Effects of deep percolation on dissolved inorganic nitrogen exports from forested headwater catchments

We examined the effects of deep percolation on dissolved inorganic nitrogen (DIN) exports from two adjacent weathered granite headwater catchments with different deep percolations of water in the Kiryu Experimental Watershed (KEW), Japan. The DIN output in streamflow was estimated from a regression equation between stream discharge and the DIN load, determined from both monthly sampling data and event-based sampling data. The range of deep percolation of DIN was estimated by multiplying observed DIN concentrations in bedrock groundwater by the deep percolation of water estimated from an annual water budget analysis. We found that the deep percolation of DIN corresponded to 34–76 % and ?18 to 8 % of the total DIN output in catchments where the deep percolation of water was 37–45 % and ?6 to 3 % of annual precipitation, respectively. This means that the deep percolation of DIN is not negligible when estimating the total output of DIN in the former catchment. Moreover, the fact that deep percolating water from upper catchments discharged into a lower catchment in KEW suggests that deep percolation of DIN affects downstream N budgets. Therefore, it is important to account for the deep percolation of DIN when evaluating N budgets in forested headwater catchments as well as downstream catchments.     

Water,sediment and nutrient movement in forested and non-forested catchments in Kumaun Himalaya

Overland flow, and soil and nutrient loss were assessed for four sites under original forest cover, and for four sites affected by soil deposition, landslide or cultivation in the Kumaun Himalaya during the 1981 and 1982 monsoon seasons. Overland flow was positively related with rainfall quantity and intensity and was reduced by the growth of ground vegetation during the later months of the monsoon season. Average overland flow was only 0.50% of the total incident rainfall indicating that these catchments are subsurface flow systems. Soil loss was positively related with overland flow, both being greater for non-forested compared to forested sites. Rainfall added a significant amount of nutrients. This extra system input was greater than loss through overland flow and runoff soil. The forested sites lost less nutrients compared to non-forested sites. The loss of nutrients was in the order: Ca > K > P > N. The forests of the catchments in Himalaya should be protected to avoid the impairment of hydrologic processes.     

Soil physical and micronutrient changes following clearing of a tropical rainforest

One of the options for achieving an adequate food supply in tropical Africa is by bringing more land into production. This often requires clearing and developing new vegetation areas for agricultural production. In sub-Saharan Africa, large areas of forest are being cleared for cultivation without adequate knowledge as to the consequences of the clearing method employed. This study was therefore initiated to, among other objectives, assess the effects of some forest clearing methods on soil compaction, texture, and micronutrients. Treatments were the following five clearing methods: (1) mechanical (MC), (2) semi-mechanical (SMC), (3) slash and burn (manual) (SB), (4) mechanical – no planting (MCNP), and (5) slash and burn – no planting (SBNP). After clearing, we planted maize and cowpea in every other row during the first year, and planted maize and cassava during the second year in the plots of treatments 1–3. Changes in soil texture, bulk density, and exchangeable Fe, Zn, Mn, and Cu were determined. Soil bulk density increased (with depth) in all treatments from the intitial (0–15cm) level of 1.1gcm^–3 to between 1.27 and 1.39gcm^–3 2 years after clearing, with the highest levels occurring in the MC plots. This indicated that clearing was accompanied by soil compaction. Some changes were noted in soil textural composition, but these were not of practical significance. Exchangeable Mn, Fe, and Cu (0–15cm) decreased markedly after clearing, especially under MC in the first year. Zinc levels changed little during the study period. The decline in micronutrient levels was paralleled by a decline in soil organic carbon.     

