Water Quality Monitoring

by Dave Stevens

Preface – What Are We Measuring?

In 2004 the Friends of Taunton Bay conducted an extensive bay monitoring program that looked at components of bay health. While this examination gave some indication of the health of the bay, it did not establish a comprehensive baseline of water quality to monitor potential changes.

The FTB Executive Committee decided to research water quality monitoring in other saltwater estuaries and to put together a plan to monitor water quality in Taunton Bay. A sub-team of the FTB board collaborated with Mark Whiting, Ph.D., Chair, Board of Supervisors, Hancock Soil and Water Conservation District and drafted a plan over the winter months. In March of this year, led by our President Alice Noyes, we wrote grant proposals to four entities for funding of the project. We have been awarded three of those grants to fully fund the startup and 2022 expenses of the project.

In phase I, starting this June, we will use a boat to sample at the four sites shown in the aerial view on this page.These four sites will form our starting baseline to see what (if any) variation there is in water quality within the bay structure. Testing will occur roughly every three weeks, to coincide with the highest and lowest of the monthly tides. Additional samples will be taken and analyzed where data
indicates a specific need; such as extra-low-tide sampling at specific sites, or investigating areas where there maybe septic or runoff issues. Depending on the variability between sites and depths, we may decrease the number of sites in phase II, and
concentrate more intensely where the data call for more intense investigation. The first year study will test our methods, identify the most reliable indicators, and create a baseline of data with which
to compare past and future studies.

What are we measuring?

Conductivity (salinity), temperature, pH-alkalinity, and dissolved oxygen will be sampled with a YSI hand-held multi-meter (pictured above).

Turbidity (water clarity or sedimentation) will be measured with a phone app called HydroColor (developed by the U. of Maine), which will be compared with secchi disk, and turbidity tube measures of turbidity to see which is most effective. In addition, surface water samples will be collected for lab analysis. With those we can examine several factors including:

• Bacteria – E. coli or coliform
• Pollution – nitrogen and total phosphorus
• Dissolved inorganic carbon
• Chlorophyll-a
• Heavy metals
• TSS (total suspended solids)

Fall 2022 – Early Results

In late 2021, the FTB Executive Board discussed, planned for, and authorized seeking grants for a two-year water quality testing program for Taunton Bay. We wrote in the Spring newsletter about the proposed scope of this project and how fortunate we were to be fully funded by three generous sponsors.
At the time of this writing, FTB volunteers had sampled four designated sites a total of six times each, over the four months of June-September; three at high tides and three at low tides. The four sites are: 1. Gordon’s Wharf in Sullivan, 2. Egypt Bay south in Hancock, 3. Middle channel in front of the Center for Cooperative Aquaculture Research (U of Maine), 4. The Narrows between the lower bay and Hog Bay.
This reports our initial findings. Sample counts are yet too small to make any definitive statements, however early results show an estuary that is well mixed, is a very marine-dominated system, and has numerous positive water quality attributes, with a few concerns. The freshwater influence is seen both at high tide and low tide.

Temperature:

The water temperature has ranged from a low of 56 degrees Fahrenheit (F) at Gordon’s Wharf in mid-June to a
high of 74 degrees (F) at Hog Bay Narrows at low tide in August.
Not surprisingly, at all sites water temps tend to be slightly higher at low tides than high tides (impact of the cooler ocean water reducing temperature of the warmed bay water). They also tend to be warmer as one gets further northeast into the bay and especially into shallower water. For example, in mid-June when the water temp at Gordon’s Wharf was 56F, it was 63-64F in the upper channels. In all sampled cases, water temps also tend to be cooler at greater depths, however the ratio of cooling changes depending on depth, tide stage and amount of mixing. Gordon’s Wharf (well mixed and less than 20 feet deep) has the least drop in temp differential of the four sites (bottom temperature averages 99% of the top temp). Sites #2 and #4 (both shallower and less mixing) have a bottom/top differential of 97%. CCAR inlet (site #3)–the deepest site)–has a ratio of 93% at a depth of 10 meters (the maximum length of our temperature cable).
To look at the impact of the bay on water temperature we compared our average readings at Gordon’s Wharf and Hog Bay Narrows to the temperature at the same time period from the NOAA buoy (ATGM-1) in Frenchman’s Bay off Bar Harbor (Figure 1). What we see is a temperature difference at Gordon’s Wharf of between 1.5 and 8 degrees (F). We see an additional increase of 5-6 degrees (F) from GW to Hog Bay Narrows.

