THE POTENTIAL FOR INCREASING STREAMFLOW FROM SIERRA NEVADA WATERSHEDS1

The Sierra Nevada produces over 50 percent of California's water. Improvement of water yields from the Sierra Nevada through watershed management has long been suggested as a means of augmenting the state's water supply. Vegetation and snowpack management can increase runoff from small watersheds by reducing losses due to evapotranspiration, snow interception by canopy, and snow evaporation. Small clearcuts or group selection cuts creating openings less than half a hectare, with the narrow dimension from south to north, appear to be ideal for both increasing and delaying water delivery in the red fir-lodgepole pine and mixed-conifer types of the Sierra west slope. Such openings can have up to 40 percent more snow-water equivalent than does uncut forest. However, the water yield increase drops to 1/2-2 percent of current yield for an entire management unit, due to the small number of openings that can be cut at one time, physical and management constraints, and multiple use/sustained yield guidelines. As a rough forecast, water production from National Forest land in the Sierra Nevada can probably be increased by about 1 percent (0.6 cm) under intensive forest watershed management. Given the state of reservoir storage and water use in California, delaying streamflow is perhaps the greatest contribution watershed management can make to meeting future water demands.     

Validating a New Model for N Sequestration in Forest Soil Organic Matter

A conceptual model for N sequestration into the terrestrial nitrogen(N) sink is presented. The model uses foliar litter-fall data, limit values for litter decomposition, and calculated N concentration at the limit value (N_limit), giving the N concentration in the hypothesized stable remains. The N_limit values were determined extrapolating a linear relationship between accumulated litter mass loss and the increasing litter N concentration to the limit value. Thesequestration rates for N in boreal forest humus were calculated and validated for a Scots pine (Pinus sylvestris L.) monocultural stand and mixed stands with Scots pine, Norway spruce (Picea abies L.), and silver birch (Betula pendula L.). The calculated stable N fraction was compared to actually measured amounts of N in humus layers that started to accumulate 2984, 2081, 1106, and 120 yr BP. Sequestration rates of N were measured to be 0.255, 0.221, 0.147, and 0.168 g m^-2 yr^-1 and modeled to be 0.204, 0.207, 0.190, and 0.190 g m^-2 yr^-1, respectively, with missing fractions being 11.0, 1.5, 30.8, and 13.3%, respectively. The more N-rich the litter, the larger was the N fraction sequestered. This was found for experimental Scots pine needle litter (n = 6) and for 53 decomposition studies, encompassing seven litter species. The amounts of N sequestered annually ranged from ca. 1–2 kg ha^-1 yr^-1 under nutrient-poor boreal conditions to about 30 kgha^-1 yr^-1 in temperate, more nutrient-rich forests.     

Multicriteria Decision Aid in Supporting Decisions Related to Groundwater Protection

In the recent decades, there have been frequent conflicts between groundwater resources and environmentally hazardous activities. An example is the construction of the new highway through the important glaciofluvial esker aquifer Nybroåsen, which passes the protection zone of the water supply for the Kalmar municipality, in the southeastern part of Sweden. The decision to build the new road through this important aquifer has been strongly questioned by the municipality and the public because the value of the water resources in Nybroåsen was not taken into consideration during the first phase of the decision-making process. Multicriteria decision aid (MCDA) is applied as a tool to structure and analyze the four road alternatives proposed in the environmental impact assessment for the above conflict. The alternatives, including the existing road, are in conflict with water resources, agriculture, natural, and cultural values. The impacts on the water resources have been predicted by a two-dimensional physically based time-variant flow and solute groundwater model, which has been calibrated and evaluated. The MCDA illustrates how it can be used to identify (1) actors and their concerns, (2) ranking of alternative road scenarios according to actors preferences, and (3) coalition groups of actors, i.e., groups that have similar views with regard to the road alternatives. The analysis shows that the two best compromise solutions obtained in the MCDA were unacceptable by the strongest coalition group, showing that either the family of criteria was not well chosen or new alternatives should have been developed.     

Environmental indicators for long-range atmospheric transported heavy metals based on national moss surveys

Environmental indicators for long-range atmospheric transported heavy metals have been developed. The indicators are based on data for Pb and Cd from national moss surveys which are performed regularly in Norway. The interpolation programme kriging has been used to transform the data from irregular grids to regular grids. Contour maps have been produced, and areas above estimated background levels for Pb and Cd in mosses have been calculated. The indicators are used to characterise the atmospheric deposition of long-range atmospheric transported heavy metals and monitor the changes with time.     

A Screening Procedure for Identifying Acid-Sensitive Lakes from Catchment Characteristics

Monitoring of Wilderness lakes for potential acidification requires information on lake sensitivity to acidification. Catchment properties can be used to estimate the acid neutralizing capacity (ANC) of lakes. Conceptual and general linear models were developed to predict the ANC of lakes in high-elevation (2170 m) Wilderness Areas in Californias Sierra Nevada mountains. Catchment-to-lake area ratio, lake perimeter-to-area ratio, bedrock lithology, vegetation cover, and lake headwater location are significant variables explaining ANC. The general linear models were validated against independently collected water chemistry data and were used as part of a first stage screen to identify Wilderness lakes with low ANC. Expanded monitoring of atmospheric deposition is essential for improving the predictability of lake ANC.     

Blast phenomena in urban tunnel systems

Traffic infrastructure in urbanised areas is increasingly projected in tunnels underground or covered over, these days. A consequence is that in case of an incident with hazardous materials the safety level for fellow road users in tunnels is considerably less than it is in surface infrastructure. To reduce the consequences of incidents for fellow tunnel users, urban tunnels are sometimes interrupted by open spaces of limited length. Open spaces allow, for instance, the release of smoke in case of a fire. In this way, possible lethal effects are limited to the tunnel section in which the incident occurred. To what extent an open space may also be effective in the mitigation of blast effects from an explosion in a tunnel system is subject of this paper.

To this end, the blast effects originating from the rupture of a 50 m³ LPG pressure vessel in an urban tunnel system have been computed by numerical simulation. The results show that an open space in a tunnel system has a significant mitigating effect on the blast effects indeed. However, as a consequence of the ingress of a high-velocity jet flow that follows on a primary blast wave, a second blast wave develops in the tunnel section following on an open space. The strength of this second blast wave is not very dependent on the length of the open space. It shows that an open space in a tunnel system may not always limit the lethal effects of explosion incidents in tunnels to the tube in which the incident occurred. The second blast wave in the tunnel section following on an open space may have lethal consequences for fellow tunnel users by car window failure.