Non-flood Period Research Articles

Relative influence of forest and cropland on fluvial transport of soil organic carbon and nitrogen in the Nen River basin, northeastern China

Riverine transport of carbon and nitrogen strongly impacts terrestrial and aquatic ecosystem functions but is itself affected by changes in land cover and land use. China’s Nen River basin has experienced widespread conversion from forest to cropland in the past century, making it representative of similar global land use changes. We assessed organic carbon and nitrogen transport in this basin during 2018 and 2019, using water samples collected at one-hour intervals during the twelve flood events in two sub-basins (the Yalu and Yin rivers) dominated by forests and cropland, respectively. We also assessed dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) concentrations from 19 sampling sites distributed throughout the Nen River basin, in combination with hydrological records, to investigate the impacts of land cover on riverine carbon and nitrogen fluxes. The forested Yalu river basin showed significantly higher DOC content and lower TDN content than Yin river basin. Riverine DOC concentrations during non-flood periods in the forested Yalu river basin were significantly higher than in the cultivated Yin river basin, but riverine TDN concentrations were lower. Throughout the Nen River basin and its sub-basins, riverine TDN content was proportional to cropland area. During the twelve flood events, riverine DOC and TDN varied widely over time in the Yin and Yalu river basins, possibly due to dilution effects of water originating from different land covers within the basins. Our results demonstrate that land cover is the principal cause of changes in riverine DOC and TDN content in this region.

Study on the Ecological Operation of Artificial River-Communicating Lakes during Non-Flood Period

River-communicating lakes in the middle and lower reaches of the Yangtze River connect with river through culverts and sluices except Poyang Lake and Dongting Lake. Its water quality is poorer due to the lack of natural exchange of water, especially in dry season. Taking Huayang Lake group as an example, the feasibility of ecological operation and the specific plan during non-flood period were studied by data analysis, field investigation and numerical simulation. Data analysis result presents the concentration of TN and TP decreases with the increase of water level, but the tendency slows down when the water level exceeds a certain value. In addition, based on the current sluice gate dispatching mode, relationship between river and lakes, flood control security, improvement of water environment and the simulated results, the ecological operation plan was obtained, that is, using Yangwan and Huayang sluices to control the water level in the lake from October to December at 13 m, January to February at 12.5 m and March to April at 11.8 m.

Characteristics of Hydrogen and Oxygen Isotopes in Different Water Bodies in Hilly and Gully Regions of the Loess Plateau

Studying the isotope characteristics and water body transformation relationships among different water bodies in the hilly and gully region of the Loess Plateau can provide a theoretical foundation for evaluating regional climate, ecology, and water resources. In this study, daily and monthly averaged δD and δ18O in precipitation, river water, and shallow groundwater were measured in 2017 in the Jiuyuangou watershed, which has a good ecological condition. The compositional relationship between the stable hydrogen and oxygen isotopes in difference water bodies was explored, the influence factors and spatio-temporal variation of δ18O in precipitation and river water were analyzed, and the stable isotope conversion ratios between different water bodies in the study area were calculated using the two-terminal mixed model. The main conclusions of the study are as follows:the d-excess of river water showed an increasing trend with elevation during the observation period; the δ18O of river water was enriched with increasing distance from the river source and decreased with increasing altitude; temperature, wind speed, and relative humidity had significant effects on the hydrogen and oxygen isotopes of precipitation; precipitation and shallow groundwater replenish the river during the non-flood period, the proportions of which were 46% and 54%, respectively; and during the flood season, the shallow groundwater is replenished by river water and precipitation, the proportions were 60% and 40%, respectively. These results indicate that there is a good conversion relationship between "precipitation-river-shallow groundwater" in the study area. The implementation of soil and water conservation measures has had some influence on the conversion of different water bodies in small watersheds. The results provide a basis for the establishment of water cycle models for hilly and gully regions of the Loess Plateau.

