The global transport and deposition of anthropogenic nitrogen (N) to downwind ecosystems are significant and continue to increase. Indeed, atmospheric deposition can be a significant source of N to many watersheds, including those in remote, unpopulated areas. Bacterial denitrification in lake sediments may ameliorate the effects of N loading by converting nitrate (NO3-) to N2 gas. Denitrification also produces nitrous oxide (N2O), a potent greenhouse gas. The ecological effects of atmospheric N inputs in terrestrial ecosystems and the pelagic zone of lakes have been well documented; however, similar research in lake sediments is lacking. This project investigates the effects N of deposition on denitrification and N2O production in lakes. Atmospheric N inputs might alter the availability of NO3- and other key resources to denitrifiers. Such altered resources could influence denitrification, N2O production, and the abundance of denitrifying bacteria in sediments. The research contrasts these responses in lakes at the ends of gradients of N deposition in Colorado and Norway. Rates of denitrification and N2O production were elevated in the sediments of lakes subject to anthropogenic N inputs. There was no evidence, however, that N deposition has altered sediment resources or the abundance of denitrifiers. Further investigation into the dynamics of nitric oxide, N2O, and N2 during denitrification found no difference between deposition regions. Regardless of atmospheric N inputs, sediments from lakes in both Norway and Colorado possess considerable capacity to remove NO3- by denitrification. Catchment-specific properties may influence the denitrifying community more strongly than the rate of atmospheric N loading. In this regard, sediments appear to be insulated from the effects of N deposition compared to the water column. Lastly, surface water N2O concentrations were greater in high-deposition lakes compared to low-deposition lakes. To understand the potential magnitude of deposition-induced N2O production, the greenhouse gas inventory methodology of Intergovernmental Panel on Climate Change was applied to available datasets. Estimated emissions from lakes are 7-371 Gg N y-1, suggesting that lakes could be an important source of N2O.
One of the best ways to learn about an ancient society is to examine their architecture. Form imitates and is limited by utility and this can especially be seen in how humans set up their communities. However, with house structures, a new social dimension is added and can create many factors in its making. Social complexity and hierarchies can be reflected through the communal structures and layout and provide insight into how people organize themselves. In this paper, over 400 Hohokam structures from the Preclassic and Classic periods were compiled into a general dataset and 322 of which had sufficient data relevant to the research questions were used to determine any notable characteristics. The organization of the structures in this way provided a measurable process in determining these social and cultural aspects. The shapes of the Hohokam homes seemed to stay consistent over time with only the location and size of the entrance varying from site to site. Structures made in the Preclassic period had a smoother distribution of sizes than that of the Classic period structures. However, the changes in individual houses was not statistically significant. There is evidence that supports the notion that, as the Hohokam civilization developed, hierarchies began to form in their social complexity. Yet, it is not great enough to make any broad claims. The information derived from this paper can support further implications of growing social inequalities and the formation of classes within this community.