Non-rainy Days Research Articles

Influence of rainfall on fungal aerobiota in the urban atmosphere over Tianjin, China: A case study

Fungal aerosols, which play significant roles in affecting human health and regional climate, are closely affected by rainfall. But knowledge about the influence of rainfall on fungal aerobiota in the urban atmosphere remains limited. Here, airborne total suspended particles and size-segregated particles were collected from urban Tianjin, China, to investigate such an impact by high-throughput gene sequencing. On non-rainy days, the genera Cladosporium (16.0%), Alternaria (7.9%) and Aspergillus (6.1%) dominated in fungal aerobiota. On rainy days, in addition to Cladosporium (11.1%) and Aspergillus (5.5%), the genus Schizophyllum which is apt to release spores under humid environment became more abundant (8.2%). Airborne fungi were mainly identified as plant endophytes on non-rainy days, while wood saprophytes dominated on rainy days. Precipitation had a significant impact on the fungal aerobiota in small size ranges (<1.1 μm, p < 0.05) and caused an increase in the proportions of the major fungal genera in the particle-size smaller than 1.1 μm (e.g., Cladosporium , Aspergillus and Penicillium ), which may pose more threat to human health. This study provides important insights into precipitation-induced perturbation of fungal aerobiota, especially for those in small size ranges. Moreover, our results revealed the vital role of plants playing in releasing fungi into the air in different pathways on non-rainy and rainy days. • The genus Schizophyllum apt to release spores in humid air became more abundant (8.2%) on rainy days. • Plants released fungi into the air in different pathways on non-rainy and rainy days. • Rainfall had a significant impact on the fungal aerobiota in size smaller than 1.1 μm.

Accounting for seasonal effects on cyclist-vehicle crashes

Crash data is usually aggregated over time where temporal correlation contributes to the unobserved heterogeneity. Since crashes that occur in temporal proximity share some unobserved characteristics, ignoring these temporal correlations in safety modeling may lead to biased estimates and a loss of model power. Seasonality has several effects on cyclists’ travel behavior (e.g., the distribution of holidays, school schedules, weather variations) and consequently cyclist-vehicle crash risk. This study aims to account for the effect of seasonality on cyclist-vehicle crashes by employing two groups of models. The first group, seasonal cyclist-vehicle crash frequency, employs four vectors of the dependent variables for each season. The second group, rainfall involved cyclist-vehicle crash frequency, employs two vectors of the dependent variables for crashes that occurred on rainy days and non-rainy days. The two model groups were investigated using three modeling techniques: Full Bayes crash prediction model with spatial effects (base model), varying intercept and slope model, and First-Order Random Walk model with a spatial–temporal interaction term. Crash and volume data for 134 traffic analysis zones (TAZ’s) in the City of Vancouver were used. The results showed that the First-Order Random Walk model with spatial–temporal interaction outperformed the other developed models. Some covariates have different associations with crashes depending on the season and rainfall conditions. For example, the seasonal estimates for the bus stop density are significantly higher for the summer and spring seasons than for the winter and autumn seasons. Also, the intersection density estimate for a rainy day is significantly higher than a non-rainy day. This indicates that on a rainy day each intersection to the network adds more risk to cyclists compared to a non-rainy day.

Is There Daily Growth Hysteresis versus Vapor Pressure Deficit in Cherry Fruit?

