A method to monitor and measure the water transparency in LHAASO-WCDA using cosmic muon signals

The Large High Altitude Air Shower Observatory（LHAASO） is to be built at Daocheng, Sichuan Province, China. As one of the major components of the LHAASO project, a Water Cherenkov Detector Array（WCDA）, with an area of 78000 m^2, contains 350000 tons of purified water. The water transparency and its stability are critical for successful long-term operation of this project. To gain full knowledge of the water Cherenkov technique and investigate the engineering issues, a 9-cell detector array has been built at the Yangbajing site, Tibet, China. With the help of the distribution of single cosmic muon signals, the monitoring and measurement of water transparency are studied. The results show that a precision of several percent can be obtained for the attenuation length measurement,which satisfies the requirements of the experiment. In the near future, this method could be applied to the LHAASOWCDA project.

Water Turbidity as One of the Trophic State Indices in Butrinti Lake

In this paper we are presenting observations, data and some conclusions regarding the water turbidity and transparency of the aquatic ecosystem of Butrinti Lake in southern Albania. Located amidst a major tourist attraction area, Butrinti Lake is fed by fresh waters from surrounding areas and discharges into Ionian Sea. Although development is preset in the area, it is still minor as part of the area is a National Park. Turbidity, as an optical property which describes the cloudiness of the water, is a measure of the degree to which the water becomes less transparent due to the presence of suspended particulates, including sediments and phytoplankton. The water turbidity parameters were measured every two weeks over a year, monitoring three selected stations in this water ecosystem. Turbidity of water in such ecosystems is measured in FTU (Formazin Turbidity Units) using a portable turbid meter (in our case type HANNA HI 93703-11), which measures the intensity of light scattered at 90 degrees, as a beam of light passes through a water sample. In addition, turbidity is evaluated using a Secchi disk. The depth (Secchi depth) until the disk can be no longer seen by the observer is recorded as a measure of the transparency of the water (inversely related to turbidity). The Secchi disk has the advantages of integrating turbidity over depth (where variable turbidity layers are present). The relationship between the depth of the viewing disk and the turbidity can be characterized by an inverse curvilinear one. The defined trend line can be expressed by the same curve related to the data of Butrinti Lake. An R2 Value of 0.85 was calculated for the above equation. Variations were observed on turbidity level of the selected stations in this ecosystem. These differences on the turbidity values of selected stations of water body can be explained by the communications sea-lagoon, fresh water supply as well as by the pollution due to human activity near a certain station. The monitored water ecosystem can be characterized by certain level of turbidity, based on the trophic state classification by Hakanson and Carlson. Furthermore, relationship between turbidity and trophic state evaluated by other bio-indicators of the monitored ecosystems is analyzed.

Spatial and temporal variations of two cyanobacteria in the mesotrophic Miyun reservoir, China

Spatial variations in phytoplankton community within a large mesotrophic reservoir （Miyun reservoir, North China） were investigated in relation to variations in physico-chemical properties, nutrient concentrations, temperature and light conditions over a 5 month period in 2009. The dynamics of phytoplankton community was represented by the dominance of cyanobacteria through summer and fall, following with a short term dominance of chlorophyta in late fall, and a relatively high abundance of diatom in October; on the other hand, maximum phytoplankton biomass was recorded in the north shallow region of Miyun reservoir with a higher nutrients level. Particular attention was paid to the impacts of environmental conditions on the growth of two cyanobacteria genera, the toxin-producing Microcystis and the taste ＆ odor-producing Oscillatoria. Microcystis biomass was in general greatly affected by water temperature and mixing depth/local water depth ratio in this reservoir, while the Oscillatoria biomass in the surface and middle layers was greatly affected by total dissolved phosphorus, and that in the bottom layer was related with the Secchi depth/local water depth ratio. Abundant Oscillatoria biomass was observed only in late September when Microcystis biomass decreased and allowed sufficient light go through.