Lead: Piet Verburg
Marc Schallenberg, John Quinn
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
How much of the nutrient load into the lake accumulates in the sediment and how has that changed in the past centuries?
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?
How does the ecosystem of the lake affect the release of nutrients, in
How has the interaction between the lake's ecosystem and nutrients in the water column changed in the past centuries?
Will harvesting of macrophytes reduce
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.
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).
Lake Horowhenua Trust
Horizons Regional Council
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