Freshwater ecosystems provide multiple ecosystem services to our society globally and they are increasingly under pressure from human-mediated changes. Macrophytes are one of the most important components of freshwater ecosystems, with key services including water nutrient removal, sediment stabilisation, carbon storage, habitat, and food provision amongst others. But macrophytes are increasingly lost from freshwaters as water quality and clarity decline, and with the introduction of invasive species. Better understanding of how freshwater macrophyte traits and the environment are connected spatially and temporarily is of vital importance to predict future changes in freshwater ecosystem function and to inform conservation and restoration management.
Here, we present a case study for the New Zealand native milfoil Myriophyllum triphyllum. We use macrophyte trait data collected by NIWA’s (National Institute of Water and Atmospheric Research) Aquatic Plant Group. This aquatic plant database is populated with information on minimum, maximum and mean colonization depths, plant heights and covers, presence of invasive species… collected periodically since 1982 for 79 lakes. Plant functional traits were then related to available environmental physico-chemical data using a RLQ (Fourth Corner Method) analysis approach. Preliminary results show significant correlation between M. triphyllum maximum colonization depth and maximum cover with light and pH respectively suggesting light and CO₂ availability as main drivers for M. triphyllum distribution. M. triphyllum minimum light requirements “threshold” and its interactions with other variables such as pH and invasive species presence are discussed from a biogeographic perspective.
This ongoing research will undertake an analysis for 15 more native macrophytes, supporting NIWA’s lake restoration research project RotoTurf. Ultimately, this analysis would allow better interpretation of the species-specific biogeography of New Zealand’s native freshwater macrophytes as well as the inference of the triggers that may drive their decline, and the thresholds for their restoration.