Design and performance of subirrigation system in maize (Zea mays) in Kumulur farm, Trichy district, Tamil Nadu, India

Subirrigation system can furnish water to plants. The upward flux and the discharge rate must satisfy the plant’s lifesaving irrigation needs during summer. The experiment was laid out in A-block of Eastern farm, Agricultural Engineering College and Research Institute, Kumulur, Trichy, Tamil Nadu. Subirrigation system spacing was arrived using Moody's equation calculated as 10 m. The experiment was laid out in spilt plot design with three replications. Four drain spacing levels (7.5, 10, 12.5 and 15 m) were the main plot treatments and two levels of depth and diameter of drain pipes (75 cm, 60 cm & 75 mm, 63 mm) were the sub plot treatments. The highest volumetric water content was recorded in 7.5 m spacing + 45 cm soil depth + lower reach (S1T3T1). Capillary rise on water table management system under subirrigation mode was fixed as 33.5 cm and the average deep percolation loss was obtained in 0.3 cm/d at development stage of crop period. The highest maize yield (4.30 t/ha) was obtained in 7.5 m spacing + 60 cm drain depth + 75 mm diameter (S1D3). The highest water use efficiency of (0.86 kg/m3) was recorded in 7.5 m spacing + 60 cm drain depth + 75 mm drain diameter (S1D3). This subirrigation system could furnish water to plants due to upward flux and the same system also functioned efficiently under drainage modes and removed the waterlogging during wet periods.

Intra-Annual Patterns in the Benthic-Pelagic Fluxes of Dissolved and Particulate Matter

In coastal temperate environments, many processes known to affect the exchange of particulate and dissolved matter between the seafloor and the water column follow cyclical patterns of intra-annual variation. This study assesses the extent to which these individual short term temporal variations affect specific direct drivers of seafloor-water exchanges, how they interact with one another throughout the year, and what the resulting seasonal variation in the direction and magnitude of benthic-pelagic exchange is. Existing data from a multidisciplinary long-term time-series from the Western Channel Observatory, United Kingdom, were combined with new experimental and in situ data collected throughout a full seasonal cycle. These data, in combination with and contextualized by time-series data, were used to define an average year, split into five ‘periods’ (winter, pre-bloom, bloom, post-bloom, and autumn) based around the known importance of pelagic primary production and hydrodynamically active phases of the year. Multivariate analyses were used to identify specific sub-sets of parameters that described the various direct drivers of seafloor-water exchanges. Both dissolved and particulate exchange showed three distinct periods of significant flux during the year, although the specific timings of these periods and the cause-effect relationships to the direct and indirect drivers differed between the two types of flux. Dissolved matter exchange was dominated by an upward flux in the pre-bloom period driven by diffusion, then a biologically induced upward flux during the bloom and an autumn downward flux. The latter was attributable to the interactions of hydrodynamic and biological activity on the seafloor. Particulate matter exchanges exhibited a strongly hydrologically influenced upward flux during the winter, followed by a biologically induced downward flux during the bloom and a second period of downward flux throughout post-bloom and autumn periods. This was driven primarily through interactions between biological activity, and physical and meteorological drivers. The integrated, holistic and quantitative data-based analysis of intra-annual variability in benthic/pelagic fluxes presented in this study in a representative temperate coastal environment, demonstrates not only the various process’ inter-connectivity, but also their relative importance to each other. Future investigations or modeling efforts of similar systems will benefit greatly from the relationships and baseline rules established in this study.

Which Processes Sustain Biota in Open-Ocean Deep Chlorophyll Maxima?

<p>Deep chlorophyll maxima (DCM) are productive layers widespread throughout the global ocean. In the DCM, marine phytoplankton are adapted to low light conditions at the cost of elevated cellular iron (Fe) requirements, leading to Fe deficient growth. To sustain productivity, nutrient demands must be met by sources such as the dissolution of sinking lithogenic particles, recycling of biogenic particles and physical transport from below. The <em>GEOTRACES</em> programme has expanded the global ocean datasets for a suite of trace metals and also noble gases. Here, we exploit helium measurements to derive a vertical flux estimate of nitrate (NO<sub>3</sub>), phosphate (PO<sub>4</sub>), silica (Si) and Fe into the DCM in the subtropical North Atlantic and equatorial Pacific. We apply the Si* relation to show differences in nutrient deficiency between waters in the DCM and the upward flux into the DCM. The offset in Si* between the DCM and upward flux may be enhanced or reduced by the dissolution of sinking particles or internal recycling. We show that the upward Fe flux to the DCM is of similar magnitude to Fe supplied through regeneration. In contrast, we show that the upward Fe flux outweighs estimates of Fe supplied to the DCM via recycling or lithogenic particles in the subtropical North Atlantic. The muted role of lithogenic particles in our estimates leads to the question: what assumptions must be made about aeolian deposition to increase the relevance of lithogenic particles at the DCM?</p>

