Johnstone River Catchment Research Articles

Soil organic matter and geochemical characteristics shape microbial community composition and structure across different land uses in an Australian wet tropical catchment

AbstractSoil characteristics vary across land uses, and soil microbial communities are likely to respond to such variations. However, such responses are not well understood. In this study, we examined how specific changes in soil organic matter (SOM) and geochemical characteristics influenced the bacterial and fungal community composition and structure across land uses. Soil samples were collected from grazing, sugarcane, forest and banana land uses in the Johnstone River catchment (wet tropics), northeastern Australia. High‐throughput sequencing of 16S rRNA gene and ITS amplicons were employed to characterise soil bacterial and fungal communities, respectively. Bacterial and fungal α‐diversity did not differ across land uses, whereas strong shifts in their community composition and structure were evident. Patterns in microbial community composition were strongly (p < 0.01) associated with changes in soil total organic carbon and nitrogen (TOC and TN), TOC:TN ratio, hot‐water extractable organic carbon (HWEOC) and soil geochemical characteristics (e.g., pH, Co, Mn, K, Mg and P contents). Distinct bacterial community composition was observed in forest soils, while fungal communities were similar in banana and forest soils compared with sugarcane and grazing. Overall, our results showed that SOM characteristics were the major driver on structuring soil microbial communities across land uses, while soil bacterial communities were more sensitive to variations in SOM and geochemical characteristics compared with fungi. Results from this study have implications for developing more targeted management practices across different land uses to improve soil health and ecosystem function in a wet tropical area.

Tracing the sources of sediment and associated particulate nitrogen from different land uses in the Johnstone River catchment, Wet Tropics, north-eastern Australia

While the ecosystem of the Great Barrier Reef (GBR), north-eastern Australia, is being threatened by the elevated levels of sediments and nutrients discharged from adjacent coastal river systems, the source of these detrimental pollutants are not well understood. Here we used a combined isotopic (δ13C, δ15N) and geochemical (Zn, Pt and S) signatures and stable isotope analysis in R (SIAR) mixing model to estimate the contribution of different land uses to the sediment and associated particulate nitrogen delivered to the Johnstone River. Results showed that rainforest was the largest contributor of suspended and bed sediments in the river estuary (both 33.1%), followed by banana (26.7%, 20.4%), sugarcane (21.5%, 21.4%) and grazing (18.7%, 25.1%). However, bananas and sugarcane land uses had the highest contribution to sediments delivered to the coast per unit of area. This will help land managers to prioritise on-ground activities to improve water quality in the GBR lagoon.

Using an improved SWAT model to simulate hydrological responses to land use change: A case study of a catchment in tropical Australia

Land use change is one of the dominant driving factors of watershed hydrological change. Thus, hydrological responses to land use changes require detailed assessments to ensure sustainable management of both water resources and natural ecosystems. The Soil and Water Assessment Tool (SWAT) model has been widely used to simulate the impacts of land use change on water balance. However, the original SWAT model has poor performance in estimating the leaf area index (LAI) of different vegetation types for tropical areas. The objective of this study was to simulate the impact of different land use change scenarios (deforestation, afforestation and urbanization) on the water balance, using an improved SWAT model with vegetation growth calibrated from MODIS LAI data. The North Johnstone River catchment in wet tropical eastern Australia was selected as the case study area. Results showed that the modified SWAT model was able to reproduce smoothed MODIS LAI with NSE ≥ 0.59 (NSE < 0 for default SWAT), R2 ≥ 0.70 (R2 ≤ 0.66 for default SWAT), and |PBIAS| ≤ 2.5% (|PBIAS| ≥ 42% for default SWAT), and to predict monthly streamflow well with NSE ≥ 0.92 (NSE ≥ 0.90 for default SWAT), R2 ≥ 0.94 (R2 ≥ 0.90 for default SWAT). It is noted that SWAT-T had |PBIAS| ≤ 10% while |PBIAS| ≤ 5% for default SWAT. Land use change impacted all hydrological variables, with the impact on surface runoff being the most notable at yearly scale (8.9%, 5.7%, −9.5% and 15.9% for scenario 1, 2, 3 and 4, respectively). Absolute changes of surface runoff under land use change scenarios differed across months, with the most notable absolute change occurring during the wet season (December to May) (1.2 ~ 6.6 mm, 1.0 ~ 3.5 mm, −7.3 ~ -1.1 mm and 3.0 ~ 9.0 mm for scenario 1, 2, 3 and 4, respectively). Urbanization increased surface runoff (5.7% and 15.9% for scenario 2 and 4, respectively) and decreased lateral runoff (−0.7% and −1.3%) and groundwater (-0.9% and −3.5%), but produced no clear change in total runoff (0.2% and 0.2%), actual evapotranspiration (−0.3% and −0.3%), and soil water (0.5% and 0.7%) at the annual time scale. Furthermore, afforestation could decrease surface runoff (−9.5% for scenario 3) and soil water (−2.0%), increase evapotranspiration (1.7%), and lead to slight changes (absolute values ≤0.8%) in other hydrological variables at the annual time scale. A strong positive correlation (r ≥ 0.94) was observed between annual rainfall and total runoff for forest-evergreen, range-grasses, and urban land use. Forest-evergreen generally produced less total runoff than range-grasses and urban land use under conditions of the same rainfall, terrain slope, and soil texture. In addition, urban land use generally produced more surface runoff and less lateral runoff and groundwater than forest-evergreen and range-grasses under the same conditions. These results contribute important information for development of effective adaptation strategies and future policy plans for sustainable water management in tropical eastern Australia.