Figure 1. Comparison of water temperatures in the lower bay (Gordon’s
Wharf) and upper bay (Hog Bay above the Narrows) in relationship to the
NOAA buoy in Frenchman Bay (ATGM-1).
Figure 2. A comparison (linear correlation) between turbidity tube and Secchi disk measures of visibility. The correlation equation is y = 23.032(x) + 59.121 and R-square is 0.6189.

pH:

pH measures the acidity or alkalinity of the water. In Taunton Bay it has been very consistent so far )–averaging 7.9 across all samples. As a comparison, pure water is 7.0, and seawater is normally more basic, 8.0-8.5. Marine life, especially juvenile shellfish, grow best at optimal pH levels, (at risk below 7.5). Our individual low sample was 7.7 and our high was 8.0. The majority of samples rounded between 7.8 and 7.9.

Dissolved Oxygen (DO):

DO is considered an important measure of water quality as it is a direct indicator of an aquatic resource’s ability to support aquatic life. DO is a measure of the absolute amount of “free” (think useable) oxygen in the water. Low levels of DO (below 5mg/L) can lead to stressful or deadly conditions for plants or sea animals. The meter we use gives us the percentage relative to normal 100% saturation (water holding 100% of normal saturation given the temperature, the amount of dissolved salts (salinity) and atmospheric pressure). Our samples to date show that Taunton Bay has very high amounts of dissolved oxygen. High tides have averaged 101% near the bottom of the water column and 104% at the surface. Low tides have averaged 92% near the bottom and 98% at the surface. Any measure over 100% is considered super saturated, which means even more oxygen is available for aquatic creatures. This super-saturation happens primarily due to two phenomena: sunny days with lots of photosynthesis and/or turbulent water conditions (think churn at Tidal Falls). Our low reading of DO to date is still acceptable)–86.9% at the CCAR inlet on a low tide 10 meters below the surface. This amount of DO will support any native species that we have in the bay.

Salinity:

Ocean water normally has a salinity of about 35 grams per kilogram (g/kg) of seawater, or 35 ppt (parts per thousand). Seawater generally ranges from 33 ppt to 38 ppt. Our samples in Taunton Bay
have averaged 31.1 ppt on high tides (fresh input of water from Frenchman Bay) and 30.8 ppt on low tides. Salinity is slightly higher at depth than on the surface (on low tides 30.7 at the surface versus 30.9 at depth). It is important to remember that we have only been sampling since mid-June and it has been a dry year so far. It will be interesting to see what happens to salinity at low tides during the rainy seasons of late autumn and spring.

Turbidity:

We have experimented with three methods of assessing water clarity (turbidity) and have settled on two)–a Secchi disk and a turbidity tube. The two are easy to employ and we have found fairly positive correlation between the two methods (see Figure 2), so either are good measures of water clarity or visibility. We have only sampled on days with low wind. On these days, the bay water is fairly clear for an estuary, with occasional pockets of turbidity (also common for an estuary). The turbidity is patchy and unpredictable (not a function of a given site), but more sampling is needed to determine if we can ascertain a causal relationship.

Laboratory Water Samples:

We have experienced a number of issues in our water grab sampling analysis and are changing the analytical laboratory we use. We had anticipated some level of learning curve to fine tune our processes and find partners who could deliver what we need. The lab data as of early September reported many “non-detects” for items that we suspect are in the water at some level (e.g. iron and phosphorus). We have located a
different laboratory which has the capability to provide us with a more refined analysis. Samples so far show “non-detect” or very low levels of arsenic, copper, iron, lead, and manganese. Levels of calcium and magnesium are slightly lower than what is reported for “normal” seawater, which makes sense since we should find some mixing with freshwater sources. Uranium is reported between 2.9 and 3.1 ug/L, which again is slightly diluted from what is reported as the average in the Atlantic (3.3 parts per billion). While coliform and E. coli bacteria samples were under acceptable limits for swimming at GW in June, in August results were above Maine’s acceptable limits of 235 MPN*/100ml. The range of E. coli present was 69 to 388 and coliform ranged from 488 to 1120 MPN/100ml (lower at GW and CCAR inlet and higher at Egypt Stream and Hog Bay channels). This seems to indicate that the primary source is from upper parts of the bay (not ocean water), although this is an obvious avenue for further exploration. We wish to note that both Egypt and Hog Bays have areas of shellfish restrictions/closures due to bacterial contamination. Both also have large bird populations which may account for some of the elevated numbers.

Summary:

In general, the water quality monitoring program is off to a good start. We are learning almost every time we sample and are incorporating these best practices into our processes. We plan to monitor through November of this year and start again in May of 2023. Our results so far have created a beginning baseline for water quality in Taunton Bay. In October we will reduce our comprehensive “scatter-gun” approach and start concentrating on identified areas of concern.

*MPN= Most Probable Number

Relating Lectures:

Water Quality Program Kickoff: Dave Stevens, 2022

Predicting & Monitoring Water Quality in the bay: Dr. Lauren Ross, U of Maine Orono, and Hannah Horecka, Dept. of Marine Resources, 2022