Critical Step 1.3.1: Managing sediment and nutrient legacies

Project team: 

Lead: Piet Verburg

Marc Schallenberg, John Quinn


Project description:

In some lakes, a substantial input of nutrients to the water column can come from the historical legacy of sediment-bound nutrients released under conditions of hypoxia or high pH. Lake Horowhenua (Horizons Region) is a shallow (±2 m maximum depth) dune lake (300 ha) with a long history of eutrophication. It is among the most eutrophic lakes in the country (TLI 6-7). In Lake Horowhenua, during summer, abundant macrophyte growth results in high pH and low oxygen concentrations in bottom water, enhancing the release of phosphorus from the sediment. The high inorganic phosphorus concentrations relative to nitrogen stimulate blooms of cyanobacteria during summer. The rate of phosphorus release from the sediment depends on the nutrient content in the sediment, sediment chemistry and on water column characteristics. This project studies how the release of phosphorus from the sediment is controlled by sediment chemistry and by conditions in the water column, and how a P legacy in the sediment affects primary production, P cycling and lake water quality. Lake-bed sediment core analysis enables quantification of current and historical infilling rates and phosphorus and nitrogen input rates in this lake affected by problematic legacy loads. Harvesting of macrophytes will be examined as a tool to mitigate sediment nutrient legacy impacts by reducing hypoxia and pH. The project will address the following key research questions:

  1. How much of the nutrient load into the lake accumulates in the sediment and how has that changed in the past centuries?

  2. Which proportion of nutrients in the sediment is released seasonally and how does it relate to sediment chemistry and hypoxia and pH in the water column?

  3. How does the ecosystem of the lake affect the release of nutrients, in particular phosphorus?

  4. How has the interaction between the lake's ecosystem and nutrients in the water column changed in the past centuries?

  5. Will harvesting of macrophytes reduce summer time bottom water anoxia and pH, and thereby reduce internal loading of phosphorus?

Findings of our study will inform lake restoration strategies and will specifically evaluate the potential for weed harvesting to help restore the lake to lower nutrient status, providing improved ecosystem services and freshwater values. This work is carried out in collaboration with the Lake Horowhenua Trust and Horizons Regional Council.


Links to other critical steps:

Impacts will be assessed using before-after, high-frequency, measurements of limnological attributes with instrumented buoys (CS1.2.1), remote sensing (CS1.2.2) and community/iwi indicators (CS1.2.4).



Action partnerships:

  • Lake Horowhenua Trust

  • Horizons Regional Council


Current work:


Key sites:

Lake Horowhenua

Outputs:

Journal Publications

Commissioned Reports

  • Waters S, Kelly D, Vandergoes M, Rees A, Li X, Cochran L, Homes A. 2018. Lake Wairarapa - investigating historic reference state, present-day macrophyte communities and legacy nutrients in the lake sediment. Prepared for Greater Wellington Regional Council. Cawthron Report No. 3157.  56 pp.

  • Tempero GW. 2018. Addendum to Ecotoxicological Review of Alum Applications to the Rotorua Lakes. ERI Report No. 52. Client report prepared for Bay of Plenty Regional Council. Environmental Research Institute, Faculty of Science and Engineering, University of Waikato, Hamilton, New Zealand.

  • Tempero GW, Hamilton DP. 2016. Lake Rotorua and Lake Rotoehu: Total and Non-crystalline Aluminium Content in Bottom Sediments. ERI Report No. 89. Client report prepared for Bay of Plenty Regional Council. Environmental Research Institute, Faculty of Science and Engineering, The University of Waikato, Hamilton, New Zealand. 44 pp.

Conference Presentations

  • Bevins C, Holt K, Verburg P, Gibbs M. 2017. A record of natural and human-induced environmental change from Punahau Lake Horowhenua. Geoscience Society of New Zealand Annual Conference, Auckland.

  • Prentice MJ, Hamilton DP, Willis A, O'Brien KR, Burford MA.  2017. Contribution of organic phosphorus to phytoplankton phosphorus demand in a phosphate-depauperate lake. Oral presentation, 5th Biennial Symposium of the International Society for River Science: Integrating Multiple Aquatic Values. Hamilton, New Zealand. 19-24 November 2017.

  • Saeed H, Hartland A, Mucalo M, Hamilton DP. 2017. Within-lake measurement of phosphorous bioavailability: a multimethod approach. Oral presentation, 5th Biennial Symposium of the International Society for River Science: Integrating Multiple Aquatic Values. Hamilton, New Zealand. 19-24 November 2017.

  • Verburg P, Schallenberg M, Holt K, Procter J, Bevins C, Brown L. 2017. Nutrient cycling in Lake Horowhenua and restoration by harvesting macrophytes. Oral presentation, 5th Biennial Symposium of the International Society for River Science: Integrating Multiple Aquatic Values. Hamilton, New Zealand. 19-24 November 2017.

  • Verburg P, Schallenberg M, Holt K. Procter J. 2016. Managing sediment and nutrient legacies. Oral Paper presented at the New Zealand Freshwater Sciences Society Annual Meeting, Invercargill, 5-8 December 2016.

  • Verburg P. 2016. Sediment and nutrient legacies In Lake Horowhenua. Resilience in lakes Workshop, Oral Paper presented at the New Zealand Freshwater Sciences Society Annual Meeting, Invercargill, 5-8 December 2016.

  • Verburg P. 2016. Sediment coring to determine the nutrient load in Lake Horowhenua. Meeting with the Lake Horowhenua Trust and Te Mana o Te Wai governance group. Levin, July 2016.