Relatin Dissolved Oxygen Concentration to Fish Distribution in Jarecki Lake

Abstract Water temperature and dissolved oxygen (DO) profiles were measured once every month from mid July to mid February in a relatively deep sand-pit lake in southeast Nebraska. These profiles showed depleted DO concentrations below the thermocline during summer stratification indicating areas fish will likely avoid in summer months. Colder temperatures in fall caused complete mixing of the water column allowing fish to inhabit all depths of the lake. An inverse temperature stratification occurred directly below the ice during winter months as ice cover cooled the surface water to below 4 degrees Celsius. Ice cover also blocked air – water oxygen transfer and reduced light for photosynthesizing algae. Associated with winter ice cover, DO concentrations in the hypolimnion decreased significantly, once again reducing available fish habitat. It is likely anglers will have a higher success rate catching fishing in water above 6 meters (m) (~20 feet) in a eutrophic sandpit lake during hot summer months and below ice cover in winter. Fish can utilize all depths of the lake during fall turnover and could theoretically be caught by anglers anywhere in the lake.

A diatom record of late Holocene climate variation in the northern range of Yellowstone National Park, USA

The changes in diatom species composition in a sediment core from Crevice Lake, Yellowstone National Park, spanning the past 2550 yr, were used to reconstruct long-term limnological and ecological conditions that may be related to late Holocene climate variability. Planktic forms dominate the fossil diatom assemblages throughout this record, but changes in species dominance indicate varying nutrient levels over time, particularly phosphorus. The changes in the nutrient concentrations in the lake were probably driven by changes in temperature and wind strength that affected the duration of watercolumn mixing and thus the extent of nutrient recycling from deep waters. Prior to 2100 cal before present (BP), Stephanodiscus minutulus and Synedra tenera dominated, suggesting long cool springs with extensive regeneration of phosphorus from the hypolimnion that resulted from isothermal mixing. From 2100 to 800 cal BP, these species were replaced by Cyclotella michiganiana and Cyclotella bodanica. These species are characteristic of lower nutrient concentrations and are interpreted here to reflect warm summers with long periods of thermal stratification. From 800 to 50 cal BP, S. minutulus dominated the diatom assemblage, suggesting a return to lengthy mixing during spring. The most dramatic late Holocene changes in the fossil diatom assemblages occurred during the transition from the Medieval Period to the Little Ice Age, approximately 800 cal BP.