Angela Lundberg

Continuous long-term measurements of soil-plant-atmosphere variables at a forest site

It is a major challenge in modern science to decrease the uncertainty in predictions of global climate change. One of the largest uncertainties in present-day global climate models resides with the understanding of processes in the soil-vegetationatmosphere-transfer (SVAT) system. Continuous, long-term data are needed in order to correctly quantify balances of water, energy and CO2 in this system and to correctly model it. It is the objective of this paper to demonstrate how a combined system of existing sensor, computer, and network technologies could be set up to provide continuous and reliable long-term SVAT-process data from a forested site under almost all environmental conditions. The Central Tower Site (CTS) system was set up in 1993‐1994 in a 25 m high boreal forest growing on a highly heterogeneous till soil with a high content of stones and blocks. It has successfully monitored relevant states and fluxes in the system, such as atmospheric fluxes of momentum, heat, water vapour and CO2, atmospheric profiles of temperature, water vapour, CO2, short-and long-wave radiation, heat storage in soil and trees, sap-flow and a variety of ecophysiological properties, soil-water contents and tensions, and groundwater levels, rainfall and throughfall. System uptime has been more than 90% for most of its components during the first 5 years of operation. Results from the first 5 years of operation include e.g., budgets for energy, water and CO2, information on important but rarely occurring events such as evaporation from snow-covered canopies, and reactions of the forest to extreme drought. The carbon budget shows that the forest may be a sink of carbon although it is still growing. The completeness of the data has made it possible to test the internal consistency of SVAT models. The pioneering set-up at the CTS has been adopted by a large number of SVAT-monitoring sites around the world. Questions concerning tower maintenance, long-term calibration plans, maintenance of sensors and data-collection system, and continuous development of the computer network to keep it up to date are, however, only partly of interest as a research project in itself. It is thus difficult to get it funded from usual researchfunding agencies.

Evaporation of intercepted snow: measurement and modelling

Abstract Snow storage on a coniferous forest canopy was measured using γ-ray attenuation and tree weighing systems, along with measurements of throughfall, using two plastic sheet net rainfall gauges. Meteorological parameters were measured with an automatic weather station. Estimates of evaporation of intercepted snow show an average rate of 0.24 mm h −1 and a maximum cumulative total of 3.9 mm in 7 h. Comparison with evaporation determined by a combination method with two different estimates of aerodynamic resistance (the “standard” rain aerodynamic resistance r aL and a snow aerodynamic resistance r aS —an order of magnitude larger than r aL ) showed that r aL overestimated the evaporation by a factor of 2.6, whereas r aS gave fair agreement with the measured evaporation. A multilayer model may be needed to take into account the variations of latent heat source area. Using the long-term measurements of the weight of snow on a single tree the total interception evaporation was estimated to be of the order 200 mm year −1 .

Evaporation of intercepted snow : analysis of governing factors

Insufficient understanding of winter hydrology conditions still hampers progress in predicting springtime discharge. The least known term in the winter water balance is evaporation, particularly of ...

Evaporation and storage of intercepted rain analysed by comparing two models applied to a boreal forest

Rainfall and throughfall were measured during the summer of 1995. Rainfall interception is often simulated by a version of the well-known Rutter-Gash analytical model. In this study this model was compared to a model based on an exponential saturation equation. The concept of the ‘minimum method’ for deriving canopy storage capacity and free throughfall coefficient by the Leyton-analysis, is compared to the concept of maximum storage capacity by reversing the models. Measured evaporation rate during rain events was found to be lower than simulated by the Penman equation using different known formulations for aerodynamic resistance. The concept of a high internal canopy resistance and decoupling of the canopy from the atmosphere should be analysed further in order to explain low evaporation during rainfall. # 1999 Elsevier Science B.V. All rights reserved.

