Water Monitoring

Water Quality Data

Stony Brook Water Flow Data
The Stony Brook flow-meter is located near the Cathouse.

MHC Lakes and Stony Brook Water Quality Monitoring

Water Sampling Locations map [PH]

(select image for larger view)


Description of Sampling Locations

Site 1: This point is located where Stony Brook enters the campus properties. It is on the upstream side of the culvert that passes under Morgan St. It is reached by climbing down the riprap on the eastern side of the culvert.

Site 2: Located where the Upper Lake Hiking Trail crosses Stony Brook. A foot bridge spans the brook at this point. Samples are taken from the downstream side of the bridge.

Site 3: This point is on the eastern side of Upper Lake dam. Samples are taken on the upstream side of the dam.

Site 4: Samples are taken from the upstream side of the "Cat House" dam. The samples are drawn from the western side of the stream.

Site 5: This point is immediately upstream from Lower Lake dam.

Site 6: Located just below the Lower Lake dam, close to Morgan Street.

Site 7: This point is on the small stream that flows from the Orchard's Golf course into Upper Lake. The point is near the outflow of the stream, but above the area where stream water might mix with lake water.

Site 8 (not shown): This point is also on the stream that flows from the Orchard's Golf Course. It is farther upstream than Point #7. The point is immediately upstream from the junction where the stream passes under Silver St. (sampled per certain period of time).

Sampling Intervals: Samples with the YSI probe are taken on a biweekly basis. We are currently sampling at all sites. As the weather becomes colder, and the lakes and streams freeze, many sampling points are no longer safely accessible. 

The watershed based approach is the guiding principal of water quality management and regulation by state and federal agencies.Please refer to EPA Web site for basic information about drinking water contaminants.

Equipment: YSI  6600v2 & YSI Professional Plus (Nitrate & Ammonium) (YSI = Yellow Spring Inc.  http://www.ysi.com/index.html)


Renge -5 to 45 Celsius, Accuracy +/- 0.15, Resolution 0.01

Is measured using a temperature probe. The Federal Water Pollution Control Administration refer to temperature as one of the most important and most influential water quality characteristics to life in water. Most fish simply can't stand warm water (and low levels of dissolved oxygen which depends on water temperature). Thermal pollution may result when industries, especially electrical power companies, release the water used for cooling their machines into waterways. Water temperatures, even miles from the release points, may rise dramatically.


Renge 0 to 200%, Accuracy +/- 1% air saturation, Resolution 0.1% air saturation

Dissolved Oxygen saturation (percent dissolved oxygen), measures the saturation level of oxygen at the present water temperature. The sensor (with self-cleaning wipers) is the newest optical type, based on the luminescence lifetime method. Oxygen gets into water by diffusion from the surrounding air by aeration and a by-product of photosynthesis from aquatic plants and algae. DO saturation is temperature dependent. The measure of DO is one of the most frequent and most important methods for the investigation of water quality. If dissolved oxygen concentration in water drop below 30%, aquatic life is put under stress, if the oxygen levels that remain below  10-20% for a few hours can result in fish kills.


Renge 0 to 20 mg/L, Accuracy +/- 0.1mg/L, Resolution 0.01 to 1 mg/L

Dissolved Oxygen concentration is calculated from % air saturation, temperature and salinity. The sensor (with self-cleaning wipers) is the newest optical type, based on the luminescence lifetime method. If dissolved oxygen concentration in water drop below 2-3.0 mg/L, aquatic life is put under stress, if the oxygen levels that remain below 1-2 mg/L for a few hours can result in fish kills.


Renge 0-200 mg/L, Accuracy +/- 10%, Resolution 0.001 to 1 mg/L (Range dependent)

Nitrate nitrogen (NO3-N) is measured using an ion-selective probe. Water naturally contains less than 1 milligram of nitrate-nitrogen per liter. Higher levels indicate that the water has been contaminated. Common sources of nitrate contamination include fertilizers, animal wastes, septic tanks, municipal sewage treatment systems, and decaying plant debris. State and federal laws set the maximum allowable level of nitrate-nitrogen in public drinking water at 10 milligrams per liter (10 ppm, parts per million).


