Nobuyuki Kawasaki

Biogenic Phosphorus Compounds in Sediment and Suspended Particles in a Shallow Eutrophic Lake: A 31P-Nuclear Magnetic Resonance (31P NMR) Study

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.

Fast and precise method for HPLC-size exclusion chromatography with UV and TOC (NDIR) detection: importance of multiple detectors to evaluate the characteristics of dissolved organic matter.

A new type of high-performance liquid chromatography (HPLC)-size exclusion chromatography (SEC) system with ultraviolet (UV) absorbance detection and non-dispersive infrared (NDIR) detection of total organic carbon is described. The introduction of an online degassing tube and a low-volume HPLC column helped to reduce the analytical time and increase the sensitivity of the SEC system. This study is the first in which linear calibration curves (R(2)>0.99) were obtained for both UV absorbance and NDIR data for polystyrene sulfonate standards, which are the most suitable standards for molecular size analysis of aquatic humic substances as well as dissolved organic matter (DOM). Using the calibration curves, the molecular size distribution of DOM in water collected from Lake Kasumigaura and in pore water from lake sediments was estimated. Most of the DOM had a molecular weight less than 4000 Daltons (Da), and the amount of low-molecular-weight DOM (∼ 2000 Da) with low UV absorbance increased with depth in the sediment pore water. This result shows the importance of combining quantitative analysis by NDIR detection with qualitative analysis by UV detection to determine the chemical and physical properties of DOM. The possible sources and reactivity of DOM in Lake Kasumigaura and its sediment pore water are also discussed.

Bacterial contribution to dissolved organic matter in eutrophic Lake Kasumigaura, Japan

ABSTRACT Incubation 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 μg 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.

Improvement of COD removal by controlling the substrate degradability during the anaerobic digestion of recalcitrant wastewater

The recalcitrant landfill leachate was anaerobically digested at various mixing ratios with labile synthetic wastewater to evaluate the degradation properties of recalcitrant wastewater. The proportion of leachate to the digestion system was increased in three equal steps, starting from 0% to 100%, and later decreased back to 0% with the same steps. The chemical oxygen demand (COD) for organic carbon and other components were calculated by analyzing the COD and dissolved organic carbon (DOC), and the removal efficiencies of COD carbon and COD others were evaluated separately. The degradation properties of COD carbon and COD others shifted owing to changing of substrate degradability, and the removal efficiencies of COD carbon and COD others were improved after supplying 100% recalcitrant wastewater. The UV absorptive property and total organic carbon (TOC) of each molecular size using high performance liquid chromatography (HPLC)-size exclusion chromatography (SEC) with UVA and TOC detectors were also investigated, and the degradability of different molecular sizes was determined. Although the SEC system detected extracellular polymeric substances (EPS), which are produced by microbes in stressful environments, during early stages of the experiment, EPS were not detected after feeding 100% recalcitrant wastewater. These results suggest that the microbes had acclimatized to the recalcitrant wastewater degradation. The high removal rates of both COD carbon and COD others were sustained when the proportion of labile wastewater in the substrate was 33%, indicating that the effective removal of recalcitrant COD might be controlled by changing the substrates degradability.

Analysis of stream water quality and estimation of nutrient load with the aid of Quick Bird remote sensing imagery

Abstract Human activities have created high nutrient surpluses in agricultural lands due to the increasing rate of chemical fertilizer application and the increase in livestock production. To analyse the nutrient characteristics and estimate the nutrient load in streams, we conducted extensive field survey and water quality experiments from 2007 to 2008 in Koise River, a major river of the Lake Kasumigaura watershed, Japan. Water quality indicators of total nitrogen (TN), total phosphorus (TP) and total organic carbon (TOC) were investigated. The nutrient loads of TN, TP and TOC, as well as dissolved total nitrogen, dissolved inorganic nitrogen, dissolved organic nitrogen, particle organic nitrogen, dissolved total phosphorus, dissolved organic carbon and particle organic carbon were also estimated for the Koise River. Seasonal variation of the nutrient concentration from 2007 to 2008 was analysed considering the river discharge variation and agricultural activities. The results showed that the irrigation water from Lake Kasumigaura has the potential ability to decrease the TN concentration and increase the TOC concentration in the Koise River. Significant correlation coefficients between nutrient load and river discharge were found. The monthly pollution loads from different sources were then evaluated based on land cover classification generated from high-resolution Quick Bird remote sensing imagery. This study presents a useful interpretation of water quality data sets with a view to obtaining better information about water quality for more effective management of water resources in river basins. Editor Z.W. Kundzewicz Citation He, B., Oki, K., Wang, Y., Oki, T., Yamashiki, Y., Takara, K., Miura, S., Imai, A., Komatsu, K. and Kawasaki, N., 2012. Analysis of stream water quality and estimation of nutrient load with the aid of Quick Bird remote sensing imagery. Hydrological Sciences Journal, 57 (5), 850–860.