Evidence of Energy and Momentum Flux from Swell to Wind

Measurements of pressure near the surface in conditions of wind sea and swell are reported. Swell, or waves that overrun the wind, produces an upward flux of energy and momentum from waves to the wind and corresponding attenuation of the swell waves. The estimates of growth of wind sea are consistent with existing parameterizations. The attenuation of swell in the field is considerably smaller than existing measurements in the laboratory.

Characterization of total ecosystem-scale biogenic VOC exchange at a Mediterranean oak–hornbeam forest

Recently, the number and amount of biogenically emitted volatile organic compounds (VOCs) has been discussed in great detail. Depending on the ecosystem, the published number varies between a dozen and several hundred compounds. We present ecosystem exchange fluxes from a mixed oak–hornbeam forest in the Po Valley, Italy. The fluxes were measured by a proton transfer reaction-time-of-flight (PTR-ToF) mass spectrometer and calculated using the eddy covariance (EC) method. Detectable fluxes were observed for up to 29 compounds, dominated by isoprene, which comprised over 60 % of the total upward flux (on a molar basis). The daily average of the total VOC upward flux was 10.4 nmol m−2 s−1. Methanol had the highest concentration and accounted for the largest downward flux. Methanol seemed to be deposited to dew, as the downward flux happened in the early morning, right after the calculated surface temperature came closest to the calculated dew point temperature.We estimated that up to 30 % of the upward flux of methyl vinyl ketone (MVK) and methacrolein (MACR) originated from atmospheric oxidation of isoprene. A comparison between two methods for the flux detection (manual and automated) was made. Their respective advantages and disadvantages were discussed and the differences in their results shown. Both provide comparable results.

Methanotrophy within the water column of a large meromictic tropical lake (Lake Kivu, East Africa)

The permanently stratified Lake Kivu is one of the largest freshwater reservoirs of dissolved methane (CH4) on Earth. Yet CH4 emissions from its surface to the atmosphere have been estimated to be 2 orders of magnitude lower than the CH4 upward flux to the mixed layer, suggesting that microbial CH4 oxidation is an important process within the water column. A combination of natural abundance stable carbon isotope analysis (δ13C) of several carbon pools and 13CH4-labelling experiments was carried out during the rainy and dry season to quantify (i) the contribution of CH4-derived carbon to the biomass, (ii) methanotrophic bacterial production (MBP), and (iii) methanotrophic bacterial growth efficiency (MBGE), defined as the ratio between MBP and gross CH4 oxidation. We also investigated the distribution and the δ13C of specific phospholipid fatty acids (PLFAs), used as biomarkers for aerobic methanotrophs. Maximal MBP rates were measured in the oxycline, suggesting that CH4 oxidation was mainly driven by oxic processes. Moreover, our data revealed that methanotrophic organisms in the water column oxidized most of the upward flux of CH4, and that a significant amount of CH4-derived carbon was incorporated into the microbial biomass in the oxycline. The MBGE was variable (2–50%) and negatively related to CH4 : O2 molar ratios. Thus, a comparatively smaller fraction of CH4-derived carbon was incorporated into the cellular biomass in deeper waters, at the bottom of the oxycline where oxygen was scarce. The aerobic methanotrophic community was clearly dominated by type I methanotrophs and no evidence was found for an active involvement of type II methanotrophs in CH4 oxidation in Lake Kivu, based on fatty acids analyses. Vertically integrated over the water column, the MBP was equivalent to 16–60% of the average phytoplankton particulate primary production. This relatively high magnitude of MBP, and the substantial contribution of CH4-derived carbon to the overall biomass in the oxycline, suggest that methanotrophic bacteria could potentially sustain a significant fraction of the pelagic food web in the deep, meromictic Lake Kivu.