Hydrobiological Investigations of the Water Quality of the Water Supply Reservoirs Husinec and Římov

The two eutrophicated reservoirs Husinec (2.6 km³, 35 ha, z_max 18 m, MQ 1.87 m^3/s) and ?ímov (34.5 hm³, 216 ha, z_max 44 m, MQ 4.14 m^3/s) show concentrations of total phosphorus of 10… 50 mg/m³ and chlorophyll contents of 7… 36 mg/m³ in the summer season. For both reservoirs a good correlation exists between the chlorophyll concentration and the density of the phytoplankton (20 · 10³… 13 · 10⁶ ind./l). With average concentrations of 10… 20 mg/m³ chlorophyll a in summer, the water can be treated for producing drinking water only at a higher expenditure. The water quality will be improved by a reduction of the phosphorus load.     

Distribution of <Superscript>226</Superscript>Ra in the Arctic Ocean and the Bering Sea and its hydrologic implications

Radium-226 (²²⁶Ra) activities were measured in the surface water samples collected from the Arctic Ocean and the Bering Sea during the First Chinese National Arctic Research Expedition. The results showed that ²²⁶Ra concentrations in the surface water ranged from 0.28 to 1.56 Bq/m³ with an average of 0.76 Bq/m³ in the Arctic Ocean, and from 0.25 to 1.26 Bq/m³ with an average of 0.71 Bq/m³ in the Bering Sea. The values were obviously lower than those from open oceans in middle and low latitudes, indicating that the study area may be partly influenced by sea ice meltwater. In the Bering Sea, ²²⁶Ra in the surface water decreased northward, probably as a result of the exchange between the ²²⁶Ra-deficient sea ice meltwater and the ²²⁶Ra-rich Pacific water. In the Arctic Ocean, ²²⁶Ra in the surface water increased northward and eastward. This spatial distribution of ²²⁶Ra reflected the variation of the ²²⁶Ra-enriched river component in the water mass of the Arctic Ocean. The vertical profiles of ²²⁶Ra in the Canadian Basin showed a concentration maximum at 200 m, which could be attributed to the inputs of the Pacific water or/and the bottom shelf water with high ²²⁶Ra concentration. This conclusion was consistent with the results from ²H, ¹⁸O tracers.     

Population Dynamics,Biomass and Biomass Production of Eudiaptomus gracilis (G. O. SARS) in Two Water Areas of Differing Trophic State of Lake Balaton (Hungary)

Population dynamics and production of Eudiaptomus gracilis (G. O. Sars) were investigated in two basins of differing water quality of Lake Balaton from February through December, 1977. One of the basins (Keszthely) is considered to be hypertrophic. the other (Tihany) moderately eutrophic. Plankton samples were collected at weekly intervals. The fecundity was 9.61 ± 3.39 at Tihany, and 16.53 ± 3.60 at Keszthely. The difference between the two basins was significant (P<0.1%). At Tihany the average number of eggs per m³ was lower by 36% relative to Keszthety. The number of nauplii differed only a little between the two basins with the exception of April, when at Tihany the amount of individuals was nearly two times as great as at Keszthely. In the case of younger copepodites (Stages I … III) the difference in individual numbers between the two areas of water was marked from February to June, while in other periods it proved to be small. At Tihany, the number of young copepodites was greater by 8%, on the average, than at Keszthely. The amount of larger copepodites (IV … V) relative to the total number of younger individuals of the population was by 63% resp. 77% smaller at Tihany and Keszthely. In the whole period of these studies the number of adults was less by 44% at Keszthely than at Tihany. Their amount relative to that of nauplii was smaller by 6% at Tihany and by 45% at Keszthely. At Tihany, the population biomass was at a constant high level during winter and spring (40 to 50 mg/m³), in summer values being lower (15 … 35 mg/m³). In the Keszthely-Basin biomass showed more extreme changes, reaching a peak as high as 40 … 43 mg/m³ in April and November, but hardly exceeding 6 mg during July–August. During the period of investigation, total biomass in the Tihany-Basin was 342 mg/m³, at Keszthely 204 mg/m³. Net biomass production-two methods for estimation having been used – was higher in the Tihany-Basin (17.25 and 33.83 KJ/m²), while in the Keszthely-Basin it was considerably lower (13.06 and 9.50 KJ/m²).     

