Assessing sediment inputs to small reservoirs in Upper East Region,Ghana

Many small dams and dugouts have been constructed in the Upper East Region of Ghana to address the problem of regional water scarcity. The reservoirs were constructed primarily as water supplies for agricultural irrigation and livestock watering, aquaculture and domestic use. However, many of the reservoirs dry up during the dry season, affecting the livelihoods of their basin inhabitants. A major cause for the dried reservoirs is siltation, which reduces the reservoir’s storage capacities. The goal of this study is to quantify the annual siltation rate of four study reservoirs, using a bathymetric survey and reservoir soil sampling. The sediment yield and its relation to catchment area also were assessed. The results of this study indicate that the annual siltation rates are 1272, 3518, 2764 and 6135 t year^?1 for Doba, Dua, Zebilla and Kumpalgogo reservoirs, respectively. Analyses of the sediment yield and catchment areas illustrated that the sediment yields decreased with increasing catchment area. All the study reservoirs have lost their dead storage capacity, which was meant to store sediment until the end of their anticipated design lives. The decreasing storage capacity because of siltation will affect the livelihoods of the local basin inhabitants, as the reservoirs will not be able to achieve all their intended purposes. The results of this study indicate that, because siltation is not the only factor threatening the benefits gained from the reservoirs, the integrated assessment of all relevant factors is required.     

Mixing and sink effects of air purifiers on indoor PM2.5 concentrations: A pilot study of eight residential homes in Fresno,California

We measured real-time and integrated PM2.5 inside eight occupied single-family homes in Fresno, California to evaluate how turbulent air mixing and pollutant removal caused by a filter-based air purifier influences the levels of fine particles in everyday indoor environments. In each home, we used a real-time monitor to log PM2.5 levels every 5 min over 12 weeks during which air purifiers were operating, except for a designed 3-day shutdown period for baseline measurements. We assessed how the operation of air purifiers changed the patterns of the frequency distributions for short-term (5 min) concentrations, which included spikes produced by sporadic indoor activities or emissions. This allowed us to examine the reduction effectiveness of air purifiers on concentrations of both recently emitted and well-mixed background aerosols. We observed a systematic change in the 5-min PM2.5 distributions in different homes—while air purifiers reduced 96% of the 5-min concentrations, they increased the magnitudes of the top 4%, representing transient concentration peaks. This phenomenon is consistent with what would be theoretically expected based on passive scalar turbulence in fluid physics. We also collected gravimetric filter samples for PM2.5 composition, finding mean reductions of the long-term (2–5 days) concentrations of 29%–37% for indoor PM2.5 and endotoxin. A less significant reduction (19%–26%) was seen for Pb (Lead).

© 2016 American Association for Aerosol Research