模拟降雨下喀斯特坡耕地土壤养分输出机制

喀斯特区坡耕地水土及养分流失不仅是该区土地质量退化、土地生产力衰退主要原因,同时也是该区地下水质污染的重要因素。为揭示喀斯特坡耕地地表和地下二元空间结构下的土壤养分流失机制,以喀斯特坡耕地为研究对象,通过模拟其地表微地貌及地下孔(裂)隙构造特征,采用人工模拟降雨试验研究不同雨强下喀斯特坡耕地地表及地下水土及其氮、磷、钾流失特征。结果表明:(1)小雨强(50mm/h)和中雨强下(70mm/h),喀斯特坡耕地坡面产流主要以地下产流为主;大雨强下(90mm/h),地表径流高于地下径流;产沙方式则表现为由小雨的地表和地下产沙并重到中大雨强的地表产沙为主的一个转变过程。(2)在降雨侵蚀过程中,径流各养分输出浓度均表现出一定的初期冲刷效应,受土壤吸附作用影响,雨强对全钾(TK)和全氮(TN)的影响较全磷(TP)明显。(3)地表径流、地表泥沙和总泥沙各养分输出负荷均随雨强增大而增加,坡面径流泥沙总的TK输出负荷以泥沙为主,而TN和TP输出负荷则以径流为主;TP和TN在径流的输出负荷上以地下径流输出为主(其中TP地表负荷比在11.6%—46.2%,TN在7.0%—48.5%之间),而TK则以二者并重(地表负荷比在43.5%—57.0%之间);各养分在泥沙的输出负荷上则均以地表泥沙流失为主,其负荷比均在54.5%以上。研究结果可为喀斯特区坡耕地水土流失及养分流失的源头控制提供基本参数和科学依据。     

Effect of Soil Slope on the Appearance of Mycobacterium avium subsp. paratuberculosis in Water Running off Grassland Soil after Application of Contaminated Slurry

The study assessed the effect of soil slope on Mycobacterium avium subsp. paratuberculosis transport into rainwater runoff from agricultural soil after application of M. avium subsp. paratuberculosis-contaminated slurry. Under field conditions, 24 plots of undisturbed loamy soil 1 by 2 m² were placed on platforms. Twelve plots were used for water runoff: 6 plots at a 3% slope and 6 plots at a 15% slope. Half of the plots of each slope were treated with M. avium subsp. paratuberculosis-contaminated slurry, and half were not treated. Using the same experimental design, 12 plots were established for soil sampling on a monthly basis using the same spiked slurry application and soil slopes. Runoff following natural rainfall was collected and analyzed for M. avium subsp. paratuberculosis, coliforms, and turbidity. M. avium subsp. paratuberculosis was detected in runoff from all plots treated with contaminated slurry and one control plot. A higher slope (15%) increased the likelihood of M. avium subsp. paratuberculosis detection but did not affect the likelihood of finding coliforms. Daily rainfall increased the likelihood that runoff would have coliforms and the coliform concentration, but it decreased the M. avium subsp. paratuberculosis concentration in the runoff. When there was no runoff, rain was associated with increased M. avium subsp. paratuberculosis concentrations. Coliform counts in runoff were related to runoff turbidity. M. avium subsp. paratuberculosis presence/absence, however, was related to turbidity. Study duration decreased bacterial detection and concentration. These findings demonstrate the high likelihood that M. avium subsp. paratuberculosis in slurry spread on pastures will contaminate water runoff, particularly during seasons with high rainfall. M. avium subsp. paratuberculosis contamination of water has potential consequences for both animal and human health.     

Soil Organic Carbon Loss and Selective Transportation under Field Simulated Rainfall Events

