Tennant Method Research Articles

Issues in using the WinRHIZO system to determine physical characteristics of plant fine roots

Image analysis systems have facilitated rapid measurements of fine root length (RL), diameter (RD), volume (RV), etc. The WinRHIZO system is unlike other image analysis systems in that it can detect, and make corrections for, areas of root overlap. It is designed to be capable of using both Regent’s non-statistical method (WinRHIZO method) and Tennant’s statistical method (line-intersect method), and can simultaneously output the root measurements by both methods when they are chosen at the same time. This study tested: (1), the efficacy of the overlap correction function in the WinRHIZO system; and (2), the consistency of fine root measurements between the WinRHIZO and Tennant methods with two sets of root measurement data from winter wheat ( Triticum aestivium L.). The results showed that there were significant differences in RL, RD and RV between small root samples with and without stumps. The impact of root stumps outweighed the overlap correction efficacy in WinRHIZO. The values from the Tennant method are significantly different from those using the WinRHIZO method, although both results are statistically closely correlated. This indicated how critical it was to use without-stump root samples when using image analysis systems to measure RL, RD, RV, etc., and to keep in mind that a significant difference in root measurements may be methodologically related when comparing the results of various experiments from these two methods. Our research results bear important implications for the study of root ecology.

Construction of habitat suitability models (HSMs) for benthic macroinvertebrate and their applications to instream environmental flows: A case study in Xiangxi River of Three Gorges Reservior region, China

Based on a long-term ecological monitoring, the present study chose the most dominant benthic macroinvertebrate ( Baetis spp.) as target organisms in Xiangxi River, built the habitat suitability models (HSMs) for water depth, current velocity and substrate, respectively, which is the first aquatic organisms model for habitat suitability in the Chinese Mainland with a long-term consecutive in situ measurement. In order to protect the biointegrity and function of the river ecosystem, the theory system of instream environmental flow should be categorized into three hierarchies, namely minimum required instream flow (hydrological level), minimum instream environmental flow (bio-species level), and optimum instream environmental flow (ecosystem level). These three hierarchies of instream environmental flow models were then constructed with the hydrological and weighted usable area (WUA) method. The results show that the minimum required instream flow of Xiangxi River calculated by the Tennant method (10% of the mean annual flow) was 0.615 m 3 s −1; the minimum instream environmental flow accounted for 19.22% of the mean annual flow (namely 1.182 m 3 s −1), which was the damaged river channel flow in the dry season; and 42.91% of the mean annual flow (namely 2.639 m 3 s −1) should be viewed as the optimum instream environmental flow in order to protect the health of the river ecosystem, maintain the instream biodiversity, and reduce the impact of small hydropower stations nearby the Xiangxi River. We recommend that the hydrological and biological methods can help establish better instream environmental flow models and design best management practices for use in the small hydropower station project.

Available Quantity of Transferable Water and Risk Analysis

The area of the Western Route Project for South-to-North Water Transfer (WRP) in China, located in the upper reaches of the Yangtze River and the marginal area of the Qinghai-Tibet Plateau, has sufficient water resources that transfers could be considered. However, potential transfers are limited due to a fragile eco-environment. The eco-environmental water demand is the key constraint for determining the available quantity of water that could be transferred in view of the existing water demand for local social and economic development. Considering the effect on the eco-environment, this study investigates the available quantity of transferable water in the WRP for the dual purpose of protecting the local eco-environment and decreasing the crisis of water resources in the western areas by considering the water demand for river channel eco-environment downstream of the dams as the main constraint. In order to estimate the eco-environmental water demand, the low runoff and Tennant methods are studied. According to the results of risk analysis, the proposed schemes for water transfer have high reliability and low risk. The risk will be further reduced if in the future reservoirs are operated jointly.

