Needles in haystacks: Estimating detection probability and occupancy of rare and cryptic snakes

The species most in need of conservation or management are often also the most difficult to monitor, because of their rarity, secretive habits, or both. To combat these challenges, presence/absence (site occupancy) models can be used to track species occupancy at landscape scales. However, quantitative knowledge of detection probability (which is almost always <1) is required to reliably estimate site occupancy. Here, we present a case study that combines detection probabilities and site occupancy modeling to monitor a notoriously secretive guild of animals, North American aquatic snakes. Specifically, we use program PRESENCE to estimate detection probability (p) and probability of site occupancy (ψ) for seven snake species in relationship to site covariates, to understand the proximate and ultimate factors that influence habitat suitability. We were able to estimate p (3–46%) and ψ (12–96%) for each species and calculate the amount of unsuccessful effort necessary to declare absence of each species with statistical confidence (5–63 visits; 150–1890 trap-nights). We documented considerable interspecific variation in p and ψ; one species (Nerodia fasciata) was widespread and highly detectable, while another (Agkistrodon piscivorus) had low detectability despite its wide distribution. Five other species were secretive, or restricted to specific habitat types, or both, illustrating that complex and sometimes counterintuitive relationships exist between capture rate and occupancy. Incorporating p and ψ is essential to the success of large-scale monitoring programs for elusive species.     

冬小麦生育中期农田水分与二氧化碳通量研究

以大兴实验站冬小麦为研究对象,采用涡度相关技术监测农田显热、潜热和二氧化碳通量,依据实测数据分析了冬小麦碳、热通量的变化特征,并研究各分量在抽穗期的关系和农田群体水分利用效率的变化规律。结果表明,①CO2通量的日变化成单谷型下凹曲线,极值出现在12:00左右,潜热和显热通量则呈单峰型上凸变化;②抽穗期,CO2通量与净辐射和潜热通量都呈现出极显著相关关系,而与显热通量在晴天成极显著相关关系;③作物农田水分利用效率在08:00—11:30较高,范围在0.02~0.04 g(CO2)/g(H2O)。     

干旱区降雨过程对土壤水分与温度变化影响研究

通过定点监测并结合统计方法分析了干湿交替时节一次降雨过程前后不同土地利用方式下土壤水分与土壤温度的动态变化特征.结果表明,降雨过程对土壤水分和土壤温度在时间动态变化和深度变化过程有着重要影响;降雨影响周期中土壤含水率在一定深度范围内有一次明显的升高过程,从降雨前到降雨后呈现低→高→低的变化趋势,其变异程度随着深度的增加...     

光照强度和土壤水分对辣椒品质和产量的影响

通过3个光照水平（自然光照—L1、遮阴30%—L2和遮阴70%—L3）及4个土壤水分水平（土壤相对含水率分别为田间持水率的40%～55%—W1、55%～70%—W2、70%～85%—W3、85%～100%—W4）试验,研究了其对辣椒品质及产量和水分利用效率（WUE）的影响。结果表明,①自然光及遮阴30%下,随着土壤含水...     

Impact of land-use type and harvesting on population structure of a non-timber forest product-providing tree in a semi-arid savanna, West Africa

Non-timber forest products (NTFPs) strongly contribute to livelihood security in the semi-arid tropics. Main factors determining the populations of NTFP-providing species are human activities. This study examined the impact of land-use, combined with rates and patterns of debarking and chopping on a NTFP-providing tree (Anogeissus leiocarpa) in Burkina Faso. We compared stands in a protected area (W National Park) with those of its surrounding communal area (fallows, croplands) in order to (i) obtain an indication on the status of the population, (ii) assess its harvesting tolerance, (iii) estimate the sustainability of present management, and (iv) derive which additional management strategies may foster its conservation. Our results reveal that the stands of A. leiocarpa are in healthy states in fallows and in the park. In croplands, the absence of saplings gives evidence of a declining population. Nearly all individuals of A. leiocarpa were harvested in croplands and fallows, while the number of harvested individuals in the park was negligible. Intensity of debarking and chopping was tree size-specific. The sprouting ability significantly increased with higher chopping intensity. We conclude that despite the land-use impact and the intense harvesting, stands of A. leiocarpa are still well preserved due to the species life history (fast growing and high sprouting) and due to indirect positive influences of human activities by providing better environmental conditions for its recruitment. Thus, the population of A. leiocarpa is not at risk to over-harvesting and land-use even though it is not protected.     

Effect of tile effluent on nutrient concentration and retention efficiency in agricultural drainage ditches

Tile drainage is a common water management practice in many agricultural landscapes in the Midwestern United States. Drainage ditches regularly receive water from agricultural fields through these tile drains. This field-scale study was conducted to determine the impact of tile discharge on ambient nutrient concentration, nutrient retention and transport in drainage ditches. Grab water samples were collected during three flow regimes for the determination of soluble phosphorus (SP), ammonium nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃-N) concentrations and their retention in three drainage ditches. Measured nutrient concentration indicated lower SP and NH₄⁺-N, and greater NO₃-N concentrations in tile effluents compared to the ditch water. Net uptake lengths were relatively long, especially for NO₃-N, indicating that nutrients were generally not assimilated efficiently in these drainage systems. Results also indicated that the study reaches were very dynamic showing alternating increases or decreases in nutrient concentration across the flow regimes. The drainage ditches appeared to be nutrient-rich streams that could potentially influence the quality of downstream waters.     