The study on the lateral movement of soil organic carbon (SOC) during soil erosion can improve the understanding of global carbon budget. Simulated rainfall experiments on small field plots were conducted to investigate the SOC lateral movement under different rainfall intensities and tillage practices. Two rainfall intensities (High intensity (HI) and Low intensity (LI)) and two tillage practices (No tillage (NT) and Conventional tillage (CT)) were maintained on three plots (2 m width × 5 m length): HI-NT, LI-NT and LI-CT. The rainfall lasted 60 minutes after the runoff generated, the sediment yield and runoff volume were measured and sampled at 6-min intervals. SOC concentration of sediment and runoff as well as the sediment particle size distribution were measured. The results showed that most of the eroded organic carbon (OC) was lost in form of sediment-bound organic carbon in all events. The amount of lost SOC in LI-NT event was 12.76 times greater than that in LI-CT event, whereas this measure in HI-NT event was 3.25 times greater than that in LI-NT event. These results suggest that conventional tillage as well as lower rainfall intensity can reduce the amount of lost SOC during short-term soil erosion. Meanwhile, the eroded sediment in all events was enriched in OC, and higher enrichment ratio of OC (ERoc) in sediment was observed in LI events than that in HI event, whereas similar ERoc curves were found in LI-CT and LI-NT events. Furthermore, significant correlations between ERoc and different size sediment particles were only observed in HI-NT event. This indicates that the enrichment of OC is dependent on the erosion process, and the specific enrichment mechanisms with respect to different erosion processes should be studied in future.     

水蚀风蚀交错区退耕坡面植被利用对产流产沙的影响

为有效利用水蚀风蚀交错区退耕封育坡面植被,确定合理的植被利用强度非常必要.本试验选取黄土高原水蚀风蚀交错区典型小流域——六道沟小流域为试验区,在多年退耕封育坡面布设径流小区,通过人工模拟降雨试验,研究植被地上部分在不同利用强度下各坡度(10°、20°和30°)坡面产流、产沙变化特征,以确定合理的利用强度. 结果表明: 次降雨过程中径流速率大体可分为两个阶段:初期迅速增长阶段和中后期增长变缓或趋于准稳定阶段.侵蚀速率的变化趋势因坡度的不同而略有差异.利用强度对产流量有显著影响,产流量随利用强度的加强而增加.坡度对侵蚀量影响显著,侵蚀量表现为20°坡面＞30°坡面＞10°坡面.以植被地上部分未利用小区为对照,相对增水量和相对增沙量均随利用强度加强而增加.结合降雨资料推测,退耕15年左右坡面植被地上部分盖度达到25%时,坡面年土壤侵蚀量基本低于容许土壤流失量.应重视该区20°坡面植被的恢复治理工作.     

腾格里沙漠东南缘沙质草地灌丛化对地表径流及氮流失的影响

以腾格里沙漠东南缘沙质草地和灌丛生境为研究对象,采用人工模拟降雨实验对草地样方、灌丛间裸地样方及含灌丛斑块样方的产流及氮流失过程进行观测,揭示了地表径流及其引起的氮流失对沙质草地灌丛化的响应.结果表明:(1)草地样方出现表面积水和地表径流的时间及开始产流需要的降雨量均大于含灌丛斑块样方和灌丛间裸地样方,裸地样方最小;灌丛生境径流系数为34.46％,显著小于裸地样方,大于含灌丛样方,产流量是沙质草地生境的2.26倍;表明灌木入侵造成的植被盖度下降引起了土壤水分入渗率的减小和地表产流的增加.(2)含灌丛样方单位体积径流含氮量瞬时值大于裸地样方,小于草地样方,三类样方瞬时值与单位时间径流量均呈线性负相关;草地样方单位时间氮流失量略小于含灌丛样方,两者均显著小于灌丛间裸地样方;灌丛生境氮流失总量为0.23 g/m2,是草地生境的2.09倍,灌丛和草地生境单位体积径流含氮量总体平均值分别为0.011 g/L、0.012 g/L;表明沙质草地灌丛化引起了养分流失的显著增加.     

Impacts of Biological Soil Crust Disturbance and Composition on C and N Loss from Water Erosion

