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Integrating GIS and Fluorometry
For Real-Time mapping of Coastal Systems
About Cawthron Institute
Cawthron Institute provides science and technology solutions to enable
the sustainable management and development of New Zealand’s coastal
and freshwater resources for the benefit of the region and the nation.
Cawthron has been operating in Nelson, New Zealand for over 80 years
and is owned by a trust that represents the local community and employs
over 150 scientific and technical staff.
Within Cawthron, the Coastal Group provides expert scientific advice
in both commercial and research settings in the fields of resource
management, coastal ecology, fisheries and aquaculture sustainability,
environmental effects of waste discharges and oil spills, biosecurity
and environmental modelling.
Overview
This article focuses on our integration of the 10-AU and SCUFA fluorometers
with desktop Geographical Information System (GIS) software for real-time
mapping and data collection. To demonstrate this, we have highlighted
two case studies: (i) tracking effluent dispersion/dilution from coastal
outfall (using Rhodamine® WT dye) and (ii) mapping chlorophyll-a depletion
around marine mussel farms.
The Monitoring Dilemma
While monitoring dye in effluent plumes or in-situ chlorophyll-a using
fluorometers is by no means new, one of the biggest dilemmas is incorporating
the data collected with positional data to create maps and/or charts.
Historically, this was done in the field by writing down position
and fluorescence readings or entering them into a laptop. However,
manual data collection can be both tedious and fraught with potential
transcription errors.
The change from analog to digital instruments has greatly enhanced
the ability to collect and log fluorescence data, but that’s only
half the story, since position data are also required. The advent
of Global Positioning Systems (GPS), and the subsequent removal of
selective availability, has meant that accurate (i.e. ± 2-5 m) real-time
position data are now both readily available and affordable. Also,
along with the improvements in instrumentation, the ability to run
desktop GIS has been rapidly improving. Therefore, in order to create
real-time maps, these three components: GPS, GIS, and fluorometry
need to be combined.
The Solution
Cawthron has created a custom add-on to Arcview ® 8.3 GIS that connects
to the different simultaneous serial data streams of the instrumentation
in the field (i.e. GPS, SCUFA, 10-AU), combines the incoming data
and maps the fluorescence in real-time as graduated dots. The fluorescence
data are overlaid on a rectified nautical chart or aerial photograph
so that the actual position of each fluorescence reading in relation
to the area being studied (e.g. outfall or mussel farm) can be determined.
This approach has numerous benefits, including the ease of use, time-saving,
the ability to collect large amounts of data, and the ability to view
and make decisions in the field regarding the data collected.
The Arcview® add-on was written in Visual Basic for Applications (VBA®)
and enables the user to select which serial port the instruments are
connected to (Figure 1), the frequency with which data are to be collected
(the capture interval) and the file name to log the data to. In addition,
there is a real-time window that displays current position and fluorescence.
Figure 1. Screen shot of Arcview® serial data capture form.
Once a connection is made the incoming data are parsed into individual
variables. For general monitoring, much of the GPS data is extraneous
and just the position and time data are required. This includes Latitude,
Longitude, Speed, Direction, and Time. Therefore, only certain GPS
sentences are used in the add-on and are converted on the fly to local
New Zealand Map Grid coordinates. All GPS and fluorometric data are
parsed and logged in Arcview® as individual fields within a shapefile.
Case Study 1: Mapping Dye from a Coastal Outfall using a 10-AU
Fluorometer
This integrated logging system was used for a recent study on the
south coast of New Zealand’s North Island, to study dye dispersion
from a nearshore coastal outfall discharging tertiary treated wastewater.
Rhodamine® WT dye was injected into the wastewater at a constant rate
(Figure 2) and effluent dilution and dispersion were mapped on both
an ebb and flood tide. Continuous fluorescence readings were taken
from a vessel using a 10-AU field fluorometer set up for flow-through
measurements and linked to a portable PC and GPS. Data were collected
by running a series of transects through the effluent plume both perpendicular
to and along the effluent plume path. To verify effluent concentrations,
grab samples were collected every 15 minutes using a sequential autosampler
positioned downstream of the injection point.
Figure 2. Configuration of dye injection system in relation to autosampler
and outfall.
A screen shot of the 4,300 data points collected on the four hour
ebb tide study is presented in Figure 3. Receiving water dilutions
of each data point were calculated from the effluent concentrations
measured in the grab samples. Contours of these dilution factors were
manually digitized using the GIS software to better illustrate the
dispersion and dilution pattern of the effluent (Figure 4).
Figure 3. Graduated symbols of all data points collected for mapping
dye dilution/dispersion.
Figure 4. Post-generated dilution contours of ebb tide data points.
Case Study 2: Mapping chlorophyll-a around a mussel farm
Another example of the application of this integrated GIS-fluorometry
system is the real-time mapping of chlorophyll-a depletion around
coastal mussel farms. In order to assess the sustainability of mussel
farms around New Zealand’s coast, the concentrations of chlorophyll-a
(which represents phytoplankton) are measured at 3m (i.e. the active
feeding depth) and incorporated into modelled predictions of sustainability.
This information can then also be used by the farmer to optimise farm
management.
The SCUFA can be employed in a similar way to the 10-AU in outfall
dye studies, providing continuous measurements of chlorophyll-a (post-calibrated)
through and around mussel farms (Figure 5). Typically, currents are
also collected simultaneously with the GPS positions and fluorometry
data, to give insight into the patterns of water movement around the
farms.
In the example below (Figure 5), two synoptic snap-shots were taken
in a bay containing four small farms (delineated by black dotted lines).
The data were then plotted in 2-dimensional colour contours using
an appropriate interpolation method. Depletion areas (blue regions)
are evident in the vicinity of the farms, allowing the magnitude of
depletion to be assessed and the behaviour of the water through the
bay to be observed. The results are then compared against outputs
from various models to improve our confidence in their predictive
capabilities.
Figure 5. Subsurface (3m) contours of Chlorophyll-a concentration
in the vicinity of four mussel farms under two different tidal states.
Conclusion:
Cawthron’s integration of Turner fluorometers with GPS and GIS for
real-time mapping has had major benefits in the way we use these instruments.
The efficiency with which data are collected ensures research is conducted
in a cost effective manner. Further, field data can be tracked visually
and any anomalies in spatial distribution are immediately apparent.
This helps ensure data validation and overall data integrity.
For details on this and/or other capabilities that Cawthron offers,
please contact Paul Barter (paul.barter@cawthron.org.nz)
or:
Cawthron Institute
98 Halifax Street East
Nelson, New Zealand
http://www.cawthron.org.nz
Email: info@cawthron.org.nz |
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