A global perspective on environmental flow assessment: emerging trends in the development and application of environmental flow methodologies for rivers

AbstractRecognition of the escalating hydrological alteration of rivers on a global scale and resultant environmental degradation, has led to the establishment of the science of environmental flow assessment whereby the quantity and quality of water required for ecosystem conservation and resource protection are determined.A global review of the present status of environmental flow methodologies revealed the existence of some 207 individual methodologies, recorded for 44 countries within six world regions. These could be differentiated into hydrological, hydraulic rating, habitat simulation and holistic methodologies, with a further two categories representing combination‐type and other approaches.Although historically, the United States has been at the forefront of the development and application of methodologies for prescribing environmental flows, using 37% of the global pool of techniques, parallel initiatives in other parts of the world have increasingly provided the impetus for significant advances in the field.Application of methodologies is typically at two or more levels. (1) Reconnaissance‐level initiatives relying on hydrological methodologies are the largest group (30% of the global total), applied in all world regions. Commonly, a modified Tennant method or arbitrary low flow indices is adopted, but efforts to enhance the ecological relevance and transferability of techniques across different regions and river types are underway. (2) At more comprehensive scales of assessment, two avenues of application of methodologies exist. In developed countries of the northern hemisphere, particularly, the instream flow incremental methodology (IFIM) or other similarly structured approaches are used. As a group, these methodologies are the second most widely applied worldwide, with emphasis on complex, hydrodynamic habitat modelling. The establishment of holistic methodologies as 8% of the global total within a decade, marks an alternative route by which environmental flow assessment has advanced. Such methodologies, several of which are scenario‐based, address the flow requirements of the entire riverine ecosystem, based on explicit links between changes in flow regime and the consequences for the biophysical environment. Recent advancements include the consideration of ecosystem‐dependent livelihoods and a benchmarking process suitable for evaluating alternative water resource developments at basin scale, in relatively poorly known systems. Although centred in Australia and South Africa, holistic methodologies have stimulated considerable interest elsewhere. They may be especially appropriate in developing world regions, where environmental flow research is in its infancy and water allocations for ecosystems must, for the time being at least, be based on scant data, best professional judgement and risk assessment. Copyright © 2003 John Wiley & Sons, Ltd.

CLASSIFICATION OF ENVIRONMENTAL FLOW REQUIREMENTS AND APPLICABILITY OF HYDROLOGICAL APPROACH

There is a growing concern over river environment degradation related to artificial flow control. Many countries in the world are now trying to develop appropriate environmental flow setting methodologies to handle this problem. Leaders in this field are U. S., Australia, South Africa and some European countries. Current methodologies used in those countries are reviewed and categorized into four groups. Most basic methodology is the one based on hydrological indices. Environmental flow requirements are classified into three types according to their objectives. Relationship with flow regime components is now clear.Availability of hydrological approach is then discussed. The Tennant Method and the Range of Variability Approach (RVA) are applied to Japanese rivers. Result of macroscopic application of the Tennant Method suggested that some action should be taken at least 30% of Japanese rivers to enhance low flow. RVA is tested in the Kitakami River basin and it turned out to be a useful approach to assess the flow regime alteration by reservoir control.

Effect of irrigation frequency on root water uptake in sugar beet

A 2-year trial was performed on autumn-sown sugar beet grown in pots in order to study the influence of irrigation frequency on the water used by plants along the soil profile. The outdoor pots, containing one plant each, were 1.3 m high and had circular openings, through which Time Domain Reflectometry (TDR) apparatus wave guides could be inserted. Three irrigation intervals were compared and plants were watered whenever the soil layer explored by roots had lost 30% (SWD1), 50% (SWD2) and 70% (SWD3) of the total available water (TAW). During the irrigation season, the water extracted by the plants from each layer along the soil profile (RWU) was determined by monitoring volumetric soil moisture content (θ), by TDR. At harvest time, root length density (RLD) along the soil profile was assessed using the Tennant method. The applied irrigation frequencies significantly affected the RWU. With the SWD3 protocol, irrigation was at longer irrigation intervals (9 days) and watering volumes were as high as 84 mm. In this treatment, the plants lost almost 60% of total water from the lower soil layer (0.6–1.0 m). In treatment SWD1, the irrigation interval was very short (3 days), and water extraction from 0.0–0.6 m soil depth was 92.0%. In the intermediate treatment, the irrigation interval was 5.5 days and a more uniform water depletion was observed along the root zone, approximately equal between the 0–0.6 and 0.6–1.0 m soil layer. Water extraction of sugar beet plants at the deeper soil layers in response to long irrigation intervals was related to an increase in water uptake efficiency of the deeper younger roots and not to an increase in root length density, which, on the contrary, decreased. This morpho-physiological acclimatization to progressive soil water deficit was coupled with an increase of the root/shoot ratio.