In this study, we conducted rainfall simulation experiments in a cool desert ecosystem to examine the role of biological soil crust disturbance and composition on dissolved and sediment C and N losses. We compared runoff and sediment C and N losses from intact late-successional dark cyanolichen crusts (intact) to both trampled dark crusts (trampled) and dark crusts where the top 1 cm of the soil surface was removed (scraped). In a second experiment, we compared C and N losses in runoff and sediments in early-successional light cyanobacterial crusts (light) to that of intact late-successional dark cyanolichen crusts (dark). A relatively high rainfall intensity of approximately 38 mm per 10-min period was used to ensure that at least some runoff was generated from all plots. Losses of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and ammonium (NH₄⁺ ) were significantly higher from trampled plots as compared to scraped and intact plots. Sediment C and N losses, which made up more than 98% of total nutrient losses in all treatments, were more than 4-fold higher from trampled plots relative to intact plots (sediment C g/m², intact = 0.74, trampled = 3.47; sediment N g/m², intact = 0.06, trampled = 0.28). In light crusts, DOC loss was higher relative to dark crusts, but no differences were observed in dissolved N. Higher sediment loss in light crusts relative to dark crusts resulted in 5-fold higher loss of sediment-bound C and N. Total C flux (sediment + dissolved) was on the order of 0.9 and 7.9 g/m² for dark and light crusts, respectively. Sediment N concentration in the first minutes after runoff from light crusts was 3-fold higher than the percent N of the top 1 cm of soil, suggesting that even short-term runoff events may have a high potential for N loss due to the movement of sediments highly enriched in N. Total N loss from dark crusts was an order of magnitude lower than light crusts (dark = 0.06 g N/m², light = 0.63 g/m²). Overall, our results from the small plot scale (0.5 m²) suggest that C and N losses are much lower from intact late-successional cyanolichen crusts as compared to recently disturbed or early-successional light cyanobacterial crusts.     

The Effect of Leaf Litter Cover on Surface Runoff and Soil Erosion in Northern China

The role of leaf litter in hydrological processes and soil erosion of forest ecosystems is poorly understood. A field experiment was conducted under simulated rainfall in runoff plots with a slope of 10%. Two common types of litter in North China (from Quercus variabilis, representing broadleaf litter, and Pinus tabulaeformis, representing needle leaf litter), four amounts of litter, and five rainfall intensities were tested. Results revealed that the litter reduced runoff and delayed the beginning of runoff, but significantly reduced soil loss (p<0.05). Average runoff yield was 29.5% and 31.3% less than bare-soil plot, and for Q. variabilis and P. tabulaeformis, respectively, and average sediment yield was 85.1% and 79.9% lower. Rainfall intensity significantly affected runoff (R = 0.99, p<0.05), and the efficiency in runoff reduction by litter decreased considerably. Runoff yield and the runoff coefficient increased dramatically by 72.9 and 5.4 times, respectively. The period of time before runoff appeared decreased approximately 96.7% when rainfall intensity increased from 5.7 to 75.6 mm h⁻¹. Broadleaf and needle leaf litter showed similarly relevant effects on runoff and soil erosion control, since no significant differences (p≤0.05) were observed in runoff and sediment variables between two litter-covered plots. In contrast, litter mass was probably not a main factor in determining runoff and sediment because a significant correlation was found only with sediment in Q. variabilis litter plot. Finally, runoff yield was significantly correlated (p<0.05) with sediment yield. These results suggest that the protective role of leaf litter in runoff and erosion processes was crucial, and both rainfall intensity and litter characteristics had an impact on these processes.     

喀斯特坡面生物结皮发育特征及其对土壤水分入渗的影响

作为地表植被恢复的先锋种群和景观的重要组成部分,生物土壤结皮(BSCs)对地表过程具有重要影响。为探明喀斯特地区BSCs发育特征及其对土壤水分入渗的影响,本研究选取喀斯特代表性坡面开展了BSCs实地调查和人工模拟降雨试验,探究了BSCs覆盖土壤的水分入渗过程,试验设计了5个BSCs盖度水平(0、28%、40%、70%、97%)和2个雨强(42和132 mm·h^-1)。结果表明: 在不同土地利用条件下,BSCs发育水平存在显著差异,但在同一土地利用条件下,BSCs发育水平沿坡面的空间变化规律不明显。与裸地相比,地表发育BSCs可使地表粗糙度增大,显著延长初始产流时间,促进土壤水分入渗。在小雨(42 mm·h^-1)和强降雨(132 mm·h^-1)下,BSCs覆盖小区初渗速率分别为裸地小区的1.7～1.9和1.2～1.9倍,平均入渗速率分别为裸地小区的2.5～3.0和1.4～3.3倍。在试验雨强下,BSCs盖度与初始产流时间均呈显著正相关,BSCs促进水分入渗的临界盖度为65%～70%,在强降雨条件下,BSCs对地表径流的阻滞作用有所削弱。Horton模型对喀斯特坡面BSCs覆盖下土壤水分入渗过程模拟结果最优,其次为Kostiakov模型和Philip模型。综上,喀斯特坡面BSCs发育的空间变异程度高,对水分入渗过程影响显著。     

