Temporal changes in nutrients in a deep oligomictic lake: the role of external loads <em>versus</em> internal processes

The impact of climate change on stratification and mixing patterns has important effects on nutrient availability and plankton dynamics in deep lakes. We demonstrate this in a long-term study of Lake Maggiore, a deep oligomictic lake located in the subalpine lake district in Northern Italy. Studies...

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Autores principales:	Michela Rogora, Martina Austoni, Rossana Caroni, Paola Giacomotti, Lyudmila Kamburska, Aldo Marchetto, Rosario Mosello, Arianna Orru', Gabriele Tartari, Claudia Dresti
Formato:	article
Lenguaje:	EN
Publicado:	PAGEPress Publications 2021
Materias:	phosphorus nitrogen atmospheric deposition long-term trends eutrophication climate change Geography. Anthropology. Recreation G Physical geography GB3-5030 Environmental sciences GE1-350
Acceso en línea:	https://doaj.org/article/1eab57790b964338b52936f3e961cc1b
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spelling	oai:doaj.org-article:1eab57790b964338b52936f3e961cc1b2021-11-27T08:43:03ZTemporal changes in nutrients in a deep oligomictic lake: the role of external loads <em>versus</em> internal processes10.4081/jlimnol.2021.20511129-57671723-8633https://doaj.org/article/1eab57790b964338b52936f3e961cc1b2021-11-01T00:00:00Zhttps://www.jlimnol.it/index.php/jlimnol/article/view/2051https://doaj.org/toc/1129-5767https://doaj.org/toc/1723-8633 The impact of climate change on stratification and mixing patterns has important effects on nutrient availability and plankton dynamics in deep lakes. We demonstrate this in a long-term study of Lake Maggiore, a deep oligomictic lake located in the subalpine lake district in Northern Italy. Studies on physical, chemical and biological features of the lake have been performed continuously since the 1980s. The lake recovered from eutrophication in response to a reduction of catchment nutrient loads and reached a stable oligotrophic status by the end of the 1990s, with average total phosphorus concentrations in the water column around 10 µg L-1. However, both reactive and total phosphorus have slightly increased since 2010, leading to a shift in the lake trophic state towards mesotrophy. The increase in phosphorus has been limited to the hypolimnetic layers, concentrations being fairly stable or decreasing in the epilimnion. Reactive silica also progressively increased in the hypolimnion, while nitrate and total nitrogen concentrations have steadily decreased in both deep and surface layers, especially in the summer period. These changes were assessed in relation to catchment loads, atmospheric deposition and climate-related variations in stratification and mixing patterns and in nutrient retention. Long-term changes in primary production, represented by chlorophyll levels, and biovolume of the main algal groups were also considered. During the eutrophication period and until the 1990s, in-lake phosphorus concentrations were tightly related to external loads; successively, phosphorus and its vertical distribution up the water column became more controlled by internal processes, in particular by stratification and mixing regime. An increase of thermal stability and a reduced frequency and intensity of deep mixing events has fostered oxygen depletion and phosphorus and silica accumulation in the hypolimnion. Another consequence of reduced deep mixing events, has been a reduction in nutrient replenishment of the upper layers at spring mixing. External loads are still the main driver of change for nitrogen compounds: the decrease in the atmospheric load of nitrogen that occurred in the Lake Maggiore area over the last decade, as an effect of reduced nitrogen emissions, has caused decreasing concentration of inorganic nitrogen in the lake. However, the phytoplankton community changes observed might also play a role in nitrogen dynamics, particularly in the nitrate minima observed during summer in recent years. Michela RogoraMartina AustoniRossana CaroniPaola GiacomottiLyudmila KamburskaAldo MarchettoRosario MoselloArianna Orru'Gabriele TartariClaudia DrestiPAGEPress Publicationsarticlephosphorusnitrogenatmospheric depositionlong-term trendseutrophicationclimate changeGeography. Anthropology. RecreationGPhysical geographyGB3-5030Environmental sciencesGE1-350ENJournal of Limnology, Vol 80, Iss 3 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	phosphorus nitrogen atmospheric deposition long-term trends eutrophication climate change Geography. Anthropology. Recreation G Physical geography GB3-5030 Environmental sciences GE1-350
