Tracking Carbon along the Urban Watershed Continuum to Coastal Zones

Abstract:

Watersheds experiencing urbanization are constantly evolving in their structure and function, and their carbon cycle subsequently evolves across both space and time. We investigate how urbanization influences spatial and temporal evolution of the carbon cycle from small streams to major rivers in the Chesapeake Bay watershed using a variety of approaches such as stable isotopes, in situ water quality sensors, and remote sensing. Along the urban watershed continuum, we show that there is spatial evolution in: (1) the amount, chemical form, and reactivity of carbon, and (2) ecosystem metabolism and transformation of carbon sources from headwaters to coastal waters. Over shorter time scales, the interaction between land use and climate variability alters magnitude and sources of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) as revealed by stable isotopes and in situ sensors. Over longer time scales, land use change has altered particulate carbon transport in coastal waters and the evolution of river sediment plumes as suggested by remote sensing data. Furthermore, there are increased long-term bicarbonate alkalinity concentrations in streams and rivers, and we present new analytical approaches for studying river alkalinization due to human inputs and accelerated chemical weathering. In summary, urbanization alters carbon over space and time with major implications for downstream ecosystem metabolism, biological oxygen demand, carbon dioxide production, and river alkalinization.