Figure 1. An air boat was used for the field crew to collect water and sediment samples from interior shallow water wetlands at Keithsburg Division of Port Louisa National Wildlife Refuge. - Photo Credit: USFWS; Mike Coffey

Figure 2. Student workers wash sediment samples for invertebrates. - Photo Credit: USFWS; Mike Coffey

Figure 3. Student workers wash separate the invertebrates into different taxa for identification and counting. - Photo Credit: USFWS; Mike Coffey

In June of 2012, a team of biologists and students assessed the abundance and diversity of benthic (bottom dwelling) macroinvertebrates to determine water quality conditions at the Keithsburg Division of Port Louisa National Wildlife Refuge.

Keithsburg Division is a backwater lake and wetland system adjacent to the Upper Mississippi River. Refuge staff including Youth Conservation Corps, STEP and SCEP students, Rock Island Ecological Services staff and staff from the Savanna District of Upper Mississippi River National Wildlife and Fish Refuge all helped with the blitz.

Biologists from the U.S. Fish and Wildlife Service use many methods to assess the benthos community. An assessment completed at the refuge unit in 1995 washed bottom sediments through a sieve to collect the invertebrates and then preserved them for later identification back at the laboratory. In 2012, we used a similar method to collect the invertebrates, but instead identified the invertebrates in the field. This approach was used to also test the application of the one day blitz approach. The field identification approach may not allow resolution to the genus or species level, but can provide a useful snap shot of the invertebrate production and biodiversity.The results of the 2012 benthos blitz were similar to the 1995 assessment and indicated that the waters at Keithsburg Division are limited by hyper-eutrophic water quality conditions.

There were low numbers of mostly pollution tolerant organisms such as aquatic worms and bloodworms that typically survive in organic rich sediments with low dissolved oxygen concentrations. There are four major water quality trophic conditions: nutrient poor oligotrophic, nutrient moderate mesotrophic, high nutrient eutrophic,hyper-eutrophic . The excessive productivity of algae and plants from high nutrient inputs depletes the dissolved oxygen in the sediments. Low dissolved oxygen in lake sediments inhibits the production of many kinds of benthic macroinvertebrates. Water samples were also taken and showed…Resource managers and biologists will use these results to better manage the backwater lakes and wetlands, delineate the sources of nutrients, and develop strategies with landowners and stakeholders to reduce nutrient inputs.

Most of the land use around Keithsburg Division is corn and soybean fields. The low lying cropfields in sandy soils depend on irrigation and nutrient applications to sustain the crops. Additional studies with hydrologists will help determine whether these cropfields are an important source and pathway for the nutrient inputs. River backwaters provide a critical ecological service by treating run-off of the nutrient loads from cropfields so that the Mississippi River water is cleaner as it flows into the Gulf of Mexico. However, the nutrient loads should not be so excessive at any one backwater as to limit the function of producing a healthy fishery and sufficient, quality food for migratory birds.

The link below is for an article on nutrients in the Upper Mississippi River. For more information, please contact Cathy Henry Port Louisa National Wildlife Refuge Manger (cathy_henry@fws.gov) or Contaminants Biologist Mike Coffey at the Greater Illinois and Iowa Ecological Services Field Office (michael_coffey@fws.gov).

http://www.boku.ac.at/hfa/lehre/812001/papers/Houser_Hydrobiol10.pdf