Information For Water Management Research Articles

Response of Hot Pepper Yield, Fruit Quality, and Fruit Ion Content to Irrigation Water Salinity and Leaching Fractions

It has been proved that irrigation with high saline water and leaching fraction (LF) affect crop yield, but the effects of irrigation water salinity (ECiw) and LF on fruit quality remain largely elusive. We therefore investigated the effects of ECiw and LF on the yield, fruit quality, and ion content of hot peppers. An experiment using irrigation water with five levels of salinity (ECiw of 0.9, 1.6, 2.7, 4.7, and 7.0 dS·m−1) and two LFs (0.17 and 0.29) was conducted in a rain shelter. The experiment took the form of a completely randomized block design, and each treatment was replicated four times. We increased the salinity of the irrigation water by adding 1:1 milliequivalent concentrations of NaCl and CaCl2 to a half-strength Hoagland solution. The plants were irrigated for 120% and 140% evapotranspiration, corresponding to an LF of 0.17 and 0.29. Results showed that the total fruit yield decreased significantly with an increase in the ECiw as a result of reduction both in the fresh weight of fruit and the number of fruit per plant. An increase in the ECiw also led to a decrease in the total dry biomass of fruit and plant, as well as decreasing water use efficiency (WUEF). Salinity reduced the appearance of the fruit by both decreasing the length (FL) and maximum width (FMW) of the fruit. However, increased ECiw also improved the taste of the hot peppers by increasing the total soluble solid (TSS) content, as well as adding to their nutritional quality with a higher content of Vitamin C (VC). Their storage quality was also improved because of an improvement in the firmness of the fruit (Fn) as well as a reduction in the fruit water content (FWC). An increase in the LF led to an increase in the total fruit yield, total dry biomass of fruit and plant, and WUEF; it also increased the FWC and VC content, and decreased the FMW and fruit shape index (FSI). The threshold-slope linear response and sigmoidal-sharp models were both a good fit for the measured total fruit yield, and the LF had no significant effect on the model parameters. The relative TSS and Fn increased linearly as the electrical conductivity (EC) of soil-saturated paste extract (ECe) increased, whereas they decreased linearly as the relative seasonal evapotranspiration (ETr) increased regardless of the LFs. The relative FW, FL, and FMW decreased linearly with the increased ECe, and increased linearly with the increased ETr regardless of the LFs. The relative fruit Na+ concentration increased linearly as the ECe increased. The regression correlations between the total fruit yield, fruit quality parameters, ion contents, and ECe or ETr could provide important information for salinity and irrigation water management with a compromise between the hot pepper yield and fruit quality.

Littoral benthic macroinvertebrate response to water‐level fluctuations in three reservoirs of the Willamette River Basin, Oregon

AbstractHigh‐head dams throughout the Willamette River Basin, Oregon create deep reservoirs that undergo inter‐seasonal and intra‐seasonal water‐level fluctuations (WLFs). The magnitude of WLFs is dependent on competing objectives of flood control, recreation, and water releases to maintain downstream habitat and facilitate migration of Endangered Species Act–listed salmonids. These reservoirs are drawn down to minimum conservation pool in winter, refilled to full pool by late spring and undergo variable WLFs, typically between 4 and 15 m, throughout summer. Here, we investigate the impact of seasonal WLFs on the density, biomass, and species composition of littoral benthic macroinvertebrates at Fall Creek, Hills Creek, and Lookout Point reservoirs. We sampled the submerged littoral zone during spring and summer using an adapted quadrat sampling method and assessed differences in species assemblages using a non‐parametric multivariate statistical technique. Descriptors of variation in substrate, WLF, temperature, and depth were incorporated to identify environmental variables associated with variation in assemblage composition. We hypothesized that density and biomass would decrease and assemblage composition would shift between seasons in response to WLFs. We found statistically significant differences in assemblage composition between seasons and among reservoirs, but density and biomass did not respond similarly. Observed variation in assemblages was associated with surface water temperature, water depth, substrate, and WLF. None of these variables alone explained observed variation. We provide evidence that seasonal WLFs influence macroinvertebrate assemblage composition and alter habitat characteristics. Our procedure effectively quantifies changes in species assemblages in impounded systems with low densities and dynamic littoral zones and can inform water management decisions with relatively modest costs.

