Long-term feedbacks result in the recovery of the CO2 sink in a remnant peatland following water table lowering

<p>Peatland biological, physical and chemical properties change over time in response to the long-term water table position. Such changes complicate predicting the response of peatland carbon stocks to sustained drying. Here we use Eddy Covariance measurements of CO<sub>2</sub> exchange to study the effect of sustained water table lowering on peatland carbon dynamics. We compare measurements from a near-pristine peatland with those of a drying remnant, both raised bogs dominated by <em>Empodisma robustum</em> (Restionaceae), across two different time periods separated by a 16-year interval. We found that the remnant bog was initially a source of CO<sub>2 </sub>following water table lowering. However, the CO<sub>2</sub> sink recovered and strengthened after the 16-year interval between measurements. The increase in CO<sub>2 </sub>sink strength in the remnant bog was primarily due to increased photosynthetic uptake of CO<sub>2</sub>, which exceeded that of the near-pristine site in both time periods. Additionally we found the loss of CO<sub>2 </sub>via ecosystem respiration to have declined with time, however, ecosystem respiration remained elevated compared to the near-pristine site. These trends of increasing photosynthesis and declining ecosystem respiration resulted in the CO<sub>2 </sub>sink in the dry bog reaching half the sink strength of the near-pristine bog. We consider two factors to have been key for the recovery of the CO<sub>2</sub> sink in the remnant bog. These were 1) resilience of the peat-forming plant community to water-table change and 2) the expansion of ericoid shrubs. Our results demonstrate that the peatland carbon sink can recover from drying over a multi-decadal timescale, but questions remain as to the long-term trajectory of dry bogs and the stability of carbon fixed after water table lowering.</p>

Three complete plant-pollinator networks along a secondary successional gradient in critically endangered Renosterveld, South Africa

Despite the global recognition of the importance of pollination as an ecosystem function, there remains a dearth of community level studies on the African continent. Here we present three complete pollination networks, along a secondary successional gradient, in critically endangered Renosterveld vegetation within an agri-environment, South Africa. Site selection was based on historical land-use and contemporary vegetation data resulting in a pristine site, a late successional site where agriculture was halted >15 years ago, and an early successional site where agriculture was halted <five years ago. In total, 240 hours of pollinator-plant observations were recorded over a single flowering season. The pristine site was highly specialised in comparison to global datasets – most likely as a result of relative climatic stability through the Quaternary which allowed specialisation to manifest and persist. Both non-pristine sites showed noticeable differences in characteristics when expressed through network indices; however, the early successional site was closer in nature to the pristine site as a result of vegetation structure. Notwithstanding a lack of replication across the successional gradient precluding robust statistical analyses, this study provides important data which allows for the comparison of pollination dynamics in an understudied and vulnerable vegetation type, to plant-pollinator networks at the global and regional scale. In addition, apparent changes to network indices as a result of habitat alteration, suggest that successional trajectory plays an important role in pollination dynamics.

Development of an Integrated Mariculture for the Collagen-Rich Sponge Chondrosia reniformis

In this study, novel methods were tested to culture the collagen-rich sponge Chondrosia reniformis Nardo, 1847 (Demospongiae, Chondrosiida, Chondrosiidae) in the proximity of floating fish cages. In a trial series, survival and growth of cultured explants were monitored near a polluted fish farm and a pristine control site. Attachment methods, plate materials, and plate orientation were compared. In a first trial, chicken wire-covered polyvinyl chloride (PVC) was found to be the most suitable substrate for C. reniformis (100% survival). During a second trial, survival on chicken wire-covered PVC, after six months, was 79% and 63% for polluted and pristine environments, respectively. Net growth was obtained only on culture plates that were oriented away from direct sunlight (39% increase in six months), whereas sponges decreased in size when sun-exposed. Chicken wire caused pressure on explants and it resulted in unwanted epibiont growth and was therefore considered to be unsuitable for long-term culture. In a final trial, sponges were glued to PVC plates and cultured for 13 months oriented away from direct sunlight. Both survival and growth were higher at the polluted site (86% survival and 170% growth) than at the pristine site (39% survival and 79% growth). These results represent a first successful step towards production of sponge collagen in integrated aquacultures.

Decrease in Microbial Diversity Along a Pollution Gradient in Citarum River Sediment

ABSTRACTPollution of water resources is a major risk to human health and water quality throughout the world. Here, we studied the effect of river pollution on the microbial community composition in the Citarum River Basin, West Java, Indonesia. Sediment was collected at six sampling points along a gradient of pollution, from the pristine source of the river to the heavily polluted downstream site in the densely populated urban area of Bandung. After DNA extraction, microbial diversity and potential for nitrogen cycling were analyzed based on 16S rRNA gene amplicon sequencing and metagenomics. Comparing the pristine sediment to the polluted site showed a lower microbial diversity and higher dominance of anaerobic processes than at the polluted site. The most dominant phylum within the Bacteria were theProteobacteria, which shifted fromBeta- andDeltaproteobacteriain the pristine site toAlpha- andGammaproteobacteriain the polluted sediment. With pollutionActinobacteria, Bacteroidetes,andFirmicutesincreased in relative abundance. Relative high abundance ofSoil Crenarchaeotic groupwas found in all sample sites, whilst the methanogenic archaea became more abundant with increased pollution and anaerobicity. The study of the nitrogen cycling potential revealed that ammonium oxidation and denitrification appeared to be abundant processes in the pristine site, whereas ammonification seemed to be more important in the polluted site. Increased water treatment would restore water quality and microbial diversity in Citarum river sediments.

Effects of urban pollution on UV spectral irradiances

Spectral measurements of UV irradiances at Tokyo are compared with corresponding measurements at a pristine site (Lauder New Zealand) to identify the causes of the reductions in urban UV irradiances, and to quantify their effects. Tropospheric extinctions in Tokyo were found to be up to ~40% greater than at Lauder. Most of these differences can be explained by differences in cloud and aerosols, but ozone differences are also important in the summer. Examining spectral signatures of tropospheric transmission of both sites shows that reductions due to mean NO2 and SO2 amounts are generally small. However, at times the amount of NO2 can be 10 times higher than the mean amount, and on these days it can decrease the UVA irradiance up to 40%. If SO2 shows comparable day to day variability, it would contribute to significant reductions in UVB irradiances. The results indicate that at Tokyo, interactions between the larger burden of tropospheric ozone and aerosols also have a significant effect. These results have important implications for our ability to accurately retrieve surface UV irradiances at polluted sites from satellites that use backscattered UV. Supplementary data characterising these boundary layer effects are probably needed.