Background Scenario

Human civilization has flourished around major rivers and coastal areas for obvious reasons. It is estimated that as of 1998 more than a half of the world population lives and works within 200 kilometers of a coastline (Hinrichsen, Don. Coastal Waters of the World: Trends, Threats, and Strategies. Washington D.C. Island Press, 1998.) It is this growth in human activity that provides significant changes in the land surrounding our waterways. With a catastrophic weather event such as a hurricane or a long period of sustained rainfall, the results of increased erosion have short term and long ranging effects on the coastal biological communities. Sediments flowing into the coastal waters carry chemicals from the land that may accumulate in the tissues of aquatic organisms. Nutrient levels fluctuate as a result of agricultural run-off that may, in turn, cause variations in coastal productivity. Oxygen levels drop significantly in bottom waters as decomposition of the organic material occurs during months of little water column mixing. A heavy increase in sand, silt and clay alter the bottom topography and local habitats, thus resulting in a change in the diversity and distribution of coastal marine species. The problems of coastal management become increasingly more complex as we view the effects of human influence directly from specific sensors carried on the satellites.

Sediment plumes and water turbidity

In some parts of the ocean, the water is so clear that visibility may exceed several 100 feet. The conditions that promote decreased clarity may include a range of outside factors. Biologically, high turbidity may be due to an increase in the numbers of microscopic organisms or from an increase in bottom sediment disruption from abundant benthic animals. Organic particles from decaying material as well as inorganic particles can be suspended in the water column contributing to a decrease in clarity. Particulates from the land that enter our waterways may be the result of urban runoff, soil erosion from agricultural lands that lack buffer zones, sewage treatment effluent and other point and non-point source pollution.

Naturally flooding events may overload the drainage basin with high levels of dissolved solids, thus setting the stage for an immediate local effect as the sediment plume progresses into the open waters. High turbidity alters the dynamics of the water community by decreasing the available sunlight for photosynthesis. Water temperatures increase as the available light is absorbed by the suspended particles. Organisms, particularly the benthic population, may be stressed as the limits of their normal tolerance are exceeded.

Large sediment plumes can be monitored using space technology. The migration of the suspended solids into an embayment is visible using Landsat imagery and reflectivity products derived from AVHRR sensors. Ocean color satellite images may indicate areas of high nutrients entering an embayment. Sea surface temperature, turbidity products, and chlorophyll estimates from satellite sensors can be combined with local observations to enhance our understanding of the effects of increased sediments in the coastal waters.

Nutrient overload and algal blooms

The coastal ocean zones are unique in the sense that they withstand constant change. Weather events such as hurricanes have for millions of years battered, flooded and eroded our coastlines and inland rivers. Soil particles and dissolved organic molecules have found their way into the estuaries and onto the continental shelf. The ecological systems have rebounded even with substantial changes in the local environments. After Hurricane Floyd in 1989, there was much concern that the flushing that occurred as a result of the flooding would have long ranging effects on the biological health of the Pamlico Sound. (find appropriate reference here. )…. It may not these catastrophic events that are causing the changes in the coastal waters, but rather the extended influence of increased human activity along our rivers and streams.

Nutrient overloading and the resulting eutrophication of the waters is a complex issue. The distribution of the nutrients in the coastal waters are influenced by the hydrology , geology and water chemistry of the outfall area. The source of these nutrients and their transport downstream is a more difficult concept to define especially in a large watershed such as the Mississippi River Basin. Management of upriver point and non-point sources of nitrogen balances the human need for chemical usage with the natural ability of the wetlands to self-regulate the ecosystem.

Historical Background on Mercury Poisoning in Japan

A greater understanding of the distribution of toxic chemicals in the coastal waters of Japan occurred from a well documented case of early industrialism. The dumping of chemical products as early as 1925 into Minamata Bay quickly destroyed the fishing in this area. The people of the villages surrounding this bay were mostly farmers and fisherman. For a period of over 30 years, an estimated 27 tons of Mercury compounds were put into these waters. As fish was a primary food source in the communities around the bay, thousands of people ingested toxic levels of methyl mercury. The illness, which is characterized by a degeneration of the nervous system, was called “Minamata disease”. As devastating as this disease was for the people of this area, it raised our awareness of the toxicology of mercury. The levels of mercury in our environment are closely monitored and routine sampling occurs to measure the accumulation of this metal in marine animal tissue.

Characteristics of the Flood of 1993 of the Mississippi River

The Great Midwest Flood of 1993 was the "most devastating flood in modern United States history" impacting more than nine states with economic damages near $20 billion (Kolva). This event, like all major flooding events, was the result of unusual quantities of precipitation throughout the basin. Rains in the upper Mississippi River Basin exceeded normal averages early in the year and were followed with more than record precipitation in June and July. The long duration of this event caused most of the major rivers in this basin system to be at flood stage for several months. The large increase in water volume eventually made its way to the Gulf of Mexico.

The coastal zone near the mouth of the Mississippi River typically experiences a seasonal drop in dissolved oxygen levels during the late spring and early summer. The normal influx of freshwater from spring rains and dissolved nutrients triggers phytoplankton growth in the late spring in coastal waters. The decomposition of this organic matter is the cause of low oxygen in the bottom waters. The “dead zone” or hypoxia zone generally has a dissolved oxygen value of less than 2 parts per million. Following the flood of 1993, the dead zone covered nearly 17,000 square kilometers , a notable increase from the 10,000 square kilometer average from the 1985-1992 period. In the three years that followed the flood, the zone of hypoxia was as large as or larger than the flood year (Goolsby, Battaglin and Hooper, 1997).

Future research and Coastal initiatives

The Gulf of Mexico has received much attention as an area of ecological concern. The industrialization along the Gulf coast and the agricultural interests from the entire drainage basin has increased the level of water quality awareness in recent years. Support for extended research on the state of the Gulf coastline has come from many federal agencies, including NOAA, EPA, and USGS. The EPA formed the Mississippi River/Gulf of Mexico Watershed Nutrient Task Force in 1997. Public law also calls for an action plan to be developed to reduce and control the hypoxia in the Gulf of Mexico. The National Center for Coastal Ocean Science in 2002 published a detailed update to the Gulf of Mexico Hypoxia Assessment (http://www.nos.noaa.gov/products/pubs_hypox.html#update), which further strengthens the importance of our coastal waters to a variety of interests. From a national level to a local focus, many communities are fostering programs that seek to reduce run-off from storm drain management practices to increased pressure for buffer zoning around the waterways.

References

Klova, J. R., ____. Effects of the Great Midwest Flood of 1993 on Wetlands, National Water Summary on Wetland Resources, United States Geological Survey Water Supply Paper 2425.On-line at:http://water.usgs.gov/nwsum/WSP2425/flood.html

Goolsby, D. A., Hooper, R.P., and Battaglin, W. A., 1997.Sources and Transport of Nitrogen in the Mississippi River Basinpresented at American Farm Bureau Federation Workshop
"From the Corn Belt to the Gulf...Agriculture and Hypoxia in the
Mississippi River Watershed", July 14-15, 1997, St. Louis, Missouri. On-line at: http://wwwrcolka.cr.usgs.gov/midconherb/st.louis.hypoxia.html