GLAMS: A Graphical Method for Capturing Land and Water Management Practices in Agroecosystems

Abstract Modification of native ecosystems through land use can affect the biophysical functioning of agroecosystems, with spatial arrangement (configuration) through time often determining the degree to which landscapes experience dysfunctional states. An improved understanding is needed of how spatial and temporal patterns in land use affect ecohydrological dysfunctions, such as how landscapes leak or fail to retain water and soil, at scales relevant to farm management. We develop and apply a Graphical LAndscape Map Survey method, or ‘GLAMS’, for measuring changes in landscape function based upon a 3D graphic of a hypothetical sub-catchment. GLAMS was applied within four Landcare Groups comprised of farmers from the Western Catchments of Southeast Queensland, Australia. The aim was to capture the behaviors of farmers who manage land use under natural variations in precipitation, especially extended dry periods, and with the associated risks from ecohydrologically dysfunctional or ‘leaky’ landscapes. GLAMS provided variable spatial and temporal resolution which allowed quantification of the land use responses for three different property sizes: (1) small, less than 100 ha; (2) medium, 100–500 ha; and (3) large, larger than 500 ha. Responses were quantified using Bayesian Belief Networks to provide probability estimates of the likelihood of a given action, taking place within a particular part of the landscape, considering both climatic and ecohydrological risks. The findings indicated that GLAMS was more intuitive to farmers than traditional question-based surveys, resulting in a low cost technique that is rapid to implement while providing spatially explicit information relevant to farm and catchment management.     

Multiple Methods in the Study of Driving Forces of Land Use and Land Cover Change: A Case Study of SE Kajiado District,Kenya

This landscape-scale study combines analysis of multitemporal satellite imagery spanning 30 years and information from field studies extending over 25 years to assess the extent and causes of land use and land cover change in the Loitokitok area, southeast Kajiado District, Kenya. Rain fed and irrigated agriculture, livestock herding, and wildlife and tourism have all experienced rapid change in their structure, extent, and interactions over the past 30 years in response to a variety of economic, cultural, political, institutional, and demographic processes. Land use patterns and processes are explored through a complementary application of interpretation of satellite imagery and case study analysis that explicitly addresses the local–national spatial scale over a time frame appropriate to the identification of fundamental causal processes. The results illustrate that this combination provides an effective basis for describing and explaining patterns of land use and land cover change and their root causes.     

Impact of land use and land cover change on groundwater recharge and quality in the southwestern US

Humans have exerted large‐scale changes on the terrestrial biosphere, primarily through agriculture; however, the impacts of such changes on the hydrologic cycle are poorly understood. The purpose of this study was to test the hypothesis that the conversion of natural rangeland ecosystems to agricultural ecosystems impacts the subsurface portion of the hydrologic cycle by changing groundwater recharge and flushing salts to underlying aquifers. The hypothesis was examined through point and areal studies investigating the effects of land use/land cover (LU/LC) changes on groundwater recharge and solute transport in the Amargosa Desert (AD) in Nevada and in the High Plains (HP) in Texas, US. Studies use the fact that matric (pore‐water‐pressure) potential and environmental‐tracer profiles in thick unsaturated zones archive past changes in recharging fluxes. Results show that recharge is related to LU/LC as follows: discharge through evapotranspiration (i.e., no recharge; upward fluxes <0.1 mm yr^?1) in natural rangeland ecosystems (low matric potentials; high chloride and nitrate concentrations); moderate‐to‐high recharge in irrigated agricultural ecosystems (high matric potentials; low‐to‐moderate chloride and nitrate concentrations) (AD recharge: ～130–640 mm yr^?1); and moderate recharge in nonirrigated (dryland) agricultural ecosystems (high matric potentials; low chloride and nitrate concentrations, and increasing groundwater levels) (HP recharge: ～9–32 mm yr^?1). Replacement of rangeland with agriculture changed flow directions from upward (discharge) to downward (recharge). Recent replacement of rangeland with irrigated ecosystems was documented through downward displacement of chloride and nitrate fronts. Thick unsaturated zones contain a reservoir of salts that are readily mobilized under increased recharge related to LU/LC changes, potentially degrading groundwater quality. Sustainable land use requires quantitative knowledge of the linkages between ecosystem change, recharge, and groundwater quality.     