Predicted Native Fish Response, Potential Rewards and Risks from Flow Alteration in a New Mexico Arid Mountain Stream

AbstractWater and natural resource managers are concerned with evaluating how fish habitat and populations may respond to water diversions and small‐scale flow augmentations. We used two‐dimensional hydraulic models, habitat suitability curves and an individual‐based population viability model to assess whether flow augmentations of about 0.28–0.57 m3/s would create suitable habitat for federally listed native fish loach minnow Rhinichthys cobitis and spikedace Meda fulgida in a reach of the Gila River, New Mexico, and then examined how fish population viability may change under a variety of colonization and extinction scenarios. These simulations help to inform water management decisions in a reach of the Gila River where river diversions currently exist and new diversions and augmentations are being proposed. Our results suggest that the flow augmentations evaluated will result in small changes (on average across life stages, −0.22% to 4.06%) in suitable habitat for loach minnow and spikedace depending on augmentation scenario and fish life stage. While these percent changes are small, they would result in a reduction in the dewatering of the river channel in a river reach where native fish abundance is thought to be low. Actual native fish responses to these habitat changes are unknown; however, these flow augmentations could potentially allow these native species to re‐colonize this river segment from upstream or downstream sources increasing species distribution and likely population viability. Maintaining viable populations of native fish in this river reach is dependent on complex factors including persistence of suitable habitat for multiple life stages, connectivity with other populations and minimizing risk of invasion from non‐native species. We recommend that these predictions from the habitat and population models be tested and verified in an adaptive management framework linking modelling, experimental management, monitoring and reassessment to inform water management decisions in the Gila River. Copyright © 2017 John Wiley & Sons, Ltd.

Exceedance Probability of the Standardized Precipitation-Evapotranspiration Index in the Texas High Plains

Drought is a common occurrence in many arid and semi-arid regions that can have large negative impacts on water resources and agricultural production. Since agricultural drought is affected by both water supply and demand (precipitation and evapotranspiration), it is beneficial to include both in agricultural drought monitoring. The Standardized Precipitation-Evapotranspiration Index (SPEI) was found to be a suitable drought index for monitoring agricultural drought. In this study, the SPEI calculated from agro-meteorological weather stations was used to determine exceedance probabilities at five levels in the Texas High Plains. In addition, the kriging method was used to interpolate between the stations to generate spatial maps for the exceedance probabilities. No significant differences were found between stations, indicating any station should be suitable to represent the Texas High Plains. Results showed drought conditions occurred at all five probability levels during the summer growing season for this region. Although differences were not significantly different, the interpolated maps showed a trend where minor differences in the SPEI values were associated with the West-East precipitation gradient. However, there was no trend associated with the North-South air temperature gradient. A risk analysis showed that the SPEI probability values can provide policy and decision makers with additional information for better water management in the Texas High Plains.

A platform for probabilistic Multimodel and Multiproduct Streamflow Forecasting

AbstractWe develop and test a probabilistic real‐time streamflow‐forecasting platform, Multimodel and Multiproduct Streamflow Forecasting (MMSF), that uses information provided by a suite of hydrologic models and satellite precipitation products (SPPs). The SPPs are bias‐corrected before being used as inputs to the hydrologic models, and model calibration is carried out independently for each of the model‐product combinations (MPCs). Forecasts generated from the calibrated models are further bias‐corrected to compensate for the deficiencies within the models, and then probabilistically merged using a variety of model averaging techniques. Use of bias‐corrected SPPs in streamflow forecasting applications can overcome several issues associated with sparsely gauged basins and enable robust forecasting capabilities. Bias correction of streamflow significantly improves the forecasts in terms of accuracy and precision for all different cases considered. Results show that the merging of individual forecasts from different MPCs provides additional improvements. All the merging techniques applied in this study produce similar results, however, the Inverse Weighted Averaging (IVA) proves to be slightly superior in most cases. We demonstrate the implementation of the MMSF platform for real‐time streamflow monitoring and forecasting in the Mara River basin of Africa (Kenya & Tanzania) in order to provide improved monitoring and forecasting tools to inform water management decisions.

