Effects of Nitrogen and Phosphorus on Chlorophyll a in Lakes of China: a Meta-Analysis

Whether or not chlorophyll a (Chla) is limited by nitrogen (N) or phosphorus (P), or both, remains highly debated. In part this is due to the lack of a robust statistical rarely considered using a statistical method in studies of peer-review research of lakes. Individual studies only used the use of the relationship between Chla and nutrients to judge the effects of N and P, ignoring the spatial heterogeneity of the ecological environment. Here, we evaluated the effects of nitrogen and phosphorus on Chla via a meta-analysis. The dataset consists of 1024 observations from 34 lakes in China. The results show that Chla is one of the most important indicators of water eutrophication, both nutrients were related Chla trophic state, and that TP plays an important role over TN, especially in the hypereutrophic Chla conditions. With the increase of TN/TP, Chla concentration is decreased, which may be the co-limited of TN and TP. These three values largely explained the increment of eutrophication Chla, although the relative effects differed across nutrients, with changes in the TN total contributing 5.2% of the increment in Chla, while the TP change contributed 272.0% of the increment in Chla. At spatial scales, logarithm-transformed response ratio (ln RR) of Chla indicated that the lake shifts from N limitation (64.0% > 28.0%) in oligo-mesotrophic to P limitation (170.0% > 99.0%) in eutrophic and co-limitation (66.0% and 46.0%) by N & P in hypereutrophic. These results demonstrate that TP reduction can mitigate eutrophication in most large lakes but a dual TN and TP reduction may be needed in eutrophic lakes, especially in hypereutrophic states. This study highlights the differential effects of the three factors concentration, which may offer important implications for better management of the response of the eutrophication lakes to nutrients (N and P) in the future.