Deep Creek Validation Study Report

The results of the 1975 and 1976 validation studies are presented. In 1975, light and nutrient levels (nitrogen, phosphorus) were manipulated in order to permit testing of the Desert Biome Aquatic Model; during 1976, routine sampling was done to follow recovery from the light manipulation and to provide an independent validation of the model. In the course of these studies, additional insight was obtained into the structure and function of the Deep Creek ecosystem (Curlew Valley, Idaho-Utah). Coverage of the stream with plastic sheets eliminated all of the light from Station 3C (black plastic) and 70 % from Station 3B (white plastic). Station 3A served as a control. In general, the predicted reductions in plant biomass were obtained. All of the vegetation within the black-covered section died and floated away within 1 mo after the stream was treated. Covering with white plastic caused a shift from a Potamogeton- to a Chara-dominated community. The impact of the light alterations on the plants extended through 1976. No change was detected in organic matter storage or transport as a result of the manipulation. A greater percentage of fish was found under the white plastic than under either the control or black plastic. Apparently, the white plastic provided additional "cover" over that of the control, but still allowed plant growth and the persistence of food organisms. Under the black plastic no plant growth occurred, and few invertebrates or fish were found there. on the of or macrophytes (Cladophora) in the stream. But the addition of PO, (approximately PO,-P) and PO, plus NH,NO3 (approximately PO,-P, 4.19 NH3-N and 4.41 NO3-N) resulted in measurable increases in plant biomass, with the latter showing the most dramatic changes. frequent reworking by the stream and benthic organisms. Below this is a layer about 10 cm in depth which, although anaerobic, appears to be biologically active and which may be reworked by the stream at least annually. Sediments deeper than about 15 cm do not appear to be biologically active and probably are reworked by the stream only infrequently. Measurements of undisturbed sediments gave respiration values ranging from 98. 7-152.3 mg O 2 ·m-2. hr- 1• A series of measurements showed that the rates of erosion and deposition of sediments at Station 3 are about equal, and that the storage component is in dynamic equilibrium with the relatively constant flow regimen. Dissolved organic carbon was similar at Deep Creek Stations 1-3 and showed no important variation between up- and downstream locations. The mean concentrations of dissolved organic carbon and fine particulate organic carbon at Station 3 for 1975 were 1.7 and 1.8 g C/m 3, and for 1976 were 1.5 and 0.7 g C/m 3. Values followed discharge patterns at Stations 2 and 3, but not at Station 1. Particulate matter was highest at Station 1 and lowest at Station 2. The lack of variation in upstream-downstream and between-site concentrations of dissolved and fine particulate organic carbon indicates a steady state condition and that the system is efficient in processing or storing these materials. Import of coarse particulate organic matter usually exceed export; lack of accrual of these materials in the sediments indicates that they too are actively processed. The mean distances traveled by dislodged Potamogeton and Cladophora were 49.5 and 33.3 m, respectively.