Wildfire and salvage harvesting effects on runoff generation and sediment exports from radiata pine and eucalypt forest catchments, south-eastern Australia

This study examined the effect of wildfire and salvage harvesting on runoff generation and sediment exports from three small forest catchments in south-eastern Australia. In 2006, wildfire burnt a radiata pine catchment and two adjacent natural eucalypt forest catchments which formed part of a long-term hydrological research project. Subsequently, only the pine plantation catchment was salvage harvested. The combined effect of fire and salvage harvesting in the pine catchment caused a substantial increase in runoff compared to the burnt eucalypt forest catchments and pre-fire conditions, particularly in response to high intensity, short duration summer storms. Post-fire maximum suspended sediment concentrations from fixed-interval sampling greatly exceeded pre-fire values for both eucalypt and pine catchments, while sediment (suspended and bedload) exported from the pine catchment exceeded each of the eucalypt catchments by a minimum of 180 and 33 times. However, the export increase was probably closer to 320 and 71 times based on a survey of eroded channels in the pine catchment combined with measured post-survey exports. Notably, seven summer storm events accounted for approximately 80% of the pine catchment sediment yield. Hillslope process measurements indicated that the highest runoff velocities occurred in log drag-lines formed by cable harvesting, while soil water repellency was more extensive in the harvested pine catchment than in the adjacent eucalypt catchment. The latter effect probably resulted from higher burn severity in the pines combined with reduced soil moisture due to less shading after harvesting. Runoff modelling indicated that the log drag-lines acted as an extension to the drainage network and increased peak flows at the harvested catchment outlet by 48% for a high intensity summer storm event, while substantial reductions in modelled runoff were achieved through increasing the hillslope surface roughness coefficient. It is recommended that post-fire salvage operations should avoid the formation of log drag-lines when using cable harvest techniques and maximise surface cover to limit increases to runoff, erosion and catchment sediment exports.     

Some nutrient dynamics associated with litterfall and litter decomposition in hoop pine plantations of southeast Queensland, Australia

Litterfall was collected over a 12-month period with littertraps in hoop pine (Araucaria cunninghamii) plantations aged 10, 14 and 62 years in southeast Queensland, Australia. The bulk of litterfall occurred during spring, mainly as hoop pine foliage with the annual litterfall ranging between 6.0 and 10.9 t ha⁻¹, respectively, for the younger stands (10 and 14 years) and the mature 62-year old stand. The amount of nitrogen (N) and phosphorous (P) recycled annually through litterfall was lower in the younger stands (28–37 kg N ha⁻¹ and 4.4–5.3 kg P ha⁻¹) compared with that of the mature stand (85 N ha⁻¹ and 6.2 kg P ha⁻¹). The N and P retranslocated during senescence varied across the three stands studied with a trend for N and P retranslocation to increase as availability of soil mineral-N decreased.

Decomposition of the hoop pine foliage component of litter was also studied in the same stands using a litterbag technique and mass-balance analysis. The estimated half-life of hoop pine foliage mass ranged between 1.5 and 1.8 years. Litter-mass loss was strongly correlated with litter substrate quality indicators of N, C, P, C/N ratio, lignin, lignin/N ratio and polyphenols. During the course of the study, there was no difference in litter-mass loss between the stands of different ages. During the 15-month period, the order of element release from the hoop pine litter was K>Na>C>Mg>P, with N, Ca and Mn generally demonstrating varying degrees of net accumulation. During the course of the study, the lignin/C ratio of the hoop pine litter increased from 0.61 to 0.96. This suggested that the litter-C was predominantly in a recalcitrant form and, therefore, the associated N was unlikely to be rapidly released in the hoop pine litter layer.     

Nutrient cycles and successional changes following shifting cultivation practice in moist semi-deciduous forests in Nigeria

The nutrient contents of moist semi-deciduous forest, successional regrowth and cultivated soils were studied along with successional changes following clear-cutting and burning. Water-soluble N, P, Ca, Mg and K were measured in the primary forest, successional regrowth, cultivated soils and soils of secondary forests ranging from 1 to 6 years after cessation of cultivation. Clearing and burning of the forest releases stored essential nutrients to soils under cultivation. K and N seem to be lost more rapidly in soils under cultivation than in soils under successional regrowth.It was observed that under shifting cultivation essential nutrients build up temporarily; P and Ca rapidly build up in cultivated soils to values much higher than their original values in the forest soils. Six years after the cessation of cultivation, the soil nutrient level of the successional regrowth was still far from being restored to the level of the primary forest soils.Seedlings and resprouts were equally important in the vegetation recovery of burnt and unburnt clear-cut forest. Seedlings of pioneer woody species established themselves in the burnt and unburnt plots within 4 months. Secondary regrowth in the burnt plot appeared better than in the unburnt plot, although resprouts played a more significant role in the unburnt plot.     

