To Save for Water QualityNorwalk River Watershed Association
Historic Readings of Water Quality in the Norwalk River:
The Trends at Perry Avenue…
The best published record of the water quality in the Norwalk River comes from a 17-year series of sample measurements recorded by the USGS at near the Perry Avenue bridge in Norwalk. Perhaps the most important component of riverwater is dissolved oxygen. Fish, insect larvae, and all other forms of animal life in the river die if the oxygen is depleted. The typical amount of oxygen in riverwater is about 10-12 mg/l (milligrams per liter), and Connecticut requires the amount of oxygen to remain above 5 mg/l except in the most extreme droughts. In a 17-year series of data collected by the USGS near the Perry Avenue bridge in Norwalk, the dissolved oxygen had an average value of 11.7, and a minimum reading of 6.04. A slight downward trend may be due to the fact that in recent years a larger percentage of the measurements were made in the summertime when the oxygen levels are low.
Any discussion of Connecticut’s riverwater is officially divided into five distinct categories:
|AA||Water for public reservoirs|
|A||Other drinkable river water|
|B||Undrinkable but satisfactory|
How can we decide whether a river’s water is “good”? The most direct approach would be to drink a large quantity of the water and discover any consequences a short time later (but don’t try that!). Two variations on this approach are used for actual tests of riverwater:
The first method is to start with a list of waterborne materials that are known to be good or bad, and then, rather than drinking the water sample, analyze it scientifically to determine how much of these good and bad ingredients it contains. The results of these tests can give a wealth of information about the dangers posed by the water and the trends over time in a positive or negative direction.
The second method is to examine the health of all the tiny river-dwelling animals that “drink” the water continuously. If they are numerous and thriving, it tells us that certain minimal conditions must be present in the water. If the river is polluted by a series of severe episodes (like the weekly discharge of a load of poisons), the tiny animals might all be dead, but most water samples would indicate an excellent water quality (except during the brief episodes).
Method 1: Water Samples
The United States Geological Survey (USGS) tests water samples from many of the Nation’s rivers on a regular basis. The most important results are published once a month, and the entire set of results is released to the public annually.
For the Norwalk River, the USGS has performed tests approximately once per month since 1980 at a site near the Perry Avenue bridge in Norwalk. The entire set of USGS data is held in an archival database (STORE-T) administered by the US Environmental Protection Agency (EPA). The archival data from the EPA has been combined here with the more recent data from the USGS’s Connecticut website to give a complete picture of the sampling data.
Many other organizations beside the USGS have made important measurements of the water quality of the Norwalk River. One organization that is particularly active in this field is the Nature Center for Environmental Activities in Westport. It has earned governmental certification for its rigorous quality control standards and has begun an ambitious program to sample the watershed at many points to get a map of the water quality. We would be happy to publicize that data or any other significant datasets that have been collected within the Norwalk River watershed. If you have any such data, please contact us. Thanks!
1. Important “basic” components
The following components of riverwater can be measured relatively easily by students or “volunteer monitors” and play a vital role in determining a river’s condition.
OXYGEN. Fish, insects, and all other forms of animal life require oxygen to survive. The amount of oxygen dissolved in a river’s water is one of the most important indicators of the river’s overall health. It can be expressed as a total amount of dissolved oxygen per liter of water or as a percentage of the maximum amount that can be dissolved in still water at the ambient temperature. Agitated water can have percentages over 100%, as can water with active chemical or biological processes.
NITROGEN. When excess nitrogen pours from a river into a confined region such as Long Island Sound, it often creates algae blooms which deplete the water’s oxygen and kills aquatic life. Consequently, this element is watched very closely. It occurs in three main forms in riverwater: nitrites, nitrates, and ammonia, and it can be separated into organic and inorganic components. The USGS currently measures (or used to measure): total nitrite, dissolved nitrite, total nitrite plus nitrate, dissolved nitrite plus nitrate, dissolved ammonia, total ammonia plus organic, and dissolved ammonia plus organic.
PHOSPHOROUS. Excess phosphorous produces rapid plant growth which can choke off waterways. The following variables have been recorded total phosphorous, dissolved phosphorous, and dissolved ortho phosphorous.
pH. The concentration of hydrogen ion activity (essentially the opposite of acidity) dictates a solution’s pH. Neutral water has a pH value of 7.0, and the value decreases as the water’s acidity increases. Every aquatic organism has a certain range of pH values that it can tolerate. Considering all of the problems with acid rain, many people are surprised to learn that our rivers tend to be more base than acidic. The variable comes in two forms: pH (Field Measurement) and pH (Lab Measurement).
ALKALINITY. A water’s alkalinity refers to its capacity to neutralize acids. Since this acid “buffering” capacity is often produced by bicarbonates in the water, the alkalinity parameter is related to the bicarbonates, and the carbonates. Three other carbon measurements are also made: total organic carbon, dissolved organic carbon, and organic suspended carbon.
CHLORIDE. The presence of excess chloride in riverwater can indicate a source of salt (perhaps roadsalt) entering the river. A closely related element, but important mainly in drinking water, is fluoride.
2. Other basic measurements
The following measurements are usually collected whenever a water analysis is made, though they do not involve specific materials in the water. Three other parameters, the color, taste, and odor of the water, are mentioned in Connecticut’s water-quality regulations but are not quantified in the USGS data.
