Spatial identification of critical nutrient loads of large shallow lakes

Spatial identification of critical nutrient loads of large shallow lakes: Implications for Lake Taihu (China)

Janssen, Annette B.G. (Netherlands Institute of Ecology; Wageningen University & Research)
de Jager, Victor C.L. (Netherlands Institute of Ecology)
Janse, Jan H. (Netherlands Institute of Ecology; PBL Netherlands Environmental Assessment Agency)
Kong, Xiangzhen (Netherlands Institute of Ecology; Peking University)
Liu, S. (TU Delft Coastal Engineering; Deltares)
Ye, Qinghua (TU Delft Coastal Engineering; Deltares)
Mooij, Wolf M. (Netherlands Institute of Ecology; Wageningen University & Research)

2017-08-01

Ongoing eutrophication frequently causes toxic phytoplankton blooms. This induces huge worldwide challenges for drinking water quality, food security and public health. Of crucial importance in avoiding and reducing blooms is to determine the maximum nutrient load ecosystems can absorb, while remaining in a good ecological state. These so called critical nutrient loads for lakes depend on the shape of the load-response curve. Due to spatial variation within lakes, load-response curves and therefore critical nutrient loads could vary throughout the lake. In this study we determine spatial patterns in critical nutrient loads for Lake Taihu (China) with a novel modelling approach called Spatial Ecosystem Bifurcation Analysis (SEBA). SEBA evaluates the impact of the lake's total external nutrient load on the local lake dynamics, resulting in a map of critical nutrient loads for different locations throughout the lake. Our analysis shows that the largest part of Lake Taihu follows a nonlinear load-response curve without hysteresis. The corresponding critical nutrient loads vary within the lake and depend on management goals, i.e. the maximum allowable chlorophyll concentration. According to our model, total nutrient loads need to be more than halved to reach chlorophyll-a concentrations of 30–40 μg L⁻¹ in most sections of the lake. To prevent phytoplankton blooms with 20 μg L⁻¹ chlorophyll-a throughout Lake Taihu, both phosphorus and nitrogen loads need a nearly 90% reduction. We conclude that our approach is of great value to determine critical nutrient loads of lake ecosystems such as Taihu and likely of spatially heterogeneous ecosystems in general.

Algal blooms
Bifurcation analysis
Eutrophication
Load-response curve
PCLake
Spatial heterogeneity

http://resolver.tudelft.nl/uuid:9ca0d208-ace1-4674-9a58-2b0d5fa4f5cc

https://doi.org/10.1016/j.watres.2017.04.045

0043-1354

Water Research, 119, 276-287

Institutional Repository

journal article

© 2017 Annette B.G. Janssen, Victor C.L. de Jager, Jan H. Janse, Xiangzhen Kong, S. Liu, Qinghua Ye, Wolf M. Mooij