Greenhouse Gas Emissions from Inland Waters: Reach Through Global Scale

Abstract

Freshwater ecosystems emit disproportionately high amounts of carbon dioxide, methane, and nitrous oxide relative to their global surface area.  It is thus imperative to maintain robust and quantitative greenhouse gas budgets, as well as to understand the factors driving these emissions.  Synthesis at the global level can be reliant on assumptions and aggregations from the level of sampling or based upon broader modeling efforts.

Greenhouse gas concentrations and emissions are driven largely by physical and biogeochemical variables that vary climatically and geographically, or even at scales within stream reaches. Physical drivers include stream slopes that affect gas exchange rates, and temperature effects on gas solubility.  Biogeochemical drivers include dissolved oxygen, temperature, and nutrient concentrations via their effects on stream metabolic processes.  In the first talk of this series, we discuss the differences in CO2 and CH4 concentrations and drivers between streams across the United States when streams are compared using high-frequency grab samples collected from stream runs.  We then test the limitations of this work by using a warm, low-gradient Piedmont stream which separates into pools and riffles by summer.  This stream violates the assumptions of streamflow implicit in some inter-stream comparison and the assumptions needed for traditional methods of measuring both physical and biogeochemical drivers of gas processes.

In the second part of this talk, we focus on nitrous oxide (N2O) emissions. N2O is the third most important greenhouse gas driving global climate change, after methane and carbon dioxide, and is a harmful ozone-depleting gas. Atmospheric nitrous oxide concentrations are increasing at a rate that exceeds worst-case IPCC scenario predictions. Inland waters, including rivers, lakes, reservoirs, and estuaries, are among the most uncertain net sources of N2O to the atmosphere. In this presentation, we will discuss a novel process-based global-scale modeling approach to quantify N2O emissions from inland waters, as well as a recent international effort to synthesize, standardize, and regionalize all existing N2O emissions estimates from inland waters. We will also discuss emerging evidence showing the prevalence of N2O undersaturation in rivers and lakes across climate zones, and the implications of these findings for the global nitrous oxide budget.

Bio

Dr. Amanda Gay DelVecchia is an Assistant Professor in the Department of Geography at the University of North Carolina at Chapel Hill.  Her work focuses on how biogeochemistry varies across the hydrologic and physical templates of freshwater ecosystems, and how this heterogeneity interacts with the biota present.  Her research occurs across perennial and non-perennial, lentic (non-flowing) and lotic (flowing), above and belowground waters, and combines field based approaches with synthesis of existing broad-scale datasets.  She holds a PhD in Systems Ecology from the University of Montana. 

Bio

Dr. Taylor Maavara is a Senior Independent Research Fellow at the University of Leeds in England. Her research focuses on quantifying the anthropogenic impacts to biogeochemical cycling in inland and coastal aquatic ecosystems. She uses both modelling and field approaches to address biogeochemical research questions from catchment- to global-scale, with some emphasis on understanding watershed-level impacts like river damming, and climate feedbacks including greenhouse gas emissions from aquatic systems. She holds a PhD in Earth & Environmental Sciences from the University of Waterloo in Canada, and was previously the NSERC postdoctoral fellow at Lawrence Berkeley National Laboratory in California, and a G. Evelyn Hutchinson Fellow at Yale University. She is a mountain climber and canoe tripper, and occasionally writes freelance for outdoor adventure magazines in Canada and the US.