Natural recolonization of a productive tropical pond: Day to day variations in the photosynthetic parameters

Chlorophyll pigments (CHL), primary productivity (PP) and particulate nitrogen (N_p) in relation to several environmental factors were monitored during planktonic colonization of an aquaculture pond (Layo, Côte d'Ivoire). How interactions between the organisms are established in an initially azoic environment were investigated. From March, 15 (D1) to March, 31 (D16), the system transformation went through three stages. First, a precolonization by heterotrophic microbial community from D1 to D2 (N_p < 1 m maximum at D2: 243 mg m^–2; CHL around 0). Then, a pioneer microalgal community developped from D3 to D7 (maximum CHL on D6: 19 mg m^–2; PP: 1.0 g C m^–2 d^–1) with a significant contribution of picoplankton (CHL and PP < 3 m: 33 and 23% of the total, respectively). Finally, a second microalgal colonization was noticed from D9 to D12 (maximum CHL: 55 mg m^–2, PP: 2.8 g C m^–2 d^–1), largely dominated by nanoplankton (CHL and PP > 3 m: 95 and 99% of the total, respectively). Overall, photosynthetic activity appeared to be closely linked to algal biomass. The study of autotrophic biomass and activity in different size classes in relation to the other parameters allowed us to precise the origin of the biomass fluctuations. The first bloom appeared to be controlled by selective grazing on small algae. The second algal development ended when N requirement represented at least 69% of N supply (in the N — NH₄ form). This control was enhanced by the appearance of rotifers, leading to a more complex equilibrium.     

中国太湖五里湖内不同凤眼莲密度圈闭内的沉降率

The dynamic model of physical-biological engineering for purifying water quality in Lake Taihu needs the parameter of sedimentation rate (SR). Especially, it is seldom reported how SR is influenced by interactions between algae and aquatic plant. So 6 enclosures with each area of 5×5 m² were constructed in Wulihu with 2 m depth, a small hypereutrophic bay of Taihu Lake, China. Enclosures, in which the original water quality was the same as that in surrounding lake, were input Eichhomia crassipes at various original densities from 0-6 kg·m^-2 on August 9, 1996. SR had been measured separately at depths of 0.6, 1.2f 1.8 m in each enclosure during 20 days. Main results were as follows:1) SR average in enclosures (17.3g·m^-2 d^-1) was as much as about 1/14 that in the surrounding lake; 2) The deeper was it, the higher rate was it in each enclosure, generally; 3) SR cures versus original densities of Eichhomia crassipes (ODE) in enclosures had the ship of "V" at different depths; SR minimuma were observed in the enclosure with original meso-density of Eichhomia crassipes (EMESO, 4kg·m^-2), the average of SR minimuma was about 8.55 g ·m^-2 d^-1) SR in enclosures with original hypo-density (EHYPO, 0-3kg·m^-2) were mainly negative related with water temperature and light intensity;while those with original hyperdensity (EHYPR, 5-6kg·m^-2) were mainly negative related with transparency (SD) instead.These SR-distribution characteristics may be explained by interactions between dead algae and relics of Eichhomia crassipes.     

A remote sensing contribution to hydrologic modelling in arid and inaccessible watersheds,Pishin Lora basin,Pakistan

