STOICHIOMETRY AS A DRIVER OF ELEMENTAL CYCLING IN TROPICAL AND TEMPERATE MONTANE STREAMS
Elemental cycling is fundamental to life and can be an indicator of ecosystem condition and function. We have long known that the cycles of elements, both nutrients and toxins, are intimately linked, but there are still many aspects of linked elemental cycles we do not understand and new links we have not explored. For example, classic stoichiometry studies typically focus on carbon (C), nitrogen (N), and phosphorus (P) while much less literature is devoted to other elements. Expanding the framework to incorporate new interactions and new elements is an important next step for ecological stoichiometry given that ~25+ elements are required to build organisms and given the potential for toxic elements to interact with essential elements. Throughout my PhD, I have used ecological stoichiometry as a unifying theme. Ecological stoichiometry describes how the balance of energy and elements affects and is affected by organisms and their interactions in ecosystems. My thesis research examines drivers of nutrient and toxic element cycles in tropical and temperate streams. First, I compare three common methods for estimating nutrient uptake in streams. I found that while the relative ranking was preserved across uptake methods, the absolute values varied. Also, in streams with high nutrient uptake, longer residence times underestimate uptake. Next, I tested the importance of climate regime and a suite of other biogeographical factors in driving nutrient uptake in streams along a temperature gradient. I compared streams in the tropical, Ecuadorian Andes with streams in the temperate, Colorado Rockies. I found that temperature has a larger influence on nutrient uptake in tropical streams. I then explore if the stoichiometric linkages between N and P extend to As. Through a series of field and lab experiments, I found that microbial As uptake is driven by relative N:P, not absolute P concentration alone. Finally, I expanded the finding that N:P drives microbial As cycling to whole-stream As retention by food webs. I quantified As, N, and P in basal resources, in higher trophic levels (invertebrates) and in invertebrate excretion. I found that some food web pathways retain more As as a result of N:P. I conclude that the utility of ecological stoichiometry is multi-faceted and in its infancy in terms of application to broader scales and systems. Understanding of biogeochemical processes will be strengthened by incorporating additional elements and considering stoichiometric interactions.
Arsenic; Ecological Stoichiometry; Nitrogen; Nutrient Cycling; Phosphorus; Streams
Flecker, Alexander S.
Hairston, Jr, Nelson George; Rosi, Emma J.; Hewson, Ian
Ecology and Evolutionary Biology
Ph. D., Ecology and Evolutionary Biology
Doctor of Philosophy
Attribution-NoDerivatives 4.0 International
dissertation or thesis
Except where otherwise noted, this item's license is described as Attribution-NoDerivatives 4.0 International