The Impact of Reservoirs on Runoff Under Climate Change: A Case of Nierji Reservoir in China

Reservoirs play an important role in responding to natural disasters (such as flood and drought) by controlling the runoff. With the climate changing, the frequency and intensity of flood and drought are likely to increase. Thus, the impact of reservoirs on runoff under climate change needs to be studied to cope with future floods and drought. In this study, the Nierji Reservoir located on the Nenjiang River Basin was chosen to explore the impact. The Nenjiany River Basin is the vital water source in the water resources transfer project in Northeast China. Climate change in Nenjiang River Basin was analyzed using the 1980 to 2013 climate observations. The results show that the temperature of the basin significantly (p < 0.05) increased while the precipitation significantly (p < 0.05) decreased. Based on the result, nine kinds of different climate scenarios were set up. For different climate scenarios, the Hydroinformatic Modeling System (HIMS) model and the HIMS model with the reservoir calculation module were used to simulate runoff during the no reservoir operation period (1980–2000) and reservoir operation period (2007–2013), respectively. The impact of reservoirs on runoff under climate change is studied. Results show that the Nierji Reservoir can effectively relieve the impact of climate change on downstream runoff. When temperature increases or precipitation decreases, there are larger differences in runoff over the non-flood period, especially during periods of no reservoir operation. Reservoir operation under climate change can provide reliability in drought protection.

Automatic Estimation of Urban Waterlogging Depths from Video Images Based on Ubiquitous Reference Objects

Video supervision equipment, which is readily available in most cities, can record the processes of urban floods in video form. Ubiquitous reference objects, which often appear in videos, can be used to indicate urban waterlogging depths. This makes video images a valuable data source for obtaining waterlogging depths. However, the urban waterlogging information contained in video images has not been effectively mined and utilized. In this paper, we present a method to automatically estimate urban waterlogging depths from video images based on ubiquitous reference objects. First, reference objects from video images are detected during the flooding and non-flooding periods using an object detection model with a convolutional neural network (CNN). Then, waterlogging depths are estimated using the height differences between the detected reference objects in these two periods. A case study is used to evaluate the proposed method. The results show that our proposed method could effectively mine and utilize urban waterlogging depth information from video images. This method has the advantages of low economic cost, acceptable accuracy, high spatiotemporal resolution, and wide coverage. It is feasible to promote this proposed method within cities to monitor urban floods.

Characteristic Analysis and Loss Accounting for Water Pollution in Plain River Network Region - A Case Study of the Yangtze Delta

Because there are many water systems, severe human activities, increasingly serious water pollution problems and great economic loss in the plain river network region, the establishment of scientific and reasonable economic loss function is necessary to guide the protection and management of water resources. Taking the Yangtze Delta as an example, the characteristics of water pollution in the same period are that the flood season is stronger than the non-flood season. The analysis based on the physical mechanism shows that the process of economic loss of water pollution not only accords with S-type curve but also gives a reason for the S-type curve from the aspect of mechanism. The water pollution loss rate function which is constructed on the basis of hyperbolic tangent function divides the development stage into such three stages as non-enrichment, enrichment and saturation of pollutants, gives turning points of each stage as well as the solution and significance of parameters and enriches the physical process of models. The results of living samples show that the comprehensive water grades can be obtained easily and quickly through the river length failure rate. Their good correlation has certain promotion significance. The total water pollution economic loss is bigger. The average economic loss in the flood period from May to July is bigger than that in the flood period from August to September and non-flood period. The living samples prove that there exists pollutant diffusion phenomenon in the flood period.

Usability of water surface reflectance for the determination of riverine dissolved methane during extreme flooding in northeastern Siberia

An extreme flooding event occurred from June to July 2017 in the Indigirka River lowland of northeastern Siberia. We used Landsat 8 satellite surface reflectance data to detect the flood inundation area and extract water color for delineating different water sources. We also took direct samples of dissolved methane concentrations in the river water. Relatively high concentrations of dissolved methane (0.7–1.1 μmol l−1, or μM) were observed in four tributary areas in 2017 during the flood's recession, while the values remained low in the main channel (0.2–0.3 μM). In contrast, the concentrations of dissolved methane were low in both the main channel and tributaries during the non-flood period of 2016 (0.1–0.2 μM). We then used 2017 satellite reflectance data with an empirical model to estimate the spatial differences of dissolved methane concentration for water sources contributing to the methane-poor main channel and methane-rich tributaries and applied the results to the calculation of riverine methane in the study region (approx. 200 × 300 km). This approach to estimating dissolved methane concentrations using satellite reflectance can provide a new tool for environmental monitoring of flood events in remote areas.

