Effects of Climatic Change on Temperature and Thermal Structure of a Mountain Reservoir

Lewis, William M.; McCutchan, James H.; Roberson, Jennifer

doi:10.1029/2018wr023555

Cited by 35 publications

(21 citation statements)

References 48 publications

(71 reference statements)

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“…For RTR and Schmidt stability, we based thresholds for mixing on the patterns found (Supporting Information S4). While these thresholds are most likely lake specific because of basin morphology, there are few studies that also give non‐zero thresholds to indicate mixing (RTR: >20, Kortmann et al, 1994; <30, Siver et al, 2018; Wedderburn Number: <1, Read et al, 2011; <3, Cortés & MacIntyre, 2020; Schmidt stability: <50 indicates if not complete mixing, then very weak stratification, Read et al, 2011; Lewis et al, 2019; Sahoo et al, 2016).…”

Section: Methodsmentioning

confidence: 99%

Ice Cover and Extreme Events Determine Dissolved Oxygen in a Placid Mountain Lake

Flaim

Andreis

Piccolroaz

et al. 2020

Water Resources Research

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A decrease in hypolimnetic dissolved oxygen (DO) is a commonly seen effect of climate change. However, in oligotrophic Lake Tovel (Italy), a deep mountain lake, annual mean DO (% saturation) has increased from near anoxia to >20% in the bottom layer (35-39 m). We analyzed long-term patterns of DO (1937-2019) using different methods (correlation and trend analysis, identification of extreme events) to link DO to drivers and indices of mixing. While spring mixing remained temporally limited, later ice-in (5.1 days decade −1) and the positive relationship between ice-in and DO the following year evidenced autumn mixing as the main driver for hypolimnetic DO increase. Extreme meteorological events also replenished hypolimnetic DO. Using DO and conductivity (1995-2019), we identified 14 deep mixing events with hypolimnetic DO > 40%. Density-based indices (Schmidt stability, relative thermal resistance, Lake Number, and Wedderburn Number) only partially captured these events that were related to snowmelt, flooding, and cold spells during spring and autumn, with a carryover effect sometimes lasting >1 year. Recently, annual mean DO in the upper layer decreased beyond temperature-dependent solubility. This decrease was not comprehensively confirmed by statistical tests but was possibly linked to atmospheric stilling. We suggest that Lake Tovel's shift from meromixis to dimixis was driven by climate warming (i.e., increasing air temperature 0.6°C decade −1) that delayed ice-in and increased autumn mixing. Our work underlines the vulnerability of mountain lakes and their different response to climate change with respect to more studied lowland lakes. Plain Language Summary Dissolved oxygen is fundamental for aquatic life. Lake Tovel (Brenta Dolomites, Italy) has a long history of limnological studies starting in the 1930s; therefore, we can study oxygen's long-term evolution. Contrary to most temperate lakes, dissolved oxygen is increasing in the deep layers of Lake Tovel since the 1990s. We linked this to later ice-in: as a consequence of climate change, Lake Tovel has lost almost 3 weeks of ice cover since the mid-1980s. This loss (5.1 days decade −1) in ice-in is much steeper than in lowland lakes. Because dissolved oxygen is replenished in lakes by mixing, a longer ice-free period means more time to mix, with oxygen reaching deeper layers. Extreme events such as heavy snowmelt, flooding, and cold spells during spring and autumn also increased mixing with effects often lasting over a year. However, in the last decade, we are beginning to see a decrease in dissolved oxygen at the surface, probably because of less wind. Years with little snow also tend to coincide with lower concentrations of dissolved oxygen in the deep layers. Changes in air temperatures, precipitation, and wind will determine the evolution of dissolved oxygen in Lake Tovel, a sentinel mid-altitude lake for climate change.

