Much attention had been paid to reducing external loading of nutrients to improve water quality, while internal loading from sediment, which has been largely neglected, is also an important source for water eutrophication. The internal load in deep lakes or reservoirs is not easy to be detected and be quantified. In this study, three different methods (mass balance method, Fick's law, and regression equation) were combined to calculate the gross or/and net P release from sediment using limited data. Our results indicated that (1) the methods of mass balance and regression equation give similar results of sediment P release rate, with values of 0.889 and 0.902 mg m(2) d(-1), respectively, while the result of Fick's law was much lower (0.400 mg m(2) d(-1)); (2) Hot periods of sediment releasing were suggested to occur from March to April and from August to September, which correspond to periods of high risks of algae blooms. The remaining months of the year were shown as net nutrient retention; (3) for the whole region, Baihedam and Chaohekuqu were identified as zones with a higher possibility to release P from sediment. (4) P loading to the Miyun Reservoir was greater in the inflow than in the outflow, suggesting a portion of the inflow P load was retained in the water or sediment; hence, release of sediment P may continue to be a major source of phosphorus in the future.

Estimating internal P loading in a deep water reservoir of northern China using three different methods

Rural populations often depend on small reservoirs for their water supply. These are not natural aquatic system but are designed to serve specific purposes and provide the means to utilize water in a variety of useful and efficient ways. Water from these sources is not only utilized for drinking purposes, but also for commercial and industrial use. Though reservoirs are constructed, they are considered as an intermediate between a river and a lake. Thus limnological characteristics of this hybrid system have been of great interest to ecologists and researchers. Several limnological attributes regarding water quality, plankton abundance, fish population are been discussed in this review article. Ecological studies on global and Indian perspective are the major highlight of this review. A few modeling approaches are also discussed which are commonly used globally to preserve and manage the pristine aquatic nature of this hybrid ecosystem.

A Review on Reservoir System and Its Ecology in Indian Perspective

Reservoirs have been regarded as hot spots for greenhouse gas emissions since the 1990s. However, there is scant research about littoral zones of reservoirs. In the present study, static closed chamber and gas chromatograph techniques were used to measure methane (CH4) and carbon dioxide (CO2) flux in the littoral area of a temperate reservoir from 2009 to 2010. The littoral area comprises three zones, namely supralittoral, eulittoral and infralittoral. The patterns of CH4 and CO2 emissions from these three littoral zones were significantly different during the sampling periods, with the eulittoral zone having the highest CH4 flux and the supralittoral zone having the highest CO2 flux. Temperature and biomass correlated with CH4 and CO2 emissions. Measurement of CO2 emissions after removing vegetation varied in each zone and according to time of sampling. A large littoral area of the reservoir sampled herein will be submerged and converted to a pelagic area with deep standing water after the South to North Water Transfer Project is completed, in 2050. The results of the present study suggest further research and monitoring are needed, and should focus on likely effects of extreme climate events and the effects of human-mediated factors on greenhouse gas emissions.

Seasonal and diurnal methane and carbon dioxide emissions from the littoral area of the Miyun Reservoir in Beijing, China

Rivers have been largely considered as the source of nitrous oxide (N2O) to the atmosphere. N2O emissions from rivers could be seriously influenced by damming and exhibit unique spatiotemporal patterns in river-reservoir systems. Multiple research studies report N2O emissions from rivers with single reservoirs, but the spatiotemporal patterns and controls of N2O emissions from cascaded river-reservoir system remains unclear. In this study, we investigated the spatiotemporal variations of N2O concentrations and fluxes along a cascade damming river (Wubu River) in Southwest China. Our results showed that N2O concentrations in Wubu River ranged from 2.5 to 283.2 nmol·L-1 with a mean of 50.7±52.3 nmol·L-1, and were generally supersaturated with gas fluxes ranging from 11.8 to 805.6 μmol·m-2·d-1. N2O concentrations and fluxes showed significant longitudinal variation with increasing fluxes from upstream to downstream. Meanwhile, for each river-reservoir-released water continuum, local variation of N2O concentrations were also prominent. Reservoir sections and released water sections had 2.7 (1.2-7.9) and 3.4 (1.3-12.2) times higher N2O concentrations than corresponding upstream river reaches and acted as hotpots for N2O emission. The N2O concentrations had significant correlations with organic carbon, phosphorus and Chl-a in surface water. Furthermore, the N2O concentrations and fluxes in reservoirs had significant correlation with hydraulic residence time and hydraulic load, suggesting that fragmentation of hydrologic conditions were important drivers for the spatial variations of N2O concentrations in the Wubu River cascade reservoirs. Our results suggested that hydraulic residence time could predict the variation pattern of N2O fluxes in this small river basin. Seasonal variations of N2O concentrations and fluxes with the highest in autumn and lowest in winter, and were mainly attributed to temperature and rainfall. N2O fluxes were much higher in Wubu River than the average levels of China’s reservoirs and global reservoirs, acting as enhanced N2O emitter. Our study highlighted that the cascade reservoirs not only acted as exciters for N2O production and emissions but also form cumulative effects and local hotpots along the longitudinal dimension, which could significantly increase the complexity of the spatiotemporal variability in riverine N2O emissions.

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Spatiotemporal Variability of the Nitrous Oxide Concentrations and Fluxes From a Cascaded Dammed River

Line 7: Unclear what control site means here as stable control conditions may be difficult to maintain under fluctuating water. Please clarify in what way these two sites served as control. (This is explained in the later text so this comment is about clarity for those only reading the abstract. However I think the word control site signals something else than what is the case here and what is called control site here does not stand out as very different from the other sites with stable water moisture, e.g. the NF site, so I wonder if it would not be good to omit using the word “control” to reduce the risk of confusion.) L17: Were N2O and CH4 measurements performed simultaneously or at different times? This is essential for the interpretation of the comparison. L 18-20: The sentence “It showed that N2O flux and CH4 flux was influenced by distinct factors and in differing ways.” is a bit vague. Would it be possible to briefly explain how N2O and CH4 fluxes and regulation differed instead? L20-22: Instead of ending the abstract with emphasizing the complexity and challenges – please highlight the unique implications from this study and how it leads forward towards better understanding the complexity and reducing the future challenges.

/pdf/responses-of-n-2-o-flux-to-water-level-fluctuation-and-other-1osvt02mhj.pdf

S. W. Jiao

Papers

Responses of N 2 O flux to water level fluctuation and other environmental factors at littoral zone of Miyun Reservoir: a comparison with CH 4 fluxes