The growth of cherry fruit is generally described using a double sigmoid model, divided into four growth stages. Abiotic factors are considered to be significant components in modifying fruit growth, and among these, the vapor pressure deficit (VPD) is deemed the most effective. In this study, we investigated sweet cherry fruit growth through the continuous, hourly monitoring of fruit transversal diameter over two consecutive years (2019 and 2020), from the beginning of the third stage to maturation (forth stage). Extensometers were used in the field and VPD was calculated from weather data. The fruit growth pattern up to the end of the third stage demonstrated three critical steps during non-rainy days: shrinkage, stabilization and expansion. In the third stage of fruit growth, a partial clockwise hysteresis curve of circadian growth, as a response to VPD, appeared on random days. The pattern of fruit growth during rainy days was not distinctive, but the amount and duration of rain caused a consequent decrease in the VPD and indirectly boosted fruit growth. At the beginning of the fourth stage, the circadian growth changed and the daily transversal diameter vs VPD formed fully clockwise hysteresis curves for most of this stage. Our findings indicate that hysteresis can be employed to evaluate the initial phenological phase of fruit maturation, as a fully clockwise hysteresis curve was observable only in the fourth stage of fruit growth. There are additional opportunities for its use in the management of fruit production, such as in precision fruit farming.

Analysis of the Flow Performance of the Complex Cross-Section Module to Reduce the Sedimentation in a Combined Sewer Pipe

The difference in the amount of stormwater and sewage in a combined sewer system is significantly large in areas where heavy rainfall is concentrated. This leads to a low water level and slow flow velocity inside the pipes, which causes sedimentation and odor on non-rainy days. A complex cross-section module increases the flow velocity by creating a small waterway inside the pipe for sewage to flow on non-rainy days. While considering Manning’s equation, we applied the principle where the flow velocity is proportional to two-thirds of the power of the hydraulic radius. The flow velocity of a circular pipe with a diameter of 450 mm and the corresponding complex cross-section module was analyzed by applying Manning’s equation and numerical modeling to show the effects of the complex cross-section module. The tractive force was compared based on a lab-scale experiment. When all conditions were identical except for the cross-sectional shape, the average flow velocity of the complex cross-section module was 14% higher while the size of the transported sand grains was up to 0.5 mm larger. This increase in flow velocity can be even higher if the roughness coefficient of aging pipes can be decreased.

Effect of Road Traffic on Air Pollution. Experimental Evidence from COVID-19 Lockdown

The increasing concentration of human activities in cities has been leading to a worsening in air quality, thus negatively affecting the lives and health of humans living in urban contexts. Transport is one of the main sources of pollution in such environments. Several local authorities have therefore implemented strict traffic-restriction measures. The aim of this paper is to evaluate the effectiveness and limitations of these interventions, by analyzing the relationship between traffic flows and air quality. The used dataset contains concentrations of NO, NO2, NOx and PM10, vehicle counts and meteorology, all collected during the COVID-19 lockdown in the city of Padova (Italy), in which severe limitations to contain the spread of the virus simulated long and large-scale traffic restrictions in normal conditions. In particular, statistical tests, correlation analyses and multivariate linear regression models were applied to non-rainy days in 2020, 2018 and 2017, in order to isolate the effect of traffic. Analysis indicated that vehicle flows significantly affect NO, NO2, and NOx concentrations, although no evidence of a relationship between traffic and PM10 was highlighted. According to this perspective, measures to limit traffic flows seem to be effective in improving air quality only in terms of reducing nitrogen oxide.

Trend characteristics of rainy days and evaporation at a tropical rainforest region in East Malaysia, Borneo

Impact of climate change over the hydrological system in a region can be identified through statistical characterization of hydrometerological parameters such as rainfall, temperature, humidity and evaporation. In order to understand the influence of climate change, statistical trend characteristics of rainy days, non-rainy days and evaporation rate in the Limbang River Basin (LRB) in Sarawak, Malaysia, Northern Borneo was assessed in the present research. Annual rainfall and monthly evaporation data, over a period of 46 years, (1970 - 2015) corresponding to three rain gauging stations, the Limbang DID, Ukong and Long Napir were used in the research. Linear regression model, Mann Kendall and Sen’s slope estimator techniques were applied to detect the statistical trends in rainy days and evaporation. A statistically significant increasing trend in annual rainy days was found at all the stations. Non-rainy days showed a statistically significant decreasing trend at Limbang DID and Ukong. Monthly evaporation rates showed an overall increasing trend and the greatest increasing trend in evaporation was observed in September (2.55 mm/year) for the Limbang DID and in December (2.61 mm/year) for Ukong. Evaporation measured at the Ukong station also showed a non-significant decrease during June and September. A comparison of the evaporation controlling meteorological variables such as rainfall, temperature and relative humidity indicates inter-influence at various strengths. Along with local precipitation characteristics, wind and fluctuation of atmospheric temperature over the region plays a vital role in increased rate of evaporation from the region. Overall, the analysis identified a statistically significant increasing trend in rainy days and evaporation in the LRB. The results of the present research can be used as critical planning data for micro and macro hydroelectric projects in the river basin.

