Winter Flooding Research Articles

Responses of Swamp Cypress (Taxodium distichum) and Chinese Willow (Salix matsudana) Roots to Periodic Submergence in Mega-Reservoir: Changes in Organic Acid Concentration

Organic acids are critical as secondary metabolites for plant adaption in a stressful situation. Oxalic acid, tartaric acid, and malic acid can improve plant tolerance under waterlogged conditions. Two prominent woody species (Taxodium distichum-Swamp cypress and Salix matsudana-Chinese willow) have been experiencing long-term winter submergence and summer drought in the Three Gorges Reservoir. The objectives of the present study were to explore the responses of the roots of two woody species during flooding as reflected by root tissue concentrations of organic acids. Potted sample plants were randomly divided into three treatment groups: control, moderate submergence, and deep submergence. The concentrations of oxalic acid, tartaric acid, and malic acid in the main root and lateral roots of the two species were determined at four stages. The results showed that T. distichum and S. matsudana adapted well to the water regimes of the reservoir, with a survival rate of 100% during the experiment period. After experiencing a cycle of submergence and emergence, the height and base diameter of the two species showed increasing trends. Changes in base diameter showed insignificant differences between submergence treatments, and only height was significant under deep submergence. The concentrations of three organic acids in the roots of two species were influenced by winter submergence. After emergence in spring, two species could adjust their organic acid metabolisms to the normal level. Among three organic acids, tartaric acid showed the most sensitive response to water submergence, which deserved more studies in the future. The exotic species, T. distichum, had a more stable metabolism of organic acids to winter flooding. However, the native species, S. matsudana, responded more actively to long-term winter flooding. Both species can be considered in vegetation restoration, but it needs more observations for planting around 165 m above sea level, where winter submergence is more than 200 days.

Studying the Effects of Roads Geometry and Design Parameters on the Pavement Drainage System

Background: Water floods have a considerable impact on roads sustainability by creating roads cracks, breaking down and holes, and failure for some other parts. The existence of good drainage system serviced the road and draining the water resulted from rain floods is crucial. These significant influences can be classified as positive or negative, low, moderate, or high. Aim and Objectives: This paper discusses the water floods and rainfall effects on roads and highways in Jordan as well as the drainage system on road sustainability and performance. The main aim of this paper is to investigate and analyse water as rainfall or floods affecting roads and highways in Jordan. The importance of this study is represented by studying and analysing the effects of rainfall and water floods on road construction and sustainability in Jordan after the latest high rain sizes of this winter and water floods, which affect the roads and highways in a good percentage. The other importance of the study is represented in offering solutions to problems caused by the environmental effects, specially floods and high rainfall rates. Methodology: all data and information about status of Jordanian roads during winter and floods are collected from real cases of about 40 main and semi-main roads in Jordan. Results and Conclusions: A good drainage system and repair operations and maintenance generally have a positive impact on road sustainability and survival age. The effects of slopes of the road and surface of the asphalt, rainfall intensity, and water flow velocity on drainage length and drainage time and water depth are discussed here. Doi: 10.28991/cej-2021-03091636 Full Text: PDF

Fall and Winter Diets of Eastern Gray Squirrels in a Seasonally Flooded Ecosystem in Alabama

As scatterhoarders, Sciurus carolinensis (Eastern Gray Squirrel) usually rely on food they buried during fall to survive cold winter months. However, the range of this species includes areas of the southeastern United States where winter flooding commonly restricts access to buried food during the recovery season. In this study, we investigated the effects of winter flooding on the diet of Eastern Gray Squirrels in bottomland hardwood forests of west-central Alabama. We examined the diet of 42 Eastern Gray Squirrels through DNA analysis of stomach contents collected during fall (September–November) 2016 and winter (December–February) 2015–2016, 2016–2017, and 2018–2019. Eastern Gray Squirrels ate 21 different types of plants, with 6 principal foods (>1% of any squirrel's stomach contents) during fall and 12 principal foods during winter. Throughout both seasons, Juglandaceae (walnut) and Quercus spp. (oak) were the most important foods and together made up 94.1% of the fall diet and an average of 78.6% of the winter diet. In contrast to other studies, we found more varied diets during winter (12 primary foods eaten) than fall (6). Additionally, a majority of the plant types consumed during winter at our study area were not hard-mast plants, and many had not been previously recorded as part of the diet of the Eastern Gray Squirrel. Our results suggest Eastern Gray Squirrels cope with reduced availability of scatterhoarded food due to winter flooding by increasing the diversity of foods they eat to include more herbaceous plants.

