Grass or Trees? Performance of riparian buffers under natural rainfall conditions, Australia

Riparian vegetation can trap sediment and nutrients derived from hillslopes. Most research into the effectiveness of riparian buffers has been experimental and little quantitative data exists on performance under natural field conditions. This study reports on grass and tree buffer performance under natural rainfall conditions in two contrasting Australian environments. Buffers receiving runoff from hillslopes cropped with bananas were monitored over a 4-year period in the wet topics of Far North Queensland (FNQ). Runoff, bedload and suspended loads were measured leaving the crop and leaving 15 m wide dense grass and remnant rainforest riparian buffers. The grass buffer was able to trap \u3e80% of incoming bedload and between 30 and 50% of the suspended sediment and nutrient loads. An adjacent rainforest buffer acted as a temporary store of bedload, and a source area for suspended material. Grass and plantation Eucalyptus globulus buffers receiving runoff from grazed pasture were monitored over a 4-year period in a Mediterranean environment of SW Western Australia. Subsurface flow dominated nutrient and sediment transport in this location. A key result was the seasonal difference between the grass and E. globulus buffers. Sediment and nutrient transport occurred throughout the year in the E. globulus buffer, but only in the winter in the grass buffer. Half the annual loads moving within the E. globulus buffer were transported during intense summer storms. This study demonstrates the benefits of grass buffers, particularly on sloping tropical cropped land and identifies limitations on the effectiveness of tree buffers, although these may have ecological benefits

Before and after riparian management: Sediment and nutrient exports from a small agricultural catchment, Western Australia

Riparian vegetation can trap sediment and nutrients coming from hillslopes and reduce stream bank erosion. This study presents results from a 10 year stream monitoring program in a small agricultural catchment near Albany, Western Australia. In 1996, a 1.6 km stream reach was fenced, planted with eucalyptus species and managed separately from the adjacent paddocks. Stream flow, nutrient and sediment concentration data were collected at the downstream end of the fenced riparian area between 1991 and 2000, so there are data for the “before” and “after” riparian management periods. Suspended sediment concentrations fell dramatically following riparian management; the average event mean concentration (EMC) dropped from 254 mg/l to 15.8 mg/l. Maximum suspended sediment concentrations dropped by an order of magnitude. As a result, sediment exports from the catchment reduced noticeably following riparian management, mainly due to reduced stream bank erosion. In contrast, riparian management had limited impact on nutrient exports. There was no detectable change in total phosphorus EMC, a 67% increase in filterable reactive phosphorus average EMC and a 37% decrease in average total nitrogen EMC between the before and after periods. This study demonstrates the benefits of riparian management in reducing stream bank erosion, and suggests that in this environment, with sandy soils with low phosphorus retention, there are limitations on the effectiveness of riparian management for reducing nutrient exports

Performance of grass and eucalyptus riparian buffers in a pasture catchment, Western Australia, part 2: water quality

Declining water quality on the south coast of Western Australia has been linked to current agricultural practices. Riparian buffers were identified as a tool available to farmers and catchment managers to achieve water quality improvements. This study compares 10 in wide regenerating grass and Eucalyptus globulus buffer performance. Surface and subsurface water quality were monitored over a 3-year period. Nutrient and sediment transport were both dominated by subsurface flow, in particular through the B-horizon. and this may seriously limit the surface-runoff-related functions of the riparian buffers. Riparian buffer trapping efficiencies were variable on an event basis and annual basis. The grass buffer reduced total phosphorus, filterable reactive phosphorus. total nitrogen and suspended sediment loads from surface runoff by 50 to 60%. The E. globulus buffer was not as effective. and total load reductions in surface runoff ranged between 10 and 40%. A key difference between the grass and E. globulus buffers was the seasonality of sediment and nutrient transport. Surface runoff. and therefore sediment and nutrient transport. occurred throughout the year in the E. globulus buffer. but only during the winter in the grass buffer. As a consequence of high summer nutrient and sediment concentrations. half the annual loads moving, via surface runoff pathways through the E. globulus buffer were transported during intense summer storm. This Study demonstrates that grass and E. globulus riparian buffers receiving runoff from pasture under natural rainfall can reduce sediment and nutrient loads from surface runoff. However, in this environment the B-horizon Subsurface flow is the dominant flowpath for nutrient transport through the riparian buffers, and this subsurface flow pathway carries contaminant loads at least three times greater than surface runoff. Copyright (c) 2006 John Wiley & Sons, Ltd. [References: 66

