Investigation of nutrient limitation status and nutrient pathways in Lake Hayes, Otago, New Zealand: a case study for integrated lake assessment

We present a case study illustrating an integrated approach to lake water quality assessment, for Lake Hayes. Otago, New Zealand. This approach improved understanding of the biological importance of several macro- an micronutrients and their major pathways (including groundwater). and, coupled with trophic state monitoring, could be the basis for more effective management of lakes exhibiting algal blooms. A nutrient enrichment bioassay experiment found that additions of zinc and nitrogen stimulated productivity, indicating, that phytoplankton growth in the lake may have been limited by these nutrients. Nutrient data confirmed the potential for nitrogen limitation at times. The main source of nutrients to the lake was the surface inflow, but almost 30% of the nitrate input entered the lake via a groundwater-fed spring. highlighting the importance of nutrients in groundwater as a potential driver of algal proliferation. A recent shift in phytoplankton community structure from dominance of cyanobacteria and desmids to dominance of mobile, mixotrophic dinoflagellates indicates that the dominant phytoplankter may no longer be restricted to using, only epilimnetic and inorganic forms of nutrients. This integrated assessment of Lake Hayes also suggested strong internal phosphorus cycling. which Could explain why phytoplankton blooms Continue despite improved catchment nutrient management.