Long-term trends in streamflow from semiarid rangelands: uncovering drivers of change

In the last 100 years or so, desertification, degradation, and woody plant encroachment have altered huge tracts of semiarid rangelands. It is expected that the changes thus brought about significantly affect water balance in these regions; and in fact, at the headwater‐catchment and smaller scales, such effects are reasonably well documented. For larger scales, however, there is surprisingly little documentation of hydrological change. In this paper, we evaluate the extent to which streamflow from large rangeland watersheds in central Texas has changed concurrent with the dramatic shifts in vegetation cover (transition from pristine prairie to degraded grassland to woodland/savanna) that have taken place during the last century. Our study focused on the three watersheds that supply the major tributaries of the Concho River – those of the North Concho (3279 km²), the Middle Concho (5398 km²), and the South Concho (1070 km²). Using data from the period of record (1926–2005), we found that annual streamflow for the North Concho decreased by about 70% between 1960 and 2005. Not only did we find no downtrend in precipitation that might explain this reduced flow, we found no corresponding change in annual streamflow for the other two watersheds (which have more karst parent material). When we analyzed trends in baseflow (contributions from groundwater) and stormflow (runoff events linked to specific precipitation events), however, we found that in spite of large increases in woody plants, baseflow for all the watersheds has remained essentially consistent or has increased slightly since 1960. At the same time, stormflows were of smaller magnitude. Animal numbers have declined precipitously in the latter half of the last century. We suggest that these lower stormflows result from generally higher soil infiltrability due to generally improving range condition. There is no indication that the decline in streamflow is related to diminished groundwater flows caused by extraction of subsurface water by woody plants.     

Land-use change and water losses: the case of grassland afforestation across a soil textural gradient in central Argentina

Vegetation changes, particularly those involving transitions between tree‐ and grass‐dominated covers, often modify evaporative water losses as a result of plant‐mediated shifts in moisture access and demand. Massive afforestation of native grasslands, particularly important in the Southern Hemisphere, may have strong yet poorly quantified effects on the hydrological cycle. We explored water use patterns in Eucalyptus grandis plantations and the native humid grasslands that they replace in Central Argentina. In order to uncover the interactive effects that land cover type, soil texture and climate variability may have on evaporative water losses and water use efficiency, we estimated daily evapotranspiration (ET) in 117 tree plantations and grasslands plots across a soil textural gradient (clay‐textured Vertisols to sandy‐textured Entisols) using radiometric information from seven Landsat scenes, existing timber productions records, and ¹³C measurements in tree stems. Tree plantations had cooler surface temperatures (?5°C on average) and evaporated more water (+80% on average) than grasslands at all times and across all sites. Absolute ET differences between grasslands and plantations ranged from ～0.6 to 2 mm day^?1 and annual up‐scaling suggested values of ～630 and ～1150 mm yr^?1 for each vegetation type, respectively. The temporal variability of ET was significantly lower in plantations compared with grasslands (coefficient of variation 36% vs. 49%). Daily ET increased as the water balance became more positive (accumulated balance for previous 18 days) with a saturation response in grassland vs. a continuous linear increase in plantations, suggesting lower ecophysiological limits to water loss in tree canopies compared with the native vegetation. Plantation ET was more strongly affected by soil texture than grassland ET and peaked in coarse textured sites followed by medium and fine textured sites. Timber productivity as well as ¹³C concentration in stems peaked in medium textured sites, indicating lower water use efficiency on extreme textures and suggesting that water limitation was not responsible for productivity declines towards finer and coarser soils. Our study highlighted the key role that vegetation type plays on evapotranspiration and, therefore, in the hydrological cycle. Considering that tree plantations may continue their expansion over grasslands, problematic changes in water management and, perhaps, in local climate can develop from the higher evaporative water losses of tree plantations.     

城市土地利用异质性对湖泊水质的影响

土地利用类型与水体水质之间存在显著相关关系,这种相关关系受到土地利用类型及其空间分布的影响.人类活动造成流域中不同汇水单元间土地利用异质性,进而影响和改变了汇水单元水质状况.在自然或半自然区域内,采用多个汇水单元的综合分析能够体现出流域土地利用类型与水质的相关关系.然而,在城市区域中,可能存在由于土地利用特征差异而导致这种相关关系的抵消和降低,致使分析结果与实际存在偏差.为证实这一现象的存在,选取武汉市汉阳地区龙阳湖等4个湖泊流域为研究对象,分别从汇水单元综合分析、以影响水质的主要用地类型作为变量进行聚类分析和以湖泊流域为对象的分析等3个角度,分析汇水单元间的土地利用特征差异对水质的影响,结果显示土地利用异质性影响甚至改变了土地利用类型与水质的相关关系.因此,在研究城市土地利用与水体水质相关性时,需要同时考虑土地利用类型的特征和格局.     

