Nutrient dynamics and primary production in a pristine coastal mangrove ecosystem: Andaman Islands, India
State University ([email protected]), 2University of Notre Dame, 3SUNY-Brockport, 4South Dakota School of Mines & Technology, 5Anna University, India
Mangrove ecosystems play a key role in supporting coastal food webs and
nutrient cycles in the coastal zone. Their strategic position between the
land and the sea make them important sites for land-ocean interaction.
The land influence occurs when heavy rainfall flushes the system and
decreases the salinity of the water surrounding the mangroves. The ocean
influence occurs when there has been a lower freshwater input and
nutrients are carried in by tides. Other factors that affect a plant’s ability to
absorb nutrients include turbidity, water transparency, and the amount
of nutrients already absorbed by the plant. Turbidity and water
transparency affect light availability, which drives light-dependent reactions.
Turbid water stirs sediment which makes it harder for light to pass through,
changing the water transparency.
Net Ecosystem Production (NEP): Light Bottle - Fixed Bottle
Gross Primary Production (GPP): NEP + CR
190
30
160
8
160
130
20
130
4
130
100
10
100
0
100
160
3
12 PM
1 PM
2 PM
3 PM
4 PM
5 PM
6 PM
7 PM
8 PM
9 PM
10 PM
11 PM
12 AM
2 AM
4 AM
6 AM
8 AM
10 AM
3.5
Time
Time
DIN/DIP over Tidal Cycle
220
12
190
8
160
Time
10 AM
8 AM
6 AM
4 AM
2 AM
12 AM
11 PM
100
10 PM
0
9 PM
130
8 PM
4
7 PM
Figure 1: (A) probe measurements (B)
primary productivity (C) nutrient analysis.
250
Water Height (cm)
16
6 PM
(C)
Table 1: Nutrient concentration
ranges over tidal cycle.
Nutrient
nitrite
nitrate
ammonium
DIP
Concentration
(µM)
0.2 - 0.9
2.0 -11.5
1.3 - 7.5
0.7 - 2.8
Conclusions
The fluctuations in nutrient concentrations in creek water reflect the changes
in dominant source water. Concentrations of dissolved organic matter and
DIP were generally higher during the ebb tide indicating that the mangrove
ecosystems were a source for these constituents. Turbidity and salinity
showed a strong coupling with the tidal cycle, whereas DO concentration
increased steadily during the second low tide. This was a result of a torrential
rain event that flushed the coastal wetland, leading to input of DIP into the
creek and concomitant low values for DIN/DIP.
Our primary production assay conducted during the second high tide indicated
that the ecosystem was net autotrophic. However, N and P additions as nitrate
and DIP failed to stimulate primary productivity, but did enhance heterotrophic
respiration. P availability had a stronger influence on microbial production than
N. A similar assay conducted earlier during the ebb tide yielded greater
dissolved O2 in dark incubation than those incubated in light. This
questionable result may be an experimental artifact of placing the glass
bottles in the sun for too long prior to incubation, potentially leading to
photolysis of large organic molecules in the light bottles.
Nutrient additions did not stimulate primary production but did stimulate
heterotrophic respiration (Figure 2).
References
3.4
Dark Bottle
3.2
3.0
Unfertilized
0.030
Light Bottle
Nitrogen
Phorphous
0.000
Net Ecosystem Gross Primary
Production
Production
2.8
Control
Oulton, M., 2007, Mangrove Food Web: The University of Waikato.
Tett, P., Droop, M.R., Heaney, S.I., 1985, The Redfield Ratio and Phytoplankton Growth Rate,
Journal of the Marine Biological Association of the United Kingdom, v.65 no.2, p. 487-504.
Wetzel, R.G., and Likens, G.E., 1991, Limnological Analysis, New York, Springer, 391 p.
0.015
Community
Respiration
Water Height (cm)
12
ppt
190
Water Height (cm)
40
12 PM
1 PM
2 PM
3 PM
4 PM
5 PM
6 PM
7 PM
8 PM
9 PM
10 PM
11 PM
12 AM
2 AM
4 AM
6 AM
8 AM
10 AM
220
NTU
16
Results – Primary Productivity
Aerobic Respiration: Consume O2 & sugar to produce CO2, water, & heat.
Community Respiration (CR): Fixed Bottle - Dark Bottle
220
Primary production at Wright Myo creek is therefore likely not limited by
nutrients but is controlled by other conditions such as light availability. In
contrast, community respiration increased upon nutrient addition, indicating
that heterotrophic microbial community respiration was limited by P.