印度东北部(竹思)(竹劳)竹林凋落物的质量、分解动态和营养释放

(竹思)(竹劳)竹属是优先竹种,仅分布在印度东北部到孟加拉、尼泊尔、不丹和缅甸一带,其在森林生态系统的生态作用不为人知。由于凋落物质量、凋落物分解及营养释放形态的分析是了解任何系统中土壤肥力管理的基础,因此在卡查、阿萨姆和印度东北部的湿热带林中开展研究,目的是了解凋落物分解形态,研究目的如下:(1)凋落物的初期化学成分;(2)凋落物的失重和近似碳功能;(3)叶、箨凋落物的营养释放形态。用叶代技术测量思劳竹属叶和箨凋落物的分解损失。叶凋落物中含有较高浓度的氮、磷和钾,而箨凋落物中含有很高的碳、灰分和纤维素。失重以原干重来表示,并以时间呈指数下降。叶和箨指数的方程式如下:Y=175.38 e-0.3048x.,r=0.9689和Y=139.55 e-0.2674x.,箨凋落物的损失率比叶低,但它的C/N,L/N和L/P值较高。氮释放形式是两相同的,磷浓度的初期上升,而后呈下降趋势,而钾的释放则在整个分解过程发生。叶和箨凋落物中有机复合物的浓度在分解过程中下降。本文也对凋落物分解过程中保存土壤肥力的意义进行了讨论。     

Leaf exchange in a Mediterranean shrub: water, nutrient, non-structural carbohydrate and osmolyte dynamics

Leaf exchange is an abrupt phenological event that drastically modifies the morphology and physiology of the aerial portion of the plant. We examined if water and osmolyte differences between old leaves and new organs trigger leaf exchange, and whether the differences are closely linked to the resource resorption process in senescing leaves. We monitored concentrations of osmolyte, water, non-structural carbohydrate, nitrogen and potassium in senescing leaves and in emerging new leaves and inflorescences of a Mediterranean leaf exchanger (Cistus laurifolius L.) growing in NE Spain. Old leaves rehydrated markedly during most of the senescence process, which co-occurred with the extension of new shoots, suggesting the lack of a clear-cut switch in water supply from old to new organs. The accumulation of osmolytes in the early stage of leaf senescence might account for this rehydration. Osmolyte dynamics in old leaves depended largely on the progression of resource resorption from senescing organs but were mostly unrelated to water content during late senescence. We conclude that dehydration of old leaves is not a prerequisite for the triggering of leaf exchange. The finding that most nutrients and carbohydrates accumulated in new organs before senescing leaves massively exported resources, and the absence of relevant differences between the dynamics of old leaves at the base of inflorescences and those at the base of vegetative shoots, indicate that the nutrient and carbohydrate demands of new organs do not trigger leaf exchange.     

Growth versus storage: responses of Mediterranean oak seedlings to changes in nutrient and water availabilities

We compare dry mass (DM) and storage of starch (St) and nitrogen (N) in seedlings of three Mediterranean oaks, two evergreens (Quercus coccifera L. and Q. ilex L. subsp. ballota (Desf.) Samp) and one deciduous (Q. faginea Lam.), across different scenarios of nutrient and water availabilities. Three fertilization (5, 50 and 200 mg of N per plant and growing period) and watering (28–39, 55–71 and 70–85 g H₂O 100 g _soil ^?1 gravimetric soil water) treatments were applied to current-year seedlings between May and October 2002 in two independent experiments. The three species showed a similar response to fertilization, storing nitrogen instead of increasing biomass, in agreement with adaptations to nutrient-poor habitats. However, they differed in their responses to water, reflecting the different water requirements in the field: Q. coccifera, from arid zones, showed no response to water regarding DM and St; Q. faginea, from humid zones, required higher water availability to simultaneously increase growth and storage; while Q. ilex, spanning over most of the water availability range, exhibited a balanced increase of both functions when water increased moderately. In the two evergreen species, N concentration increased with water supply, whereas the reverse occurred in Q. faginea. The latter species favoured growth over storage at moderate water supply (according to its more competitive strategy), although it was the species which accumulated more St and N at the end of the experiments (autumn).     