High Contribution of Recalcitrant Organic Matter to DOC in a Japanese Oligotrophic Lake Revealed by 14C Measurements

Carbon isotopes (14C and 13C) of dissolved organic carbon (DOC) in a Japanese oligotrophic lake (Lake Towada) were measured to study the origin and cycling of dissolved organic matter (DOM) in Lake Towada. Lake water samples were collected at 3 depths (0, 30, and 80 or 85 m) during 4 months (April, June, August, and October) in 2006. 14C measurements of DOC were performed by accelerator mass spectrometry (AMS) at the National Institute for Environmental Studies (NIES-TERRA) in Japan. ∆14C and δ13C values of DOC in Lake Towada showed light carbon isotopic values ranging from -750 to -514‰ and -29.0 to -27.8‰, respectively. These values are similar to those of humic substances reported. The very low carbon isotopic values of DOC in Lake Towada suggest a very small contribution of DOC derived from fresh phytoplankton to the lake DOC. There is an extremely high linear relationship between the ∆14C and δ13C of DOC in Lake Towada when all data points are plotted (r2 = 0.818, p < 0.01), suggesting that the DOC in Lake Towada has 2 specific sources contributing heavy and light carbon isotopes. Although the freshly produced DOC of phytoplankton origin can be decomposed easily, the variation in the autochthonous DOC should influence the carbon isotopic values of DOC in Lake Towada.

Direct evidence for the alteration of 13C natural abundances during early diagenesis in Lake Kasumigaura, Japan

In sediment trap materials or suspended particulate organic matter, δ13C values must be averaged over at least several years to determine δ13C shifts during sedimentation. To overcome this problem, we studied isotopic modification of sedimentary organic carbon during early diagenesis in sediment samples collected intermittently from a site at the center of Lake Kasumigaura, Japan, over a period of nearly 30 years, beginning in 1979. We examined the degree of apparent isotope discrimination by comparing long-term changes in the carbon isotope composition of the surface sediment (top 2 cm) with the isotope composition profile from 0 to 15 cm. The downcore C isotope composition profile was close to the values calculated from the long-term changes in the isotope composition of the surface sediment, suggesting that the sedimentary carbon isotope composition was generally conserved (±0.6‰) during early diagenesis (up to 30 years). However, at greater core depths, significant 13C enrichment of up to 1.5‰ was sometimes observed, especially in the periods of relatively oxidative conditions.

Comparison between humic-like peaks in excitation-emission matrix spectra and resin-fractionated humic substances in aquatic environments

The intensity of the 340/430-nm peak in the three-dimensional excitation-emission matrix spectra of water samples has been used as an index of the concentration of aquatic humic substance (AHS). However, whether this peak corresponds uniquely to AHS has not been definitively verified. Therefore, in this study, our objectives were: (1) to determine whether the 340/430-nm peak in the spectra of lake and river water samples does, in fact, correspond uniquely to AHS; (2) to determine what type of dissolved organic matter (DOM), in terms of hydrophobicity, accounts for the peak; and (3) to determine the advisability of using excitation-emission matrix spectroscopy to rapidly estimate AHS concentrations. We found that the 340/430-nm peak originates not only from the AHS fraction of DOM but also from a portion of the hydrophilic fraction. By analyzing the quantitative relationship between AHS concentration and 340/430-nm peak intensity for DOM samples, we found the intensity can be used to estimate AHS concentration in lake water when the concentration is strongly affected by influent river water or when the ratio of ultraviolet (UV) absorbance to dissolved organic carbon concentration is relatively high.