Retention time as a primary determinant of colour and light attenuation in two tropical Australian reservoirs

Abstract

1. The light climates of Darwin River Reservoir (DRR) and Manton River Reservoir (MRR), in northern Australia, are compared for an 8‐year period. The reservoirs are subject to the same wet/dry tropical climate and have similar catchment characteristics, but differ in their basin morphology, retention time and trophic status. 2. Median euphotic depths in DRR and MRR were 9.7 and 4.4 m, respectively. Seasonal variation in each reservoir’s euphotic depth was best explained by colour, based on a stepwise linear regression. Turbidity was excluded from the two regressions, while chlorophyll a concentration was significant only for the MRR regression. 3. Both reservoirs showed the same seasonal pattern for colour. Wet season inflow increased reservoir colour, and was followed by a reduction in colour due to photodegradation and microbial decomposition of humic material, reaching a minimum before the next wet seasons inflow. 4. Although the colour of catchment run‐off into both reservoirs was similar, MRR colour was two to three times greater than that measured in DRR. The higher colour and greater light attenuation of MRR is attributed primarily to its shorter retention time, and therefore shorter time for colour removal. Annual retention time accounted for 97% of the variability of average annual colour (measured as absorption at 440 nm), based on a linear regression of log10 transformed data for both reservoirs. 5. Long retention times favour reduced colour, increasing water transparency, particularly in water bodies of low trophic state and inorganic turbidity.

Biogeochemistry of nitrogen and phosphorus in Australian catchments, rivers and estuaries: effects of land use and flow regulation and comparisons with global patterns

“…DIN:SRP ratios in surface waters are usually very low (<1.0) but the hypolimnia contain large concentrations of ammonia. Australian reservoirs commonly show large cyanobacterial blooms, especially during periods of drought when water residence times are long, DIN:SRP ratios in surface waters are very low and water clarity is maximal (Harris and Baxter 1996;Townsend et al 1996). Such blooms are also common in lowland river reaches, especially during low flow periods when stratification occurs in weir pools and stagnant reaches (Bormans et al 1997;Sherman et al 1998).…”

Dynamics of a toxic cyanobacterial bloom (Cylindrospermopsis raciborskii) in a shallow reservoir in the semi-arid region of northeast Brazil

“…wind, light conditions) can also modify the phytoplankton slructure, as cyanobacteria communities are strongly driven by physical conditions such as local weather (e.g. Toth & Padisak 1986, Paerl 1988, Townsend et al 1996, Soranno 1997. Other climatological factors which play a role in the global climate have been recently studied in marine ecosystems, such as the El Niiio-Southern Oscillation (ENSO) cycles in the modification of phytoplankton communities (e.g.…”

A classification system for large reservoirs of the contiguous United States

“…Support for the classification system using tangential reservoir characteristics such as reservoir morphology, watershed characteristics, and fish assemblage descriptors upheld our conclusion that the proposed classes truly differed from each other. The variables examined to seek support for our classification have often been applied to classify reservoirs (e.g., Dolman 1990;Godinho et al 1998;Miranda 1999;Bulley et al 2007), predict reservoir characteristics (Jenkins 1970;Ground and Groeger 1994;Verstraeten et al 2003;Jones et al 2004), or explain reservoir phenomena (Townsend et al 1996;Shoup et al 2007). This agreement among data sets suggests that habitat impairment is linked to key physical and chemical characteristics of the reservoir basin and its watershed, and that this impairment is in turn reflected on the fish assemblages and fisheries.…”