An Inexpensive and Simple Experimental Approach for the Estimation of Solute Import into Groundwater and Subsequent Export Using Inflow/Outflow Data

In agricultural catchments where groundwater (GW) base flow discharge contributes substantially towards stream flow, the information linking GW inflow/outflow with contaminant import/export is scarce. However, this information is essential to address aquatic ecosystem health hazard/risk associated with nitrate export and subsequent loading in sensitive surface water bodies (SWB). The objectives of this study were to assess the temporal dynamics of (i) rain water inflow/outflow behaviour in three agricultural catchments in the humid tropics of far-northeast Queensland of Australia, (ii) solute import via inflow and subsequent export in outflow, and (iii) the association between GW inflow/outflow and solute import/export. Approximately 71% of the average seasonal rainfall percolated (inflow) into the porous basaltic regolith of the Johnstone River Catchment (JRC) compared with 44% into the alluvial regolith in the Mulgrave River Catchment (MRC) and 29% into the metamorphic regolith in the Tully River Catchment (TRC), respectively. The outflows from the basaltic, alluvial, and metamorphic regoliths were 56%, 36%, and 55% of the inflows, respectively. The cumulative nitrate import per season was 25 k/ha in the JRC compared with 11 kg/ha in MRC and 34 kg/ha in TRC. The corresponding exports were 24 kg/ha, 8 kg/ha 26 kg/ha in JRC, MRC, and TRC, respectively. The total dissolved solute (TDS) exports were 82%, 77%, 75%, of the corresponding imports in JRC, MRC, and TRC, respectively. Simple correlations indicated that nitrate export was positively correlated with the outflow in each one of the regolith and similar trends were observed between inflow and import. The import/export mass balance for nitrate shows that 73% to 96% of the imports were exported during the same rainy season, suggesting the potential for nitrate associated ecosystem health hazard/risk in sensitive SWB receiving the outflows.

Soluble phosphate in fluctuating groundwater under cropping in the north-eastern wet tropics of Australia

