Bending of the concentration discharge relationship can inform about in-stream nitrate removal

Nitrate (NO3-) excess in rivers harms aquatic ecosystems and can induce detrimental algae growths in coastal areas. Riverine NO3- uptake is a crucial element of the catchment-scale nitrogen balance and can be measured at small spatiotemporal scales, while at the scale of entire river networks, uptake measurements are rarely available. Concurrent, low-frequency NO3- concentration and streamflow (Q) observations at a basin outlet, however, are commonly monitored and can be analyzed in terms of concentration discharge (C–Q) relationships. Previous studies suggest that steeper positive log (C)–log (Q) slopes under low flow conditions (than under high flows) are linked to biological NO3- uptake, creating a bent rather than linear log (C)–log (Q) relationship. Here we explore if network-scale NO3- uptake creates bent log (C)–log (Q) relationships and when in turn uptake can be quantified from observed low-frequency C–Q data. To this end we apply a parsimonious mass-balance-based river network uptake model in 13 mesoscale German catchments (21–1450 km2) and explore the linkages between log (C)–log (Q) bending and different model parameter combinations. The modeling results show that uptake and transport in the river network can create bent log (C)–log (Q) relationships at the basin outlet from log–log linear C–Q relationships describing the NO3- land-to-stream transfer. We find that within the chosen parameter range the bending is mainly shaped by geomorphological parameters that control the channel reactive surface area rather than by the biological uptake velocity itself. Further we show that in this exploratory modeling environment, bending is positively correlated to percentage of NO3- load removed in the network (Lr.perc) but that network-wide flow velocities should be taken into account when interpreting log (C)–log (Q) bending. Classification trees, finally, can successfully predict classes of low (∼4 %), intermediate (∼32 %) and high (∼68 %) Lr.perc using information on water velocity and log (C)–log (Q) bending. These results can help to identify stream networks that efficiently attenuate NO3- loads based on low-frequency NO3- and Q observations and generally show the importance of the channel geomorphology on the emerging log (C)–log (Q) bending at network scales.

Low Specific Phosphorus Uptake Affinity of Epilithon in Three Oligo- to Mesotrophic Post-mining Lakes

Epilithon contributes to phosphorus (P) cycling in lakes, but its P uptake traits have been rarely studied. We measured the chemical composition of epilithon and its inorganic P uptake kinetics using isotope 33P in three deep oligo- to mesotrophic post-mining lakes in April, July, and October 2019. Over the sampling period, epilithon biomass doubled, while the P content in biomass dropped to 60% of the April values, and the seasonal changes in P content expressed per epilithon area were only marginal and statistically not significant. High epilithic C:P molar ratios (677 on average) suggested strong P deficiency in all investigated lakes. Regarding the kinetic parameters of phosphorus uptake, maximum uptake velocity (Vmax, seasonal range 1.9–129 mg P g OM–1 h–1) decreased by an order of magnitude from April to October, while half-saturation constant (KS, seasonal range 3.9–135 mg P L–1) did not show any consistent temporal trend. Values of epilithic specific P uptake affinity (SPUAE, seasonal range 0.08–3.1 L g OM–1 h–1) decreased from spring to autumn and were two to four orders of magnitude lower than the corresponding values for seston (SPUAsest), which showed an opposite trend. Considering our results, we suggest a possible mechanism underlying a stable coexistence of planktonic and epilithic microorganisms, with plankton prospering mostly in summer and autumn and epilithon in winter and spring season. Additionally, a phenomenon of reversible abiotic P adsorption on epilithon was observed.

Uptake of phosphorus by epilithon in three oligo- to mesotrophic post-mining lakes

Epilithon contributes to phosphorus (P) cycling in lakes, but its P uptake traits have been rarely studied. We measured the chemical composition of epilithon and its inorganic P uptake kinetics using isotope 33P in three deep oligo- to mesotrophic post-mining lakes in April, July, and October 2019. Over the sampling period, epilithon biomass doubled, while the P content in biomass dropped to 60% of the April values. High epilithic C:P molar ratios (677 on average) suggested strong P deficiency in all investigated lakes. Regarding the kinetic parameters of phosphorus uptake, maximum uptake velocity (Vmax, seasonal range 0.9–101 mg P g OM–1 h–1) decreased by an order of magnitude from April to October, while half-saturation constant (KS, 1.6–103 mg P L–1) did not show any consistent temporal trend. We found a general decrease in the specific P uptake affinity (0.1–2.2 L g OM–1 h–1) and the estimated in-situ P uptake (0.04–2.3 µg P g OM–1 h–1) of epilithon over the season, which might have resulted from changes in epilithon community composition, a decreasing ratio of living biomass to extracellular polymers and detritus, rapid internal recycling, and/or thickening of the epilithic biofilm. Additionally, we observed a phenomenon of reversible abiotic P adsorption on epilithon.

