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Show 20 Water Quality in the Great Salt Lake Basins, Utah, Idaho, and Wyoming, 1998- 2001 try UJO me w B 14 12 S 10 B 8 6 4 2 0 1,200 ! 1,000 \ 800 600 400 200 0 - • I I 1- -' 1. • - • • - - ^ 2 CA O ^^-^ F - ^ • ^ J- 3<$ F - ^ r^- v - ^-"^~\> ^ ,••• ^ - K^ s rr\+> * 1 1 • ••• i i 1 <> - o - - • ^-^ - O -"•"^ />~^ *# ^ - - « - r i i i 0 40 60 URBAN INDEX Figure 32. In samples collected in July, the number of pesticides detected and the specific conductance, in microsiemens per centimeter, of the water generally increased with increasing urban index values. nutrient concentrations and in the number of pesticides detected likely reflects the use of these compounds on lawns, parkways, roadways, and other areas of the urban landscape. High concentrations of nutrients and pesticides can be toxic to many stream organisms, and the presence of these chemicals in stream water can limit the numbers and kinds of organisms found in urban streams. In addition, water temperature can increase in the more highly urbanized areas as the amount of impervious surface area increases. For example, during storms, rainwater falling on hot pavement heats up and then runs into streams, increasing their temperature. Also, the temperature of the land surface in urban areas is often several degrees warmer than in the surrounding countryside. As the temperature of the ground surface in urban areas increases, the temperature of streams flowing through these areas may also increase. Many biological organisms have a limited temperature range in which they survive. An increase in stream temperature favors those organisms able to tolerate higher temperatures, thus altering the biological community. The quality of physical habitat, while substantially different among sites, did not show a strong correlation with the level of urbanization in the watershed. With the exception of substrate particle size, the differences in physical habitat among sites appeared most strongly related to natural gradients, such as basin size and altitude. The size of substrate ( bottom material) in streams decreased as the intensity of urbanization increased. Small particles, such as sand and silt, were more common at more urbanized sites, where they may have been washed into streams from unvegetated areas, such as construction sites. In addition, dirt and silt accumulate on impervious areas ( blacktop, rooftops, sidewalks) and can easily be washed into streams during rainstorms. When large amounts of these fine particles enter a stream channel they can clog the spaces between rocks on the stream bottom and reduce the availability of the stable habitat preferred by bottom- dwelling organisms. Algae and invertebrates living on the bottom of a stream channel are good indicators of changes in water quality and habitat conditions. As physical and chemical conditions change with urbanization, the number and type of organisms in a stream also changes. For example, as the intensity of urbanization increased, the relative abundance ( percentage of all individuals collected) of algae that are tolerant to organic pollution, salinity, and silt increased, while the relative abundance of algae sensitive to pollution ( intolerant algae) decreased ( fig. 33). The increase in the abundance of algae tolerant of organic lU 80 o ta 60 < HI > LU 40 CC HI o DC LU D- 0 O Algae tolerant of organic pollution O Algae tolerant of salinity O Intolerant algae O © Q Q OOO OQQ o8o O n OO 8o og, 0- 25 26- 50 51- 75 76- 100 URBAN INDEX Figure 33. As the level of urbanization increases, the percentage of algae tolerant of salinity ( red) and organic pollution ( green) increases, while the percentage of algae sensitive to pollution ( blue) decreases. pollution corresponded to an increase in water- column nutrient concentrations. Likewise, the increase in silt- tolerant algae corresponded to a decrease in substrate particle size in the stream channel. Similarly, as the intensity of urbanization increased, the number of kinds of invertebrates ( richness) sensitive to pollution decreased and the number of kinds of invertebrates tolerant of pollution increased ( fig. 34). Generally, invertebrate organisms considered intolerant, such as mayflies and stoneflies, prefer lower water temperatures, require more stable substrate and flow regimes, and require good water quality. In contrast, the presence of tolerant invertebrates, such as midges and worms, generally increases under conditions of degraded habitat or poor water quality. O Tolerant invertebrates O Sensitive invertebrates o o o o o o 26- 50 51- 75 76- 100 URBAN INDEX Figure 34. As urban intensity in the watershed increases, the number of invertebrate taxa sensitive to pollution ( blue) decreases while the number of invertebrate taxa tolerant to pollution ( red) increases. Although not measured directly in this study, the amount of water diversion and exchange in these streams likely is responsible, in part, for these alterations in biological communities. As discussed in the section " Water development affects quantity and quality of water resources," the quality of water is affected by diversions. For example, stream temperature was substantially lower in urban streams with continuous |