Soluble reactive phosphorus (SP) present in groundwater (GW) is generally considered insignificant, and therefore of little consequence to the quality of waters receiving base-flow discharges. In this study we investigated whether: (i) significant quantities of SP were present in GW (GW-SP); (ii) potential existed for GW-SP to be exported to streams via base-flow discharge; and (iii) the exports are a health risk to ecosystems receiving base-flow discharges. Investigations were carried out at two sites in the Tully River Catchment (TRC) during three consecutive rainy seasons, and 24 wells in the Johnstone River Catchment (JRC) were also monitored during one rainy season, in the north-eastern wet tropics of Australia. In the TRC, the GW-SP varied temporally, within and between rainy seasons, from 2 to 158 μg P/L at Site 1 and from 3 to 31 μg P/L at Site 2. The temporal variations in GW-SP were driven by fluctuating water-table at Site 2, but no such trend was observed at Site 1. The SP in drain-water (DW-SP) varied temporally from 0.6 to 110 μg P/L at Site 1, compared with 2–83 μg P/L at Site 2. The positive association between DW-SP and GW-SP at Site 2 indicated an export of SP from GW to a drain via base-flow discharge. In the JRC, the GW-SP in the 24 wells varied temporally from 0 to 300 μg P/L with the means across the wells ranging from 5 to 190 μg P/L, with the variations driven by fluctuating water-tables. More than 50% of the GW-SP or DW-SP concentrations in TRC were significantly higher than the P trigger values, 2–5 μg P/L, proposed to sustain the health of aquatic ecosystems in this region; a similar result was observed in the JRC. Speciation analysis via filtering (i.e. P passing through a 0.45-μm filter) for selected GW samples indicated substantial quantities of soluble organic P in some wells, ranging from 5 to 89% (mean 38%) of the total soluble P (SP plus soluble organic P). Because the soluble organic P was not included in GW-SP determinations, the hazard/risk mentioned above is an underestimate. The GW-SP exported during rainy seasons, from both catchments, ranged from 0.16 to 0.43 kg P/ha. Our findings indicate there were significant quantities of SP and soluble organic P in GW, it was exported to streams, and there is a health risk to receiving surface water bodies.

Isolating the water quality responses of multiple land uses from stream monitoring data through model calibration

Summary Quantifying relationships between stream water quality and catchment land uses is a major goal of many water quality monitoring programs. This is a challenging task that is rarely achieved through simple analysis of raw data alone. Multiple regression analysis provides one approach, which despite significant limitations, can be successful when very large data sets are available and only annual estimates are required. However, regression techniques have limited application to sub-annual data sets. We present a new method for isolating the water quality responses of different land uses from monitoring data through hydrological model calibration, using a process of simultaneous calibration at several monitoring sites. In addition to model parameters, model algorithm complexity and the number of land-attribute groups are also used as calibration ‘parameters’. This helps increase model parameter uniqueness and model predictive certainty. We applied the technique to water quality data from the Johnstone River catchment (1602 km 2 ) in north-east Australia, using the HSPF model. The data comprised >4000 samples from over five years of monitoring at 16 sites, which drained sub-catchments of differing land area and proportions of each land use. Monitoring occurred at flow gauging sites during high stream flows, and regularly at all sites during non-event periods. Variables modelled included discharge, suspended sediment, and various forms of nitrogen and phosphorus. The calibration process aimed to maximise both goodness-of-fit and parameter sensitivity. We achieved a substantial simplification of HSPF algorithms without appreciable reduction in goodness-of-fit, by a combination of: fixing parameters, tying parameters, and introducing new, simpler equations. Two key calibration tools were reducing the number of land-use groups (by combining land uses) and tying parameters between the three flow paths modelled (surface flow, interflow and base flow). These in turn removed insensitive parameters, increased the sensitivity of remaining parameters, and increased model predictive power. For calibration of suspended sediment, we found our conceptual model was too complex for the information content of the data, so it was necessary to group certain land uses and simplify algorithms in HSPF. In contrast, for nitrate, our conceptual model was too simple, with successful calibration requiring a finer resolution of land use in the catchment. A major advantage of our technique is that it can isolate land-use effects from stream monitoring data on a modelling time step that is unachievable by regression analysis, with a sensitivity that enables detection of relatively small differences in time and/or space. The technique also enhances confidence in estimates, it identifies ‘sensitive’ and ‘insensitive’ parameters and processes, and it provides a robust calibration by reducing the parameter solution space. Further, by using a hydrological model the technique can account for spatial and temporal variation in land use and rainfall. It is also predictive, so it can be used to assess impacts of land-use-change scenarios within the catchment. Additionally, it can provide insights into the type and amount of data required to isolate land-use effects on different water quality parameters, which can be used to enhance the effectiveness and cost-efficiency of the monitoring program design.

