Mechanics of the energy balance in large lowland rivers, and why the bed matters

Bray, E. N.; Dozier, Jeff; Dunne, Thomas

doi:10.1002/2017gl075317

Cited by 8 publications

(10 citation statements)

References 29 publications

(37 reference statements)

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“…Ground-surface water fluxes also influence river water temperatures due to differences in temperature between groundwater and surface water (Irvine et al, 2017). The absolute and relative contributions of these heat transfer components vary depending on factors such as climate (Cozzetto, McKnight, Nylen, & Fountain, 2006), geomorphological setting (Webb, 1995), albedo of river bed sediment (Bray, Dozier, & Dunne, 2017), shading (Johnson, 2004), wind (Story, Moore, & Macdonald, 2003) and river flow (Garner, Malcolm, Sadler, & Hannah, 2017;Webb, Clack, & Walling, 2003).…”

Section: Physical Mechanismsmentioning

confidence: 99%

River water temperatures are higher during lower flows after accounting for meteorological variability

Booker

Whitehead

2021

River Research & Apps

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River water temperature is known to be important for water quality and ecosystem processes. We quantified the degree to which lower river flows are associated with warmer river water, after accounting for seasonality and meteorological variability.We applied a systematic methodology to analyse observed mean daily river water temperature and mean daily river flow from 47 sites draining mountain, hill, and lowland catchments across the Canterbury region of Aotearoa New Zealand. We fitted regression models to remove seasonal patterns from all variables, then removed correlations between water temperature and each of three meteorological variables (solar radiation, air temperature, and earth temperature) before quantifying water temperature-river flow relationships. Strong seasonal patterns were present in water temperature and each meteorological variable across all sites. Many sites also showed strong seasonal patterns in river flows. We demonstrated that seasonal patterns must be accounted for before day-to-day associations between water temperature and meteorological variables or river flow can be characterised. Higher water temperatures were associated with lower flows for 46 of 47 sites, even after having accounted for seasonality and associations with each meteorological variable.Increases in water temperature associated with a hypothetical reduction in river flow from the median to the fifth percentile varied with the site but were 0.5 C on average. This finding has important implications for river flow management because it indicates that increased river water temperatures would accompany reduced river flows regardless of site or catchment characteristics.

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Section: Physical Mechanismsmentioning

confidence: 99%

River water temperatures are higher during lower flows after accounting for meteorological variability

Booker

Whitehead

2021

River Research & Apps

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“…We also assumed that the ablation zone covers 12% of the Ice Sheet as determined by Ryan et al (2019). It is safe to assume that the large majority of the energy absorbed by the sediment eventually contributes to melting of ice since less than 8% of incoming radiation that reaches the streambed is reflected away before being absorbed by a shallow water column (Bray et al, 2017) and because runoff can be retained within the Ice Sheet for 1-6 months before export (Rennermalm et al, 2013b). Thus, there is plenty of time for heat to transfer from the water to the ice.…”

Section: Impact Of Albedo Changes On Surface Meltingmentioning

confidence: 99%

“…Previous research using synoptic numerical models show that for shallow streams (0.5 m depth), 38% of the incoming spectrally integrated solar radiation is absorbed by the bed compared to 51% by the water column (Bray et al, 2017). As a result, for terrestrial streams, dark sediment along the streambed can facilitate enough energy absorption to increase water temperatures by over 2 °C (Bray et al, 2017). Isenko et al (2005) observed that this process also occurs in supraglacial streams resulting in stream temperatures up to 0.4 °C when sediment was present.…”

Section: Introductionmentioning

confidence: 99%

“…Supraglacial water bodies (lakes, streams) have a significantly lower albedo than the surrounding clean ice (0.21 for water bodies compared to 0.55 for clean ice) and, as such, disproportionately contribute to negative surface mass balances (Pope et al, 2016;Ryan et al, 2018). Previous research using synoptic numerical models show that for shallow streams (0.5 m depth), 38% of the incoming spectrally integrated solar radiation is absorbed by the bed compared to 51% by the water column (Bray et al, 2017). As a result, for terrestrial streams, dark sediment along the streambed can facilitate enough energy absorption to increase water temperatures by over 2 °C (Bray et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

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Intra-seasonal variability in supraglacial stream sediment on the Greenland Ice Sheet

Leidman

Rennermalm²,

Muthyala³

et al. 2023

Front. Earth Sci.

