Exam 23: Biogeochemical Cycles

Most aerobic autotrophs produce and consume oxygen in order to live.

Undecomposed organic matter in the form of fossil fuels and carbon in sedimentary rocks represents a net positive flux of oxygen to the atmosphere.

Nitrogen can be returned to the atmosphere when certain bacteria convert it from nitrate into nitrogen gas,which is a process called ________.

Global estimates of denitrification in terrestrial ecosystems vary widely but are of the order 200*1012 g/yr,and more than half of that total occurs in wetland ecosystems.If restoration results in an increase in wetland area by approximately 25%,it would be expected that losses of nitrogen through denitrification would be closer to

Carbon cycles more quickly through cold and dry ecosystems than it does through warm and wet ecosystems.

There is more carbon per unit of soil in cold polar regions than in the warm tropics.

Which of the following represents the largest anthropogenic source of sulfur released to the atmosphere?

Large quantities of nutrients are bound tightly in ________ structure; they are not readily available until released by the activities of decomposers.

In the later stages of nitrogen saturation,soils tend to become more acidic,which increases the concentration of aluminum ions in the soil solution.

The largest pool of nitrogen is

Hydrogen sulfide is transformed into sulfate or elemental sulfur by

The process of nitrification produces a form of nitrogen that is easily lost from soil through leaching.

The sulfur biogeochemical cycle is a sedimentary cycle with essentially no gaseous cycle.

In ________ biogeochemical cycles,the main reservoirs of nutrients are the atmosphere and the oceans.

The element ________ is a basic constituent of all organic compounds and is involved in the fixation of energy by photosynthesis.

The largest active carbon pool is

The nitrogen cycle is a series of chemical transformations,which makes it relatively insensitive to environmental conditions such as temperature and moisture.

Consider the following: on an annual basis,C exchange from photosynthesis is 120 Gt,decomposition is 60 Gt,respiration is 60 Gt,ocean uptake of CO2 is 92 Gt of C,ocean release is 91 Gt C,release of C to the atmosphere from anthropogenic sources (fossil fuel use and land use change)is 6 Gt,and the atmosphere is increasing by 3.2 Gt of C.If terrestrial processes are responsible for the remaining C for net balance of the C cycle,then which of the following is likely?

Flowing water aquatic systems (streams and rivers)contain high levels of organic matter so are rarely dependent on inputs from terrestrial system.

Phosphorus is typically in short supply in aquatic and terrestrial ecosystems.