Evaluating the ecological health of aquatic habitats in a megacity through a multimetric index model based on macroinvertebrates

Globally, urban water bodies suffer from a variety of ecological pressures which profoundly change freshwater ecosystem services and pose a great threat to aquatic biodiversity. To identify the effects of these pressures on aquatic communities, we systematically investigated the macroinvertebrates in different water types (e.g., mountain rivers, plain rivers, lakes, and reservoirs) in all water systems in Beijing, a megacity in China, to reveal the key environmental factors and response mechanisms affecting the spatial distribution of macroinvertebrate communities. A total of 188 macroinvertebrate taxa were identified at 61 survey sections, and environmental factors such as flow velocity, water depth, water temperature, and total nitrogen content were found to sub-stantially affect the structure and spatial distribution of the macroinvertebrate communities. A multimetric index (MMI) model based on macroinvertebrates was developed to assess the ecological quality of each water type, and the developed MMI was demonstrated to be widely applicable. In the MMI, each community metric was weighted based on the goodness of fit for each biological metric and environmental metric to obtain the observed MMI values of the measured sample sites, and further model training and prediction was performed based on all sample site data. The MMI results revealed that the overall ecological quality of mountain rivers with less anthropogenic interference was relatively good (MMI = 0.62 +/- 0.28), the overall ecological quality of lakes experiencing ecological disturbance and undergoing ecological restoration practices was moderate (MMI = 0.43 +/- 0.09), and the overall ecological quality of plain rivers and reservoirs with strong anthropogenic interference was relatively poor (MMI = 0.24 +/- 0.12 and 0.32 +/- 0.12, respectively). Specific recommendations for ecological protection of different water types were formulated, providing a scientific basis and decision-making support for urban ecological planning and sustainable development.