Water at an Organic Farm

           Winona State has recently entered a partnership with an organic farm, Featherstone Farms, in Rushford.  See links for an aerial photograph and topographical map of the farm.  This farm is located in a beautiful valley typical of many valleys in the driftless region of this area.  The farm borders Money Creek and is situated adjacent to a traditional (non-organic) dairy farm.  Because of the hilly terrain, the farmers have set up several ponds along the natural drainage area of the property including a swimming pond for their children.  One portion of their land is even an area they are trying to restore to a natural wetland.  The farmers, being curious, and responsible land stewards, are very interested in having their property characterized.  Your colleagues in the Biology and Geoscience departments are also working at this farm, characterizing it biologically and geologically.
            The purpose of this lab is to begin to chemically characterize the water for iron, nitrates, and phosphorus.  You and your partner must develop a testable hypothesis regarding the water around the farm.  One example of a good testable hypothesis for chloride (not one of the analytes to be tested here) may be, “The amount of chloride in the runoff catch basins is higher than in Money Creek.”  In your experiment you would collect several representative samples from the catch basins and several from the creek, measure the chloride content in the different samples, and determine whether the two populations were statistically different.
            This project only began in March so the possibilities are wide open.  See the aerial photograph and topographical map for a detailed picture of the farm.  Because of time limits choose only one analyte from iron, phosphorus, or nitrate and choose only two sampling populations, i.e. catch basins vs. creek, one area of the creek vs. another, etc.  Note, this does not mean you only need to take two samples.  Keep in mind the information discussed in class about sampling strategies and quality control.

  Which analyte should I choose?

             Here is some information about iron, phosphorus, and nitrates that may help you decide which one your team would like to work on.

  Iron: Iron is an essential metal nutrient that is frequently found in the environment from other than natural sources.  Iron in steel is by far the most frequently produced metal.  Iron can be found in natural waters from corroded metals, industrial wastes, acid mine drainage, and when water is highly anaerobic and is in contact with iron containing minerals.  It is not an overly toxic metal, since it is an essential nutrient.  Nevertheless it can damage materials such as bathroom fixtures and clothing when it is at a high level.  The U.S. Public Health Service has put a limit of 0.05mg/L for iron in water.

Phosphorus: Phosphorus is the primary pollutant associated with the eutrophication of our surface waters. Excess phosphorus causes nuisance algae blooms and reduced water transparency, making waters unsuitable for swimming or other activities. Phosphorus comes from both point and non-point sources. Point sources consist mainly of municipal and industrial wastewater discharges. Non-point sources include runoff from agricultural fields, feedlots, urban areas, and on-site sewage treatment systems.  Most municipalities are striving for phosphorus levels below 1mg/L.

Nitrates: Nitrate pollution has become a major ground and surface water problem in some agricultural areas.  Feedlots are the major source of this pollution although excessive fertilizer use is also implicated in nitrate pollution.  This can be a particularly serious problem in infants who can develop “blue baby syndrome” from excess nitrates in their diet.  Another worry with excess nitrates is the possibility that the nitrite produced in the stomach from the consumption of nitrates can react with amines in the diet to produce the carcinogenic N-nitrosamines.  The safe level for nitrates in the water is 10mg/L.

Week 1 Sampling

            Develop, with your partner, a testable hypothesis for determining the amount of iron in the environment.  Devise a sampling scheme that will effectively test your hypothesis.  Keep in mind that taking samples in the environment can potentially add a lot of variability.  Take an appropriate number of samples to effectively account for this variability. 

            Take samples for your experiment.  Be sure to record all relevant information about the sampling location and sampling time.  Information that might be relevant would include temperature, weather, distance from road, pH, etc. When we get back in the lab, measure your samples’ volume and preserve the samples for analysis later in the semester.  Iron is preserved by adding two drops trace metal grade nitric acid to the bottle and refrigerating, phosphorus is preserved by adding 1mL concentrated HCl to the bottle and refrigerating, and nitrates are preserved by adding 2mL concentrated H2SO4 to the bottle and refrigerating.

            After your sample is preserved.  Make up some of the reagents that you will be using when you analyze your samples later in the semester.  See procedure below for your analyte. 

