Changes In Hydrological Regime Research Articles

Does the size structure of the littoral community reflect water level fluctuations in shallow waterbodies?

The littoral zone of shallow water bodies (SWB) is highly susceptible to water level fluctuations (WLF) caused by ongoing climate-related hydrologic regime changes. The present study assessed the macrozoobenthos structure in the littoral of three temperate SWB after pronounced WLF and accompanying reduction of macrophyte coverage caused by excessive precipitation. The three SWB differed in environmental conditions – S1 (transparent lake covered with submerged macrophytes dominated by Ceratophyllum demersum); S2 (turbid lake without macrophyte coverage) represented the two interconnected backwater basins of the Sutla River watershed; and SK (Škrčev kut oxbow; highly turbid lake sparsely covered by floating-leaved Nuphar lutea) located in the Krapina River watershed (Croatia). With the aim to disentangle the littoral food web structure, and interactions among environmental conditions as well as structural and functional traits of the littoral community within the three SWB, the macrozoobenthos functional traits, trophic guilds and body size were correlated with the littoral environmental conditions, and with the traits of the potential macrozoobenthos prey (zooplankton) and predators (fish). Our results suggest that the littoral macrozoobenthos assemblage responded to the water level increase mainly by the decline of macroinvertebrate diversity and abundance. Due to loss of habitat heterogeneity, in general, larger-sized macroinvertebrates dominated the littoral zone of turbid SWB, particularly with high WLF, while smaller-sized detritivores and grazers prevailed in the littoral zone of the transparent SWB covered by submerged macrophytes. The correlations between different macrozoobenthos, zooplankton and fish size classes indicated that the larger-sized predatory macroinvertebrates prey on smaller-sized zooplankters and avoid predation of mid-sized fish. On the other hand, the abundance of smaller-sized macroinvertebrate detritivores and grazers, which were significantly correlated with concentrations of suspended detritus and algae, prevailed in the SWB covered by submerged macrophytes. Within the macrophyte-covered littoral habitats, macroinvertebrates coexisted with small-sized fish and zooplankters as well as with large-sized pelagic zooplankters, likely seeking shelter from fish. We assume that the increased abundance of larger-sized specimens affected macroinvertebrates and fish within the littoral community upon water level increase. Such a pattern could be recognized as an indicative trait in the evaluation of ecosystem functioning. Furthermore, we conclude that the structural and functional traits of the SWBs’ littoral communities could help us predict the ecological consequences of the climate-induced WLF.

A hydro-climatological outlook on the long-term availability of water resources in Cauvery river basin

The past few decades have witnessed massive shifts in land-use patterns, land management practices and water demand in the river basins of peninsular India. Changes in hydrologic regimes of different components of the water cycle pose immense challenge to water security at the catchment scale. This paper provides a comprehensive overview and a quantitative assessment of the long-term availability of water resources in the Cauvery river basin, a major river basin in peninsular India. The Cauvery has been a contentious river for decades regarding water sharing among its riparian states of Karnataka and Tamil Nadu. Moreover, the river basin is characterized by extensive regional variability in both surface water and groundwater distributions and has faced acute water management challenges at multiple space and time scales. A descriptive overview of the major water security challenges faced by the basin is presented along with a detailed synthesis of hydrological modelling approaches and statistical methods to assess the basin’s long-term water availability. The Variable Infiltration Capacity (VIC) model is implemented to evaluate the long-term water balance components at the catchment scale for the period 1951–2016. Decadal Land Use Land Cover (LULC) in the basin for the years 1985, 1995 and 2005 are analysed. The statistical trends in hydrometeorology and extreme climatology of the basin are evaluated at seasonal and annual scales. Seasonal flow behaviour and influence of climate and human activities on streamflow are also assessed. A drought duration analysis is performed to infer about the implications of spatial distribution of water availability across the basin. The results show significant trends in the water balance components and the basin’s hydro-climatology. The LULC analysis shows notable changes in land use patterns due to human activities. Alterations in the predictability and temporal variability of streamflow are observed after the construction of dams which may affect the downstream water availability. This research highlights the importance of comprehensive synthesis of hydrological modelling approaches with hydrological signatures to understand the dynamics of hydrological processes at catchment scale with an objective of providing insights for effective planning and allocation of water resources and judicious management of water demands.