The lack of adequate field measurements often hampers the construction and calibration of rainfall‐runoff models over many of the world's watersheds. We adopted methodologies that rely heavily on readily available remote sensing datasets as viable alternatives for assessing, managing, and modelling of such remote and inadequately gauged regions. The Soil and Water Assessment Tool was selected for continuous (1998–2005) rainfall‐runoff modelling of one such area, the northeast part of the Pishin Lora basin (NEPL). Input to the model included satellite‐based Tropical Rainfall Measuring Mission precipitation data, and modelled runoff was calibrated against satellite‐based observations, the latter included: (i) monthly estimates of the water volumes impounded by the Khushdil Khan (latitude 30°40′N, longitude 67°40′E), and the Kara Lora (latitude 30°34′N, longitude 66°52′E) reservoirs, and (ii) inferred wet versus dry conditions in streams across the NEPL. Calibrations were also conducted against observed flow reported from the Burj Aziz Khan station at the NEPL outlet (latitude 30°20′N; longitude 66°35′E). Model simulations indicate that (i) average annual precipitation (1998–2005), runoff and recharge in the NEPL are 1300 × 10⁶ m³, 148 × 10⁶ m³, and 361 × 10⁶ m³, respectively; (ii) within the NEPL watershed, precipitation and runoff are high for the northeast (precipitation: 194 mm/year; runoff: 38 × 10⁶ m³/year) and northwest (134 mm/year; 26 × 10⁶ m³/year) basins compared to the southern basin (124 mm/year; 8 × 10⁶ m³/year); and (3) construction of delay action dams in the northeast and northwest basins could increase recharge from 361 × 10⁶ m³/year up to 432 × 10⁶ m³/year and achieve sustainable extraction. The adopted methodologies are not a substitute for traditional approaches, but they could provide first‐order estimates for rainfall, runoff, and recharge in the arid and semi‐arid parts of the world that are inaccessible and/or lack adequate coverage with field data. Copyright © 2011 John Wiley & Sons, Ltd.     

Near‐bed shear stress,turbulence production and dissipation in a shallow and narrow tidal channel

Near‐bed, highly resolved velocity profiles were measured in the lower 0.03 m of the water column using acoustic Doppler profiling velocimeters in narrow tidal channels in a salt marsh. The bed shear stress was estimated from the velocity profiles using three methods: the log‐law, Reynolds stress, and shear stress derived from the turbulent kinetic energy (TKE). Bed shear stresses were largest during ebbing tide, while near‐bed velocities were larger during flooding tide. The Reynolds stress and TKE method gave similar results, while the log‐law method resulted in smaller bed shear stress values during ebbing tide. Shear stresses and turbulent kinetic energy followed a similar trend with the largest peaks during ebbing tide. The maximum turbulent kinetic energy was on the order of 1 × 10^{? 2} m²/s². The fluid shear stress during flooding tide was approximately 30% of the fluid shear stress during ebbing tide. The maximum TKE‐derived shear stress was 0.7 N/m² and 2.7 N/m² during flooding and ebbing tide, respectively, and occurred around 0.02 m above the bed. Turbulence dissipation was estimated using the frequency spectrum and structure function methods. Turbulence dissipation estimates from both methods were maximum near the bed (~0.01 m). Both the structure function and the frequency spectrum methods resulted in maximum dissipation estimates on the order of 4 × 10^{? 3} m²/s³. Turbulence production exceeded turbulence dissipation at every phase of the tide, suggesting that advection and vertical diffusion are not negligible. However, turbulence production and dissipation were within a factor of 2 for 77% of the estimates. The turbulence production and dissipation decreased quickly away from the bed, suggesting that measurements higher in the water column cannot be translated directly to turbulence production and dissipation estimates near the bed. Copyright © 2015 John Wiley & Sons, Ltd.     

