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Ceratophyllum demersum L. occurs in winter in the dormant form, in summer in the vegetative form. Factors that affect growth and dormancy in Ceratophyllum were studied. After several weeks of severe winter conditions the plants changed from dormant to quiescent state. Under natural conditions Ceratophyllum plants remain quiescent for several months, due to unfavourable growth conditions. Experimentally the dormancy could also be broken by high and low temperature treatments (shocks), and most effectively by addition of GA3. An attempt to induce dormancy in full-grown plants by the addition of ABA under extreme summer or winter conditions proved unsuccessful. The IAA and ABA contents in the plants were measured during the year. In winter the concentration of ABA was high and that of IAA low, whereas in summer the IAA concentration increased and that of ABA was variable. IAA only slightly antagonized the inhibition of growth by ABA. Both the growth regulators were readily taken up from the culture medium, as was confirmed by a study with the radioactive labelled compounds. The uptake rate of IAA was significantly higher than that of ABA, being 762 μg and 3.26 μg per plant in 24 h. respectively. GA3 was found to have a strong antagonistic effect on the ABA induced growth inhibition. The total GA activity in dormant and quiescent plants was similar, in full grown plants it was much lower. In the dormant state a large part of GA was in a bound form, whereas during quiescence relatively more GA occurred in a free state in the plants. [ABSTRACT FROM AUTHOR]

The photosynthetic and growth characteristics of Ceratophyllum demersum L. were investigated under laboratory conditions which simulated those encountered in the plants' normal environment. The carbon fixation rate of C. demersum measured with 14C at light and carbon saturation at pH 8.0 was 4.48 mg C (g ash‐free dry weight)−1 h−1. It was lower at pH 6.5 than at pH 8.0. The light use efficiencies in quiescent plants and actively growing plants were 6.3 and 8.7 × 10−9 kg CO2 J−1, respectively, with corresponding maximum photosynthetic rates of 2.67 and 4.36 mg C (g ash‐free dry weight)−1 h−1. Photorespiration in actively growing plants consumed 24% of the carbon fixed. Incubation with DCMU demonstrated that about one‐third was refixed. The optimum temperature for carbon fixation was 25°C. The C3‐photosynthetic pathway was the main operational route as indicated by the early photosynthetic products (largely C3‐acids) and the absence of Krantz anatomy and the chlorophyll a:b ratio (2.7). The maximum relative growth rates ranged from 0.025 to 0.041 g ash‐free dry weight (g ash‐free dry weight)−1 day−1 in the field (Lake Vechten, 1 to 3 m depth classes). [ABSTRACT FROM AUTHOR]

Best management practices (BMPs) can be used effectively to reduce nutrient loads transported from non-point sources to receiving water bodies. However, methodologies of BMP selection and placement in a cost-effective way are needed to assist watershed management planners and stakeholders. We developed a novel modeling-optimization framework that can be used to find cost-effective solutions of BMP placement to attain nutrient load reduction targets. This was accomplished by integrating a GIS-based BMP siting method, a WQM-TMDL-N modeling approach to estimate total nitrogen (TN) loading, and a multi-objective optimization algorithm. Wetland restoration and buffer strip implementation were the two BMP categories used to explore the performance of this framework, both differing greatly in complexity of spatial analysis for site identification. Minimizing TN load and BMP cost were the two objective functions for the optimization process. The performance of this framework was demonstrated in the Tippecanoe River watershed, Indiana, USA. Optimized scenario-based load reduction indicated that the wetland subset selected by the minimum scenario had the greatest N removal efficiency. Buffer strips were more effective for load removal than wetlands. The optimized solutions provided a range of trade-offs between the two objective functions for both BMPs. This framework can be expanded conveniently to a regional scale because the NHDPlus catchment serves as its spatial computational unit. The present study demonstrated the potential of this framework to find cost-effective solutions to meet a water quality target, such as a 20% TN load reduction, under different conditions., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

This paper presents a screening-level modeling approach that can be used to rapidly estimate nutrient loading, assess numerical nutrient standard exceedance risk of surface waters leading to potential classification as impaired for designated use, and explore best management practice (BMP) implementation to reduce loading with a relatively low data requirement. The modeling framework uses a hybrid statistical and process based approach to estimate source of pollutants, their transport and decay in the terrestrial and aquatic parts of watersheds. The framework is developed in the ArcGIS environment and is based on the total maximum daily load (TMDL) balance model. Nitrogen (N) is currently addressed in the framework, referred to as WQM-TMDL-N. Loading for each catchment includes non-point sources (NPS) and point sources (PS). The probability of a nutrient load to exceed a target load is evaluated using probabilistic risk assessment, by including the uncertainty associated with export coefficients of various land uses. In an application of this modeling approach to the Tippecanoe River watershed in Indiana, USA, total nitrogen (TN) loading, confidence interval and risk of standard exceedance leading to potential impairment were estimated. Model results suggest that decay coefficients decrease, and delivery fractions increase with increasing stream order. The spatial distribution pattern of delivered incremental TN yield shows a trend similar to that of the delivery fraction in this watershed. The target TN exceedance risk increases considerably when switching from Indiana draft-N benchmark to far lower EPA-proposed TN criteria, suggesting that load reduction to meet the latter criteria may benefit from BMP implementation through source control and delivery reduction., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Environmental contamination by explosives is a worldwide problem. Of the 20 energetic compounds, 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) are the most powerful and commonly used. Nitroamines are toxic and considered as possible carcinogens. The toxicity and persistence of nitroamines requires that their fate in the environment be understood and that contaminated soil and groundwater be remediated. This study, written as a minireview, provides further insights for plant processes important for the transformation and degradation of explosives. Plants metabolize TNT and the distribution of the transformation products, conjugates, and bound residues appears to be consistent with the green liver model concept. Metabolism of TNT in plants occurs by reduction as well as by oxidation. Reduction probably plays an important role in the tolerance of plants towards TNT, and, therefore a high nitroreductase capacity may serve as a biochemical criterion for the selection of plant species to remediate TNT. Because the activities and the inducibilities of the oxidative enzymes are far lower than of nitroreductase, reducing processes may predominate. However, oxidation may initiate the route to conjugation and sequestration leading ultimately to detoxification of TNT, and, therefore, particularly the oxidative pathway deserves more study. It is possible that plants metabolize RDX also according to the green liver concept. In the case of plant metabolism of HMX, a conclusion regarding compliance with the green liver concept was not reached due to the limited number of available data.