Dispersion and Transport of Cryptosporidium Oocysts from Fecal Pats under Simulated Rainfall Events

The dispersion and initial transport of Cryptosporidium oocysts from fecal pats were investigated during artificial rainfall events on intact soil blocks (1,500 by 900 by 300 mm). Rainfall events of 55 mm h⁻¹ for 30 min and 25 mm h⁻¹ for 180 min were applied to soil plots with artificial fecal pats seeded with approximately 10⁷ oocysts. The soil plots were divided in two, with one side devoid of vegetation and the other left with natural vegetation cover. Each combination of event intensity and duration, vegetation status, and degree of slope (5° and 10°) was evaluated twice. Generally, a fivefold increase (P < 0.05) in runoff volume was generated on bare soil compared to vegetated soil, and significantly more infiltration, although highly variable, occurred through the vegetated soil blocks (P < 0.05). Runoff volume, event conditions (intensity and duration), vegetation status, degree of slope, and their interactions significantly affected the load of oocysts in the runoff. Surface runoff transported from 10^0.2 oocysts from vegetated loam soil (25-mm h⁻¹, 180-min event on 10° slope) to up to 10^4.5 oocysts from unvegetated soil (55-mm h⁻¹, 30-min event on 10° slope) over a 1-m distance. Surface soil samples downhill of the fecal pat contained significantly higher concentrations of oocysts on devegetated blocks than on vegetated blocks. Based on these results, there is a need to account for surface soil vegetation coverage as well as slope and rainfall runoff in future assessments of Cryptosporidium transport and when managing pathogen loads from stock grazing near streams within drinking water watersheds.     

Dispersion and transport of Cryptosporidium Oocysts from fecal pats under simulated rainfall events

The dispersion and initial transport of Cryptosporidium oocysts from fecal pats were investigated during artificial rainfall events on intact soil blocks (1,500 by 900 by 300 mm). Rainfall events of 55 mm h(-1) for 30 min and 25 mm h(-1) for 180 min were applied to soil plots with artificial fecal pats seeded with approximately 10(7) oocysts. The soil plots were divided in two, with one side devoid of vegetation and the other left with natural vegetation cover. Each combination of event intensity and duration, vegetation status, and degree of slope (5 degrees and 10 degrees ) was evaluated twice. Generally, a fivefold increase (P < 0.05) in runoff volume was generated on bare soil compared to vegetated soil, and significantly more infiltration, although highly variable, occurred through the vegetated soil blocks (P < 0.05). Runoff volume, event conditions (intensity and duration), vegetation status, degree of slope, and their interactions significantly affected the load of oocysts in the runoff. Surface runoff transported from 10(0.2) oocysts from vegetated loam soil (25-mm h(-1), 180-min event on 10 degrees slope) to up to 10(4.5) oocysts from unvegetated soil (55-mm h(-1), 30-min event on 10 degrees slope) over a 1-m distance. Surface soil samples downhill of the fecal pat contained significantly higher concentrations of oocysts on devegetated blocks than on vegetated blocks. Based on these results, there is a need to account for surface soil vegetation coverage as well as slope and rainfall runoff in future assessments of Cryptosporidium transport and when managing pathogen loads from stock grazing near streams within drinking water watersheds.     

模拟降雨条件下生物结皮坡面产流产沙对雨强的响应

生物结皮是黄土丘陵区退耕地广泛存在的地被物.本研究通过人工模拟降雨试验分析了雨强对生物结皮坡面产流产沙的影响.结果表明: 生物结皮坡面产流产沙随降雨历时的延长先增加、10~18 min趋于平稳.相对于裸土坡面,生物结皮显著延长了坡面初始产流时间,抑制了坡面产流产沙,可降低21%~78%的坡面径流量和77%~95%的产沙量.雨强主要通过影响生物结皮坡面径流而影响其产沙.随着雨强的增加,生物结皮坡面产流产沙与雨强的相关性出现了由不显著相关向显著相关的转折,雨强＞1.5 mm·min^-1时,生物结皮坡面的减流减沙作用随着雨强的增加而降低.本研究结果为降雨条件下生物结皮坡面产流产沙过程的模型模拟奠定了基础.     