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On the surface of the Greenland Ice Sheet, the presence of low-albedo features greatly contributes to ablation zone meltwater production. Some of the lowest albedo features on the Ice Sheet are water-filled supraglacial stream channels, especially those with abundant deposits of consolidated cryoconite sediment. Because these sediments enhance melting by disproportionately lowering albedo, studying their spatial extent can provide a better understanding of Greenland’s contribution to global sea level rise. However, little is known about the spatial distribution of supraglacial stream sediment, or how it changes in response to seasonal flow regimes. Here, we surveyed a supraglacial stream network in Southwest Greenland, collecting imagery from seven uncrewed aerial vehicle (UAV) flights over the course of 24 days in 2019. Using Structure-from-Motion-generated orthomosaic imagery and digital elevation models (DEMs), we manually digitized the banks of the supraglacial stream channels, classified the areal coverage of sediment deposits, and modeled how the terrain influences the amount of incoming solar radiation at the Ice Sheet surface. We used imagery classified by surface types and in-situ spectrometer measurements to determine how changes in sediment cover altered albedo. We found that, within our study area, only 15% of cryoconite sediment was consolidated in cryoconite holes; the remaining 85% was located within supraglacial streams mostly concentrated on daily inundated riverbanks (hereafter termed floodplains). Sediment cover and stream width are highly correlated, suggesting that sediment influx into supraglacial drainage systems widens stream channels or darkens previously widened channels. This reduces albedo in floodplains that already receive greater solar radiation due to their flatness. Additionally, the areal extent of stream sediments increased in August following seasonal peak flow, suggesting that as stream power decreases, more sediment accumulates in supraglacial channels. This negative feedback loop for melting may delay Greenland’s runoff to the latter end of the melt season. This study shows in unprecedented detail where and when sediment is deposited and how these deposits potentially impact the Ice Sheet surface energy balance. These findings may allow for better prediction of how supraglacial floodplains, and the microbiomes they contain, might change in response to increased melting.

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“…Dam operations have been shown to increase the connectivity between rivers and their adjoining sediments (Sawyer et al., 2009), enhancing the exchange of heat between rivers and their underlying sediments (Gerecht et al., 2011). Thus, changes to riverbed temperature may affect the energy balance of rivers in a substantive way because of the thermal coupling between the river and riverbed (Bray et al., 2017; Neilson et al., 2010).…”

Section: Introductionmentioning

confidence: 99%

Riverbed Temperature and Heat Transport in a Hydropeaked River

Ferencz

Muñoz

Neilson

et al. 2021

Water Resources Research

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Dam regulation has altered the thermal regimes of many rivers (Ling et al., 2017;Steel & Lange, 2007). It is well understood and documented that dam operations influence downstream river temperatures over a range of spatial and temporal scales. Factors such as dam size (thermal mass of reservoir) (Johnson et al., 2004), type of release (hypolimnetic vs. epilimnetic) (Olden & Naiman, 2010), discharge management practices (Wright et al., 2009), and the size and timing of releases (Carron & Rajaram, 2001;Daniels & Danner, 2020;Mihalevich et al., 2020) control how downstream temperatures are altered. Such studies are often motivated by the desire to better predict ecological consequences of dam regulation on river ecosystems, and the recognition of the strong linkage between temperature and ecological health in aquatic ecosystems (Olden & Naiman, 2010) has influenced regulation and management practices such as thermal maximum daily loads from dams into receiving waters (Hester & Doyle, 2011).

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Mechanics of the energy balance in large lowland rivers, and why the bed matters

Cited by 8 publications

References 29 publications

River water temperatures are higher during lower flows after accounting for meteorological variability

River water temperatures are higher during lower flows after accounting for meteorological variability

Intra-seasonal variability in supraglacial stream sediment on the Greenland Ice Sheet

Riverbed Temperature and Heat Transport in a Hydropeaked River

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