Introduction

Since 1994, the Iowa Department of Natural Resources and the University Hygienic Laboratory (UHL) have sampled fish and benthic macroinvertebrates to assess the biological integrity of Iowa's streams and rivers. Benthic macroinvertebrates are small animals, such as aquatic insects, crustaceans, leeches, and snails that live on the stream bottom. The numbers and types of aquatic organisms found in a stream are useful indicators of the stream's health because they reflect changes in water quality and habitat.

Biological assessments are an important part of the 305(b) Water Quality Reporting process, as they provide quantitative data on which assessments of water quality can be made.

Sampling

1. Ambient sites are sampled annually for benthic macroinvertebrates at 16 river locations that are also monitored for water quality on a monthly basis.
   
2. Reference sites represent stream conditions that are least disturbed by human activities, and are used to set biological criteria for measuring the health of other streams. The current rate of sampling is 20 sites, once per year. These sites are also revisited once every five years, to monitor water quality trends in the stream. A map is available depicting both Reference and Ambient site locations.
   
3. Test sites are sampled or "tested" to determine how much a stream's biological health is impacted by disturbances such as channelization, livestock grazing, manure spills, wastewater discharges and urban runoff. Currently, 40 sites are sampled once per year.
   
4. Watershed sites are used to determine the location and amount of biological impairment in a watershed, and identify problem areas that need to be addressed. So far, 48 sites in three watersheds have been sampled. More watershed sampling is planned to support development of stream restoration plans, including TMDLs (Total Maximum Daily Loads). A TMDL is a blueprint for an impaired water body that defines the problem, identifies the source of pollutants and outlines what control methods can be implemented which will result in improved water quality so it again meets its designated uses.

All biologically sampled sites 1995-2002

Fish are sampled using electrofishing gear. Battery-powered, backpack shockers are used in small streams and a generator-powered, barge shocker is used in larger streams. Sampling is accomplished in one pass (downstream to upstream) through the sampling area. The electrical current in the water temporarily stuns fish swimming near the shocker electrodes. The fish are netted and transferred to a holding bucket or live well for processing. The fish are identified, counted, and examined for diseases and parasites and then released to the stream.

Ecoregions and Reference Streams
Ecological regions (or "ecoregions") and reference stream sites provide a framework for stream biological assessment. Ecoregions are areas in which there is relative similarity among various ecological systems, such as lakes, streams, and wetlands. Iowa has ten ecoregions that are defined by geology, landform, land use, natural vegetation, and soils. Stream reference sites have been identified in each ecoregion. Reference sites represent relatively natural stream habitats that support healthy biological communities. The Iowa DNR is using reference sites to establish biological criteria for determining the health status of other streams. To minimize the risk of water quality impacts, reference sites are not located near known pollution sources. Reference sites are bordered by well-vegetated buffer strips and have good physical habitat characteristics.

Biological Indicators

The Iowa DNR uses a Benthic Macroinvertebrate Index of Biotic Integrity (BM-IBI) and a Fish Index of Biotic Integrity (F-IBI) to obtain a broad assessment of stream biological health. The BM-IBI and F-IBI combine many individual measurements or “metrics” to obtain a more complete estimate of stream health. A metric, as the term is used here, is any characteristic of the aquatic community that can be measured reliably and reflects upon stream health. The BM-IBI and F-IBI both contain twelve metrics. The metrics relate to species diversity, relative abundance of sensitive and tolerant organisms, and proportion of individuals belonging to specific feeding and habitat groups. The F-IBI also has a fish abundance metric and a fish health condition metric. The individual metric scores are summed to obtain an index score ranging from 0 (poor) – 100 (optimum). Qualitative scoring ranges of poor, fair, good, and excellent have been established. To determine whether a stream is meeting expectations for supporting aquatic life, the Iowa DNR compares the BM-IBI and the F-IBI scores from that stream against the range of index scores from reference sites located in the same ecoregion.

Helping to inventory Iowa’s biological resources is an important aspect of the biological sampling project. The loss of many fish and freshwater mussel species that once lived in Iowa has been reported. Despite these losses, Iowa’s streams support a sizeable amount of biological diversity. So far, 102 species of fish and approximately 320 species of benthic macroinvertebrates have been collected. Information from these collections helps determine the geographic ranges of fish species of endangered or threatened status in Iowa. In the case of benthic macroinvertebrates, many new discoveries are being made. For example, UHL staff have documented numerous mayfly and stonefly species not previously reported for Iowa. Minnows are the most diverse group of fish (33 species) living in Iowa’s streams. Perches (including darters) (13 species), Suckers (11), and Sunfish (10) have the next largest numbers of species. The midge larva (Chironomidae), an immature life stage of aquatic fly, is the most frequently collected type of benthic macroinvertebrate. Other common benthic macroinvertebrates are net-spinning caddisflies, mayflies, riffle beetles, and aquatic worms. Ten fish species and ten types of benthic macroinvertebrates account for more than 60% of all organisms sampled.

Information collected in the IDNR/UHL stream bioassessment project is used to guide surface water management decisions. Aside from assisting in the development of 305(b) Water Quality Reporting, several other uses of bioassessment information include:

• Stream status and trend monitoring
  
• Water quality standards development and refinement
  
• Problem investigation
  
• Evaluation of pollution control and habitat restoration actions
  
• Development of restoration plans for impaired waters -- TMDL (Total Maximum Daily Load)
  
• Conservation of biological resources
  
• Evaluation of stream recovery following fish kills