Effects of throughfall and litterfall manipulation on concentrations of methylmercury and mercury in forest‐floor percolates

The forest floor was shown to be an effective sink of atmospherically deposited methylmercury (MeHg) but less for total mercury (Hg_total). We studied factors controlling the difference in dynamics of MeHg and Hg_total in the forest floor by doubling the throughfall input and manipulating aboveground litter inputs (litter removal and doubling litter addition) in the snow‐free period in a Norway spruce forest in NE Bavaria, Germany, for 14 weeks. The MeHg concentrations in the forest‐floor percolates were not affected by any of the manipulation and ranged between 0.03 (Oa horizon) and 0.11 (Oi horizon) ng Hg L^–1. The Hg_total concentrations were largest in the Oa horizon (24 ng Hg L^–1) and increased under double litterfall (statistically significant in the Oi horizon). Similarly, concentrations of dissolved organic C (DOC) increased after doubling of litterfall. The concentrations of Hg_total and DOC correlated significantly in forest‐floor percolates from all plots. However, we did not find any effect of DOC on MeHg concentrations. The difference in the coupling of Hg_total and MeHg to DOC might be one reason for the differences in the mobility of Hg species in forest floors with a lower mobility of MeHg not controlled by DOC.     

Chemical input/output balance for a moderately polluted forest catchment in southern Poland

A four-year study in a forest catchment exposed to a moderate level of anthropogenic pollution indicated heavy accumulation of hydrogen (H⁺), manganese (Mn), zinc (Zn), copper (Cu) and lead (Pb) in the ecosystem and phosphorous (P), potassium (K) and cadmium (Cd) to a lesser extent. Nitrogen, which is also accumulated, is leached mainly as NO₃ ^–, even though the input is dominated by NH₄ ⁺. Magnesium (Mg), calcium (Ca) and sodium (Na) are leached from the catchment, presumably due to intensive weathering processes in deeper layers of mineral soil. Chloride ion (Cl^–) is also lost from the ecosystem. The output of sulphate (SO₄ ^2–) with stream water exceeds its input only slightly. Although it appears that the catchment as a whole has a large buffering capacity (average stream water pH=7.43, rainfall pH=4.33), the upper biologically active soil layers are probably more susceptible to acidification and pollution. With constant accumulation of H⁺ and heavy metal ions this may lead to degradation of forest health.     

Mulching mode and planting density affect canopy interception loss of rainfall and water use efficiency of dryland maize on the Loess Plateau of China

High and efficient use of limited rainwater resources is of crucial importance for the crop production in arid and semi-arid areas. To investigate the effects of different soil and crop management practices(i.e., mulching mode treatments: flat cultivation with non-mulching, flat cultivation with straw mulching, plastic-covered ridge with bare furrow and plastic-covered ridge with straw-covered furrow; and planting density treatments: low planting density of 45,000 plants/hm~2, medium planting density of 67,500 plants/hm~2 and high planting density of 90,000 plants/hm~2) on rainfall partitioning by dryland maize canopy, especially the resulted net rainfall input beneath the maize canopy, we measured the gross rainfall, throughfall and stemflow at different growth stages of dryland maize in 2015 and 2016 on the Loess Plateau of China. The canopy interception loss was estimated by the water balance method. Soil water storage, leaf area index, grain yield(as well as it components) and water use efficiency of dryland maize were measured or calculated. Results showed that the cumulative throughfall, cumulative stemflow and cumulative canopy interception loss during the whole growing season accounted for 42.3%–77.5%, 15.1%–36.3% and 7.4%–21.4% of the total gross rainfall under different treatments, respectively. Soil mulching could promote the growth and development of dryland maize and enhance the capability of stemflow production and canopy interception loss, thereby increasing the relative stemflow and relative canopy interception loss and reducing the relative throughfall. The relative stemflow and relative canopy interception loss generally increased with increasing planting density, while the relative throughfall decreased with increasing planting density. During the two experimental years, mulching mode had no significant influence on net rainfall due to the compensation between throughfall and stemflow, whereas planting density significantly affected net rainfall. The highest grain yield and water use efficiency of dryland maize were obtained under the combination of medium planting density of 67,500 plants/hm~2 and mulching mode of plastic-covered ridge with straw-covered furrow. Soil mulching can reduce soil evaporation and retain more soil water for dryland maize without reducing the net rainfall input beneath the maize canopy, which may alleviate the contradiction between high soil water consumption and insufficient rainfall input of the soil. In conclusion, the application of medium planting density(67,500 plants/hm~2) under plastic-covered ridge with bare furrow is recommended for increasing dryland maize production on the Loess Plateau of China.     

