Spatial statistics of hydrography and water chemistry in a eutrophic boreal lake based on sounding and water samples

Abstract

Spatial variability, an essential characteristic of lake ecosystems, has often been neglected in field research and monitoring. In this study, we apply spatial statistical methods for the key physics and chemistry variables and chlorophyll a over eight sampling dates in two consecutive years in a large (area 103 km) eutrophic boreal lake in southern Finland. In the four summer sampling dates, the water body was vertically and horizontally heterogenic except with color and DOC, in the two winter ice-covered dates DO was vertically stratified, while in the two autumn dates, no significant spatial differences in any of the measured variables were found. Chlorophyll a concentration was one order of magnitude lower under the ice cover than in open water. The Moran statistic for spatial correlation was significant for chlorophyll a and NO+NO-N in all summer situations and for dissolved oxygen and pH in three cases. In summer, the mass centers of the chemicals were within 1.5 km from the geometric center of the lake, and the 2nd moment radius ranged in 3.7-4.1 km respective to 3.9 km for the homogeneous situation. The lateral length scales of the studied variables were 1.5-2.5 km, about 1 km longer in the surface layer. The detected spatial "noise" strongly suggests that besides vertical variation also the horizontal variation in eutrophic lakes, in particular, should be considered when the ecosystems are monitored.

Overview: Recent advances in the understanding of the northern Eurasian environments and of the urban air quality in China – a Pan-Eurasian Experiment (PEEX) programme perspective

“…Organic carbon in lakes Spatial variability, an essential characteristic of lake ecosystems, has often been neglected in field research and monitoring. The detected spatial "noise" strongly suggests that, besides vertical variation, the horizontal variation should also be considered in the ecosystem monitoring and, most importantly, when the role of dissolved organic carbon (DOC) in the CO 2 flux is estimated (Manasypov et al, 2015;Leppäranta et al, 2018). In natural waters with an increasing level of coloured dissolved organic matter (CDOM) concentration, the water colour is shifted towards brown.…”

Overview: Recent advances on the understanding of the Northern Eurasian environments and of the urban air quality in China - Pan Eurasian Experiment (PEEX) program perspective

“…Spatial variability, an essential characteristic of lake ecosystems, has often been neglected in field research and monitoring. The detected spatial "noise" strongly suggests that besides vertical variation also the horizontal variation should be considered in the ecosystem monitoring and, most importantly when the role of dissolved organic carbon (DOC) on the CO2 flux is estimated (Manasypov et al, 2015;Leppäranta et al, 2018). In natural waters with increasing level of colored dissolved organic matter (CDOM) concentration, the water color is shifted towards brown.…”