Quantifying the cooling effect of rain events on outdoor thermal comfort in the southern coastal stations of the Caspian Sea.

Pleasant outdoor thermal conditions depend on a wide range of climatic elements. The impact of rainfall events, as important climatic elements, on providing thermal comfort, has been less explored in the available literature. The work presented herein investigates the impact of Rainy Days as well as a Day Prior to (Dprior) and a Day Post rain (Dpost) events on thermal conditions in the southern coastal region of the Caspian Sea. In this study, rainfall events during 1961-2017 observational period were categorized based on their intensity. Then, human thermal comfort during non-rainy (sunny) and rainy days was estimated and compared by using the radiation-driven Physiological Equivalent Temperature (PET) index, Universal Thermal Climate Index (UTCI) and Perceived Temperature (PT) index. Furthermore, difference between the average of thermal conditions in rainy days compared to a day prior and a day post rain events was calculated separately for comfort, cold and heat stress thresholds of each bioclimatic index. Finally, the correlation between the average of indices for rainy days and the frequency of rainfall events of each specific year was computed. Results suggested that overall average of studied indices for all rainy days is lower than the average for days prior and post the rain events. PET index has shown to be most impacted and reduced as a result of rain events and therefore more indicative of a cool ing effect. The observed difference in total average of PET in rainy days compared to non-rainy days were 8.30°C, 5.86°C and 8.85°C for Babolsar, Rahst and Gorgan stations, respectively. Generally, the cooling effect of rain events on the temperature for a day prior rain events is higher than a day post rainfall. Finally, the trend analysis on rainy days in the studied period revealed that the average of bioclimatic indices in western stations (Babolsar and Rasht) are increasing whereas a decreasing trend was observed for Gorgan as more of an eastern station.

Crop type identification and spatial mapping using Sentinel-2 satellite data with focus on field-level information

Accurate monitoring of croplands helps in making decisions (for insurance claims, crop management and contingency plans) at the macro-level, especially in drylands where variability in cropping is very high owing to erratic weather conditions. Dryland cereals and grain legumes are key to ensuring the food and nutritional security of a large number of vulnerable populations living in the drylands. Reliable information on area cultivated to such crops forms part of the national accounting of food production and supply in many Asian countries, many of which are employing remote sensing tools to improve the accuracy of assessments of cultivated areas. This paper assesses the capabilities and limitations of mapping cultivated areas in the Rabi (winter) season and corresponding cropping patterns in three districts characterized by small-plot agriculture. The study used Sentinel-2 Normalized Difference Vegetation Index (NDVI) 15-day time-series at 10 m resolution by employing a Spectral Matching Technique (SMT) approach. The use of SMT is based on the well-studied relationship between temporal NDVI signatures and crop phenology. The rabi season in India, dominated by non-rainy days, is best suited for the application of this method, as persistent cloud cover will hamper the availability of images necessary to generate clearly differentiating temporal signatures. Our study showed that the temporal signatures of wheat, chickpea and mustard are easily distinguishable, enabling an overall accuracy of 84%, with wheat and mustard achieving 86% and 94% accuracies, respectively. The most significant misclassifications were in irrigated areas for mustard and wheat, in small-plot mustard fields covered by trees and in fragmented chickpea areas. A comparison of district-wise national crop statistics and those obtained from this study revealed a correlation of 96%.