Sedimentology and stratigraphy of a modern halite sequence formed under Dead Sea level fall

AbstractHalite sequences in the geological record accumulated in deep hypersaline basins. However, such halite sequences are interpreted based on modern analogues of halite deposition in shallow hypersaline environments. Recently, halite deposition in the deep, hypersaline Dead Sea has been studied together with its coeval environmental and limnogeological forcing. This is the closest modern analogue for deep environments. Therefore, stratigraphy, sedimentology and petrography of a well‐dated, high‐resolution modern Dead Sea halite sequence are explored. The sequence was deposited during a ca 30 m lake‐level decline since the onset of modern halite deposition in 1980, and was compared with sub‐annual lake levels, precipitation and flood records. The sedimentology of the sequence documents the trend of shallowing water depth, including individual floods. The sequence base is composed of alternating bottom growth‐cumulate halite annual couplets, typical of deep hypolimnetic water deposition. Up‐sequence, the annual couplets disappear and towards its top are composed of cumulate layers with dissolution features, typical of shallow epilimnetic water deposition. Halite deposition rate is reduced by 60% at the shallow lakefloor compared with the deep lakefloor, mainly due to the summer undersaturation that leads to depocentre ‘halite focusing'. The top of the sequence contains shoreline deposits, halolites (halite ooids) and polygonal surface cracks, indicating subaerial exposure. This study shows petrographic indicators for summer thermal dissolution (partially dissolved crystals), which are distinct from dissolution features by winter floods that generate a regional truncation surface. Spatial variations in halite thickness and facies, indicating much thinner and spatially limited halite units compared to modelled halite units based on mass balance considerations were also observed. These observations provide criteria for: (i) recognizing water depths and shallowing lake‐level trends from halite sequences throughout the geological record; and (ii) interpreting palaeolimnology, water column structure and the relations between stratigraphic horizons and corresponding shorelines.

Does mixed vs separate sheep and cattle grazing reduce soil compaction?

AbstractDegradation of soil in the United Kingdom (UK) is compromising the ecosystem services that flow from this natural capital asset, including water flow regulation. Soil compacted by grazing livestock, for example, results in an increase in overland flow following rainfall and is thought to be one of the key factors contributing to increased severity of UK winter flooding in recent years. Practical farm‐scale changes in livestock management that lead to improvements in water flow regulation therefore need to be identified. This pilot study aimed to assess the impact of (i) changing stocking composition, and (ii) temporary grazing exclusions, on soil natural capital quality on a sheep and beef cattle farm in Northumberland, England. I found evidence of improved soil bulk density under mixed sheep and cattle grazing compared to cattle‐only grazing over a 3‐month summer grazing season; bulk density in 'cattle‐only' pastures increased from 0.836 to 0.875 g cm−3 from June to September 2017, compared with a small decrease of 0.875–0.871 g cm−3 in 'cattle to mixed sheep and cattle' pastures (difference significant at p < .05 level). Changing from sheep‐only grazing to mixed grazing, and exclusion of grazing, did not significantly influence bulk density change (p > .05). This study indicates that rapid improvements in soil physical properties can be achieved through realistic changes to livestock management. If this finding can be confirmed over multiple grazing seasons, this potentially offers a straightforward means to enhance soil health on grazed land in the UK, improving delivery of water flow regulation and other ecosystem services.

Indirect emissions of nitrous oxide in a cropland watershed with contrasting hydrology in central France

