The Kings River Experimental Watersheds: Infrastructure and data

The Kings River Experimental Watersheds (KREW) were established in 2002 to expand our knowledge of catchment physical, chemical, and biological processes in Sierra Nevada headwater forests, and to better understand the impacts of prescribed burning and forest thinning on these processes. Two elevation strata (high and low) were selected for the KREW sites, with four independent catchments and one nested catchment within each stratum. Both high and low elevation study areas were instrumented for continuous measurements of meteorology, streamflow, and turbidity. Atmospheric and stream chemistry, suspended sediment concentration, and bedload sediment delivery were measured on a regular schedule. Soil chemical and physical properties and vegetation were systematically sampled before and after the initial thinning and prescribed burning treatments, which were implemented between 2012 and 2016. Post-treatment data collection continues today as we explore opportunities for the second round of possible treatments. The critical research infrastructure and long-term baseline data collection has been instrumental in building partnerships with downstream managers, end users, non-governmental organizations, academic researchers, and national research programmes. Contributions to date include fundamental understanding of magnitude and variability of nutrient deposition; carbon, nutrient, and major ion dynamics in headwater streams; aquatic algae and macroinvertebrate populations; vegetation composition and structure; and streamflow responses to precipitation in the two elevation strata. Data from the experimental watersheds also support calibration and validation of diverse hydrologic models used for water resources planning.     

Comparison of streamflow recession between plantations and native forests in small catchments in Central-Southern Chile

In central Chile, many communities rely on water obtained from small catchments in the coastal mountains. Water security for these communities is most vulnerable during the summer dry season and, from 2010 to 2017, rainfall during the dry season was between 20% and 40% below the long-term average. The rate of decrease in stream flow after a rainfall event is a good measure of the risk of flow decreasing below a critical threshold. This risk of low flow can be quantified using a recession coefficient (α) that is the slope of an exponential decay function relating flow to time since rainfall. A mathematical model was used to estimate the recession coefficient (α) for 142 rainstorm events (64 in summer; 78 in winter) in eight monitored catchments between 2008 and 2017. These catchments all have a similar geology and extend from 35 to 39 degrees of latitude south in the coastal range of south-central Chile. A hierarchical cluster analysis was used to test for differences between the mean value of α for different regions and forest types in winter and summer. The value of α did not differ (p < 0.05) between catchments in winter. Some differences were observed during summer and these were attributed to morphological differences between catchments and, in the northernmost catchments, the effect of land cover (native forest and plantation). Moreover, α for catchments with native forest was similar to those with pine plantations, although there was no difference (p < 0.05) between these and Eucalyptus plantations. The recession constant is a well-established method for understanding the effect of climate and disturbance on low flows and baseflows and can enhance local and regional analyses of hydrological processes. Understanding the recession of flow after rainfall in small headwater catchments, especially during summer, is vital for water resources management in areas where the establishment of plantations has occurred in a drying climate.     

Effects of bedrock groundwater discharge on spatial variability of dissolved carbon,nitrogen, and phosphorous concentrations in stream water within a forest headwater catchment

The quantitative evaluation of the effects of bedrock groundwater discharge on spatial variability of stream dissolved organic carbon (DOC), dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorous (DIP) concentrations has still been insufficient. We examined the relationships between stream DOC, DIN and DIP concentrations and bedrock groundwater contribution to stream water in forest headwater catchments in warm-humid climate zones. We sampled stream water and bedrock springs at multiple points in September and December 2013 in a 5 km² forest headwater catchment in Japan and sampled groundwater in soil layer in small hillslopes. We assumed that stream water consisted of four end members, groundwater in soil layer and three types of bedrock groundwater, and calculated the contributions of each end member to stream water from mineral-derived solute concentrations. DOC, DIN and DIP concentrations in stream water were compared with the calculated bedrock groundwater contribution. The bedrock groundwater contribution had significant negative linear correlation with stream DOC concentration, no significant correlation with stream DIN concentration, and significant positive linear correlation with stream DIP concentration. These results highlighted the importance of bedrock groundwater discharge in establishing stream DOC and DIP concentrations. In addition, stream DOC and DIP concentrations were higher and lower, respectively, than those expected from end member mixing of groundwater in soil layer and bedrock springs. Spatial heterogeneity of DOC and DIP concentrations in groundwater and/or in-stream DOC production and DIP uptake were the probable reasons for these discrepancies. Our results indicate that the relationships between spatial variability of stream DOC, DIN and DIP concentrations and bedrock groundwater contribution are useful for comparing the processes that affect stream DOC, DIN and DIP concentrations among catchments beyond the spatial heterogeneity of hydrological and biogeochemical processes within a catchment.     

