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Marine gravity anomaly from satellite altimetry a comparison of high-occurrence season

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Marine gravity anomaly from satellite altimetry a comparison of  high-occurrence season Powered By Docstoc
					                                                                                The Thirteenth Workshop of OMISAR




      Investigation of Oceanographic and Marine Environmental Condition
   surrounding Nipah Island: in-situ Measurements and Satellite Observations


                   Nani Hendiarti*, Andri Purwandani, Marina Frederik, Retno Andiastuti,

                              Center for Technology for Natural Resources Inventory,
        Agency for the Assessment and Application of Technology, M.H. Thamrin 8, Jakarta 10340, Indonesia
                                  *Phone: 62-21-3169690, FAX: 62-21-3169720


Abstract
    Coastal processes are of special importance for        1. Introduction
national relevance particularly in marine
                                                               The Indonesian archipelago is characterized by
environmental and fishery studies. Satellite data
                                                           strong seasonal variations in the upper oceanic
from different sensors (SPOT, Terra-ASTER,
                                                           circulation influenced by monsoonal winds. The
Aqua-MODIS, NOAA-AVHRR,) were applied to
                                                           variation of seasonal solar heating over the
analyze spatial distribution of sea surface pattern
                                                           continents of Asia and Australian drives the
induced by dynamical processes surrounding Nipah
                                                           monsoons, which change wind direction twice a year
Island, a small island in the Riau province’s island
                                                           (Tomascik et al., 1997; Webster et al., 1998). In
cluster. In situ data from ‘PotRets P. Nipah’
                                                           Indonesian waters, the monsoons induce the
expedition, conducted between July 29 and August 7,
                                                           occurrence of different dynamic processes. One of
2004 using R/V Baruna Jaya I were used to study
                                                           the important coastal processes is the occurrence of
occurrence of dynamical processes and its influence
                                                           coastal discharge since the islands of Indonesia are
on distribution of existing material in the
                                                           characterized by a large number of rivers and
surrounding waters.
                                                           wetlands such as mangrove and aquaculture areas.
     Analysis of in situ data show that during the
                                                                The investigation area surrounding Nipah Island
cruise period, the waters surrounding Nipah Island is
                                                           is located in the border of Indonesia with Singapore.
characterized by chlorophyll a concentrations higher
                                                           This area also part of the shallow Sunda Shelf, which
than 1 mg/m3 and suspended particulate matter
                                                           covers the western portion of the Indonesian seas,
higher than 50 mg/l. The water, which may be
                                                           extending from the coasts of Malaysia and the South
influenced by coastal discharge, is observed to have
                                                           China Sea to the Java Sea.
chlorophyll concentration higher than 5 mg/m3,
suspended matter of more than 100 mg/l and sea                 Characteristics of the Riau Islands waters vary
surface temperature higher than 29 C. This                spatially and temporally from the influence of
condition is also observed from satellite images.          incoming water from the Java Sea and the South
River outflow transports nutrients to the sea, which       China Sea as well as Malaka Strait. High discharge
resulted in high concentration of chlorophyll a, and       rates into the Java Sea contain terrigeneous material
high abundance of phytoplankton. 33 species of             from the numerous rivers in Java, Sumatra and
phytoplankton identified from 4 stations were              Kalimantan islands (Tomascik et al., 1997) as well as
dominated by Diatom Group of Bacillariophyceae.            discharged material from diffuse sources and coastal
Besides, high concentrations of TSM in this area can       erosion. During dry season, the Java Sea water
be also affected by sea sand mining activities.            moves westward and spreads to the Karimata Strait
However, an increase of water turbidity may                (Hendiarti, 2003); and reversed in direction during
produce less abundance of zooplankton, which was           the other monsoon.
found only 8 species of Protozoa and Copepode
                                                               Sea sand mining exploitation, which is operated
Group. Therefore, fish abundance estimated using
                                                           for many years in Riau Islands waters, may also
split beam acoustic was small, particularly for
                                                           contribute on the environmental degradation of the
pelagic fish was very little.
                                                           area.
Keywords: oceanographic         condition,    coastal
                                                               This paper describes the study of oceanographic
discharge, satellite images
                                                           processes and the environmental condition in the
                                                           waters surrounding Nipah Island, in relation to the
                                                           investigation of potential resources of the area.