Grass or Trees? Performance of riparian buffers under natural rainfall conditions, Australia

Riparian vegetation can trap sediment and nutrients derived from hillslopes. Most research into the effectiveness of riparian buffers has been experimental and little quantitative data exists on performance under natural field conditions. This study reports on grass and tree buffer performance under natural rainfall conditions in two contrasting Australian environments. Buffers receiving runoff from hillslopes cropped with bananas were monitored over a 4-year period in the wet topics of Far North Queensland (FNQ). Runoff, bedload and suspended loads were measured leaving the crop and leaving 15 m wide dense grass and remnant rainforest riparian buffers. The grass buffer was able to trap \u3e80% of incoming bedload and between 30 and 50% of the suspended sediment and nutrient loads. An adjacent rainforest buffer acted as a temporary store of bedload, and a source area for suspended material. Grass and plantation Eucalyptus globulus buffers receiving runoff from grazed pasture were monitored over a 4-year period in a Mediterranean environment of SW Western Australia. Subsurface flow dominated nutrient and sediment transport in this location. A key result was the seasonal difference between the grass and E. globulus buffers. Sediment and nutrient transport occurred throughout the year in the E. globulus buffer, but only in the winter in the grass buffer. Half the annual loads moving within the E. globulus buffer were transported during intense summer storms. This study demonstrates the benefits of grass buffers, particularly on sloping tropical cropped land and identifies limitations on the effectiveness of tree buffers, although these may have ecological benefits

Performance of grass and eucalyptus riparian buffers in a pasture catchment, Western Australia, part 1: riparian hydrology

Rainfall takes many flowpaths to reach a stream. and the success of riparian buffers in Water quality management is significantly influenced by riparian hydrology. This paper presents results from hydrometric monitoring of riparian buffer hydrology in a pasture catchment. Runoff processes and riparian flowpaths were investigated on two planar hillslopes with regenerating grass and E. globulus buffers. Surface runoff and subsurface flows (A- and B-horizons) were measured for 3 years using surface runoff collectors. subsurface troughs and piezometers. Water volumes moving through the riparian buffers via the measured flowpaths Were ranked B-horizon \u3e\u3e surface runoff approximate to A-horizon. Runoff volumes through the B-horizon troughs were an order of magnitude greater than those recorded for the most productive surface runoff plots or the A-horizon troughs. Subsurface runoff and saturation-excess overland flow (SOF) were limited to the winter months, whereas infiltration-excess overland flow (IEOF) can Occur all year round during intense storms. Surface runoff was recorded on 33 occasions, mostly during winter (late May-early October). and total annual Surface runoff volumes collected by the 20 unconfined (2 in wide) runoff plots varied between \u3e 80 and \u3c 20 m(3). Subsurface flow only occurred in winter, and the 6 m wide B-horizon Subsurface troughs flowed above 11 s(-1) continuously. whereas the A-horizon troughs flowed infrequently (\u3c 6 days per year). In summer, surface runoff occurred as IEOF during intense storms in the E. globulus buffer, but not in the grass buffer. Observations suggest that surface crusting reduced the soil\u27s infiltration capacity in the E. globulus buffer. During winter, SOF and seepage were observed in both buffers, but subsurface flow through the B-horizon was the dominant flowpath. Key hydrologic differences between the grass and tree buffers are the generation of IEOF in the E. globulus buffer during intense summer storms. and the smaller subsurface runoff Volumes and fewer flow days in the E. globulus buffer. Low Surface runoff volumes are likely to limit the potential of these buffers to filter pollutants front Surface runoff. High subsurface flow volumes and saturated conductivities are also likely to limit the residence time of water in the subsurface domain. Based on their hydrologic performance, the key roles of riparian buffers in this landscape are likely to be displacing sediment and nutrient-generating activities away from streams and stabilizing channel morphology. Copyright (c) 2006 John Wiley & Sons, Ltd. [References: 61

