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0047 Reconnaissance of Water Quality of Lake Henry and Lake Meredith Reservoir, Crowley County, Southeastern Colorado, April-October 1987 ByJoseph R. Sullivan, Jr. Abstract Lake Henry and Lake Meredith Reservoir are off-stream storage reservoirs for the Colorado Canal. Water stored in each lake primarily is used for irrigation. Water-quality data were collected from both lakes to assess the physical, chemical, and biological quality of each lake; to compare water-quality data to established standards; to esti- mate the trophic status of each lake; and to com- pare the water quality between the two lakes. Onsile measurements of water temperature, dis- solved oxygen, pH, specific conductance, and light transparency were made at seven sites in Lake Henry and ten sites in Lake Meredith Reservoir. Onsite measurements of water temperature, dis- solved oxygen, pH, and specific conductance were made at the"inflow and outflow of Lake Henry and the inflows of Lake Meredith. Water samples were collected near the center of each lake for labora- tory analysis of chemical and biological constitu- ents in May, June, August, and October. Addi- tionally, samples were collected near the inflows and outflow of Lake Meredith Reservoir for con- centrations of total nutrients, for selected total trace elements, and for chlorophyll a in May, June, and August. Lake Henry was thermally stratified on May I and not stratified on June 29. During the sampling period, dissolved-oxygen concentrations ranged from 4.7 to 7.8 milligrams per liter; the pH ranged from 8.1 to 8.6. Dissolved-oxygen concen- trations and pH are affected by photosynthesis and respiration. Specific conductance ranged from 889 to 1,010 microsiemens per centimeter but did not vary vertically or areally within the lake. Secchi-disk measurements were uniform through- out the lake and measured 1.5 feet on May I and 0.5 foot during the remainder of the sampling period. Light transparency in Lake Henry is affected by phytoplankton biomass and non algal suspended material. Total-nitrogen concentrations ranged from 0.86 to 1.4 milligrams per liter, and total- phosphorus concentrations ranged from 0.030 to 0.106 milligram per liter during the sampling period. Dissolved-solids concentrations ranged from 598 to 704 milligrams per liter, and calcium and sulfate comprised the largest percentage of the major chemical constituents. Concentrations of total-recoverable iron occasionally exceeded the water-quality standard set for Lake Henry by the Colorado DepaI1ment of Health. Concentrations of other trace elements were less than the State water-quality standards for Lake Henry or less than the detection limits for the analysis. Phytoplankton densities in Lake Henry ranged from 33,000 to 930,000 cells per milliliter. Blue-green algae accounted for the greatest per- centage of the phytoplankton density. The trophic status of Lake Henry is eutrophic using Secchi- disk depth and total phosphorus and is borderline eutrophic using chlorophyll a as indicated by the trophic-state index and is eutrophic as indicated by the fixed-boundary system. Lake Meredith Reservoir was thermally stratified on May I and not stratified on June 30. Dissolved-oxygen concentrations ranged from 1.4 to 10.3 milligrams per liter, and dissolved-oxygen concentrations near the lake bottom on June 30 and August 20 and 21 were less than the water- quality standard. Specific conductance ranged from 2,520 to 3,040 microsiemens per centimeter but did not vary vertically or areally within the lake. Secchi-disk measurements ranged from 0.5 to 1.5 feet and were largest on May I. Light trans- parency in Lake Meredith is affected by phyto- plankton biomass and nonalgal suspended mate- rial. Abstract 1