The importance of spatiotemporal variability in irrigation inputs for hydrological modelling of irrigated catchments

Irrigation contributes substantially to the water balance and environmental condition of many agriculturally productive catchments. This study focuses on the representation of spatio‐temporal variability of irrigation depths in irrigation schedule models. Irrigation variability arises due to differences in farmers' irrigation practices, yet its effects on distributed hydrological predictions used to inform management decisions are currently poorly understood. Using a case study of the Barr Creek catchment in the Murray Darling Basin, Australia, we systematically compare four irrigation schedule models, including uniform vs variable in space, and continuous‐time vs event‐based representations. We evaluate simulated irrigation at hydrological response unit and catchment scales, and demonstrate the impact of irrigation schedules on the simulations of streamflow, evapotranspiration and potential recharge obtained using the Soil and Water Assessment Tool (SWAT). A new spatially‐variable event‐based irrigation schedule model is developed. When used to provide irrigation inputs to SWAT, this new model: (i) reduces the over‐estimation of actual evapotranspiration that occurs with spatially‐uniform continuous‐time irrigation assumptions (biases reduced from ∼40% to ∼2%) and (ii) better reproduces the fast streamflow response to rainfall events compared to spatially‐uniform event‐based irrigation assumptions (seasonally‐adjusted Nash‐Sutcliffe Efficiency improves from 0.15 to 0.56). The stochastic nature of the new model allows representing irrigation schedule uncertainty, which improves the characterization of uncertainty in simulated catchment streamflow and can be used for uncertainty decomposition. More generally, this study highlights the importance of spatio‐temporal variability of inputs to distributed hydrological models and the importance of using multi‐variate response data to test and refine environmental models.David McInerney, Mark Thyer, Dmitri Kavetski, Faith Githui, Thabo Thayalakumaran, Min Liu, George Kuczer

Treatment of meat processing wastewater for carbon, nitrogen and phosphorus removal in a sequencing batch reactor : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Process & Environmental Technology at Massey University

The typical New Zealand meat processing industry wastewater was treated by a laboratory scale Sequencing Batch Reactor (SBR) to determine an effective operating cycle for biological carbon, nitrogen and phosphorus removal. The Activated Sludge Model No. 1 and Model No. 2 with modifications were used to simulate the treatment of meat processing wastewater using the SBR. The average values of main pollution parameters of the wastewater were characterised as 1390 mg total COD L-1, 755 mg soluble COD L-1, 75 mg L-1 NH3 - N, 145 mg L-1 TKN and 34 mg L-1 TP. The readily biodegradable COD (RBCOD) accounts for 15 - 18% of the total COD, while the inert soluble and particulate portion were 4% each. In order to establish an effective operating cycle for the simultaneous removal of nutrients and organic carbon, different dissolved oxygen (DO) concentrations in the mixed liquor, duration of operating phases and hydraulic retention time (HRT) of a 6 h cycle were tested. The most effective cycle consisted of seven phases. The first two hours of the anaerobic period was followed by the aerobic and anoxic periods. The first aerobic period was maintained at a DO concentration of 0.5 ±0.25 mg L-1 for 1 h, the second aerobic period for 1 h at a DO concentration of 3.75 ±0.25 mg L-1 and the third aerobic period for half an hour at 0.5 ±0.25 mg L-1 DO concentration. A half an hour anoxic period followed the first aerobic period. A settling period of 0.75 h followed the third aerobic period. The last quarter of an hour was for decanting and idling. The solids retention time (SRT) was 15 d, while the HRT was 2.5 d. Greater than 99% removal of biodegradable soluble COD, NH3 - N and PO4 - P was achieved in the effective operating cycle where the TN and TP in the wastewater were reduced to 10 mg L-1 and 1.0 mg L-1, respectively. In addition the soluble COD was reduced to 98 mg L-1. The key kinetic and stoichiometric parameters for ASM 1 and ASM 2 models were determined using batch tests. The heterotrophic maximum specific growth rate, yield coefficient and the half saturation constant were 2.0 d-1, 0.63 mg cell COD (mg COD)-1 and 8 mg L-1 respectively. The maximum specific growth rate of autotrophs was 0.65 - 0.80 d-1. The anaerobic phosphorus removal stoichiometric coefficients were also determined in batch tests. During the anaerobic period, when 1 g of acetate COD was initially present, 1.48 g of PHA COD was stored while 0.48 g of P was released. The batch trials conducted using acetate to assess the influence of Mg2+ in P uptake showed that the Mg2+ could limit the P uptake and the uptake rate could be represented by Monod type kinetics. In the Monod kinetic expression the Mg2+ half saturation constant was found to be 4.7 mg L-1 The molar ratio of Mg2+ with P was 0.21 during the anaerobic period, and 0.33 during the aerobic period. The SBR performance was modelled using ASM 1 and ASM 2 models after the addition of more processes in these models. Ammonification of the soluble organic N process rate was modified in the ASM 1 model. Similarly it was necessary to add anoxic P uptake and anoxic growth processes involving PHA of Bio-P bacteria in the ASM 2 model. Glycogen storage and glycogen lysis processes of Bio-P bacteria were added in the ASM 2 model to understand the involvement of glycogen in P removal. Also a modification was performed to the storage process of poly-P in the ASM 2 model to account for potential Mg2+ limitation in meat processing wastewater treatment for P removal. During the settling period anoxic hydrolysis was assumed to be negligible. The calibrated ASM 1 and ASM 2 models in general well simulated the effluent NH3 - N, NO3 - N and PO4- P of SBR cycles carried out in distinctly different periods of time and in different batch tests. As the calibrated modified ASM 2 model was able to predict the performance of an SBR cycle conducted over a time period of three months, it was used to identify the most promising treatment strategies of the SBR performance. Variation in duration of feed cycle during the first non-aerated mixed period did not affect the effluent NO3 - N, NH3 - N and PO4 - P concentrations significantly. DO concentration of 3.75 mg L-1 during the third aerobic period instead of 0.5 mg L-1 increased the effluent NO3 - N and PO4 - P concentrations. The simulations confirmed that the operating conditions identified in a 6-h cycle period for the simultaneous organic carbon and nutrient removal are effective

