Differences in biogenic phosphorus (P) compounds between sediment and suspended particles in aquatic environments are important for understanding the mechanisms of internal P loading, but these differences are still unknown. We used solution-state (31)P-nuclear magnetic resonance spectroscopy ((31)P NMR) with NaOH-ethylenediaminetetraacetic extraction to detect the multiple P compounds in suspended particles and sediment in the eutrophic Lake Kasumigaura, including orthophosphate monoesters, orthophosphate diesters, pyrophosphate, and polyphosphate. We tested the hypothesis that there is a significant difference between these groups in suspended particles and sediment. Biogenic P other than orthophosphate was found in significantly higher proportions in suspended particles (74.3% of total P) than in sediment (25.6%). Orthophosphate monoesters were comparatively more abundant in suspended particles, as indicated by the ratio of orthophosphate diesters to monoesters (average, 0.31 for suspended particles; 1.05 for sediment). The compounds identified as orthophosphate monoesters by (31)P NMR spectroscopy originated mainly from phospholipids (α-glycerophosphate and β-glycerophosphate) and ribonucleic acid (RNA-P), whereas the orthophosphate diesters included mostly DNA (DNA-P). These results suggest that the dynamics of orthophosphate diesters, the production of DNA-P, or the degradation of phospholipids, play an important role in P cycling in Lake Kasumigaura.

Carbon-normalized yields of amino acids in size-fractionated seawater samples and bacterial cultures were used in a novel application to estimate the carbon content of heterotrophic marine bacteria. The estimated carbon content (6.3 ± 1.6 fg C cell ) of open ocean bacteria derived using this approach was lower than most values estimated in previous studies. Based on these values, living heterotrophic bacteria accounted for 6.8 ± 1.1% of suspended particulate organic carbon (POC) in surface waters at Stn ALOHA in the North Pacific gyre. Living cyanobacteria accounted for 13.3 ± 2.2% of suspended POC in surface waters. Carbon-normalized yields of muramic acid, D-alanine and D-glutamic acid, unique biomarkers of bacteria, were used to estimate that bacterial detritus accounted for 4.3 ± 2.9% of suspended POC in surface waters. The relative contribution of bacterial detritus to suspended POC increased dramatically with increasing depth, indicating that some components of bacterial detritus are resistant to decomposition in the deep ocean. The total living and detrital bacterial contribution to suspended POC in surface waters was ~25%. KEY WORDS: Bacterial carbon content · Bacterial detritus · Bacterial biomarkers · Suspended particulate organic carbonResale or republication not permitted without written consent of the publisher

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dIncubation experiments using filtered waters from Lake Kasumigaura were conducted to examine bacterial contribution to a dissolved organic carbon (DOC) pool. Bacterial abundance, bacterial production, concentrations of DOC, total dissolved amino acids (TDAA), and total dissolved neutral sugars (TDNS) were monitored during the experiments. Bacterial production during the first few days was very high (20 to 35 g C liter ؊1 day ؊1 ), accounting for 40 to 70% of primary production. The total bacterial production accounted for 34 to 55% of the DOC loss during the experiment, indicating high bacterial activities in Lake Kasumigaura. The DOC degradation was only 12 to 15%, whereas the degradation of TDAA and TDNS ranged from 30 to 50%, suggesting the preferential usage of TDAA and TDNS. The contribution of bacterially derived carbon to a DOC pool in Lake Kasumigaura was estimated using D-amino acids as bacterial biomarkers and accounted for 30 to 50% of the lake DOC. These values were much higher than those estimated for the open ocean (20 to 30%). The ratio of bacterially derived carbon to bulk carbon increased slightly with time, suggesting that the bacterially derived carbon is more resistant to microbial degradation than bulk carbon. This is the first study to estimate the bacterial contribution to a DOC pool in freshwater environments. These results indicate that bacteria play even more important roles in carbon cycles in freshwater environments than in open oceans and also suggests that recent increases in recalcitrant DOC in various lakes could be attributed to bacterially derived carbon. The potential differences in bacterial contributions to dissolved organic matter (DOM) between freshwater and marine environments are discussed.