Hydrology under change: long-term annual and seasonal changes in small agricultural catchments in Norway

Abstract In agricultural catchments, hydrological processes are highly linked to particle and nutrient loss and can lead to a degradation of the ecological status of the water. Global warming and land use changes influence the hydrological regime. This effect is especially strong in cold regions. In this study, we used long-term hydrological monitoring data (22–26 years) from small agricultural catchments in Norway. We applied a Mann–Kendall trend and wavelet coherence analysis to detect annual and seasonal changes and to evaluate the coupling between runoff, climate, and water sources. The trend analysis showed a significant increase in the annual and seasonal mean air temperature. In all sites, hydrological changes were more difficult to detect. Discharge increased in autumn and winter, but this trend did not hold for all catchments. We found a strong coherence between discharge and precipitation, between discharge and snow water equivalent and discharge and soil water storage capacity. We detected different hydrological regimes of rain and snow-dominated catchments. The catchments responded differently to changes due to their location and inherent characteristics. Our results highlight the importance of studying local annual and seasonal changes in hydrological regimes to understand the effect of climate and the importance for site-specific management plans.

Potential hydrological regime requirements for spawning success of the Chinese sturgeon Acipenser sinensis in its present spawning ground of the Yangtze River

AbstractReservoir impoundment often alters the hydrological regimes of the river and consequently leads to the extinction of some sensitive species. This study analysed the spawning response of a critically endangered (CR) species, Chinese sturgeon Acipenser sinensis, under the changing hydrological regimes caused by the Three Gorges Reservoir (TGR). Based on our statistic analysis, we inferred that the long duration (>100 days) and large magnitude (>1.8 * 106 m3/s) of high flow pulse in the flood season and low accumulated water temperature in October (<660°C) and November (<540°C) were key hydrological regimes to induce the spawning success of Chinese sturgeon. Such hydrological regimes could not be satisfied after the third phase of the TGR impoundment in 2005, which decreased the suitability of the flow (HSIF) and temperature (HSIT) regimes for the spawning of Chinese sturgeon. However, a significant complementary relationship between high HSIF and low HSIT was found in all years of successful spawning after 2005, but it did not occur in the nonspawning years of 2013, 2015 and 2017, which could be the reason for spawning failure in these years. In the years 2018 and 2019, although the complementary relationship existed, the spawning failure in these 2 years was probably due to few parent fish. Therefore, we suggest that future conservation measures should focus on both optimizing operations of the TGR to ensure suitable hydrological conditions and restocking with adult fish to ensure successful spawning.

The Late Quaternary Hydrological Changes in the Eastern Tarim Basin Inferred From 10Be Exposure Ages of River Terraces

AbstractReliable information on the dynamics of hydrological changes is crucial for the social and economic stabilities and sustaining developments in arid Central Asia. However, the few long‐term hydrological records limit understanding of the relationship between meltwater runoff and climate changes, because the short‐term observations show a paradoxical runoff trend with climate warming across Central Asia. Here, we made a systematic analysis on the 10Be exposure ages of the river terraces developed in the eastern Tarim Basin and reconstructed the hydrological regime changes during the past 170 ka. These data, together with the ages of the river terraces in the water source areas, suggest that the exposure ages of river terraces in the eastern Tarim Basin reflect the depositional time of alluvial sediments. The meltwater runoff displays an inverse relation with the North Hemisphere Summer Insolation and temperature changes on both orbital and millennial time scale, indicating that low temperatures favor high runoff fluxes. The observed correlation between the hydrological regimes and temperature changes suggests that the runoff will decrease and thus climate will become drying with global warming in arid Central Asia.