大型水生植物—藻类混合型富营养湖泊的生态管理模式——以固城湖为例

Lake Gucheng is located in the southeast of Nanjing, with an area of 24.3 km², an average depth of 2 meters. The macrophytes of the lake were used to be abundant and their biomass was about 4.96 mg·m^-2. The annual average contents of total phosphorus (TP), total nitrogen (TN), PO^3- -P, COD_Mn and BOD₅ 0.03, 1.31, 0.005, 3.61 and 1.46 mg·L^-1, respectively. Thus, the water quality of this lake is quite well. Recently, the water quality in pari of the lake became worse because of some unreasonable exploitation and utilization of bioresources. The interactions between phytoplankton (N₁), macrophyte (N₂), fish (N₃), crab (N₄) were studied here. The macrophyte has great influences on both phytoplanktons, fish and crab, controlling the water quality and maintaining the fishery productivity. On the other hand, the phytoplankton, fish and crab also influence the macrophyte. It is key method of ecological management to maintain the macrophyte by fishery culture. Therefore, a modified Lotka-Volterra model has been established to estimate the interaction between N₁, N₂, N₃, N₄ and the influences of some water environmental parameters on these aquatic organism, environmental and economic effect. The main model consists four compart-mental models and four submodels, involved 12 external variables, 8 state variables, 19 universal constants and 11 parameters. The values of most parameters were found from our experiments and calibrated by the model and actually measured data. The model has been validated by comparison the computed and experimental data of phytoplankton and macrophyte. The theoretical outputs showed a good agreement with the measured data. This model predicated that if the standing crop offish and crab was higher than 2.65 ·m^-2 during springtime in this lake, macrophytes would not grow, chlorophyll a content would arrive 34.8 mg·m^-3 and the water quality would decrease. If the macrophyte grow well, the maximum fishery productivity would be about 1 600 t. In this case, the annually averaged phytoplankton chlorophyll a content should be 3.69 mg·m^-3, which is lower than the criterion (10 mg·m^-3) for eutrophic state. From 1991 to 1996, Lake Gucheng was managed with this model, its water quality maintain quite well, chlorophyll a content decreased from 3.51 (1991) to 1.89 mg·m^-3 (1994). Meanwhile, the fishery productivity increased and the economic effect heightened year by year.     

A natural tracer investigation of the hydrological regime of Spring Creek Springs, the largest submarine spring system in Florida

This work presents results from a nearly two-year monitoring of the hydrologic dynamics of the largest submarine spring system in Florida, Spring Creek Springs. During the summer of 2007 this spring system was observed to have significantly reduced flow due to persistent drought conditions. Our examination of the springs revealed that the salinity of the springs' waters had increased significantly, from 4 in 2004 to 33 in July 2007 with anomalous high radon (²²²Rn, t_1/2=3.8 days) in surface water concentrations indicating substantial saltwater intrusion into the local aquifer. During our investigation from August 2007 to May 2009 we deployed on an almost monthly basis a continuous radon-in-water measurement system and monitored the salinity fluctuations in the discharge area. To evaluate the springs' freshwater flux we developed three different models: two of them are based on water velocity measurements and either salinity or ²²²Rn in the associated surface waters as groundwater tracers. The third approach used only salinity changes within the spring area. The three models showed good agreement and the results confirmed that the hydrologic regime of the system is strongly correlated to local precipitation and water table fluctuations with higher discharges after major rain events and very low, even reverse flow during prolong droughts. High flow spring conditions were observed twice during our study, in the early spring and mid-late summer of 2008. However the freshwater spring flux during our observation period never reached that reported from a 1970s value of 4.9×10⁶ m³/day. The maximum spring flow was estimated at about 3.0×10⁶ m³/day after heavy precipitation in February-March 2008. As a result of this storm (total of 173 mm) the salinity in the spring area dropped from about 27 to 2 in only two days. The radon-in-water concentrations dramatically increased in parallel, from about 330 Bq/m³ to about 6600 Bq/m³. Such a rapid response suggests a direct connection between the deep and the surficial aquifers.     

Periphyton communities in Amazonian black- and whitewater habitats: Community structure, biomass and productivity