Nitrous oxide (N2O) is an important greenhouse gas. Its atmospheric concentration have increased with the industrialisation and the use of N fertilizer. The contribution of freshwater systems to N2O emissions is still very uncertain, while regional transfer of nitrogen depends on soil and hydrology. Riverine and spring N2O dissolved in water was therefore measured over two years in the 3453 km2 Haut-Loir watershed (France). This temperate cropland watershed is characterized by two different hydrological systems east and west of the Loir River. The eastern rivers, fed by the emergence of the deep Beauce aquifer, exhibited significantly higher dissolved N2O concentrations (Beauce region, mean: 2.93 μg-N L−1) than the western rivers (Perche region, mean: 0.87 μg-N L−1), which were largely influenced by runoff during winter flooding. The eastern rivers had large nitrate concentrations all over the year; in the Perche, nitrate underwent a seasonal cycle with large loads during winter floods, but there were no consistent seasonal patterns in N2O. The ratios of N2O in excess of equilibrium on nitrate, often used as a proxy of emission factor (EF), were much smaller than the default IPCC values, both for rivers (0.014% versus 0.25% for IPCC EF5r) and the Loir spring (0.085% versus 0.6% for the IPCC EF5g for groundwater and springs). EF5r were significantly different between the two parts of the watershed only in winter, because of the seasonal variability of NO3−. Moreover dissolved N2O is controlled not only by NO3−, as it is considered in the calculation of the EF5, but also by water pH and dissolved organic carbon. A good prediction of dissolved N2O was obtained using these physicochemical variables and hydrological regions. Thus, these results suggest that the spatial variability of riverine N2O depends on local hydrology, while further research is needed to understand the seasonal variability.

Atmospheric river orientation determines flood occurrence

AbstractAtmospheric Rivers (ARs) have been linked to many of the largest recorded UK winter floods. These large‐scale features can be 500–800 km in width but produce markedly different flood responses in adjacent catchments. Here we combine meteorological and hydrological data to examine why two impermeable catchments on the west coast of Britain respond differently to landfalling ARs. This is important to help better understand flood generation associated with ARs and improve flood forecasting and climate‐change impact assessment. Analysis of 32 years of a newly available ERA5 high‐resolution atmospheric reanalysis and corresponding 15‐min river flow data show that the most impactful ARs arise through a combination of the orientation and magnitude of their water vapour flux. At the Dyfi catchment, AR orientations of between 238–258° result in the strongest hydrological responses, whereas at the Teifi the range is 224–243°. We believe this differential flood response is the result of catchment orientation and topography enhancing or suppressing orographic rainfall totals, even in relatively low‐relief coastal catchments. Further to the AR orientation, ARs must have an average water vapour flux of 400–450 kg m−1 s−1 across their lifetime. Understanding the preferential properties of impactful ARs at catchments allows for the linking of large‐scale synoptic features, such as ARs, directly to winter flood impacts. These results using two test catchments suggest a novel approach to flood forecasts through the inclusion of AR activity.

The impact of climate change on flow conditions and wetland ecosystems in the Lower Biebrza River (Poland).

Water plays a key role in the functioning of wetlands and a shortage or contamination of it leads to changes in habitat conditions and degradation of ecosystems. This article scrutinizes the impact of climate change on the hydrological characteristics of floods (maximum flow, duration, volume) in the River Biebrza wetlands (North-East Poland). We analysed the trends in duration and volume of flood and maximum discharges in the historical period 1970–2000 and predicted these for the future periods 2020–2050 and 2070–2100, respectively. Next we assessed the impact on the wetland ecosystems. The basis of our assessments consists of statistical analyses of hydrographs and calculations by the Soil and Water Assessment Tool hydrological model and considering nine bias-corrected climate models. The results indicate that both volume and duration of winter floods will keep increasing continuously under Representative Concentration Pathways 4.5 and 8.5. The reduction in peak annual floods is expected to decline slightly in both scenarios. On the other hand, the analysis of trends in mean and standard deviation revealed negligible tendencies in the datasets for summer and winter hydrological seasons within the three time frames analysed (1970–2000; 2020–2050; 2070–2100). We foresee several future implications for the floodplain ecosystems. Shifts in transversal ecosystem zonation parallel to the river will likely take place with more highly productive flood tolerant vegetation types. Nutrient availability and algal blooms during spring inundations will likely increase. Slowdown of organic matter turnover later in summer will lead to a higher peat accumulation rate. Logistical problems with summer mowing and removal of bushes in winter may enhance shrub encroachment.

