Lake Ogallala Water Quality Report October 11, Prepared by. Mark Peyton Senior Biologist

Transcription

1 Lake Ogallala Water Quality Report 2012 October 11, 2012 Prepared by Mark Peyton Senior Biologist The Central Nebraska Public Power And Irrigation District

2 INTRODUCTION Since 1986, The Central Nebraska Public Power and Irrigation District ( Central ) has conducted dissolved oxygen ( D.O. ) monitoring in Lake Ogallala, immediately downstream of Kingsley Dam and Lake McConaughy. That monitoring consists of continuous data collection of water passing through the Kingsley Hydroelectric Plant ( Hydro ), continuous data collection at the buoy line, and weekly profiles from 1 June to 15 October at eight locations in Lake Ogallala. Water samples at the eight locations are taken at one-meter intervals utilizing a YSI-56 portable dissolved oxygen meter calibrated at each location using the Winkler Method for determining dissolved oxygen content. Temperatures are also recorded, as are secchi disk readings. Starting in 1999, Central installed a continuous recording D.O. meter at the outlet of Lake Ogallala (Keystone Diversion) to complement the continuous data collections at the Hydro and the buoy line. In addition, on four occasions D.O. and temperature profiles using a YSIPro-20 portable dissolved oxygen meter were taken between 19 July and 11 September at 22 sample locations established in 1999 in the Keystone arm of the Lake Ogallala. These profiles were taken early in the morning, which during 1999 and 2000 were a time of stress on trout found in this arm of Lake Ogallala. During 2012, 15 series of profiles of Lake McConaughy at the control tower were also taken on a weekly basis from 6 June through 15 October. Central also monitored plant growth in the Keystone Basin on five occasions between 3 July and 11 September. The results of the 2012 monitoring are presented in this report. PROFILE DATA Weekly monitoring at eight stations commenced on 6 June 2012 and was completed on 15 October Once again the North End of the lake stratified early in the season and remained stratified for dissolved oxygen until early October. Station #5 also stratified early in the year maintaining an area of low dissolved oxygen on the bottom until early September. Secchi disk readings were fairly stable through the season, usually between meters and ranging from a high of 2.9 meters to a low of 0.8 meters.

3 DIVERSION D.O. Continuous monitoring at the buoy line and Keystone Diversion Dam ( Diversion ) commenced on 1 June and continued through 14 October. A graph showing D.O. readings at the buoy line and at the Diversion for the time period 1 June 14 October is included (Figure #1). As can be seen in Figures #2-4, the Lake became distinctly stratified by 3 July and remained so through September.

4 The intake of water in Lake McConaughy that is passed through the hydroelectric plant and then out into Lake Ogallala is located in the lower five meters of Lake McConaughy. D.O. at that depth was already below 3.0 ppm, identified as the minimum for the survival of trout, on 6 June and by 3 July it was registering 0ppm. To offset the lack of D.O. in the water entering Lake Ogallala, Central runs a portion of the water through the Bypass Valve, shooting it into the air and aerating it so that the total mix of water that passes through the Hydro and that which passes through the Bypass is at or above specified D.O. levels. During 2012 Central cycled the hydroelectric plant with the plant generally running from 10:00 AM until Midnight. D.O. readings at the buoy line showed a widely variable range due to the cycling with readings below 3.0 PPM on 24, 25, and 26 August while the plant was offline. Even with aeration of water through the Bypass Valve the deeper areas in the north end of Lake Ogallala as well as some of the shallow, plant filled areas of the Keystone Basin dropped below 3.0 parts per million (ppm) in D.O. D.O. measured at the Keystone Diversion registered below 3.0 ppm on 122 out of 744 samples taken in July with the first sub-3.0 reading on the night of 1 July. The D.O. dropped below 3.0 ppm on 24 of 31 nights.

5 In August the D.O. dropped below 3.0 ppm on 298/744 samples. Because of the problems with fish kills in the late 90 s associated with the shallow area of the Keystone Basin bi-weekly D.O. sampling is done from mid-july September. The following Figures #7 - #13 show the results of that sampling. KEYSTONE BASIN PROFILES Profiles were taken at the 22 stations in the Keystone Arm on 14 and 28 July, 11 and 23 August, and 7 and 22 September. Sample sites are presented in Figure #7.