Value of ENSO-Forecasted Drought Information for the Management of Water Resources of Small to Mid-Size Communities

Abstract. There have been great advances in climate forecasting ability in recent years. However, the use of this information in water management decision-making has been lacking. The temporal and spatial scales of forecasts and the difficulty of understanding forecast products have been cited as key reasons for the lack of use of these forecasts. The Community Water Deficit Index (CWDI) was previously developed as a tool to use El Nino Southern Oscillation (ENSO) forecasts to forecast droughts in small to mid-sized communities of the southeastern U.S. This study investigated the monetary value and benefits of using CWDI as a seasonal drought forecasting technique. The efforts were focused on determining the usefulness of drought information for municipal water management, the usefulness of water restrictions imposed by municipal water management, and the extent to which advance knowledge of probabilistic drought forecasts mitigates negative impacts. The results indicate that water use restrictions are effective for coping with drought, and the benefits of using forecasts and water management adjustments should involve planning. It was also found that by using drought forecasts, and thus having a drought preparedness plan, communities can save both water and money.

Effects of Evapotranspiration on Regional Land Surface Temperature in an Arid Oasis Based on Thermal Remote Sensing

Evapotranspiration (ET) is crucial to arid and semiarid environments because it substantially affects the energy and water cycles. Based on the estimation of continuous ET from barren or sparsely vegetated areas, this letter investigated how ET affects the regional land surface temperature (LST) in the Shiyanghe river catchment area, a typical inland river catchment in Northwest China. ET was estimated during 2008–2011 using a three-temperature model and MODIS data sets. LST was retrieved from the MODIS product (MOD11A2). Results taken from transects that began in the oasis area and ended in the desert reveal that ET decreased, with the daily average ET in the oasis being approximately 1.4 mm larger than that in the desert. By contrast, the LST in the oasis was 8 K lower than that in the desert. Statistical results suggested that ET and LST showed a negative relationship ( $R^{2}=0.83$ ). Further analysis showed that the correlation was strongly dependent on the water availability in barren or sparsely vegetated areas. It is concluded that in water-limited barren or sparsely vegetated regions, the negative correlation between ET and LST may provide alternative information for water management, such as identifying groundwater recharge in arid regions.

Implementing participatory monitoring in river management: The role of stakeholders' perspectives and incentives

Involving local stakeholders in monitoring has the potential to stimulate learning and improve management responses. However, there is limited understanding about factors which influence implementation and success. This paper reviews local stakeholders' perceptions with respect to the construction of longitudinal dams in the Dutch river Waal, and explores their incentives to be involved in monitoring the effects of this intervention. Interviews with key stakeholders showed that concerns and (dis)trust are important incentives for participating in monitoring. Surveys of local residents, recreational anglers and boaters, and shipping professionals mapped their level of trust, attachment to the river landscape and evaluation of the effects of the longitudinal dams. Our case study shows that incentives for participation differ between stakeholder groups, and that research into their perceptions of the local environment can inform water managers on how to involve these groups in participatory monitoring.

Integration of GRACE, ground observation, and land-surface models for groundwater storage variations in South Korea

ABSTRACTTerrestrial water storage (TWS) comprises all forms of water stored in the Earth’s surface. The gravity recovery and climate experiment (GRACE) twin satellite provides an efficient method of assessing TWS changes (TWSCs) by measuring variations in the Earth’s gravity. GRACE-derived TWS is equivalent to the sum of all forms of water such as surface water, soil moisture, snow water equivalent, and groundwater. Therefore, groundwater storage and its variations can be estimated when other variables are determined. We used Level-3 data (RL 05) to estimate monthly TWSC in South Korea. Data were obtained from land-surface models (LSMs) of global land data assimilation system (GLDAS), ground observations from water management information system (WAMIS) and rural agricultural water resources information system (RAWRIS). GRACE-derived groundwater storage changes (GWSCs) were −0.18 ± 6.5 cm month−1 on average, indicating the decrease of groundwater. We validated the GRACE-derived GWSC by comparing the changes with well-derived GWSC obtained from in situ groundwater observation wells of Korean national groundwater monitoring networks (NGMNs). This satellite-based remote-sensing methodology can provide an efficient tool for the nationwide planning and management of groundwater.