Modeling climate change impact on streamflow as affected by snowmelt in Nicolet River Watershed, Quebec

Frequent spring flooding in Southern Quebec’s Nicolet River watershed has a history of causing severe damage, which is likely to worsen as climate change progresses. Employing the ArcSWAT model, an attempt was made to assess the potential impacts of climate change on the Nicolet River watershed’s seasonal and annual streamflow, particularly that portion affected by snowmelt. Calibrated and validated against observed streamflow data for the periods of 1986–1990 and 1991–2000, respectively, the model reliably predicted daily streamflow (e.g., percent bias within ±15%, Nash-Sutcliffe model efficiency >0.50, and the ratio of root mean square error to the standard deviation ≤0.70). In an effort to investigate the impacts of climate change on streamflow, future climate datasets were generated for 2053–2067 by implementing the eleven sets of existing Regional Climate Model (RCM) simulations produced for the North American Regional Climate Change Assessment Program (NARCCAP) in the ArcSWAT model. The ArcSWAT model’s hydrological responses were closely tied to changes of climate variables: a strong correlation existed between simulated runoff and precipitation, and between temperature and predicted evapotranspiration, snowfall, and winter snowmelt. Projected future climate data showed increases in both average temperature (+2.5 °C) and precipitation (+21%). Significant greater total precipitation was forecasted for the winter season, while total snowfall was projected to decrease by 6%. However, the snowmelt showed an increasing trend for the late winter and earlier spring period. Streamflow was expected to increase annually and in most seasons except spring. Annual peak flows volumes would increase by 13% in the future and the occurrence of peak flows would shift to the winter (vs. the spring), indicating a greater risk of winter flooding in the future. The individual impact of temperature and precipitation on peak flows showed that increases in peak flows were mainly tied to increased precipitation, while the shift in their timing was mostly tied to warming temperatures.

On the effects of winter flooding on the hydrological balance of rice areas in northern Italy

Recent research suggests that groundwater overdraft can be mitigated by application of water onto agricultural lands for direct groundwater recharge. This technique is often called Agricultural Managed Aquifer Recharge (Ag-MAR) and is carried out in wintertime. Winter flooding of rice paddies could be considered as a form of Ag-MAR. Currently, it is implemented in Europe as an environmentally friendly practice, which could also bring many agronomic and hydrological benefits; however, especially the latter aspects have been poorly investigated in the past. Results of a hydrological study focused on winter flooding in three rice areas in northern Italy and lasting 18 months (winter seasons 2017–2018 and 2018–2019, and summer season 2018) are presented in this paper. The objective of winter flooding was to maintain higher groundwater levels till the beginning of the agricultural season in order to increase rice irrigation efficiency and protect some groundwater dependent ecosystems. Main findings are: (1) the percolation efficiency of winter flooding is very high (92–97% of the water volume applied on the fields); (2) local groundwater levels underneath the recharge areas increase at a similar rate as during the summer flooding and reach peak values that are close; (3) however, the rate of level decrease after the end of the flooding period is much faster with the winter flooding, when pre-flooding groundwater levels are re-established in 1 month, in contrast with at least 2 months with the summer flooding: this is due to the fact that the areas adopting winter flooding are less extended and more fragmented than the ones flooded during the agricultural season; (4) consequently, to maintain higher groundwater levels until the beginning of the cropping season, winter flooding should last longer and involve larger areas.

Does Future Climate Bring Greater Streamflow Simulated by the HSPF Model to South Korea?

Evaluating the impact of climate change on water resources is necessary for improving water resource management and adaptation measures at the watershed level. This study evaluates the impact of climate change on streamflow in South Korea using downscaled climate change information based on the global climate model (GCM) and hydrological simulation program–FORTRAN model. Representative concentration pathway (RCP) scenarios 4.5 and 8.5 W/m2 were employed in this study. During the distant future (2071–2099), the flow increased by 15.11% and 24.40% for RCP scenarios 4.5 and 8.5 W/m2, respectively. The flow is highly dependent on precipitation and evapotranspiration. Both precipitation and evapotranspiration increased, but the relative change of precipitation was greater than the relative change of evapotranspiration. For this reason, the flow would show a significant increase. Additionally, for RCP 8.5 W/m2, the variability of the flow according to the GCM also increased because the variability of precipitation increased. Moreover, for RCP 8.5 W/m2, the summer and autumn flow increased significantly, and the winter flow decreased in both scenarios. The variability in autumn and winter was so great that the occurrence of extreme flow could intensify further. These projections indicated the possibility of future flooding and drought in summer and winter. Regionally, the flow was expected to show a significant increase in the southeastern region. The findings presented for South Korea could be used as primary data in establishing national climate change adaptation measures.

