Role of dissolved organic matter in hypolimnetic mineralization of carbon and nitrogen in a large, monomictic lake

Abstract

We tested the hypothesis that dissolved organic matter (DOM) is delivered to deep layers by convective mixing in winter, where it contributes to the mineralization of C, N, and P in the oxygenated hypolimnion of large (surface area 674 km 2 , maximum depth 104 m), monomictic Lake Biwa. Basin-scale, seasonal measurements of DOM concentrations revealed that dissolved organic carbon (DOC) and nitrogen (DON) accumulated in the epilimnion during warm seasons and were redistributed into the deeper layer during winter overturn. Hypolimnetic DOC and DON decreased in concentration over the stratification period, indicating mineralization; the contributions of DOM to the total mineralization of C and N were 8% and 30%, respectively. Higher contribution of N relative to C suggests that the N-rich DOM was mineralized at depth. We failed to detect a significant contribution of dissolved organic phosphorus to P mineralization in the hypolimnion, which could be explained by substantial depletion in P relative to C and N of DOM; C : P and N : P ratios were 1,978 and 147, respectively. The data suggest that convective mixing in this monomictic basin delivers DOM to hypolimnetic depths, where it is mineralized during subsequent periods of stratification.

Seasonal variation in viral-induced mortality of bacterioplankton in the water column of a large mesotrophic lake (Lake Biwa, Japan)

“…In the present study, BGE was consistently low in deeper layers, where there is low substrate concentration and substantial depletion in nitrogen and phosphorus in DOM (Kim et al 2006). This suggests that substrate condition (Lopez-Urrutia & Moran 2007) rather than viral shunt was a major factor affecting BGE in the deeper layer of Lake Biwa.…”

“…Lake Biwa is a large (surface area, 674 km 2 ), deep (maximum depth, 104 m), tectonic lake located in the central part of Honshu Island, Japan. The present study was conducted in the monomictic, mesotrophic north basin, which has a water residence time of 5.5 yr (Kim et al 2006).…”

Critical nutrient thresholds needed to control eutrophication and synergistic interactions between phosphorus and different nitrogen sources

“…The dissolved nutrients being taken up metabolically from the solution by phytoplankton aggregate into organic particles, and organisms can be decomposed into inorganic nutrients through the mineralization process (Halemejko and Chrost 1984). However, the effects of the mineralization process are estimated to be small and it was generally not taken into consideration in the nutrient limitation bioassays (Bloesch et al 1977;Gao et al 2000Gao et al , 2006Gardner et al 1989;Kagami et al 2013;Kim et al 2006;Kolzau et al 2014). In this case, a particular nutrient could limit the growth of the phytoplankton once its concentration declined to a certain degree.…”

Assessing carbon dynamics in natural and perturbed boreal aquatic systems

“…The thermocline, which was in place in all lakes during the stratified period, therefore acts as a semi-permeable barrier to dissolved gases. The transfer of GHG and O 2 to the epilimnion likely is controlled by the cumulated partial pressure of each gas and the storage capacity of both water layers [Kim et al, 2006].…”