Influence of hydrological regime on spatiotemporal distribution of boron in sediments in the Three Gorges Reservoir, China

Hydropower dam construction can alter the continuity of the river flow, thereby influencing geochemical cycle of seldom monitored trace elements due to the change of hydrological regime by reservoir regulation. Here, we investigated the response of hydrological regime on migration of boron (B) in the sediments of Three Gorges Reservoir (TGR) using multiple geochemical approaches. Although B concentrations in TGR sediments increased slightly during five consecutive water seasons, the potential ecological risk exhibited relatively low. The spatial distribution patterns of B with high heterogeneity in TGR sediments were influenced by periodic water-level fluctuation. This high spatial heterogeneity significantly correlated with the distribution of fine-grain sediments, which was attributed to the change of hydrological regime (including the decrease of water flow velocity, sediment accumulation, and extended residence time of suspended fine-grain sediments). In order to remove the sediment size effect, the geochemical normalization approach was applied, and revealed that the slope of normalization curve remarkably decreased from 0.9402 to 0.3682. This indicated that a small amount of B was still accumulated in the mid- and downstream of TGR after removing the hydrological regime effect. Further source identification using geochemical baseline model and principal component analysis, exposed that this slight accumulation of B in sediments originated from the anthropogenic input (8.45%). Our findings provide a geochemical insight on the environmental impacts of reservoir operation on toxic element cycling, with potential implications for ecological assessment of hydropower worldwide.

Climate change impact on the inflow to the reservoirs of the Moscow water supply system

The dynamics of long-term fluctuations in the inflow to the reservoirs of the Moscow water supply system for different time intervals is analysed. The article deals with part of the Moscow drinking water supply system, namely Moskvoretskaya Water System and Vazuza Hydrotechnical System (MVHS). A significant change in the parameters of the inflow distribution is shown. It is concluded that it is necessary to clarify the rules for the operation of reservoirs system under conditions of hydrological regime changes.

Analysis of Hydrologic Regime Changes Caused by Small Hydropower Plants in Lowland Rivers

Hydropower remains the most important and largest source of renewable energy. However, besides many additional benefits, such as dams for water supply, irrigation, flood control, recreation, navigation, etc., hydropower generation has a negative impact on the environment. This study aimed to investigate the hydrologic changes in Lithuanian lowland rivers caused by small hydropower plants (HPPs). Thirty-two indicators of hydrologic alteration (IHA) were studied in 11 rivers downstream of hydropower plants in the post-impact and pre-impact periods. The findings showed that HPPs and reservoirs considerably disturbed the primary flow of river ecosystems downstream. The largest changes in mean IHA values were found for low and high pulse characteristics (up to 57%) and the number of reversals (up to 44%). Only small or no deviations of the timing of annual extreme flows were found. The number of reversals, a low pulse count, and a fall rate were the flow characteristics that fell outside their historical ranges of variability most often. Six (out of 11) hydropower plants were identified that provoked hydrologic alterations of a moderate degree.

Variations in runoff, sediment load, and their relationship for a major sediment source area of the Jialing River basin, southern China

