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Danvers River Estuary Salinity Distribution Activity

GLS225: Estuaries and Pollution

Hubeny: Fall 2013

Goal: This exercise is designed to give you experience with analyzing and interpreting real world water column temperature and salinity data in order to classify the Danvers River Estuary.

Objectives: After completing this exercise you will have:

·  Contoured data in both map and cross section views

·  Corrected depth measurements for tidal stage

·  Calculated a profile’s vertical exaggeration

·  Used Excel for basic computations and plotting

·  Used real data to classify the Danvers River Estuary

·  Used your problem solving skills to establish a procedure to answer the scientific question posed

Introduction: A number of us collected water column data from the Danvers River Estuary with a YSI geochemical probe. We collected temperature and salinity readings at 1-meter depth intervals at nine total stations. These data are available in an Excel document. We will use these data to classify the estuary based on contoured plots and compare our classification to the calculation of river volume to tidal volume, as we discussed in class. For this exercise you will need to produce 1) and contoured map of surface salinity in the estuary, 2) a contoured fence-type profile diagram illustrating salinity variability with depth along the length of the estuary, and 3) water column plots of temperature, salinity, and σt for selected field locations along the transect.

Procedure:

·  Hypothesis: Before you get started, form a hypothesis as to the type of estuary you think that the Danvers River Estuary is. Keep in mind that this is a coastal plain estuary, is mesotidal, and has relatively limited riverine input.

·  Surface salinity contour map: I suggest using Google Earth to plot each station using its latitude and longitude. You can then print out this map, add the surface salinity values, and contour the data to illustrate the salinity distribution within the estuary. Use a contour interval of 0.2psu.

·  Salinity profile diagram: The first step is to produce a depth profile of the estuary. You will need to plot in Excel distance between sites (use GoogleEarth for this), and tide corrected depths for each site (correct to mean low water using the tide table provided; note that you will need to convert your depths to meters before you tide correct). On this plot, put data points at each tide corrected depth measured and write the salinity measurement (this might be easiest to do by hand after printing out the blank profile). Finally, contour the salinity values with a contour value of 0.2psu. Be sure to calculate and report your vertical exaggeration (VE) for the profile. The VE is the ratio of vertical scale (cm on paper/ meters in real life) to horizontal scale, and you can calculate be measuring the same length on your paper for each scale and dividing horizontal distance by vertical distance (be sure to keep consistent units!)

·  Water column plots: You will plot water column profiles of temperature, salinity, and σt for stations B, F, and I. Use the online calculator for water density to calculate σt. If you use Excel (which I recommend) you are going to want to plot an xy scatter plot in which you connect the points. Excel is clumsy in plotting this sort of plot. You will want the depth column to the right of your measured variable when you select the columns to plot, and you will need to remove any labels within cells. When you print out the plots, be sure that all three plots for each station have the same y-axis scale.

Product: Your final product will consist of the figures that are outlined above as well as a write-up of the activity. Your write-up should include a title, introduction to the project, methods used, results/discussion of the data, and a conclusion. Within your write-up you should address the following:

  1. Use your contoured profiles to classify the estuary based on mixing (pay attention to magnitude of units!). Does your classification support your hypothesis?
  2. Do the other data (temperature and density from water column plots) support your classification (think about ‘clines and mixing processes!)?
  3. Please calculate the freshwater: tidal volume ratio (R/V) to quantitatively confirm your estuary classification. I provide here quantities for your calculation: Chase et al. (2002) report that the average freshwater input from rivers to Salem Sound is 100,000m3/day (based on data collected in 1997). Remember that to calculate the freshwater input you need to report during one tidal cycle. A tidal cycle in the Danvers River Estuary is 12 hours and 14 minutes. Chase et al. (2002) also report that the area of Salem Sound is 36.6km2 and that the mean tidal amplitude is 2.75m. Does your calculated R/V ratio support your classification from the field data?
  4. Please read the article that I provide on the salinity distribution of the Danvers River Estuary. Do you think that the mixing dynamics have been affected by humans? If so, what do you think was different with the estuary prior to development in the area? Would our data look different after a precipitation event?
  5. We sampled during a flood tide. How might the data be different if we were to resample during an ebb tide?

