Reading Questions
Mulholland et al. 2008. Stream denitrification across biomes and its response to anthropogenic
nitrate loading. Nature. 452; 202-206.
1) What is the big picture question being asked by the team of authors?
a. What is the effect of nitrogen loading, primarily anthropogenic, on streams and
rivers?
b. Can flowing waters be sites of permanent nitrogen removal from ecosystems via
denitrification?
2) What are some of the strengths of this research?
a. Experimental work coupled with modeling.
b. Highly replicated across space thus accounting for the variation among stream
ecosystems. This allows for results to be more generalizable.
3) How does this research link terrestrial ecosystem processes with aquatic ecosystem
processes?
a. Examining how nitrogen inputs across the watershed influence stream
ecosystems.
b. Although streams have very little surface area compared to other parts of the
critical zone, streams integrate what is occurring across the watershed in both
space and time.
4) What parts of the nitrogen cycle are studied in this paper? Why are these particular
processes of interest?
a. Biotic uptake of nitrate
b. Denitrification
c. Both are mechanisms in which nitrogen is retained in or removed from
ecosystems.
5) There are two examples in this paper which demonstrate how the nitrogen and
carbon cycles are linked. What are they?
a. Autotrophic primary production and nitrogen uptake
b. Denitrification is a process that uses nitrate as the final electron acceptor when
microorganisms metabolize labile (highly available/easy to decompose) forms of
organic carbon when oxygen is not readily available (anoxic).
6) What are the three results of the model? What do the model results say about the
importance of small streams across the landscape?
a. There is an interaction between stream size, nutrient loading, and nitrogen
dynamics.
b. If stream nitrogen loading can be minimized, small streams are extremely
efficient at removing nitrogen via biotic processes.