Bending of the concentration discharge relationship can inform about in-stream nitrate removal

Nitrate (NO3−) excess in rivers harms aquatic ecosystems and can induce detrimental algae growths in coastal areas. Riverine NO3− uptake is a crucial element of the catchment scale nitrogen balance and can be measured at small spatiotemporal scales while at the scale of entire river networks, uptake measurements are rarely available. Concurrent, low frequency NO3− concentration and stream flow (Q) observations at a basin outlet, however, are commonly monitored and can be analyzed in terms of concentration discharge (C-Q) relationships. Previous studies suggest that more positive log(C)-log(Q) slopes under low flow conditions (than under high flows) are linked to biological NO3− uptake, creating a bent rather than linear log(C)-log(Q) relationship. Here we explore if network scale NO3− uptake creates bent log(C)-log(Q) relationships and when in turn uptake can be quantified from observed low frequency C-Q data. To this end we apply a parsimonious mass balance based river network uptake model in 13 mesoscale German catchments (21–1450 km2) and explore the linkages between log(C)-log(Q) bending and different model-parameter combinations. The modelling results show that uptake and transport in the river network can create bent log(C)-log(Q) relationships at the basin outlet from log-log linear C-Q relationships describing the NO3− land to stream transfer. We find that the bending is mainly shaped by geomorphological parameters that control the channel reactive surface area rather than by the biological uptake velocity itself. Further we show that in this exploratory modelling environment, bending is positively correlated to percentage NO3− load removed in the network (Lr.perc) but that network wide flow velocities should be taken into account when interpreting log(C)-log(Q) bending. Classification trees, finally, can successfully predict classes of low (~ 4 %), intermediate (~ 32 %) and high (~ 68 %) Lr.perc using information on water velocity and log(C)-log(Q) bending. These results can help to identify stream networks that efficiently attenuate NO3− loads based on low frequency NO3− and Q observations and generally show the importance of the channel geomorphology on the emerging log(C)-log(Q) bending at network scales.

Kinetic parameters estimation for increasing the efficiency of nutrient absorption in fruit trees

The selection of rootstocks presenting traits of interest, such as resistance to pests and diseases, and compatibility with scion capable of producing fruits attractive to the market, has revolutionized fruit crops worldwide. However, the enormous potential of plants to be selected based on their nutrient uptake efficiency is yet to be properly explored; it can be done based on knowledge about kinetic parameters such as Influx, Maximum uptake velocity, Constant ion affinity with the carrier, and Minimum concentration. The adaptation of a methodology elaborated for annual crops to set kinetic parameters, as well as the Brazilian development of the Influx software, enabled selecting not only peach rootstocks with different nutrient uptake capacities, but also observing the influence the grafting of a particular cultivar crown has on rootstock’s ability to uptake a given nutrient from the soil. Thus, fruit tree rootstocks and cultivars can always be selected based on traits desired by fruit growers and consumers, with emphasis on yield and quality of fruits. They can also be more efficient in taking up nutrients from low natural-fertility soils that require lower nutrient amounts, a fact that increases fertilizer use rationalization and reduces environmental contamination processes resulting from excessive nutrient applications.

Intra-individual physiological response of recreational runners to different training mesocycles: a randomized cross-over study

