Question

The average discharge of the entire Mississippi River basin in 2005 was 19,900 m3/sec (measured at Saint Francisville, MS). The total annual nitrogen load for the same year was estimated to be 295,000 metric tons (as N).

a. Calculate the average concentration of total N (in mg/L).

b. Calculate the average daily flux of total N (kg/day)

Answer 1

(a) The average concentrataion of N = mass of N loaded /Volume of river basin

= (295000 metric tons per year) / (19900 m³/s)

= (2.95 x 10⁸ kg/year) / (19900 x1000 L/s)

=(2.95 x 10⁸ kg/year) / ((19900 x1000 L/s)x24 x 3600 s/day x 365 day /year )

= 1.12 x 10^-5 kg/L

= 1.12 x 10^-2 g/L

= 1.12 x 10¹ mg/L

= 11.2 mg/L

Convert any one into single unit like in year or second. Here we converted denominator from seconds to year.

(B)

Here we know flux of Nitrogen in metrric tons per year , we need to convert this into kg/day.

Flux of N in kg/day == 295000 metric tons per year

= 295000 x 10³ kg / year

1 year = 365 days

= 295000 x 10³ kg / 365 days

= 808219.2 kg/day