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1.
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.  相似文献   

2.
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.  相似文献   

3.
The suspended sediment yields of two adjacent, paired, catchments on blanket peat in mid-Wales were compared before and after preafforestation drainage works. Catchment A was ploughed whilst an adjacent catchment (B) was left unploughed. After eight months Catchment B was also ploughed. The ploughing strategy in both catchments was designed to minimize sediment loss. However, suspended sediment loss increased 2·5 times following ploughing in Catchment A, whilst no such increase occurred at this time in Catchment B. Subsequently, suspended sediment yields in Catchment B increased 4·8 times after it was ploughed. Organic sediment was lost mainly from furrow sides, and erosion pins showed maximum ground recession in summer, due to peat wastage. Summer desiccation prepared sediment for transport, and organic suspended sediment loads were highest in the autumn. Sediment loads were limited by vegetation colonization and some reduction in sediment loss was due to the presence of unploughed strips adjacent to stream courses.  相似文献   

4.
Hugh G. Smith 《水文研究》2008,22(16):3135-3148
Historically upland headwater catchments in south‐eastern Australia have undergone extensive gully erosion that has removed large amounts of sediment to lowlands. Recent research suggests these upland areas may continue to dominate fine sediment loads in lowland rivers. Improved understanding of sediment transfer through upland headwater catchments may have implications for interpreting downstream sediment supply. In this study a nested catchment design was utilized to examine suspended sediment yields and delivery from a small tributary sub‐catchment (1·64 km2) to the study catchment outlet (53·5 km2). Monitoring of suspended sediment concentration and discharge was undertaken for a period of nearly two years and used to estimate suspended sediment loads. Estimated total suspended sediment exports over the period of monitoring were 24·16 t from the sub‐catchment and 550·3 t from the catchment, which are generally less than previous reported small catchment yields in south‐eastern Australia. The extent of sediment delivery was examined using between‐site ratios of specific sediment yield per unit area and incised channel length. Sediment delivery was high under average rainfall conditions, but seasonally dependent. Both suspended sediment yields and the extent of delivery peaked over spring months, supplemented by remobilization of sediment stored during summer months in the main catchment channel. The findings of this study suggest much of the suspended sediment exported from small incised upland sub‐catchments (1–2 km2) may be delivered to downstream reaches under average rainfall conditions, which, in conjunction with the findings of previous research supports the potential importance of contributions from these areas to suspended sediment loads in lowland rivers during high flow periods. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

5.
Nitrogen and phosphorus concentrations were measured and exports were calculated in the subtropical Richmond River catchment between July 1994 and June 1996. A stratified sampling approach was adopted owing to the extreme and rapid changes in riverine discharge, which varied by up to 10 000 times over the study period. Nutrient concentrations were lowest during baseflow. During storm discharge, dissolve inorganic and organic and particulate nitrogen and phosphorus concentrations increased two‐ to five fold, and followed hysteresis patterns that were attributed to the integration and/or depletion of catchment nutrient sources during an event. Dissolved organic nitrogen and particulate phosphorus were the dominant nutrient forms. Land use and antecedent conditions had a large influence on nutrient concentrations and exports. During the 1995–96 year (slightly above the mean annual discharge) 96% of nitrogen and 98% of phosphorus loads were transported in less than 6% of the time. When averaged across the catchment, monthly riverine nutrient loads varied by up to 1061‐fold during the study and exports were approximately four‐fold greater during the second year relative to the first. The subtropical Richmond River catchment has greater intra‐ and potential interannual variability in nutrient loads and exports when compared with temperate catchments from other parts of the world. It is suggested that in tropical and subtropical Australian catchments with large intra‐ and interannual variation in discharge, the need for parameterizing the antecedent conditions, such as the degree of nutrient storage, may make it difficult to model spatial and temporal (short time‐scale) nutrient exports. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