Statistical characterization of impact of system variables on temporal dynamics of groundwater in highly weathered regoliths

AbstractIn situations where the water table fluctuates during the rainy season the characterization of the impact of system variables on the temporal dynamics of the groundwater (GW) is essential to improve the understanding at catchment or regional scale behaviour of GW. In this study the appropriateness of the statistical parameters; mean, median, the 80th percentile (PC80), coefficient of variation (CV), correlation coefficient (r), and multiple regression models were assessed to characterize the impact of system variables on the temporal dynamics of hydraulic head relative to ground surface (HH) during rainy seasons. The study was conducted from 1999 to 2003 in the wet tropical Johnstone River catchment (JRC) in north‐east Queensland, Australia. Piezometer wells were installed at 32 sites under cropping to 5–90 m depth on different soil types, landscape positions, and varying proximity to surface water bodies (i.e. four system variables). The HH was measured, at least at 10–15 day intervals during 1–5 consecutive rainy seasons. The HH in the 32 wells fluctuated throughout each of the five rainy seasons. The mean HH averaged over the seasons ranged from 1·1 to 17·2 m across the wells, the median from 0·9 to 17·3 m, and the PC80 from 0·3 to 16·1 m. The temporal behaviour of HH characterization by mean of means of HH, the mean of medians of HH, and the mean of PC80 of HH, indicated the HH can be classified to belong to three different groups for each one of these parameters. The impact of the system variables on temporal dynamics, explored using multiple regression procedure, indicated that the model for median was marginally better than mean. The CV was found to be most appropriate parameter to characterize the impact of GW system variable (aquifer type), a component of the system variables, on temporal dynamics. The interactions of GW (i) belonging to different GW system and (ii) at shoulder with footslope in a landscape were best characterized by simple linear correlations. Copyright © 2007 John Wiley &amp; Sons, Ltd.

Chloride as a signature indicator of soil textural and hydrologic stratigraphies in variable charge deep profiles

AbstractSoil properties that influence water movement through profiles are important for determining flow paths, reactions between soil and solute, and the ultimate destination of solutes. This is particularly important in high rainfall environments. For highly weathered deep profiles, we hypothesize that abrupt changes in the distribution of the quotient [QT = (silt + sand)/clay] reflect the boundaries between textural units or textural (TS) and hydrologic (HS) stratigraphies. As a result, QT can be used as a parameter to characterize TS and as a surrogate for HS. Secondly, we propose that if chloride distributions were correlated with QT, under non‐limiting anion exchange, then chloride distributions can be used as a signature indicator of TS and HS. Soil cores to a depth of 12·5 m were taken from 16 locations in the wet tropical Johnstone River catchment of northeast Queensland, Australia. The cores belong to nine variable charge soil types and were under sugarcane (Saccharum officinarum‐S) production, which included the use of potassium chloride, for several decades. The cores were segmented at 1 m depth increments and subsamples were analysed for chloride, pH, soil water content (θ), clay, silt and sand contents. Selected bores were capped to serve as piezometers to monitor groundwater dynamics. Depth incremented QT, θ and chloride correlated, each individually, significantly with the corresponding profile depth increments, indicating the presence of textural, hydrologic and chloride gradients in profiles. However, rapid increases in QT down the profile indicated abrupt changes in TS, suggesting that QT can be used as a parameter to characterize TS and as a surrogate for HS. Abrupt changes in chloride distributions were similar to QT, suggesting that chloride distributions can be used as a signature indicator of QT (TS) and HS. Groundwater data indicated that chloride distributions depended, at least partially, on groundwater dynamics, providing further support to our hypothesis that chloride distribution can be used as a signature indicator of HS. Copyright © 2005 John Wiley &amp; Sons, Ltd.