Chlorophyll a-concentrations, AFWD (ash-free-dry-weight) and photosynthesis rates were estimated for periphyton assemblages in Amazonian black-and white-water habitats over 14 months. Cellulose-acetate strips were incubated in situ and showed few major differences in periphyton quality as compared to natural substrata. The only exceptions were submersed Igapó forest leaves, which exhibited higher proportions of green algae and cyanobacteria though not producing differences in total periphyton biomass. Enclosure experiments showed a considerable nutrient release by inundated non-senescent Igapó forest leaves. Periphyton biomass and productivity were found to be highest in black-and white water mixing zones, where biomass peaked at 41.6 mg Chla/m² and 19.8 g/m² AFDW. Production was estimated to be 380 gC/m²·a. Maximum biomass of periphyton in floating meadows was 46 mg Chla/m² and 10.6 g/m² AFDW, with an annual production of 170 gC/m²·a. Solimões main channel periphyton values were low: maximum Chla was 7.1 mg/m², AFDW 0.8 g/m² and annual production was estimated to be 30 gC/m². Blackwater periphyton values were lower compared to whitewater and mixed water values but an enlarged trophogenic zone has to be taken into account. Highest Chla content reached 30.9 mg/m², AFDW 1.43 g/m². Estimated annual production was 110 gC/m². Observed mean periphyton productivity of Amazonian blackwater habitats approximately corresponded to mesotrophic attached algae productivity in temperate zones, whereas productivity of whitewater periphyton approached those of temperate eutrophic lakes. The role of periphyton in the Amazon food web is discussed.     

Application of a spreadsheet hydrological model for computing the long-term water balance of Lake Awassa,Ethiopia

Abstract

The water balance of the closed freshwater Lake Awassa was estimated using a spreadsheet hydrological model based on long-term monthly hydrometeorological data. The model uses monthly evaporation, river discharge and precipitation data as input. The net groundwater flux is obtained from model simulation as a residual of other water balance components. The result revealed that evaporation, precipitation, and runoff constitute 131, 106 and 83 × 10⁶ m³ of the annual water balance of the lake, respectively. The annual net groundwater outflow from the lake to adjacent basins is 58 × 10⁶ m³. The simulated and recorded lake levels fit well for much of the simulation period (1981–1999). However, for recent years, the simulated and recorded levels do not fit well. This may be explained in terms of the combined effects of land-use change and neotectonism, which have affected the long-term average water balance. With detailed long-term hydrogeological and meteorological data, investigation of the subsurface hydrodynamics, and including the effect of land-use change and tectonism on surface water and groundwater fluxes, the water balance model can be used efficiently for water management practice. The result of this study is expected to play a positive role in future sustainable use of water resources in the catchment.     

Modification of the Penman method for computing bare soil evaporation

The Penman equation, which calculates potential evaporation, was modified by Staple (1974, Soil Science Society of America Proceedings 38 : 837) to include in it the relative vapour pressure h_s of an unsaturated soil to predict actual evaporation from a soil surface. This improved the prediction when the difference between the temperature of the soil surface and ambient air is relatively small. The objectives of this study were (i) to revise it further using the actual temperature of the soil surface and air to provide the upper boundary condition in computing evaporative flux from the soil surface and (ii) to determine the range of water content for which the modified form of the Penman equation is applicable. The method adopted was tested by a series of outdoor experiments with a clay soil. The method of Staple (1974) overestimated the rate of evaporation above the water content 0·14 m³ m^?3 (up to 30% deviation), whereas the new method agreed well with the measured rates (maximum 7% deviation). Below 0·14 m³ m^?3 water content, both methods underestimated, but the Staple (1974) method deviated more from the measured values: the deviations were above 70% and around 30% for the Staple (1974) and the new methods respectively. Although the new method provided accurate solutions for a wider range of water content from saturation to the lower limit of the liquid phase of a particular soil, the modification did not respond to the vapour phase of the soil moisture. Therefore, in the dry range (i.e. in the vapour phase in which the flow was entirely as vapour), either resistance models or a Fickian equation should be used. Although the effect of salinity on the measured rates was significant, the model erroneously calculated the same rates for both saline and non‐saline conditions. The effect of soil texture can easily be accounted by defining appropriate matric potential water content ψ_m(θ) and soil relative humidity water content h_s(θ) relationships. Copyright © 2007 John Wiley & Sons, Ltd.     