USLE/RUSLE模型中植被因子变化特征及其影响因素

植被因子是USLE/RUSLE模型中最重要的影响因子,其数值变化特征及其影响因素广受关注。以广东省五华县源坑水小流域2011—2013年的径流小区次降雨水沙观测数据为基础,分析了径流小区C值在不同时间尺度的变化特征及其受降雨、植被类型的影响。研究表明:(1)不同时段间C值存在一定波动,其中旱季的C值均大于雨季,夏秋两季的C值较大,且较为接近。各径流小区的C值普遍存在11、8、7月较大,6、5、1月较小的现象,且草本植物C值受植被覆盖度影响较大。(2)降雨量与径流小区C值呈正相关关系,桉树、松树、糖蜜草径流小区C值与次降雨量、各降雨量区间平均值的相关系数分别为0.360**、0.349**、0.291**,0.912*、0.909*、0.822,相较于草本植物,木本植物的C值受降雨影响更大,仅以植被盖度衡量C值有待商榷。(3)相较裸土小区,桉树、松树、糖蜜草小区2011—2013年的土壤流失减幅分别为14.2%、21.5%、23.2%,其C值分别为0.814、0.748、0.772,3种植物中糖蜜草与松树均具有相对较好的水保效益,桉树的水保效益稍逊。     

Nutrient losses in runoff from grasslandand shrubland habitats in southern New Mexico: II. Field plots

Losses of dissolved nutrients (N, P, K, Ca, Mg, Na,Cl, and SO₄) in runoff were measured on grasslandand shrubland plots in the Chihuahuan desert ofsouthern New Mexico. Runoff began at a lowerthreshold of rainfall in shrublands than ingrasslands, and the runoff coefficient averaged 18.6%in shrubland plots over a 7-year period. In contrast,grassland plots lost 5.0 to 6.3% of incidentprecipitation in runoff during a 5.5-year period. Nutrient losses from shrubland plots were greater thanfrom grassland plots, with nitrogen losses averaging0.33 kg ha^–1 yr^–1 vs0.15 kg ha^–1 yr^–1, respectively, during a 3-year period. Thegreater nutrient losses in shrublands were due tohigher runoff, rather than higher nutrientconcentrations in runoff. In spite of these nutrientlosses in runoff, all plots showed net accumulationsof most elements due to inputs from atmosphericdeposition. Therefore, loss of soil nutrients byhillslope runoff cannot, by itself, account for thedepletion of soil fertility associated withdesertification in the Chihuahuan desert.     

绿色屋面降雨径流水质及消减污染负荷研究

2011年5月至11月对12场降雨时段的屋面径流和干湿沉降进行采样监测,比较了屋面径流(绿色屋面和沥青屋面)、干湿总沉降和降雨中污染物的浓度和污染负荷,并运用多元统计方法分析了降雨特征对绿色屋面径流水质的影响。结果表明,从径流水质层面上分析,绿色屋面是总悬浮物(TSS)的汇,对p H值有较好的中和作用,对于总磷(TP)、溶解态铜(DCu)和溶解态锌(DZn)是非源非汇,是电导率(EC)、总氮(TN)、氨态氮(NH+4-N)、硝态氮(NO-3-N)、化学需氧量(COD)、5日生化需氧量(BOD5)和溶解态铅(DPb)的源;从污染负荷的角度分析,绿色屋面是NH+4-N、TSS和BOD5的汇,对于TN、DPb、DCu、DZn、TP和COD是非源非汇,是NO-3-N的源;与控制屋面相比,绿色屋面可以消减TSS、TP、BOD5、COD、NH+4-N、DZn和DPb的污染负荷,分别消减了90.53%、49.38%、41.31%、36.48%、35.45%、28.27%和14.20%;但是增加了NO-3-N和TN的污染负荷,分别增加了821.02%和275.48%;绿色屋面径流污染物的浓度与降雨量、降雨历时和降雨强度呈负相关关系,而与降雨间隔呈正相关关系。研究结果为绿色屋面的科学设计及正确评价绿色屋面对径流水质的影响提供依据。     

