Distributions of biogeochemical parameters in the pool and interstitial waters in sand bar system of the Kizu River

Distributions of biogeochemical parameters in temporary pools (TAMARI), riparian side arm of river (WANDO) and interstitial waters were investigated in the sand bars along the lower reaches of the Kizu River. Dissloved inorganic nitrogen (DIN) and phosphate (DIP) concentrations in TAMARI and WANDO waters varied greatly compared with those in river waters. Low concentrations of DIN and DIP were often observed simultaneously in TAMARI waters. The DIN concentrations of most intersitial waters were similar or high in comparison to those of river waters. Low concentrations of DIN and DIP were often observed separately in intersitial waters. Concentrations of biogeochemical constituents clearly varied greatly in the waters of sand bar systems, and the relationships between each biogeochemical constituents were different between surface water (TAMARI and WANDO) and subsurface (intersitial) waters of the Kizu River.Article信州大学山地水環境教育研究センター研究報告 2: 63-67(2004)departmental bulletin pape

Basic limnological study in an alpine Lake Puma Yumco, the pre-Himalayas, China

Lake Puma Yumco is a typical alpine lake (altitude; 5,030m) located in the pre-Himalayas of Tibet, China. This study was the first limnologicak investigation. Puma Yumco (28°34'N,90°24'E) has the following morphometric properties: maximum length of 31 km; maximum width of 14 km; mean width of 9 km; shoreline of 90 km; surface area of 280 km²; shoreline development of 1.5. Transparency was approximately 10 m. Dissolved oxygen was l7 mg O₂ L⁻¹ and showed saturated values. Saljnity was 360 mg L⁻¹. The chemical type of the lake water was Mg-Ca-HCO₃-SO₄. Total nitrogenous nutrients and phosphate were extremely low at 1μM and 0.02 μM, respetively. Chlorophyll-a concentration was 0.2 mg chl.a m⁻³. Phytoplankton and zooplankton were dominated by Aphanocapsa. and Diaptomidae. The grain size of lake sediment was that of silt in most cases.Article信州大学山地水環境教育研究センター研究報告 2: 83-90(2004)departmental bulletin pape

An Estimation of Precipitation Retention Time Using Depth Metres in the Northern Basin of Lake Biwa

To facilitate climate change adaptations and water management, estimates of precipitation retention time (time required for precipitation to reach a lake) can help to accurately determine a water body’s terrestrial water storage capacity and water cycle. Although estimating the precipitation retention time on land is difficult, estimating the lag between precipitation on land and a rise in lake water levels is possible. In this study, the delay times (using a depth metre installed in the mooring system in the northern basin of Lake Biwa from August 2017 to October 2018) were calculated using response functions, and it evaluated the precipitation retention time in the catchment. However, as several delays between the river surface flow (<1 d) and shallow subsurface flow (≈45 d) remained unidentified, the delay times resulting from direct precipitation on the lake as well as from internal seiches were determined. The results suggest that delay times of approximately 20 d correspond to the paddy–waterway system between the river inflow and the subsurface flow, and that this effect corresponds to that of large rivers such as the Ane River. These findings can enhance water management strategies regarding the regulation of river flows, adapting to climate change-induced fluctuations in precipitation

Highly efficient silica sink in monomictic Lake Biwa in Japan

In order to clarify the mechanisms underlying high efficiency of the silica sink in monomictic Lake Biwa in Japan, vertical flux of biogenic silica (BSi) was measured using sediment traps over a period of 15 months. The sediment traps were deployed at depths of 30 and 70 m. On a global scale, BSi fluxes in Lake Biwa were very high, ranging from 20 to 1087 mg Si.m−2.d−1 at the 30 m trap and 12–999 mg Si.m−2.d−1 at the 70 m trap throughout the observation period. The BSi fluxes at both traps increased significantly during the winter period and the ratio of BSi fluxes in the winter period to annual BSi fluxes ranged from 27 to 62%. In the winter period, when nutrients are supplied from the hypolimnion to the epilimnion, the distribution of photosynthetically active diatoms was almost homogeneous in all layers, including the aphotic layer. At this time, the diatoms assimilated dissolved silica (DSi) in a wider layer containing a part of aphotic layer in order to produce rigid frustules, which accumulated rapidly in bottom sediments as DSi concentration in the water column decreased. Thus, size of the silica sink in Lake Biwa is enhanced during the winter holomictic mixing period through interaction between physical (thermocline disruption: transfer of diatoms to deep layers by vertical convection), chemical (nutrient supply from deep layers) and biological (dominance of active diatoms in all layers) processes