Problem: Water stratification is when water masses with different properties - salinity (halocline), oxygenation (chemocline), density (pycnocline), temperature (thermocline) - form layers that act as barriers to water mixing which could lead to anoxia or euxinia.[1] These layers are normally arranged according to density, with the least dense water masses sitting above the more dense layers. Water stratification also creates barriers to nutrient mixing between layers. This can affect the primary production in an area by limiting photosynthetic processes. When nutrients from the benthos cannot travel up into the photic zone, phytoplankton may be limited by nutrient availability. Lower primary production also leads to lower net productivity in waters.[2] High lake had a lot of fresh and salt water mixing, therefore presented layers of stratified water.The water was poor in nutrients.Low lake had no such problems and it was a very abundant and prolific fishing spot. Which lake had more phytoplankton?

A: Low lake

Problem: Huge amounts of chemicals, such as fertilizers and pesticides, are applied to farm fields (see Figure below ). Some of the chemicals are picked up by rainwater. Runoff then carries the chemicals to nearby rivers or lakes. Dissolved fertilizer causes too much growth of water plants and algae. This can lead to dead zones where nothing can live in lakes and at the mouths of rivers. Some of the chemicals can infiltrate into groundwater. The contaminated water comes up in water wells. If people drink the polluted water, they may get sick. Jimbo and Jedd are both farmers who have lakes and water wells downstream from their farms. Jimbo's products have been in high demand recently, so he has started to use very high amounts of fertilizers on his farms. Jedd has recently decreased the amount of fertilizer he uses because his products aren't wanted as much by the people in his town. Who will be less likely to cause excess growth of water plants in their respective lakes?

A: Jedd

Problem: When humans dig up and use fossil fuels, we have an impact on the carbon cycle ( Figure below ). This carbon is not recycled until it is used by humans. The burning of fossil fuels releases more carbon dioxide into the atmosphere than is used by photosynthesis. So, there is more carbon dioxide entering the atmosphere than is coming out of it. Carbon dioxide is known as a greenhouse gas , since it lets in light energy but does not let heat escape, much like the panes of a greenhouse. The increase of greenhouse gasses in the atmosphere is contributing to a global rise in Earth's temperature, known as global warming or global climate change. Two different countries produced their electricity using different methods. Burma used fossil fuels such as coal and oil, while Bhutan used renewable energy sources. Which country released more carbon dioxide into the atmosphere ?

A: Burma

Problem: Protozoa generally feed by engulfing and digesting other organisms. As consumers, they have various roles in food chains and webs. Some are predators. They prey upon other single-celled organisms, such as bacteria. In fact, protozoa predators keep many bacterial populations in check. Other protozoa are herbivores. They graze on algae. Still others are decomposers. They consume dead organic matter. There are also parasitic protozoa that live in or on living hosts. For example, the protozoan that causes malaria lives inside a human host. For their part, protozoa are important food sources for many larger organisms, including insects and worms. Students learned about protozoa in school this week. Dan and Jim were interested and read more on the subject. Dan read more about predatory and parasitic protozoa, while Jim read more about herbivore and decomposer protozoa. Which student read more about protozoa that graze on algae?

A:
Jim