On the Hydrodynamic Behavior of the Changed River–Lake Relationship in a Large Floodplain System, Poyang Lake (China)

Poyang lake floodplains are hydrologically complex and dynamic systems which exhibit dramatic intra-annual wetting and drying. The flow regime of the Yangtze River was previously known to play an important role in affecting Poyang Lake and its extremely productive floodplains (river–lake relationship). The recent severe declines and recessions in the lake are closely linked to the changed river–lake relationship, resulting in significant hydrological, ecological, and economic problems. This study aims to examine the spatiotemporal heterogeneity of the floodplain hydrodynamic behaviors with respect to impacts of the changed river–lake relationship, characterized by the lake water level, inundation area, and inundation duration based on a floodplain hydrodynamic model of Poyang Lake, and to further quantify the severity of dryness recently endured since 2000. Simulation results show that, in general, the current modified river–lake relationship is more likely to affect the hydrological seasonality of the floodplain system since 2000, relative to the flooding and drying cycles during past decades (1953–2000). The present hydrodynamic behaviors suffered significant change due to the greatest interference from the altered river–lake relationship, particularly for the falling period in October. On average, the floodplain water level and inundation duration decreased by 6 m and 12 days during October, respectively. Additionally, the highest monthly shrinkage rate in floodplain inundation shifted from the period of October–November to September–October, with the mean inundation area decreasing by around 50%, demonstrating an advanced and prolonged dry condition. The spatial responses of the hydrodynamics in the low-slope floodplains are most likely to be affected by the dynamic river–lake relationship, as expected. This study assessed the effects of the altered river–lake relationship on the hydrological regime of the Poyang Lake floodplains in terms of spatiotemporal distributions and changing processes for the periodic inundated behavior, which can support the relevant study of the subsequent ecological effects on the wetlands.

On the role of operational dynamics in biogeochemical efficiency of a soil aquifer treatment system

Sustainable irrigation with treated wastewater (TWW) is a promising solution for water scarcity in arid and semi-arid regions. Soil aquifer treatment (SAT) provides a solution for both the need for tertiary treatment and seasonal storage of wastewater. Stresses over land use and the need to control the obtained water quality makes the optimization of SAT of great importance. This study looks into the influence of SAT systems' operational dynamics (i.e., flooding and drying periods) as well as some aspects of the inflow biochemical composition on their biogeochemical state and the ultimate outflow quality. A series of four long-column experiments was conducted, aiming to examine the effect of different flooding/drying period ratios on dissolved oxygen (DO) concentrations, oxidation–reduction potential (ORP) and outflow composition. Flooding periods were kept constant at 60 min for all experiments while drying periods (DPs) were 2.5 and 4 times the duration of the flooding periods. Our results show that the longer DPs had a significant advantage over the shorter periods in terms of DO concentrations and ORP in the upper parts of the column as well as in the deeper parts, which indicates that larger volumes of the profile were able to maintain aerobic conditions. DO concentrations in the deeper parts of the column stabilized at ∼3–4 mg L−1 for the longer DPs compared to ∼1–2 mg L−1 for the shorter DPs. This advantage was also evident in outflow composition that showed significantly lower concentrations of NH4+-N, dissolved organic carbon (DOC) and total Kjeldahl nitrogen (TKN) for the longer DPs (∼0.03, ∼1.65 and ∼0.62 mg L−1 respectively) compared to the shorter DPs (∼0.5, ∼4.4 and ∼3.8 mg L−1, respectively). Comparing experimental ORP values in response to different DPs to field measurements obtained in one of the SAT ponds of the SHAFDAN, Israel, we found that despite the large-scale differences between the experimental 1-D system and the field 3-D conditions, ORP trends in response to changes in DP, qualitatively match. We conclude that longer DP not only ensure oxidizing conditions close to the surface, but also enlarge the active (oxidizing) region of the SAT. While those results still need to be verified at full scale, they suggest that SAT can be treated as a pseudo-reactor that to a great extent could be manipulated hydraulically to achieve the desired water quality while increasing the recharge volumes.