Carbon dynamics in small tropical catchments under preserved forest and cacao agroforestry systems

Agroforestry Systems - Inland waters such as streams that receive carbon from terrestrial landscapes usually have a net heterotrophic metabolism and emit significant amounts of CO2 to the...     

Effects of clear-cutting on streamwater quality in forest catchments in central Sweden

Hydrochemical studies were conducted in three forested catchments in central Sweden during a 12-year period (1977–1989). During this period, 50% and 95% of the surface of two of the areas were clear - felled. The third area was left untouched as a control for reference. A qualitative analysis of clear-cut effects was conducted to investigate changes in streamwater quality by use of Principal Component and SIMCA analyses. During the 8 years of clear-cutting, with reference to the control period, the average runoff increased by 85% and 110% (220 mm and 274 mm year⁻¹), respectively, in the two areas felled to 50% and 95%. Significant changes in the status of the streamwater were detected for the two clear-felled catchments, whereas the changes detected in the control catchment were not significant, and within the limits of natural variation.In relation to the reference period, the changes in the clear-felled catchments were identified as dependent mainly on increased concentrations of K⁺, NH₄⁺, NO₃⁻, org-N, and tot-N. Concentrations of H⁺ decreased, while changes in concentrations of Ca²⁺, Mg²⁺, Na⁺, SO₄²⁻, and Cl⁻ were less distinct. At the end of the 8 year investigation period, run-off and chemical composition of the streamwater successively returned to pre-cut conditions.     

Comparison of water quality in two catchments with different forest types in the headwater region of the Hun River,Northeast China

In the headwater catchments of the Hun River,Northeast China, secondary forests(SF) have been replaced by plantations since the 1960 s. Concern has been growing over this loss and the decline in water quality caused by the plantations. To test the effects of plantations on water quality, we selected two separate catchments covered by SF and Pinus koraiensis plantations(KP) to monitor physical and chemical properties of various hydrological variables including throughfall, stemflow,through-litterfall and runoff(flowing out of outlets of the catchments). The physical properties of water declined after water flowed through the two catchments as compared with rainwater. The pH of runoff in both catchments also dramatically decreased. The concentrations of Cl^-, NO_3^- and NH_4^+ in the runoff from the two catchments were similar(concentrations of Cl-and NH_4^+ in both catchments were similar to those in rainwater). Total P concentration in runoff of the SF catchment was higher than that of the KP catchment(P concentrations in both catchments were also higher than in rainwater) because P concentrations in litter and soil of the SF catchment were higher than those in the KP catchment. In summary, the rainwater became acidic in both catchments, but the responses of most water quality variables were similar in the two catchments, suggesting that appropriate ratios of KP in SF are feasible for secondary forest recovery and for preserving water quality(KP did not cause a decline in quality) in the headstream regions in Northeast of China.     

Cold air drainage and modeled nocturnal leaf water potential in complex forested terrain

Spatial variation in microclimate caused by air temperature inversions plays an important role in determining the timing and rate of many physical and biophysical processes. Such phenomena are of particular interest in mountainous regions where complex physiographic terrain can greatly complicate these processes. Recent work has demonstrated that, in some plants, stomata do not close completely at night, resulting in nocturnal transpiration. The following work was undertaken to develop a better understanding of nocturnal cold air drainage and its subsequent impact on the reliability of predawn leaf water potential (Psi(pd)) as a surrogate for soil water potential (Psi(s)). Eight temperature data loggers were installed on a transect spanning a vertical distance of 155 m along a north facing slope in the Mica Creek Experimental Watershed (MCEW) in northern Idaho during July and August 2004. Results indicated strong nocturnal temperature inversions occurring from the low- to upper-mid-slope, typically spanning the lower 88 m of the vertical distance. Based on mean temperatures for both months, inversions resulted in lapse rates of 29.0, 27.0 and 25.0 degrees C km(-1) at 0000, 0400 and 2000 h, respectively. At this scale (i.e., < 1 km), the observed lapse rates resulted in highly variable nighttime vapor pressure deficits (D) over the length of the slope, with variable impacts on modeled disequilibrium between soil and leaf water potential. As a result of cold air drainage, modeled Psi(pd) became consistently more negative (up to -0.3 MPa) at higher elevations during the night based on mean temperatures. Nocturnal inversions on the lower- and mid-slopes resulted in leaf water potentials that were at least 30 and 50% more negative over the lower 88 m of the inversion layer, based on mean and maximum temperatures, respectively. However, on a cloudy night, with low D, the maximum decrease in Psi(pd) was -0.04 MPa. Our results indicate that, given persistent cold air drainage and nighttime stomatal opening, serious errors will result if Psi(s) is estimated from Psi(pd).     