Increased tree-ring network density reveals more precise estimations of sub-regional hydroclimate variability and climate dynamics in the Midwest, USA

Understanding the historic variability in the hydroclimate provides important information on possible extreme dry or wet periods that in turn inform water management plans. Tree rings have long provided historical context of hydroclimate variability of the U.S. However, the tree-ring network used to create these countrywide gridded reconstructions is sparse in certain locations, such as the Midwest. Here, we increase (n = 20) the spatial resolution of the tree-ring network in southern Indiana and compare a summer (June–August) Palmer Drought Severity Index (PDSI) reconstruction to existing gridded reconstructions of PDSI for this region. We find both droughts and pluvials that were previously unknown that rival the most intense PDSI values during the instrumental period. Additionally, historical drought occurred in Indiana that eclipsed instrumental conditions with regard to severity and duration. During the period 1962–2004 CE, we find that teleconnections of drought conditions through the Atlantic Meridional Overturning Circulation have a strong influence (r = −0.60, p < 0.01) on secondary tree growth in this region for the late spring-early summer season. These findings highlight the importance of continuing to increase the spatial resolution of the tree-ring network used to infer past climate dynamics to capture the sub-regional spatial variability. Increasing the spatial resolution of the tree-ring network for a given region can better identify sub-regional variability, improve the accuracy of regional tree-ring PDSI reconstructions, and provide better information for climatic teleconnections.

Hydroclimatic controls on non-stationary stream water ages in humid tropical catchments

Streams in humid tropical countries provide a wide range of ecosystem services, yet a good understanding of their hydrological functioning is severely limited by lack of data. The transit time of water is a fundamental characteristic of catchment functioning and can often be related to water quality dynamics, thus providing potentially important information for water managers in these environments. In this study, we applied the widely used lumped convolution integral model in a moving window approach to acknowledge the time-variance of transit time distributions (TTD) and resulting moments such as the mean transit time (MTT). We show that for a two-year (2012–2014) rainfall-runoff stable isotope record from almost daily sampling in a humid tropical 30km2 catchment in southern Costa Rica, the MTTs are generally short (<one year), but exhibit distinct inter and intra-annual patterns. The drier year (2012–13), which was under the influence of El-Niño causing less precipitation, exhibited MTTs up to one year. In contrast, the wetter year (2013–14) resulted in MTT estimates <100days. Similar patterns were found at an intra-annual scale: the dry season MTTs were on average 185days and only 15days during the wet season. This can be explained by high rainfall volumes (>3m/year) and events occurring throughout the year, the seasonality of rainfall and distinct moisture origin (Pacific, Atlantic and land surface), the likely dominance of quick near-surface flow paths and relatively low subsurface storage of the underlying volcanic and sedimentary rocks. The moisture origin of rainfall was found to be the most dominant driver of time-variable TTDs as indicated by the changing average wind directions following the transition from the dry into the wet season. This isotope study revealed a highly dynamic system that is likely to be sensitive to environmental change.

