Mueller, S, Mitrovic, SM & Baldwin, DSB 2016, 'Oxygen and dissolved organic carbon control release of N, P and Fe from the sediments of a shallow, polymictic lake', Journal of Soils and Sediments, vol. 16, no. 3, pp. 1109-1120.View/Download from: Publisher's site
Purpose We examined potential causes of nutrient release
from the sediments of a shallow polymictic reservoir that,
unlike many other shallow lakes, had not received large
amounts of nutrient loading. It was hypothesised that the sediments
released greater amounts of nutrients under anoxic
rather than oxic conditions and that nitrogen (N) and phosphorus
(P) release was limited by the availability of different types
of organic substrate.
Materials and methods Sediment incubation experiments under
oxic and anoxic conditions were conducted in summer and
in winter. One anoxic incubation experiment with the addition
of different types of dissolved organic substrate (glucose, acetate,
formate and propionate) was carried out. Concentrations
of nitrite and nitrate (NOx
−-N), ammonium (NH4
reactive P (srP) and iron (Fe(II)) were monitored in the supernatant
of the incubation chambers over 28 days. Thermal stratification
was monitored in situ for 17 months and sediment
composition was analysed.
Results and discussion NOx
−-N concentration increased by
5.67±0.33 mg N l−1 in anoxic conditions but was much lower
in oxic treatments. Release of srP was low in anoxic and oxic
treatments (0.004±0.001 mg P l−1) but was stimulated by
0.027±0.015 mg P l−1 under additions of formate. Fe(II) release
was mostly stimulated by glucose additions (25.59±
4.28 mg Fe l−1). P release was much lower than observed in
eutrophic lakes. P release does not appear to be as a result of
the reduction of Fe minerals and concurrent dissolution of
orthophosphate, often reported as the most prevalent pathway
for P release from anaerobic lake sediments.
Conclusions Iron and P flux from lake sediments can be independent
from each other and can be controlled by dissolved
organic C. Further, the study confirms the role of oxygen
availability in controlling nutrient release from the sediments.
Müller, S & Mitrovic, SM 2015, 'Phytoplankton co-limitation by nitrogen and phosphorus in a shallow reservoir: progressing from the phosphorus limitation paradigm', Hydrobiologia, vol. 744, no. 1, pp. 255-269.View/Download from: Publisher's site
Phosphorus (P) limitation has been regarded as the rule in freshwater systems and the basis for phytoplankton growth management. We hypothesised that P would be the limiting nutrient for phytoplankton growth in Grahamstown Dam, a shallow, mesotrophic reservoir, across different seasons and on different experimental time scales. Seven fully factorial microcosm assays with additions of nitrogen (N) and P were conducted in situ during different seasons. The influence of longer experimental duration was examined in two 18-day mesocosm assays. Additions of N and P in combination evoked significantly higher phytoplankton biomass and biovolumes of individual algal genera compared with controls and other treatments in both types of experiment. There were some significant responses to P additions in the microcosm assays in winter. Some genera first responded to combined P and N addition and then to P only addition during the mesocoms assays. Our results show that P was not the limiting nutrient across all seasons but that phytoplankton was mostly co-limited by N and P. A longer experimental time scale did not change this outcome at the biomass level. This implies that input of N as well as of P should be considered in the management of phytoplankton growth.
Phyu, YL, Palmer, CG, Warne, MS, Dowse, R, Mueller, S, Chapman, JC, Hose, GC & Lim, RP 2013, 'Assessing The Chronic Toxicity Of Atrazine, Permethrin, And Chlorothalonil To The Cladoceran Ceriodaphnia Cf. Dubia In Laboratory And Natural River Water', Archives Of Environmental Contamination And Toxicology, vol. 64, no. 3, pp. 419-426.View/Download from: Publisher's site
The majority of ecotoxicological data are generated from standard laboratory-based experiments with organisms exposed in nonflowing systems using highly purified water, which contains very low amounts of dissolved organic matter and suspended particulates. However, such experimental conditions are not ecologically relevant. Thus, there is a need to develop more realistic approaches to determining toxicity, including both lethal and sublethal effects. This research provides information on the effect of natural water constituents, such as suspended particulates and dissolved organic matter, in river water (RW) on the chronic toxicity (7-day reproductive impairment) of the pesticides atrazine, chlorothalonil, and permethrin to the freshwater cladoceran Ceriodaphnia cf. dubia. Standard bioassays were conducted under standard laboratory and more environmentally realistic conditions (using RW). The 7-day IC25 (reproduction impairment) values of atrazine, chlorothalonil, and permethrin to C. cf. dubia ranged from 862.4 to >1000, 51.3 to 66.4, and 0.19 to 0.23 µg/L, respectively. Using the Globally Harmonized System of Classification and Labelling of Chemicals, atrazine is classified as moderately to highly toxic, whereas permethrin and chlorothalonil were both highly toxic. The presence of dissolved organic matter and suspended particles in natural RW did not significantly (p > 0.05) change the toxicity of any of the pesticides to C. cf. dubia compared with that tested in laboratory water (LW). For the tested pesticides, toxicity testing in LW provided an adequate estimate of the hazard posed.