Chemical characteristics and limnology of Loskop Dam on the Olifants River (South Africa), in light of recent fish and crocodile mortalities

Abstract

A declining crocodile population and fish mortalities attributed to pansteatitis, along with increasing blooms of Microcystis aeruginosa and Ceratium hirundinella, have led to serious concerns about water quality in Loskop Dam, on the Olifants River, South Africa. Major impacts include acid mine drainage and eutrophication associated with sewage effluent. However, the specific causes of pansteatitis remain elusive. In 2011 the water chemistry and limnology of Loskop Dam were studied to determine factors that may be influencing aquatic ecosystem health. Long-term monitoring data collected by the Department of Water Affairs were analysed for trends using a seasonal Mann-Kendall trend test, and were used to determine the trophic state of Loskop Dam using the Carlson index. Multiple sites were sampled which showed the reservoir was heterogeneous with regard to nutrient concentrations, algal biomass and dissolved metals. Specifically, the transitional zone was characterised by frequent algal blooms, resulting in fluctuating dissolved oxygen (range = 2.1-14.5 mg/ℓ) and pH (range = 7.35-10.59) levels. Using total phosphorus, Secchi depth, and chlorophyll-a concentrations, the trophic state of Loskop Dam was classified as meso-to eutrophic. Significant positive trends were observed in total (Tau = 0.422) and dissolved inorganic (Tau = 0.193) phosphorus.The reservoir showed a monomictic pattern of summer stratification (October to April) and holomictic winter circulation (June to July), with an increase in the depth and extent of anoxia in the hypolimnion when compared to previous research. Simultaneous elevated concentrations of manganese (>370 µg/ℓ) and iron in nearbottom water samples coincided with hypolimnetic anoxia. Aluminium concentrations exceeded the target water quality range (>10 µg/ℓ) during summer (December) in both surface and near-bottom water samples. We conclude that fish in Loskop Dam are periodically exposed to several physiological stressors including elevated ammonia, aluminium, iron and manganese and possibly hydrogen sulphide, as well as low dissolved oxygen. While these factors have never individually been linked to pansteatitis, their combined impacts have not been studied. To ensure the sustainability of Loskop Dam, catchment management plans must focus on reducing phosphorus inputs, and continue seeking treatment solutions for mine-water associated with abandoned and working coal mines.

Influence of limnological zones on the spatial distribution of fish assemblages in three Brazilian reservoirs

“…To corroborate this classification, we assessed the significance of differences in measurements of turbidity and algae (measured by pheophytin a) between lacustrine and riverine sites. For this purpose, we employed a Mann-Whitney test corrected by Bonferroni criteria (Zar, 2009) Some authors have classified sites near the dam as lacustrine and those more distant as riverine (Petesse et al, 2007;Dabrowski et al, 2013). However, like Sanches et al (2014) we observed riverine zones near the dam and lacustrine zones distant from the dam because of the relative influence of tributaries or deep flooded canyons, respectively.…”

Number of Grooming Partners Is Associated with Hookworm Infection in Wild Vervet Monkeys (Chlorocebus aethiops)

“…The near absence of protozoan species other than Entamoeba coli in this study population was unexpected, as most other studies of vervet monkeys have revealed a number of protozoa. It may be that the water quality at LDNR has impacted the distribution of protozoan species in the area [Oberholster and Ashton, 2008;Oberholster et al, 2012;Dabrowski et al, 2013], although this is unclear.…”

Trophic ecology and persistence of invasive silver carpHypophthalmichthys molitrixin an oligotrophic South African impoundment

“…proportional contribution of stomachs in which it occurred), but was never sampled in FBD (Dabrowski et al 2013(Dabrowski et al , 2014a Previous bioenergetics (Cooke and Hill 2010) and species distribution models (Chen et al 2007, Herborg et al 2007, Lohmeyer and Garvey 2009 (Table 2) reported in this study, relative to H. molitrix from other lentic waterbodies (minimum 1.78, Spatura and Gophen (1985)), suggest that they might be nutritionally stressed (Online Resource A).…”

“…Hypophthalmichthys molitrix are known to strain bacteria by using mucus produced by large supra-branchial organ (Opuszyński 1981, Kolar et al 2007 (Dabrowski et al 2013) which, was observed in several H. molitrix stomachs (< 1%…”