The effect of stream regulation on the physico‐chemical properties of the palmiet river, South Africa

Abstract

AbstractThe effect of regulation, by multiple impoundment, on ‘discontinuity’ (recovery) ‘distances’ (sensu Ward and Stanford, 1983) for various physico‐chemical attributes of the Palmiet River (a short, steep gradient, cool temperate, acid, low‐nutrient system) was investigated. Physico‐chemical features were measured monthly, from February 1986 to August 1987, at 11 sites along the river, but concentrating on two zones: one below an upper‐reach impoundment, Nuweberg Dam, and one below a middle‐reach impoundment, Arieskraal Dam. Median total suspended solids, nitrates, nitrites and ammonium all increased below both dams with varying levels of ‘recovery’. Median spot temperatures, pH and alkalinity increased below Nuweberg, but decreased below Arieskraal Dam, whereas the converse was true for soluble reactive phosphate. Nuweberg had no effect on conductivity and total dissolved solids, while Arieskraal caused a slight decrease. The river remained well oxygenated down its length.Distinct seasonal variations were recorded for: flow rate, with flow reversal below Nuweberg and flow constancy below Arieskraal; temperature, with seasonal shifts and dampening of annual temperature range below both dams; alkalinity, with seasonal shifts below Arieskraal, and nitrites and nitrates, but not for any other attributes. At least partial recovery was noted in all cases, but in some instances, recovery was incomplete to the estuary. The implications of such alterations, for invertebrates, in terms of reduction in habitat diversity as well as for food supply must be considerable and studies are currently under way to determine community structure and diversity.