AbstractInvestigation of the variations in runoff, sediment load, and their dynamic relation is conducive to understanding hydrological regime changes and supporting channel regulation and fluvial management. This study is undertaken in the Xihanshui catchment, which is known for its high sediment‐laden in the Jialing River of the Yangtze River basin, southern China, to evaluate the change characteristics of runoff, sediment load, and their relationship at multi‐temporal scales from 1966 to 2016. The results showed that runoff changed significantly for more months, whereas the significant changes in monthly sediment load occurred from April to September. The contributions of runoff in summer and autumn and sediment load in summer to their annual value changes were greater. Annual runoff and sediment load in the Xihanshui catchment both exhibited significant decreasing trends (p < 0.05) with a significant mutation in 1993 (p < 0.05). The average annual runoff in the change period (1994–2016) decreased by 49.58% and annual sediment load displayed a substantial decline with a reduction of 77.77% in comparison with the reference period (1966–1993) due to climate change and intensive human activity. The power functions were satisfactory to describe annual and extreme monthly runoff–sediment relationships, whereas the monthly runoff–sediment relationship and extreme monthly sediment‐runoff relationship were changeable. Spatially, annual runoff–sediment relationship alteration could be partly attributed to sediment load changes in the upstream area and runoff variations in the downstream region. Three quantitative methods revealed that the main driver for significant reductions of annual runoff and sediment load is the human activity dominated by soil and water conservation measures, while climate change only contributed 22.73%–38.99% (mean 32.07%) to the total runoff reduction and 3.39%–35.56% (mean 17.32%) to the total decrease in sediment load.

A Changing Hydrological Regime: Trends in Magnitude and Timing of Glacier Ice Melt and Glacier Runoff in a High Latitude Coastal Watershed

AbstractWith a unique biogeophysical signature relative to other freshwater sources, meltwater from glaciers plays a crucial role in the hydrological and ecological regime of high latitude coastal areas. Today, as glaciers worldwide exhibit persistent negative mass balance, glacier runoff is changing in both magnitude and timing, with potential downstream impacts on infrastructure, ecosystems, and ecosystem resources. However, runoff trends may be difficult to detect in coastal systems with large precipitation variability. Here, we use the coupled energy balance and water routing model SnowModel‐HydroFlow to examine changes in timing and magnitude of runoff from the western Juneau Icefield in Southeast Alaska between 1980 and 2016. We find that under sustained glacier mass loss (−0.57 ± 0.12 m w. e. a−1), several hydrological variables related to runoff show increasing trends. This includes annual and spring glacier ice melt volumes (+10% and +16% decade−1) which, because of higher proportions of precipitation, translate to smaller increases in glacier runoff (+3% and +7% decade−1) and total watershed runoff (+1.4% and +3% decade−1). These results suggest that the western Juneau Icefield watersheds are still in an increasing glacier runoff period prior to reaching “peak water.” In terms of timing, we find that maximum glacier ice melt is occurring earlier (2.5 days decade−1), indicating a change in the source and quality of freshwater being delivered downstream in the early summer. Our findings highlight that even in maritime climates with large precipitation variability, high latitude coastal watersheds are experiencing hydrological regime change driven by ongoing glacier mass loss.

Statistical analysis of maximum runoff of the Southern Buh River using the method of ‘Indicators of Hydrologic Alteration’

Knowledge of maximum river runoff trends is of great practical importance, especially for design and operation of hydraulic structures. This article presents the results of the research of the Southern Buh River's maximum runoff. The water of the river is widely used for hydropower engineering, industrial and municipal water supply, agriculture, irrigation, shipping, tourism etc.
 The research of the maximum runoff was based on the Indicators of Hydrologic Alteration (IHA) method which is widely used in the whole world. This method enables calculation of quantitative statistical characteristics of rivers', lakes', reservoirs' runoff and determination of the degree of their hydrological regime changes. The IHA is used for water bodies having natural or regulated runoff. However, the IHA method was not widely used in Ukraine before.
 The purpose of this publication is using the Indicators of Hydrologic Alterations method in order to study the characteristics of maximum runoff and their changes along the Southern Buh River.
 The research was carried out based on the data of observations at 5 gauge stations located along the Southern Buh River. The research uses the mean daily discharges that has been recorded since the beginning of observations up to 2018 and 2019 inclusive. The river's runoff at each of gauge stations was divided into five components: "Extremely low runoff", "Low runoff", "High runoff pulses", "Small floods", "Large floods". This made it possible to separate three classes of high (maximum) runoff, for which the IHA statistics were calculated, from the total runoff.
 It was discovered that the long-term high runoff changes differed in each of its three components, although they had general trends. The most significant changes were found for large floods, with no significant changes found for high runoff pulses. General trends of high runoff showed that over time the values of maximum discharges tend to decrease, with the increasing duration of high runoff periods.
 The values of the main statistical indicators of high runoff gradually increase from the river's source to its mouth, which fully corresponds to the physical and geographical conditions of its formation. Nevertheless, some features of high runoff were still found. Thus small floods and high runoff pulses have the largest duration in the upper reach of the river.
 On average, the Southern Buh River experiences large floods once in every 10 years, small floods - once in every 2 years, high runoff pulses - 4-8 times a year in its upper reach and 9-14 times a year in its middle reach.