枣树冠层改变降雨截留历时过程同位素和化学特征

基于冠层截留历时过程降雨同位素和化学特征的研究很少,但却有助于揭示冠层截留特征及其对降雨同位素和化学特征的影响,于2016年9月17-18日和10月22-23日对黄土高原丘陵沟壑区的2场降雨事件林外降雨、穿透降雨和树干茎流历时过程进行连续采样及室内分析,研究降雨过程中矮化枣树冠层截留对降雨同位素和化学成分的改变、2016年7-10月4棵矮化枣树树干茎流以及林外降雨取样测定,分析矮化枣树形态特征对其树干茎流率的影响。结果表明:(1)矮化枣树树干茎流率可达2.3%~5.6%,2场降雨事件中当降雨量分别达到1.4,1.2mm时,开始产生树干茎流;(2)通过比较2场降雨事件历时过程穿透降雨、树干茎流同林外降雨的稳定同位素和水化学特征算术平均值得出,穿透降雨、树干茎流δ~2 H分别富集1.6‰~4.0‰和6.6‰~8.9‰,Cl~-浓度分别增加到林外降雨1.4~3.0倍和13.3~13.4倍,SO_4~(2-)浓度分别增加到1.5~2.7倍和4.8~7.1倍,穿透降雨和树干茎流相对林外降雨呈现一定滞后;降雨历时过程中稳定同位素δ~2 H与前时刻降雨以及截留过程进一步蒸发有关,水化学成分改变受植被截留影响逐渐减弱。     

不同林龄白桦次生林降雨水化学特征研究

通过对不同林龄白桦次生林林外降雨、穿透雨、树干茎流和枯透水中的Cl~-,NO_3~-N,Na~+,K~+,Ca2-,Mg~(2+)等进行测定,以研究4个林龄之间降水化学性质的差异.结果表明:林外降雨中Ca~(2+)的含量最高,Na~+含量最低,养分元素平均含量(以mg/L计)排列顺序为:Ca~(2+)>Cl~->K~+>NO_3~--N>Mg~(2+)>Na~+,各元素在林外降雨中的季节变化较大.变化幅度最小的是Cl~-;穿透雨中NO_3~--N,Ca~(2+)含量在25 a白桦次生林中最低,Cl~-,Mg~(2+)含量在38 a中最低,而Na~+,K~+含量在56 a中最低;树干茎流中Cl~-,NO_3~--N,K~+含量在38 a白桦次生林中最低,而Na~+,Ca~(2+),Mg~(2+)含量在56 a中最低;枯透水中Cl~-,NO_3~--N,Na~+,K~+含量在25 a白桦次生林中最低,Mg~(2+)含量在38 a中最低,而Ca~(2+)含量在56 a中最低.     

Rainfall redistribution of a virgin Pinus koraiensis forest and secondary Betula platyphylla forest in Northeast China

A virgin Pinus koraiensis forest in the Xiaoxing’an Mountains was selected to study its rainfall redistribution effect via 97 rainfall occurrences during a growing season. The following results were obtained: 1) The canopy interception of the P. koraiensis virgin forest amounted to 98168 mm during a growing season (May to September), which was 19.6 per cent of the total rainfall and 1.3 times that of a secondary Betula platyphylla forest. Compared with other forest types in China (11.4%–36.5%), the ratio of the canopy interception in the virgin pine forest was at a medium level. 2) The throughfall of the virgin pine forest was 395.77 mm, which accounted for 78.7% of total precipitation, and the stem-flow was 8.78 mm, accounting for 1.74% of total precipitation. Compared with the secondary birch forest, the virgin pine forest had lower throughfall but higher stem-flow. 3) Cubic regression equations (p < 0.01) which describe the relation between throughfall, stem-flow and canopy interception in the virgin pine forest and rainfall in an open field were fitted. A linear regression equation (p < 0.01) was found to be a better fit for the relationship between throughfall of the secondary birch forest and rainfall outside the forest. Factors affecting throughfall and stem-flow were analyzed, with results providing a good reference to the study of rainfall redistribution in coniferous and broadleaved mixed forests. __________ Translated from Science of Soil and Water Conservation, 2006, 4(6): 61–65 [译自: 中国水土保持科学]     