Simulated rainwater effects on anion exchange capacity and nitrate retention in Ferrosols

Nitrate (NO3) accumulations (up to 1880 kg NO3-N/ha for a 12-m profile) in the soils of the Johnstone River catchment (JRC) may pose a serious environmental threat to the Great Barrier Reef lagoon if the NO3 were released. The leaching of artificial rainwater through repacked soil columns was investigated to determine the effect of low NO3/low ionic strength inputs on the NO3 chemistry of the JRC profiles. Repacked soil columns were used to simulate the 11.5-m profiles, and the soil solution anion and cation concentrations were monitored at 10 points throughout the soil column. As the rainwater was applied, NO3 leached down the profile, with substantial quantities exiting the columns. Anion exchange was discounted as the major mechanism of NO3 release due to the substantial net loss of anions from the system (up to 2740 kg NO3-N/ha over the experimental period). As the soils were dominated by variable charge minerals, the effect of changing pH and ionic strength on the surface charge density was investigated in relation to the release of NO3 from the exchange. It was concluded that the equilibration of the soil solution with the low ionic strength rainwater solution resulted in a lessening of both the positive and negative surface charge. Nitrate was released into the soil solution and subsequently leached due to the lessening of the positive surface charge. Loss of NO3 from the soil profile was slow, with equivalent field release times estimated to be tens of years. Although annual release rates were high in absolute terms (up to 175 kg NO3-N/ha.year), they are only slightly greater than the current loss rates from fertilised sugarcane production (up to 50 kg NO3-N/ha.year). In addition to this, the large-scale release of NO3 from the accumulations will only occur until a new equilibrium is established with the input rainwater solution.

The effect of ionic strength variation and anion competition on the development of nitrate accumulations in variable charge subsoils

The leaching of N fertilisers has led to the formation of nitrate (NO3) accumulations in deep subsoils (&gt;5 m depth) of the Johnstone River catchment. This paper outlines the chemical mechanism by which these NO3 accumulations are formed and maintained. This was achieved via a series of column experiments designed to investigate NO3 leaching in relation to the soil charge chemistry and the competition of anions for exchange sites. The presence of variable charge minerals has led to the formation positive surface charge within these profiles. An increase in the soil solution ionic strength accompanying the fertiliser leaching front acts to increase the positive (and negative) charge density, thus providing adsorption sites for NO3. A decrease in the soil solution ionic strength occurs after the fertiliser pulse moves past a point in the profile, due to dilution with incoming rainwater. Nitrate is then released from the exchange back into the soil solution, thus buffering the decrease in the soil solution ionic strength. Since NO3 was adsorbed throughout the profile in this experiment it does not effectively explain the situation occurring in the field. Previous observations of the sulfate (SO4) profile distribution indicated that large SO4 accumulations in the upper profile may influence the NO3 distribution through competition for adsorption sites. A subsequent experiment investigating the effect of SO4 additions on NO3 leaching showed that NO3 adsorption was minimal in the upper profile. Adsorption of NO3 did occur, though only in the region of the profile where SO4 occupancy was low, i.e. in the lower profile. Therefore, the formation of the NO3 accumulations is dependent on the variable charge mineralogy, the variation of charge density with soil solution ionic strength, and the effects of SO4 competition for adsorption sites.

Assessment of variables controlling nitrate dynamics in groundwater: Is it a threat to surface aquatic ecosystems?

The impact of fertilised cropping on nitrate-N dynamics in groundwater (GW) was assessed in a catchment from piezometers installed: (i) to different depths, (ii) in different soil types, (iii) on different positions on landscape, and (iv) compared with the Australian and New Zealand Environmental and Conservation Council guideline values provided for different aquatic ecosystems. The GW and NO 3-N concentration dynamics were monitored in 39 piezometer wells, installed to 5–90 m depth, under fertilized sugarcane ( Saccharum officinarum-S) in the Johnstone River Catchment, Australia, from 1999 January through September 2002. The median nitrate-N concentration ranged from 14 to 1511 μg L −1, and the 80th percentile from 0 to 1341 μg L −1. In 34 out of the 39 piezometer wells the 80th percentile or 80% of the nitrate-N values were higher than 30 μg L −1, which is the maximum trigger value provided in the ANZECC table for sustainable health of different aquatic ecosystems. Nitrate-N concentration decreased with increasing well depth, increasing depth of water in wells, and with decreasing relief on landscape. Nitrate-N was higher in alluvial soil profiles than on those formed in-situ. Nitrate-N increased with increasing rainfall at the beginning of the rainy season, fluctuated during the peak rainy period, and then decreased when the rain ceased. The rapid decrease in GW after the rains ceased suggested potential existed for nitrate-N to be discharged as lateral-flow into streams. This may contribute towards the deterioration in the health of down-stream aquatic ecosystems.