Изменение седиментационных потоков плутония в донные отложения бухты Севастопольская в период до и после аварии на ЧАЭС

Бухта Севастопольская, расположенная в северной акватории Чёрного моря, подвергалась радиоактивному загрязнению техногенными радионуклидами, включая 238,239+240Pu, и испытывала другие виды техногенной нагрузки. Одним из них явилось строительство заградительных молов на входе в бухту в 1975–1986 гг., которое привело к изменению её гидрологического режима. Целью данной работы было оценить изменение седиментационных потоков 238Pu и 239+240Pu в донные отложения устьевой части бухты Севастопольская в период до и после аварии на Чернобыльской АЭС (1962–1986 и 1986–2013 соответственно). Плутоний в осадках определяли радиохимическим методом, с последующим измерением активности радиоизотопов на альфа-спектрометре. Скорость осадконакопления определяли с помощью геохронологической датировки слоёв осадка по изменению отношения активностей 238Pu/239+240Pu в керне донных отложений. Затем рассчитывали скорость седиментации осадочного вещества в донные осадки. Установлено, что в период после 1986 г. среднегодовая скорость осадконакопления и скорость седиментации осадочного вещества в устье бухты увеличились на 63 и 70 % соответственно. Оценка седиментационных потоков 238,239+240Pu за два исследуемых периода показала, что поток 238Pu в донные отложения увеличился после 1986 г. на 150 %, а поток 239+240Pu — на 49 %. Повышенная процентная доля 238Pu в седиментационном потоке плутония после 1986 г. указывает на чернобыльское происхождение плутония в слоях донных отложений выше 11 см. Суммарный эффект увеличения седиментационных потоков 238,239+240Pu в устье бухты в постчернобыльский период обусловлен ростом интенсивности радиоактивных выпадений после аварии на ЧАЭС и влиянием гидротехнических сооружений на режим седиментационных процессов в акватории (увеличением скорости седиментации осадочного вещества).

A dry future for the Everglades favors invasive herpetofauna

The Greater Everglades Ecosystem is a globally important ecoregion, home to 68 threatened or endangered species and the largest designated wilderness area in the Eastern United States. Anthropogenic manipulations of the natural hydrology have led to widespread degradation of this ecosystem and monitored population declines across multiple taxa. Simultaneous introductions of hundreds of non-native species into South Florida and their subsequent invasion into the Everglades has further impacted native Everglades communities. Predictions for future climate change suggest that the Everglades is headed towards a drier future, making it crucial to understand how changes in hydrological regimes will impact both native and non-native fauna. Our study combines the results of a landscape-scale experimental manipulation conducted to assess the impact of differing hydrological regimes at the Loxahatchee Impoundment Landscape Assessment between 2018 and 2020 with a community composition analysis of data collected across multiple habitat types throughout Everglades National Park between 2000 and 2002. Both datasets used a variety of survey methods to extensively characterize the amphibian and reptile amphibian assemblage across habitat types and hydrological regimes. An NMDS analysis indicated that variation in hydrology is the primary axis structuring reptile and amphibian habitat usage across the Everglades, with non-native species more likely to be indicators of drier habitat types. This result concurred with those from the landscape-scale manipulation, in which non-native species were significantly favored by drier hydrological conditions. Taken together, these results suggest that a drier future within the Greater Everglades Ecosystem may facilitate further spread of South Florida’s diverse non-native amphibian and reptile assemblage.

