|Dawson, Michael N||University of California-Merced (UC Merced)||Principal Investigator|
|Copley, Nancy||Woods Hole Oceanographic Institution (WHOI BCO-DMO)||BCO-DMO Data Manager|
Physical parameters describing Palau marine lakes, 2011-2015. Reported parameters include surface area, distance to ocean, tidal efficiency, depth, and stratification.
* NOTE: The P.I.'s are using this dataset to write papers. Please contact them before using these data to make sure you are not duplicating efforts.
Lake Bathymetry Mapping
The bathymetry of the lakes was recorded with a purpose-built lightweight, low-power echosounder unit with integrated GPS and AHRS (attitude and heading reference system), towed behind a kayak. (Data courtesy of Herwig Stibor, Thomas Stieglitz.)
Lake Bathymetry Analysis
Raw bathymetry data were down-sampled to include one sample every 2 m distance along the survey track. Data were visually inspected and false soundings removed. In some lakes, GPS reception was partially compromised along the steep shorelines. Where required to not compromise data density, the survey track was reconstructed from field notes and AHRS data (less than 5% of data where applicable). During the bathymetry surveys, tidal water level was not recorded. Therefore, tidal water level variations were corrected for by modeling tidal water level in each lake. The water level for each lake was correlated with tidal water level measured at a reference station at CRRF or predicted tide (x-tide database), by determining tidal lag time and tidal efficiency (see below) from data previously collected concurrently in the respective lake and at this reference station. Subsequently, bathymetry data was reduced to a grid with 2m resolution by kriging of a further down-sampled subset of data using every third data point. Lake-specific variograms were applied, and contour lines and total lake volumes were calculated in a GIS. (Data courtesy of Thomas Stieglitz.)
Distance from lake to ocean & lake surface area
Lake shorelines and island coastlines were manually extracted from satellite data (Microsoft Bing). The nearest, mean and median distance of each lake to the respective island’s coastline as well as lake surface area was calculated in a GIS. The perimeter was measured in meters using the ‘Measure Line’ tool in QGIS 3.4.
Habitable surface area for benthic organisms was estimated either as (1) a multiple of the perimeter and depth of the chemocline, i.e. assuming a cylindrical model for the lake, or (2) as the area of a frustum, i.e. a truncated cone, using the perimeter of the lake at the surface, the average length of transects, and the average angle of the transect from the vertical (estimated using the sine of maximum depth / transect length).
Tidal lag time and tidal efficiency were calculated from concurrently measured tidal water level in a lake and the adjacent ocean. The tidal lag time — the time between high tide in the adjacent ocean and high tide in the lake — was determined by least-square fit between lake and ocean tide measured using HOBO 30-foot depth Titanium water level data loggers (Part # U20-001-01-Ti). Tidal efficiency was calculated as the ratio between amplitude of ocean tide and lake tide (e.g. Ayers, JF and Vacher, HL, 1986. Hydrogeology of an Atoll Island: A Conceptual Model from a Detailed Study of a Micronesian Example. Groundwater 24(2) 185-198.). Larger tidal lag time and smaller tidal efficiency respectively indicate a less efficient hydrological connection between ocean and lake.
Error-checking: Estimates of basic dimensions (depth, distance, length, surface area) were double-checked manually for a subset of measurements by a second person using using Google Earth.
- added conventional header with dataset name, PI name, version date
- reformatted date from dd-Mon-yy to yyyy-mm-dd (ISO date format)
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|lake||common name for lake||unitless|
|lake_code||3-letter code for sampled lake name||unitless|
|volume_m3||estimated volume of the lake (m3)||meters^3|
|surface_area_m2||Surface area of the lake (m2).||meters^2|
|distance_to_ocean_min_m||Minimum distance from a lake’s edge to the surrounding lagoon (m)||meters|
|distance_to_ocean_mean_m||Mean distance from a lake’s edge to the surrounding lagoon (m).||meters|
|distance_to_ocean_median_m||Median distance from a lake’s edge to the surrounding lagoon (m).||meters|
|tidal_efficiency||the ratio between amplitude of ocean tide and lake tide.||unitless|
|mean_transect_length_m||average of distance_trans for the lake from https://www.bco-dmo.org/dataset/541181||meters|
|max_actual_depth_m||maximum depth_m for the lake from https://www.bco-dmo.org/dataset/541181||meters|
|perimeter_m||circumference of lake (m).||meters|
|habitable_surface_area_cylinder||An estimate of the area of the benthic zone above the chemocline; based on the model of lake shape as a cylinder.||meters^2|
|habitable_surface_area_frustum||An estimate of the area of the benthic zone above the chemocline; based on the model of lake shape as a truncated cone.||meters^2|
|stratified||whether a lake is vertically stratified (1) or holomictic (0)||unitless|
|tidal_lag_time_minutes||the time between high tide in the adjacent ocean and high tide in the lake||minutes|
|Dataset-specific Instrument Name|| |
HOBO 30-foot depth Titanium water level data loggers (Part # U20-001-01-Ti)
|Generic Instrument Name|| |
|Dataset-specific Description|| |
Used to determine tidal lag time, the time between high tide in the adjacent ocean and high tide in the lake.
|Generic Instrument Description|| |
Electronic devices that record data over time or in relation to location either with a built-in instrument or sensor or via external instruments and sensors.
Small boats - CRRF
|Start Date|| |
|End Date|| |
Palau marine lakes
This document is created by info v 4.1f 5 Oct 2018 from the content of the BCO-DMO metadata database. 2020-02-18 11:45:24