Accuracy analysis of IMERG and CMORPH precipitation data over North China

Large-scale agricultural production in North China makes the study of precipitation in this area vital. The performance of the Integrated Merged Multisatellite Retrievals for the Global Precipitation Measurement (IMERG) and the Climate Prediction Center morphing technique (CMORPH) precipitation products for 2015 was evaluated against daily precipitation data from 404 rain gauges in North China. Relative errors, correlation coefficients, Pearson’s chi-squared test values, and root mean square errors, as well as the probability of detection (POD), false alarm ratio, and critical success index, were used to analyze the accuracy of both IMERG and CMORPH precipitation products on daily, monthly, and seasonal timescales. The probability density function (PDF) was also considered. Overall, both products overestimated ground precipitation, especially in summer. Positive correlation coefficients between satellite-derived and rain-gauge monthly precipitation data were higher over plains and coastal areas, compared with plateau regions. The PODs of both IMERG and CMORPH data were highest in summer. The PODs of IMERG data were much higher than for CMORPH data in autumn. The PODs over coastal regions, plains, and plateaus at lower latitudes also were considerably better than over inland and plateau areas at higher latitudes. The precipitation products performed best over coastal areas, plains, and areas with high rainfall. Both CMORPH and IMERG products were prone to identifying non-rainy days as rainy days. They also overestimated light (0.1-9.9 mm d-1) and moderate (10-24.9 mm d-1) precipitation events, although the IMERG product was more sensitive to precipitation. Accordingly, we find that both of these satellite-derived precipitation products require further modification to enable them to substitute for gauge precipitation data in North China.

A combined sewer design method using tractive force considering wastewater flow on non-rainy days and its application for improvement methods of sewer

A combined sewer design method using tractive force considering wastewater flow on non-rainy days and its application for improvement methods of sewer

동복호 유역에 설치된 수질오염물질 처리시설들의 효율성 평가

The pollutant load discharged in Dongbok lake watershed was estimated as BOD 893.4 kg/day, TN 729.3 kg/day and TP 55.9 kg/day in 2017 year. The largest amount of the load was the livestock and land-based pollutants, but the domestic wastewater-based amount also accounted for 12.4%, most of which were originated from the non-treated sewage in the living system. The number of public sewage treatment facilities installed to Dongbok lake watershed was 34, and the average removal efficiency of pollutant by them was BOD 90.6%, T-N 53.9% and T-P 58.7%. As a result, the load discharged from the facilities accounted for 1.0% of BOD, 13.2% of T-N and 12.3% of T-P in the total amount discharged from point sources. Meanwhile, 7 artificial wetland facilities for non-point pollutant treatment were installed and operated in the watershed. The average removal efficiency of the wetland during rainfall was BOD 2.8%, COD -14.9%, SS 71.7%, T-N 42.5%, and T-P 22.1%, but the contribution rate of water quality improvement during normal (non-rainy) day by these facilities was very low: BOD -1.5%, T-N 3.0%, and T-P 0.4%.

Variation in reproductive output as a function of maternal age and weather conditions in the cultured Asian yellow pond turtle, Mauremys mutica

Abstract Biotic factors (e.g., maternal age) and abiotic factors (e.g., weather) play vital roles in reproduction. However, there is little information about the combined effects of maternal age and weather on the reproductive output of cultured Asian yellow pond turtles, Mauremys mutica. To address this issue, we surveyed and compared the reproductive output of 13-year-old and 25-year-old female turtles on non-rainy and rainy days. The results showed that older females produced larger eggs than younger females regardless of the weather conditions. Females laid larger clutch sizes (number of eggs per nest) under non-rainy conditions compared with those under rainy conditions. However, the variation in clutch frequency (number of clutches per day) was independent of maternal age and weather. There was no effect of an interaction between maternal age and weather on egg mass, clutch size or clutch frequency. Our results suggest that maternal age and weather had significant effects on egg mass and clutch size, respectively. These results imply that maternal age, together with weather conditions (mainly conditions of rain), can affect the reproductive output of M. mutica. Our results provide useful information for the artificial breeding and stock management of M. mutica.