                                                                                                             3-1
Oceanographic and Marine Environmental Condition surrounding Nipah Island




2. Datasets and Methods                                          variables to observe the dynamical processes.
    The investigations of oceanographic processes                    Chlorophyll a concentrations were determined
and environmental condition in waters surrounding                by the spectrometric method. Seawater samples of
Nipah Island were performed on the basis of in situ              0.3-2 litres were filtered through 47 mm Whatman
and satellite remote sensing data. In situ                       GF/F filters and grinded in the 90% acetone.
measurements were used to characterize the                       Wavelength absorbance from the acetone extract
oceanographic condition. Satellite data in visible and           was measured at 630, 645, 665, and 750 nm using a
thermal infrared spectral range were used to derive              stand alone spectrophotometer (Shimadzu UV-1600).
the concentrations of water constituents and sea                 Chlorophyll a concentration was calculated using
surface temperatures.                                            spectrometric equation of Parsons and Strickland
2.1. In situ measurements                                        (1968).
    Field campaign named ‘PotRets’ expedition                        Phytoplankton and zooplankton abundance were
(Potential Resources investigation surrounding                   determined using fraction method. The sample was
Nipah Island) was conducted from 29 July to 7                    set aside in the Sedgwick-rafter counting cell, and
August 2004 using R/V Baruna Jaya I.                             the phytoplankton and zooplankton species were
                                                                 identified using microscope.
     The     field    campaign     was      providing
oceanographic data of the investigation area, which                  Total suspended matter (TSM) was measured
is characterized by shallow waters. The reason for               gravimetrically, by determining dry weight of total
the selected stations was to obtain representative               suspended matter (Parson and Strickland, 1968).
water types with biological activities resulting from            Whatman GF/F filters were prepared by heating in
coastal processes. Figure 1 shows map of sampling                special treatments and weighting. Seawater samples
site and location of the stations.                               of 0.5-2 liters were filtered. TSM concentrations
                                                                 were determined by the difference to basic weight,
                                                                 and are calculated as TSM / litre.
                                                                        Secchi disk depth and seawater color are
                                                                 simple methods and effective tools to estimate the
                                                                 water clarity. Secchi disk is attached to a rope and
                                                                 lowered until it is no longer visible, which is called
                                                                 the Secchi depth. Seawater color observed from
                                                                 above can be influenced by the white glitter from the
                                                                 sun, reflected blue sky light, dark shadows of clouds,
                                                                 and by the blue-green-brown light scattered back
                                                                 from the subsurface water (Jerlov, 1976). This water
                                                                 color is classified using the Forel-Ule scale, which is
                                                                 divided into twenty-two colored levels encased in
                                                                 tubes from blue via green to brown color.
                                                                      Temperature, salinity and the depth profiles
                                                                 were acquired using Conductivity, Temperature and
Fig. 1: Map of sampling site                                     Depth (CTD) Guidline 6000 device for the Baruna
                                                                 Jaya I. Current profiles were measured using current
                                                                 meters MORS in each station at three depths (5, 10
Measurements methods                                             and 15 m) for about one hour measurements. The
                                                                 profiles were averaged every 5 minutes.
     During field observations, different in situ
variables were measured. Measurements of the                          Two dimensional hydrodynamics model and
concentrations of nutrients, chlorophyll a and total             flow trace of suspended material transport model
suspended matter as well as the abundance of                     were applied in the area of investigation. Tidal data
phytoplankton and zooplankton in selected stations               from ‘Depwilhan’ (2004), wind data from Metsin
were used to study the connection between                        (Singapore) and bathymetry fom ‘Dishidros’ (1998)
parameters. Secchi depth and water color were                    were used as boundary conditions (described in
monitored at day-time stations. Vertical profiles of             Purwandani, 2004).
water temperatures and salinity measured at all
stations included the current profiles are the main




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                                                                                The Thirteenth Workshop of OMISAR




