Energy Budgets and Pond Stratification Controls: an undergraduate study
Abstract
The thermal stratification of shallow freshwater bodies is known to significantly affect both internal water quality and pollutant retention efficiency. Mirror Pond is a small (1.98 Ha), shallow (max depth 1.25 m) reservoir presently utilized as an urban run-off retention pond. High frequency temperature profiles and meteorological data collected for a period of 1 week reveal that Mirror Pond stratifies on a daily cycle. Analysis of the pond energy budget suggests the daily cycle is primarily dependent on the vertical attenuation of the short-wave radiation flux and a constant (over one week) heat loss term. The daily temperature stratification provides for daily density stratification that significantly limits vertical diffusive transport. This daily stratification of ponds will exert considerable influence on its internal biogeochemical cycles and its chemical retention capabilities A low energy rain event (mean wind speeds less than before and after event) during the time period under study displaced 10-25 per cent of the pond volume. During this rain event, the pond did not exhibit daily thermal stratification: pond temperatures remained vertically homogeneous for most of one 24-hour period. Analysis of vertical thermal structure and mean meteorological conditions during the rain event, indicates that the decreased short-wave radiation flux during the rain event should have been adequate to stratify the system given the low wind speeds (Condie and Webster, 2001). Simple adjustments of the heat input as 'cold rain' were also inadequate to create a vertically homogeneous and mixed pond thermal structure. The kinetic energy of the rain and/or the kinetic energy of runoff may be contributing factors to the mixing of this pond. Formulations to characterize the stratification in shallow water bodies may not accurately account for mixing in low winds and rain event. This will result in an underestimation of mixing events and impact interpretations of pond export and chemical retention.
- Publication:
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AGU Spring Meeting Abstracts
- Pub Date:
- May 2002
- Bibcode:
- 2002AGUSM.H42D..14B
- Keywords:
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- 1806 Chemistry of fresh water;
- 1845 Limnology;
- 1878 Water/energy interactions;
- 1894 Instruments and techniques