Nitrogen and Phosphorus Limitation of Phytoplankton Growth in New Zealand Lakes: Implications for Eutrophication Control |
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Authors: | Jonathan M Abell Deniz Özkundakci David P Hamilton |
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Institution: | (1) Centre for Biodiversity and Ecology Research, University of Waikato, Private Bag 3105, Hamilton, 3240, New Zealand |
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Abstract: | We examine macronutrient limitation in New Zealand (NZ) lakes where, contrary to the phosphorus (P) only control paradigm,
nitrogen (N) control is widely adopted to alleviate eutrophication. A review of published results of nutrient enrichment experiments
showed that N more frequently limited lake productivity than P; however, stoichiometric analysis of a sample of 121 NZ lakes
indicates that the majority (52.9%) of lakes have a mean ratio of total nitrogen (TN) to total phosphorus (TP) (by mass) indicative
of potential P-limitation (>15:1), whereas only 14.0% of lakes have mean TN:TP indicative of potential N-limitation (<7:1).
Comparison of TN, TP, and chlorophyll a data between 121 NZ lakes and 689 lakes in 15 European Union (EU) countries suggests that at the national scale, N has a
greater role in determining lake productivity in NZ than in the EU. TN:TP is significantly lower in NZ lakes across all trophic
states, a difference that is driven primarily by significantly lower in-lake TN concentrations at low trophic states and significantly
higher TP concentrations at higher trophic states. The form of the TN:TP relationship differs between NZ and the EU countries,
suggesting that lake nutrient sources and/or loss mechanisms differ between the two regions. Dual control of N and P should
be the status quo for lacustrine eutrophication control in New Zealand and more effort is needed to reduce P inputs. |
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