Oligotrophic patterns in southern Chilean lakes: the relevance of nutrients and mixing depth

Southern Chilean monomictic, temperate lakes are generally oligotrophic with high water transparency, low productivity and some apparent resistance to disturbances such as phosphorus additions. This paper attempts to explain low chlorophyll-a values using descriptive and experimental approaches. Thr...

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Autor principal:	SOTO,DORIS
Lenguaje:	English
Publicado:	Sociedad de Biología de Chile 2002
Materias:	oligotrophy mixing depth nitrogen temperate lakes
Acceso en línea:	http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0716-078X2002000200009
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spelling	oai:scielo:S0716-078X20020002000092003-05-12Oligotrophic patterns in southern Chilean lakes: the relevance of nutrients and mixing depthSOTO,DORIS oligotrophy mixing depth nitrogen temperate lakes Southern Chilean monomictic, temperate lakes are generally oligotrophic with high water transparency, low productivity and some apparent resistance to disturbances such as phosphorus additions. This paper attempts to explain low chlorophyll-a values using descriptive and experimental approaches. Three different scales are used, (a) a micro scale both in space and time, with experimental manipulations of N, P and total light in 24 enclosures in lake Llanquihue, (b) a longer time scale analysing 18 months of data in several sites within lake Llanquihue grouped as salmon farming sites, town bays and control sites, and (c) a broader time scale (9 years) by monitoring lakes Puyehue, Rupanco and Llanquihue, all in the Araucanian lake region and Yelcho lake in the north Patagonian region. In the Llanquihue in-lake sampling, total phosphorus values varied between 1 and 12 mug L-1 between sites, showing marginal site effects, P = 0.09 (salmon sites had greater values), however, chlorophyll a (Chl-a) concentrations were generally low (< 2 mug L-1) and did not show site effects. Dissolved inorganic nitrogen (DIN) concentrations were lower than 30 mug L-1 and showed a better predictive power than Chl-a. The analysis between lakes showed the lowest mean Chl-a values in Lake Yelcho (0.7 mug L-1) and the highest in lake Puyehue (2.1 mug L-1 ). Similar patterns were found for mean total P values, however there were no clear temporal trends through the 9 year sampling. The N/P molar ratio for the dissolved forms was generally below 20. In the enclosure experiment N had a positive significant effect on Chl-a concentration but neither P nor light had significant effects. Another outstanding result was that Chl-a values in the control bags were significantly higher than values in the lake. In all the lakes TN values did not exceed 20 mumol L-1 and TP did not exceed 0.8 mumol L-1 and thus N limitation could be proposed as playing an important role in regulation Chl-a and productivity. Another key-regulating factor of productivity and biomass could relate to the deep mixing which is a particular characteristic of Southern Hemisphere lakes, indeed, mixing depth has a negative effect and yields the best predictive power on Chl-a. This effect could also explain Chl-a increase in control bags with respect to lake since the epilimnion is artificially reduced in the former. If mixing depth influences productivity, then lake food webs should be linked to the benthos rather than to the pelagic zone particularly in the deepest mixing lakesinfo:eu-repo/semantics/openAccessSociedad de Biología de ChileRevista chilena de historia natural v.75 n.2 20022002-06-01text/htmlhttp://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0716-078X2002000200009en10.4067/S0716-078X2002000200009
institution	Scielo Chile
collection	Scielo Chile
language	English
topic	oligotrophy mixing depth nitrogen temperate lakes
spellingShingle	oligotrophy mixing depth nitrogen temperate lakes SOTO,DORIS Oligotrophic patterns in southern Chilean lakes: the relevance of nutrients and mixing depth
description	Southern Chilean monomictic, temperate lakes are generally oligotrophic with high water transparency, low productivity and some apparent resistance to disturbances such as phosphorus additions. This paper attempts to explain low chlorophyll-a values using descriptive and experimental approaches. Three different scales are used, (a) a micro scale both in space and time, with experimental manipulations of N, P and total light in 24 enclosures in lake Llanquihue, (b) a longer time scale analysing 18 months of data in several sites within lake Llanquihue grouped as salmon farming sites, town bays and control sites, and (c) a broader time scale (9 years) by monitoring lakes Puyehue, Rupanco and Llanquihue, all in the Araucanian lake region and Yelcho lake in the north Patagonian region. In the Llanquihue in-lake sampling, total phosphorus values varied between 1 and 12 mug L-1 between sites, showing marginal site effects, P = 0.09 (salmon sites had greater values), however, chlorophyll a (Chl-a) concentrations were generally low (< 2 mug L-1) and did not show site effects. Dissolved inorganic nitrogen (DIN) concentrations were lower than 30 mug L-1 and showed a better predictive power than Chl-a. The analysis between lakes showed the lowest mean Chl-a values in Lake Yelcho (0.7 mug L-1) and the highest in lake Puyehue (2.1 mug L-1 ). Similar patterns were found for mean total P values, however there were no clear temporal trends through the 9 year sampling. The N/P molar ratio for the dissolved forms was generally below 20. In the enclosure experiment N had a positive significant effect on Chl-a concentration but neither P nor light had significant effects. Another outstanding result was that Chl-a values in the control bags were significantly higher than values in the lake. In all the lakes TN values did not exceed 20 mumol L-1 and TP did not exceed 0.8 mumol L-1 and thus N limitation could be proposed as playing an important role in regulation Chl-a and productivity. Another key-regulating factor of productivity and biomass could relate to the deep mixing which is a particular characteristic of Southern Hemisphere lakes, indeed, mixing depth has a negative effect and yields the best predictive power on Chl-a. This effect could also explain Chl-a increase in control bags with respect to lake since the epilimnion is artificially reduced in the former. If mixing depth influences productivity, then lake food webs should be linked to the benthos rather than to the pelagic zone particularly in the deepest mixing lakes
author	SOTO,DORIS
author_facet	SOTO,DORIS
author_sort	SOTO,DORIS
title	Oligotrophic patterns in southern Chilean lakes: the relevance of nutrients and mixing depth
title_short	Oligotrophic patterns in southern Chilean lakes: the relevance of nutrients and mixing depth
title_full	Oligotrophic patterns in southern Chilean lakes: the relevance of nutrients and mixing depth
title_fullStr	Oligotrophic patterns in southern Chilean lakes: the relevance of nutrients and mixing depth
title_full_unstemmed	Oligotrophic patterns in southern Chilean lakes: the relevance of nutrients and mixing depth
title_sort	oligotrophic patterns in southern chilean lakes: the relevance of nutrients and mixing depth
publisher	Sociedad de Biología de Chile
publishDate	2002
url	http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0716-078X2002000200009
work_keys_str_mv	AT sotodoris oligotrophicpatternsinsouthernchileanlakestherelevanceofnutrientsandmixingdepth
_version_	1718439527972864000

Oligotrophic patterns in southern Chilean lakes: the relevance of nutrients and mixing depth

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