2.2. Satellite data                                      Table 1: Water characteristics observed from in situ
                                                         measurements.
    The investigations were performed using Aqua-
MODIS, NOAA-AVHRR, Terra-SPOT and SPOT 5                                             Range of values
data. MODIS (Moderate Resolution Imaging                 Parameter         Near surface   Near bottom            Unit
Spectroradiometer) data of 4 km and 1 km spatial                              water
resolution were provided by Goddard Space Flight         Nitrat (NO3)     0.060 - 0.879        0.005-0.121      M
Center - NASA. These data were processed using the
                                                         Silicate         0.224 - 0.958        0.170-1.301      M
SeaWiFS Data Analysis System (SeaDAS) provided
                                                         Orthophosphat    0.001 - 0.248        0.001-0.126      M
by NASA, to derive concentrations of chlorophyll a
and suspended particulate matter. Chlorophyll            Chlorophyll a    1.20 - 8.24          1.20 - 7.89      mg/m3
images were produced using Ocean Chlorophyll             Phytoplankton      1,272 - 111,936 (abundance)         cell/m3
3-band algorithm (O’Reilly et. al., 2000). The           Phyto- species   Diatom: Bacillariophyceae (29 sp.),
concentrations of TSM were obtained using a single                        Non-diatom: Dinophyceae,Cyanophyceae (4 sp.)
band algorithm based on reflectance distribution in      TSM              4.47 - 107.0         8.47 - 215.4     mg/l
the 551 nm Aqua-MODIS channel.                           Turbidity        2.6 - 70             2.95 - 174       NTU
    SST (sea surface temperature) images with 1 km       Secchi depth                    25 - 250               cm
resolution were derived from the thermal infrared        DO               5.06 - 8.57          4.36 – 8.31      ml/L
channels of the AVHRR of the NOAA (National              PH               7.83 - 8.12          7.99 – 8.13
Oceanographic and Atmospheric Administration) of                              479 – 2,925 (abundance)
                                                         Zooplankton                                            cell/m3
weather satellites. The SST images were produced
                                                         Zoo- species     Protozoa (3 sp.) and Copepode (5 sp.)
using an improved algorithm of multi channel
approach of McMillin and Crosby (1984). SST              Water Color      V/green           XVI/light brown
image with 15 m spatial resolution derived from the
thermal infrared channels (channel 10 – 14) of
Terra-ASTER data on April 23, 2004 was produced
using     the      following    SST      algorithm.          High concentrations of nitrate and silicate were
                                                         found at the stations in the western part of the
SST = 1.16 + (-1.07 *T10) + (0.49*T11) + (1.13* T12)     investigation area (Fig. 2, above). This is due to the
     + (0.78*T13)+ (-0.32*T14)                           influence of river discharge from the islands into the
                                                         sea waters contain terrigeneous material (e.g.
where, T10, T11, T12, T13, T14 are brightness            nutrients and organic matter). The highest
temperature for each channel.                            concentration of silicate near bottom layer was
    False color composite image with 10 m spatial        found at the station near the coasts of Karimum
resoltion was derived from three channels of SPOT 5      Island. Silicate is the main nutrient component
data on August 25, 2000. This image is used to           needed by phytoplankton especially from Diatom
observe sea surface features in relation to surface      Groups for their growth.
water circulation.                                           The concentration of chlorophyll in this area is
                                                         relatively high with more than 1 mg/m3. The highest
                                                         concentrations of more than 5.5 mg/m3 were
3. Characteristics of water type and biological          measured at the station near the coasts of Karimun
   processes                                             Island (Fig. 2, below). The range of concentration in
     During the cruise period between 29 July and 7      a year derived from monthly chlorophyll images was
August 2004, the range of nutrients (nitrate and         1.5 – 5.5 mg/m3. Higher concentrations were
silicate), chlorophyll a and TSM concentrations as       observed between May and November with the
well as water temperatures and salinity at the surface   concentration more than 3 mg/m3 (Figures not
water were 0.06-0.879 M, 0.224-0.958 M, 1.2-8.5        shown). River outflow transports nutrients to the sea,
mg/m3, 4.5-107 mg/l, 28.5-28.95 C and                   which resulted in high concentration of chlorophyll
28.75-30.25 PSU, respectively. At the depth of 24 m      a, and high abundance of phytoplankton.
(near bottom), the ranges slightly increased for
nutrients and suspended particulate matter to
0.005-0.121 mg/l nitrate, 0.17-1.30 mg/l silicate and
8.5-215.4 mg/l TSM, respectively. The complete
results are presented in Table 1.




                                                                                                                   3-3
Oceanographic and Marine Environmental Condition surrounding Nipah Island



                                                                 produce the mud in big volume to settle on the
                                                                 bedrock. This condition may caused the deceased of
                                                                 zooplankton abundance in the area.
                                                                     Thirty three species of phytoplankton was
                                                                 identified from 4 stations, which was dominated by
                                                                 Diatom Group of Bacillariophyceae (29 species),
                                                                 Fig. 4 above. Phytoplankton abundance maximum
                                                                 was found for Skeletonemia sp. with 111,936 cell/m3.
                                                                 However, an increase of the concentrations of
                                                                 suspended particulate matter may produce less
                                                                 abundance of zooplankton. Only 8 species of
                                                                 zooplankton from Protozoa and Copepode Groups
                                                                 was identified, and have 2,874 cell/m3 of abundance
                                                                 maximum for Codonellopsis sp (Fig. 4).

Fig. 2: Concentration of nitrate and silicate at 1 m
depth (above), surface chlorophyll and suspended
particulate matter at 20 m depth (below).


    Chlorophyll a the green pigment absorbs light
and uses the energy in the photosynthesis for the
production of organic matter. SST images derived
from NOAA-AVHRR were observed the variation of
SST values. Furthermore, the range of SST values
derived from Terra-ASTER data on April 23, 2004
with 15 m spatial resolution was 28.5–30C (Fig. 3).