Sub‐surface water contribution to recession flow in a mountain headwater stream system based on single monitoring campaign

Discharge in mountain streams may be a mixture of snowmelt, water from surface runoff, and deep return flow through valley bottom alluvia. We used δ¹⁸O and δ²H, solute concentrations, and ²²²Rn to determine water sources of a headwater stream located at the McDonald Creek watershed, Glacier National Park, USA, during summer recession flow period. We analysed minimal water isotope ranges of ?17.6‰ to ?16.5‰ and ?133‰ to ?121‰ for δ¹⁸O and δ²H, respectively, potentially due to dominance of snow‐derived water in the stream. Likewise, solute concentrations measured in the stream through the watershed showed minimal variation with little indication of subsurface water input into the stream. However, we observed ²²²Rn activities in the stream that ranged from 39 to 2646 Bq/m³ with the highest value measured in middle of the watershed associated with channel constriction corresponding to changes in local orientation of underlying rocks. Downstream from this point, ²²²Rn activity decreased from 581 to 117 Bq/m³ in a series of punctuated steps associated with small rapids and waterfalls that we hypothesized to cause radon degassing with a maximum predicted loss of 427 Bq/m³ along a 400 m distance. Based on mass balance calculations using ²²²Rn activity values, streamflow, and channel characteristics, we estimated that groundwater contributed between 0.3% and 29% of total flow. Overall, we estimated a 5.9% of groundwater contribution integrated for stream reach measured at McDonald Creek during recession flow period. Finally, a lower mean hyporheic flux of 14 m³/day was estimated compared to the groundwater flux of 70 710 m³/day. These assessments highlight the potential for radon as a conservative tracer that can be used to estimate subsurface water contribution in mountain streams within a complex geologic setting. Copyright © 2015 John Wiley & Sons, Ltd.     

Evidence for induced seismicity in the vicinity of Fierza reservoir,Northern Albania

The reservoir of Fierza on the Drini River, Northern Albania, is Albania's largest reservoir and it is one of the world's largest reservoirs of high dams (reservoir volume at maximum water level, 2.8 * 10⁹ m³; dam height, 167 m and dam capacity 8 * 10⁶ m³). We compare pre-and postimpounding seismicity of the area surrounding the Fierza reservoir. An increase of seismic microactivity was observed after the impounding of the reservoir. More than 300 microearthquakes, occurred in the immediate vicinity of the main body of the reservoir, with local magnitude ranging between 1.3 and 3.6. A significant change of theb value in the magnitude-frequency relationship was observed. One swarm of microtremors occurred in the northern part of the reservoir on April 4–5, 1981, where an alteration of the tensor of natural tectonic stresses is revealed. The theoretical additional stress and displacement induced by water-load in the bank of the reservoir were estimated for four cross-profiles of the reservoir area and the maximum values resulted near the location of the above swarm.     

Studies on Primary Productivity and some Hydrochemical Aspects of a Polluted Water-body of the Himalayan Jhelum Valley

The lake without any outlet (11 ha, 55000 m³, z_max 2,25 m) has a weak thermal stratification with maximum surface temperatures of 32.5 °C. The annual variation of temperature and depth of visibility is unimodal, with the maxima or minima in August. Phytoplankton consists mainly of Cyanophyceae. The primary production determined by the light-dark bottle technique (oxygen method) varies in the annual variation between 0.3… 0.5 g m^?2 d^?1 C (winter) and 3.4… 4.6 g m^?2 d^?1 C (summer); as the annual means of 1975 and 1976 there were found 1.9 and 2.4 g m^?2 d^?1 C, resp., gross production at a utilization of 0.42… 2.85% of the radiation energy. The chemism is a well-buffered hydrogen-carbonate water (pH 8.1… 9.0) with 74… 90 mg/1 Na and 20.5… 31.5 mg/1 K and with a good nutrient supply (20… 40 μg/1 PO₄—P and 100… 240 μg/1 NO₃—N) at the same time.     