spellingShingle	phosphorus nitrogen atmospheric deposition long-term trends eutrophication climate change Geography. Anthropology. Recreation G Physical geography GB3-5030 Environmental sciences GE1-350 Michela Rogora Martina Austoni Rossana Caroni Paola Giacomotti Lyudmila Kamburska Aldo Marchetto Rosario Mosello Arianna Orru' Gabriele Tartari Claudia Dresti Temporal changes in nutrients in a deep oligomictic lake: the role of external loads <em>versus</em> internal processes
description	The impact of climate change on stratification and mixing patterns has important effects on nutrient availability and plankton dynamics in deep lakes. We demonstrate this in a long-term study of Lake Maggiore, a deep oligomictic lake located in the subalpine lake district in Northern Italy. Studies on physical, chemical and biological features of the lake have been performed continuously since the 1980s. The lake recovered from eutrophication in response to a reduction of catchment nutrient loads and reached a stable oligotrophic status by the end of the 1990s, with average total phosphorus concentrations in the water column around 10 µg L-1. However, both reactive and total phosphorus have slightly increased since 2010, leading to a shift in the lake trophic state towards mesotrophy. The increase in phosphorus has been limited to the hypolimnetic layers, concentrations being fairly stable or decreasing in the epilimnion. Reactive silica also progressively increased in the hypolimnion, while nitrate and total nitrogen concentrations have steadily decreased in both deep and surface layers, especially in the summer period. These changes were assessed in relation to catchment loads, atmospheric deposition and climate-related variations in stratification and mixing patterns and in nutrient retention. Long-term changes in primary production, represented by chlorophyll levels, and biovolume of the main algal groups were also considered. During the eutrophication period and until the 1990s, in-lake phosphorus concentrations were tightly related to external loads; successively, phosphorus and its vertical distribution up the water column became more controlled by internal processes, in particular by stratification and mixing regime. An increase of thermal stability and a reduced frequency and intensity of deep mixing events has fostered oxygen depletion and phosphorus and silica accumulation in the hypolimnion. Another consequence of reduced deep mixing events, has been a reduction in nutrient replenishment of the upper layers at spring mixing. External loads are still the main driver of change for nitrogen compounds: the decrease in the atmospheric load of nitrogen that occurred in the Lake Maggiore area over the last decade, as an effect of reduced nitrogen emissions, has caused decreasing concentration of inorganic nitrogen in the lake. However, the phytoplankton community changes observed might also play a role in nitrogen dynamics, particularly in the nitrate minima observed during summer in recent years.
format	article
author	Michela Rogora Martina Austoni Rossana Caroni Paola Giacomotti Lyudmila Kamburska Aldo Marchetto Rosario Mosello Arianna Orru' Gabriele Tartari Claudia Dresti
author_facet	Michela Rogora Martina Austoni Rossana Caroni Paola Giacomotti Lyudmila Kamburska Aldo Marchetto Rosario Mosello Arianna Orru' Gabriele Tartari Claudia Dresti
author_sort	Michela Rogora
title	Temporal changes in nutrients in a deep oligomictic lake: the role of external loads <em>versus</em> internal processes
title_short	Temporal changes in nutrients in a deep oligomictic lake: the role of external loads <em>versus</em> internal processes
title_full	Temporal changes in nutrients in a deep oligomictic lake: the role of external loads <em>versus</em> internal processes
title_fullStr	Temporal changes in nutrients in a deep oligomictic lake: the role of external loads <em>versus</em> internal processes
title_full_unstemmed	Temporal changes in nutrients in a deep oligomictic lake: the role of external loads <em>versus</em> internal processes
title_sort	temporal changes in nutrients in a deep oligomictic lake: the role of external loads <em>versus</em> internal processes
publisher	PAGEPress Publications
publishDate	2021
url	https://doaj.org/article/1eab57790b964338b52936f3e961cc1b
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Temporal changes in nutrients in a deep oligomictic lake: the role of external loads <em>versus</em> internal processes

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