'Water Quality Monitoring'
When my father would tell me that I was dense, I did not take it as a compliment, but I did not quite understand the insult either. It did not occur to me that what he meant to tell me was that I was incapable of learning, stupid, even, because I knew that for my father, to be dense was to be a jackass: stubborn. But density is oh so much more. There is a certain power in density, mass divided by volume, in certain circumstances that my father may have, in some askew manner, been actually keying me in on.
In the world of our river, density comes mostly in to play in the interplay between salt water and fresh. If you just consider the comparison between a glass of fresh water, and a glass of water of the same volume into which a table spoon of salt has been added, it is plain that the added salt would make the water weigh more and, therefore, be more dense than the glass of fresh water. But water is water right? So when salt water meets fresh, they should mix and find some medium between the two, right? This is true, but the mixing is not instantaneous. The variables of density, temperature and flow affect the time that it takes for the solution to find this medium point.
There is a fun way to test this effect. You will need four glasses, two of which are filled with water, blue and yellow food coloring and ½ cup of salt. One glass of water will remain as is, but into the other you should add the ½ cup of salt. Should the salt not dissolve entirely upon stirring, you can heat the water slightly in a microwave, stirring occasionally until dissolved. Add 4 drops of yellow food coloring to the fresh water, and 4 drops of blue to the salty water. Pour half of each color into one of the empty glasses so that you know have a two half glasses of yellow (fresh) water and two half glasses of blue (salty) water at approximately the same temperature. Slowly add the salty water to the fresh and ved versa and compare how the two mix and become another color or find where you can see where the two remain separate. If you have tries the experiment, or perhaps if you have not, you will note that the salty water tends to stay towards the bottom of the glass. The same happens in a tidal estuary such as in the Soundview area and farther upstream, only instead of water being added from above, you have two walls of water moving towards one another. The salt water is carried upstream by the tides and the fresh water is carried downstream by gravity. There is a point where these two meet and it is called the salt wedge. The Denser salt water pushes under the fresh water, settling towards the bottom, as the
Lighter fresh water floats over the top.
This wedge can stretch for miles as it does in the Hudson, or it can be much more vertical if the flow of the river is equally matched by the rise of the tide. In the case of the Hudson, the salt wedge is carefully watched since Poughkeepsie gets much of its drinking water directly from the Hudson. If the salt wedge runs too far north, the flow is increased to push it back down south. Sampling the water at different depths will show the differing salinities.
Fresh water means less than .5 parts per thousand (ppt) of salt, while brackish water is between .5 ppt and 17ppt, and oceans average 35 ppt. Most estuaries, like the Bronx River Estuary, are brackish. At our last monitoring of Drew Gardens miles above the mouth, Sally found2-3 ppt salinity from a surface sample. As a I walked upstream to get a few pictures of The Phipps Youth Employment Program students that were being introduced to water quality monitoring, I saw a nice size blue crab crawling across the bottom of the river in an area were the flow was quite slow.
I thought that the water would be dangerously low in salt for this creature which thrives 10ppt-25ppt but there could be mitigating factors. One is that the test we had done was surface which means that towards the bottom it could have been a little more salty. There is also an interesting study from 2005(POSEY Martin H. (1) ; ALPHIN Troy D. (1) ; HARWELL Heather (1) ; ALLEN Bryan (1) ) that discusses the tendency for juvenile blue crabs to seek areas of lower salinity(3ppt) in the summer and the fall. The theory put forward by the authors is that they are actually looking for waters safer from predators since salinity and predators were positively related. In any case, it shows the river’s improvement and, should this crab not be atypical, demonstrates the importance of this part of the estuary to all waters down river.
Dad may have been right about my being dense, but now I know that density can also have its advantages.
DG
July 21st, 2008
Knowledge is like a virus in that once you learn one thing, it is hard to stop it from stretching into learning another. The simple act of reading or listening can cause a word or an idea to hang in your mind until another comes across and makes the connection permanent. It is as though we are all our own zone of proximal development. On April 23rd I was lucky enough to work with the Friends of the Bronx Zoo to, ostensibly train or re train 7 people in water quality monitoring. The zoo has a history of monitoring several FOZ were interested in getting back into the flow. As I spoke about pH and buffers, I had a fairly clear idea that I knew what I was talking about. As I added water to the pH 4 buffer, I wanted to show how to dilute it and raise the pH. Instead, it actually went down before hovering back around pH 4. “You have just proved that it is a buffer,” Dione, one of the FOZ said. “That is why it is a buffer, and not just a solution with a pH of 4. It is making sure that the pH stays stable.” I thanked my student and then moved on. Dione, as it turns out, has a PhD in chemistry and should have been the one speaking to the group. But, that little thing she pointed out to me sent me off to look for more information.
One of the parameters that the Bronx River Stewards measure is pH. Most people know something about pH and its relationship to acids and bases, but just what does that mean, and why is it important to our river? What does the pH level tell us?
The term pH is derived from the French puissance d’hydrogene, meaning “strength of hydrogen”, referring to the hydrogen ion that affects acidity. The pH scale runs from 0-14 with values less than 7 being acidic and values greater than 7 being basic. At 7, there is equilibrium between the two. The scale is logarithmic, with each level having a difference of a power of ten from the other. So pH 5 is ten times more acidic than pH 6.
pH values of natural water vary, but below 5 or above 9 are detrimental to organisms, and normal values range from 6.5 to 8.5. Most aquatic life, however, has adapted to specific pH and sustained change can cause damage to a population.
