A Simple Index of Lake Ecosystem Health Based on Species-Area Models of Macrobenthos

An effective biological index should meet two criteria: (1) the selected parameters have clear relationships with ecosystem health and can be measured simply by standard methods and (2) reference conditions can be defined objectively and simply. Species richness is a widely used estimate of ecosystem condition, although it is increased by nutrient enrichment, a common disturbance. Based on macrobenthos data from 91 shallow Yangtze lakes disconnected from the mainstem, we constructed an observed species (S)-area (A) model to predict expected species richness (S), and then developed an observed to expected index (O/E-) by calculating the S/S ratio. We then compared O/E- with three other commonly used indices regarding their ability to discriminate cultivated and urban lakes: (1) River Invertebrate Prediction and Classification System (RIVPACS; O/E-), (2) Benthic Index of Biotic Integrity (B-IBI), and (3) Average Score Per Taxon (ASPT). O/E- showed significant positive linear relationships with O/E-, B-IBI and ASPT. Quantile regressions showed that O/E- and O/E- had hump-shape relationships with most eutrophication metrics, whereas B-IBI and ASPT had no obvious relationships. Only O/E-, O/E₅₀ and B-IBI significantly discriminated cultivated from urban lakes. O/E- had comparable or higher performance with O/E-, B-IBI and ASPT, but was much simpler. Therefore, O/E- is a simple and reliable index for lake ecosystem health bioassessment. Finally, a framework was proposed for integrated biological assessment of Yangtze-disconnected lakes.