Bloom-induced internal release controlling phosphorus dynamics in large shallow eutrophic Lake Taihu, China

Understanding phosphorus fractions and influential factors on urban road deposited sediments

Phosphorus (P) is a primary pollutant that builds-up on urban road surfaces. Understanding the fraction and load characteristics of P, as well as their relationship with urban factors, is helpful for assessing the ecological risk of urban receiving water bodies. This study presents the characteristics of build-up loads of P fractions in road-deposited sediments (RDS) in Guangzhou, China, analyzes their correlation with three urban factors (road, traffic, and land-use area), and then estimates the exceedance probability of P in stormwater runoff over the past 10 years. The results showed that detrital apatite phosphorus (De-P) performed the highest build-up load on urban road surfaces, followed by apatite phosphorus (Ca-P), iron-bound phosphorus (Fe-P), exchangeable phosphorus (Ex-P), aluminum-bound phosphorus (Al-P), organophosphorus (POP), dissolved inorganic phosphorus (DIP), occluded phosphorus (Oc-P), and dissolved organic phosphorus (DOP). Depression depth, road materials, and land-use fractions affected the P fractions. The P in the RDS may have originated from three distinct sources: road background, domestic waste, and untreated wastewater discharge. In the most recent 10 years, the event mean concentrations of total P in the RDS have had a 30 % probability of exceeding 0.4 mg L-1, which indicates a serious threat of P to receiving water bodies. The outcomes of this study are expected to provide valuable guidance for elucidating the principal categories of urban non-point source P pollution and enhancing the ecological health of urban water environments.

Prediction of hydrological and water quality data based on granular-ball rough set and k-nearest neighbor analysis

Hydrological and water quality datasets usually encompass a large number of characteristic variables, but not all of these significantly influence analytical outcomes. Therefore, by wisely selecting feature variables with rich information content and removing redundant features, it not only can the analysis efficiency be improved, but the model complexity can also be simplified. This paper considers introducing the granular-ball rough set algorithm for feature variable selection and combining it with the k-nearest neighbor method and back propagation network to analyze hydrological and water quality data, thus promoting overall and fused inspection. The results of hydrological water quality data analysis show that the proposed method produces better results compared to using a standalone k-nearest neighbor regressor.

Spatial and temporal variation in lake macroinvertebrate communities is decreased by eutrophication

Eutrophication impacts freshwater ecosystems and biodiversity across the world. While temporal monitoring has shown changes in the nutrient inputs in many areas, how spatial and temporal beta diversity change along the eutrophication gradient under a changing context remains unclear. In this regard, analyses based on time series spanning multiple years are particularly scarce. We sampled benthic macroinvertebrates in 32 sites across three lake habitat types (MACROPHYTE, OPEN WATER, PHYTOPLANKTON) along the eutrophication gradient of Lake Taihu in four seasons from 2007 to 2019. Our purpose was to identify the relative contributions of spatial and temporal dissimilarity (i.e., inter-annual dissimilarity and seasonal dissimilarity) to overall benthic biodiversity. We also examined spatio-temporal patterns in community assembly mechanisms and how associated variation in benthic macroinvertebrate communities responded to nutrient indicators. Results showed that eutrophication caused macroinvertebrate community homogenization both along spatial and temporal gradients. Though spatial variability dominated the variation of species richness, abundance and community dissimilarity, seasons within years dissimilarity, inter-annual dissimilarity and seasonal dissimilarity were much more sensitive to eutrophication. Moreover, eutrophication inhibited a strong environmental control in benthic macroinvertebrate community assembly, including a dominant role of deterministic process in the spatial variation of macroinvertebrate communities and transition from stochastic to deterministic process in the temporal assembly of macroinvertebrate communities along the eutrophication gradient. In addition, some sites in PHYTOPLANKTON habitats showed similar spatial dissimilarity and spatial SES as sites in MACROPHYTE habitats, and the decreased spatial dissimilarity of three habitats implying that lake ecosystem recovery projects have achieved their goal at least to a certain degree.