1.5-1.6 Measuring Inputs of Nitrogen and Phosphorus in an Urban Environment.

1.5-1.6 Measuring Inputs of Nitrogen and Phosphorus in an Urban Environment. As we have seen in our discussions of nutrients throughout this unit, nutrients can come from multiple sources. Scientists recently quantified the various sources of nitrogen and phosphorus that enter the Mississippi River from St. Paul, Minnesota. Using the data below listing the amount of nitrogen coming into the river, we can calculate the percentages of each source. Source Nitrogen (kg/km 2 /year) Phosphorus (kg/km 2 /year) Atmospheric deposition 1 300 40 Household pet waste 2 100 280 Residential fertilizer 3 800 0 Weathering 0 10 County compost 200 30 To calculate the percentage of each nitrogen source, we can begin by calculating the sum of all sources: Total nitrogen = 1,300 kg/km 2 /year + 2,100 kg/km 2 /year + 3,800 kg/km 2 /year + 0 kg/km 2 /year + 200 kg/km 2 /year=7,400 kg/km 2 /year We can then calculate each percentage by dividing each source by the total of all nitrogen sources (rounded to two significant digits): Percent nitrogen from atmospheric deposition = 1,300 kg/km 2 /year / 7,400 kg/km 2 /year × 100% = 18% Percent nitrogen from household pet waste = 2,100 kg/km 2 /year / 7,400 kg/km 2 /year × 100% = 28% Percent nitrogen from residential fertilizer = 3,800 kg/km 2 /year / 7,400 kg/km 2 /year × 100% = 51% Percent nitrogen from weathering = 0 kg/km 2 /year / 7,400 kg/km 2 /year × 100% = 0% Percent nitrogen from county compost = 200 kg/km 2 /year / 7,400 kg/km 2 /year × 100% = 3% YOUR TURN Using the phosphorus data from the table, calculate the percentage of each phosphorus source that enters the Mississippi River from the city of St. Paul. 40kg/km^2/year / 360kg/km^2 /year x 100% = 11%

280kg/km^2/year / 360 kg/km^2 /year x 100% = 78% 0kg/km^2/year / 360g/km^2/year x 100% = 0% 10kg/km^2/year /360g/km^2/year x 100% = 0.02% 30kg/km^2/year /360g/km^2 / year x 100% = 0.08% 1.5-1.6 Raising Mangoes In Haiti, farmers are being encouraged to plant mango trees to help reduce runoff and increase the uptake of water by the soil and the trees. Consider a group of Haitian farmers that decides to plant mango trees. Mango saplings cost $10 each. Once the trees become mature, each tree will produce $75 worth of fruit per year. A village of 225 people decides to pool its resources and set up a community mango farm. Their goal is to generate a per capita income of $300 per year for everyone in the village. 1. How many mature trees will the village need to meet the goal? Total annual income desired: $300/person × 225 persons = $67,500 Number of trees needed to produce $67,500 in annual income: $67,500 ÷ $75/tree = 900 trees 2. Each tree requires 25 m 2 of space. How many hectares must the village set aside for the mango farm? 900 trees × 25 m 2 /tree = 22,500 m 2 = 2.25 ha YOUR TURN Each tree requires 20 L of water per day during the 6 hot months of the year (180 days). The water must be pumped to the farm from a nearby stream. How many liters of water are needed each year to water the farm of 900 trees? 20L/1 Tree 180days 20L*180days = 3600L