Froude numbers in the range of 0. The Microprofile Index Table 6, Gore is a technique for measuring the relative roughness of the stream bottom for a small area 0. This is useful for estimating the thickness of the laminar layer and the availability of protection for macroinvertebrates.
High faunal diversity is found in areas with relatively high Microprofile values Table 6, Gore Using these four measurements velocity, depth, Froude number, and Microprofile Index , appropriate indicator species, those with the same requirements as the conditions for highest faunal diversity for a particular area, can be identified. If the environmental tolerance limits for a specific species have a range similar to the environmental conditions necessary for high faunal diversity, that species is considered a good indicator Gore Using benthic macroinvertebrates as indicators for appropriate velocity ranges as shown by Gore is a concept that can easily be applied to sediment yield.
Using the same techniques, proper indicator species to determine appropriate sediment levels can be identified. For example, this method would be more useful than relying on survival and emergence of salmonid embryos. The migration of salmonids from the spawning grounds introduces many confounding variables, including the effects of dams, downstream pollution problems, and commercial fisheries.
Benthic macroinvertebrates would be more useful in determining the effects of sediment in an area because they are less affected by many off-site environmental conditions and human influences but are very sensitive to localized pollution loadings. Benthic macroinvertebrate populations will also reflect differences in gradient, stream geometry, and bed particle size as shown in Figure 9.
In another study, Newlon and Rabe stated that the two most important factors affecting macroinvertebrates are substrate and suspended sediment. They found that there are four to five physical and chemical factors that have significant influence over biomass and diversity of macroinvertebrates. These factors include substrate, suspended sediment, gradient, water temperature, and stream order and width. Minshall supports these findings and provides a literature review of insect-substratum relationships.
Aquatic plants are affected by both increased bedload and suspended load. An increase in bedload may bury an area in which a plant species is growing. Subaqueous plants will be significantly affected by increased suspended sediment loads because primary plant production is reduced with increases in turbidity. This results in a decrease in benthic organism diversity and density because of a limited food supply.
The reduction in the benthic organism popula-tion finally results in a reduced food supply for fish and if the food benthic organisms is limited, the fish will migrate to other reaches of the stream. It would be possible to take data developed on the relationship of sediment to planform characteristics and flow to develop a habitat suitability index for various species. Data such as water temperature, dissolved oxygen, and percentage of cover would be necessary. Sediment quality is another widespread problem in freshwater and marine systems EPA Sediment quality problems can occur throughout stream types, but tend to occur where there are fine textural stream bottoms and at the lower end of the stream system i.
The contaminated sediments can have both direct adverse impacts on bottom fauna, and indirect effects as the toxic substances move up the food chain. Because of the variability of conditions encountered in stream systems, lake systems, estuaries, and oceans, a variety of tests may be needed to characterize the physical, chemical, and biological systems that may be affected.
In addition, microbial and benthic species will likely reflect sediment contamination that is not revealed by sampling only fish Burton In other words, toxic impacts may be occurring in a river, lake, estuary, or ocean, even though sampling in the water column over the sediments may show water that meets water quality standards. Because there is no single method that captures all the spatial and temporal impacts of contaminated sediment upon all organisms, a compendium has been developed to present several complementary methods to assess sediment contamination EPA Figure 8.
Composition of aquatic organism communities by stream order. Some states Oregon, DEQ, have proposed a tiered evaluation to determine potential sediment contamination. Their approach starts with an analysis of the physical properties to determine where the fines i. This is Tier I testing.
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Once the fines are located, a chemical analysis can be conducted based on potential categories of problems metals, pesticides, coliforms, PCB's, and hydrocarbon derivatives , which is Tier II testing. If the chemical level exceeds established standards or toxic thresholds established by the scientific community, then a third level of testing is indicated.
This Tier III level is bioassays. Determination of trends in sediment quality depends on sampling over long periods of time.
Natural controls on turbidity levels
If long-term sample results are available, trends can be established, but this may be complicated by changes in analytical methods over the time frame. This has been a particular problem with some metals such as cadmium. During the past decade, research in the area of stream sediments has focused almost entirely on the effects of fine sediment on salmonid spawning. The trend seems to be to greater quantification and greater accuracy in testing and monitoring. There have been recent studies of macroinvertebrates, which are becoming an important factor in aquatic habitat evaluation as it relates to fish.
