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Abstract Globally, lake surface water temperatures have warmed rapidly relative to air temperatures, but changes in deepwater temperatures and vertical thermal structure are still largely unknown. We have compiled the most comprehensive data set to date of long-term (1970–2009) summertime vertical temperature profiles in lakes across the world to examine trends and drivers of whole-lake vertical thermal structure. We found significant increases in surface water temperatures across lakes at an average rate of + 0.37 °C decade−1, comparable to changes reported previously for other lakes, and similarly consistent trends of increasing water column stability (+ 0.08 kg m−3decade−1). In contrast, however, deepwater temperature trends showed little change on average (+ 0.06 °C decade−1), but had high variability across lakes, with trends in individual lakes ranging from − 0.68 °C decade−1to + 0.65 °C decade−1. The variability in deepwater temperature trends was not explained by trends in either surface water temperatures or thermal stability within lakes, and only 8.4% was explained by lake thermal region or local lake characteristics in a random forest analysis. These findings suggest that external drivers beyond our tested lake characteristics are important in explaining long-term trends in thermal structure, such as local to regional climate patterns or additional external anthropogenic influences.
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Long-term Deepwater Dissolved Oxygen Dynamics in a Hypereutrophic Reservoir Following Shifts in Watershed Management and Lake Warming
Abstract Long-term declines in lake hypolimnetic dissolved oxygen (DO) have been attributed to eutrophication, reduced water clarity, or rising temperatures. DO dynamics in human-made reservoirs may also be influenced by their distinct characteristics (for example, hydrology) and by the high levels of watershed inputs (suspended sediments, nutrients) these systems may receive, particularly in agricultural landscapes. We used a 31 year dataset in a reservoir that has experienced agricultural land management change to ask: (1) What are the long-term trends in two hypolimnetic DO metrics (DO concentration in early summer and summer anoxic factor), and (2) what are the key drivers of these metrics?. We used linear regressions to assess temporal trends, and exhaustive variable selection to identify drivers. Potential drivers included metrics of watershed discharge, temperature, stability, and potential productivity (chlorophyll, nonvolatile suspended sediments; NVSS). We found that deepwater early summer DO concentrations decreased, but there was no temporal trend for anoxic factor. Deepwater DO was best predicted by surface temperature, with warming temperatures related to lower DO. However, the top five models performed similarly, and all included a temperature or stratification metric. Higher stability was related to lower DO. For anoxic factor, the top two models performed similarly with stability, surface temperature, and NVSS identified. Anoxic factor increased with higher surface temperature, lower NVSS, and higher stability. Our findings suggest that DO dynamics were linked to previously recognized drivers (for example, temperature), as well as NVSS, a driver that is rarely acknowledged and may reflect land use and management within the watershed.
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- PAR ID:
- 10634898
- Publisher / Repository:
- Springer Science + Business Media
- Date Published:
- Journal Name:
- Ecosystems
- Volume:
- 28
- Issue:
- 5
- ISSN:
- 1432-9840
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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