Purpose Pronounced differences in individual physiological adaptation may occur following various training mesocycles in runners. Here we aimed to assess the individual changes in performance and physiological adaptation of recreational runners performing mesocycles with different intensity, duration and frequency. Methods Employing a randomized cross-over design, the intra-individual physiological responses [i.e., peak ($${\dot{\text V}}{\text O}_{2 {\rm peak}}$$ V ˙ O 2 peak ) and submaximal ($${\dot{\text V}}{\text O}_{2 {\rm submax}}$$ V ˙ O 2 submax ) oxygen uptake, velocity at lactate thresholds (V2, V4)] and performance (time-to-exhaustion (TTE)) of 13 recreational runners who performed three 3-week sessions of high-intensity interval training (HIIT), high-volume low-intensity training (HVLIT) or more but shorter sessions of HVLIT (high-frequency training; HFT) were assessed. Results $${\dot{\text V}}{\text O}_{2 {\rm submax}}$$ V ˙ O 2 submax , V2, V4 and TTE were not altered by HIIT, HVLIT or HFT (p > 0.05). $${\dot{\text V}}{\text O}_{2 {\rm peak}}$$ V ˙ O 2 peak improved to the same extent following HVLIT (p = 0.045) and HFT (p = 0.02). The number of moderately negative responders was higher following HIIT (15.4%); and HFT (15.4%) than HVLIT (7.6%). The number of very positive responders was higher following HVLIT (38.5%) than HFT (23%) or HIIT (7.7%). 46% of the runners responded positively to two mesocycles, while 23% did not respond to any. Conclusion On a group level, none of the interventions altered $${\dot{\text V}}{\text O}_{2 {\rm submax}}$$ V ˙ O 2 submax , V2, V4 or TTE, while HVLIT and HFT improved $${\dot{\text V}}{\text O}_{2 {\rm peak}}$$ V ˙ O 2 peak . The mean adaptation index indicated similar numbers of positive, negative and non-responders to HIIT, HVLIT and HFT, but more very positive responders to HVLIT than HFT or HIIT. 46% responded positively to two mesocycles, while 23% did not respond to any. These findings indicate that the magnitude of responses to HIIT, HVLIT and HFT is highly individual and no pattern was apparent.

The Influence of 30 Years Outdoor Weathering on the Durability of Hydrophobic Agents Applied on Obernkirchener Sandstones

The durability of eleven different water repellents applied on one sandstone type was studied after a long-term weathering at seven different locations in Germany. By measuring colour changes, it could be shown that the formation of black crusts, the deposition of particles and biogenic growth caused a gradual darkening as well as significant changes in total colour over time. Additionally, the water absorption behaviour was investigated with two different methods: applying a low pressure using the pipe method and capillary water absorption measurements from a wet underlay. Afterwards, the test results were analysed with four different evaluation methods: calculation of the protection degree from pipe method and capillary water absorption, determination of the velocity of water uptake during capillary water absorption and calculation of the damaged depth of the stone surface using single-sided NMR technique. The growing damaged depth leads to an increase of the water uptake velocity and to a decrease of the protection degree of the applied hydrophobing agents. Three protective agents based on isobutyltrimethoxysilane showed already after two years of outdoor weathering a clear loss of performance, which significantly increased after 30 years of exposure.

Exercise tolerance during flat over-ground intermittent running: modelling the expenditure and reconstitution kinetics of work done above critical power

Purpose We compared a new locomotor-specific model to track the expenditure and reconstitution of work done above critical power (W´) and balance of W´ (W´BAL) by modelling flat over-ground power during exhaustive intermittent running. Method Nine male participants completed a ramp test, 3-min all-out test and the 30–15 intermittent fitness test (30–15 IFT), and performed a severe-intensity constant work-rate trial (SCWR) at the maximum oxygen uptake velocity (vV̇O2max). Four intermittent trials followed: 60-s at vV̇O2max + 50% Δ1 (Δ1 = vV̇O2max − critical velocity [VCrit]) interspersed by 30-s in light (SL; 40% vV̇O2max), moderate (SM; 90% gas-exchange threshold velocity [VGET]), heavy (SH; VGET + 50% Δ2 [Δ2 = VCrit − VGET]), or severe (SS; vV̇O2max − 50% Δ1) domains. Data from Global Positioning Systems were derived to model over-ground power. The difference between critical and recovery power (DCP), time constant for reconstitution of W´ ($$\tau_{{W^{\prime}}}$$τW′), time to limit of tolerance (TLIM), and W´BAL from the integral (W´BALint), differential (W´BALdiff), and locomotor-specific (OG-W´BAL) methods were compared. Results The relationship between $$\tau_{{W^{\prime}}}$$τW′ and DCP was exponential (r2 = 0.52). The $$\tau_{{W^{{\prime}}}}$$τW′ for SL, SM, and SH trials were 119 ± 32-s, 190 ± 45-s, and 336 ± 77-s, respectively. Actual TLIM in the 30–15 IFT (968 ± 117-s) compared closely to TLIM predicted by OG-W´BAL (929 ± 94-s, P > 0.100) and W´BALdiff (938 ± 84-s, P > 0.100) but not to W´BALint (848 ± 91-s, P = 0.001). Conclusion The OG-W´BAL accurately tracked W´ kinetics during intermittent running to exhaustion on flat surfaces.