Figure 9. General faunistic zonation patterns of the benthos in pristine streams. A comprehensive paper on the effects of sediment on aquatic habitat was written by Alexander and Hansen The focus of the paper is on brook trout but the methodology provides a complete and comprehensive review of their particular study area.
This study encompassed 15 years' worth of work with daily monitoring and measurements. Instead of moving fish embryos to a lab setting, Alexander and Hansen introduced sand into a stream system for a total of 5 years and monitored the response of the aquatic habitat.
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They collected aquatic data for 5 years prior to the experiment and continued the monitoring after the introduction of sand was halted. This provided data before, during, and after the excess fines were introduced into the low-gradient stream. Besides measuring the effects on brook trout, Alexander and Hansen also studied the effects on the macroinvertebrate population.
While not being overly quantitative, the data are complete enough to draw strong conclusions with statistical significance. A review paper written by Kondolf and Wolman provides an excellent overview of salmonid spawning-gravel sizes. This is a literature review of 22 sources that reported particle-size distributions for many fish species.
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Kondolf and Wolman analyzed the data and plotted cumulative size distributions to calculate particle size mean, geometric mean, sorting index, skewness, and graphic mean. The limitations of their study and studies that they analyzed were adequately discussed. The paper is mostly a discussion of the statistical tests that were performed, but it is an excellent source of data because only 4 of the 22 sources are in open literature Kondolf and Wolman Evaluating the health of a stream system is difficult, and it is not possible to do an in-depth and thorough investigation each time an evaluation is necessary.
This requires other, less intensive techniques for monitoring. Fish have been used as indicator species. As the number of fish declines, a system is thought to be degrading. It takes at least a season to monitor and compare differences in populations of fish. Because of the number of factors that influence fish dams, fishing, and pollution for example it is difficult to evaluate the effects of a single component in the system.
Fish are not great indicators of excess sedimentation. Separating the effects of sediment from other environmental factors can be impossible in a natural system. Sometimes the effects are obvious when there are excessive amounts of fine sediment, but often they are not apparent. A slight decline in the fish population may be attributed to sediment but may actually be the result of dams in the stream system.
To eliminate this problem, other indicator species should be found. Those species are preferable that are more sensitive to very small changes in sediment quality and quantity, less mobile, and have shorter life cycles. This would allow more frequent monitoring which would produce information about sediment in a limited geographic area.
Gore presents a technique that determines tolerances of benthic macroinvertebrates to water depth and current velocity. This same technique could be employed to determine the tolerance of specific macroinvertebrates to fine sediment. Gore was able to find an indicator species Rhithrogena hageni that had tolerances closely matching the depth and current conditions for optimum community diversity. Finding sediment-sensitive macroinvertebrates seems to be the next logical step for monitoring of fine sediment in stream systems.
There seems to be a lack of negative data in the literature. Studies that have been completed and have failed to produce positive results generally are not published.
Suspended Matter in the Aquatic Environment
This is a tremendous source of data that are being lost. If these data were available, many researchers could save time and energy by learning from previous mistakes. Negative results should not be viewed as failure, but as a valuable learning experience which furthers the goals of research.
In addition, there is also a significant lack of long-term data, and there are few studies that are ongoing. Short studies provide a great deal of information but they need to be monitored to determine their relative effectiveness or value. This can be accomplished by an ongoing study that is maintained for many years, or it can be accomplished by later studies in the same area.
Research focusing on aquatic effects of sediment in lakes and reservoirs is limited. This is especially true for research in the Western United States. Lakes in the Northeastern United States have been more thoroughly studied because of the influence of the Great Lakes region. The emphasis in lake studies is different from studies of the stream environment. Because lakes are sediment sinks and essentially closed systems for sediment , toxins are of great concern.
Once a lake has been polluted, it is difficult to clean. Sediment is important in these environments because many inorganic toxins bind to fine sediments. A large percentage of lake sediment literature is aimed towards sediment toxicity. Lake pollution generally gains local but not regional or national interest. This is a result of ecologic isolation; if one lake is polluted or destroyed, it usually does not have an impact on other systems unless there is a stream emanating from the lake.
Concern does arise on a regional or national level when megafauna, such as birds or deer, are affected. This is very different from streams which express environmental changes throughout their systems. Lake and reservoir classification systems can be described using five broad categories.