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Section: Methodsmentioning

confidence: 99%

Ice Cover and Extreme Events Determine Dissolved Oxygen in a Placid Mountain Lake

Flaim

Andreis

Piccolroaz

et al. 2020

Water Resources Research

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“…In summer the surface water is warmed up by solar heating and reaches 24 °C whereas bottom water remains to about 8-9 °C. In the literature, these layers are classified as epilimnion, which is the first upper layer, metalimnion (with sharp thermocline), and hypolimnion at the bottom [27,47]. The maximum difference in temperature between surface and bottom water was observed in July (17.7 • C in 2015 and 15.8 • C in 2016).…”

Section: Physical Parametersmentioning

confidence: 99%

Assessment of Seasonal Changes in Water Chemistry of the Ridracoli Water Reservoir (Italy): Implications for Water Management

Toller

Giambastiani

Greggio

et al. 2020

Water

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The Ridracoli artificial basin is the main water reservoir of the Emilia-Romagna region (Northeast Italy). The reservoir was made by construction of a dam on the Bidente River in 1982. It is used as the main drinking water supply of the region and for hydropower production. The physical and chemical parameterseters (temperature, pH, electrical conductivity, and dissolved oxygen) of shallow water are continuously monitored whereas vertical depth profiles of water chemical data (major anions and cations, as well as heavy metals) are available on a bimonthly base. The dataset used in this research is related to the years 2015 and 2016. Data show that the reservoir is affected by an alternation of water stratification and mixing processes due to seasonal change in water temperature, density, and the reservoir water level. In late summer and winter months, the water column is stratified with anoxic conditions at the bottom. During the spring, on the other hand, when storage is at its maximum, water recirculation and mixing occur. The reservoir is characterized by a dynamic system in which precipitation, dissolution, and adsorption processes at the bottom affect water quality along the reservoir depth column. The temperature stratification and anoxic conditions at the reservoir bottom influence the concentration and mobility of some heavy metals (i.e., Fe and Mn) and, consequently, the quality of water that reaches the treatment and purification plant. This study is relevant for water resource management of the reservoir. Assessing the seasonal changes in water quality along the reservoir water column depth is fundamental to plan water treatment operations and optimize their costs. The reservoir assessment allows one to identify countermeasures to avoid or overcome the high concentrations of heavy metals and the stratification problem (i.e., artificial mixing of the water column, new water intakes at different depths operating at different times of the year, blowers, etc.).

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“…Commonly, many reservoirs have fixed-level "off-takes" that are situated below the thermocline, hence releasing waters from the hypolimnion which causes downstream cold-water pollution (CWP) [7] . The CWP is thought to be a key threat to a number of species, primarily due to the importance of warm-water temperature for important life stages, therefore, penetratingly understanding of temperature structure in reservoirs is one of the important contents in water quality assessment of hydropower project [8] .…”

Section: Introductionmentioning

confidence: 99%

Monitoring and analysis of vertical thermal structure of the Three Gorges Reservoir

Dai

Li²,

et al. 2019

E3S Web Conf.

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Water temperature plays a crucial role in water ecological environment both in the reservoir and downstream area. Three Gorges Project (TGP) is the largest hydraulic engineering in the world, and changes of water quality attract much more attention, especially in the thermal structure since impoundment. In order to clearly understand water temperature distribution after impoundment in the Three Gorges Reservoir (TGR), we monitored the temperature distribution of the Taipingxi section which was not far from the dam from early April to the end of July. According to the analyzing of the monitoring data of transverse and vertical temperature variation, we could find that the temperature mixed uniformly in transverse direction. Excepting April, there was basically had no temperature difference in vertical direction, even in April, the maximum temperature difference was only 1.39°C within 100 meters (April 22), the average temperature gradient was only 0.014°C/m; Both the temperature of water and atmosphere have similar variation tendency, but the response of the water temperature to atmosphere is delayed, especially the bottom water temperature. The result indicate that the reservoir has mixed thermal structure during impoundment phase, so the release temperature had little change after the impoundment, the work provide a scientific basis for the development of pollution control and ecological protection measure.

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Effects of Climatic Change on Temperature and Thermal Structure of a Mountain Reservoir

Cited by 35 publications

References 48 publications

Ice Cover and Extreme Events Determine Dissolved Oxygen in a Placid Mountain Lake

Ice Cover and Extreme Events Determine Dissolved Oxygen in a Placid Mountain Lake

Assessment of Seasonal Changes in Water Chemistry of the Ridracoli Water Reservoir (Italy): Implications for Water Management

Monitoring and analysis of vertical thermal structure of the Three Gorges Reservoir

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