西江中下游生态公益林对降水截留分配效应研究

为了评估生态公益林涵养水源服务功能,选择德庆县三叉顶自然保护区生态公益林,定位观测2006年6月～2007年6月100次大气降水事件的截留分配效应。结果表明,观测期内降水总量为1 317.60mm,林冠截留量、树干茎流量和穿透水量分别是318.37,87.85和911.38 mm,林冠截留率、茎流率和穿透率分别为24.16%,6.67%和69.17%。林外降水量大于1.3 mm时才能观测到穿透雨,林外降水量达到3.0mm时才开始有树干茎流出现。林冠截留量、树干茎流量和穿透量与降水量均呈正相关,相关系数R2分别为0.788 8,0.957 7和0.965 9;林冠截留率与林外降水量呈负相关,而树干茎流率和穿透率呈正相关,相关系数R2分别为0.835 6,0.803 4和0.874 2。     

亚热带米槠天然林不同深度土壤胞外酶活性对隔离降雨的响应

随着全球变暖的加剧,降雨格局也在发生变化,土壤酶是森林生态系统化学过程的重要参与者,能够快速反映土壤环境的变化.因此研究亚热带土壤胞外酶活性对降水变化的响应,可有效评估气候变化对土壤有机质分解、转化的影响.以福建三明格氏栲自然保护区内的米槠天然林为研究对象,设置对照(CT)、隔离30％降雨(TE1)和隔离60％降雨(T...     

元江稀树灌丛降雨再分配及其与气象因子的关系

中国西南干热河谷地区广泛分布有稀树灌丛植被,气候条件干热,水热矛盾异常明显,然而对其降雨再分配缺乏研究。本研究选择了元江干热河谷稀树灌丛进行了1a的监测,开展降雨再分配及其影响因素分析。结果表明,观测期间总降雨量为762.9mm,穿透雨量、树干径流量和林冠截留量分别为639.3、14.6mm和109.0mm,分别占总降雨量的83.8%、1.9%和14.3%,当降雨量>1.1mm时开始产生穿透雨;降雨量>1.4mm时,开始产生树干径流。降雨再分配各分量与降雨量、降雨强度和气温均具有显著的相关关系(P<0.01),其中降雨量是与降雨再分配关系最密切的气象因子,即随着降雨量的增加,穿透雨量、树干径流量均增大,穿透雨率、树干径流率先增加后趋于稳定,而林冠截留率先减小后趋于稳定。该地区植被分布稀疏、群落结构简单、群落层次少、郁闭度低等原因造成稀树灌丛的穿透雨率相对较高,林冠截留率较低。     

辽东山溪河岸林群落特征对降雨再分配及其养分特征的影响

为明确不同物种组成和群落结构的河岸林对降雨再分配及其养分特征的影响,于2014年5—10月对辽东山地典型河岸林群落(落叶松林、蒙古栎林和槭树林)大气降雨、穿透雨和树干茎流过程及其水质特征进行研究。结果表明:落叶松林、蒙古栎林和槭树林穿透雨量分别占大气降雨量的81.9%,77.9%,73.1%,树干茎流量分别占大气降雨量的1.2%,4.4%,4.3%。与大气降雨相比,穿透雨和树干茎流中铵态氮、氯离子、硝态氮和总磷的浓度较高,不同林型铵态氮、氯离子、硝态氮和总磷的浓度和输入量差异显著。不同物种组成和群落结构的河岸林通过树木的形态特征及群落的结构特征对降雨进行再分配,通过林冠表层的物理特征、化学特征和生理特性等改变降雨理化性质,加之雨量、雨强的影响共同作用使铵态氮、氯离子、硝态氮和总磷的浓度和输入量发生改变。