Joint Spatial Modeling of Nutrients and Their Ratio in the Sediments of Lake Balaton (Hungary): A Multivariate Geostatistical Approach

Abstract

Eutrophication, water quality, and environmental status of lakes is a global issue that depends not only on external loadings from industrial, agricultural, and municipal sources but often also on internal loadings from lake sediments. In the latter case, in addition to the quality and quantity of nutrients stored in sediments, their relative content may be an important factor. In the example of Lake Balaton, we jointly modeled the spatial distribution of the nutrients nitrogen (N) and phosphorus (P) and their ratio (i.e., N:P) in the sediments of the lake and then provided spatial predictions at different scales (i.e., point, basin, and entire lake) with the associated uncertainty. Our aim was to illustrate the merits of applying multivariate geostatistics when spatial modeling of more than one variable is targeted at various scales in water ecosystems. Variography confirmed that there is a spatial interdependence between the nutrients. The results revealed that multivariate geostatistics allows this interdependence to be taken into account and exploited to provide coherent and accurate spatial models. Additionally, stochastic realizations, reproducing the joint spatial variability, can be generated that allow providing spatially aggregated predictions with the associated uncertainty at various scales. Our study highlighted that it is worthy of applying multivariate geostatistics in case spatial modeling of two or more variables, which jointly vary in space, is targeted in water ecosystems.

Pollution and Release Characteristics of Nitrogen, Phosphorus and Organic Carbon in Pond Sediments in a Typical Polder Area of the Lake Taihu Basin

“…In order to restore the flood regulation and storage capacity and water environment improvement of Zhushan Bay, the project of returning Zhushanwei polder to Lake Taihu has passed the planning and design approval stage. However, years of fish farming and lotus root planting activities in Zhushan Bay in Taihu Lake have led to serious organic pollution in sediments of polder ponds [15].…”

“…The sediment of ponds is known to be nutrient reservoirs with a 50-to 500-fold rise compared to those in the overlying water [13]. The accumulated nutrients, caused by the settling of particulate material of agricultural activities in the ponds, imparts consistent nutrient loading to the overlying water column and surrounding water environment even after external loading has been reduced [14,15]. In several case studies, the practices of returning polder to lake showed a positive role in enhancing regulation and storage kinetic energy and improving the water ecological environment [16].…”