On the role of operational dynamics in biogeochemical efficiency of a soil aquifer treatment system

Sustainable irrigation with treated wastewater (TWW) is a promising solution for water scarcity in arid and semi-arid regions. Soil aquifer treatment (SAT) provides a solution for both the need for tertiary treatment and seasonal storage of wastewater. Stresses over land use and the need to control the obtained water quality makes the optimization of SAT of great importance. This study looks into the influence of SAT systems' operational dynamics (i.e. flooding and drying periods) as well as some aspects of the inflow biochemical composition on their bio-geo-chemical state and the ultimate outflow quality. A series of four long-column experiments was conducted, aiming to examine the effect of different flooding/drying period ratios on dissolved oxygen (DO) concentrations, oxidation-reduction potential (ORP) and outflow composition. Flooding periods were kept constant at 60 minutes for all experiments while drying periods (DP) were 2.5 and 4 times the duration of the flooding periods. Our results show that the longer DP had a significant advantage over the shorter periods in terms of DO concentrations and ORP in the upper parts of the column as well as in the deeper parts, which indicates that larger volumes of the profile were able to maintain aerobic conditions. This advantage was evident also in outflow composition analyses that showed significantly lower concentrations of DOC, TKN and ammonium in the outflow for the longer DP. Comparing experimental ORP values in response to different DP to field measurements obtained in one of the SAT ponds of the SHAFDAN, Israel, we found that despite the major scale differences between the experimental 1D system and the field 3D conditions, ORP trends in response to changes in DP, qualitatively match. We conclude that longer DP not only ensure oxidizing conditions close to the surface, but also enlarge the active (oxidizing) region of the SAT. While those results still need to be verified in full scale, they suggest that SAT can be treated as a pseudo-reactor that to a great extent could be manipulated hydraulically to achieve the desired water quality while increasing the recharge volumes.

Plasticity in life history traits of a cyprinid fish in an intermittent river

The extreme seasonal environmental variation of intermittent rivers has a profound effect on freshwater fish communities. Yet, few studies have examined the consequences of the seasonal cycles of flooding and drying to fish condition and reproduction in these ecosystems. In this study, we compared the body condition, reproduction and diet of two chub populations from two adjacent sites (a perennial and an intermittent site) on the main stem of a Mediterranean river (Evrotas River, S. Greece). The study was conducted in spring 2017, three months after flow resumption and before the onset of chub reproductive period. Condition (net weight adjusted for length) of fish did not differ significantly between the two sites, despite lower aquatic macroinvertebrate availability at the intermittent site. Fish at the intermittent site compensated for the lower aquatic prey availability by increasing their feeding intensity and by shifting to higher terrestrial prey consumption. In addition, chub liver weight (adjusted for length) and gonadal weight (adjusted for length) were significantly higher at the intermittent site, indicating higher somatic and reproductive investment. These results highlight the resilience of fish populations inhabiting streams with extreme variation in flow, due to natural and/or anthropogenic drought.

Perhitungan Kecepatan Sedimentasi Melalui Pendekatan Usle dan Pengukuran Kandungan Tanah dalam Air Sungai yang Masuk ke dalam Waduk Sermo

Dam is one of the essential man-made buildings which was developed to various beneficialy purposes such as irrigation, fresh water supply, flooding and drying control, and also tourism. Due to those mentioned functions, condition of the dam has to be maintained continuously especially from sedimentation. Sedimentation is being a serious threat for the continuity of dam services. Protecting dam from sedimentation is not only managing dam area, but also we have to care all watershed area, because the sedimentation is caused by erotion on the area. In order to know the rate of the sedimentation within the dam, measurement and prediction must be done. One of methods to predict and measure the sedimentation is by analyzing geospatial data using USLE Approach, and analyzing suspended sediment in river’s water toward to the dam. By those both analysis, rate of sedimentation happened within the dam can be calculated. This paper try to use geospatial (GIS) based analysis to estimate the sedimentation rate using USLE approach within Ngrancah Watershed. The USLE Formula requires four types of maps, they are soil type, slope, land cover, and rain erosivity maps. Each of maps is classified to the specific standards, then will be analized by overlaying to another map. Another method will be used to estimate these dimentation rate is the suspended sediment measurement. This method was determined using sediment transport formula. The data used are samples of river water ing Ngerancah Watershed that was flow toward to the Sermo Dam, and daily volume of inflow water. Those resulted values, then were compared each other. Based on the calculation, sedimentation rate resulted using USLE Approach is 276.100,917 m3 per year or 8,675 mm thickness per year. While the calculation based on the measurement of suspended sediment in river’s water is 270.206,363 m3 per year or 8,490 mm thickness per year. The difference value between the both methods is 5894,555 m3 per year or 0,185 mm thickness per year. Based on the watershed monitoring guidelines published by The Ministry of Forestry of Indoensia, the Sermo Dam sedimentation rate is categorized in poor class, because the sedimentation rate is exceeding 5 mm per year, as the safe limit of dam sedimentation rate.