Regional scale nutrient modelling: exports to the Great Barrier Reef World Heritage Area

Clearing of native vegetation and replacement with cropping and grazing systems has increased nutrient exports to the Great Barrier Reef (GBR) to a level many times the natural rate. We present a technique for modelling nutrient transport, based on material budgets of river systems, and use it to identify the patterns and sources of nutrients exported. The outputs of the model can then be used to help prioritise catchment areas and land uses for management and assess various management options. Hillslope erosion is the largest source of particulate nutrients because of its dominance as a sediment source and the higher nutrient concentrations on surface soils. Dissolved nutrient fractions contribute 30% of total nitrogen and 15% of total phosphorus inputs. Spatial patterns show the elevated dissolved inorganic nitrogen export in the wetter catchments, and the dominance of particulate N and P from soil erosion in coastal areas. This study has identified catchments with high levels of contribution to exports and targeting these should be a priority

Sources of sediment to the Great Barrier Reef World Heritage Area

To reduce sediment exports discharging to the Great Barrier Reef (GBR), it is essential to identify the sources of exported sediment. We used modelling of spatial sediment budgets (the SedNet model) to identify sources and deposition of sediment as it is transported through river networks. Catchments with high levels of land clearing, cattle grazing and cropping show the largest increases in sediment export compared with natural conditions. Hillslope erosion supplies 63% of sediment to the rivers. Gully erosion and riverbank erosion are lower sources of sediment at the GBR catchment scale, but they are important in some catchments. Overall, 70% of sediment exported from rivers comes from just 20% of the total catchment area, showing that much of the problem can be addressed in a relatively small area. This is a much more manageable problem than trying to reduce erosion across the entire GBR catchment. Areas of high contribution are all relatively close to the coast because of the high erosion and high sediment delivery potential

Before and after riparian management: Sediment and nutrient exports from a small agricultural catchment, Western Australia

Riparian vegetation can trap sediment and nutrients coming from hillslopes and reduce stream bank erosion. This study presents results from a 10 year stream monitoring program in a small agricultural catchment near Albany, Western Australia. In 1996, a 1.6 km stream reach was fenced, planted with eucalyptus species and managed separately from the adjacent paddocks. Stream flow, nutrient and sediment concentration data were collected at the downstream end of the fenced riparian area between 1991 and 2000, so there are data for the “before” and “after” riparian management periods. Suspended sediment concentrations fell dramatically following riparian management; the average event mean concentration (EMC) dropped from 254 mg/l to 15.8 mg/l. Maximum suspended sediment concentrations dropped by an order of magnitude. As a result, sediment exports from the catchment reduced noticeably following riparian management, mainly due to reduced stream bank erosion. In contrast, riparian management had limited impact on nutrient exports. There was no detectable change in total phosphorus EMC, a 67% increase in filterable reactive phosphorus average EMC and a 37% decrease in average total nitrogen EMC between the before and after periods. This study demonstrates the benefits of riparian management in reducing stream bank erosion, and suggests that in this environment, with sandy soils with low phosphorus retention, there are limitations on the effectiveness of riparian management for reducing nutrient exports