Long-term water balances in La Violada Irrigation District (Spain): II. Analysis of irrigation performance

The analysis of long-term irrigation performance series is a valuable tool to improve irrigation management and efficiency. This work focuses in the assessment of irrigation performance indices along years 1995-2008, and the cause-effect relationships with irrigation modernization works taking place in the 4000 ha surface-irrigated La Violada Irrigation District (VID). Irrigation management was poor, as shown by the low mean seasonal irrigation consumptive use coefficient (ICUC = 51%) and the high relative water deficit (RWD = 20%) and drainage fraction (DRF = 54%). April had the poorest irrigation performance because corn (with low water demand in this month) was irrigated to promote its emergence, whereas winter grains (with high water demands in this month) were not fully irrigated in water-scarce years. Corn, highly sensitive to water stress, was the crop with best irrigation performance because it was preferentially irrigated to minimize yield losses. The construction of a new elevated canal that decreased seepage and drainage fractions, the entrance in operation of six internal reservoirs that would increase irrigation scheduling flexibility, and the on-going transformation from surface to sprinkler irrigation systems are critical changes in VID that should lead to improved ICUC, lower RWD and lower DRF. The implications of these modernization works on the conservation of water quantity and quality within and outside VID is further discussed.     

Impact of upstream changes in rain-fed agriculture on downstream flow in a semi-arid basin

The downstream impacts of increasing water consumption in the upstream rain-fed areas of the Karkheh Basin, Iran are simulated using the semi-distributed SWAT model. Three scenarios are tested at subbasin and basin levels: converting rain-fed areas to irrigation agriculture (S1), improving soil water availability through rainwater harvesting (S2), and a combination of both (S3). The results of these scenarios were compared against the baseline period 1988-2000. The S1 scenario shows a 10% reduction in mean annual flow at the basin level, varying from 8-15% across the subbasins. The reductions in mean monthly flows are in the range of 1-56% at the basin level, with June witnessing the highest flow reduction. Flow reductions are comparatively higher in the upstream parts of the basin, as a result of a relatively higher potential of developing rain-fed areas coupled with comparatively lower amount of available runoff. The impacts of S2 are generally small with reductions of 2-5% and 1-9% in mean annual and mean monthly flows, respectively. The results of S3 are in general similar to those of S1. Although the estimated annual flow reductions remain well within the available water resources development potential, measures needs to be taken to avoid excessive flow reductions in May, June and July. It is recommended that only a limited agricultural area should be converted from rain-fed to irrigated agriculture (about 0.1 million ha), and should practice supplementary irrigation. The supplies should also be augmented through developing additional water storage. Adopting such measures is extremely important for the upper subbasins Gamasiab and Qarasou where comparatively higher flow reductions were estimated.     

Yield and seasonal water productivity of sunflower as affected by tillage and cropping systems under dryland conditions in the Limpopo Province of South Africa

Sustainable food production in semi-arid tropical countries can be achieved through efficient utilization of rainwater. A field experiment to assess the grain yield, seasonal water use (WU), water use efficiency (WUE) and precipitation use efficiency (PUE) of sunflower (Helianthus annuus L.) intercropped with cowpea (Vigna unguiculata L.) on two tillage systems was conducted during the 2007/2008 and 2008/2009 cropping seasons at the University of Venda (22°58′ S, 30°26′ E at 596 m above sea level). The experiment was configured as a 2 × 2 × 2 factorial design with three replications. The tillage treatments were conventional tillage (CT) (control) and in-field rainwater harvesting (IRWH) system. The IRWH is a special crop production technique that promotes runoff on 2.0-m wide no-till strip between crop rows and collects the runoff water in basins where it infiltrates into the soil profile. The treatments in the cropping system (CS) consisted of a sole crop (sunflower or cowpea) and an intercrop (sunflower × cowpea). Results of the experiment revealed that IRWH led to a significant (P < 0.05) increase in sunflower grain yield in the second season but cowpea grain yield was not influenced by tillage systems. IRWH resulted in significantly higher WU, WUE and PUE of both crops compared to CT system in the second season. The CS had significant effects on sunflower grain yield in both seasons but none on the cowpea grain yield. WU was significantly higher in intercrops than in sole cowpea and sole sunflower in the first and second season, respectively. WUE and PUE were significantly greater in sole sunflower than in the intercrops but less in the sole cowpea than in the intercrops.     

基于激光激发叶绿素荧光分析的叶片水分利用效率模型

以无损检测为前提,采用激光为激发光源,对杨树活体叶片进行荧光光谱采集,对采集到的光谱数据进行处理分析得到水分利用效率的荧光光谱敏感波段,建立基于叶片温度修正下的植物水分利用效率与荧光光谱的数学回归模型,模型的复相关系数R2=0.975.并对建立的数学回归模型进行效果检验,相关系数r=0.8746,模型的检测效果较好.