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Classifying Mixing Regimes in Ponds and Shallow Lakes
Author(s) -
Holgerson Meredith A.,
Richardson David C.,
Roith Joseph,
Bortolotti Lauren E.,
Finlay Kerri,
Hornbach Daniel J.,
Gurung Kshitij,
Ness Andrew,
Andersen Mikkel R.,
Bansal Sheel,
Finlay Jacques C.,
CianciGaskill Jacob A.,
Hahn Shan,
Janke Benjamin D.,
McDonald Cory,
Mesman Jorrit P.,
North Rebecca L.,
Roberts Cassandra O.,
Sweetman Jon N.,
Webb Jackie R.
Publication year - 2022
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/2022wr032522
Subject(s) - stratification (seeds) , environmental science , temperate climate , waves and shallow water , biogeochemical cycle , convective mixing , mixed layer , hydrology (agriculture) , atmospheric sciences , oceanography , convection , ecology , geography , geology , meteorology , seed dormancy , botany , germination , geotechnical engineering , dormancy , biology
Lakes are classified by thermal mixing regimes, with shallow waterbodies historically categorized as continuously mixing systems. Yet, recent studies demonstrate extended summertime stratification in ponds, underscoring the need to reassess thermal classifications for shallow waterbodies. In this study, we examined the summertime thermal dynamics of 34 ponds and shallow lakes across temperate North America and Europe to categorize and identify the drivers of different mixing regimes. We identified three mixing regimes: rarely ( n = 18), intermittently ( n = 10), and often ( n = 6) mixed, where waterbodies mixed an average of 2%, 26%, and 75% of the study period, respectively. Waterbodies in the often mixed category were larger (≥4.17 ha) and stratification weakened with increased wind shear stress, characteristic of “shallow lakes.” In contrast, smaller waterbodies, or “ponds,” mixed less frequently, and stratification strengthened with increased shortwave radiation. Shallow ponds (<0.74 m) mixed intermittently, with daytime stratification often breaking down overnight due to convective cooling. Ponds ≥0.74 m deep were rarely or never mixed, likely due to limited wind energy relative to the larger density gradients associated with slightly deeper water columns. Precipitation events weakened stratification, even causing short‐term mixing (hours to days) in some sites. By examining a broad set of shallow waterbodies, we show that mixing regimes are highly sensitive to very small differences in size and depth, with potential implications for ecological and biogeochemical processes. Ultimately, we propose a new framework to characterize the variable mixing regimes of ponds and shallow lakes.