Infiltration and Anti-Filtration Recharge-Pumping Well and Laboratory Recharge Tests

Infiltration and anti-filtration recharge-pumping wells (hereinafter, referred to as IAF recharge-pumping wells) can enable rain-flood flowing in rivers or channel recharge to aquifers, in flood periods, and pump groundwater to be utilized in non-flood periods. In this study, a round IAF recharge-pumping well and a square IAF recharge-pumping well were developed, the structure and characteristic were introduced, the calculation equations of single-well recharge quantity of IAF recharge-pumping wells, in unconfined aquifers were deduced, and the steady-state flow recharge test was conducted in the laboratory. The conclusions were as follows. The theoretical equation of the single-well recharge quantity was reasonable. Compared to existing anti-filtration recharge wells, the new IAF recharge-pumping well had stronger anti-deposit and anti-scour abilities and the single-well recharge quantity increased by 400%. Compared to the square IAF recharge-pumping well, the round IAF recharge-pumping well had a better inlet flow pattern and a larger single-well recharge quantity. With an increase in the test times, the single-well recharge quantity gradually decreased and tended to be stable. The existence of the pumping pipe had a little influence on the single-well recharge quantity.

Analysis of Winter Concrete Construction in Water Conservation Project

The construction of water conservancy projects should commence during optimal atmospheric conditions and non-flood period to ensure completion before the flood season begin in summer. In most areas of Northern China, the temperature during winter remain at lower level, in which environmental factors play the most important role in the construction of water conservancy projects. In particular, low temperature directly affects the strength of concrete and delays its solidification, this highly affects the quality and progress of concrete construction. In order to overcome this barrier, better planning, for reasonable and effective construction techniques and targeted control measures should be adopted to reduce the adverse effects of low temperature to assure a strong and safe architecture.

Effectiveness of a newly reconstructed floodplain oxbow to reduce NO3-N loads from a spring flood

Enhancing NO3-N processing in floodplains offers opportunities to achieve water quality improvements in agricultural watersheds but few studies have quantified the effectiveness of newly reconstructed oxbows to reduce loads delivered from floods. In this study, we evaluated NO3-N retention during a spring storm water runoff event in a newly reconstructed oxbow (<1 year old) located along Morgan Creek in eastern Iowa. A 30-h flood connected the oxbow to the creek for approximately nine hours and delivered 14.7 kg of NO3-N into the oxbow. Using a NO3-N sensor, oxbow NO3-N concentrations were observed to increase from 0.7 to 5.3 mg/l after the flood event, but decreased to background conditions over the next 21 days. We estimated NO3-N retention to be 0.30 g N m−2 d−1 and the NO3-N retention efficiency to be 74.2% for the single flood event. The NO3-N mass reduction in the oxbow intersected with predicted mass reduction from a first-order denitrification decay model after 21 days which suggests that denitrification was largely responsible for the observed NO3-N decrease. However, the effectiveness of the oxbow for reducing watershed-scale N loads appears to be limited, since the oxbow is located in a low-nutrient floodplain and would only retain NO3-N loads when delivered to the oxbow via flooding. Study results suggest that oxbows provides valuable ecosystem services during non-flooding periods and are activated for NO3-N load reduction during floods.

Direct and Indirect Effects of Tides on Ecosystem‐Scale CO2 Exchange in a Brackish Tidal Marsh in Northern California

AbstractWe investigated the direct and indirect influence of tides on net ecosystem exchange (NEE) of carbon dioxide (CO2) in a temperate brackish tidal marsh. NEE displayed a tidally driven pattern with obvious characteristics at the multiday scale, with greater net CO2 uptake during spring tides than neap tides. Based on the relative mutual information between NEE and biophysical variables, this was driven by a combination of higher water table depth (WTD), cooler air temperature, and lower vapor pressure deficit (VPD) during spring tides relative to neap tides, as the fortnightly tidal cycle not only influenced water levels but also strongly modulated water and air temperature and VPD. Tides also influenced NEE at shorter timescales, with a reduction in nighttime fluxes during growing season spring tides when the higher of the two semidiurnal tides caused inundation at the site. WTD significantly influenced ecosystem respiration (Reco), with lower Reco during spring tides than neap tides. While WTD did not appear to affect ecosystem photosynthesis (gross ecosystem production, GPP) directly, the impact of tides on temperature and VPD influenced GPP, with higher daily light‐use efficiency and photosynthetic activity during spring tides than neap tides when temperature and VPD were lower. The strong direct and indirect influence of tides on NEE across the diel and multiday timescales has important implications for modeling NEE in tidal wetlands and can help inform the timing and frequency of chamber measurements as annual or seasonal net CO2 uptake may be underestimated if measurements are only taken during nonflooded periods.

