are shown in Table 1.
2.6. Chlorophyll a analysis Samples for Chl-a were filtered using Whatman GF F filters. Particles on the filter
were extracted with 90 acetone at 48C in the dark for 24 h. Chl-a concentrations were determined by a fluorometric method Parsons et al., 1987.
3. Results
3.1. Nutrients Concentrations of DIN nitrate 1 nitrite 1 ammonium, DIP orthophosphate and DISi
silicate in situ water samples and rainwater are shown in Table 2. Station A is located within the Jiaozhou Bay, while station C and D are further
offshore in the Yellow Sea. The results of the nutrient analyses show that the DIN concentrations ranged from 3.75 to 8.15 mM at these three stations. At station A, DIN
was double the concentration compared with stations C and D, and DIN of station D was 30 higher than C. The DIP concentrations decreased from 0.36 mM at station A to 0.06
mM at station D, i.e., by 6-fold. With respect to DISi, station C has a higher concentration than both A and D. For example, DISi of station C has a concentration
L . Zou et al. J. Exp. Mar. Biol. Ecol. 249 2000 111 –121
115 Table2
Dissolved inorganic N:P and Si concentrations at three stations and for rainwater samples Station
A C
D Rainwater
DIN mM 8.15
3.75 4.83
11.65 DIP mM
0.36 0.21
0.06 0.14
DISi mM 8.92
15.60 4.51
0.50 N:P:Si
22:1:25 18:1:74
80:1:75 83:1:3.5
over three times higher than that of station D, and the DISi at station A has a concentration almost double that of station D 8.92 mM compared to 4.51 mM.
Compared with the nutrients in the seawater, the DIN concentration in the rainwater of 11.65 mM was much higher than the seawater samples. The DIP concentration in
rainwater was lower than the samples from station A and C, but higher than that from station D. DISi in rainwater was 0.50 mM, i.e., about 10 of that of the seawater from
station D.
3.2. Chlorophyll a The Chl-a concentrations are presented in Fig. 2. Concentrations of Chl-a in surface
23
water at stations A, C and D decreased from 2.68 to 0.08 mg m . The concentrations of
Chl-a in nutrient and rainwater incubations at these three stations were compared to the batch control. At station A, Chl-a concentration for rainwater incubation was similar to
23
that of the control of 3.60 mg m . Chl-a concentrations under rainwater-amended
conditions at station C and D were higher than those for the controls, especially at station D, where the Chl-a concentration was almost twice as high as the batch control.
Changes in Chl-a concentration due to addition of nutrients CN, changes due to nutrients and rainwater CR, changes due to rainwater were estimated by the following
equations and the results are shown in Table 3 CN 5 [Chl-a 2 Chl-a ] dose of nutrient
1
N C
CR 5 [Chl-a 2 Chl-a ] rainwater dose 2
R C
where Chl-a , Chl-a , and Chl-a represent Chl-a concentration of incubations in
N R
C
nutrient, rainwater and control, respectively. It is evident from Table 3 that the significant Chl-a increase in response to nutrient
23
additions takes place in the case of phosphate, ranging from 0.025 to 0.050 mg m ,
indicating P limitation for phytoplankton growth. With respect to DIN, Chl-a ranges
23 1
2
from 0.016 to 0.061 mg m for NH , while the incubation range for NO
is from
4 3
23
0.006 to 0.029 mg m Table 3. The phosphate limitation relative to nitrogen for Chl-a
32
is probably due to the low concentration of PO and the elevated N P ratio 80:1 in
4
this region. The effect of DISi on Chl-a was not as significant as that of the other plant
23
nutrients at these stations with 0.003 mg m . The influence of Fe was significant at
23
stations C and D, with CN 0.040 and 0.025 mg m , respectively. But the average CN of
Fe was under zero because of the low CN at station A. In the case of rainwater, negative
116 L
. Zou et al. J. Exp. Mar. Biol. Ecol. 249 2000 111 –121
23
Fig. 2. Chl-a concentrations mg m of start, control, nutrients and rainwater incubations in situ. Start, group
at beginning of incubation; control group; 1rain, group incubated under rainwater; 1NO , group incubated
3
under nitrate; 1NH , group incubated under ammonium; 1P, group incubated under phosphate; 1Si, group
4
incubated under silicate; Fe, group incubated under FeIII.
Table 3
23 23
23 21
Chl-a concentration of start and control mg m , CN mg m
per mM of nutrient and CR mg m l
of rainwater
1
Station Start
Control NO
NH P
Si Fe
Rainwater
3 4
A 2.68
3.60 0.014
0.016 0.050
20.003 20.82
21.20 C
0.17 0.72
0.029 0.061
0.045 0.005
0.040 3.80
D 0.08
0.10 0.006
0.018 0.025
0.006 0.025
3.80 Average
0.016 0.032
0.04 0.003
20.25 2.13
L . Zou et al. J. Exp. Mar. Biol. Ecol. 249 2000 111 –121
117
Fig. 3. Relationship between EV and TQ.
23 21
CR was observed at station A, that is, 21.20 mg m l
; while significant but positive
23 21
CRs occurred at stations C and D, i.e., 3.80 mg m l
. Results of the effects of light on Chl-a concentrations are shown in Fig. 3.
Concentrations of Chl-a were reduced when light radiation decreased.
4. Discussion