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Salem, Massachusetts

23 September 2013

Units are meters, initial timezone is EDT

1.83 12:00 AM

1.95 12:10 AM

2.06 12:20 AM

2.18 12:30 AM

2.28 12:40 AM

2.38 12:50 AM

2.47 1:00 AM

2.56 1:10 AM

2.63 1:20 AM

2.69 1:30 AM

2.75 1:40 AM

2.79 1:50 AM

2.82 2:00 AM

2.84 2:10 AM

2.85 2:20 AM

2.85 2:30 AM

2.84 2:40 AM

2.81 2:50 AM

2.78 3:00 AM

2.74 3:10 AM

2.69 3:20 AM

2.64 3:30 AM

2.57 3:40 AM

2.50 3:50 AM

2.42 4:00 AM

2.34 4:10 AM

2.25 4:20 AM

2.16 4:30 AM

2.06 4:40 AM

1.96 4:50 AM

1.85 5:00 AM

1.75 5:10 AM

1.63 5:20 AM

1.52 5:30 AM

1.41 5:40 AM

1.29 5:50 AM

1.17 6:00 AM

1.06 6:10 AM

0.94 6:20 AM

0.83 6:30 AM

0.72 6:40 AM

0.61 6:50 AM

0.51 7:00 AM

0.41 7:10 AM

0.33 7:20 AM

0.25 7:30 AM

0.19 7:40 AM

0.13 7:50 AM

0.09 8:00 AM

0.07 8:10 AM

0.05 8:20 AM

0.05 8:30 AM

0.07 8:40 AM

0.09 8:50 AM

0.13 9:00 AM

0.18 9:10 AM

0.24 9:20 AM

0.31 9:30 AM

0.38 9:40 AM

0.46 9:50 AM

0.55 10:00 AM

0.64 10:10 AM

0.73 10:20 AM

0.83 10:30 AM

0.93 10:40 AM

1.03 10:50 AM

1.14 11:00 AM

1.25 11:10 AM

1.36 11:20 AM

1.47 11:30 AM

1.59 11:40 AM

1.70 11:50 AM

1.82 12:00 PM

1.93 12:10 PM

2.05 12:20 PM

2.16 12:30 PM

2.27 12:40 PM

2.38 12:50 PM

2.48 1:00 PM

2.57 1:10 PM

2.66 1:20 PM

2.73 1:30 PM

2.80 1:40 PM

2.86 1:50 PM

2.90 2:00 PM

2.94 2:10 PM

2.97 2:20 PM

2.98 2:30 PM

2.98 2:40 PM

2.98 2:50 PM

2.96 3:00 PM

2.93 3:10 PM

2.90 3:20 PM

2.85 3:30 PM

2.80 3:40 PM

2.73 3:50 PM

2.67 4:00 PM

2.59 4:10 PM

2.51 4:20 PM

2.42 4:30 PM

2.33 4:40 PM

2.23 4:50 PM

2.13 5:00 PM

2.02 5:10 PM

1.91 5:20 PM

1.80 5:30 PM

1.69 5:40 PM

1.57 5:50 PM

1.45 6:00 PM

1.33 6:10 PM

1.21 6:20 PM

1.09 6:30 PM

0.97 6:40 PM

0.85 6:50 PM

0.74 7:00 PM

0.62 7:10 PM

0.52 7:20 PM

0.41 7:30 PM

0.32 7:40 PM

0.23 7:50 PM

0.16 8:00 PM

0.09 8:10 PM

0.04 8:20 PM

-0.00 8:30 PM

-0.03 8:40 PM

-0.04 8:50 PM

-0.04 9:00 PM

-0.03 9:10 PM

-0.01 9:20 PM

0.02 9:30 PM

0.07 9:40 PM

0.12 9:50 PM

0.18 10:00 PM

0.25 10:10 PM

0.32 10:20 PM

0.40 10:30 PM

0.48 10:40 PM

0.56 10:50 PM

0.65 11:00 PM

0.75 11:10 PM

0.84 11:20 PM

0.94 11:30 PM

1.04 11:40 PM

1.14 11:50 PM