Temporal and spatial variation characteristics of runoff processes and its causes in Huaihe Basin

径流变化特征及成因研究对于农业灌溉、流域水资源配置与管理等具有重要理论与现实意义，而淮河流域是我国重要农业区，因而淮河流域径流过程特征及机理研究更突显其重要性.利用非参数Mann-Kendall趋势检验和小波转换等方法系统分析了淮河中上游息县、王家坝和蒋家集等9个水文站点径流资料，分析淮河流域中上游径流年内分配、年际变化、径流趋势、突变特征及周期变化等径流过程变化特征，并探讨了径流变化特征的成因.研究发现：①淮河中上游径流量主要集中于5-9月，约占年径流总量的70.37%，变差系数介于0.16~0.85之间，径流年际极值比则介于1.7~23.9之间，径流年际变化剧烈；②淮河中上游径流量整体呈下降趋势，尤其是4-5月径流下降趋势显著，季节变化不明显；③各站点年径流量在2000s呈显著周期变化，班台、王家坝、鲁台子和蚌埠站在该尺度上存在2.0~3.4 a尺度的小周期，息县、潢川和蒋家集站处于高能区.季节和汛期与非汛期的显著周期集中出现在1960s、1980s和2000s，1960s周期主要为2~8 a.④潢川站年径流量对气候因子的响应最为明显，其对混合ENSO指数和太平洋中高纬年代际振荡指数（PDO）的响应分别通过了95%和99%的显著性检验.PDO对各站点月径流的直接影响最为显著，且主要集中在6月份，多呈显著负相关关系，以班台站最为显著，分别在1、4和6月通过了95%的显著性检验.南方涛动指数、北大西洋涛动指数和Nino3.4区海表温度距平指数（Nino3.4）对研究区月径流量的响应存在显著滞后性，Nino3.4对研究区月径流量滞后期的影响主要发生在潢川和蒋家集站，而北极涛动指数和PDO指数无滞后性响应.;The study on runoff variation characteristics and genesis is of great theoretical and practical significance for agricultural irrigation and water resource management. The Huaihe Basin (HRB) is an important agricultural area in China. Therefore, its characteristics and mechanism of runoff are very important. The runoff data from the nine hydrological stations in the middle and upper reaches of HRB are analyzed in its distribution, abrupt change characteristics and cycle variation, and the causes of runoff variation characteristics. It is found that the runoff of the middle and upper reaches of HRB accounts for about 70.37% of the total runoff from May to September, with the variation coefficient between 0.16 and 0.85, and the inter-annual extreme value ratio between 1.7 and 2.3. The runoff fluctuates in the middle reaches of HRB, and the trend of the runoff in the middle and upper reaches of HRB is decreasing, especially the runoff in April and May is significant and the seasonal variation is not obvious. The annual runoff of each site is significantly changed in 2000s. The runoffs in stations Bantai, Wangjiaba, Lu Taizi stations have a small cycle of 2.0-3.4 years. The runoffs in the county, Huangchuan and Jiang Jiake stations were in the high energy area. The seasonality of flood in gand non-flooding periods are mainly in the 1980s and the 1960s. The response of the annual runoff to the climatic factors in Huangchuan Station is the most obvious, with significance of 95% and 99% for Multivariate ENSO Index and Pacific Decadal Oscillation (PDO) indices, respectively. The direct impact of PDO on the monthly runoff of each site was the most significant and mainly concentrated in June with a negative correlation. The results showed that the response of Southern Oscillation Index, North Atlantic Oscillation and the Nino3.4 sea surface temperature (Nino3.4) to the monthly runoff in the study area was significantly delayed, and Nino3.4 had a significant effect on the monthly diameter of the study area. The effect of the lag period is mainly in Huangchuan and Jiangjiaji, while the Arctic Oscillation and PDO indices have no lag response.

