Effectiveness of Chinese pine (Pinus tabulaeformis) plantation at reducing runoff and erosion rates in Anjiagou Watershed in Semi-arid Region of Gansu, China.

China's Loess Plateau regions have experienced severe soil erosion for many decades due to fragmented landscapes, steep slopes, and concentrated rainfall storm-events. Restoring sub-optimal or marginal farming fields, mostly on steep, hilly terrain, to plantation forests has been a long-standing strategic policy in China aimed at rehabilitating degraded environments and reducing soil and water erosion. While there are numerous studies that have focused on the effects of forests at controlling soil erosion at relatively short time scales, few have addressed longer-term effects of plantation forests on reducing runoff and the mechanisms that inhibit erosion. Chinese pine (Pinus tabulaeformis) has been widely planted in abandoned or reclaimed lands that were formerly farmed in Northwest China; however, there is limited knowledge about the effectiveness of the tree species at reducing soil and water erosion. In this study, we examined reduction rates of runoff and erosion by Chinese pine plantation in comparison with agricultural land as a control (i.e., wheat, a dominant agricultural commodity in the region), based on long-term monitoring of modified standard erosion plots with slopes of 10°, 15°, and 20°. Results showed that as the slope of the land increased, rates of erosion increased for both plantation and agricultural land use. However, the runoff and soil erosion rates under Chinese pine plantation forest were about 11% and 60% lower, respectively, than those under agricultural land use of the same slope. Scaling with the slope, the highest reduced runoff and erosion rates by Chinese pine forest were 17% and 72%, respectively, on 20° slope. Also, it was found that runoff rates from the forested land were positively related to erosive rainfall (i.e., rainfall when runoff generated), and varied with forest canopy coverage. The rates of runoff and erosion can be well model led with multiple regression models. Taken together, this study provides insight into the importance and potential of Chinese pine plantations in the conservation of soil and water in China's Loess Plateau.

Analysis and estimation of nonpoint source pollution under different land use in Anjiagou watershed, Gansu, China.

Agriculture-related nonpoint source pollution has been a worldwide issue in the past few decades. Estimating pollutant sources at the basin scale remains a challenge due to the complexity of pollutant transport mechanisms affected by land use, variable climatic condition, geological formation, and lack of long-term observation data. This study was based on the long-term plot observational data of surface runoff and water quality and used principal component analysis and other statistical analyses to analyze the variation of water quality affected by different land uses (cropland, tree forest, shrub, grassland, and wildland). The mean concentration method with the local calibrated/verified SWAT (soil and water assessment tool) model was used to quantify the load of nonpoint source (NPS) pollutants on slope areas under different land uses in the Anjiagou Watershed. Our research results determined permanganate index (CODMn), ammonia nitrogen (NH3-N), total nitrogen (TN), fluoride (F-), nitrite nitrogen (NO2-N), total phosphorus (TP), and hexavalent chromium (Cr6+) as the significant pollutants while 5-day biochemical oxygen demand (BOD5) was identified to be below the water quality standards of Grade V (water for agricultural and general landscape use) in the studied watershed. Pollutants were discharged through either hillslope at a total rate of 2.4 kg ha-1, accounting for 67.6% of the total, or through waterway channels (32.4%). The pollutant concentrations were from 23.5 mg L-1 to 37.4 mg L-1, varying with pollutants and land uses. All examined water quality indicators exceeded the minimum safety standards defined by the regulations of the Gansu provincial government by averaging 3.5 times higher than the safety threshold. The pollutants from hillslopes exceeded water quality standards by a factor of 3.4-4.4 times compared with from the waterway channel by 1.9. Implementing soil and water conservation measures can mitigate pollutants to some extent, particularly during the process of highland runoff converging into waterways. At the watershed level, between 33 and 38% of the runoff and pollutants were discharged from croplands, between 59 and 66% from forest land, < 2% from grassland, and 1% from wildland. This study also demonstrates a simple but novel method to estimate NPS pollutants using long-term plot observations in conjunction with SWAT models, which can be used in other watersheds with similar conditions.

Influences of sampling methodologies on pesticide-residue detection in stream water.