FLOW RATE. Officially listed as instantaneous discharge, this is the amount of water flowing past a fixed point on the shoreline per unit of time. The flow rate in South Wilton is recorded daily by an automatic measurement device, and a graph of that data for any calendar period can be obtained from this site.
TEMPERATURE. Both water temperature and air temperature are recorded.
ELECTRICAL CONDUCTANCE. Officially listed as specific conductance, this indicates the presence of salts and other impurities in the water.
TURBIDITY.The opaqueness or non-clarity of the water. Since opaqueness is often caused by suspended solids, the turbidity parameter is related to suspended sediments, fine suspended sediments, total solids, and dissolved solids.
3. Advanced measurements.
The following measurements are not usually included in a “basic” set, suitable to be done by students or volunteers. Many of them require complex equipment or intricate procedures.
BACTERIA. Bacteria give a warning of possibly dangerous biological contaminents in the water. These measurements are exceedingly important but are difficult to perform reliably. The following bacteria counts are provided by the USGS: enterococci, fecal coliform, and fecal streptococci.
METALS. Many different metals can create medical problems if they’re ingested even in small amounts. Consequently, the USGS measures and reports trace quantities of all of the following elements: aluminum, antimony, barium, beryllium, cadmium, calcium, chromium, cobalt, copper, iron, lead, magnesium, manganese, molybdenum, nickel, potassium, silver, sodium, uranium, and zinc.
NON-METALS.The following components of the water are also measured: silica, sulfate, total hardness, and cal hardness.
Method 2: Aquatic Animals
The small animals that live in streambeds, often clinging to the bottom surfaces of rocks, are called benthic macroinvertebrates. “Benthic” refers to the location, at the bottom of a body of water, and “macroinvertebrates” refers to simple organisms that are large enough to be seen by the unaided eye.
Some of these organisms are very sensitive to pollution, while others are only moderately sensitive and a third group is largely insensitive. When a survey is made of these creatures, the best result is to find a large variety of species including many of the pollution-sensitive types. The actual count of the individual specimens is not nearly as important as the diversity.
Back in 1982, a detailed report was published giving the results of a benthic macroinvertebrate study on the Norwalk River [“Derivation of Site Specific Water Quality Criteria for the Norwalk River at Georgetown, Ct.” by L.E. Dunbar and E. Pizzuto]. It listed 38 different varieties (taxa) that were observed, and several of them were pollution sensitive. Other studies have generally produced good or borderline-good results. A new study is currently in preparation, and we hope to publish the results when they are available.
So?? Is it Good or Bad?
Connecticut’s riverwater is officially divided into five distinct categories:
|AA||Water for public reservoirs|
|A||Other drinkable river water|
|B||Undrinkable but satisfactory|
The water at the Perry Avenue bridge should fall into category B. This quality of riverwater is defined in a CT-DEP document, Water Quality Standards (effective April 8, 1997), which places requirements on 13 different parameters. These requirements can be characterized (in part) as follows:
|1.||Aesthetics||Good to excellent.|
|2.||Dissolved Oxygen||Not less than 5 mg/l at any time.|
|4.||Color||Essentially no visible discoloration.|
|5.||Suspended Solids||None which would impair the most sensitive uses.|
|6.||Silt and Sand||Normal roadsand is allowed “provided all reasonable controls or Best Management Practices are used.”|
|7.||Turbidity||Shall not exceed 5 NTU over ambient levels.|
|8.||Bacteria||Fecal coliform shall not exceed a geometric mean of 200 colonies per 100 ml in any group of samples nor shall 10% of the samples exceed 400 colonies per 100 ml. There are also limits on enterococci in established bathing waters.|
|9.||Taste and Odor||None that impair the water’s uses.|
|10.||pH||6.5 to 8.0|
|11.||Temperature||No increases that impair water’s use.|
|12.||Chemicals||None that impair the water’s use.|
|13.||Benthic Invert.||Water quality shall be sufficient to sustain a diverse macroinvertebrate community of indigenous species.|
The most troublesome entry on this list is item 8, which specifies the limits on bacteria. Comparing these limits with the fecal coliform measured on the Norwalk River, it seems that the river fails this test. Item 10, pH, is generally in the specified range, and item 2, dissolved oxygen, is always above the required 5.0. (Lower DO values were measured at some points on the river during a severe drought in 1995, but the regulations allow for bad readings in major droughts.)
Is it Getting Better or Worse?
In the area of bacteria, the data seem to show an improvement around 1990 followed by a worsening in the later 1990’s. This subject is currently being addressed very agressively by several organizations, and we should have more definite information when the current studies are complete.
In the areas of nitrogen and phosphorous (which are potentially damaging to the waters of Long Island Sound but are not mentioned in the official class-B criteria) there has been a statistically significant improvement, at least from 1980 to 1992. This is documented in a USGS report on 14 Connecticut rivers. The Norwalk River is the only one that has a significant improvement in all of the studied variables. Two modern wastewater-treatment plants went online along the Norwalk River in the mid-1990’s (in Ridgefield and Georgetown), so the apparent improvement that extends into the 1990’s is probably real, though small.
By far the most conspicuous trend in the data lies in the trace metal measurements (lead, copper, and many others), where a dramatic improvement has occurred, but starting from extremely bad initial levels. The river’s chloride and electrical conductance measurements seem to be increasing, indicating possible salt problems in the river.