P.R. van Oel

Increasing pressure on freshwater resources due to terrestrial feed ingredients for aquaculture production

As aquaculture becomes more important for feeding the growing world population, so too do the required natural resources needed to produce aquaculture feed. While there is potential to replace fish meal and fish oil with terrestrial feed ingredients, it is important to understand both the positive and negative implications of such a development. The use of feed with a large proportion of terrestrial feed may reduce the pressure on fisheries to provide feed for fish, but at the same time it may significantly increase the pressure on freshwater resources, due to water consumption and pollution in crop production for aquafeed. Here the green, blue and gray water footprint of cultured fish and crustaceans related to the production of commercial feed for the year 2008 has been determined for the major farmed species, representing 88% of total fed production. The green, blue and gray production-weighted average feed water footprints of fish and crustaceans fed commercial aquafeed are estimated at 1629 m3/t, 179 m3/t and 166 m3/t, respectively. The estimated global total water footprint of commercial aquafeed was 31-35 km3 in 2008. The top five contributors to the total water footprint of commercial feed are Nile tilapia, Grass carp, Whiteleg shrimp, Common carp and Atlantic salmon, which together have a water footprint of 18.2 km3. An analysis of alternative diets revealed that the replacement of fish meal and fish oil with terrestrial feed ingredients may further increase pressure on freshwater resources. At the same time economic consumptive water productivity may be reduced, especially for carnivorous species. The results of the present study show that, for the aquaculture sector to grow sustainably, freshwater consumption and pollution due to aquafeed need to be taken into account.

Downstreamness: A Concept to Analyze Basin Closure

In many places in the world, increasing water demands have led to the development of infrastructure for freshwater storage and irrigation. Especially in water-scarce regions, this development has led to a growing number of concerns about basin closure. These concerns ask for a structured approach for analyzing the occurrence of basin closure to facilitate sustainable responses. In this paper, the downstreamness concept is proposed for analyzing the availability and commitments of freshwater in river basins. The downstreamness of a location is the ratio of its upstream catchment area to the entire river basin area. The downstreamness of a function on the basin, such as water availability or water demand, is defined as the downstreamness-weighted integral of that function divided by its regular integral. An approach to determine the downstreamness of surface water storage capacity, stored surface water volumes, and water demands is described. Applying the proposed approach is helpful for the spatiotemporally explicit assessment of basin closure and its drivers. Water management policies rely on the valuations of trade-offs between commitments of upstream and downstream uses and technical implementations of upstream and downstream measures. The concept of downstreamness can assist in analyzing subbasin points of view as an integral part of a basin perspective. In this way, the effects of anthropogenic processes driving basin closure can be better understood. To illustrate the use of the concept, the authors describe its application to the Jaguaribe Basin in the semiarid northeast of Brazil.