Towards developing relationships between catchment attributes and the ecological integrity of New Zealand lakes

A major challenge facing conservation managers is to provide adequate protection for a full range of freshwater habitats and biodiversity values.  As part of a systematic conservation process in New Zealand, we have developed a series of predictive catchment pressure indicators from a range of spatial datasets which describe and quantify vegetation cover, riverine nutrient transport, invasive species distributions, and disruptions to hydrological connectivity, characterizing aspects of the ecological condition of lake-catchments nationally.  Although we have a reasonable understanding of the potential changes to the chemical properties in lakes experiencing catchment modifications, less is known about effects of these pressures on higher trophic levels of lake foodwebs.  We quantitatively examined the relationships between our predictive pressure indicators and an array of indicators of ecological integrity of New Zealand polymictic lowland lakes such as lake trophic level index, macrophyte cover, benthic biodiversity, fish community composition, zooplankton community composition, and δ¹³C- and δ¹⁵N-inferred foodweb structure.  Despite large variability in foodweb composition between lakes there were some consistent patterns in the ways pressure gradients affected the foodwebs. Thus, we determined the indicators of ecological integrity most sensitive to anthropogenic pressures, and assessed their utility for ranking ecological integrity of New Zealand's shallow lakes at a national scale.