Impact of pre-existing sulphate on retention of imported chloride and nitrate in variable charge soil profiles

In variable charge soils, anion retention and accumulation through adsorption at exchange sites is a competitive process. The objectives of this study in the wet tropics of far north Queensland were to investigate (i) whether the pre-existing high sulphate in variable charge soils had any impact on the retention of chloride and nitrate, derived mostly from the applied fertilizer; and (ii) whether chloride competed with nitrate during the adsorption processes. Soil cores up to 12.5 m depth were taken from seven sites, representing four soil types, in the Johnstone River Catchment. Six of these sites had been under sugarcane ( Saccharum officinarum-S) cultivation for at least 50 years and one was an undisturbed rainforest. The cores were segmented at 1.0 m depth increments, and subsamples were analysed for nitrate-N, cation (CEC)- and anion-exchange capacities (AEC), pH, exchangeable cations (Ca, Mg, K, Na), soil organic C (SOC), electrical conductivity (EC), sulphate-S, and chloride. Sulphate-S load in 1–12 m depth under cropping ranged from 9.4 to 73.9 t ha −1 (mean=40 t ha −1) compared with 74.4 t ha −1 in the rainforest. Chloride load under cropping ranged from 1.5 to 9.6 t ha −1 (mean=4.9 t ha −1) compared to 0.9 t ha −1 in the rainforest, and the nitrate-N load from 113 to 2760 kg ha −1 (mean=910 kg ha −1) under cropping compared to 12 kg ha −1 in the rainforest. Regardless of the soil type, the total chloride or nitrate-N input in fertilisers was 7.5 t ha −1, during the last 50 years. Sulphate-S distribution in soil profiles decreased with depth at >2 m, whereas bulges of chloride or nitrate-N were observed at depths >2 m. This suggests that chloride or nitrate adsorption and retention increased with decreasing sulphate dominance. Abrupt decreases in equivalent fraction of sulphate (EFSO 4), at depths >2 m, were accompanied by rapid increases in equivalent fraction of chloride (EFCl), followed by nitrate (EFNO 3). The stepwise regression for EFCl and EFNO 3 indicated that nitrate retention was reduced by the pre-existing sulphate and imported chloride, whereas only sulphate reduced chloride adsorption. The results indicate that chloride and nitrate adsorption and retention occurred, in the order chloride>nitrate, in soils containing large amounts of sulphate under approximately similar total inputs of N- and Cl-fertilisers.

Nitrate Dynamics in Shallow Groundwater and the Potential for Transport to Off-Site Water Bodies

Large quantities of the nitrate leaching below the crop root-zone, particularly during the wet season, in the tropical Far North Queensland (FNQ) of Australia, may be entering off and on-site the water bodies. The objectives of this study were to (i) provide quantitative information on NO3-N in the shallow fluctuating groundwater (GW) that develops during the rainy season (January through May) in the Johnstone River Catchment (JRC) of FNQ and (ii) determine whether this NO3-N is potentially transportable to creeks/streams. The NO3-N concentration and GW table heights were monitored, at least at weekly intervals, in 6 piezometers, installed to 8.5–12.0 m depth in 6 different soil types under fertilized sugarcane (Saccharum Officinarum-S) in the JRC during the 1999 rainy season.Depending on the location of piezometers on the landscape and time of water sampling, the GW table fluctuated between from 1.5 to 11.5 m abovethe piezometer bottom. The NO3-N concentration in the fluctuating GW also showed spatio-temporal dynamics and it ranged from 0.60 to 3.70 mg L-1. The NO3-N adsorbed at anion exchanges sites, up to 10 m depth, ranged from 154 to 3956 kg ha-1, compared with 21 kgha-1 under rainforest. In the fluctuating GW, the NO3-N concentration increased with increasing GW table height and the NO3-N adsorbed at anion exchange sites (R2 = 0.96). The NO3-N load in the GW ranged from 40 to 110 kg ha-1 and it increased with increasing GW table and GW NO3-N concentration. The estimated N-load in the GW that was discharged into creeks/streams when the GW receded ranged from 21 to 81 kg ha-1. The results provide evidence that a(i) a major proportion of the NO3-N that was leaching below the sugarcane root-zone entered the shallow GW that developed during the rainy season, and (ii) a significant proportion of the NO3-N inthe GW was transported to creeks/streams when the GW table receded.

