Journal
WATER RESOURCES RESEARCH
Volume 58, Issue 7, Pages -Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1029/2022WR032522
Keywords
density gradient; lake; mixing; morphology; precipitation; pond; stratification; surface area; temperature; thermal dynamics
Categories
Funding
- St. Olaf College Collaborative Undergraduate Research and Inquiry program (MAH)
- St. Olaf College Helterbrand/Varshavsky Center for Integrated Research
- Macalester College Collaborative Summer Research Program
- BEYOND 2020 project - Marine Research Programme by the Irish Government [PBA/FS/16/02]
- Minnesota Stormwater Research and Technology Transfer Program via the University of Minnesota Water Resources Center
- Minnesota Stormwater Research Council
- MANTEL ITN through the European Union's Horizon 2020 Research and Innovation Programme under the Marie Skodowska-Curie [722518]
- University of Missouri School of Natural Resources
- North Central Region Water Network [0057039]
- National Science Foundation [1559769]
- Ducks Unlimited Canada
- Saskatchewan Ministry of Agriculture's Agricultural Development Fund [20160015]
- Great Plains Cooperative Ecosystems Study Unit [G16AC00003]
- Div Of Biological Infrastructure
- Direct For Biological Sciences [1559769] Funding Source: National Science Foundation
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The study reveals that the mixing regimes of shallow waterbodies are highly sensitive to small differences in size and depth. Shallow lakes tend to mix more frequently, while shallow ponds mix less often. Precipitation events weaken stratification and can cause short-term mixing.
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.
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