Investigation of Pathogenic Bacterial Transport by Waterbirds: A Case Study of Flooded and Non-Flooded Rice Systems in Mississippi

Waterbirds may facilitate pathogen transport in rice fields from autumn to winter. This study investigated pathogen dynamics in two types of rice fields, those considered conventionally managed and a low-external-input-sustainable-agriculture (LEISA) rice system in the Mississippi Alluvial Valley, winter 2017–2018. In each system, fields were (1) left unflooded or (2) flooded from November to March. Fecal indicator and pathogenic bacteria (enterococci, Clostridium perfringens, Escherichia coli, Salmonella spp., and Campylobacter spp.) were quantified in soil before and after winter flooding, and bird fecal matter estimated on both farm types. Water samples were tested for enterococci, C. perfringens and E. coli before fields were drained. The LEISA flooded fields had greater detections of C. perfringens in the soil than conventional non-flooded fields. There was an observed decreasing trend of C. perfringens detection associated with lower bird abundances among treatment groups. All observed pathogen levels in both systems were below EPA standards. Results suggest that long-term waterbird stopovers can influence pathogen indicators in soil, but not at levels to threaten human and environmental health standards. Future studies should focus on long-term monitoring of pathogen introduction in rice fields that harbor wintering waterfowl or other waterbirds.

Occasional Floods On The Rivers Of Russian Plain In The 20<sup>Th</sup> –21<sup>St</sup> Centuries

The article focuses on the study of flood flow changes on the rivers of the European Territory of Russia (ETR) in the last thirty years. This is an extremely important problem, as with floods, whose contribution to the structure of the annual flow of European rivers in recent decades has been increasing, the most destructive floods are associated. On the example of 55 representative hydrological gauge stations located on the ETR in regions with different conditions of runoff formation, the features of both summer and winter floods formation are considered. It has been established that over the past thirty years on the most rivers there has been an intensive reduction in the ratio of volumes and maximum flood discharges in relation to the similar characteristics of the basic runoff. Increased groundwater supply is observed, and the absence of significant freezing of the soil leads to an increase in infiltration. The volumes of flood runoff and the basic runoff become comparable or the proportion of the latter begins to prevail. The main reason for the increase in minimum water discharge is associated with an increase in flood flow under the influence of more intense and prolonged thaws. A distinctive feature of the water regime of recent decades has been the flood peaks in almost any season of the hydrological year. In the middle and southern part of the ETR – in the basins of the Volga, Oka, Vyatka, Don Rivers – there is an increase in low-water flow and in the quota of flood in annual flow. On some rivers of the ETR, the spring flood runoff currently accounts for less than 50% of the annual runoff.

Future shift in winter streamflow modulated by the internal variability of climate in southern Ontario

Abstract. Fluvial systems in southern Ontario are regularly affected by widespread early-spring flood events primarily caused by rain-on-snow events. Recent studies have shown an increase in winter floods in this region due to increasing winter temperature and precipitation. Streamflow simulations are associated with uncertainties mainly due to the different scenarios of greenhouse gas emissions, global climate models (GCMs) or the choice of the hydrological model. The internal variability of climate, defined as the chaotic variability of atmospheric circulation due to natural internal processes within the climate system, is also a source of uncertainties to consider. Uncertainties of internal variability can be assessed using hydrological models fed by downscaled data of a global climate model large ensemble (GCM-LE), but GCM outputs have too coarse of a scale to be used in hydrological modeling. The Canadian Regional Climate Model Large Ensemble (CRCM5-LE), a 50-member ensemble downscaled from the Canadian Earth System Model version 2 Large Ensemble (CanESM2-LE), was developed to simulate local climate variability over northeastern North America under different future climate scenarios. In this study, CRCM5-LE temperature and precipitation projections under an RCP8.5 scenario were used as input in the Precipitation Runoff Modeling System (PRMS) to simulate streamflow at a near-future horizon (2026–2055) for four watersheds in southern Ontario. To investigate the role of the internal variability of climate in the modulation of streamflow, the 50 members were first grouped in classes of similar projected change in January–February streamflow and temperature and precipitation between 1961–1990 and 2026–2055. Then, the regional change in geopotential height (Z500) from CanESM2-LE was calculated for each class. Model simulations showed an average January–February increase in streamflow of 18 % (±8.7) in Big Creek, 30.5 % (±10.8) in Grand River, 29.8 % (±10.4) in Thames River and 31.2 % (±13.3) in Credit River. A total of 14 % of all ensemble members projected positive Z500 anomalies in North America's eastern coast enhancing rain, snowmelt and streamflow volume in January–February. For these members the increase of streamflow is expected to be as high as 31.6 % (±8.1) in Big Creek, 48.3 % (±11.1) in Grand River, 47 % (±9.6) in Thames River and 53.7 % (±15) in Credit River. Conversely, 14 % of the ensemble projected negative Z500 anomalies in North America's eastern coast and were associated with a much lower increase in streamflow: 8.3 % (±7.8) in Big Creek, 18.8 % (±5.8) in Grand River, 17.8 % (±6.4) in Thames River and 18.6 % (±6.5) in Credit River. These results provide important information to researchers, managers, policymakers and society about the expected ranges of increase in winter streamflow in a highly populated region of Canada, and they will help to explain how the internal variability of climate is expected to modulate the future streamflow in this region.