Nitrate retention under sugarcane in wet tropical Queensland deep soil profiles

Nitrate leaching below the crop root-zone in variable charge soils may be adsorbed at anion exchange sites, thereby temporarily reducing the risk of contamination of water bodies. The objectives of this study were (i) to investigate whether nitrate adsorption, accumulation, and retention in the Johnstone River Catchment of Far North Queensland wet tropics is widespread; (ii) to assess the capacity of soil in the Johnstone River Catchment to retain nitrate; and (iii) to deduce the consequences of nitrate adsorption/desorption on contamination of water bodies. Soil cores ranging from 8 to 12.5 m depth were taken from 28 sites across the catchment, representing 9 Ferrosol soil types under sugarcane (Saccharum officinarum-S) cultivation for at least 50 years and from rainforest. The cores were segmented at 0.5-m depth increments and subsamples were analysed for nitrate-N, cation and anion exchange capacities, pH, exchangeable cations (Ca, Mg, K, Na), soil organic C, electrical conductivity, sulfate-S, and chloride. Nitrate-N concentration under sugarcane ranged from 0 to 72.5 mg/kg, compared with 0 to 0.31 mg/kg under rainforest, both Pin Gin soils. The average N load in 1–12 m depth across 19 highly oxidic profiles of the Pin Gin soil series was 1550 kg/ha, compared with 185 kg/ha under 8 non-Pin Gin soils and 11 kg/ha in rainforest on a Pin Gin soil. Most of the nitrate retention was observed at depth of 2–12 m, particularly at 4–10 m, indicating that the accumulation was well below the crop root-zone. The average maximum potential nitrate retention capacity was 10.8 t/ha for the Pin Gin and 4.7 t/ha for the non-Pin Gin soil. Compared with the current N load, the soils still possess a large capacity to adsorb and retain nitrate in profiles. Retention of large quantities of the leached nitrate deep in most of the profiles has reduced the risk of contamination of water bodies. However, computations show that substantial quantities of the nitrate leached below the root-zone were not adsorbed and remain unaccounted for. This unaccounted nitrate might have entered both on- and off-site water bodies and/or have been denitrified.

A decision support process to compare Riparian revegetation options in Scheu Creek catchment in North Queensland

While riparian vegetation can play a major role in protecting land, water and natural habitat in catchments, there are high costs associated with tree planting and establishment and in diverting land from cropping. The distribution of costs and benefits of riparian revegetation creates conflicts in the objectives of various stakeholder groups. Multicriteria analysis provides an appropriate tool to evaluate alternative riparian revegetation options, and to accommodate the conflicting views of various stakeholder groups. This paper discusses an application of multicriteria analysis in an evaluation of riparian revegetation policy options for Scheu Creek, a small sub-catchment in the Johnstone River catchment in north Queensland, Australia. Clear differences are found in the rankings of revegetation options for different stakeholder groups with respect to environmental, social and economic impacts. Implementation of a revegetation option will involve considerable cost for landholders for the benefits of society. Queensland legislation does not provide a means to require farmers to implement riparian revegetation, hence the need for subsidies, tax incentives and moral suasion.

Integrated Catchment Management in northern Australia: From concept to implementation

In 1990, the Queensland Government initiated an Integrated Catchment Management (ICM) program in response to community concerns about the sustainability of the states' natural resources. This paper outlines the characteristics of this new policy approach and reviews the progress of ICM implementation in the Johnstone River catchment (JRC) on the wet tropical coast (WTC) of Queensland. Conceptual and process aspects of ICM are detailed and the technical, economic and institutional environment in which ICM operates in the JRC are discussed. Mechanisms are presented to facilitate the implementation of the institutional and individual change required to translate the ICM philosophy and its associated planning activities into meaningful outcomes for stakeholders.