Monthly Precipitation Patterns in a Region Vulnerable to Climate-Related Hazards—A Case Study from Poland

Precipitation totals at annual and monthly scale are key elements affecting water availability for a number of human activities. Thus, the multi-year variability and probability distribution of precipitation form the basis information for water management and damage risk assessment (caused by drought and heavy rains). The main goal of this paper is to analyse the precipitation patterns and to determine the non-exceedance probability (p, %) of extreme monthly precipitation in the region influenced by lignite mining and dominated by traditional agricultural production. Monthly precipitation totals recorded in 1961–2010 at four weather stations close to the analysed region were examined, including comparative analysis of precipitation patterns between the stations. Different non-exceedance probability (p, %) was determined with focus on extreme precipitation. Annual and monthly precipitation was characterised by a large variation of values. Temporal variability was larger than the spatial variability. The highest average sums were registered in July and the lowest in February. Minimum monthly precipitation (&lt;10 mm) were recorded between January and April, and in October at all four weather stations. Maximum totals, amounting to more than 200 mm, were noted in July. The largest share of absolute minimum and maximum monthly precipitation was recorded at the turn of 20th and 21st centuries. Temporal and spatial distribution of precipitation for very dry, abnormally dry and extremely dry months (p ≤ 20%) were characterised by lower dispersion of values compared with wet months (p ≥ 80%). The precipitation probability distribution at p ≤ 20% may be useful to determine agricultural drought risk assessment in the region. Monthly precipitation at p ≥ 80% may be the background for planning drainage system efficiency and assessment of flooding risk of lignite deposits.

Statistically Extracted Fundamental Watershed Variables for Estimating the Loads of Total Nitrogen in Small Streams

Accurate estimation of total nitrogen loads is essential for evaluating conditions in the aquatic environment. Extrapolation of estimates beyond measured streams will greatly expand our understanding of total nitrogen loading to streams. Recursive partitioning and random forest regression were used to assess 85 geospatial, environmental, and watershed variables across 636 small (<585 km2) watersheds to determine which variables are fundamentally important to the estimation of annual loads of total nitrogen. Initial analysis led to the splitting of watersheds into three groups based on predominant land use (agricultural, developed, and undeveloped). Nitrogen application, agricultural and developed land area, and impervious or developed land in the 100-m stream buffer were commonly extracted variables by both recursive partitioning and random forest regression. A series of multiple linear regression equations utilizing the extracted variables were created and applied to the watersheds. As few as three variables explained as much as 76 % of the variability in total nitrogen loads for watersheds with predominantly agricultural land use. Catchment-scale national maps were generated to visualize the total nitrogen loads and yields across the USA. The estimates provided by these models can inform water managers and help identify areas where more in-depth monitoring may be beneficial.

Comparison of random forests and other statistical methods for the prediction of lake water level: a case study of the Poyang Lake in China

Modeling of hydrological time series is essential for sustainable development and management of lake water resources. This study aims to develop an efficient model for forecasting lake water level variations, exemplified by the Poyang Lake (China) case study. A random forests (RF) model was first applied and compared with artificial neural networks, support vector regression, and a linear model. Three scenarios were adopted to investigate the effect of time lag and previous water levels as model inputs for real-time forecasting. Variable importance was then analyzed to evaluate the influence of each predictor for water level variations. Results indicated that the RF model exhibits the best performance for daily forecasting in terms of root mean square error (RMSE) and coefficient of determination (R2). Moreover, the highest accuracy was achieved using discharge series at 4-day-ahead and the average water level over the previous week as model inputs, with an average RMSE of 0.25 m for five stations within the lake. In addition, the previous water level was the most efficient predictor for water level forecasting, followed by discharge from the Yangtze River. Based on the performance of the soft computing methods, RF can be calibrated to provide information or simulation scenarios for water management and decision-making.

Satellite-based evapotranspiration over Gezira Irrigation Scheme, Sudan: A comparative study