Estimation of winter leaf area index and sky view fraction for snow modelling in boreal coniferous forests: consequences on snow mass and energy balance

Leaf area index (LAI) and canopy coverage are important parameters when modelling snow process in coniferous forests, controlling interception and transmitting radiation. Estimates of LAI and sky view factor show large variability depending on the estimation method used, and it is not clear how this is reflected in the calculated snow processes beneath the canopy. In this study, the winter LAI and sky view fraction were estimated using different optical and biomass‐based approximations in several boreal coniferous forest stands in Fennoscandia with different stand density, age and site latitude. The biomass‐based estimate of LAI derived from forest inventory data was close to the values derived from the optical measurements at most sites, suggesting that forest inventory data can be used as input to snow hydrological modelling. Heterogeneity of tree species and site fertility, as well as edge effects between different forest compartments, caused differences in the LAI estimates at some sites. A snow energy and mass balance model (SNOWPACK) was applied to detect how the differences in the estimated values of the winter LAI and sky view fraction were reflected in simulated snow processes. In the simulations, an increase in LAI and a decrease in sky view fraction changed the snow surface energy balance by decreasing shortwave radiation input and increasing longwave radiation input. Changes in LAI and sky view fraction affected directly snow accumulation through altered throughfall fraction and indirectly snowmelt through the changed surface energy balance. Changes in LAI and sky view fraction had a greater impact on mean incoming radiation beneath the canopy than on other energy fluxes. Snowmelt was affected more than snow accumulation. The effect of canopy parameters on evaporation loss from intercepted snow was comparable with the effect of variation in governing meteorological variables such as precipitation intensity and air temperature. Copyright © 2012 John Wiley & Sons, Ltd.     

Preliminary evaluation of the runoff processes in a remote montane cloud forest basin using Mixing Model Analysis and Mean Transit Time

In this study, the Mean Transit Time and Mixing Model Analysis methods are combined to unravel the runoff generation process of the San Francisco River basin (73.5 km²) situated on the Amazonian side of the Cordillera Real in the southernmost Andes of Ecuador. The montane basin is covered with cloud forest, sub‐páramo, pasture and ferns. Nested sampling was applied for the collection of streamwater samples and discharge measurements in the main tributaries and outlet of the basin, and for the collection of soil and rock water samples. Weekly to biweekly water grab samples were taken at all stations in the period April 2007–November 2008. Hydrometric data, Mean Transit Time and Mixing Model Analysis allowed preliminary evaluation of the processes controlling the runoff in the San Francisco River basin. Results suggest that flow during dry conditions mainly consists of lateral flow through the C‐horizon and cracks in the top weathered bedrock layer, and that all subcatchments have an important contribution of this deep water to runoff, no matter whether pristine or deforested. During normal to low precipitation intensities, when antecedent soil moisture conditions favour water infiltration, vertical flow paths to deeper soil horizons with subsequent lateral subsurface flow contribute most to streamflow. Under wet conditions in forested catchments, streamflow is controlled by near surface lateral flow through the organic horizon. Exceptionally, saturation excess overland flow occurs. By absence of the litter layer in pasture, streamflow under wet conditions originates from the A horizon, and overland flow. Copyright © 2011 John Wiley & Sons, Ltd.     

Infiltration,runoff and soil loss in Andisols affected by forest fire (Canary Islands,Spain)

Depending on the severity of the fire, forest fires may modify infiltration and soil erosion processes. Rainfall simulations were used to determine the hydrological effects of fire on Andisols in a pine forest burned by a wildfire in 2007. Six burned zones with different fire severities were compared with unburned zones. Infiltration, runoff and soil loss were analysed on slopes of 10% and 30%. Forest floor and soil properties were evaluated. Unburned zones exhibited relatively low infiltration (23 and 16 mm h^?1 on 10% and 30% slope angles, respectively) and high average runoff/rainfall ratios (43% and 50% on 10% and 30% slope angles, respectively), which were associated with the extreme water repellency of the forest floor. Nonetheless, this layer seems to provide protection against raindrop impact and soil losses were found to be low (8 and 16 g m^?2 h^?1 for 10% and 30% slope angles, respectively). Soil cover, soil structure and water repellency were the main properties affected by the fire. The fire reduced forest floor and soil repellency, allowing rapid infiltration. Moreover, a significant decrease was noted in soil aggregate stabilities in the burned zones, which limited the infiltration rates. Consequently, no significant differences in infiltration and runoff were found between the burned and the unburned zones. The decrease in post‐fire soil cover and soil stability resulted in order‐of‐magnitude increases in erosion. Sediment rates were 15 and 31 g m^?2 h^?1 on the 10% and 30% slope angles, respectively, in zones affected by light fire severity. In the moderate fire severity zones, these values reached 65 and 260 g m^?2 h^?1 for the 10% and 30% slope angles, respectively. Copyright © 2012 John Wiley & Sons, Ltd.     

