Responses of consumers and food resources to a high magnitude,unpredicted flood in the upper Mississippi River basin

The Mississippi and Missouri Rivers experienced flooding in 1993 that fell outside the annual predictable flood period of spring and early summer. Flooding began in late June, peaked in late July (25 232 m³/s on the upper Mississippi and 21 240 m³/s on the Missouri) and remained at or near flood stage into October 1993. This study was performed to determine if disturbance by an unpredicted flood event would alter trophic dynamics of river–floodplain systems by creating shifts in the composition of organic matter available to consumers. The Ohio River, which did not flood during the same period, was examined for comparison. Stable isotopic ratios of carbon and nitrogen from samples collected in 1993 and 1994 were used to characterize potential food sources and determine linkages between food sources and invertebrate and fish consumers. Pairwise contrasts, performed separately for each river, indicated there were few interannual differences in δ¹³C and δ¹⁵N of organic matter sources and consumers. Between sample period (flood year versus normal water year) trends in both flooded rivers were similar to between‐year trends observed for the Ohio River. Trophic structure of the Mississippi and Ohio Rivers was similar in both years, with fine and ultra‐fine transported organic matter and dissolved organic matter representing the major sources of organic matter. Overlapping isotopic signatures in the Missouri River made tracking of sources through the consumers difficult, but similarities in δ¹³C and δ¹⁵N between years indicated trophic structure did not change in response to the flood. The results suggest that consumers continued to rely on sources of organic matter that would be used in the absence of the unpredicted 1993 flood. It is proposed that trophic structure did not change in response to flooding in the Mississippi and Missouri Rivers because both rivers exhibited the same trends observed in the Ohio River. Copyright © 2001 John Wiley & Sons, Ltd.     

Monitoring the health of large rivers with macroinvertebrates: Do dominant taxa help or hinder the assessment?

Macroinvertebrate communities in the Mississippi River are often dominated by a few taxa (e.g. oligochaetes in the fine sediments and hydropsychid caddisflies on rocks) that exploit the natural abundance of fine organic particles. These taxa are moderately to highly tolerant of pollution, and the combination of high abundance and high pollution tolerance could result in the river being assessed as highly polluted. We examined how the presence or absence of dominant oligochaetes or hydropsychid caddisflies affected biometric values and responses used to monitor environmental stress in large rivers. Responsiveness was assessed across five simulated impairments created by removing different subsets of sensitive taxa from the original data for macroinvertebrates in the Upper Mississippi River near Cape Girardeau, MO. For many metrics, removal of the dominant taxa changed values, and increased the difference between existing conditions and simulated impairments. For macroinvertebrate data from fine‐sediment habitat, 8–9 of 12 metrics responded to the two most severe impairments simulated with or without dominant oligochaetes, but none changed for less severe impairments. For rock habitat, more metrics responded to moderate or severe impairments simulated when dominant hydropsychids were excluded. Few metrics performed better with dominant taxa. Overall, removal of dominant macroinvertebrate taxa improved both the accuracy and interpretability of several metrics commonly used to monitor effects of water pollution on large‐river faunas dominated by a few taxa. Removing them also makes observed responses more comparable to those frequently quantified for wadeable streams and rivers. Copyright © 2009 John Wiley & Sons, Ltd.     

The Historical Struggle with Floods on the Mississippi River Basin

For the past 150 years a titanic struggle has been underway between the people of the Mississippi River basin and its floods. Humans first tried to control the floods with structures, channel straightening, levees, dams, and reservoirs, but after 100 years and the expenditure of billions of dollars; losses to property and lives continued to grow. Efforts since the 1950s to encourage land-use changes in flood-prone areas and the use of flood insurance often have been thwarted by government relief and continuing human desire to reside in floodplains. During the massive floods in 1993, 1996, and 1997 only ten percent of the residents of flooded areas had flood insurance. The river system brings enormous economic value to the United States, and interests in protecting and enhancing the natural environment of the river are often in direct conflict with economic interests. Flood mitigation is often caught in the middle of the debate about how to manage the river system to satisfy all interests. Recent floods have taught several key lessons about environmental blessings and dangers, and reveal that the nation's policies regarding flood mitigation/relief must change with more emphasis on personal responsibility. The huge and costly infrastructure built to control the major rivers for floods and navigation is aging and will soon need replacement, offering an opportunity to better handle future flood mitigation to satisfy the basin's complex mix of economic, human, and environmental interests.     

Physicochemical factors affecting larval fish densities in mississippi river floodplain ponds,Louisiana (U.S.A.)

We collected water-quality data from 15 artificial floodplain ponds along the Mississippi River during May 1988 and quantified shoreline length, shoreline sinuousity, volume, and depth variation. Ponds regarded as high-quality nurseries (based upon larval fish densities) contained higher dissolved oxygen concentrations and lower total organic carbon concentrations than ponds of lower nursery quality (p < 0.02). High-quality nurseries also maintained higher conductivity and turbidity than low-quality nurseries (p < 0.05). Results indicated that dissolved oxygen and pH probably fluctuated less in high quality nurseries and therefore provided better conditions for survival and growth of larval fishes. Total organic carbon and conductivity were directly related to pond morphometry (p < 0.004) and affected dissolved oxygen and pH in ponds. Large, high-volume ponds with sinuous shorelines and variable depths tended to contain both high conductivities and low total organic carbon concentrations. Pond morphometry may have affected water quality and subsequently determined the nursery value of artificial floodplain ponds.