Dams impact carbon dynamics in U.S. rivers

Aug 08, 2012

Dissolved organic carbon (DOC)—which leaches into freshwater systems from plants, soils, and sediments, and from other detritus present in the water itself—is the major food supplement for microorganisms and plays an important role in several environmental processes and in the global carbon cycle. In some aquatic systems such as estuaries the optically measurable colored component of dissolved organic matter (CDOM) is often proportional to the concentration of DOC.

CDOM forms when light-absorbing compounds are released into the water by decaying organic material and through photochemical degradation of certain organic compounds. Hence, CDOM reflects not just the environment and ecosystem, which is the source of the detritus, but also processes that deliver the organic matter into aquatic systems. Human activities, such as logging, agriculture, and waste water treatment, also affect CDOM levels in aquatic systems. It is relatively easy and inexpensive to measure the CDOM content in small volumes of water.

To examine the circumstances under which CDOM reflects DOC concentration, Spencer et al. measured CDOM and DOC concentrations in water collected from 30 across the United States; the rivers represent a wide range of climate, watershed environments, ecosystems, and anthropogenic influence. Overall, the authors find that the CDOM level reflects the DOC concentration in the river water, except in four large rivers, namely, the Colorado, Columbia, Rio Grande, and St. Lawrence rivers.

These four rivers either drain from the Great Lakes or have significant restrictions within their watersheds such as building and other similar modifications. These activities result in long residence times of water, which may increase phytoplankton production, the relative contribution from human sources, or degradation of land-derived material by photochemical processes. As a result, there may have been a decoupling of CDOM from DOC, i.e., the amount of CDOM in these four rivers may have decreased without a concomitant decrease in DOC content. On the basis of their findings, the authors suggest that CDOM measurements in rivers are a useful way to investigate water quality and to monitor delivery of DOC into coastal regions as ecosystems respond to human activity and changes in climate in the near future.

Explore further: Mountain of electrical waste reaches new peak

More information: “Dissolved organic carbon and chromophoric dissolved organic matter properties of rivers in the USA” Journal of Geophysical Research-Biogeosciences, doi:10.1029/2011JG001928, 2012.

Related Stories

Study of agricultural watersheds and carbon losses

Jun 19, 2009

Dissolved organic carbon (DOC) losses from tile drains are an underquantified portion of the terrestrial carbon cycle. This is particularly important in the eastern corn belt where tile drainage dominates the agricultural ...

Urban impacts on phosphorus in streams

Aug 11, 2011

Although phosphorus is an essential nutrient for all life forms, essential amounts of the chemical element can cause water quality problems in rivers, lakes, and coastal zones. High concentrations of phosphorus in aquatic ...

Recommended for you

Mountain of electrical waste reaches new peak

16 hours ago

A record amount of electrical and electronic waste hit the rubbish tips in 2014, with the biggest per-capita tallies in countries that pride themselves on environmental consciousness, a report said Sunday.

China's struggle for water security

Apr 18, 2015

Way back in 1999, before he became China's prime minister, Wen Jiabao warned that water scarcity posed one of the greatest threats to the "survival of the nation".

Canada revises upward CO2 emission data since 1990

Apr 18, 2015

Canada revised its greenhouse gas emission data from 1990 to 2013 in a report Friday, showing it had higher carbon dioxide discharges each year, and a doubling of emissions from its oil sands.

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.