Emilio Mayorga | USGS Science

USGS2013

Global carbon dioxide emissions from inland waters

Carbon dioxide (CO 2 ) transfer from inland waters to the atmosphere, known as CO 2 evasion, is a component of the global carbon cycle. Global estimates of CO 2 evasion have been hampered, however, by the lack of a framework for estimating the inland water surface area and gas transfer velocity and by the absence of a global CO 2 database. Here we report regional variations in global inland water surface area, dissolved CO 2 and gas transfer velocity. We obtain global CO 2 evasion rates of 1.8   petagrams of carbon (Pg   C) per year from streams and rivers and 0.32   Pg   C   yr −1 from lakes and reservoirs, where the upper and lower limits are respectively the 5th and 95th confidence interval percentiles. The resulting global evasion rate of 2.1   Pg   C   yr −1 is higher than previous estimates owing to a larger stream and river evasion rate. Our analysis predicts global hotspots in stream and river evasion, with about 70 per cent of the flux occurring over just 20 per cent of the land surface. The source of inland water CO 2 is still not known with certainty and new studies are needed to research the mechanisms controlling CO 2 evasion globally.

Nature↗

USGS2008

The regional and global significance of nitrogen removal in lakes and reservoirs

Human activities have greatly increased the transport of biologically available nitrogen (N) through watersheds to potentially sensitive coastal ecosystems. Lentic water bodies (lakes and reservoirs) have the potential to act as important sinks for this reactive N as it is transported across the landscape because they offer ideal conditions for N burial in sediments or permanent loss via denitrification. However, the patterns and controls on lentic N removal have not been explored in great detail at large regional to global scales. In this paper we describe, evaluate, and apply a new, spatially explicit, annual-scale, global model of lentic N removal called NiRReLa (Nitrogen Retention in Reservoirs and Lakes). The NiRReLa model incorporates small lakes and reservoirs than have been included in previous global analyses, and also allows for separate treatment and analysis of reservoirs and natural lakes. Model runs for the mid-1990s indicate that lentic systems are indeed important sinks for N and are conservatively estimated to remove 19.7 Tg N year -1 from watersheds globally. Small lakes (<50 km 2 ) were critical in the analysis, retaining almost half (9.3 Tg N year -1 ) of the global total. In model runs, capacity of lakes and reservoirs to remove watershed N varied substantially at the half-degree scale (0-100%) both as a function of climate and the density of lentic systems. Although reservoirs occupy just 6% of the global lentic surface area, we estimate they retain ~33% of the total N removed by lentic systems, due to a combination of higher drainage ratios (catchment surface area:lake or reservoir surface area), higher apparent settling velocities for N, and greater average N loading rates in reservoirs than in lakes. Finally, a sensitivity analysis of NiRReLa suggests that, on-average, N removal within lentic systems will respond more strongly to changes in land use and N loading than to changes in climate at the global scale. ?? 2008 Springer Science+Business Media B.V.

Biogeochemistry↗