## Gulf of Mexico Dead Zone

Excess loading to the Gulf of Mexico has resulted in a hypoxic zone. The USGS has identified major sources of nutrient loading to the Mississippi River Basin using a hydrochemical model called SPARROW.

## The Upper Great Miami Watershed

Buck Creek runs along the Wittenberg Campus and joins with the Mad River and into the Upper Great Miami River and then the Ohio River, the Mississippi River, and ultimately the Gulf of Mexico. The SPARROW model estimates the relative incremental yields (associated only with that segment). This is an area-normalized calculation in order to assess the relative nutrient loading associated with any watershed size. Note the Upper Great Miami delivers among the highest incremental yields for its relative area.

## Task 1: Compare Average Hourly Yields

1) How do hourly Buck Creek baseflow nitrate and orthophosphate yields per square km during our collections compare to the range of hourly average incremental yield of Total N (nitrate+nitrite+ammonia) and Total P (ortho+ reactive phosphate) for the Upper Great Miami Watershed (See Figure Above)? (5 pt)

A.To calculate hourly yield in Buck Creek multiply the concentration in mg/L by the number of liters/s. Then calculate mg/s. Then calculate g/s. Then g/hr. FInally, you should normalize g/hr (divide by the) to the watershed area (~300 square km).

Baseflow during sampling was approximately- 1 cubic meter/s, or 1000 l/s

B. To calculate the range of mean annual hourly yields associated with the Upper Great Miami you must locate the Upper Great Miami in the above figure and convert the range of concentrations associated with this watershed into g/km2/yr. To do this you will need to know the number of grams in a kilogram. Then you will need to convert the g/km2/yr into g/km2/hour (hint: this will be a smaller number).

2) Using USGS Ohio River Monthly Data determine the average percentage of total N and total P that nitrate and orthophosphate represent respectively during the month of September (e.g. NO2+NO3/Total N*100). (2 pt) You might notice that NO2+NO3 represent the majority of total N.

3) Calculate the range (lowest to highest) and average hourly-area normalized yield of total N and total P for the Ohio River during the month of September based on all September averages. You will want to sort your data by month, this will require relabeling the month year column as month only and getting rid of any merged cells. You will need to area normalize the yields given by the USGS and convert them into g/km2/hr.

To do this, remember that the yields reported in the USGS spreadsheet represent a monthly total mass. To determine an hourly total mass you will need to divide by the number of hours in the month of September You will then need to nomalize (divide by) to the area of the Ohio River Basin above the USGS gauging station is 326,860 km2.

Is this range similar to the range seen for the Upper Great Miami in the Sparrow model? Explain (2 pt)

4) Create 2 bar graphs showing the mean hourly area-normalized N and P yields for the highest, lowest, and mean September on record (10 pt)

A.To calculate hourly yield in Buck Creek multiply the concentration in mg/L by the number of liters/s. Then calculate mg/s. Then calculate g/s. Then g/hr. FInally, you should normalize g/hr (divide by the) to the watershed area (~300 square km).

Baseflow during sampling was approximately- 1 cubic meter/s, or 1000 l/s

B. To calculate the range of mean annual hourly yields associated with the Upper Great Miami you must locate the Upper Great Miami in the above figure and convert the range of concentrations associated with this watershed into g/km2/yr. To do this you will need to know the number of grams in a kilogram. Then you will need to convert the g/km2/yr into g/km2/hour (hint: this will be a smaller number).

2) Using USGS Ohio River Monthly Data determine the average percentage of total N and total P that nitrate and orthophosphate represent respectively during the month of September (e.g. NO2+NO3/Total N*100). (2 pt) You might notice that NO2+NO3 represent the majority of total N.

3) Calculate the range (lowest to highest) and average hourly-area normalized yield of total N and total P for the Ohio River during the month of September based on all September averages. You will want to sort your data by month, this will require relabeling the month year column as month only and getting rid of any merged cells. You will need to area normalize the yields given by the USGS and convert them into g/km2/hr.

To do this, remember that the yields reported in the USGS spreadsheet represent a monthly total mass. To determine an hourly total mass you will need to divide by the number of hours in the month of September You will then need to nomalize (divide by) to the area of the Ohio River Basin above the USGS gauging station is 326,860 km2.

Is this range similar to the range seen for the Upper Great Miami in the Sparrow model? Explain (2 pt)

4) Create 2 bar graphs showing the mean hourly area-normalized N and P yields for the highest, lowest, and mean September on record (10 pt)

## Task 2: Related Blog Post

Discuss either N or P behavior between scales (time and space/size). Focus on thinking critically about one comparison (3 pt). This can even include thinking of questions you have about comparing between scales. To help: recall the Sparrow Model is based on annual data collection for watersheds ~the size of the Upper Great Miami. Our Buck Creek Samples were a single point measure during the month of September from a relatively small watershed area. The Ohio River data you examine represented multiple months of comparison for a much larger spatial extent. You may refer to the results from your calculations or the created bar graph (5 pt). Include a picture that will help illustrate what you are saying and give the source (2 pt)