Evaporation of intercepted snow : review of existing and new measurement methods

Abstract Knowledge of the annual water balance within a catchment is still hampered by an insufficient understanding of winter conditions. The least known term of the winter water balance is evaporation — particularly that from intercepted snow. Methods to measure interception and evaporation are reviewed. Undisturbed meteorological conditions, high time resolution and continuous measurements of intercepted mass were taken as criteria for an ideal method. The ideal method should work during periods of melt and sublimation and above rough forest surfaces. None of the existing methods fulfils all the criteria. Most traditional hydrological methods to estimate winter-time evaporation, such as runoff and snow-course studies, non-weighing lysimeters, and precipitation and throughfall measurements, produce too little information to distinguish the causes of the observed changes. Among micrometeorological methods, only the eddy-correlation technique is suitable, and should be used in combination with interception measurements. Of the methods primarily designed to quantify interception, i.e. collection of intercepted snow, visual or photographic observations, displacement transducers, weighing of branches and trees and gamma-ray attenuation, only the last two yield continuous interception records. In combination with continuous measurements of throughfall and drip, these methods can be used to study the evaporation process. The gamma-ray method can be used to measure whole-canopy losses, whereas the other two methods deal only with losses from a branch or a single tree. The weighing-lysimeter technique produces the same information as the method of weighing a cut tree but employs a more complex set-up. The weighing-tree method combined with measurement of drip is one of the current methods that is most suitable for process studies. A new device for this purpose is presented, which differs from earlier designs by allowing a continuous weighing of drip in a tray of 2m width placed around the tree. The tray was fastened to the tree with wires and was automatically raised and lowered, thus allowing continuous measurements of both intercepted mass (with the tray raised) and evaported mass (with the tray lowered). A maximum evaporation rate of 0.3 mm h−1 was recorded with this device on 22–23 March 1990 at a site close to Lulea in northern Sweden. This maximum value was measured when wet snow was present, and confirmed earlier reports of high evaporation rates. The maximum evaporated mass during 24 h was 3.3 mm.

New Approach to the Measurement of Interception Evaporation

Abstract Evaporation of water intercepted by vegetation represents an important (sometimes major) part of evapotranspiration in temperate regions. Interception evaporation is an important process where insufficient measurement techniques hamper progress in knowledge and modeling. An ideal technique to study the interception evaporation process should monitor intercepted mass (and its vertical distribution) and interception loss with high accuracy (0.1 mm) and time resolution (1 min), and give correct area estimates. The method should be inexpensive, require minor supervision during extended periods, and work in dense forests. Net precipitation techniques, in which interception evaporation is determined from the difference between gross precipitation (measured with funnels) and throughfall (measured with funnels, troughs, or plastic sheet net-rainfall gauges) fulfill many of the requirements but usually have a too-low accuracy and time resolution for process studies. Precipitation measurements are normally...

Estimation of temporal changes in oxidation rates of sulphides in copper mine tailings at Laver, Northern Sweden

Tailings containing pyrrhotite were deposited in an impoundment at a copper mine at Laver, Northern Sweden, which operated between 1936 and 1946. Since then the oxidation of sulphides has acidified recipient water courses and contaminated them with metals. Measurements from surface water sampled in 1993, 2001 and 2004-05 from a brook into which the tailing impoundment drains indicate that the amounts of sulphide-associated elements such as Cu, S and Zn released into the brook have decreased over time, while pH has increased. The mass transport of S in the brook during 1993 and 2001 corresponded well with the amount of S estimated to be released from the tailings by oxidation. Secondary precipitates such as covellite and gypsum, which can trap sulphur, were shown in earlier studies to be present in only low amounts. The annual release of elements from the tailings was estimated from the volume of tailings assumed to oxidise each year, which depends on movement of the oxidation front with time. The results indicate that the oxidation rate in the tailings has decreased over time, which may be due to the increased distance over which oxygen needs to diffuse to reach unoxidised sulphide grains, or their cores, in the tailings.