紫色土流域次降雨条件下碳、磷非点源输出过程及其流失负荷

通过对位于川中丘陵区的紫色土流域在次降雨过程中溶解态有机碳(DOC)和不同形态磷素的输出进行动态监测,分析降雨过程DOC和P输出负荷,并探讨降雨径流对C、P迁移和水环境的影响。研究结果表明:(1)3次降雨共产生地表径流20399.8 m3,碳、磷输出负荷为83.19 kg和5.1 kg,次降雨过程径流C、P输出动态差异较大,其中径流DOC浓度随降雨历时的延长而降低,随后迅速升高,在达峰值后逐渐降低并趋于平稳。(2)降雨径流过程中磷素迁移主要以颗粒态(PP)为主,磷酸盐(PO3-4-P)是径流溶解态总磷(DTP)的主要存在形式,3次降雨PP输出负荷分别为1167.491、1891.331、984.74 g;PO3-4-P输出负荷分别为108.37、338.8、167.79 g。(3)3次降雨径流DOC输出浓度分别为3.37、4.77、6.97 mg/L,总磷(Total phosphorus,TP)输出浓度分别为0.11、0.43、0.74 mg/L;次降雨径流C/P比分别为192、48和42.1,相比于暴雨而言,大雨和中雨带来的水质问题需引起关注。     

Design and Construction of an Urban Runoff Research Facility

As the urban population increases, so does the area of irrigated urban landscape. Summer water use in urban areas can be 2-3x winter base line water use due to increased demand for landscape irrigation. Improper irrigation practices and large rainfall events can result in runoff from urban landscapes which has potential to carry nutrients and sediments into local streams and lakes where they may contribute to eutrophication. A 1,000 m² facility was constructed which consists of 24 individual 33.6 m² field plots, each equipped for measuring total runoff volumes with time and collection of runoff subsamples at selected intervals for quantification of chemical constituents in the runoff water from simulated urban landscapes. Runoff volumes from the first and second trials had coefficient of variability (CV) values of 38.2 and 28.7%, respectively. CV values for runoff pH, EC, and Na concentration for both trials were all under 10%. Concentrations of DOC, TDN, DON, PO₄-P, K⁺, Mg²⁺, and Ca²⁺ had CV values less than 50% in both trials. Overall, the results of testing performed after sod installation at the facility indicated good uniformity between plots for runoff volumes and chemical constituents. The large plot size is sufficient to include much of the natural variability and therefore provides better simulation of urban landscape ecosystems.     

Assessment of Tannery Waste in Semi-arid Soils Under a Simulated Rainfall System

The use of tannery sludge in arid soils could be promising due to the high content of organic carbon and nitrogen. However, tannery waste also contains high amounts of Cr and salts that could leach into drainage water in response to rainfall. In order to study the effects of two tannery wastes as organic fertilizers on two types of semi-arid soils, simulated rainfall experiments were carried out. Soils collected from under and outside a mesquite tree canopy were amended with fleshing waste and/or tannery sludge and incubated 0 to 6 months prior to being subjected to simulated rainfall. The parameters measured were: infiltration, runoff, soil and Cr losses, and NH₄⁺-N and NO₃^?-N released after a rainfall event. Results showed that fleshing waste added to soils from outside the canopy tree was the most effective treatment for decreasing runoff, soil losses, and Cr, NH₄⁺-N and NO₃^?-N loss in runoff and infiltration, in general. However, the same treatment had the opposite results for soil under the canopy. These results indicate that the types of waste and soil must be taken into consideration when attempting to improve physical and chemical characteristics of semi-arid soils. Thus, the use of tannery waste represents a potential hazard, not only causing soil erosion but also Cr contamination in adjacent sites and aquifers.     

When Wet Gets Wetter: Decoupling of Moisture, Redox Biogeochemistry, and Greenhouse Gas Fluxes in a Humid Tropical Forest Soil

