Phosphorus and nitrogen loading restraints are essential for successful eutrophication control of Lake Rotorua, New Zealand

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Author(s)
Smith, Val H
Wood, Susanna A
McBride, Chris G
Atalah, Javier
Hamilton, David P
Abell, Jonathan
Griffith University Author(s)
Year published
2016
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Anthropogenic activity has greatly enhanced the inputs of nitrogen (N) and phosphorus (P) to lakes, causing widespread eutrophication. Algal or cyanobacterial blooms are among the most severe consequences of eutrophication, impacting aquatic food webs and humans that rely on lakes for ecosystem services. In New Zealand, recent debate on the relative importance of N versus P control for limiting occurrences of algal blooms has centered on the iconic Lake Rotorua (North Island). Water quality in Lake Rotorua has declined since the late 1800s following catchment vegetation clearing and subsequent land-use intensification, as ...
View more >Anthropogenic activity has greatly enhanced the inputs of nitrogen (N) and phosphorus (P) to lakes, causing widespread eutrophication. Algal or cyanobacterial blooms are among the most severe consequences of eutrophication, impacting aquatic food webs and humans that rely on lakes for ecosystem services. In New Zealand, recent debate on the relative importance of N versus P control for limiting occurrences of algal blooms has centered on the iconic Lake Rotorua (North Island). Water quality in Lake Rotorua has declined since the late 1800s following catchment vegetation clearing and subsequent land-use intensification, as well as from sewage inputs. A multimillion dollar restoration programme began in the early 2000s, with key mitigation actions including nutrient load targets for the entire catchment and alum dosing in 2 tributaries. In this manuscript we analyse 2 water quality datasets (>10 yr) from Lake Rotorua and compare these with a global lake dataset. Generalised additive models predicted highly significant (p < 0.001) declines in total phosphorus (TP), total nitrogen (TN), and chlorophyll a (Chl-a) in surface waters between 2001 and 2015. Alum dosing had a negative (i.e., reducing) and highly significant effect on TP and Chl-a (p < 0.001). Correlations of Chl-a on TP and TN were highly significant, but the difference between the 2 correlation coefficients was not, indicating a need to control both nutrients to reduce algal productivity. This conclusion is reinforced by recent bioassay studies which show co-limitation by N and P. Collectively, our data and previous studies provide strong support for the current strategy of limiting both N and P loads to Lake Rotorua for effective eutrophication control.
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View more >Anthropogenic activity has greatly enhanced the inputs of nitrogen (N) and phosphorus (P) to lakes, causing widespread eutrophication. Algal or cyanobacterial blooms are among the most severe consequences of eutrophication, impacting aquatic food webs and humans that rely on lakes for ecosystem services. In New Zealand, recent debate on the relative importance of N versus P control for limiting occurrences of algal blooms has centered on the iconic Lake Rotorua (North Island). Water quality in Lake Rotorua has declined since the late 1800s following catchment vegetation clearing and subsequent land-use intensification, as well as from sewage inputs. A multimillion dollar restoration programme began in the early 2000s, with key mitigation actions including nutrient load targets for the entire catchment and alum dosing in 2 tributaries. In this manuscript we analyse 2 water quality datasets (>10 yr) from Lake Rotorua and compare these with a global lake dataset. Generalised additive models predicted highly significant (p < 0.001) declines in total phosphorus (TP), total nitrogen (TN), and chlorophyll a (Chl-a) in surface waters between 2001 and 2015. Alum dosing had a negative (i.e., reducing) and highly significant effect on TP and Chl-a (p < 0.001). Correlations of Chl-a on TP and TN were highly significant, but the difference between the 2 correlation coefficients was not, indicating a need to control both nutrients to reduce algal productivity. This conclusion is reinforced by recent bioassay studies which show co-limitation by N and P. Collectively, our data and previous studies provide strong support for the current strategy of limiting both N and P loads to Lake Rotorua for effective eutrophication control.
View less >
Journal Title
Inland Waters
Volume
6
Issue
2
Copyright Statement
© 2016 International Society of Limnology. This is an electronic version of an article published in Inland Waters, Vol 6, No 2, Pages: 273-283 and DOI: 10.5268/IW-6.2.998. Inland Waters is available online at: www.fba.org.uk/journals with the open URL of your article.
Subject
Physical geography and environmental geoscience
Ecology
Ecology not elsewhere classified
Environmental management
Pollution and contamination