EDTA-enhanced transport of copper from contaminated soil and its implications : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University

An understanding of the interacting physical and chemical processes involved is necessary for efficient and environmentally responsible remediation of copper-contaminated soils through EDTA-enhanced mobilisation, using either ex situ or in situ methods. In order to study these processes, leaching experiments were performed on repacked columns and intact cores, with various initial and boundary conditions, in two contrasting soils containing varying amounts of copper. One soil was an alluvial Manawatu fine sandy loam, which was low in organic matter, and the other a volcanic Opotiki sandy loam with a higher organic matter content. In both soils, the EDTA moved without any observable adsorption when the soil pH was above 5.0. But, uncontaminated Opotiki soil with a pH of 4.5, did adsorb EDTA to some extent. Leaching with an excess of 0.01 M EDTA, extracted all but 40 mg kg-1 of the copper that was initially present in the repacked Manawatu soil and all but 90 mg kg-1 of the copper from the Opotiki repacked soil. In the intact Opotiki soil cores the EDTA reduced the copper concentration in the top 25 mm of the intact core from 240 to 80 mg kg-1. EDTA not only leached the copper from the soil, but also a substantial amount of iron. Opotiki soil with pulses of EDTA left in it for up to a month before leaching showed a time-dependent drop in the amount of copper leached, and a corresponding increase in the amount of iron leached. Increased EDTA residence time in the Manawatu soil prior to leaching in general also showed a time-dependent increase in iron leached. With increasing EDTA residence time in the soil, the mass of copper leached dropped markedly in the low-Cu Manawatu soil. However, the copper remained in the soil solution, and so prone to leaching, for at least a month in the medium and high-Cu Manawatu soils. These results are consistent with CuEDTA2- being gradually transformed to the more stable Fe(III)EDTA- and Cu2+ in all cases. Copper contaminated Opotiki repacked soil columns and intact cores growing the grass Agrostis tenuis on were used to investigate the relative importance of plant uptake and leaching of copper. Application of 1800 µmol of EDTA to 0.9 kg of the contaminated soil in a repacked column increased the leaf copper concentration from 30 µg g-1 to 300 µg g-1. The same amount of EDTA applied to 1.0 kg of soil in the intact cores, increased the herbage copper concentration to 60 µg g-1. Leaching the columns and cores with water about a month after the EDTA application removed 25 to 169 times more copper than was taken up by the herbage. The convection dispersion equation (CDE), coupled with a source/sink term accounting for time-dependent reactions taking chemical species into or out of solution, was used to model the EDTA-enhanced transport of copper in contaminated soils. In general, the model successfully described the copper concentration in the leachate and soil, despite the quite different amounts and concentrations of EDTA applied, and the varying lengths of time it was left in the soil before leaching. However, the values for the key parameters had to be adjusted appropriately, with faster rate constants for the Manawatu soil than the Opotiki soil. The observed differences in behavior between the repacked and intact Opotiki soil could be simulated by increasing the dispersivity from 3 to 23 mm, while leaving unchanged the parameters describing the chemistry. The results on the kinetics of the EDTA and the soil copper reaction, and for the stability of the CuEDTA2- and its interaction with physical processes, suggest that in situ remediation of copper contaminated soils is possible. However, the applied EDTA should be leached immediately or within few days. It would also require that the residence time of soil water moving through the profile to the water table was in excess of a month. EDTA-enhanced phytoremediation of copper might be possible if leaching can be avoided. If drainage occurs the copper moving below the root zone is likely to be at least an order of magnitude greater than that taken up by the vegetation