Hydrology and microtopography control carbon dynamics in wetlands: Implications in partitioning ecosystem respiration in a coastal plain forested wetland

Wetlands store a disproportionately large fraction of organic carbon relative to their areal coverage, and thus play an important role in global climate mitigation. As destabilization of these stores through land use or environmental change represents a significant climate feedback, it is important to understand the functional regulation of respiratory processes that catabolize them. In this study, we established an eddy covariance flux tower project in a coastal plain forested wetland in North Carolina, USA, and measured total ecosystem respiration (Re) over three years (2009–2011). We evaluated the magnitude and variability of three respiration components – belowground (Rs), coarse woody debris (RCWD), and aboveground plant (Ragp) respiration at the ecosystem scale, by accounting microtopographic variation for upscaling and constraining the mass balance with Re. Strong hydrologic control was detected for Rs and RCWD, whereas Ragp and Re were relatively insensitive to water table fluctuations. In a relatively dry year (2010), this forested wetland respired a total of about 2000g CO2-C m-2 y-1 annually, 51% as Rs, 37% as Ragp, and 12% as RCWD. During non-flooded periods Rs contributed up to 57% of Re and during flooded periods Ragp contributed up to 69%. The contribution of Rs to Re increased by 2.4% for every cm of decrease in water level at intermediate water table level, and was nearly constant when flooded or when the water level more than 15cm below ground. The contrasting sensitivity of different respiration components highlights the need for explicit consideration of this dynamic in ecosystem and Earth System Models.

Transcription of mcrA Gene Decreases Upon Prolonged Non-flooding Period in a Methanogenic Archaeal Community of a Paddy-Upland Rotational Field Soil.

Methanogenic archaea survive under aerated soil conditions in paddy fields, and their community is stable under these conditions. Changes in the abundance and composition of an active community of methanogenic archaea were assessed by analyzing mcrA gene (encoding α subunit of methyl-coenzyme M reductase) and transcripts during a prolonged drained period in a paddy-upland rotational field. Paddy rice (Oryza sativa L.) was planted in the flooded field and rotated with soybean (Glycine max [L.] Merr.) under upland soil conditions. Soil samples were collected from the rotational plot in the first year, with paddy rice, and in the two successive years, with soybean, at six time points, before seeding, during cultivation, and after harvest as well as from a consecutive paddy (control) plot. By the time that soybean was grown in the second year, the methanogenic archaeal community in the rotational plot maintained high mcrA transcript levels, comparable with those of the control plot community, but the levels drastically decreased by over three orders of magnitude after 2years of upland conversion. The composition of active methanogenic archaeal communities that survived upland conversion in the rotational plot was similar to that of the active community in the control plot. These results revealed that mcrA gene transcription of methanogenic archaeal community in the rotational field was affected by a prolonged non-flooding period, longer than 1year, indicating that unknown mechanisms maintain the stability of methanogenic archaeal community in paddy fields last up to 1year after the onset of drainage.

Risk Assessment of Nitrogen and Phosphorus Loss in a Hilly-Plain Watershed Based on the Different Hydrological Period: A Case Study in Tiaoxi Watershed

Non-point source pollution is widely considered a serious threat to drinking water. Eutrophication in Chinese watershed is mainly due to nitrogen and phosphorus output from agricultural source. Taihu Lake is a typical eutrophic lake in China, a basin representative for the study of the temporal-spatial characteristics of pollution loading of nitrogen and phosphorus to provide scientific basis for reasonable estimation and targeted control measures of nitrogen and phosphorus loss. Based on data from nitrogen and phosphorus loss in agricultural land, livestock breeding, domestic discharge and aquaculture, this study calculated the levels of nitrogen and phosphorus comprehensive loss risk for each pollution source. Using the superposition of ArcGIS raster data, we also described the spatial distribution of nitrogen and phosphorus comprehensive loss risk by the formula of comprehensive loss risk. The results showed that critical risk areas of nitrogen and phosphorus loss mainly originated from livestock breeding and agricultural land during flood period in Tiaoxi watershed. Agricultural land and livestock breeding sources formed major parts of nitrogen loss, accounting for 30.85% and 36.18%, respectively, while phosphorus loss mainly originated from livestock breeding (56.28%). During non-flood period, integrated management of livestock breeding and domestic discharge requires much attention to control nitrogen and phosphorus loss in the critical risk area. Finally, it is of great practical significance to propose spatial-temporal targeted measurements to control nitrogen and phosphorus pollution in watershed for various periods and different areas.

