Anthropogenic changes to inland water nutrient cycles: From sky to sea
Dr. Taylor Maavara
Earth and Environmental Sciences Area
Lawrence Berkeley National Laboratory
Rivers are the great connectors of the freshwater cycle, providing essential services to humans and ecosystems, including drinking water, transportation channels, food security, waste assimilation, and water purification. River systems also harbour >10% of known biodiversity for <1% of the Earth’s surface. Essential nutrient elements such as phosphorus (P), nitrogen (N), silicon (Si), and carbon (C) are transported and transformed along the land-ocean aquatic continuum (LOAC), forming the basis for freshwater food webs in saturated and unsaturated subsurface environments, lakes, rivers, wetlands, reservoirs, and floodplains, and ultimately for marine food webs in estuarine and coastal environments. Enhanced nutrient loading, urbanization, land use change, and river channelization and impoundments have massively altered nutrient fluxes. Moreover, secure water supplies are also threatened globally by climate change. In this seminar, I will discuss three case studies exemplifying the large-scale, human-driven changes to nutrient cycles cascades, from mountain headwaters to coastal zones. The first will focus on the development of a stochasticmechanistic modeling approach to quantify the past, present and future alterations to both relative and absolute fluxes of C, N, P and Si cycling via the worldwide damming of rivers, and how these changes in turn can affect coastal ecology. My second case study will build on the same modeling approach to predict natural and anthropogenic nitrous oxide (N2O) emissions from open waters along the LOAC. Finally, I will discuss the development of a Bayesian model platform to quantify the climate-driven alterations to N cycling in a mountain watershed, where up to half of the N originates from bedrock weathering. Together, these three case studies present a wholistic quantification of the feedbacks between watershed-level human alterations (damming), their global consequences (enhanced greenhouse gas emissions), and local watershed responses (mountain N cycling).
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