Understanding the spatio-temporal variation of actual evapotranspiration (ETa) over irrigated agricultural areas helps to manage water. Many remote sensing (RS) methods have been developed recently to estimate ETa. Nevertheless, selecting the suitable method is still a challenge. The objective of this research is to evaluate four RS methods for estimating ETa over the large-scale Gezira Scheme of Sudan. Three methods, namely Surface Energy Balance Algorithm for Land (SEBAL), Mapping EvapoTranspiration at High Resolution with Internalized Calibration (METRIC) and Simplified Surface Energy Balance (SSEB), were applied using Landsat images. Another RS dataset, i.e. ETa product from Moderate Resolution Imaging Spectroradiometer (MODIS) satellite (MOD16A2), was also used in the comparison. The ETa methods were validated using field-scale water balance (WB) estimates during the 2004 crop season. Furthermore, the present study suggested the use of Normalized Difference Vegetation Index (NDVI) and integrated NDVI (iNDVI) as an approach to assessing the performance of the ETa estimates from RS on daily and seasonal scales, respectively. Several performance measures were evaluated, and a score was given for each method in order to extract the most valuable information for water management out of four different methods. Based on ranking criteria, SSEB gave the best performance followed by SEBAL. METRIC is not suitable for estimating ETa where ground-data are limited. MOD16A2 was less sensitive to detection of ETa at field level because of pixel resolution, but it had high score at the scheme level. All methods showed similar spatial patterns of seasonal ETa, with a decreasing ETa gradient from southeast to northeast of the scheme. In conclusion, SSEB and MOD16A2 are seen as suitable operational ETa methods on the regional scale as both methods require less application time compared to the other complex models. SSEB has the advantage of estimating ETa on field scale and on daily basis. The results of this study contribute to improving the understanding of performance of such methods in large irrigation schemes in arid climate zones.

A field-based method to derive macroinvertebrate benchmark for specific conductivity adapted for small data sets and demonstrated in the Hun-Tai River Basin, Northeast China

Ionic mixtures, measured as specific conductivity, have been increasingly concerned because of their toxicities to aquatic organisms. However, identifying protective values of specific conductivity for aquatic organisms is challenging given that laboratory test systems cannot examine more salt-intolerant species nor effects occurring in streams. Large data sets used for deriving field-based benchmarks are rarely available. In this study, a field-based method for small data sets was used to derive specific conductivity benchmark, which is expected to prevent the extirpation of 95% of local taxa from circum-neutral to alkaline waters dominated by a mixture of SO42− and HCO3− anions and other dissolved ions. To compensate for the smaller sample size, species level analyses were combined with genus level analyses. The benchmark is based on extirpation concentration (XC95) values of specific conductivity for 60 macroinvertebrate genera estimated from 296 sampling sites in the Hun-Tai River Basin. We derived the specific conductivity benchmark by using a 2-point interpolation method, which yielded the benchmark of 249 μS/cm. Our study tailored the method that was developed by USEPA to derive aquatic life benchmark for specific conductivity for basin scale application, and may provide useful information for water pollution control and management.

System Analysis for Water Management Information Strategy of Agricultural Reservoir managed by City and County

Water management information system used by KRC(Korea Rural Community Corporation) operates widely including RIMS, RAWRIS and etc. Other systems are operated by each government department, for example, K-water(Korea Water Resources Corporation)`s WAMIS. Even though small scale reservoirs managed by city/country is just about 12% of total water resource, the reservoirs are important for controlling and securing water resource as the reservoirs, including about 14,700 reservoirs nationwide, are located at main subwater shed. So, it is necessary for KRC to execute integrated informatization. In this research, system analysis was performed to comprise the integrated water management information system including the reservoirs controlled by city and country at first. And then, improvement plan for informatization of the reservoirs controlled by city and country was proposed. This study proposed the improvement plan for informatization of the reservoirs managed by the city and country, which was systematically proposed through systemic analysis including from reservoir site to the integrated water management information system. The objects includes 1. Reservoir (basin, facilities, water depth-area curve, benefiter area), 2. Field supervision organization for the reservoir 3. Local government administrative organization, 4. Center organization 5. Network for information transfer, 6. integrated water management information system. As the reservoirs controlled by city and country are important considering managing water and facilities, operated by local government with minimum budget due to budget problem, securing sufficient budget is necessary to form an specialized organization controlling facilities and the water management system in terms of drought and flood control.

