Sedimentary phosphorus in contrasting, shallow New Zealand lakes and its effect on water quality

ABSTRACT

The eutrophication of lake ecosystems due to anthropogenic activities has impacted lakes worldwide and shallow lakes are particularly vulnerable. The retention of phosphorus (P) in lake sediments and its subsequent release to the water column is often a key factor in degraded water quality, algal blooms and delayed responses to lake restoration efforts. Despite this link between sedimentary P and poor ecosystem outcomes, a limited amount of research has been conducted on P dynamics in New Zealand’s lakes. In this study, sediments in six shallow lakes across the country were analysed for geochemistry and P fractionation. Total sedimentary P content varied widely and was related to inflow concentrations and hydrological retention times. The P binding capacity of the sediments was related to iron (Fe) and aluminium (Al) concentrations, while the Fe:P ratio was correlated to the release of P under anoxic conditions. P fractions and release rates were poorly correlated with traditional water quality parameters, however the mobile-P_SL and reducible-P fractions were strongly correlated with the frequency of summertime algal blooms. This relationship may provide an indicator to assess harmful algal bloom frequency in unmonitored lakes, and a valuable tool to assess internal loading risk and inform lake restoration methods.

KEYWORDS:

• Nutrient cycling
• internal loading
• P binding
• P release
• shallow lakes
• algal blooms
• eutrophication

Acknowledgments

This research was supported by the New Zealand Ministry of Business, Innovation and Employment (UOWX1503; Enhancing the health and resilience of New Zealand lakes), the Department of Conservation Arawai kakariki programme, Ngā Puna Rau Rangitīkei and Horizons Regional Council as part of the Te Mana o te Wai project, and the University of Canterbury. We would like to acknowledge Susie Wood (Cawthron), Jenny Webster-Brown (University of Canterbury), Lena Schallenberg (University of Otago), David Feek (Massey University), Logan Brown and David Brown (Horizons Regional Council), Alton Perrie, Grant Nader, John Tatersal (Greater Wellington Regional Council), Robert Martin, Neville Lomax (Ngāti Hauiti), and Hugh Robertson (Department of Conservation) who all provided useful input, and/or assistance in the field.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by Ministry of Business, Innovation and Employment [grant number UOWX1503]; Department of Conservation New Zealand; University of Canterbury.