Reference and current Trophic Level Index of New Zealand lakes: benchmarks to inform lake management and assessment |
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| Authors: | Jonathan M Abell Paul van Dam-Bates Deniz Özkundakci David P Hamilton |
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| Institution: | 1. Ecofish Research Limited, Victoria, Canada jmabell01@gmail.com https://orcid.org/0000-0002-5934-9616;3. Ecofish Research Limited, Victoria, Canada;4. Environmental Research Institute, University of Waikato, Hamilton, New Zealand;5. Waikato Regional Council, Hamilton, New Zealand https://orcid.org/0000-0002-5442-4576;6. Australian Rivers Institute, Griffith University, Nathan, Australia https://orcid.org/0000-0002-9341-8777 |
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| Abstract: | ABSTRACT Knowledge of trophic status is fundamental to understanding the condition and function of lake ecosystems. We developed regression models to predict chlorophyll a concentrations (chl a) in New Zealand lakes for reference and current states, based on an existing dataset of total nitrogen (TN) and total phosphorus (TP) concentrations for 1031 lakes. Models were then developed to predict Secchi depth based on chl a and a sediment resuspension term applicable to shallow lakes. Estimates of all four Trophic Level Index (TLI) variables (chl a, TN, TP and Secchi depth) were analysed to estimate reference and current state TLI for the nationally representative sample of 1031 lakes. There was a trend of eutrophication between reference and current states, with systematic differences among lake geomorphic types. Mean chl a increased 3.5-fold (2.42?mg?m?3 vs. 8.32?mg?m?3) and mean Secchi depth decreased (indicating lower clarity) by approximately one-third (9.62?m vs. 6.48?m) between reference and current states. On average, TLI increased by 0.67, with the TLI increase >1 in approximately one-third (31%) of lakes. This study informs the status of lake ecosystems in NZ and provides benchmarks to guide management and assessment. |
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| Keywords: | Baseline chlorophyll eutrophication nutrients Secchi depth trophic status water quality |
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https://orcid.org/0000-0002-5934-9616;3. Ecofish Research Limited, Victoria, Canada;4. Environmental Research Institute, University of Waikato, Hamilton, New Zealand;5. Waikato Regional Council, Hamilton, New Zealand