Detecting changes in sediment sources in drought periods: the Latrobe River case study

The transfer of sediments through the landscape (sediment connectivity) depends on hydrological conditions. This study aimed at assessing changes in sediment sources engendered under extreme drought. A sediment budget model that considered hillslope sediment connectivity was applied to the Latrobe River catchment (South-east Australia) in a relatively normal period (1990-1996) followed by part of the ‘Millennium Drought’ (1997-2005). Bayesian inference was applied to optimize monthly streamflow and calibrate sediment parameters against mean annual specific sediment yields at ten monitoring stations. In 1990-1996, assessed sediment yield at the outlet was 68 kt/y; 60% of sediments originated from net hillslope erosion and 40% from streambank erosion. In 1997-2005, sediment yield decreased to 13kt/y, 27% from net hillslope erosion against 65% from streambank erosion. During the drought, both hillslope gross erosion and hillslope sediment connectivity decreased dramatically. Streambank protection is of the utmost importance under all hydrologic conditions and especially during drought periods.JRC.D.2-Water and Marine Resource

Nitrate and ferrous iron concentrations in the lower Burdekin aquifers: assessing denitrification potential

The lower Burdekin is one of Australia’s premier irrigation districts with more than 80,000 ha of sugarcane and other crops. Because it is located adjacent to the Great Barrier Reef Lagoon, there is strong interest in understanding the fate of nitrogen applied as fertiliser. Natural denitrification is increasingly recognised for its ability to reduce nitrate concentrations in groundwater and we therefore analysed water samples for a range of constituents (nitrate, ferrous iron, dissolved oxygen, redox potential, pH) from 57 monitoring bores to investigate the denitrification potential of the lower Burdekin aquifers. Nitrate concentrations ranged from <0.1 to 14.4 mg/L NO3-N (three times the ANZECC environmental standard of 5 mg/L). Ferrous concentration varied from 1 to 360 mg/L, dissolved oxygen was < 2 mg/L, redox potential varied from -120 to +235 mV, and pH ranged from 5.9 to 7.6. Elevated nitrate levels were observed in 16% of the bores located mostly in the Home Hill area. These areas also had low ferrous levels. High ferrous levels were found mostly in the Ayr area and at shallow depths. The data in general showed an inverse relationship between nitrate and iron, and between nitrate and ammonium. Furthermore, undetectable amounts of nitrate were measured in the nested bores located along the coast. These geochemical conditions favour the presence of ferrous iron and a reduced environment conducive to denitrification. These results suggest that denitrification is one of the mechanisms involved in reducing the amount of nitrate in the lower Burdekin aquifers and hence reducing the potential for nitrate to move from the groundwater into the near-shore marine environment