The significance of atmospheric nutrient inputs and canopy interception of precipitation during ecosystem development in piñon-juniper woodlands of the southwestern USA

In arid ecosystems, widely spaced vegetation and prolonged dry periods may enhance canopy capture of nutrients from dry deposition. Additionally, differences in precipitation type, plant canopy architecture, and soil nutrient limitation could affect canopy exchange of atmospherically derived nutrients. We collected bulk precipitation and throughfall underneath piñon pine (. Pinus edulis) and one-seed juniper (. Juniperus monosperma) along a substrate age gradient to determine if canopy interception or throughfall chemistry differed among tree species, season, or substrate age. The Substrate Age Gradient of Arizona consists of four sites with substrate ages ranging from 1ky to 3000ky-old, which exhibit classic variations in soil nitrogen (N) and phosphorus (P) availability with substrate age. Greater nutrient inputs below canopies than in intercanopy areas suggest throughfall contributes to the "islands of fertility" effect. Canopy interception of precipitation did not differ between tree species, but was greater in the summer/fall than winter/spring. We found that net canopy retention of atmospherically derived N was generally greater when N availability in the soil was low, but retention also occurred when N availability was relatively high. Taken together, our results were inconclusive in determining whether the degree of soil nutrient limitation alters canopy exchange of plant growth-limiting nutrients. © 2013 Elsevier Ltd

Rainfall interception by two deciduous Mediterranean forests of contrasting stature in Slovenia

Measurements of precipitation above the canopy, throughfall and stemflow were\ud made on the south and north-facing slopes of a deciduous forest on the experimental\ud watershed of the Dragonja river in SW Slovenia. The Dragonja watershed was\ud chosen for the experimental watershed, being of interest because of intensive natural\ud reforestation in the last decades that caused a decrease in minimum and maximum\ud flows. At the same time no noticeable precipitation and temperature changes were\ud observed. Two forest plots were selected. One is located on the north-facing slope\ud (1419 m2) and the other on the south-facing slope (615 m2). Analyses and modelling\ud were made for a one-year period from October 2000 to September 2001. The leaf\ud area index (LAI) was estimated by three methods, one direct and two indirect ones.\ud The obtained values of LAI with the direct method were 6.6 and 6.9 for the south and\ud north slopes, respectively. Measurements and regression analyses gave the mean\ud annual throughfall value (± standard error) on the south plot 67.1 (± 9.6) % of gross\ud precipitation, and 71.5 (± 11.6) % on the north plot. The average stemflow values\ud were 4.5 (± 0.8) % of gross precipitation in the south plot and 2.9 (± 0.6) % in the\ud north plot. The average annual interception losses amount to 28.4 (± 4.1) and 25.4 (±\ud 4.0) % for the south and north slopes, respectively. In the study a significant influence\ud of the south-east wind was proven. With regression analyses and the classification\ud decision tree model it was established that at the events with more than 7 mm of\ud precipitation and south-east wind with a speed higher than 4 m/s an unusually low\ud amount of throughfall occurred and thus high interception losses. The analytical\ud Gash model of rainfall interception (Gash, 1979; Gash et al., 1995) was successfully\ud applied. The results of the modelling corresponded well to the observed values and\ud were within the limits of the standard error of the observed values

Tropical montane cloud forest

Tropical montane cloud forests (TMCFs) are covered in clouds and fog, by definition, and are abundant with mosses, lichens and epiphytes. The hydrology of these ecosystems is poorly understood due to the extreme wetness, complex topography, and remoteness, TMCF are also susceptible to several types of disturbance. The two main objectives of this thesis were to (i) study the fire history in a TMCF and (ii) investigate the changes in water input in a secondary TMCF. Field studies were conducted in southern Mexico and northern Costa Rica. The Chimalapas region of Oaxaca, Mexico was subjected to fires during the El Niño events of 1997 to 1998. Previous fires were evident from charcoal, which was collected in soil pits. Radiocarbon dating indicated that at least nine fire episodes have occurred in this area during the past 10, 000 years and the findings suggest that there have been repeated fires in the investigated TMCFs. The Costa Rican study aimed to estimate total soil water input from horizontal rain and fog (HP) in the edge and interior of a secondary TMCF. Net capture was defined as HP that reached the soil and was calculated as throughfall + stemflow - vertical precipitation. Over the 11-month measurement period, accumulated net capture decreased linearly from the forest edge (ca. 1200 mm) to the centre of the plot which was 20 m into the forest (ca.-1900 mm). Sixty-eight percent of the variability in weekly net capture could be explained by the plot position and the seasonal variation in HP input. In conclusion, the study demonstrated the potential to manage edges and emergent trees in landscapes with secondary TMCF for improved water input

