11 research outputs found
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Profound daily vertical stratification and mixing in a small, shallow, wind-exposed lake with submerged macrophytes
Mixing and stratification patterns in lakes are critical attributes because they are important regulators of distribution of gases, solutes and organisms. While numerous studies have focused on mixing and stratification in large lakes, the ecology and hydrodynamics of small lakes remain grossly understudied. This is critical because small lakes are far more abundant than large lakes globally. We studied a small (<1000 m2) and shallow (<0.6 m) lake with clear water and dense submerged charophyte stands located on Ăland, SE Sweden, between March 25th and May 29th to investigate the thermal regimes, surface heat fluxes and stratification and mixing processes. Daytime vertical temperature differences developed in the water column ranging from 3 °C in March to 15 °C in May. Cooling of surface waters led to full convective mixing of the water column each night. The lake shallowed from March to May. The largest temperature differences were recorded in the early afternoon although wind speeds were highest at this time. The dense charophyte cover rapidly attenuated depth penetration of wind-induced mixing and radiative fluxes. Dense macrophyte stands can engineer their own environment by facilitating build-up of steep temperature and chemical gradients. This interaction should have implications for small lakes worldwide
Impact of Nutrition and Salinity Changes on Biological Performances of Green and White Sturgeon
Green and white sturgeon are species of high conservational and economic interest, particularly in the San Francisco Bay Delta (SFBD) for which significant climate change-derived alterations in salinity and nutritional patterns are forecasted. Although there is paucity of information, it is critical to test the network of biological responses underlying the capacity of animals to tolerate current environmental changes. Through nutrition and salinity challenges, climate change will likely have more physiological effect on young sturgeon stages, which in turn may affect growth performance. In this study, the two species were challenged in a multiple-factor experimental setting, first to levels of feeding rate, and then to salinity levels for different time periods. Data analysis included generalized additive models to select predictors of growth performance (measured by condition factor) among the environmental stressors considered and a suite of physiological variables. Using structural equation modeling, a path diagram is proposed to quantify the main linkages among nutrition status, salinity, osmoregulation variables, and growth performances. Three major trends were anticipated for the growth performance of green and white sturgeon in the juvenile stage in the SFBD: (i) a decrease in prey abundance will be highly detrimental for the growth of both species; (ii) an acute increase in salinity within the limits studied can be tolerated by both species but possibly the energy spent in osmoregulation may affect green sturgeon growth within the time window assessed; (iii) the mechanism of synergistic effects of nutrition and salinity changes will be more complex in green sturgeon, with condition factor responding nonlinearly to interactions of salinity and nutrition status or time of salinity exposure. Green sturgeon merits special scientific attention and conservation effort to offset the effects of feed restriction and salinity as key environmental stressors in the SFBD