密云水库上游流域土地利用与地表径流营养物的关系

定量刻画土地利用与水体营养物浓度的关系,有助于指导流域土地利用管理,以控制水体富营养化.以往研究较多关注土地利用的数量结构,对其强度、空间分布等刻画相对不足.本研究以密云水库上游流域为例,基于覆盖全流域52个子流域的水质采样,通过遥感解译和空间计算,提取土地利用强度、所处坡度、与河道及监测断面距离以及位置邻接关系等信息,构建土地利用与总氮、总磷和化学需氧量浓度的多元线性回归方程.结果表明: 土地利用与总氮、总磷和化学需氧量浓度回归方程的决定系数由未纳入任何信息的0.294、0.471和0.223分别增加到0.532、0.685和0.489,显著提高了模型的解释能力.在厘定每一空间位置土地利用对监测断面营养物浓度贡献率的基础上,比较与河道不同迁移路径距离下土地利用对营养物浓度的平均累积贡献率及面积累计百分比,确定了距离河道1 km范围内的河岸带为水体富营养化的关键控制范围.最后提出了优化农田施肥管理、加强牲畜粪便处理、建设林地过滤带和河岸缓冲带等水质污染控制和调控的措施建议.     

Developing a disturbance index for five East African forests using GIS to analyse historical forest use as an important driver of current land use/cover

A means of deriving a disturbance index reflecting forest use history is demonstrated here to establish a disturbance gradient and enable comparison of different forest areas within and across individual forests. Detailed reference is made to Kakamega Forest in western Kenya for which a long‐term time series has been established, although the study is spread to four further forests in Kenya and Uganda. A wide variety of sources are drawn upon for spatially resolved data that are integrated in a geographic information system. Three indices are derived: for commercial disturbance, local disturbance, and forest cover change. Results show a wide range of disturbance values (from low to heavy) for the research sites within Kakamega Forest, while results for Budongo and Mabira Forest sites show low and moderate levels, respectively. Correlations of low disturbance levels with nature or national reserves appear to be marked, while a correlation of disturbance with differing management authority is also suggested with Kenya Wildlife Service achieving the lowest disturbance levels. Results from the index are reviewed against other means of estimating disturbance with the conclusion that disturbance evaluations should be both spatially resolved and long‐term in nature.     

毛乌素裸沙丘斑块的实际蒸发量及其对降雨格局的响应

 裸沙表面的蒸发虽然是一个物理问题,但对于沙地植被演替的初始阶段非常重要。目前存在的地表蒸发的机理性模型大多是瞬时或者短时期的 ,而年尺度以上的蒸发量与降水和蒸发驱动下的土壤水分系统的状态变化及其对蒸发过程的反馈密切相关。一些估算毛乌素年蒸发量的实验结 果之间分歧很大且缺乏准确的机理性解释。该文利用生态系统模型中的土壤水分运动和蒸发模块计算了毛乌素裸沙丘从日到年际尺度的实际蒸 发量,发展了一个以单次降雨量和降雨频率为驱动因素的降雨-蒸发模型对年蒸发量进行简单的估算,并研究了年蒸发量对降雨格局的响应。结 果表明毛乌素裸沙丘的多年平均蒸发量为166 mm,占多年平均降雨量的56%。虽然研究区1959～1992年降雨总量无显著变化趋势,但是裸沙丘斑 块的实际蒸发量呈现较明显的增加趋势（1.30 mm&;#8226;a^－1）。小降雨事件对蒸发量贡献的显著增加（0.69 mm&;#8226;a^－1）是导致实际蒸发量增大的重 要原因。大强度降雨事件的频度和雨量对降雨总量的贡献要远高于对蒸发总量的贡献,小于12 mm的降雨事件在年际比较稳定,很大程度上保证 了年蒸发量100 mm左右的基数值。这些因素使得年蒸发量的变异程度小于年降雨量的变异程度。由于降雨格局的年际变化会对蒸发量产生直接 的影响,降雨-蒸发模型可以相对有效地预测年度蒸发量,而用年降雨量预测年蒸发量误差较大。