Upland humid tropical forest soils are often characterized by fluctuating redox dynamics that vary temporally and spatially across the landscape. An increase in the frequency and intensity of rainfall events with climate change is likely to affect soil redox reactions that control the production and emissions of greenhouse gases. We used a 24-day rainfall manipulation experiment to evaluate temporal and spatial trends of surface soil (0–20 cm) redox-active chemical species and greenhouse gas fluxes in the Luquillo Experimental Forest, Puerto Rico. Treatments consisted of a high rainfall simulation (60 mm day^?1), a fluctuating rainfall regime, and a control. Water addition generated high temporal and spatial variation in soil moisture (0.3–0.6 m³ m^?3), but had no significant effect on soil oxygen (O₂) concentrations. Extractable nitrate (NO₃ ^?) concentrations decreased with daily water additions and reduced iron (Fe(II)) concentrations increased towards the end of the experiment. Overall, redox indicators displayed a weak, non-deterministic, nonlinear relationship with soil moisture. High concentrations of Fe(II) and manganese (Mn) were present even where moisture was relatively low, and net Mn reduction occurred in all plots including controls. Mean CO₂ fluxes were best explained by soil C concentrations and a composite redox indicator, and not water addition. Several plots were CH₄ sources irrespective of water addition, whereas other plots oscillated between weak CH₄ sources and sinks. Fluxes of N₂O were highest in control plots and were consistently low in water-addition plots. Together, these data suggest (1) a relative decoupling between soil moisture and redox processes at our spatial and temporal scales of measurement, (2) the co-occurrence of aerobic and anaerobic biogeochemical processes in well-drained surface soils, and (3) an absence of threshold effects from sustained precipitation on redox reactions over the scale of weeks. Our data suggest a need to re-evaluate representations of moisture in biogeochemical models.     

赤红壤植蔗坡地坡面径流及溶解态氮磷流失特征

为探究南方高强度、高频次降雨下赤红壤区坡耕地土壤侵蚀及氮磷养分流失的特征,基于野外径流小区原位观测试验,通过测定自然降雨下赤红壤植蔗坡地坡面径流和溶解态氮磷流失量,探讨自然降雨下甘蔗种植对赤红壤坡面径流及溶解态氮磷流失的影响。结果表明：(1)2019年和2020年,径流量分别为1111.3 m~3/hm~2和3269.4 m~3/hm~2,硝态氮(NO~-₃-N)流失量分别为1.39 kg/hm~2和15.60 kg/hm~2,铵态氮(NH~+₄-N)流失量分别为0.37 kg/hm~2和1.02 kg/hm~2,可溶性磷流失量分别为0.20 kg/hm~2和0.27 kg/hm~2。2019年和2020年植蔗坡地径流及溶解态氮磷流失量均集中在6月份,占流失总量的45%以上,硝态氮(NO~-₃-N)是径流氮素流失的主要形式,占79%以上。此外,2019年和2020年5月至8月,侵蚀性降雨场次分别为18次和23次,侵蚀性降雨量分别为407.8 mm和668.0 mm。(2)不同侵蚀性降雨条件下,植蔗坡地溶解态氮磷流失量及其...     

Water flux and energy use in wild house mice (Mus domesticus) and the impact of seasonal aridity on breeding and population levels

Summary Water turnover rate (WTR), urine concentration and field metabolic rate (FMR) were examined in house mice, Mus domesticus, permanently inhabiting roadside verge areas and seasonally invading crops in semi-arid wheatlands in South Australia. FMR was approximately proportional to body mass^0.5 and mean values varied from 4.8 ml CO₂ g^–1h^–1 (2.9 kJ g^–1d^–1) in autumn and winter, to 7.0 ml CO₂ g^–1h^–1 (4.2 kJ g^–1d^–1) in maturing crops during spring. WTR was independent of body mass, indicating that larger mice were selecting a diet containing moister foods. WTR was low in summer and high in winter, and in mice from crops varied from 165 ml l^–1 body water d^–1 (122 ml kg^–1d^–1) to 1000 ml l^–1d^–1 (725 ml kg^–1d^–1). Seasonal changes in WTR were less extreme on the roadside, where a greater diversity of food was available. In the crops, breeding occurred throughout summer during two of three years, but the population increased only in the one summer when mice had marginally higher WTR. On the roadside breeding and population growth were continuous during summer, except in a drought year. Avcrage urine concentration was inversely related to WTR, and varied from 2.0 to 4.8 Osm l^–1. The data indicate that the water conserving abilities of mice equal those of many desert rodents. The water conserving abilities of mice living in crops during summer were fully extended, and in some years aridity limited breeding success and population levels. The degree of moisture stress to which mice are exposed during summer appears to depend not only on rainfall but also on other factors such as availability of food and shelter, and the level of weed infestation in crops.