A comparison of three canopy interception models for a leafless mixed deciduous forest stand in the eastern United States

Canopy interception of incident precipitation is a critical component of the forest water balance during each of the four seasons. Models have been developed to predict precipitation interception from standard meteorological variables because of acknowledged difficulty in extrapolating direct measurements of interception loss from forest to forest. No known study has compared and validated canopy interception models for a leafless deciduous forest stand in the eastern United States. Interception measurements from an experimental plot in a leafless deciduous forest in northeastern Maryland (39°42'N, 75°5'W) for 11 rainstorms in winter and early spring 2004/05 were compared to predictions from three models. The Mulder model maintains a moist canopy between storms. The Gash model requires few input variables and is formulated for a sparse canopy. The WiMo model optimizes the canopy storage capacity for the maximum wind speed during each storm. All models showed marked underestimates and overestimates for individual storms when the measured ratio of interception to gross precipitation was far more or less, respectively, than the specified fraction of canopy cover. The models predicted the percentage of total gross precipitation (PG) intercepted to within the probable standard error (8.1%) of the measured value: the Mulder model overestimated the measured value by 0.1% of PG; the WiMo model underestimated by 0.6% of PG; and the Gash model underestimated by 1.1% of PG. The WiMo model’s advantage over the Gash model indicates that the canopy storage capacity increases logarithmically with the maximum wind speed. This study has demonstrated that dormant-season precipitation interception in a leafless deciduous forest may be satisfactorily predicted by existing canopy interception models

Hydrological controls on nutrient exportation from old-growth evergreen rainforests and Eucalyptus nitens plantation in headwater catchments at Southern Chile

Soil cover disturbances have a direct effect on biogeochemistry, potentially enhancing nutrient loss, land degradation and associated changes in ecosystem services and livelihood support. The objective of this study was to assess how canopy affected throughfall chemistry and how hydrology affected stream nutrient load responses in two watersheds dominated by native old-growth evergreen rainforest (NF) and exotic plantation of Eucalyptus nitens (EP), located at the Coastal mountain range of southern Chile (40˚S). We measured nitrogen (NO3-N, NH4-N, Organic-N, Total-N) and total phosphorus (Total-P) at catchment discharge, and δ18O in throughfall precipitation and stream discharge in both catchments, in order to separate throughfall (or new water) contributions during storm events. It was hypothesized that all nutrients showed an increase in concentration as discharge increased (or enhanced hydrological access), in EP; but not in NF. Our results indicated that Organic-N, Total-N and Total-P concentrations were positively related to discharge. However, 3 NO− -N showed a negative correlation with catchment discharge

Effects of potassium/sodium fertilization and water availability on wood properties of Eucalyptus grandis trees

In Brazil. most Eucalyptus plantations are located in regions experiencing periods of water shortage where fertilizers such as potassium (K) are intensively used to achieve high productivity. Recently. sodium(, a) has also been considered a potential nutrient. As well as tree growth, wood properties are also an important factor to consider in order to measure the impacts of silvicultural practices and water deficit on forest productivity, since they are determinants for quality and yield of pulp and paper. In a split-plot experimental design with 4-year-old Eucalyptus grandis trees, located in Sao Paulo State, Brazil, we evaluate the effects or K and Na supply compared with a control treatment under two water supply regimes (37% throughfall reduction versus no throughfall reduction) on stem volume, heartwood proportion. basic density, fiber, and vessel properties. K and Na fertilization increased stem volume 2. 7 and 1.9 fold. respectively, with a nonsignificant effect of 37% throughfall reduction. Na fertilization was more detrimental to wood properties that K fertilization, affecting heartwood proportion, basic density, and fiber wall thickness. K fertilization affected only heartwood proportion and basic density. The 37% throughfall reduction only affected wood basic density. increasing it. Effects of fertilization treatments did not change regardless changes in water supply.Despite the detrimental effects of fertilizers (stronger with Na supply) in wood properties there is a large beneficial effect on stem volume (stronger with K supply), even under a water availability reduction, that would be compensates the loss of wood quality for pulp and paper production