Primary Production or Respiration
(mg C L-1 hr-1)
respiration
C6H12O6 + 6O2
50
190
250
The dissolved inorganic nitrogen to dissolved inorganic phosphate (DIN/
DIP) ratio was very low relative to an optimal ratio of 16, suggesting
growth is nitrogen limited (Tett et al., 1985).
The study was conducted at Wright Myo mangrove creek on South Andaman.
Dissolved O2 (mL)
6CO2 + 6H2O
Salinity
20
Time
Study Location: Andaman Islands, India
Terms and Reactions
photosynthesis
220
Turbidity
250
4
2
(Oulton, 2007)
Photosynthesis: CO2, water, & light energy produce glucose & O2.
60
4.5
2.5
*
Winkler Method: Technique based on the oxidation of manganous
hydroxide by oxygen dissolved in the sample. The product is transformed
to manganic sulfate which liberates iodine from previously added
potassium iodide. The quantity of free iodine is equivalent to the amount of
dissolved oxygen. It is determined by titration with a standard solution of
sodium thiosulfate (Wetzel and Likens, 1991).
250
Water Height (cm)
(B)
5 PM
Background
5
4 PM
The analysis of nutrients was conducted at the
Institute of Ocean Management laboratories at
Anna University in Chennai, India using
standard water chemistry methods.
5.5
Dissolved Oxygen
3 PM
The primary production experiments were
carried out at low and high tide to examine
the impact of nutrient availability with
tides. The experiments were conducted in situ
using the Winkler method. Simultaneous fourhour incubation of light and dark bottles
representing a fixed control, non-fertilized,
fertilized with nitrate, and fertilized with
phosphate enabled the measurement of both
net oxygen production and dark respiration.
Select parameters (blue) are plotted with water height (red) as a function of
time. DO and turbidity show an inverse relationship between water height
levels while salinity closely mimics the changing water height.
2 PM
Over a full tidal cycle, nutrient concentrations
and other parameters were measured using a
probe (e.g. DO, temp, turbidity, salinity). These
measurements were taken every hour for the
first tidal cycle and then every two hours for
the second tidal cycle to evaluate water
quality changes in incoming and ebbing
tides.
1 PM
As part of summer field course we investigated changes in the water
chemistry in a pristine mangrove creek located at Wright Myo in the
Andaman Islands, India. This study was conducted during the wet season
(June 2012) to evaluate the influence of the coastal mangrove wetlands on
the water quality and productivity in adjoining pelagic waters. Over
approximately twenty-four hours, we measured nutrient concentrations and
other ancillary parameters to evaluate water quality changes in incoming and
ebbing tides. We further conducted primary production assays in the creek to
investigate the factors that controlled primary production. Our results indicate
that nutrient concentrations varied with the stage of the tide, with
generally greater concentrations of dissolved organic matter and dissolved
inorganic phosphate (DIP) occurring during ebb tide. The ratio of dissolved
inorganic nitrogen (DIN) and DIP was also generally lower during the ebb
tide, but remained low during the subsequent high tide post a rain event.
Productivity assay conducted during a high tide showed that net ecosystem
production (NEP) was positive implying autotrophy exceeded respiration.
However, nutrient addition assays revealed that despite low DIN/DIP ratio
heterotrophic respiration was limited by the availability of phosphorus.
Results – Water Parameters & Nutrients
(A)
12 PM
Methods
12 PM
1 PM
2 PM
3 PM
4 PM
5 PM
6 PM
7 PM
8 PM
9 PM
10 PM
11 PM
12 AM
2 AM
4 AM
6 AM
8 AM
10 AM
Abstract
DIN/DIP
1Portland
Concentration (mg/L)
ID: B53A-0649
Emily N. Jenkins1, K. Nickodem2, A. L. Siemann2, A. Hoeher3, P. V. Sundareshwar4, R. Ramesh5, R. Purvaja5, K. Banerjee5, S. Manickam5, H. Haran5
Unfertilized Nitrogen Phosphorus
-0.015
Figure 2: Measurement of dissolved O2 via Winkler Method for high tide at 6:30am (left) and
corresponding CR, NEP, and GPP (right). Control sample was fixed at time = 0.
Acknowledgements
This project was a module for South Dakota School of Mines & Technology
Environmental Field Camp in India. It was a joint program with students
from the US and Anna University’s Institute of Ocean Management.