Iron:

The procedure we will be using for iron analysis is a spectroscopic one.  In the first week make up 100mL of a 25g/L solution of trisodium citrate and the standard iron solution (356mg of ferrous ammonium sulfate [FeSO4.(NH4)2SO4.6H2O] transfer to a 500mL volumetric flask, dissolve in 100mL H2O containing 1mL 6M H2SO4, dilute to mark).  Do not make the o-phenanthroline solution or hydroxylamine solution until the second week of the experiment later in the semester.   Because the procedure is so sensitive, dirty glassware is a prime source of error.  Therefore be sure all glassware has been rinsed in a nitric acid cleaning solution.  Before being filled, the cuvettes should be rinsed 2 or 3 times with the solution being measured.  A detailed procedure for the second week will be provided to you as a handout.

Phosphorus:

            Phosphorus in the form of phosphate will also be determined spectroscopically.  During the first week, prepare the phosphate stock standard by dissolving 136.1mg dried KH2PO4 in 1L of 0.1% H2SO4 (0.5mL concentrated H2SO4 per liter).  Refrigerate.  Also prepare the ammonium vanadomolybdate solution by dissolving 1.0g ammonium vanadate (NH4VO3) in a mixture of 300mL H2O and 200mL HNO3.  Add 40.0g of ammonium molybdate [(NH4)6Mo7O24.4H2O] to 400mL H2O.  The ammonium molybdate does not fully dissolve at this stage but it will in the next step.  Mix the two solutions and dilute to 1L with water.  A detailed procedure for the second week will be provided to you as a handout.

Nitrate:

            Nitrate will also be analyzed spectroscopically.  During the first week of the experiment, prepare a nitrate stock standard at a concentration of 1000ppm by dissolving 163mg dried KNO3 and diluting to 100mL in H2O.  Also during the first week prepare the sulfanilic acid reagent by dissolving 1g sulfanilic acid in 80mL warm water, add 10mL HCl and dilute to 100mL.  Prepare the N-(1-naphthyl)-ethylenediamine hydrochloride (C10H7NHCH2.2HCl) by dissolving 0.1g of the reagent in 50mL water plus 5mL 1M HCl, dilute to 100mL with water and store in a brown bottle. A detailed procedure for the second week will be provided to you as a handout.

            In your report, indicate what your hypothesis was regarding the analyte’s concentration in the environment.  Explain the sampling procedure you undertook to effectively test your hypothesis.  Describe the quality control procedures you undertook in the field and in the lab to ensure the most reliable as possible results.  Include any calculations you did for determining the number of samples you needed to take.  Also, report the average amount and 95% confidence intervals for the amount of analyte in your samples.  Include your calibration curve and the experimentally determined molar absorbtivity.  Clearly show all calculations.  Finally, discuss your results.  What are their significance?  How could the experiment be improved in the future?  Your abstract should be viewed as an executive summary.  I will be giving these to the farmers at Featherstone.

Pre-lab Week 1

1.      Pick an analyte to study and develop a testable hypothesis for the presence of this analyte in the environment.

2.      Devise a sampling strategy that will effectively test your hypothesis, keeping in mind what was discussed in class and the variability that often accompanies taking real samples in the environment.

3.      One of the analytes measured in this experiment is iron.  The procedure used for iron concentration makes use of the o-phenanthroline spectroscopic method for measuring iron.  Replicate analyses of an iron solution containing 15mg/L of iron gave an average iron concentration of 15.11mg/L and a standard deviation of 1.40mg/L using the o-phenanthroline method.  If you are willing to accept a relative error of 10% and would like to be 90% confident that your sampling accurately reflects the number of amount of iron in the environment, how many samples do you need to take?

4.  The nitrate stock standard used in this experiment is 1000ppm NO3- prepared by dissolving 163mg of dried KNO3 in 100mL water.  NaNO3 can also be used if no KNO3 is available.  What weight of NaNO3 should be used to make a 100mL solution of 1000ppm NO3-?

Prelab Week 2

1.      Explain how Beer’s law can be used to determine the amount of iron, phosphorus, or nitrate in your sample.

2.      Look up the safety precautions necessary to take when dealing with all of the chemicals required in your procedure.  Report those here.