The influence of episodic flooding on a pelagic ecosystem in the East China Sea

Abstract. This study was designed to determine the effects of flooding on a pelagic ecosystem in the East China Sea (ECS) with a focus on plankton activity and plankton community respiration (CR). In July 2010, a flood occurred in the Changjiang River. As a comparison, a variety of abiotic and biotic parameters were monitored during this flooding event and during a non-flooding period (July 2009). During the flood, the Changjiang diluted water (CDW) zone covered almost two-thirds of the ECS, which was approximately 6 times the area covered during the non-flooding period. The mean nitrate concentration was 3-fold higher during the 2010 flood (6.2 vs. 2.0 µM in 2009). CR was also higher in the 2010 flood: 105.6 mg C m−3 d−1 vs. only 73.2 mg C m−3 d−1 in 2009. The higher CR in 2010 could be attributed to phytoplankton respiration, especially at stations in the CDW zone that were not previously characterized by low sea surface salinity in 2009. In addition, zooplankton (&gt; 330 µm) were another important component contributing to the high CR rate observed during the 2010 flood; this was a period also associated with a significant degree of fCO2 drawdown. These results collectively suggest that the 2010 flood had a significant effect on the carbon balance in the ECS. This effect might become more pronounced in the future, as extreme rainfall and flooding events are predicted to increase in both frequency and magnitude due to climate change.

Simulated Desorption Kinetics of Lead by the Dominant Plant Roots Released Low Molecular Weight Organic Acids from the Water-Level-Fluctuating Zone in the Three Gorges Reservoir

Vegetations grow vigorously in the water-level-fluctuating zone (WLFZ) of Three Gorges Reservoir (TGR) during the non-flooded period. Low molecular weight organic acids (LMWOAs) excreted from the roots of these plants may active the heavy metals in soil. In order to investigate the desorption kinetics of Pb in the vegetation covered soil of TGR, the LMWOAs released from Cynodon dactylon and Echinochloa crusgalli roots, which are the dominant species in WLFZ, were analyzed both qualitatively and quantitatively. Furthermore, single and mixed species of LMWOAs were also used in the simulation. The results showed that the variety and content of LMWOAs secreted from Cynodon dactylon roots were larger and higher than those of Echinochloa crusgalli. Citric acid, malonic acid, acetic acid and malic acid were the same LMWOAs released from the two types of plants. The contents of acetic acid were the highest among all LMWOAs, which were 0.765 and 0.261 mmol·kg-1 in Cynodon dactylon and Echinochloa crusgalli roots, respectively.Citric acid, malonic acid and acetic acid were the same LMWOAs detected from their rhizosphere soils. In the citric acid, malonic acid and acetic acid desorption test, the desorption captivities of Pb were inhibited when the concentration of LMWOAs was lower than 1 mmol·L-1. The desorption ability displayed a decreasing order of malonic acid > citric acid > acetic acid. However, the three LMWOAs promoted the desorption of Pb in soil when their concentrations were higher than 1 mmol·L-1, respectively. The desorption ability displayed a decreasing order of citric acid > malonic acid > acetic acid. During the entire process of desorption, 0-240 min was the fast reaction stage, and the remaining time was the slow reaction stage. The pseudo-second order kinetics equation could fit best for the kinetic process.