Analysis of PWV Derived from the GNSS CORS Stations for Determining the Onset of the Southwest Monsoon in Thailand

This research shows a new threshold for identifying the onset of southwest monsoons using Precipitable Water Vapor (PWV) obtained from GNSS Continuously Operating Reference Stations (CORS) in Thailand by analyzing data from 2007 to 2016. It was found that PWV values for rainy days are higher than non-rainy days. The average PWV for the years 2007-2016 of CHAN station in May was used to determine the new threshold. This new threshold is met when the average value of PWV in May exceeds 58.50 mm for three consecutive days. During the ten years of the study period, the onset date calculated from this method varies by no more than 1-3 days from that calculated by the Thai Meteorological Department (TMD) method, except for 2008 and 2010, when the variance is more than three days. As for other regions namely the central region, the northeast region, and the northern region, it was found that the calculation of the onset of the monsoon season typically varies by 3-5 days.

Assessment of Rainfall Distributions and Characteristics in Coastal Provinces of the Vietnamese Mekong Delta under Climate Change and ENSO Processes

Rainwater is considered a promising alternative water source for coastal areas where freshwater resources are increasingly under pressure. This study evaluates rain regime characteristics that influence the ability to exploit rainwater in the coastal provinces of the Vietnamese Mekong Delta (VMD). In particular, it considers the impact of climate change and El Niño–Southern Oscillation (ENSO) processes. We analyzed rainfall data from 102 monitoring stations across the VMD from 1989 to 2017. Using statistical methods, we explored (1) characteristics of the rainy season, including the dates of onset and cessation and season length; (2) average rainfall volumes; and (3) the maximum number of consecutive nonrainy days during the rainy season and over the year. We also analyzed changes in these characteristics over time, in parallel with ENSO processes and climate change. Trend lines were determined using nonparametric methods, utilizing Sen’s slope estimation and the Mann–Kendall test. Results showed a tendency for the rainy season to start earlier and end later in the western coastal zone of the study area, with season length gradually decreasing towards the East Sea and inland. The shortest rainy season was found in the estuary zone (in the northeast of the VMD). Rainfall was abundant on the west coast, again diminishing gradually towards the East Sea and inland. Rain was also quite plentiful during four dry season observation months in the study area, but it lacked the predictability needed for effective exploitation. The number of consecutive days without rain averaged 96 annually, with a difference of 29 days between the largest and smallest observations. The difference between the provinces with the longest and shortest periods without rain averaged 41 days. Although the impact of climate change on the rain regime is complex, we can say that the rainy season now tends to start earlier, end later, and be lengthier, though without exhibiting clear trends. ENSO processes significantly impacted rainfall regime characteristics, especially the dates of onset and cessation, and season length.

Stronger Global Warming on Nonrainy Days in Observations From China

AbstractNonrainy days have rather different hydrologic and radiative conditions than rainy days, but few investigations considered how these different conditions contribute to the observed global warming. Here, we show that global warming is considerably stronger on nonrainy days using observations from China. We find that trends in mean temperature on nonrainy days are about 0.1 ° C/10 yr higher than on rainy days, and that about 80% of the total temperature increase is contributed by nonrainy days. The main reason is likely to be a stronger sensitivity of downwelling longwave radiation to greenhouse forcing on nonrainy days due to fewer clouds and water vapor compared with rainy days, which is not a hydrological effect but mainly a radiative effect. Our findings are consistent with the stronger mean temperature trends in drier regions and imply that the different temperature sensitivities on nonrainy and rainy days may have profound effects on natural and social systems.