Biofiltration of Pyridine by Shewanella putrefaciens in a Corn‐Cob Packed Biotrickling Filter

In this study, a new strain of microorganism Shewanella putrefaciens was used for biofiltration of a pyridine laden air stream in a corn‐cob packed biotrickling filter. In the biotrickling filter tested with S. putrefaciens, the maximum removal of pyridine is determined to be 100% at less than the average inlet concentration of 0.653 g m^–3 and more than 93% at a higher average inlet concentration of 1.748 g m^–3 (phase VIII) with an empty bed residence time (EBRT) of 106 s. However, when the biotrickling filter was operated at a low EBRT of 53 s and almost the same average inlet concentration of 1.752 g m^–3 (phase VII), the removal level attained was not greater than 85%. The maximum elimination capacity (EC) of the biotrickling filter was 102.34 g m^–3h^–1 at an inlet pyridine load of 119.62 g m^–3h^–1 with an EBRT of 53 s in phase VII. The maximum deviation of the EC from the 100% conversion line varied from 0.257 to 10.166% when going from phase I to VIII. Kinetic analysis showed that the maximum removal rate, r_max, and saturation constant, K_s, values for pyridine were calculated as 0.24 g m^–3h^–1 and 6.44 g m^–3, respectively, with a correlation coefficient, R², of 0.9939 and a standard deviation of error of 23.94%. The information contained herein indicates that the corn‐cob packed biotrickling filter inoculated by S. putrefaciens should provide excellent performance in the removal of gaseous pyridine.     

Dynamics in land cover and its effect on stream flow in the Chemoga watershed,Blue Nile basin,Ethiopia

The objective of this study was to analyse changes in stream flow patterns with reference to dynamics in land cover/use in a typical watershed, the Chemoga, in northwestern highland Ethiopia. The results show that, between 1960 and 1999, total annual stream flow decreased at a rate of 1 · 7 mm year⁻¹, whereas the annual rainfall decreased only at a rate of 0 · 29 mm year⁻¹. The decrease in the stream flow was more pronounced during the dry season (October to May), for which a statistically significant decline (0 · 6 mm year⁻¹) was observed while the corresponding rainfall showed no discernible trend. The wet season (June to September) rainfall and stream flow did not show any trends. Extreme low flows analysed at monthly and daily time steps reconfirmed that low flows declined with time, the changes being highly significant statistically. Between 1960 and 1999, the monthly rainfall and stream flow amounts of February (month of lowest long‐term mean flow) declined by 55% and 94% respectively. Similarly, minimum daily flows recorded during the three driest months (December to February) showed statistically highly significant declines over the same period. It declined from 0 · 6 m³ s⁻¹ to 0 · 2 m³ s⁻¹ in December, from 0 · 4 m³ s⁻¹ to 0 · 1 m³ s⁻¹ in January and from 0 · 4 m³ s⁻¹ to 0 · 02 m³ s⁻¹ in February (1 · 0 m³ s⁻¹ = 0 · 24 mm day⁻¹ in the Chemoga watershed). In contrast, extreme high flows analysed at monthly (for August) and daily (July to September) time steps did not reveal discernible trends. The observed adverse changes in the stream flow have partly resulted from changes in land cover/use and/or degradation of the watershed that involved destruction of natural vegetative covers, expansion of croplands, overgrazing and increased area under eucalypt plantations. The other contributory factor has been the increased dry‐season water abstraction to be expected from the increased human and livestock populations in the area. Given the significance of the stream flow as the only source of water to the local people, a set of measures aimed at reducing magnitudes of surface runoff generation and increasing groundwater recharge are required to sustain the water resource and maintain a balanced dry‐season flow in the watershed. Generally, an integrated watershed management approach, whereby the whole of the watershed can be holistically viewed and managed, would be desirable. Copyright © 2004 John Wiley & Sons, Ltd.     

Electrochemical disinfection for ballast water management: Technology development and risk assessment

Ballast water is essential in maintaining the balance and structural integrity of ships during voyage. However, it has created biological invasion threats to the ocean environment. An innovative electrochemical technology was developed in this study. The microorganisms regulated by the International Maritime Organization (D2) were used as the target organisms. It was found that the required energy to meet the D2 was below 0.006 kWh/m³. The size of disinfector (m³) was about 0.5% of treatment flow rate (m³/h). The complete disappearance of chlorine in seawater was achieved after three days. The ballast tank corrosion was not worsened due to the application of technology. The ecotoxicity studies showed no toxic effect on fish, invertebrate, and algae. Finally, the environmental risk assessment showed the treated water did not pose threats to the environment. It can therefore be concluded that the technology provides a cost-effective and environmental friendly solution to ballast water management.     

