Getting into hot water: water quality in tropical lakes in relation to their utilisation

Over-exploitation of tropical lakes and reservoirs ('lakes') causes water quality problems that occur as a result of competing socio-economic demands and the presence of feedback loops within the system that exacerbate the situation. We review well documented case studies from Brazil, India, Indonesia, Kenya, Malaysia and Mexico to examine the effect that changes in water quality and quantity have had on the utilisation of these tropical lakes. By comparing the different approaches used to improve their sustainable management, we have found that nutrient enrichment is one of the most important and widespread water quality problems, causing adverse effects such as algal blooms, nuisance levels of aquatic plants, low oxygen levels and elevated greenhouse gas emissions. These effects restrict the use of these lakes for water supply, fisheries, recreation, tourism and wildlife. We conclude that tropical lakes require better management, urgently, to restore the ecosystem services that they deliver to man and nature. However, to be effective, the development of sustainable management programmes needs to be underpinned by reliable scientific evidence and the results of extensive stakeholder engagement activities. We note that, currently, there is little information available on how tropical lakes respond to management interventions that can be used to guide these activities. Further research is needed to address this knowledge gap. Presented at International Conference on the Ocean and Earth Sciences, 18-20 November 2020, Jakarta Selatan, Indonesia (held online)

Highly-parallelized simulation of a pixelated LArTPC on a GPU

The rapid development of general-purpose computing on graphics processing units (GPGPU) is allowing the implementation of highly-parallelized Monte Carlo simulation chains for particle physics experiments. This technique is particularly suitable for the simulation of a pixelated charge readout for time projection chambers, given the large number of channels that this technology employs. Here we present the first implementation of a full microphysical simulator of a liquid argon time projection chamber (LArTPC) equipped with light readout and pixelated charge readout, developed for the DUNE Near Detector. The software is implemented with an end-to-end set of GPU-optimized algorithms. The algorithms have been written in Python and translated into CUDA kernels using Numba, a just-in-time compiler for a subset of Python and NumPy instructions. The GPU implementation achieves a speed up of four orders of magnitude compared with the equivalent CPU version. The simulation of the current induced on 10^3 pixels takes around 1 ms on the GPU, compared with approximately 10 s on the CPU. The results of the simulation are compared against data from a pixel-readout LArTPC prototype

The terrestrial invertebrate fauna of a temporary stream in southern Africa

The terrestrial invertebrate fauna of an intermittent stream was examined in the absence of surface flows within the context of the flood pulse concept. Terrestrial invertebrates were collected from three sites on the Kruis River in theWestern Cape Province, South Africa, using pitfall traps within the dry stream bed over summer months (Jan–Feb). 9848 individuals representing 19 different orders were collected. Taxa were separated and biomass determined for aerial and non-aerial  invertebrates. Significantly greater (P < 0.05) numbers of aerial than non-aerial taxa and individuals suggest that most individuals could use flight to escape the onset of surface flows. The absence of significant differences between the biomass (wet weights) of aerial and non-aerial individuals (P>0.05) suggests, however, that a large proportion of the biomass is confined to the main channel. The inability of a large portion of the biomass to escape the onset of flow through the use of flight suggests that periodically inundated areas of the stream channel constitute an ecologically significant component of temporary stream ecosystems. The concept of the flood pulse should be expanded to include aseasonal and secular variations in flow which in temporary streams create lateral movements that provide the driving mechanism for the entrainment of organic material.Key words: ephemeral, intermittent, flood pulse concept