Evidence of hydrological control of Sr behavior in stream water (Strengbach catchment, Vosges mountains, France)

Strontium and particularly 87Sr/86Sr ratios in stream water have often been used to calculate weathering rates in catchments. Nevertheless, in the literature, discharge variation effects on the geochemical behavior of Sr are often omitted or considered as negligible. A regular survey of both Sr concentrations and Sr isotope ratios of the Strengbach stream water draining a granite (Vosges mountains, France) has been performed during one year. The results indicate that during low water flow periods, waters contain lower Sr concentrations and less radiogenic Sr isotope ratios (Sr=11.6 ppb and 87Sr/86Sr=0.7246 as an average, respectively) than during high water flow periods (Sr= 13 ppb and 87Sr/86Sr=0.7252 as an average, respectively). This is contrary to expected dilution processes by meteoric waters which have comparatively lower Sr isotopic ratios and lower Sr concentrations. Furthermore, 87Sr/86Sr ratios in stream water behave in 3 different ways depending on moisture and on hydrological conditions prevailing in the catchment. During low water flow periods (discharge < 9 l/s), a positive linear relationship exists between Sr isotope ratio and discharge, indicating the influence of radiogenic waters draining the saturated area during storm events. During high water flow conditions, rising discharges are characterized by significantly less radiogenic waters than the recession stages of discharge. This suggests a large contribution of radiogenic waters draining the deep layers of the hillslopes during the recession stages, particularly those from the more radiogenic north-facing slopes. These results allow one to confirm the negligible instantaneous incidence of rainwater on stream water chemistry during flood events, as well as the existence in the catchment of distinct contributive areas and reservoirs. The influence of these areas or reservoirs on the fluctuations of Sr concentrations and on Sr isotopic variations in stream water depends on both moisture and hydrological conditions. Hence, on a same bedrock type, 87Sr/86Sr ratios in surface waters can be related to flow rate. Consequently, discharge variations must be considered as a pre-requisite when using Sr isotopes for calculating weathering rates in catchments, particularly to define the range of variations of the end-members

An overview of atmospheric deposition chemistry over the Alps: present status and long-term trends

Several research programs monitoring atmospheric deposition have been launched in the Alpine countries in the last few decades. This paper uses data from previous and ongoing projects to: (i) investigate geographical variability in wet deposition chemistry over the Alps; (ii) assess temporal trends of the major chemical variables in response to changes in the atmospheric emission of pollutants; (iii) discuss the potential relationship between the status of atmospheric deposition and its effects on forest ecosystems in the alpine and subalpine area, focusing particularly on nitrogen input. We also present results of studies performed at a local level on specific topics such as long-term changes in lead deposition and the role of occult deposition in total nitrogen input. The analysis performed here highlights the marked geographical variability of atmospheric deposition in the Alpine region. Apart from some evidence of geographically limited effects, due to local sources, no obvious gradients were identified in the major ion deposition. The highest ionic loads were recorded in areas in the foothills of the Alps, such as the pre-alpine area in North-Western Italy and the area of Canton Ticino, Switzerland. Trend analysis shows a widespread decrease in the acidity of precipitation in the last 15–20 years as a consequence of the reduced emission of S compounds. On the other hand, nitrate concentrations in rain have not changed so much, and ammonium has decreased significantly only at the Austrian sampling sites. The deposition of N is still well above the estimated critical loads of nutrient N at some forest sites in the alpine and subalpine areas, thus confirming the critical situation of both terrestrial and aquatic ecosystems regarding N inputs. Existing data highlights the importance of continuously monitoring atmospheric deposition chemistry in the Alpine area, taking account of acidifying elements, nutrients and other pollutants such as heavy metals and organic compounds. There is also a need for unifying sampling and analytical methods in order to obtain comparable data from the different regions of the Alps