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Mokupuni (large islands) of Hawaiʻi (Aliʻi Nui or Head Chief)
Kauaʻi
Niʻihau
Kahoʻolawe
Lānaʻi
Molokaʻi Maui
Hawaiʻi
Oʻahu
“Typical” Ahupua‘a
Konohiki Oversees • Water • Forestry (timber,
clothing) • Agriculture (kalo loʻi,
breadfruit, etc.) • Onshore/Nearshore
Fisheries (including aquaculture)
• Offshore Fisheries
Characterize water quality (WQ) in watershed
Study temporal and spatial variations in WQ
Determine effect of NPS pollutants on WQ
Quantify natural and NPS contributions during base-flow and storm conditions
Evaluate potential effects of NPS pollutants on nearshore biota
Determine trace element and total suspended sediment (TSS) loads to coastal ocean
UHM Watershed Study Objectives
Discrete Sampling Program
Manual quarterly sampling, usually base flow (4 years)
Automated storm sampling (4 years)
Streamflow & T, C, pH, DO & turbidity at 5-minute intervals (4 years)
Estuarine grab sampling & water quality measured in situ concurrently with DGTs (7 months)
DGT Study Design
Compare 7 months of DGT results with stream data from discrete base- & storm-flow samples collected over 4 years
Compare DGT results with data from weekly discrete samples collected concurrently with DGT retrievals over 7 months
Estuary
Lower Watershed
Upper Watershed
Components of a DGT Sampler ABS plastic outer sleeve & piston 0.45-µm, polysulfone membrane filter Polyacrylamide hydrogel (~95% water) Layer of Chelex-100® resin in hydrogel
DGT-Grab Comparison - Stream
Expected DGT concentrations (dissolved → colloids, i.e., ~0.02 µm) to be lower than discrete samples (0.2-µm filters)
DGT vs. Grab Sample Copper Mystery (So, what happened here? Manual sampling missed
something? Diel cycle in Cu?)
Mahalo! Questions?
Michael Tomlinson UHM Oceanography, Flagstaff, AZ 86004
928-266-2236, [email protected]
Continuous Monitoring Challenges Many samples, disparate intervals Cellular transmission Biofouling Calibration & biological long-term drift Data review and quality control
Many Samples, Disparate Intervals Component
Interval (min)* №/Yr
NWS Precipitation 15 35,040 USGS Streamflow 15 35,040 NOS Tides 6 87,600 NOS Meteorology (wind, T, P) 6 87,600 HiOOS NS (P, T, S, chl, turb) 4 131,400 HiOOS WQBs (T, S, DO, chl, turb) 20 26,280 HiOOS KNO (waves, currents, scatter, T) 20 26,280 HiOOS AUV (bathy, T, S, chl, scatter, curr) ~0.001 ~57,500/hr Event Sampling (varies) varies varies * Statistical analysis may require uniform interval using GRAN, Aquarius®, etc.)
Cb = bulk solution concentration δ = DBL (diffusive boundary layer) thickness Δg = diffusive gel thickness (ideally ≥10 × δ)
How the DGT
Works
DGT Assumptions & Requirements
Diffusive boundary layer thickness δ (unknown) not significant relative to length of DGT diffusion path Δg
Diffusion coefficients of the aquo ions represent most of the species present
Biofouling is not interfering with diffusion process
Ionic strength >1 mM (~60 µS/cm) pH must be >5 and <10
Discrete Sample Processing
Step 1 Filtration (0.2 µm)
Step 2 Acidification
(quartz distilled HNO3)
Step 3 FIA (8-HOQ
resin)
Step 4 ICP-MS analysis
DGT Processing Step 1 - DGT disassembly
Step 2 - Removal of resin gel
Step 3 - Resin gel leaching (24 hr)
Step 4 - ICP-MS analysis of DGT leachate
Calculating Mean Concentration
where: Cw = mean metal concentration in water M = mass diffused into DGT Δg = diffusive hydrogel thickness + membrane filter thickness DT = diffusion coefficient at any temperature t = deployment (exposure) time A = area of DGT window
WQB Sensor Information
Sensor Res/Prec Accuracy Cost
SBE 16plus CTD $23,000
Temperature 0.0001 °C 0.005 °C
Conductivity 0.00005 S/m 0.0005 S/m
SBE43 & 63 DO – 2%
WET Labs FLNTU
Chlorophyll 0.01 µg/L –
Turbidity 0.01 NTU –
ISUS NO3 Sensor ±0.5 µM ±2 µM or 10% $34,000
STOR-X Telemetry $14,000
C6 Multisensor Platform* various various $17,000
* Equipped with chlorophyll, CDOM, OB/FWA, turbidity, phycoerythrin, & crude oil sensors; battery pack; and mechanical wiper (wish list).