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<br />. <br />~j <br />~i <br /> <br />salts, th~se sources explain the continuous rise in salinity concentrations <br /> <br />~ <br /> <br />., <br /> <br />downstream to the State line. ,Sediments and nutrients probably settle' out in <br /> <br />~~, <br />j.:~ <br /> <br />w <br />o <br />o <br />'-0 <br /> <br />reservoirs along the South Platte, but the numerous erosion areas in <br /> <br />~ <br />!:.~ <br />~.~ <br /> <br />tributaries sustain high sediment levels. Nutrients decline in the downstream <br /> <br />region' even though fertilizer use, feedlot activity, and urban wastes are <br /> <br />$$: <br />.';' <br />F~~ <br /> <br />contributed to the river. This decline appears' to occur due to the uptake of <br /> <br />f; <br />'k;: <br />.~" <br /> <br />the 'nutrients through 'the evapo-transpiration process in irrigated <br /> <br />agricultural areas downstream of the Denver Metropolitan area. <br /> <br />e1 <br />l::' <br />.. ~~ <br /> <br />Although instream nutrients decrease as the South Platte flows towards the <br /> <br />'m <br />~~ <br />",~;J: <br /> <br />Colorado border algal problems in offstream reservoirs have developed 'Since <br /> <br />".11 <br />~~ <br />r:.tl <br />h:: <br /> <br />the late 1960's. North Sterling Resevoir, located near Sterling Colorado was <br /> <br />a high quality fishery in the 1960's. Since that. time the lake has become <br /> <br />''''<1 <br />r~~ <br />Iii\l <br /> <br />eutophic and, the fishery has collapsed due to serious algal problems in the <br /> <br />form of Aphanizomenon blooms. During much of the summer the lake is "pea <br /> <br />t::;';1 <br />1(" <br />l1~~! <br />:;OM. <br /> <br />soup" in appearance with excessive algal concentrations to a depth of 57 <br /> <br />f~~ <br />%~ <br />~~< <br /> <br />feet. In recent years the same problem has started developing in Prewitt <br /> <br />Reservoir near Fort Morgan; Jackson, Empire and Riverside Reservoirs are <br /> <br />similarly at risk. The eutrophication is caused by nutrient enrichment. <br /> <br />f.~'f <br />~v <br />~\' <br /> <br />Nutrient sources to the South Platte include sewage discharges from <br /> <br />I <br /> <br />metropolitan areas and samller communities, as well as nonpoint runbff from <br /> <br />,~ <br />.Q <br />"," <br />v:~ , <br /> <br />agriculture. The percentage of nutrient loading to these waters attributable <br /> <br />to nonpoint agricultural inputs is unknown. Further study is needed to <br /> <br />"1 <br />c <br />~~.... <br />ffi:~ <br /> <br />properly assess this problem. <br /> <br />~)J <br />t~2 <br /> <br />-73- <br /> <br />'f-,':j <br />{.<-l; <br />.<;1 <br /> <br />"'--" <br />11.:~ <br />1~:~ <br /> <br />~j <br /> <br />'. <br /> <br />.~ <br />