Authors: J Alex Elliott Ian D Jones Trevor Page
Publish Date: 2009/02/13
Volume: 627, Issue: 1, Pages: 129-142
Abstract
Two models were used to examine the relationship between hydraulic retention time nutrient source and total chlorophyll in a shallow lake Bassenthwaite Lake UK The first model was a derivation of the Vollenweider model and the second was the phytoplankton community model PROTECH The adapted Vollenweider model produced two different responses to changing the retention time that were phosphorus source dependent If the phosphorus was totally from a point source then annual mean chlorophyll steadily declined with increasing flushing rate However when a diffuse source was used the chlorophyll changed little and even increased with short retention times retention time 40 days The PROTECH model produced some similar responses but they were more season dependent Winter mean chlorophyll always declined with decreasing retention time regardless of nutrient source but the summer mean curves were source dependent and similar to those produced by the adapted Vollenweider model Further simulations with PROTECH using a standardized flow regime provided strong evidence as to the mechanisms behind these responses Analysis showed that the decline in chlorophyll with decreasing retention time was the prevalent response of the PROTECH simulations due to flushing loss of both nutrients and algae Furthermore the curve formed an asymptote at long retention times because other factors eg light limited growth retention times 100 days had little effect on chlorophyll However with a diffuse phosphorus source and short retention times an increase in biomass was observed when the nutrient was limiting for growthWe thank the British Atmospheric Data Centre and Mr BC Tebay for providing the meteorological data the Environmental Agency for providing the flow data and for our colleagues in CEH for collecting the biological data In this study IDJ and TP were funded by NERC Research Grant NE/F011474/1
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