Nutrient Patterns, Mainstem South Platte River, Denver to Julesburg, Colorado: Seasonal and Temporal Variations a Longterm Tom Sawyer Monitoring Program
Scott Nykerk and John Woodling, Colorado Division of Wildlife, Denver, Colorado
The nitrogen and phosphorus levels in the mainstem South Platte River have been monitored since December, 1993, through a cooperative effort of agencies performing laboratory water quality analyses and a network of schools collecting water samples. Twice monthly on the same day, teams of students collect samples at 16 mainstem South Platte sites from Denver to Julesburg, Colorado. Samples are returned to Denver and analyzed by three laboratories. Analyses of a conservative substance, sulfate, revealed that loadings and concentrations were lowest near Denver and highest at the Nebraska border. Maximum phosphorus concentrations were found downstream of Denver while maximum nitrate concentrations were found downstream of Greeley, Colorado. Maximum nitrogen and phosphorus loadings in the river were not found at the Nebraska border, but just downstream of Greeley, Colorado, where maximum flows were recorded. An extensive irrigation water diversion system resulted in much lower flows (and lower N and P loadings) in the portion of the river from Fort Morgan to Nebraska. A 95% denitrification of water stored in Jackson Reservoir reduced nitrate, and nitrogen loadings, in the mainstem river, while surfacing groundwater in the same reach decreased nitrate, and loadings, through both dilution and denitrification. Nitrite concentrations increased in the lowest 35 mile stream reach from the denitrification of surfacing groundwater as it entered surface flows. A complex system of water diversions, fertilization, denitrification, and discrete point sources such as domestic wastewater plants influence nutrient and aquatic communities in all flowing and standing waters of the basin.
Restoration of Two Platte River Basin Sandpit Lakes: Phosphorus Reduction using Aluminum Sulfate
John C. Holz and Kyle D. Hoagland, University of Nebraska-Lincoln, Department of Forestry, Fisheries, and Wildlife, Lincoln, Nebraska
Degradation of water quality in Platte River basin sandpit lakes is a concern in Nebraska. Over 800 publicly and privately owned sandpit lakes exist in the State which are used extensively for recreation by a large group of people with diverse interests (i.e. swimming, boating, fishing, hunting, SCUBA-diving, etc.). Nutrient loading, particularly phosphorus, has accelerated eutrophication of many once pristine sandpits and thus greatly reduced their recreational value. Water quality problems to date include nuisance algal blooms, low water transparency, noxious odors, dissolved oxygen depletion, and fish kills. Sediment phosphorus release (internal loading) during the growing season appears to be the main input in sandpit systems and must be controlled to alleviate water quality problems. Phosphorus inactivants such as aluminum sulfate (alum) offer a non-toxic, potentially long-term method of reducing internal phosphorus loading. Alum addition results in a floc which forms a "blanket" over the sediments and can continue to absorb and retain phosphorus for years.
In the summer of 1994, following a two year pre-treatment monitoring program, alum was added to two sandpit lakes in the Platte River basin near Fremont, NE. Post-treatment monthly monitoring data show that epilimnetic total phosphorus was reduced from >100 MgL(- 1) to 40-50 MgL(-1). Summer hypolimnetic total phosphorus was reduced from 500-1000 MgL(- 1) to 50-100 MgL(-1) indicating that the alum is controlling sediment phosphorus release. Lower phosphorus concentrations also resulted in lower summer chlorophyll a concentrations and greater water clarity. In addition, alum treatment reduced the anoxic zone, thus increasing fish habitat. Initial results indicate that alum has the potential to be an effective, non-toxic sandpit lake management tool in Nebraska. Benefits include: reduced internal phosphorus loading, decreased water column phosphorus concentrations, greater water clarity, reduced algal biomass, and a decrease in the frequency and intensity of algal blooms. The longevity of phosphorus control (and associated benefits) will determine the cost effectiveness of alum treatments.
Chronic Effects of Baseflow Levels of Atrazine on Platte River Algae
Karen J. Nelson and Kyle D. Hoagland, University of Nebraska-Lincoln, Department of Forestry, Fisheries, and Wildlife, Lincoln, Nebraska
A single species bioassay was conducted on a common diatom from the Platte River to determine the chronic effects of low levels of atrazine, the most widely used herbicide in the state and in the U.S. Five clonal axenic cultures of Craticula cuspidata were established from attached algae collections from five sites along the central Platte River near Grand Island, and four clones of the same species were obtained from the Loras College Diatom Culture Collection (i.e. no prior exposure to atrazine). Cultures were maintained in WC-enriched medium in a growth chamber at 20 degrees Celsius on a 12:12 light-dark cycle. All cultures received a chronic 10-wk treatment of 1Mg/L atrazine and growth was monitored using a fluorometer. Cultures were transferred biweekly to prevent nutrient depletion and to maintain a more constant atrazine concentration. Following the chronic treatment, clones were exposed to six concentrations of atrazine (93, 187, 375, 750, 1500, and 3000 Mg/L). EC [50] values (i.e. concentrations eliciting a 50% reduction in growth) were determined after 7, 9, and 12 days to ascertain whether prior exposure influences the ability of this species to tolerate higher levels characteristic of spring pulses of the herbicide. Atrazine levels were monitored using GC/MS or GC.
Statistical analyses indicate that the chronic atrazine exposure effect was significant during the first day of treatment (P=0.0001); however no significant difference was detected throughout the remainder of the 10-wk treatment for either the Platte River or Loras clones. Thus it appears that long-term, low level exposure to atrazine does not affect the growth rates of these clones of Craticula cuspidata. Preliminary results from the acute treatments indicate that prior chronic exposure to atrazine has a negative effect on growth rates.
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Last updated by Darren A. Jack on 3/14/97