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Developing index maps of water-harvest potential in Africa

The food security problem in Africa is tied to the small farmer, whose subsistence farming relies heavily on rain-fed agriculture. A dry spell lasting two to three weeks can cause a significant yield reduction. A small-scale irrigation scheme from small-capacity ponds can alleviate this problem. This solution would require a water harvest mechanism at a farm level. In this study, we looked at the feasibility of implementing such a water harvest mechanism in drought prone parts of Africa. A water balance study was conducted at different watershed levels. Runoff (watershed yield) was estimated using the SCS curve number technique and satellite derived rainfall estimates (RFE). Watersheds were delineated from the Africa-wide HYDRO-1K digital elevation model (DEM) data set in a GIS environment. Annual runoff volumes that can potentially be stored in a pond during storm events were estimated as the product of the watershed area and runoff excess estimated from the SCS Curve Number method. Estimates were made for seepage and net evaporation losses. A series of water harvest index maps were developed based on a combination of factors that took into account the availability of runoff, evaporation losses, population density, and the required watershed size needed to fill a small storage reservoir that can be used to alleviate water stress during a crop growing season. This study presents Africa-wide water-harvest index maps that could be used for conducting feasibility studies at a regional scale in assessing the relative differences in runoff potential between regions for the possibility of using ponds as a water management tool. ?? 2004 American Society of Agricultural Engineers.

Applied Engineering in Agriculture

Water use for aquaculture in Minnesota, 1984

Aquaculture supports a large sportfishing industry in Minnesota. Licensed fish farms that hatch and (or) harvest minnows or gamefish are located throughout the State. The volume of water used in these operations can be expressed as the minimum capacity per pound of fish, total water consumed, total water dedicated to the farming operation, or total water withdrawn. In expressing water dedicated to the farming operation, the total surface area of water bodies dedicated to aquaculture in Minnesota in 1984 was about 141,500 acres, based on interpretation of data reported in license applications. Water withdrawals to fish holding tanks amounted to 0.73 million gallons per day in 1984. Water-use calculations address the possibility of errors in reporting. About 15 percent of the licensees use municipally supplied water for their holding tanks. One thermoelectric powerplant recently began reusing the heated water from its cooling towers to raise catfish. Little change in the number of licensees since 1980 -indicates that aquaculture is a viable segment of the Minnesota economy. Trout farming has grown from 10 farms in 1978, to 23 in 1984; most use dug ponds sustained by ground-water inflow. Withdrawals for aquaculture are nonconsumptive and are small compared to other water-use categories in Minnesota.

Minnesota

Freshwater turtle assemblages and densities in agricultural ditches and aquaculture ponds of eastern Arkansas

The Mississippi Alluvial Plain (MAP) of Arkansas is a landscape where many wetlands have been altered for use as aquaculture ponds or agricultural ditches. Commercial harvest of freshwater turtles within the MAP is not restricted or limited, with reported harvest numbers for 2019 alone exceeding 4000 for spiny softshell turtles ( Apalone spinifera ) and 39,000 for red-eared sliders ( Trachemys scripta elegans ). Herein, we attempt to provide baseline estimates of freshwater turtle densities and community composition in aquaculture ponds and agricultural ditches of eastern Arkansas, the habitat types most frequently trapped by commercial harvesters. We used a capture–mark–recapture approach over 3 summers (2019–2021) to evaluate population densities and community composition of freshwater turtles in these anthropogenic aquatic habitats. We captured > 4000 individuals of 9 species of turtle. One species, the red-eared slider, dominated the turtle community in both anthropogenic aquatic habitats, comprising 66% (± 22% SD) of all captures in agricultural ditches and 63% (± 32% SD) in aquaculture ponds. Diversity and richness did not differ between aquaculture ponds and agricultural ditches. We estimated densities of the 2 most commonly captured species, the red-eared slider and spiny softshell turtle. Density of red-eared sliders ranged from 0 turtles/unit area (linear kilometers in ditches or hectares in ponds) to 500 turtles/unit area, with a median of 37 turtles/unit area. The spiny softshell turtle was more frequently captured in ponds than ditches and attained average densities of 25 (± 19) turtles/ha and 7 (± 4) turtles/linear km, respectively. Our mean density estimates were lower than those in reported literature, including estimates from similar habitats, such as urban ditches and farm ponds, which resemble our study sites in structure, use, and geographical placement. We estimate the region contains 22,317 ha of aquaculture ponds and 18,350 linear km of agricultural ditches. By extrapolating our density estimates to each anthropogenic aquatic habitat type, we estimated 2 million red-eared sliders and 427,000 spiny softshell turtles occurred in aquaculture ponds and agricultural ditches across eastern Arkansas. Our results suggest that these altered wetlands provide abundant habitat for only a few generalist turtle species.

Arkansas