Improving surface-based precipitation phase determination through air mass boundary identification

Using static, closed chambers and gas chromatography techniques, nitrous oxide (N2O) emissions have been monitored for 1 year (2009–2010) on an inland running waterbody downstream of the Nenjiang basin, China. During the freezing period, holes were dug in the ice in order to obtain nitrous oxide samples. Here, we have focused on water-air gas exchange and factors which might influence N2O emissions and flux. Initial results indicate: (1) N2O flux rates reach peak emission in January and the annual emissions of N2O were low, being estimated at 0.35± 0.20 μgm –2 h ; significant seasonal differences only appeared between January and July; (2) N2O flux rates have strong regularity and ice has been the main barrier to nitrous oxide release during winter; (3) 24-hour monitoring revealed that N2O flux remained steady during 9:00–17:00; (4) N2O emissions have significant relationships with ammonium nitrogen and total phosphorus concentrations in water (r1⁄4 0.4467, p1⁄4 0.020 and r1⁄4 0.4793, p1⁄4 0.011, respectively). The N2O flux released from the waterbody is determined by the chemical concentrations in the water. Following these results, we suggest that moderate use of N and P fertilizer at intensive agricultural areas will be beneficial in decreasing greenhouse gas emissions from this waterbody. doi: 10.2166/nh.2012.060 om https://iwaponline.com/hr/article-pdf/43/6/862/370119/862.pdf er 2019 Qiao-Qi Sun Charlotte Whitham Kun Shi (corresponding author) School of Nature Conservation, Beijing Forestry University, # 35 Tsinghua-east Road, Haidian District, Beijing 100083, China E-mail: kunshi11@yahoo.com.cn Guo-Hai Yu Xiao-Wei Sun Momoge National Nature Reserve, Baicheng, China

Radiation balance of urban snow: a water management perspective

The radiation balance of urbanised catchments differs from their rural counterparts, with snowpacks experiencing either enhanced or decreased irradiance depending on snowpack location and condition. As snowmelt is largely driven by radiation inputs, changes to localised irradiance (and melt rates) have implications for urban runoff generation. Storm- and wastewater drainage systems in cold regions are currently dimensioned for rain according to practices developed for temperate climates. They are not designed to cope with wintry conditions, which can lead to surface flooding, hydraulic overloads and poor water quality at receiving waters. Net allwave radiation measurements over snow made at the Swedish city of Lulea during April 1997 and 1998 are presented. The 1997 measurements were made in the vicinity of a matt-black-painted metal building at Lulea University of Technology, whereas the 1998 measurements are from a specially constructed 3×6-m black plastic-clad wall built on an open field just outside the town. Black minimises multiple reflections between the snow and walls, while maximising absorption of shortwave radiation by walls. The data were compared to the outputs of an urban radiation model. The results show that urban structures significantly alter radiation over snow. The temperature of the south-facing walls translates to longwave enhancements in the order of 150 W m−2 for several metres from the walls on sunny days. Shaded snow near the north-facing wall showed a net allwave radiation loss of the same order of magnitude. Radiation inputs to snow are similar both to the north and south of walls when the sky is overcast. The need to include snowmelt energetics within design and management techniques is discussed in light of the results.

Student and teacher experiences of assessing different levels of understanding

Examinations greatly influence course structures and student study strategies. A course for students in the civil and environmental engineering programme at Lulea University of Technology was reconstructed with the aim of increasing levels of understanding. A simple written test was designed to assess low levels of understanding (definitions, concepts, etc.). Laboratory work, fieldwork and extensive assignments (calculation tasks) were intended to assess medium levels of understanding (apply, use and combine algorithms, etc.). A final oral group exam that was used to assess high levels of understanding (compare/contrast, explain causes, analyse, relate) concluded the course. Peer assessment of laboratory work and assignments was also applied. The students ranked the entire course at 5 on a 6 grade scale and appreciated the extensive assignments and the assessment approach.Examinations greatly influence course structures and student study strategies. A course for students in the civil and environmental engineering programme at Luleå University of Technology was reconstructed with the aim of increasing levels of understanding. A simple written test was designed to assess low levels of understanding (definitions, concepts, etc.). Laboratory work, fieldwork and extensive assignments (calculation tasks) were intended to assess medium levels of understanding (apply, use and combine algorithms, etc.). A final oral group exam that was used to assess high levels of understanding (compare/contrast, explain causes, analyse, relate) concluded the course. Peer assessment of laboratory work and assignments was also applied. The students ranked the entire course at 5 on a 6 grade scale and appreciated the extensive assignments and the assessment approach.