To counter these changes, natural water acts as a buffer. A buffer resists change, like the pillows that my wife and I pile up to keep my 8 month old away from of the stereo. She pushes against them, put they bounce back, and Bethania cannot change my radio station (NPR builds vocabulary). The Bronx River Stewards use buffers of set values, 4, 7 or 10, to make sure that the pH meter is working correctly. The pH values of these solutions can only be changed by adding a buffer of a differing value. Natural water should react in the same way; using the natural hydrology to create a buffer against change. The problems occur when either a stronger acid (acid rain, pH 5.6) or a stronger base (concrete washout water>12) enters the system and causes a rapid change to the pH level.
But a pH change can be a secondary effect as well. For example, photosynthesis uses up dissolved carbon dioxide (pH 6.3) effectively raising the pH level. On days when photosynthesis is most likely, such as sunny days during the growing season, the pH level of the river may rise. But what appears to be a natural effect may have very human causes. Fertilizers and human waste, both generally acidic compounds which enter the Bronx River on a regular basis through stormwater runoff (CSOs) and illegal sewage connections (Yonkers), increase plant growth and even the algae blooms recently noted on the river. So the introduction of an acid causes a basic reaction. Organic respiration at night produces CO2 thereby lowering pH levels and dissolved oxygen levels, as does the massive decomposition that follows mortality.
The level of pH in the Bronx needs to be monitored closely, not just for the answer the value itself gives us, but for the chain of possible causes of that value that need to be looked into.
Thanks, Dione.
references: http://waterontheweb.org/under/streamecology/09%5Fph%2Ddraft.html, http://www.seed.slb.com/en/scictr/journal/environment/river/is54nyc.htm, http://www.geocities.com/capecanaveral/hall/9111/DOC.HTML
DG
April 30th, 2008
On Saturday, March 29th 2008, The Bronx River Alliance in conjunction with GLOBE held what I considered tot be a rather successful Water Quality Monitoring training. The Alliance worked out the logistics of invitations and materials, Rocking the Boat provided the space at Hunts Point Riverside Park and some much appreciated labor, and Peter Schmidt from Queens College, ran the show for GLOBE.
All told, 18 participants, ranging from a couple of new volunteers that have never done water quality testing, to several pros that could tell you the quantity of DO in a water sample with one hand tied behind their backs, took part in the training, but something new was learned by all. Organizations represented were Rocking the Boat ( which included VOICE members?), Green Apple Corps, Action at the Point, The Bronx Zoo, and Youth Ministries for Peace and Justice. Peter walked us through not only the reasons that we test water, but also the procedures necessary to making sure your data has some meaning to you and the larger scientific community. To demonstrate this, all of the participants were given thermometers and asked to go outside to “take the temperature.” As they came in, Peter collected the data on the board. The temps ranged from 40 degrees Fahrenheit to “Medium rare,” even though the Weather Underground claims it was about 48 degrees Fahrenheit at the time. The point was well made that you need to use the right tool and have a standard by which to compare your data.
For standards, we used the following for temperature and Dissolved Oxygen. A simple ice bath at sea level should give you a reading of 0 degrees Celsius. Make sure that you keep the thermometer in the water for three minutes and stir it. Water being the only substance that freezes from the top down, missing that stir will give you about a 4 degree difference. For DO, we made a saturated (100%) solution by simply filling a small bottle half way, capping it and the shaking it like mad for about five minutes. This mimics waterfalls were the O2 mixes with the H2O. When you run your titration, it should come out to about 100% saturated if all is working correctly.
The two new protocols introduced were the use of transparency tubes and hydrometers. These are GLOBE protocols that allow us to input this data onto the GLOBE database. The transparency tube is easier and faster than the turbidity test that we had been doing as Bronx River Stewards. The hydrometer is used to find specific gravity of water which is then converted into salinity when cross referenced with temperature.
Soon all Bronx River Stewards will have access to the Alliance’s GLOBE site where data can be entered and accessed by all. Peter walked everybody through that process at the close of our day, as well as demonstrating the amazing resource that the GLOBE web site ( see our links) is for scientists, teachers and students.
I’d like to thank everybody that participated and everybody that had a hand in making the training come off as well as it did. We started early, ran late ( thanks for washing dishes, Rosa and Kathryn!) a covered miles of material. Thanks Peter for making the trip and we hope to have you back soon( Bring the owls and the snakes) for more training and hopefully a canoe trip.
DG
March 30th, 2008
While out on an unrelated trip, we bumped into a class from Banana Kelly at Burke Bridge getting into their first water quality monitoring of the Spring. The students were hard at work, searching their memories for the protocols that they hadn’t followed in several months. Their teachers were not handing over any easy answers, opting instead to get the students to use their own knowledge and reason to aid in recall. Nice to see them out there doing the hard work that helps with the Bronx River Restoration.
DG
March 12th, 2008
The GAC crew hit the shore of the Bronx River today for their first venture into water quality monitoring this afternoon. 9 crew members and their leader, KF, learned the basics of testing, including pH, DO, transparency, velocity and more. At least 4 members were not cowed by the 7.5 degree Celsius water, and they climbed right in for sampling. The crew was quite energetic and their interest in the work made the time go by much too quickly. I hope we get to see them out on the river again in the near future.
March 11th, 2008