                                                                 Fig. 4: Phytoplankton and zooplankton abundance
                                                                 measured from 4 stations

Fig. 3: Comparison between SST image derived
from AVHRR with 1 km spatial resolution (left) and                   The marine environmental degradation was also
derived from ASTER with 15m resolution (right).                  identified by decreasing the level of water clarity and
                                                                 further affected to decrease fish stock. Therefore,
                                                                 fish abundance estimated using split beam acoustic
    This water is classified as a turbid water. Range            during the cruise was small, particularly for pelagic
of suspended particulate matter concentration from               fish was very little. This condition may also caused
in situ measurements were high at the surface with               the destruction of coral reef ecosystem in the west
1.58-107 mg/l and more at the depth near bottom                  coast of Nipah Island.
with 2.06-215.40 mg/l. The highest concentrations
were found near the coasts of Karimun Island (Fig. 2,
below). From the images, TSM concentrations near                 4. Dynamical processes
the coasts of Karimun Island were more than 40 mg/l,                 Two dimensional hydrodynamic and sediment
particularly during rainy season (December –                     transport model was applied in the waters
March), data not shown. High concentrations of                   surrounding Nipah Island for period of 1- 4 August
TSM in this area can be also affected by sea sand                2004. Maps of current vector and flow trace of the
mining activities, because these acitivities may be              material transport were produced every 1 hour



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                                                                                The Thirteenth Workshop of OMISAR



interval. Fig. 5 shows the results for the condition on   development of coastal and marine ecosystem. This
August 3, 2004, where stronger surface current is         condition may be influenced by coastal discharge as
observed in eastern part of the island. The material      well as by sea sand mining exploitation and sea
transport forced by the current may influence the         transportation activities in and around the area of
environmental condition of Nipah Island and its           investigation.
surrounding. False color composite image from
                                                               Oceanographic and marine environmental
SPOT 5 data on August 25, 2000 shows the similar
                                                          condition surrounding Nipah Island was determined
surface feature of surface water-mass transport
                                                          using in situ measurements and satellite observations.
particularly surrounding the Nipah Island.
                                                          The highest concentrations of water substances and
                                                          the lowest values of salinity were found at the
                                                          stations near the coasts of Karimun Island. Similar
                                                          condition is also observed from chlorophyll and
                                                          TSM images derived from Aqua-MODIS data
                                                          besides SST images from Terra-ASTER and
                                                          NOAA-AVHRR data. This is due to the influence of
                                                          river discharge from the islands into the sea waters
                                                          contain terrigeneous material (e.g. nutrients and
                                                          organic matter). High concentrations of TSM in this
                                                          area can be also affected by sea sand mining
                                                          activities.
                                                              River outflow transports nutrients to the sea,
                                                          which resulted in high concentration of chlorophyll
                                                          a, and high abundance of phytoplankton. The
                                                          phytoplankton species were identified dominated by
                                                          Diatom Group of Bacillariophyceae, and have more
Fig. 5: Surface current vector and flow trace of          abundance compare to zooplankton. Less abundance
material transport on August 3, 2004 resulted from        and species amount of zooplankton in this area may
2D hydrodynamics and material transport model             cause by an increase of the concentrations of
(Purwandani, 2003).                                       suspended particulate matter. Moreover, fish density
                                                          can be also decreased.
                                                              Distribution of organic and anorganic matters may
                                                          be driven by the dynamical processes. During the
                                                          cruise peiod, the range of current speed and direction at
                                                          the depth of 2 - 5 m were dominated by 0.14-0.20 m/s
                                                          and westward direction. At the depth of 12-15 m, the
                                                          ranged of current speed were increased to 0.35-0.40
                                                          m/s, and the direction modified to southwest
                                                          particularly in the western part of the area
                                                          investigation. The results from numerical simulation
                                                          show that material transport may influence the
                                                          environmental of Nipah Island and its surrounding,
                                                          particularly in eastern part of the island where
                                                          stronger current is occurred.
                                                               Therefore, it is needed to focus on rehabilitation of
                                                          mangrove areas in Nipah Island besides conservation
Fig. 6: False color composite image from SPOT 5           of coral reef in the western coasts of an island. In
data on August 25, 2000 shows surface water               relation to sea transportation activities and sea sand
transport.                                                mining exploitation surrounding the island, an
                                                          observation station for scientific purposes, such as tides
                                                          and water quality measurements, can be also
6. Conclusion                                             established in this island. Furthermore, such
                                                          measurements would improve the accuracy of
    The study shows that the water quality in area of     hydrodynamics, sediment transport and remote sensing
investigation was found not sufficient for the            models, which are applicable for monitoring the



                                                                                                               3-5
Oceanographic and Marine Environmental Condition surrounding Nipah Island



oceanographic and environmental conditions in this
area.


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Description: Marine gravity anomaly from satellite altimetry a comparison of high-occurrence season