Traditional grab sampling (GS) used widely in the study of water quality has been found lacking in spatial and temporal resolution for pesticide residue monitoring in stream water. The objectives of this article are to present a hydrograph-based sampling approach and compare it with traditional GS according to sensitivity at temporal and spatial scales and maximum concentrations of pesticide residues detected in-stream. Data collected from streams receiving water from three nested watersheds located in northwestern New Brunswick, Canada, were used in this study. The results showed that the hydrograph-based sampling method detected 20 to 30 % more pesticide cases than GS for rainfall events causing runoff. Grab sampling significantly underestimated average concentrations of pesticide residues by 50 % and maximum concentrations by 1 to 3 orders of magnitude. Using a modified sampler design, the spatial and temporal variability of pesticide residues was more accurately captured by hydrograph-based sampling, and therefore its use in monitoring programs is recommended.

Pesticide application and detection in variable agricultural intensity watersheds and their river systems in the maritime region of Canada.

Applications of pesticides in areas of agricultural production have been an environmental concern for the past several decades. Varying-sized watersheds draining regions of intense agriculture in the Maritime Provinces of Canada were monitored between 2003 and 2007 to determine the major in-use pesticides and to gain an understanding of the risks posed to aquatic ecosystems. A questionnaire collected from farmers in one watershed intensively cropped with potato indicated that 43 pesticides were applied with 18 of them being detected in that watershed. Our results across the Maritime region suggested that detection frequencies ranged from 0.0 to 22 % during the study period. Chlorothalonil, linuron, metalaxyl, and metribuzin were detected in 17-22 % of samples collected during rainfall events every year. Other pesticides, such as azinphos-methyl, atrazine, cypermethrin, permethrin, fonofos, and ß-endosulfan were detected in ≤17 % of the samples during some years of the study. Concentrations of several pesticides were found to exceed their Canadian Council of Ministers of the Environment (CCME) aquatic life water-quality guidelines in pulses after rain events. The highest proportion of detections exceeding a CCME guideline was for chlorothalonil at 12.9 %, ß-endosulfan at 6.0 %, and linuron at 3.4 %. Despite indications that remedial measures offer protection to aquatic environments, spatial and temporal gaps in the data prevented a full evaluation. A dedicated long-term multiple-watershed monitoring program for this region of Canada is therefore recommended.

Field performance of nine soil water content sensors on a sandy loam soil in new brunswick, maritime region, Canada.

An in situ field test on nine commonly-used soil water sensors was carried out in a sandy loam soil located in the Potato Research Center, Fredericton, NB (Canada) using the gravimetric method as a reference. The results showed that among the tested sensors, regardless of installation depths and soil water regimes, CS615, Trase, and Troxler performed the best with the factory calibrations, with a relative root mean square error (RRMSE) of 15.78, 16.93, and 17.65%, and a r(2) of 0.75, 0.77, and 0.65, respectively. TRIME, Moisture Point (MP917), and Gopher performed slightly worse with the factory calibrations, with a RRMSE of 45.76, 26.57, and 20.41%, and a r(2) of 0.65, 0.72, and 0.78, respectively, while the Gypsum, WaterMark, and Netafim showed a frequent need for calibration in the application in this region.

Validating Evapotranspiraiton Equations Using Bowen Ratio in New Brunswick, Maritime, Canada.

Three methods including the Penman-Monteith (PM), Priestley-Taylor (PT), and 1963 Penman equation (PE) for calculating daily reference evapotranspiration (ETo) were evaluated in the Maritime region of Canada with the data collected from 2004 to 2007. An automatically operated meteorological station located on the Potato Research Centre, Agriculture and Agri-Food Canada, Fredericton, New Brunswick, Canada, was used to collect required meteorological data for evapotranspiration modeling. A Bowen Ratio system (BR) was setup near the Environment Canada grade one weather station to provide evapotranspiration observations for the validation research of reference evapotranspiration models. The results showed that the prediction from each of the tested models had a certain degree of offset in comparison with the observations obtained by the BR method. All of the tested models slightly overestimated evapotranspiration compared to the BR system by 5-14%, depending on the method. However, the PM generated a better fit to the pooled dataset while the PT produced the best prediction for the 2007 validation dataset. The PM generated the best estimation of evapotranspiration for year 2004 during a inter-annual comparison. The BR revealed that the average daytime ET for the site was around 2.5 mm day-1(±0.1) averaged for Julian day 157-276 in 2004 to 2006 and possible condensation was 0.16 mm day-1 for the same period. Crop coefficient (Kc) varied with different models, for example, 0.42 for the PM, 0.44 for the PT, and 0.67 for the PE with a slight yearly variation. With this set of Kc values, a validation with additional dataset collected in 2007 indicated that all three equations achieved a good fit with observations using the above Kc values. The PT performed slightly better than the other two models. A single factor analysis did not show any statistically significant difference between predicted and measured ET. With a consideration of simplicity and application for scaling up to landscape, this research suggested that the PT is the preferable method for estimating ET values in this region.