A Study on River Representation for Water Impaired Analysis of Measurement Data at TPLMs

Objectives:This study assessed the applicability of the total pollutant load management (TPLM) data on the analysis of impaired waterbody and pollutant source characterization. To achieve the study objective, the TPLM data collected in the downstream of Yeongcheon-Dam within the Geumho A unit-basin, Nakdong River basin for 6 years (2013-2018) were used to analyze the accountability for precipitation conditions, seasons, and flow rates. Methods:The study area is the downstram of Yeongcheon Dam within the Geumho A unit-basin, Nakdong River basin. The TPLM data used in this study were obtained from the two monitoring stations in the mainstream of Geumho River (i.e., Jahocheon and Geumho A station) and the three tributary streams (i.e., Gochoncheon, Sillyeongcheon, and Bugancheon). Precipitation conditions were classified into rainy (&gt;10 mm/day) and non-rainy days (≤10 mm/day) to assess the TPLM data accountability for the two precipitation conditions. Seasonal accountabilities of the TPLM data were assessed for spring (March-May), summer (June-August), autumn (September-November), and winter (December-February). The TPLM data accountability for stream flow rates was assessed using the standardized daily flow rates which were estimated by % of maximum flow rate. The daily flow rates were simulated using the Hydrologic Simulation Program-Fortran (HSPF).Results and Discussion:During the study period (2013-2018), TPLM data were collected 35-41 times throughout a year in the two Geumho River mainstream stations (i.e., Jahocheon, and Geumho A), while the tributary streams (i.e., Gochoncheon, Sillyeongcheon, and Bugancheon) were monitored 36 times per year excluding every January, February, and December. The tributary streams shown the missing data months because those stations were monitored through the implementation assessment for total maximum daily load (TMDL) management. But, the mainstream data were continuously collected by the Water Environment Research Institute. The accountability assessment results shown that 28%, 25%, 28%, and 19% of TPLM data for the two mainstream stations represents spring, summer, autumn, and winter seasons. The three TPLM station data in the tributary streams could not account for winter season with the seasonal data ratios of 29% for spring, 32% for summer, 34% for autumn, and 4% for winter. Secondly, 37.9% and 23.1% of TPLM data for the two mainstream stations and the three tributary streams, respectively, were collected during rainy days. Comparing to 22% of rainy days throughout the study period, the two mainstream stations were monitored more frequently during rainy days than the tributary stations. Lastly, accountability for stream flow rates shown that the annual TPLM data cannot account for mainstream flow conditions. For the tributary stream flow rates, six years composite TPLM data could not represent the flow conditions. Therefore, the TPLM data need to be carefully reviewed before assessing impaired waterbody and pollutant source characterization. Conclusions:TPLM data was widely used in TMDL implementation and research activities. Thus, detailed TPLM monitoring plans should be developed to improve accountability for various stream characteristics including precipitation, season, and flow rate, etc. In addition, further research is needed to represent wide ranges of flow rate which are hard to be predicted due to the large uncertainties induced by precipitation, precipitation intensity, precedent rain days, and other factors (e.g., dams, wastewater treatment plants, etc.).

Effects of rainfall on the use of emergency medical services

Emergency Medical Services (EMS) is an essential component of any healthcare system in the world, providing patients with medical care and a transfer system to hospitals. This system requires for an undisrupted and flawless provision of healthcare, considering factors that are controllable and uncontrollable. The aim of this study is to determine the effects of precipitation on the use of emergency medical services. This is a retrospective observational study, for which the precipitation data used was obtained from the Turkish State Meteorological Service. The daily number of cases transferred by EMS teams was obtained from the ASOS system of the Ankara Directorate of Emergency Medical Services. Data from 2002 days were included in the study. There were 198,816 cases on non-rainy days, while the total number of cases on rainy days was 94,407. While the median of the daily number of cases of non-rainy days was 140 (45), this value was 148 (49) for rainy days. There was a statistically significant difference between the two groups in terms of daily number of cases (p

Quantitative Assessment of Agricultural Practices on Farmland Evapotranspiration Using EddyCovariance Method and Numerical Modelling

