Predicting Lake Eutrophication Responses to Multiple Scenarios of Lake Restoration: A Three-Dimensional Modeling Approach

Abstract

To improve the water quality and alleviate the eutrophication of Lake Yangchenghu, the third largest freshwater body within the Lake Taihu basin in China and an important source of drinking water, nutrient reduction strategies should be urgently addressed by decision makers, since virtually no improvement of water quality has taken place since the mid-1990s. Due to the lack of sufficient observation data and simulation results, a vertically compressed three-dimensional numerical model, the EcoTaihu model, was used to study the impact of three restoration measures on the water quality-namely, total nitrogen (TN), total phosphorus (TP) and biomass of phytoplankton (BP)-of Lake Yangchenghu: (i) total nutrient reduction, (ii) intensification of flushing by water transfer, and (iii) spatial adjustment of inflow channels. In particular, the spatial effects of the three restoration measures on the water quality were investigated. The results showed that the EcoTaihu model is applicable to other shallow lakes in China. The water quality responses to the different restoration scenarios showed significant spatio-temporal differences. The reduction of nutrient loads from inflows appeared to be the most effective measure for controlling the eutrophication and algal blooms in Lake Yangchenghu. The effectiveness of water transfer on the improvement of water quality for TN and TP was more influenced by the differences of nutrient concentrations between the transferred water and lake water, rather than flow rate, since no proportionate increase of improvement was observable in the case of larger transferred rates (60 m 3 s −1 ). The spatial narrowing of inflowing rivers in the southwestern lake could preferentially improve the water quality in the southern bay of the western lake, but would also result in a deterioration trend of water quality in the total lake and drinking water abstraction areas.measures for eutrophication control can be classified into two groups: (i) external measures aiming at reducing the load from catchment area, specifically including reduction of nutrient loads [5,6] and flushing [7][8][9], whereas (ii) in-lake measures influence the properties within the lake, including chemical precipitation [10][11][12], sediment capping [13], sediment dredging [14,15], biological uptake [16], or bio-manipulation [17]. In-lake nutrient inactive measures, like chemical precipitation and sediment capping, were successfully performed in many lakes, but a long-term success can only be obtained with sufficiently reduced external P-loadings [10]. The reduction of nutrient loads is, therefore, the preferred measure for eutrophication control and efficient reduction of chlorophyll-a [18,19] as well as cyanobacterial biomass [20]. Intensifying flushing by additional water transfer is an alternative approach, which aims at increasing the N and P export of the lake by replacing the nutrient-rich lake water with nutrient-poor transferred water. The efficiency of improvement depends on the lake size and the details of the water t...

Advances in forecasting harmful algal blooms using machine learning models: A case study with Planktothrix rubescens in Lake Geneva

“…In this context, it is important to note that these classes are mainly based on biological metrics, among which the phytoplankton (Laplace- Treyture and Feret, 2016;Le Vu et al, 2011;Phillips et al, 2013). Consequently, forecast models could help lake restoration objectives by testing scenarios with some key issues, such as eutrophication and climate change (Lehmann and Hamilton, 2018;Wang et al, 2018). Such models could also help in forecasting the HAB events and avoid financial losses by creating a decision support tool, to determine the fishing periods in lakes (Gill et al, 2018;Manning et al, 2019).…”

Mapping Long-Term Spatiotemporal Dynamics of Pen Aquaculture in a Shallow Lake: Less Aquaculture Coming along Better Water Quality

“…In Lake Yangcheng, there are many inflowing and outflowing rivers (Figure 1). According to multi-year observations, the inflowing water is generally from north to south and from west to east; its retention time is 0.38 year [38]. Lake Yangcheng is a representative lake with pen aquaculture of CMC in China.…”

“…Generally, excess nitrogen (N) and phosphorus (P) loading from the point and non-point sources in a watershed are considered as one of the main factors damaging the ecological quality of lakes [38,40,55]. In Lake Yangcheng, besides the external nutrient loadings such as industrial effluents and agriculture non-point sources, intensification through increasing use of pelleted feeds and the expansion of pen aquaculture area was another main factor inducing lake eutrophication and deteriorating of WQ [2].…”

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“…The progressive process of eutrophication of surface water leads to the deterioration of water quality. This phenomenon is not only observed in Poland [1,2], but it is also a global problem [3,4]. In many regions of the world there is also a problem of dried-up lakes [5], which results in the need to implement methods for their reconstruction [6].…”