Benefits of the European Agri-Environment Schemes for Wintering Lapwings: A Case Study from Rice Fields in the Mediterranean Region

Mediterranean European rice fields provide important habitats for migrating waterbirds. In winter, one waterbird species that particularly benefits from rice fields is the Northern Lapwing (Vanellus vanellus), a species threatened in Europe. To assess the effect of agri-environmental measures on rice field selection and use by wintering lapwings, bird counts were conducted in northeastern Spain during two consecutive winters (2005-2006 and 2006-2007). Information on two mandatory post-harvest management prescriptions of the agri-environment schemes was collected, namely winter flooding (percent ground surface covered by water) and whether fields were rolled or not. The number of lapwings in rolled fields was significantly higher compared to non-rolled fields. For instance, an average rolled field with 50% water cover (percentage at which lapwing abundance more or less peaked) would host an estimated 12.03 ± 0.52 SE lapwings versus 0.18 ± 0.58 in a non-rolled field. While the maximum abundance of lapwings in rolled fields was found at an intermediate percentage of water cover (about 25 to 75%), the number of lapwings increased steadily with water cover in non-rolled fields. Rice post-harvest practices derived from the agri-environment schemes are beneficial for biodiversity, promoting the conservation of suitable habitats for waterbirds.

Low external input sustainable agriculture: Winter flooding in rice fields increases bird use, fecal matter and soil health, reducing fertilizer requirements

This study investigated a low-external-input sustainable-agriculture (LEISA) rice production system in the Mississippi Alluvial Valley (MAV) that applied ecological principles to create waterbird habitat and enhance soil fertility. Two production sites were selected for this study (LEISA and conventional). Each production site applied a flooded treatment and a fallow treatment to select fields during the non-growing season (November 2017- March 2018). Bird fecal matter inputs and soil microbial bacteria/activity and nutrient content were quantified and compared between fields. Significantly more % total nitrogen, % total carbon, microbial richness and activity (P < 0.05) were found in flooded LEISA than other study fields. Bird fecal matter inputs on LEISA flooded fields contributed an estimated 6.1–48.9 kg N/ha/season, whereas 1.9–14.8 kg N/ha/season were added to conventionally flooded fields. Long-term application of the unique LEISA rice farming system can reduce the need for synthetic fertilizer application by > 13 %, while increasing soil organic carbon. This case study provides a foundation for future research into the agronomic benefits of creating bird habitat in rice fields, while documenting how conservation strategies support agronomic production and sustainability to foster conservation adoption.

Impact of floods on concentration of persistent organic pollutants in Aoös River, Albania

ABSTRACTPersistent organic pollutants (POPs), such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and pesticides were measured in water samples from six sites on the Aoös River in southern Albania via gas chromatography. Samples were collected in September 2017 (fall) and March 2018 (spring), before and after heavy flooding of the river in December 2017, respectively. The total PCBs lowest concentration increased from 0.6 µg L−1 to 0.62 µg L−1 and highest concentration increased from 32.64 µg L−1 to 36.57 µg L−1, respectively before and after heavy floods. The total BTEX lowest concentration increased from 1.6 µg L−1 to 1.82 µg L−1 and total highest concentration increased from 45.4 µg L−1 to 49.32 µg L−1. Pesticides total lowest concentration increased from 1.37 µg L−1 to 1.53 µg L−1 and highest concentration increased from 269.57 µg L−1 to 289.26 µg L−1. In contrast, the total PAH lowest concentration remained constant 0.01 µg L−1 and the highest concentration decreased from 0.45 µg L−1 to 0.25 µg L−1. Concentrations of PCBs, BTEX and Pesticides increased after winter floods in 2017, while the concentration of PAH decreased. This study was the first to investigate the seasonal variability of various POPs in the Aoös River. I found that the levels of the selected POPs were higher than the recommended standard values, suggesting significant pollution of the river, particularly after the occurrence of winter flood events.