Sources of sediment and nutrient exports to the Great Barrier Reef

Only the abstract was published in the proceedings. There is no full text.Agricultural land uses on the Great Barrier Reef (GBR) catchment are causing an increase in pollutant loads discharging to the Great Barrier Reef World Heritage Area (GBRWHA). Research and monitoring have clearly established that changed land use activity on the catchment of the GBRWHA is directly contributing to an increase in the load of pollutants discharging to the area. Discharged pollutants are degrading GBR ecosystems, particularly those close to the coast. Pollutant loads are increasing and show no sign of reduction. Similar pollution has caused the decline of coastal ecosystems around the world. To begin to manage sediment and nutrient exports it is essential to identify the sources of sediment and nutrient that are exported to the coast. This is quite a different problem to mapping soil erosion and nutrient loss in the contributing catchments. The present study used the models, SedNet and its nutrient version ANNEX, calibrated using water quality data, to identify the sources. The sources that contribute to export at the coast were identified by modelling spatially distributed sediment and nutrient budgets in the contributing catchments. These budgets map the sources, sinks and transport of sediment and nutrients river link by river link, as it is transported to the coast. The modelling allows extrapolation into catchments and sub-catchments for which there is no water quality monitoring data, and allows us to predict where remedial measures with have the greatest ability to reduce future loads. Catchments with high levels of land clearing, beef grazing and/or fertilized cropping show the greatest increases in sediment and nutrient export. The modelling shows that soil erosion is the dominant process supplying 63 % of sediment to the rivers. Gully erosion and river bank erosion are relatively minor sources at the GBR catchment scale, although they are important in some catchments. Overall, 70 % of sediment exported to the coast comes from just 20 % of the total catchment area. Areas of high contribution are all relatively close to the coast. Targeting the areas with a disproportionately high level of contribution and large difference to natural contribution should be a priority as this will have the greatest effect on reducing sediment export to the coast. The spatial patterns of total N and P contribution to streams largely reflect the soil erosion predictions. Hillslope (soil) erosion is by far the largest source of particulate nutrients because of its dominance as a sediment source and the higher nutrient concentrations on surface soils. Gully and riverbank erosion make up less than 10% of the total nutrient sources. Our results predict that about 30 % of total nitrogen sources comes from dissolved forms in runoff, and about 15 % of phosphorus is derived from dissolved sources.PublishedNon Peer Reviewe

Sediment source changes over the last 250 years in a dry-tropical catchment, central Queensland, Australia

Rivers draining to the Great Barrier Reef are receiving increased attention with the realisation that European land use changes over the last not, vert, similar 150 years may have increased river sediment yields, and that these may have adversely affected the reef environment. Mitigation of the effects associated with such changes is only possible if information on the spatial provenance and dominant types of erosion is known. To date, very few field-based studies have attempted to provide this information. This study uses fallout radionuclide (137Cs and 210Pbex) and geochemical tracing of river bed and floodplain sediments to examine sources over the last not, vert, similar 250 years for Theresa Creek, a subcatchment of the Fitzroy River basin, central Queensland, Australia. A Monte Carlo style mixing model is used to predict the relative contribution of both the spatial (geological) sources and erosion types. The results indicate that sheetwash and rill erosion from cultivated basaltic land and channel erosion from non-basaltic parts of the catchment are currently contributing most sediment to the river system. Evidence indicates that the dominant form of channel erosion is gully headcut and sidewall erosion. Sheetwash and rill erosion from uncultivated land (i.e., grazed pasture/woodland) is a comparatively minor contributor of sediment to the river network. Analysis of the spatial provenance of floodplain core sediments, in conjunction with optical dating and 137Cs depth profile data, suggests that a phase of channel erosion was initiated in the late nineteenth century. With the development of land underlain by basalt in the mid-twentieth century the dominant source of erosion shifted to cultivated land, although improvements in land management practices have probably resulted in a decrease in sediment yield from cultivated areas in the later half of the twentieth century. On a basin-wide scale, because of the limited spatial extent of cultivation, channel sources are likely to be the largest contributor of sediment to the Fitzroy River. Accordingly, catchment management measures focused on reducing sediment delivery to the Great Barrier Reef should focus primarily on decreasing erosion from channel sources.No Full Tex