CO₂ emissions from German drinking water reservoirs estimated from routine monitoring data

Globally, reservoirs are a significant source of atmospheric CO2. However, precise quantification of greenhouse gas emissions from drinking water reservoirs on the regional or national scale is still challenging. We calculated CO2 fluxes for 39 German drinking water reservoirs during a period of 22 years (1991–2013) using routine monitoring data in order to quantify total emission of CO2 from drinking water reservoirs in Germany. All reservoirs were small net CO2 sources with a median flux of 167 g C m–2 y–1, which makes gaseous emissions a relevant process for the reservoirs carbon budgets. In total, German drinking reservoirs emit 44000 t of CO2 annually, which makes them a negligible CO2 source in Germany. Fluxes varied seasonally with median fluxes of 30, 11, and 46 mmol m–2 d–1 in spring, summer, and autumn respectively. Differences between reservoirs appeared to be primarily caused by the concentration of CO2 in the surface water rather than by the physical gas transfer coefficient. Consideration of short term fluctuations of the gas transfer coefficient due to variable wind had only a minor effect on the annual budgets. High CO2 emission only occurred in reservoirs with pH < 7 and total alkalinity < 0.2 mEq l–1. Annual CO2 emission correlated exponentially with pH, making pH a suitable proxy for CO emission from German drinking water reservoirs.

Using geochemical tracers to distinguish groundwater and parafluvial inflows in rivers (the Avon Catchment, SE Australia)

Understanding the location and magnitude of groundwater inflows to rivers is important for the protection of riverine ecosystems and the management of connected groundwater and surface water systems. Downstream trends in 222Rn activities and Cl concentrations in the Avon River, southeast Australia, implies that it contains alternating gaining and losing reaches. 222Rn activities of up to 3690 Bq m−3 imply that inflows are locally substantial (up to 3.1 m3 m−1 day−1). However, if it assumed that these inflows are solely from groundwater, the net groundwater inflows during low-flow periods exceed the measured increase in streamflow along the Avon River by up to 490 %. Uncertainties in the 222Rn activities of groundwater, the gas transfer coefficient, and the degree of hyporheic exchange cannot explain this discrepancy. It is proposed that a significant volume of the total calculated inflows into the Avon River represents water that exfiltrates from the river, flows through parafluvial sediments, and subsequently re-enters the river in the gaining reaches. This returning parafluvial flow has high 222Rn activities due to 222Rn emanations from the alluvial sediments. The riffle sections of the Avon River commonly have steep longitudinal gradients and may transition from losing at their upstream end to gaining at the downstream end and parafluvial flow through the sediment banks on meanders and point bars may also occur. Parafluvial flow is likely to be important in rivers with coarse-grained alluvial sediments on their floodplains and failure to quantify the input of 222Rn from parafluvial flow will result in overestimating groundwater inflows to rivers.

KOEFISIEN TRANSFER GAS (KLa ) PADA PROSES AERASI MENGGUNAKAN TRAY AERATOR BERTINGKAT 5 (LIMA)

ABSTRAKAerasi merupakan salah satu metode yang dapat digunakan untuk menyisihkan kandungan logam dalam air, baik air tanah, air permukaan, maupun air limbah. Salah satu jenis aerator dalam proses aerasi adalah tray aerator. Untuk menganalisis nilai koefisien transfer gas (KLa) pada proses aerasi khususnya tray aerator bertingkat 5 (lima)dengan jarak antar tray 25 cm dan tinggi total 125 cm, perlu dilakukan penelitian dengan tujuan untuk memperoleh nilai KLa. Air dialirkan ke dalam tray aerator bertingkat 5 (lima) dan diukur kandungan Disolved Oxygen (DO) dengan metode water quality checker. Hasil penelitian menunjukan terjadi peningkatan konsentrasi oksigen pada sampel setelah dilakukan aerasi dengan tray aerator bertingkat 5 (lima) dari 5,97 mg/L menjadi 6,34 mg/L dengan nilai koefisien transfer gas (KLa) sebesar 0,045/menit.Kata kunci: Tray Aerator bertingkat 5, Aerasi, Koefisien trasnsfer gas (KLa)ABSTRACTAeration method is one method for removing metalfrom water including groundwater, surface water and wastewater. One of known aerator is method is tray aerator. For analizing gas transfer coefficient (KLa) in aeration method especially in five storey tray aerator with the distance between each aerator was 25 cm and total height was 125 cm. water was discharged in five storey tray aerator and was measured the dissolved oxygen concentration by using water quality checker method. Result showed the increase of oxygen concentration in sample after being aerated in five storey tray aerator, from 5.97 mg/L to 6.34 mg/L with gas transfer coefficient (KLa) 0.045/min. Keywords: Aeration, Five story aerator, Gas transfer coefficient (KLa)