Comparison and regionalization of hydrologically based instream flow techniques in Atlantic Canada

Five hydrologically based instream flow assessment methods are compared for 70 rivers in Atlantic Canada; these methods included (i) Tennant method; (ii) 25% mean annual flow (25% MAF); (iii) median monthly flow (Q50) which includes the aquatic base flow (ABF); (iv) the flow equalled or exceeded 90% of time on a monthly flow duration curve (Q90); and (v) the statistical 7-day low flow frequency of a 10-year recurrence interval (7Q10). By comparing the different methods relative to the 25% MAF (the commonly used method in Atlantic Canada), we found that the Q90 and 7Q10 methods predicted extremely low instream flows during winter and summer months. Resource management decisions based on these extremely low flow predictions could have serious adverse consequences. The median monthly flow method (Q50) was recommended for gauged basins, whereas the Tennant method, the 25% MAF method, and the ABF methods were recommended for ungauged basins. For ungauged basins, we conducted a regional study to estimate the 25% MAF and the ABF using multiple regression analysis. Physiographic parameters were used as explanatory variables in the regression analysis. Based on the coefficient of determination, R2, the best regression results were obtained for the 25% MAF with R2 ranging from 0.957 to 0.999. Although the results for ABF were slightly lower than for the 25% MAF, R2 was still in the range of 0.868 to 0.979. Key words: environmental assessment, maintenance flow, low flow, aquatic resources.

A method for the quantification ofFrankia by estimation of hyphal length

The cellular mass ofFrankia, a filamentous actinomycete, was readily quantified by estimating hyphal length, using a modification of Tennant's method for the estimation of root length. Each sample ofFrankia was stained with Coomassie Brilliant blue G 250, dispersed well, and suspended in a 0.5% agar solution. One drop of the suspension was placed in a Petroff-Hausser counting chamber with 0.05 by 0.05mm grid squares. The number of intersections betweenFrankia hyphae and the grid lines in a standard area were counted under a microscope and converted to hyphal length. Using the formula: hyphal length (HL) in mm equals (11/14) times the number of intersections (n) times the grid dimension (0.05 mm). The validity of the line intersection method was tested by comparison with total protein estimates of replicate aliquots ofFrankia culture. Correlations between total protein and hyphal length estimates were strong (r2 from 0.76 to 0.95; standard errors of 3 to 9% of estimated length). These results show that line intersection counts may be a satisfactory routine method for quantifyingFrankia in culture and may be especially suitable for detecting small amounts of livingFrankia in less time than with other methods.

Relative Bias of Several Fisheries Instream Flow Methods

Four general categories of instream flow methods were evaluated to determine their biases relative to each other. The categories included (1) the Tennant method, (2) wetted perimeter curves, (3) habitat retention models, and (4) physical habitat simulation (PHABSIM) models. The Tennant method (30% of average flow) was one of the least biased methods, but it does not include biological data and is incapable of identifying trade-offs. No wetted perimeter methods were significantly unbiased, and methods relying on subjective identification of inflection points were biased upwards. Two habitat retention methods were significantly unbiased. These methods included (1) the mean recommendation of all riffles in a study reach where all three criteria are met, and (2) the recommendation for the single most critical riffle in a study reach where two of the three criteria are met. No PHABSIM models were unbiased. The IFG-4 model was biased upwards for small streams and low for large streams.