Variations in glacier volume and snow cover and their impact on lake storage in the Paiku Co Basin,in the Central Himalayas

Glaciers and snow cover are important constituents of the surface of the Tibetan Plateau. The responses of these phenomena to global environmental changes are sensitive, rapid and intensive due to the high altitudes and arid cold climate of the Tibetan Plateau. Based on multisource remote sensing data, including Landsat images, MOD10A2 snow product, ICESat, Cryosat-2 altimetry data and long-term ground climate observations, we analysed the dynamic changes of glaciers, snow melting and lake in the Paiku Co basin using extraction methods for glaciers and lake, the degree-day model and the ice and lake volume method. The interaction among the climate, ice-snow and the hydrological elements in Paiku Co is revealed. From 2000 to 2018, the basin tended to be drier, and rainfall decreased at a rate of −3.07 mm/a. The seasonal temperature difference in the basin increased, the maximum temperature increased at a rate of 0.02°C/a and the minimum temperature decreased at a rate of −0.06°C/a, which accelerated the melting from glaciers and snow at rates of 0.55 × 10⁷ m³/a and 0.29 × 10⁷ m³/a, respectively. The rate of contribution to the lake from rainfall, snow and glacier melted water was 55.6, 27.7 and 16.7%, respectively. In the past 18 years, the warmer and drier climate has caused the lake to shrink. The water level of the lake continued to decline at a rate of −0.02 m/a, and the lake water volume decreased by 4.85 × 10⁸ m³ at a rate of −0.27 × 10⁸ m³/a from 2000 to 2018. This evaluation is important for understanding how the snow and ice melting in the central Himalayas affect the regional water cycle.     

Banda Sea surface-layer divergence

Sea-surface temperature (SST) within the Banda Sea varies from a low of 26.5 °C in August to a high of 29.5 °C in December and May. Ekman upwelling reaches a maximum in May and June of approximately 2.5 Sv (Sv=10⁶ m³ s^?1) with Ekman downwelling at a maximum in February of approximately 1.0 Sv. The Ekman pumping annual average is 0.75 Sv upwelling. During the upwelling period, from April through December the average Ekman upwelling velocity is 2.36 × 10^?6 m s^?1 (1.27 Sv). ENSO modulation is generally within 0.5 Sv of the mean Ekman curve, with weaker (stronger) July to October upwelling during El Niño (La Niña). Combined TOPEX/POSEIDON and ERS 1993–1999 altimeter data reveal a 33 cm maximum range of sea level. Steric effects are minor, with well over 80% of the sea level change due to mass divergence (some bias due to unresolved tidal aliasing may still be present). The annual and interannual sea level behavior follows the monsoonal and ENSO phenomena, respectively. Lower (higher) sea level occurs in the southeast (northwest) monsoon and during El Niño (La Niña) events. The surface-layer volume anomaly and the surface-layer divergence, assuming a two-layer ocean, are estimated. Maximum divergence is attained during the transitional monsoon months of October/November: 1.7 Sv gain (convergence), with matching loss (divergence) in the April/May. During the El Niño growth period of 1997 the surface layer is divergent, but in 1998 when the El Niño was on the wane, the average rate of change is convergent. Surface-layer divergence attains values as high as 4 Sv. Banda Sea surface-water divergence correlates reasonably well with the 3-month lagged export of surface (upper 100?m) water into the Indian Ocean as estimated by a shallow pressure gauge array. It is concluded that the Banda Sea surface-layer divergence influences the timing and transport profile of the Indonesian throughflow export into the Indian Ocean, as proposed by Wyrtki in 1958, and that satellite altimetry may serve as an effective means of monitoring this phenomena.