6 Generally, sampling began at 5:00 AM and was completed by 6:30 AM. Lake Ogallala Circulation Project: In an effort to address conditions of low D.O. in specific areas of the Keystone Basin in Lake Ogallala, over the winter of 2009 and 2010 the Central Nebraska Public Power and Irrigation District, under the recommendation of a multi-stakeholder group that included the Nebraska Game and Parks Commission, Nebraska Public Power District, the Nebraska Department of Environmental Quality, and the University of Nebraska-Lincoln excavated 152,000 yard 3 of material in a 6,200 long canal in Lake Ogallala to help change circulation within the lake. In the process of excavating the materials 5.2 acres of wetland were impacted. To mitigate for the wetland impact 10.4 acres of a constructed wetland were required. Central utilized approximately 80,000 yards 3 of the excavated material which was placed on the Lake bottom to form a bench duplicating the elevation of the existing wetland. This material created a Mitigation Spoil of 11 acres. To assess the success of the overall project, Central committed to a continuation of its expanded D.O. monitoring to assess the success of reaching the goals of the Project. Below are the Objectifies of the Project and a summary of the effectiveness of meeting those goals in Objective 1 Increase average dissolved oxygen concentration to 5.0 mg/l and prevent dissolved oxygen concentration from falling below 3.0 mg/l in 75% of Lake Ogallala. Depending upon which readings you utilize, the success of achieving this goal is difficult to determine. The average D.O. reading taken from all samples in the 16-week weekly sampling episodes was 5.81 ppm, which is above that goal and better than that measured in 2011 (4.93 ppm).

7 One problem is the stratification that occurs in the two north sampling areas. The North End sampling area stratified in early June and Station #5 stratified in late June. As to meeting the second half of the Objective, i.e. preventing the D.O. from falling below 3.0 ppm in 75% of the lake, the D.O. was above 3.0 ppm 82% of the time. To compare, in 2009 the D.O. exceeded 3.0 ppm 68%, in 2010, 80% of the time and in % of the time.. Objective 2 Objective 3 Maintain year-round water temperature at or below 21 C in 75% of Lake Ogallala. The temperature of the water in Lake Ogallala is dependent upon the temperature of the water in Lake McConaughy and the Project is not expected to affect those temperatures. Reduce or eliminate areas devoid of dissolved oxygen in the Keystone Basin. As can be seen in Figures #8 - #11 the D.O. in 67% of the samples in the Keystone Basin during 2012 the D.O. exceeded 3.0 ppm. This is significantly lower than in 2011 (94%). The constructed channel area again reported higher D.O. readings compared to the sites just to the south of the channel on 90% of the sample dates with only one reading below 3.0 ppm in the channel compared to 60% of the readings in the sample sites adjacent to the channel in the shallow, plant filled areas. Objective 4 Create routes for fish to escape from areas of low dissolved oxygen. No fish kills were noted in the Lake Objective 5 Enhance wetland functions in the Keystone Basin by creating depth diversity that will support a diverse population of terrestrial and aquatic plants attracting a diverse population of terrestrial and aquatic insects and providing improved trout habitat. Monitoring of the wetlands continues under a separate monitoring process in association with The 404 Permit issued by the Corps of Engineers. In 2012, 83% of the vegetation sample plots showed the growth of young cattails and/or bulrush indicating that the process of vegetation of the mitigation area is occurring.

8 AQUATIC VEGETATION MONITORING Due to the daily swings in D.O. it has been proposed that the biomass of aquatic macrophytes and algae positively affect the D.O. of the Keystone Basin during the daylight hours through photosynthesis and the release of oxygen, however, during the night, when the low D.O. readings occur, the plants become another oxygen consumer. After dark the plants are no longer adding oxygen to the water to help meet the oxygen demand from both the chemicals and nutrients coming into the lake from Lake McConaughy as well as the biological demand of the fish and other animals living in Lake Ogallala. In addition, through plant respiration, the plants add to that biological demand. The results are that the D.O. in Keystone basin fluctuates dramatically on a daily basis. When the fluctuations take the D.O. to levels below 2.0 PPM fish kills have been observed. Because we hypothesize that it is the quantity of plant life in the Keystone Basis that controls, in a fashion, the severity of the daily D.O. cycle, Central and NPPD collect aquatic macrophyte density data. In 2012 Central collected aquatic plant mass data the 3 and 17 July, 14 and 27 August, 6 and 11 September. Plant material was collected in a ¼ meter square grid using a rake to pull up all vegetation. The water was forced out of the plant material and the remaining biomass was weighed. The percentages of various plant types were estimated. With the removal of rough fish in 2009 the growth of aquatic macrophytes increased significantly but they seem to be leveling off in2012 (Figure #12). This pattern is very similar to that witnessed followoing the fish renovation of 1997 (Figure #13)

9 Figure #14 shows the peak and the average per sample episode of the mass of the aquatic vegetation measured each year since Note: From there were only one three samples take each year and then ususally in the late summer when plant growth was at its peak. Since 2003 samples have been taken four seven times unless on the third or lataer sample there was no vegetation to sample. As can be seen in Figure #14 there was a report of a fish die off in 2011, however, no fish kills were reported in D.O. Profile and vegetation Data was collected by Nate Nielsen and Gabriel Wilson.