Effects of morphology in controlling propagation of density currents in a reservoir using uncalibrated three-dimensional hydrodynamic modeling

In this study, effects of basin morphology are shown to affect density current hydrodynamics of a large reservoir using a three-dimensional (3D) hydrodynamic model that is validated (but not calibrated) with in situ observational data. The AEM3D hydrodynamic model was applied for 5-month simulations during winter and spring flooding for the Maroon reservoir in southwest Iran, where available observations indicated that large-scale density currents had previously occurred. The model results were validated with near-bottom water temperature measurements that were previously collected at five locations in the reservoir. The Maroon reservoir consists of upper and lower basins that are connected by a deep and narrow canyon. Analyses of simulations show that the canyon strongly affects density current propagation and the resulting differing limnological characteristics of the two basins. The evolution of the Wedderburn Number, Lake Number, and Schmidt stability number are shown to be different in the two basins, and the difference is attributable to the morphological separation by the canyon. Investigation of the background potential energy (BPE) changes along the length of the canyon indicated that a density front passes through the upper section of the canyon but is smoothed into simple filling of the lower basin. The separable dynamics of the basins has implications for the complexity of models needed for representing both water quality and sedimentation.

Effects of winter flooding on phosphorus dynamics in rice fields

Controlling phosphorous (P) loads from rice fields is important for the conservation of aquatic ecosystems, in part because P is relatively concentrated at its sources. Recently, winter flooding, by which irrigation water is maintained in rice fields during winter, has attracted much attention as a farming strategy for environmental conservation and biodiversity maintenance. However, the effects of winter flooding on nutrient cycles have received little research attention. We evaluated the effects of winter flooding on P loads in rice fields by performing laboratory experiments with soils from rice fields with/without winter flooding. These incubation experiments showed that total and soluble reactive P concentrations in surface solutions are decreased by winter flooding. This decrease may follow co-precipitation of P with iron, which may be dissolved from winter flooded soil and rapidly precipitates in solution. Periphyton, which may increase during winter flooding, may not contribute to this decrease because puddling resets periphyton quantities on surface soils. P loads from rice fields with winter flooding over 16 days after fertilization could be reduced by an average of 26% compared with those without winter flooding, indicating that winter flooding is a valuable strategy for reducing P loads in spring when high P loads occur.

Alien water lettuce (Pistia stratiotes L.) outcompeted native macrophytes and altered the ecological conditions of a Sava oxbow lake (SE Slovenia)

Introduction of an invasive alien macrophyte water lettuce (Pistia stratiotes L.) radically changed the oxbow lake in Prilipe (SE Slovenia) which has thermal springs that enables the winter survival of this tropical invader. About 10 years after the first record of P. stratiotes, the number, abundance and biomass of indigenous and non-indigenous macrophytes as well as different abiotic parameters were measured. In that period, colonized sections (~94% of the oxbow lake) were completely covered with water lettuce, and the only reservoirs of indigenous macrophyte species were the non-colonized areas (6%). Research in 2011 found only a third of the previously recorded indigenous macrophytes, but then only in small section without P. stratiotes. Three of the species that disappeared were on the Red data list. In the colonized section a higher biomass was observed than in the non-colonized section because of high abundance of water lettuce which remained the only macrophyte. Due to the presence of P. stratiotes, the intensity of light penetrating into the depth and water circulation were reduced, as was the oxygen saturation of the water. In addition to the well documented vegetative propagation of P. stratiotes, a well-established and viable seed bank has been detected in the lake sediment and after winter floods also on lake banks. In the future, special attention should be given to the thermal water ecosystems in temperate climates since they can serve as stepping stones and recruitment centres for the establishment and spread of (sub-)tropical invasive species. Facing predicted climate change such local populations of invasive species can act as stepping stones for further dispersal.