基于规则网格的复杂断层网络处理与建模

断层建模是三维地质结构建模中的主要过程之一。断层面建模过程中需要根据断层间的空间接触或者切割关系进行几何曲面的裁剪,目前方法利用三角网求交算法进行曲面裁剪,但是该算法处理复杂断层面切割关系时往往不稳定。笔者等提出了基于规则网格的复杂断层网络处理与自动化建模的方法和流程,详细讨论了基于网格化的断层网络模型形式化理论表达、建模流程中的断层网络空间关系构建以及相交裁剪处理算法等核心步骤。利用测试数据和煤矿三维地震构造解释数据进行了验证,表明该方法可以有效处理多条互相切割、主辅关系复杂的断层网络,具有较好的算法稳定性;与SKUA—GOCAD断层建模方法对比,能够减少交互过程,提高断层建模的自动化程度。     

Mechanism of Structure Variations at Rifted Margins in the Central Segment of South Atlantic: Insights from Numerical Modeling

Rifted margins in the central South Atlantic portray spatial variability in terms of preserved width and thickness, which relates to complex rift-related fault activities. However, there is still a lack of systematic and quantitative explanations for the causes of the variations that are observed along the paired rifts. To elucidate this issue, 2D viscous-plastic thermomechanical numerical models are applied to capture the behavior of deformation, in which we investigate the effects of extensional rate, crustal strength and thickness on crust-mantle coupling, and timing of transition from rifting to breakup. Our numerical experiments demonstrate that crust-mantle decoupling accounts for crustal hyperextension, and that incorporating moderate-intensity rheology into lower crust may yield insights into the hyper-extended crust and asymmetric architecture observed in the central South Atlantic. The results also suggest that undulations in lithospheric basement cause asymmetric mantle upwelling. The lower crust of fold belts takes priority to be thermally weakened over craton and induces rift migration simultaneously. A new mechanism for the formation of failed rift is described, where the mechanical decoupling derived from thermally weakened lower crust gives access to dual rift migration. These results reinforce the interpretation on how crustal rheology shapes margins architectures and highlight the first-order effects of crust-mantle coupling.     

上黑龙江盆地前哨林场黑云母二长花岗岩锆石U-Pb年龄、地球化学特征及地质意义

上黑龙江盆地前哨林场位于兴蒙造山带东段额尔古纳微地块北缘, 北与西伯利亚古陆以蒙古—鄂霍次克缝合带相隔, 东以塔源—喜桂图断裂与兴安地块相邻。本文通过对上黑龙江盆地前哨林场黑云母二长花岗岩进行锆石U-Pb年龄、主微量及同位素地球化学系统研究, 为探讨早古生代额尔古纳微地块与相邻地块的碰撞机制提供理论依据。利用LA-ICP-MS锆石U-Pb同位素测定技术, 获得研究区黑云母二长花岗岩结晶年龄为(458.4±2.4) Ma(MSWD=0.022), 确定了岩体形成时代为早古生代中—晚奥陶纪。岩石中锆石Hf同位素?Hf(t)值介于–4.64 ~ 1.84, 其测点大部分位于球粒陨石演化线之下, 两阶段模式年龄(tDM2)介于 715 ~ 1 126 Ma。地球化学显示岩石具有富硅、富铝、富碱等特征; 稀土配分曲线表现出轻稀土(LREE)相对富集, 重稀土(HREE)相对亏损的右倾特征, 且岩石相对富集大离子亲石元素Rb、K及高场强元素Th、U、Zr、Hf, 相对亏损大离子亲石元素Ba、Sr及高场强元素Nb、Ta、P、Ti。岩石成因类型判别图显示前哨林场黑云母二长花岗岩具A型花岗岩特征, 岩石Hf同位素及微量元素特征显示岩体岩浆来源于中—新元古代古老地壳的熔融, 且存在少许幔源物质及新增生地壳物质熔融的参与, 元素特征暗示岩石形成于额尔古纳地块与西伯利亚古陆碰撞后的伸展构造环境背景下。结合前人对额尔古纳地块早古生代花岗岩形成背景的研究, 认为额尔古纳地块北缘及东北缘早古生代花岗岩形成机制不同, 前者形成于额尔古纳地块与西伯利亚古陆及蒙古—图瓦地块碰撞、拼接后伸展背景下; 后者主要形成于额尔古纳与兴安地块碰撞伸展背景下。