Closed Torey Lakes: Is It Possible to Predict Changes in Hydrological Regime?

Closed Torey Lakes: Is It Possible to Predict Changes in Hydrological Regime?

Short-term recovery of macroinvertebrate communities following a flash flood in an urban river: a case study of the Palmiet River in Durban, South Africa

Extreme floods have become frequent in the urban Palmiet River due to exacerbating climate change. Therefore, the current study aimed to explore a short-term recovery of macroinvertebrate communities following a flash flood in the Palmiet River, KwaZulu-Natal, South Africa. Different biotopes, i.e. stones, gravel sand and mud, and vegetation were sampled after the March-April heavy rain in 2018. Ephemeroptera, Odonatan, and Hemipteran have shown similar trends across weeks at all sites. Plecoptera and Coleoptera started recovering at week four However, the total abundance and taxa richness had significantly recovered during the fourth week at site 2 and 3, and fifth week at site 1. Communities have shown no significant difference for each site from weeks six to eight (ANOVA, p > 0.5), which implies that climax on macroinvertebrate communities was reached at week six. Hydrologic regime change has not influenced water quality parameters across all weeks (ANOVA, p > 0.5) and this was also reflected on the average score per taxon (ASPT), which has shown no significant difference (ANOVA, p > 0.5) across weeks at all sites. These findings provide a baseline for future studies on flood effect on urban streams and supplement the understanding of the effects of sudden hydrologic regime changes on macroinvertebrate communities.

Hydrologic variability in black ash wetlands: Implications for vulnerability to emerald ash borer

AbstractBlack ash (Fraxinus nigra) wetlands are widespread, forested landscape features in the western Great Lakes region. However, the future of these ecosystems is threatened due to impending spread of the invasive emerald ash borer (EAB), which results in tree mortality, decreased transpiration, and potential shifts to wetter, non‐forested conditions. The vulnerability to such ecohydrologic shifts likely varies according to local hydrologic regimes controlled by landscape settings, but this site‐dependent vulnerability and our ability to predict it is unknown. Here, we assessed vulnerability potential as a function of site hydrology in 15 undisturbed black ash wetlands from their three most common hydrogeomorphic settings in northern Minnesota: lowland, depression, and transition. Further, we used high‐resolution (1‐cm) surface elevation models to assess spatial variability of water levels at a subset of 10 sites. Although we observed similar ET and groundwater exchange rates among settings, lowland sites were generally drier because of elevated landscape position and greater water level drawdowns (via lower specific yield). We predict that such drier sites will exhibit greater water level increases following EAB‐induced ash mortality, compared to wetter sites where open water evaporation and shallow‐rooted understory transpiration will offset losses in tree transpiration. Moreover, compared to wetter sites, drier sites exhibited minimal microtopographic variation, limiting the number of elevated microsites for tree establishment and eventual canopy recovery after ash loss. These results suggest that site wetness is a simple and effective predictor of black ash wetland vulnerability to hydrologic regime change. To that end, we assessed the ability of common terrain metrics to predict site wetness, providing a potential tool to target vulnerable areas for active management efforts.

Influence of river-lake isolation on the water level variations of Caizi Lake, lower reach of the Yangtze River

In order to explore the water level variations of Caizi Lake under river-lake isolation, the monthly water level of the Chefuling station in Caizi Lake from 1989 to 2018 and the daily water level, rainfall and flow of local hydrological stations in 2018 were analyzed by using the Mann-Kendall trend test and wavelet analysis. Results showed that the difference of the average water level of Caizi Lake between the flood and dry seasons was 3.34 m, with a multi-year average water level of 10.42 m above sea level. The first and second main periods of the water level of Caizi Lake were 128 and 18 months, respectively, with 4 and 29 “up-down” cycles, respectively. From 2018, the next 3–4 years were likely to be the low water level period. The water level of Caizi Lake was significantly correlated with that of the Anqing hydrological station of the Yangtze River (r=0.824, P<0.01). In addition, the current hydrological staging of Caizi Lake was about 30 days behind than before the sluice was built. Under the dual influences of the river-lake isolation and the Yangtze-to-Huaihe Water Diversion Project (YHWD), the hydrological regime change of Caizi Lake and its eco-environmental effect needed long-term monitoring and research.

