Labs - Environmental Science - page 360

• Phosphate: Phosphate is an important nutrient for plant growth, usually found in fertilizers and runoff
from agricultural lands. Excessively high phosphate levels can lead to excessive growth and ultimately
eutrophication. Phosphate levels should be 0.05 mg/L in flowing water, 0.025 mg/L in still waters.
• Nitrates: Nitrates are important for plant growth, usually found in fertilizers and runoff from agricultural
lands. Excessively high nitrogen levels can lead to excessive growth and ultimately eutrophication. A
concentration greater than 0.1 mg/L is considered high and the Environmental Protection Agency (EPA)
limit is 10 mg/L.
• Alkalinity: Measures compounds that can change the pH toward the alkaline (basic). The normal range is
between 100 ppm and 250 ppm. The EPA has no standards for alkalinity.
• Biological oxygen demand (BOD): Required for aerobic organisms in a body of water. Unpolluted wa-
ters have a concentration less than 5 mg/L. High nutrient levels are associated with high BOD.
• Fecal coliform: Bacteria that ferments lactose and produces gas when grown in a lactose broth. New
tests have been developed that produce a color change in addition to gas.
• Total solids: Weight of the suspended solids and dissolved solids. All water contains some solids, but
problems can arise from suspended sewage, industrial waste, soil erosion, and excess amounts of algae.
• Total dissolved solids: Occur naturally in water but may be objectionable in drinking water due to taste.
At high levels of dissolved solids, water may be unsuitable for irrigation, because salts may leave
residue and can accumulate over time. The EPA standard is 500 mg of dissolved solids per liter of water,
but the range is 20 mg/L to 2,000 mg/L.
• Chlorine: The EPA standard caps chlorine concentration at 250 mg/L. NaCl is applied to roads in the
winter to make driving on snowy and icy roads easier and safer. These salts can run off into the streams,
increasing local chlorine concentrations. Other sources of chlorine include animal waste, potash fertil-
izers, and septic-tank effluent. Chlorine also may leach out of limestone formations.
• Hardness: Measures dissolved salts that include calcium, magnesium, or iron. Hard water is 121 ppm,
and soft water is less than 20 ppm.
• Iron: Normal range is 0.1 ppm to 0.5 ppm.
Weathering
There are two types of weathering labs:
• Chemical weathering: This lab tests the effects of acid rain on different types of rock. Rock such as
limestone, granite, and marble is exposed to dilute hydrochloric acid (HCl) and observations are made to
see the effect of the acid on the rock. Additionally, the mass of the rock can be measured before and after
exposure to dilute acid. This activity can be repeated to see the long-term effects on rock of the exposure
to dilute acid. Chemical weathering may include hydrolysis, oxidation, or dissolving reactions.
• Mechanical weathering: In this lab, shaking rock samples in a container of water simulates mechanical
weathering. Rock is weighed, placed in a container with water, and shaken; then the water is drained.
The rock is rinsed and dried and then weighed a second time, and the difference in mass is calculated.
Mechanical weathering may include wind, water (erosion), ice, plant growth, and human-related actions.
Analysis of Past Exams