The impacts of changing nutrient load and climate on a deep, eutrophic, monomictic lake

Radbourne, Alan D.; Elliott, J. Alex; Maberly, Stephen C.; Ryves, David B.; Anderson, Nicholas John. 2019 The impacts of changing nutrient load and climate on a deep, eutrophic, monomictic lake. Freshwater Biology, 64 (6). 1169-1182. https://doi.org/10.1111/fwb.13293

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Abstract/Summary

1. Nutrient availability and climate have substantial effects on the structure and function of lakes. Predicted changes to climate (particularly temperature) over the 21st century are expected to adjust physical lake functions, changing thermal and nutrient use processes. Both increasing anthropogenic nutrient inputs and net reductions following remediation will also drive ecological change. Therefore, there is an increasing necessity to disentangle the effects of nutrient and temperature change on lakes to understand how they might act in additive and antagonistic ways. 2. This study quantified internal and external nutrient loads at Rostherne Mere, U.K., a deep (zmax = 30 m), monomictic eutrophic lake (average annual total phosphorus >100 μg/L) that has a long, stable period of stratification (c. 8.5 months). A lake biophysical model (PROTECH) was used to assess the effect of changes in these loads and climate change on lake productivity in a factorial modelling experiment. 3. During the summer, phosphorus released from the sediment is largely restricted to the hypolimnion and phytoplankton production is supported by the external load. On overturn, phosphorus at depth is distributed throughout the water column with the elevated concentration persisting to support algal productivity in the following spring. 4. Consequently, the model showed that internal nutrient loading was the main driver of current and future changes in the concentration of phosphorus (responsible for up to 86% P reduction), phytoplankton chlorophyll a and cyanobacterial blooms. However, although the external phosphorus load had a relatively small influence on annual mean phosphorus concentration, it had a statistically significant effect on chlorophyll a concentration, because it supported algal production during summer stratification. 5. Climate had minimal direct impact, but a substantial indirect impact by altering the timing, depth and length of lake stratification (c. 14 days longer by 2100), and therefore altered nutrient cycling and phosphorus availability. 6. In summary, the recovery trajectory at Rostherne Mere is limited by the annual internal soluble reactive phosphorus load replenishment that realistically is unlikely to change greatly on a shorter time-scale. Therefore, the external soluble reactive phosphorus load has the potential to play an important role as it can be managed further, but is complicated by the indirect impact of climate changing stratification and flushing patterns.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	https://doi.org/10.1111/fwb.13293
UKCEH and CEH Sections/Science Areas:	Water Resources (Science Area 2017-)
ISSN:	0046-5070
Additional Information. Not used in RCUK Gateway to Research.:	Open Access paper - full text available via Official URL link.
Additional Keywords:	internal loading, multiple stressors, PROTECH modelling, Rostherne Mere, stratification
NORA Subject Terms:	Ecology and Environment
Date made live:	25 Mar 2019 13:49 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/522632

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