Renge 0-200 mg/L, Accuracy +/- 10% of reading, Resolution 0.001 to 1 mg/L (Range dependent)

Ammonium nitrogen (NH4-N) is measured with an ion-selective probe. Please note that the term "ammonia" covers both the nonionized form (NH3) and the ammonium cation (NH4+). Air in urban areas contains up to 20 µg of ammonia per m3. Air in areas where farm animals are intensively reared may contain levels as high as 300 µg/m3. Natural levels of ammonium ion in groundwater are usually below 0.2 mg/L Higher natural contents (up to 3 mg/L) are found in strata rich in humic substances or iron or in forests. Surface waters may contain up to 12 mg/L. The presence of ammonium ion at higher concentrations is an indicator of faecal pollution.


Renge 0 to 100 mS/cm-1 Accuracy +/- 5% of reading, Resolution 0.001 to 0.1 mS/cm-1 (Range dependent)

Conductivity is measured using a 4 electrode cell with autoranging. Electrical conductivity is a measure of water’s ability to conduct electricity, and therefore a measure of the water’s ionic activity and content. The use of specific conductance [SC; units of milliSiemens per centimeter (mS·cm-1)], the conductivity normalized to temperature of 25 ºC, allows valuable comparisons to be made, as conductivity of the same water changes substantially as its temperature changes. SC is generally found to be a good measure of the concentration of total dissolved solids (TDS) and salinity. Elements whose ionic forms contribute the most to these measures include: calcium (Ca2+), magnesium (Mg2+), sodium (Na+), potassium (K+), bicarbonate (HCO3-), sulfate (SO42-), and chloride (Cl-). Values of SC can differ greatly from lake to lake because the composition of inflowing tributaries reflects the geology of their watersheds.


Renge 0 to 14 units, Accuracy +/- 0.2 units, Resolution 0.01 units

Acidity is measured using a glass combination electrode. The pH value determines whether water is hard or soft. The pH of pure water is 7. In general, water with a pH lower than 7 is considered acidic, and with a pH greater than 7, basic. The normal range for pH in surface water systems is 6.5 to 8.5.

Chlorophyll a

Renge 0 to 400 µg/L, Accuracy Not Provided, Resolution 0.1 µg/L

An in situ optical fluorometer with mechanical cleaning is used to detect chlorophyll a levels, a green pigment found in algae and blue-green-algae (cyanobacteria). Optical fluorescence method is one of the most powerful and widely used not destructive technique to measure the algae concentration in water. Chlorophyll a concentrations are an indicator of phytoplankton abundance and biomass in lakes, ponds, coastal and estuarine waters. Algal biomass, measured as chlorophyll-a (chl-a), is a commonly proposed criterion of water quality, that relates to nutrient levels (N and P). Usually chl-a values are 35 µg L–1, but could be as high as ~100 µg L–1. High values of chl-a may indicate that "bloom" of algae and/or blue-green-algae may occur. In the drinking water the long term average chl-a concentration at the depth of 0.5 m below the surface shall not exceed 10 µg L–1.

BGA – Blue-Green Algae

Renge ~0 to 280,000 cells/mL† 0 to 100 RFU, Accuracy ~220 cells/mL, Resolution 1 cell/mL, 0.1 RFU

BGA – Blue-Green Algae (true bacteria) Phycocyanin sensor with self-cleaning wipers.  Blue-green algae (cyanobacteria) monitoring is of growing interest due to the problems some species can present through the production of toxins and compounds that deteriorate the quality of drinking water and through the formation of blooms. The simple technique of in-vivo fluorometry (IVF) for locating and measuring algae in real-time has been used. It is based on the direct measurement of the fluorescence of the chlorophyll a in the living algal cells. 


Renge 0 - 1000 NTU, Accuracy Accuracy +/- 5% reading or 2 NTU, Resolution Resolution 0.1 NTU Optical sensor type with mechanical cleaning. Turbidity is a unit of measurement quantifying the degree to which light traveling through a water column is scattered by the suspended organic (including algae) and inorganic particles. The scattering of light increases with a greater suspended load. Turbidity is commonly measured in Nephelometric Turbidity Units (NTU). Governments have set standards on the allowable turbidity in drinking water. In the United States, the allowable standard is 0.3 NTU, with many drinking water supply utilities striving to achieve levels as low as 0.1 NTU.


Page designed, created and maintained by Leszek Bledzki
Peter Houlihan – text and pictures marked [PH]