GRACE-Derived Terrestrial Water Storage Changes in the Inter-Basin Region and Its Possible Influencing Factors: A Case Study of the Sichuan Basin, China

We investigate terrestrial water storage (TWS) changes over the Sichuan Basin and the related impacts of water variations in the adjacent basins from GRACE (Gravity Recovery and Climate Experiment), in situ river level, and precipitation data. Although GRACE shows water increased over the Sichuan Basin from January 2003 to February 2015, two heavy droughts in 2006 and 2011 have resulted in significant water deficits. Correlations of 0.74 and 0.56 were found between TWS and mean river level/precipitation within the Sichuan Basin, respectively, indicating that the Sichuan Basin TWS is influenced by both of the local rainfall and water recharge from the adjacent rivers. Moreover, water sources from the neighboring basins showed different impacts on water deficits observed by GRACE during the two severe droughts in the region. This provides valuable information for regional water management in response to serious dry conditions. Additionally, the Sichuan Basin TWS is shown to be influenced more by the Indian Ocean Dipole (IOD) than the El Niño-Southern Oscillation (ENSO), especially for the January 2003–July 2012 period with a correlation of −0.66. However, a strong positive correlation of 0.84 was found between TWS and ENSO after August 2012, which is a puzzle that needs further investigation. This study shows that the combination of other hydrological variables can provide beneficial applications of GRACE in inter-basin areas.

Effect of phytoremediation on concentrations of benzene, toluene, naphthalene, and dissolved oxygen in groundwater at a former manufactured gas plant site, Charleston, South Carolina, USA, 1998–2014

Concentrations of benzene, toluene, naphthalene, and dissolved oxygen in groundwater at a former manufactured gas plant site near Charleston, South Carolina, USA, have been monitored since the installation of a phytoremediation system of hybrid poplar trees in 1998. Between 2000 and 2014, the concentrations of benzene, toluene, and naphthalene (BTN this pathway of uptake by trees was confirmed by the detection of benzene, toluene, and naphthalene in trees during sampling events in 2002, and later in the study in 2012. These data suggest that the phytoremediation system affects the groundwater contaminants on a seasonal basis and, over multiple years, has resulted in a cumulative decrease in dissolved-phase contaminant concentrations in groundwater. The removal of dissolved organic contaminants from the aquifer has resulted in a lower demand on dissolved oxygen supplied by recharge and, as a result, the redox status of the groundwater has changed from anoxic to oxic conditions. This study provides much needed information for water managers and other scientists on the viability of the long-term effectiveness of phytoremediation in decreasing groundwater contaminants and increasing dissolved oxygen at sites contaminated by benzene, toluene, and naphthalene.

Crop coefficient for cotton under plastic mulch and drip irrigation based on eddy covariance observation in an arid area of northwestern China

Crop coefficient (Kc) is an important parameter in irrigation management. Kc values published by Food and Agriculture Organization (FAO) are subject to uncertainties and adjustment when applied to different areas under different climates and/or irrigation methods. This study investigated Kc of cotton in an experimental site under plastic mulch and drip irrigation in the Tarim River Basin in northwestern China through a 3-year crop evapotranspiration (ETc) observation by using the eddy covariance system. The average ETc during the growing seasons in 3 years is 526mm, and the locally developed Kc values during the initial, mid, and late seasons are 0.23, 0.88, and 0.44, respectively. The relationships between Kc and leaf area index (LAI), Kc and growing degree days (GDD), and Kc and growing days after sowing (GD) were further analyzed. The relationship between weekly Kc and GDD, as well as weekly Kc and GD, during the growth stage after sowing is fitted to a third-order polynomial model (R2=0.96 and 0.95, respectively). Meanwhile, the relationship between weekly Kc and LAI is suitably described using a logarithmic model (R2=0.87). As LAI was not measured every day, daily and weekly models were reestablished based on LAI measurement days. The performance of the LAI model is low on a weekly basis (R2=0.88, 0.88, 0.72 for GD, GDD, and LAI models, respectively) but accurate on a daily basis (R2=0.81, 0.81, 0.89 for GD, GDD, and LAI models, respectively). GD is a reliable indicator to estimate Kc of cotton under plastic mulch and drip irrigation and provides a basis for evapotranspiration estimation in cotton fields by using the FAO-56 method. This study provides valuable supplementary and reference information for efficient water management in cotton cropping systems in arid regions.