Page 8 - Customer Needs and Use Assessments (CNUA) of pH Sensors

ACT In Situ pH Sensors Customer Needs and Use Assessment.............................................................................. 7
4. What is your depth range (m)?
The lower depth among the 42 respondents who answered this question averaged 0.2 m (± 0.8 m) and ranged
from 0 – 2m with a median depth of 0 meters (surface). The deepest depth averaged 538 m (± 1220 m) with
extremes that ranged from 1 to 5000 m; however, the median depth indicated a much shallower
depth of only 30 m.
5. What is your salinity range (PSU)?
The main finding with this question is that it is rare among the respondents surveyed to take in situ pH
measurements at a single salinity. Those 2.9% (2) respondents who work solely in freshwater understandably
work within a narrow range, but another 9.8% (4) reported working either at a single brackish salinity of 16 or
within a narrow range of 0 – 8.5 PSU.
The low range of salinities selected by the respondents averaged 14.3 PSU (± 13.9 PSU) with a range from 0 – 36
PSU and a median of 15.0 PSU. The upper high salinity ranged from 5 – 100 PSU, averaging 33.8 PSU (± 14.2
PSU) with a median of 35.0 PSU.
The majority of in situ pH sensor users surveyed (85.3%) appear to work within tiered, discrete salinity ranges,
which have in common an end member nominally above oceanic salinities (>36 PSU). Stepping up through
the tiers, 31.7% (13) indicated working in a salinity range between 0 – 40 PSU; 14.6% (6) indicated 10 - 35 PSU
(although one respondent listed a maximum of 100 PSU). Another 14.6% (6) worked between 20 – 40 PSU.
Finally, the remaining 24.4% (10) worked between 30-40 PSU.
6. What is your temperature range (C)?
Among the 42 respondents who answered this question, the “low” temperature in their pH working range
averaged 4.9ºC (± 6.8ºC) and ranged from -5–20ºC with a median response of 4.0ºC. “High” temperature
averaged at 27.9ºC (± 7.2ºC) with extremes that ranged from 15 to 50ºC; however, median temperature was 30ºC.
7. Please describe the amount and nature of the particles where pH is being measured (e.g. turbid,
biological particles, mineral, etc…).
Thirty-nine respondents described the particle load they encountered when measuring pH. One fifth (20.5 %)
reported working in clear water with no noticeable turbidity. Two reported the incidence of some biological
particles Biofouling was more important than particles in two cases, indicating the similarities in particle-laden
water versus relatively clean water but with instruments perhaps fouled, silted and creating a similar sampling
environment. CaCO3 from nearby reefs characterized the inorganic particulate load, but this group tended to
work in oligotrophic waters. Clays, carbonate silts, aluminosilicates are examples of inorganic particles often
encountered. Algae (phytoplankton and crustose algae), invertebrates, and detritus were commonly cited as the
most prevalent biological particles.
The remaining 79.5% of respondents reported taking pH measurements under turbid conditions, subdivided
with 25.6% under consistently turbid conditions and 53.8% under variable turbidity. So, more than half of the
respondents surveyed contend with more dynamic conditions such as in estuaries or in waters with short periods
of high productivity, blooms, episodes of run-off, near vents, seasonal events, dredging operations, or highly
turbid glacial melt. One respondent works in bodily fluids.