Simulating rewetting events in intermittent rivers and ephemeral streams: A global analysis of leached nutrients and organic matter

Climate change and human pressures are changing the global distribution and the extent of intermittent rivers and ephemeral streams (IRES), which comprise half of the global river network area. IRES are characterized by periods of flow cessation, during which channel substrates accumulate and undergo physico-chemical changes (preconditioning), and periods of flow resumption, when these substrates are rewetted and release pulses of dissolved nutrients and organic matter (OM). However, there are no estimates of the amounts and quality of leached substances, nor is there information on the underlying environmental constraints operating at the global scale. We experimentally simulated, under standard laboratory conditions, rewetting of leaves, riverbed sediments, and epilithic biofilms collected during the dry phase across 205 IRES from five major climate zones. We determined the amounts and qualitative characteristics of the leached nutrients and OM, and estimated their areal fluxes from riverbeds. In addition, we evaluated the variance in leachate characteristics in relation to selected environmental variables and substrate characteristics. We found that sediments, due to their large quantities within riverbeds, contribute most to the overall flux of dissolved substances during rewetting events (56%-98%), and that flux rates distinctly differ among climate zones. Dissolved organic carbon, phenolics, and nitrate contributed most to the areal fluxes. The largest amounts of leached substances were found in the continental climate zone, coinciding with the lowest potential bioavailability of the leached OM. The opposite pattern was found in the arid zone. Environmental variables expected to be modified under climate change (i.e. potential evapotranspiration, aridity, dry period duration, land use) were correlated with the amount of leached substances, with the strongest relationship found for sediments. These results show that the role of IRES should be accounted for in global biogeochemical cycles, especially because prevalence of IRES will increase due to increasing severity of drying events.

Leaf Barriers to Fungal Colonization and Shredders (Tipula lateralis) Consumption of Decomposing Eucalyptus globulus

> Abstract Herein we assess the importance of leaf cuticle, polyphenolic, and essential oils contents of Eucalyptus globulus leaves to hyphomycete colonization and shredder consumption. Optical and electron microscopy revealed that, at least during the first 5 weeks of conditioning, the cuticle remains virtually intact. Stomata provide the main access for hyphae to internal leaf tissues and, eventually, for spore release. We suggest that in E. globulus leaves, fungal decomposition progresses predominantly in and from the eucalyptus leaf mesophyll to the outside. Malt extract agar media supplemented with either eucalyptus essential oils or tannic acid completely inhibited (Articulospora tetracladia, Lemonniera aquatica, and Tricladium gracile) or depressed (Heliscus lugdunensis, Lunulospora curvula, and Tricladium angulatum) aquatic hyphomycetes growth. The transference of both secondary compounds to alder leaves induced similar and significant reduction in Tipula lateralis larval consumption. Results consistently indicate that eucalyptus oils are stronger deterrents than polyphenols. The waxy cuticle of E. globulus appears to be a key physical factor delaying fungal colonization during decomposition. We hypothesize that the relative influence of leaf phenols and essential oils to aquatic hyphomycetes and shredders may be related to three main factors: (a) initial distribution of such compounds in the leaves; (b) possibility of their decrease through decomposition; and (c) consumption strategies of detritivores.

A randomized controlled trial of a 2% minocycline gel as an adjunct to non-surgical periodontal treatment, using a design with multiple matching criteria

Topical locally delivered minocycline is an adjunctive to non-surgical periodontal treatment, but there are few reported trials. Previous trials have reported differences between changes in probing depth in treatment and control groups, but no differences in probing attachment level. In the present study, 30 subjects were paired according to gender, age, ethnic group, smoking habits, and probing depths. Both groups received intensive oral hygiene education and root planing with local anaesthesia. Active or placebo gel was placed subgingivally at planed sites in each subject according to a double-blind protocol, immediately after instrumentation, and 2 and 4 weeks later. A periodontal examination was made with a constant force probe before instrumentation, and 6 and 12 weeks later, 2 subjects failed to complete the study, and their pairs were therefore not included in the analysis. Results were tested with analysis of covariance. Differences between groups in mean probing depth did not reach statistical significance at any visit (baseline: test (T) = 5.93 mm, control (C) = 5.74 mm; 6 weeks: T = 3.53 mm, C = 3.63 mm; 12 weeks: T = 3.29 mm, C = 3.44 mm), but mean probing attachment levels were different (p < 0.05) at both reassessments (baseline: T = 6.86 mm, C = 6.83 mm; 6 weeks: T = 4.93 mm, C = 5.30 mm; 12 weeks T = 4.91 mm, C = 5.27 mm). There was also a difference in the number of sites with bleeding on deep probing at 12 weeks (p < 0.05). This trial showed that adjunctive minocycline gel provided a more advantageous outcome for nonsurgical periodontal treatment in terms of probing attachment level and bleeding on deep probing. This trial was a good example of experimental, as opposed to community, design, and used limited resources to show a clear result.

The effects of a basic effluent on macroinvertebrate community structure in a temporary Mediterranean river

Macroinvertebrate communities and environmental variables were assessed seasonally for 1 year in a temporary river in South Portugal receiving an effluent with high conductivity, pH, sulphates, nitrates and low oxygen content. The usefulness of the ordination method canonical correspondence analysis (CCA) and the classification method cluster analysis (UPGMA) were examined to evaluate the perturbation. Macroinvertebrate samples were segregated along the first ordination axis by CCA, which in turn correlated with sulphates and nitrates. CCA produced a two-dimensional distribution of sites similar to the grouping formed by cluster analysis. In general, three or four groups were distinguished. Immediately downstream of the effluent discharge point, only taxa tolerant to low oxygen, high pH and high sulphate and nitrate concentrations were present. Further downstream, sites had a community similar to the reference sampling locations. During flowing conditions the CCA ordination axis 1 was also correlated with several classic measures of water quality (i.e. taxon richness, diversity and biotic indices). In other periods, only the percentage of Ephemeroptera, Plecoptera and Trichoptera (%EPT) and the ratio EPT/(Chironomidae + EPT) were significantly correlated with CCA axis one. This suggests that ordination methods outperform benthic indices in detecting pollution during low flows and segregated polluted from clean/recovered sites in all periods.