Management of water and nutrient relations in European forests

The term ‘Europe’ covers a wide range of forest types and scientific philosophies, effectively preventing generalised statements. Water is regularly deficient only in Mediterranean regions and, apart from careful weeding, little active management is undertaken. In more-northern and western regions, much effort has been directed towards removal of excess soil water or providing locally drained planting sites. By contrast, nutrition is relatively amenable to the dictates of management, and relevant research dates back over a century. The greatest demands for soil nutrients occur while the green crown is being formed; thereafter efficient cycling within the tree means a much-reduced uptake. In consequence, responses to fertilizer are most likely at the establishment phase; in Europe, deficiencies have been identified for N, P, K, Mg, B and Cu. Most forest departments have now drawn up guidelines for fertilizer applications based on empirical experimentation, sometimes making use of foliar analysis. A particular feature of northern and western coniferous forests is a late-rotation N deficiency resulting from immobilization of this element in the humus layer. This was the first nutritional problem to attract the attention of forest scientists and it has now been very thoroughly explored.

It seems unlikely that the future will see any heightened interest in the management of water. In relation to nutrition management, the search must be to develop diagnostic and ameliorative measures that ensure minimum adverse effects on the environment.     

Nitrate dynamics of forested watersheds: spatial and temporal patterns in North America,Europe and Japan

The relationships of nitrogen biogeochemistry are reviewed, focusing on forested watersheds in North America, Europe and Japan. Changes in both local and global nitrogen cycles that affect the structure and function of ecosystems are described. Within northeastern United States and Europe, atmospheric deposition thresholds of ~8 and ~10 kg N ha⁻¹ year⁻¹, respectively, result in enhanced mobilization of nitrate. High nitrate concentrations and drainage water loss rates up to 22 kg N ha⁻¹ year⁻¹ have also been found near Tokyo. Although atmospheric deposition may explain a substantial portion of the spatial pattern of nitrate in surface waters, other factors also play major roles in affecting the spatial patterns of nitrogen biogeochemistry. Calcium availability influences the composition of the vegetation and the biogeochemistry of nitrogen. The abundance of sugar maple is directly linked to soil organic matter characteristics and high rates of nitrogen mineralization and nitrification. Seasonal patterns of nitrate concentration and drainage water losses are closely coupled with differences in seasonal temperature and hydrological regimes. Snow-dominated forested catchments have highest nitrate losses during snowmelt. Watersheds in the main island of Japan (Honshu) with high summer temperatures and precipitation inputs have greatest losses of nitrate occur during the late summer. Understanding future changes in nitrate concentrations in surface waters will require an integrated approach that will evaluate concomitantly the influence of both biotic and biotic factors on nitrogen biogeochemistry.     