While low cost eddy covariance (EC) techniques based on the open-path laser analyzers have been widely used, they are not very accurate and are restricted to use in non-rainy days. As an alternative, and relevant to promoting precision agriculture where water availability is proving key, the application of the EC technique based on closed-path QCLAS-EC Analyzer is described, in a study of cabbage farmland evapotranspiration (ET). This study uses the advantages of the closed-path EC method to quantitatively assess the impact of agricultural activities on farmland ET and compared with RZWQM2 (Root Zone Water Quality Model) model. The cumulative ET is shown to have increased by 1.5–3.6 mm over ten-days after planting, and decreased by 3.5–8.1 mm over 10 days, following harvesting. While irrigation contributed to ET, the cumulative ten-day ET increase is between 0.6–2.3 mm which is significantly lower than the effects due to planting and harvesting. The RZWQM2 model was used to quantify the effects of four agricultural practices. Simulation of ET attained R2 and RMSE as 0.79 and 0.013 mm/d, respectively. In addition, the RZWQM2 model successfully simulated groundwater levels, Leaf area index, and crop height (R2 values of 0.71, 0.98 and 0.97, respectively). The RZWQM2 model simulates the effects of planting, harvesting, and irrigation on ET, indicating the same directional changes of magnitude with measured data. The results provide a comprehensive and direct study based on the closed-path EC method and RZWQM2 model to assess the impact of multiple agricultural activities on farmland ET and to improve precision agriculture.

Local Governments’ Responses to Revenue Changes: The Effects of Unreserved General Fund Balances

ABSTRACT Volatile revenues affect the quality and consistency of municipal service provision. This article investigates how cities use unreserved general fund balances to mitigate annual expenditure fluctuations when confronted with volatile revenues. Based on the analysis of a panel dataset of over two thousand American cities from 2003 to 2011, the fixed-effects regression results suggest that unreserved general fund balances reduce municipal expenditure fluctuations on a year-to-year basis. The expenditure-smoothing effects were more pronounced when municipal governments experienced large revenue changes. Results are robust when excluding large cities, using different cutting-points to define ‘moderate’ or ‘large’ revenue changes, and in recession and non-recession years. This article contributes to the local expenditure stabilization literature by recognizing the unreserved general fund balances’ expenditure-smoothing effects during ‘non-rainy days.’ It adds empirical evidence to the organizational theory that financial slack works as a crucial buffer against external changes and provides managerial discretion to local administrators.

Occurrence patterns of black water and its impact on fish in cutover areas of Eucalyptus plantations.

Black runoff occasionally flows from cutover areas of Eucalyptus plantations, polluting rivers and ponds, and resulting in fish death in severe cases. However, the occurrence patterns and environmental impacts of this black water remain unclear. Herein, we analyzed the major characteristics of black water at the occurrence sites, tested the complexation reaction of ground eucalyptus leaves with a solution of Fe3+, and determined the color and absorbance of the complex solution. The results showed that the water was dark blue, with weak acidity and strong light absorbance. The water contained a high level of dissolved organic matter content, while its chemical oxygen demand, total N, total P, NO3--N, and NH4+-N concentrations were significantly higher than those in the stream water from Eucalyptus, Pinus massoniana Lamb., and Cunninghamia lanceolata stands during the growth period. Additionally, the tannic acid concentration in the black water was 1.0 mg L-1 higher than that in the stream water from the Eucalyptus stand. The input of black water increases the concentration of tannic acid and NH4+-N, and the degradation of organic matter consumes dissolved oxygen in downstream ponds, leading to fish deaths. The presence of fresh logging residues and hot, humid weather also enable black water formation. Field investigations and simulation experiments revealed fresh Eucalyptus residues decompose rapidly under high-temperature and rainfall conditions, releasing large amounts of tannic acid, which reacts with Fe3+ to form a dark blue tannic acid‑iron complex and results in black water. These results indicate that the rich Fe3+ in runoff may be a key factor in the occurrence of black water. The logging of Eucalyptus plantations during the dry season or on non-rainy days and a reduction in the logging area could prevent the occurrence of black water or mitigate the extent of its environmental hazards.