Assessing the impacts of climate change on hydrological regimes and fish EQR in two Danish catchments

Study regionTwo large-scale catchments in Denmark: Ringkøbing fiord and Mid-Zealand catchments. Study focusFuture changes in hydrological regime, extremes, groundwater levels and ecological quality ratio (EQR) for fish were assessed. Based on an ensemble of 17 bias-corrected regional climate models forced by the emission scenario RCP8.5, a dry, a medium and a wet model were identified for the future period 2071–2100. Changes in water balances for catchments, impacts on groundwater level and fish ecological quality ration (fish EQR) were evaluated. The impact changes were based on an integrated, transient, coupled groundwater and surface-water flow model, set up with a horizontal resolution of 200m × 200m for the two catchments. New hydrological insights for the regionStrengths and weaknesses of EQR assessments based on symbolic regression methods compared to expert assessments based on flow calendar and max flow changes in percent exceedance thresholds (Q95) were identified. While the modelled impact of climate change on monthly flow and flow calendar follows the same pattern at all monitoring stations, the impact on groundwater level and fish EQRs are more complex, and somewhat ambiguous across realisations and catchments.

Annual patterns of litter decomposition in the channel and riparian areas of an intermittent stream

Intermittent streams, dominant in arid and semi-arid regions, are considered to be more representative of global river networks than perennial rivers. The impacts of constant changes in hydrological regime on the functioning of these streams and associated riparian areas does, however, remain to be elucidated. In this study, litter derived from two deciduous tree species (chestnut and oak) was used to compare microbial–decomposition patterns between an intermittent stream channel and its riparian area over a 1-year period. The stream channel exhibited higher decomposition rates than the riparian area for litter from both species, and higher fungal biomass only for chestnut. Despite a prolonged absence of streambed surface water (254 days), differences in hydrological conditions in the wetter seasons (autumn and winter) shape the decomposition dynamics in both zones throughout the whole hydrological cycle. The results point out the importance of the “hydrological imprint” for the leaves’ degradation; long-term studies are advisable over short-term ones to better understand the functioning of intermittent streams.

Alteration of flood pulses by damming the Nenjiang River, China – Implication for the need to identify a hydrograph-based inundation threshold for protecting floodplain wetlands

Floodplain wetlands of low-gradient rivers are especially sensitive to alteration of hydrologic conditions. Although many studies have investigated changes in downstream hydrologic regimes caused by river dam construction, no study has specifically quantified the long-term effect of altered flood pulse on floodplain wetlands. Such knowledge is needed to develop effective dam operation strategies and plans for downstream wetland protection and restoration. We applied data time series from 1984 to 2018 to delineate the inundation extent of floodplain wetlands during the pre- (1984–2005) and post-dam (2006–2018) periods. Four segments of the 360-km river reach were selected to investigate how inundation frequency of floodplain wetlands responded to changes in flow regimes and flood pulse for both periods associated with dam operation. The results showed that the water area slightly increased as a result of recharging water from dam, while the inundation frequency of adjacent floodplain wetlands overall reduced because of lower magnitude of flood pulse. Inundation area of four segments show less variation during the post-dam period compared to the pre-dam period. These findings clearly indicate that decreased flood pulses caused by dam operations reduce both inundation frequency and areal extent of floodplain wetlands. Based on the findings, we propose an inundation threshold that can be used for dam operation to protect and restore river corridor and floodplain ecosystems.