Tree species composition influences differences in water use efficiency of upland forested microwatersheds

Water use efficiency (WUE) was compared in three upland South Moravian forested microwatersheds in the light of effects of global climate change on forest ecosystems (GCC). The experimental catchments were characterized as upland headwater forested microwatersheds of similar size and morphology and silvicultural system, but each with different dominant tree species in the stands (over 50% of forest stand composition in living stock): Norway spruce, European beech and mixed forest. WUE was evaluated according to mean daily streamflow reduction, measured at the discharge points of the recipients of the individual catchments in precipitation-free periods lasting more than 5 days. During these times, streamflow dynamics are mainly influenced by evapotranspiration processes occurring in the forest stands. Four precipitation-free periods were observed, two in the middle of the growing season and two at its end. Two of these periods were long (15 days or more), and two were shorter (6 days). The results indicated that WUE of upland forested catchments can be very different, depending upon the dominant tree species and the seasonal phase. Highest WUE at the catchment scale (never decreasing below 80%) was exhibited by beech predominating site. WUE of mixed forest was high as well, never decreasing below 69%. The lowest WUE was exhibited by spruce predominating site, especially during a long precipitation-free period in the summer where it decreased down to 39%. In the context of the landscape, upland microwatersheds with pure spruce stands could cause its accelerated dry out in the summer and pose a significant threat to sustainable water and forest management of these areas. In comparison, mixed forests stands where spruce is not the dominant species or beech stands should still be a viable option even under the effects of GCC.     

Seasonal changes of nutrient levels and nutrient resorption in Avicennia marina leaves in Yingluo Bay,China

Avicennia marina is a typical mangrove species of subtropical coastlines of China. However, little is known about the retention of nutrients by this species in oligotrophic, coastal environments. In this study, seasonal changes in nitrogen (N) and phosphorus (P) concentrations, N:P ratio and total phenolic concentration in A. marina leaves during senescence were studied. Avicennia marina leaves had high N and P concentrations but the seasonal pattern of N concentration was different from that of P concentration. The A. marina forest was N-limited as the N:P ratio of mature leaves was less than 14. Nitrogen resorption efficiency was higher than P resorption efficiency, and the concentrations of N and P in senescent leaves indicated that N resorption was mostly complete whereas P resorption was incomplete. Avicennia marina leaves contained low tannin concentrations, particularly condensed tannins, as the leaf extracts did not react with acid butanol. Total phenolic concentrations were not correlated with N concentrations in mature and senescent leaves of A. marina. These findings suggest that the high N resorption efficiency and low nutrient losses play an important role in nutrient conservation strategies for A. marina forests, whereas low tannin concentations have limited effects on nutrient cycling.     

Recovery of carbon and nutrient pools in a northern forested wetland 11 years after harvesting and site preparation

We measured the change in above- and below-ground carbon and nutrient pools 11 years after the harvesting and site preparation of a histic-mineral soil wetland forest in the Upper Peninsula of Michigan. The original stand of black spruce (Picea mariana), jack pine (Pinus banksiana) and tamarack (Larix laricina) was whole-tree harvested, and three post-harvest treatments (disk trenching, bedding, and none) were randomly assigned to three Latin square blocks (n = 9). Nine control plots were also established in an adjoining uncut stand. Carbon and nutrients were measured in three strata of above-ground vegetation, woody debris, roots, forest floor, and mineral soil to a depth of 1.5 m. Eleven years following harvesting, soil C, N, Ca, Mg, and K pools were similar among the three site preparation treatments and the uncut stand. However, there were differences in ecosystem-level nutrient pools because of differences in live biomass. Coarse roots comprised approximately 30% of the tree biomass C in the regenerated stands and 18% in the uncut stand. Nutrient sequestration, in the vegetation since harvesting yielded an average net ecosystem gain of 332 kg N ha⁻¹, 110 kg Ca ha⁻¹, 18 kg Mg ha⁻¹, and 65 kg K ha⁻¹. The likely source for the cations and N is uptake from shallow groundwater, but N additions could also come from non-symbiotic N-fixation and N deposition. These are the only reported findings on long-term effects of harvesting and site preparation on a histic-mineral soil wetland and the results illustrate the importance of understanding the ecohydrology and nutrient dynamics of the wetland forest. This wetland type appears less sensitive to disturbance than upland sites, and is capable of sustained productivity under these silvicultural treatments.     

库区森林覆盖对枯水期径流影响

据1996年～1999年黄前水库水资源系列资料，分析了库区森林覆盖率变化及其对水资源的涵养状况，指出森林覆盖率增加造成枯水期径流增加，减少断流天数，保护流域生态环境。