Total and component carbon fluxes of a Scots pine ecosystem from chamber measurements and eddy covariance.

BACKGROUND AND AIMS: Distinguishing between, and quantifying, the different components of ecosystem C fluxes is critical in predicting the responses of ecosystem C cycling to climate change. The aims of this study were to quantify the photosynthetic and respiratory fluxes of a 50-year-old Scots pine (Pinus sylvestris) ecosystem, and to distinguish respiration of branches with needles from that of stems, and that of soil. METHODS: The CO2 flux of the ecosystem was continuously measured using the eddy covariance (EC) method, and its components (respiration and photosynthesis of a branch with needles, stem and soil surface) were measured with an automated chamber system, from 2001 to 2004. KEY RESULTS: All values below are chamber based. The average temperature coefficient (Q10) of respiration was 2.7, 2.2 and 4.0, respectively, for branch (Rbran), stem (Rstem) and the soil surface (Rsoil). Respiration at a reference temperature of 15 degrees C (R15) was 1.27, 0.49 and 4.02 micromol CO2 m(-2) ground s(-1) for the three components, respectively. Over 4 years, the annual Rbran, Rstem and Rsoil ranged from 196 to 256, 56 to 83 and 439 to 598 g C m(-2) ground year(-1), respectively, with a 4-year average of 227, 72 and 507 g C m(-2) ground year(-1). Annual ecosystem respiration (Reco) was 731, 783, 909 and 751 g C m(-2) ground year(-1) in years 2001-2004, respectively, gross primary production (GPP) was 922, 1030, 1138 and 1001 g C m(-2) ground year(-1), and net ecosystem production (NEP) was 191, 247, 229 and 251 g C m(-2) ground year(-1). The average contribution of Rbran, Rstem and Rsoil to Reco was 29, 9 and 62 %, respectively. Overstorey photosynthesis accounted for 96 % of GPP. The average Reco/GPP ratio was 0.78. Net primary production (NPP) in the 4 years was 469, 581, 600 and 551 g C m(-2) year(-1), respectively, with the NPP/GPP ratio 0.54 averaged over the years. CONCLUSIONS: Respiration from the soil is the dominant component of ecosystem respiration. Differences between years in Reco were due to differences in temperature during the growing season. Rsoil was more sensitive to temperature than Rbran and Rstem, and differences in Rsoil were responsible for the differences in Reco between years.

Carbon and biomass partitioning in balsam fir (Abies balsamea).

Balsam fir (Abies balsamea (L.) Mill) was extensively sampled to investigate the effects of forest management practices, site location, within-crown position, tree component (i.e., stem, foliage, branches and roots), and tree social classes on biomass and carbon (C) partitioning at the individual tree level and across ecological regions. The sites were located in three ecologically distinct forest regions of west-central New Brunswick, Canada. There were no significant differences in %C content of trees across ecological regions or across tree social classes. However, at the individual tree level, significant differences were evident in biomass and C allocation between different parts of the tree, between treatment types (i.e., unmanaged and pre-commercially thinned stands) and between within-crown positions, indicating the need for separate estimates of biomass and C content of tree components to obtain more precise estimates of quantities at the stand level. Calculating stand C content based on constant allocation values, as is commonly done, produced errors of up to 15% compared with the values calculated in this study. Three allometric equations of biomass and C that account for partitioning among different parts of the tree were developed and compared: (1) a third-order polynomial, (2) a modified inverse polynomial and (3) a modified Weibull equation. Diameter at breast height (DBH) was used as the only explanatory variable to describe fresh biomass, dry biomass and C content. All regressions derived showed a high correlation with DBH, with most r2 values > 0.95. A comparison of the equation results showed that the modified Weibull equation gave consistent results with the best overall fit and was the simplest of the three equations investigated. The regressions can be used to estimate forest biomass and tree C content at the stand level, given specific information on DBH.