Hydrology and biogeochemistry are coupled in all systems. However, human decision-making regarding hydrology and biogeochemistry are often separate, even though decisions about hydrologic systems may have substantial impacts on biogeochemical patterns and processes. The overarching question of this dissertation was: How does hydrologic engineering interact with the effects of nutrient loading and climate to drive watershed nutrient yields? I conducted research in two study systems with contrasting spatial and temporal scales. Using a combination of data-mining and modeling approaches, I reconstructed nitrogen and phosphorus budgets for the northeastern US over the 20th century, including anthropogenic nutrient inputs and riverine fluxes, for ~200 watersheds at 5 year time intervals. Infrastructure systems, such as sewers, wastewater treatment plants, and reservoirs, strongly affected the spatial and temporal patterns of nutrient fluxes from northeastern watersheds. At a smaller scale, I investigated the effects of urban stormwater drainage infrastructure on water and nutrient delivery from urban watersheds in Phoenix, AZ. Using a combination of field monitoring and statistical modeling, I tested hypotheses about the importance of hydrologic and biogeochemical control of nutrient delivery. My research suggests that hydrology is the major driver of differences in nutrient fluxes from urban watersheds at the event scale, and that consideration of altered hydrologic networks is critical for understanding anthropogenic impacts on biogeochemical cycles. Overall, I found that human activities affect nutrient transport via multiple pathways. Anthropogenic nutrient additions increase the supply of nutrients available for transport, whereas hydrologic infrastructure controls the delivery of nutrients from watersheds. Incorporating the effects of hydrologic infrastructure is critical for understanding anthropogenic effects on biogeochemical fluxes across spatial and temporal scales.

River and riparian areas are important foraging habitat for insectivorous bats. Numerous studies have shown that aquatic insects provide an important trophic resource to terrestrial consumers, including bats, and are key in regulating population size and species interactions in terrestrial food webs. Yet these studies have generally ignored how structural characteristics of the riverine landscape influence trophic resource availability or how terrestrial consumers respond to ensuing spatial and temporal patterns of trophic resources. Moreover, few studies have examined linkages between a stream's hydrologic regime and the timing and magnitude of aquatic insect availability. The main objective of my dissertation is to understand the causes of bat distributions in space and time. Specifically, I examine how trophic resource availability, structural components of riverine landscapes (channel confinement and riparian vegetation structure), and hydrologic regimes (flow permanence and timing of floods) mediate spatial and temporal patterns in bat activity. First, I show that river channel confinement determines bat activity along a river's longitudinal axis (directly above the river), while trophic resources appear to have stronger effects across a river's lateral (with distance from the river) axis. Second, I show that flow intermittency affects bat foraging activity indirectly via its effects on trophic resource availability. Seasonal river drying appears to have complex effects on bat foraging activity, initially causing imperfect tracking by consumers of localized concentrations of resources but later resulting in disappearance of both insects and bats after complete river drying. Third, I show that resource tracking by bats varies among streams with contrasting patterns of trophic resource availability and this variation appears to be in response to differences in the timing of aquatic insect emergence, duration and magnitude of emergence, and adult body size of emergent aquatic insects. Finally, I show that aquatic insects directly influence bat activity along a desert stream and that riparian vegetation composition affects bat activity, but only indirectly, via effects on aquatic insect availability. Overall, my results show river channel confinement, riparian vegetation structure, flow permanence, and the timing of floods influence spatial and temporal patterns in bat distributions; but these effects are indirect by influencing the ability of bats to track trophic resources in space and time.