Long-lasting floods buffer the thermal regime of the Pampas

The presence of large water masses influences the thermal regime of nearby land shaping the local climate of coastal areas by the ocean or large continental lakes. Large surface water bodies have an ephemeral nature in the vast sedimentary plains of the Pampas (Argentina) where non-flooded periods alternate with flooding cycles covering up to one third of the landscape for several months. Based on temperature records from 17 sites located 1 to 700 km away from the Atlantic coast and MODIS land surface temperature data, we explore the effects of floods on diurnal and seasonal thermal ranges as well as temperature extremes. In non-flooded periods, there is a linear increase of mean diurnal thermal range (DTR) from the coast towards the interior of the region (DTR increasing from 10 to 16 K, 0.79 K/100 km, r 2 = 0.81). This relationship weakens during flood episodes when the DTR of flood-prone inland locations shows a decline of 2 to 4 K, depending on surface water coverage in the surrounding area. DTR even approaches typical coastal values 500 km away from the ocean in the most flooded location that we studied during the three flooding cycles recorded in the study period. Frosts-free periods, a key driver of the phenology of both natural and cultivated ecosystems, are extended by up to 55 days during floods, most likely as a result of enhanced ground heat storage across the landscape (~2.7 fold change in day-night heat transfer) combined with other effects on the surface energy balance such as greater night evaporation rates. The reduced thermal range and longer frost-free periods affect plant growth development and may offer an opportunity for longer crop growing periods, which may not only contribute to partially compensating for regional production losses caused by floods, but also open avenues for flood mitigation through higher plant evapotranspirative water losses.

Estimation of Ammonia Volatilization from a Paddy Field after Application of Controlled-Release Urea Based on the Modified Jayaweera–Mikkelsen Model Combined with the Sherlock–Goh Model

ABSTRACTThe continuous airflow enclosures with an acid trap method was widely used to investigate ammonia (NH3) volatilization in field; however, it could be time-consuming for the estimation of NH3 volatilization in field with the application of controlled-release urea (CRU) because NH3 volatilization with CRU application could occur during the entire crop growth period. An NH3 volatilization estimation method based on the modified Jayaweera–Mikkelsen (J-M) model combined with the Sherlock–Goh model was used to simulate NH3 volatilization in a paddy field after 255 kg N ha−1 as CRU (polymer-coated urea with the concentration of 43% nitrogen, 100% for basal) and urea (70% for basal, 30% for topdressing) during the rice growth period including flooded and non-flooded periods in Wuxi, China. Results indicated that NH3 volatilization can be modeled with the proposed measure because no significant difference (P< 0.001) was observed between the simulated values and the observed values; the correlation coefficient (r2) was 0.615 for CRU and 0.840 for urea during the flooded period, and 0.991 for CRU and 0.946 for urea during the non-flooded period. Compared with urea, NH3 volatilization was minimized by 43.2% with the application of CRU based on simulated value within the rice growth period, which was 40.40 kg N ha−1 for CRU and 78.62 kg N ha−1 for urea during the flooded period, and 5.52 kg N ha−1 for CRU and 2.33 kg N ha−1 for urea during the non-flooded period. Therefore, CRU could be a promising nitrogen fertilizer to prevent NH3 losses in the rice paddies at the investigated area.

Risk assessment and mitigation for the Hongshiyan landslide dam triggered by the 2014 Ludian earthquake in Yunnan, China

An Ms 6.5 earthquake shocked the Ludian County, Yunnan Province, China, on 3 August 2014 and triggered the Hongshiyan landslide dam. The dam, with a height of 83 m and a lake capacity of 260 × 106 m3, threatened more than 10,000 people. A unique feature of this landslide dam was that it formed between a man-made dam and a hydropower plant. An existing drainage tunnel connecting the lake and the hydropower plant became a natural drainage conduit for the landslide dam, which played an important role in the mitigation of the landslide dam risks. This paper reports a quantitative risk assessment for the Hongshiyan landslide dam considering both engineering and non-engineering risk mitigation measures. The risk assessment is divided into three stages according to the implementation of two engineering measures: construction of a diversion channel and excavation of a branch drainage tunnel. The dam breaching hydrographs, flood zones, population at risk, and likely fatalities in each of the three stages are analysed. The optimum evacuation strategy in each stage is also studied based on the principle of minimum total consequence. It is found that the diversion channel decreases the dam breaching peak discharge and the associated risks significantly. The branch drainage tunnel prevent the landslide dam from overtopping failure in non-flooded period; however, the landslide dam may fail by overtopping in a future flood if the inflow rate is larger than the outflow rate through the drainage tunnels, resulting in serious losses of lives and properties. The dam breaching risks in all the three stages could be largely reduced by the optimal evacuation decision, which shows that timely evacuation is vital to save life and properties. The study provides a scientific basis for decision making in landslide dam risk management.