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Water Hyacinths

Dec 1, 2010

Department: Center for Marine and Wetland Studies
Graduate Students: Julie Barker (advisor James Luken) and Julie Murphy (advisor Jane Guentzel)

CCU graduate students Julie Murphy and Julie Barker are researching two aspects of how Water Hyacinths are affecting the Waccamaw River, a South Carolina coastal plain river.  Murphy is looking at its effect on water quality and Barker is studying the plant to determine if it is a unique and beneficial habitat for native invertebrate species.

Water hyacinths are floating aquatic plants with large purple flowers that grow prolifically in warm fresh water.  Believed to have been introduced to North America in the late 1800's, the plant has quickly invaded many Southern fresh water systems.  The SC Department of Natural Resources has spent over $1 million fighting this fast-growing invasive species with herbicides and the grass carp fish, primarily because it out-competes native plants and blocks waterways.

Barker wants to determine what kind of habitat the water hyacinth provides for local species, comparing it to the native cutgrass and moss.  Her thesis is that it can be beneficial to local ecosystems in providing a place for invertebrates to feed, colonize, and take refuge.  To accomplish this, she is sampling both water hyacinths and native plants to determine who is living on what.

The plant has air-filled bulbs that hang down into the water and grows in large mats.  Barker states that it can be "a great place to hang out" for organisms and even a place for alligators to  hide.  Although Barker is still in the process of measuring, counting, and identifying colonizing invertebrates, preliminary findings indicate that there are upwards of 50 species living in the  roots and up to a 1,000 different organisms living on the plants and its decaying matter.  These include tadpoles, crayfish, water fleas and even an eel.  Most of these organisms were larvae  "dropped off" by bugs passing by. 

Murphy's research is focusing on how the growth and decay of water hyacinths can affect water quality parameters, including the cycling of mercury. Prior to bioaccumulation in fish, atmospherically deposited inorganic mercury (Hg2+) is transformed to methyl mercury, primarily by sulfate reducing bacteria in soils and sediments that contain high concentrations of organic matter and little to no oxygen.

These low oxygen conditions are conducive for methylmercury formation, which is the form that bioaccumulates in fish and can subsequently reach humans through fish consumption. 
Pregnant women and children in particular should avoid consumption of high mercury content fish due to its negative impacts on neurological development.  In addition to soils and sediments, large water hyacinth mats can block sunlight and oxygen from penetrating the surface waters, thus creating low oxygen environments in the water column.  Murphy is investigating how these mats can change nutrient and oxygen concentrations in the water column and if the plants accumulate nutrients and mercury as they grow. 

When compared to many other southern systems, the growth of water hyacinths in the Waccamaw River have not reached similar high biomass levels and not grown as prolifically due to climatic conditions.  This area is the northern most region for water hyacinth because the plant dies when temperatures drop below freezing and when the salinity of the water is 3-4 ppt.

Barker and Murphy are currently conducting further research in the Waccamaw River that may have implications for future management of water hyacinth.

For more information: On methylmercury- http://www.usgs.gov/themes/factsheet/146-00/ and http://toxics.usgs.gov/definitions/methylmercury.html

SC DNR's management efforts- http://www.dnr.sc.gov/magazine/aquatic/freshwaterplants.html


Julie Murphy