6.
Degradation of coastal ecosystems in the Great Barrier Reef (GBR), Australia, has been linked with a decline in water quality from land-based runoff. This paper examines the reduction in current end-of-catchment loads required for total suspended solids (TSS) and dissolved inorganic nitrogen (DIN) to achieve GBR water quality guidelines. Based on first-order estimates of sustainable pollutant loads, current TSS and DIN loads would need to be reduced by approximately 7000ktons/y (41%) and 6000tons/y (38%), respectively. Next, these estimated reductions for TSS and DIN are compared with Reef Plan targets for anthropogenic sediment (-20% by 2020) and nitrogen (-50% by 2013) loads. If successful, these targets will accomplish approximately 40% of TSS and 92% of DIN load reductions required to achieve sustainable loads to the GBR lagoon. These first-order estimates elucidate the need to establish ecologically relevant targets for river pollutant loads to the GBR for management and policy.  相似文献   

7.
Development of the Great Barrier Reef (GBR) catchments in the last 150 years has increased the loads of suspended sediment, nutrients and pesticides ('pollutants') delivered to the GBR. The scale and type of development, the pollutants generated and the ecosystems offshore vary regionally. We analysed the relative risk of pollutants from agricultural land uses and identified the sources of these pollutants from different land uses for each region to develop priorities for management. The assessment showed the Wet Tropics and Mackay Whitsunday regions to be of relatively high risk dominated by sugarcane cultivation, contributing pesticide and dissolved inorganic nitrogen (DIN). The Burdekin and Fitzroy ranked medium-high risk dominated by grazing suspended sediment inputs for both, and additionally sugarcane DIN and pesticide inputs for the Burdekin. The Burnett Mary ranked medium risk, dominated by grazing and sugarcane. Cape York was not formally ranked but is considered to be low risk.  相似文献   

8.
Nutrient and suspended sediment concentrations were measured in the dry season and during the rising and falling stages of flood events in the Annan and Daintree rivers to estimate catchment exports. These flood events were also sampled along the salinity gradient in the estuary and nearshore shelf to quantify the modification of terrestrial sediment and nutrient loads as they pass through estuaries into the Great Barrier Reef lagoon. In the Daintree River TSS concentrations were found to increase between the catchment and the estuary plume. The source of TSS may have been scour of the estuarine channel or from land use in the catchment of the lower estuary. In the dry season nitrogen enters the Annan and Daintree estuaries predominantly in the form of PON and DON in roughly equal proportions. Nitrogen exports to the GBR are mostly in the form of DON. In the wet season the majority of nitrogen enters the estuaries as DON and leaves as PON. Nitrogen removal in the estuaries and plumes appears to be biologically mediated once suspended sediment concentrations decrease to a point where phytoplankton growth is not light limited. In the dry season phosphorus enters and leaves the estuaries primarily in organic form. PIP is the dominant form of phosphorus in river water, but leaves the estuary more evenly distributed between all forms. These estuarine processes result in less nitrogen and phosphorus being delivered to the GBR lagoon than is exported from the catchment. The differences between these estuaries highlights the need for further work to explore modifications in estuaries that drain into the Great Barrier Reef lagoon.  相似文献   

9.
The sediment delivery ratio was estimated for two periods (28 years and eight years) following reforestation of seven tributary catchments (0·33 to 0·49 km2) in the headwaters of the Waipaoa River basin, North Island, New Zealand. In these catchments, gully erosion, which largely resulted from clearance of the natural forest between 1880 and 1920, is the main source of sediment to streams. Reforestation commenced in the early 1960s in an attempt to stabilize hillslopes and reduce sediment supply. Efforts have been partially successful and channels are now degrading, though gully erosion continues to supply sediment at accelerated rates in parts of the catchment. Data from the area indicate that the sediment delivery ratio (SDR) can be estimated as a function of two variables, ψ (the product of catchment area and channel slope) and A g (the temporally averaged gully area for the period). Sediment input from gullies was determined from a well defined relationship between sediment yield and gully area. Sediment scoured from channels was estimated from dated terrace remnants and the current channel bed. Terrace remnants represent aggradation during major floods. This technique provides estimates of SDR averaged over periods between large magnitude terrace‐forming events and with the present channel bed. The technique averages out short‐term variability in sediment flux. Comparison of gully area and sediment transport between two periods (1960–1988 and 1988–1996) indicates that the annual rate of sediment yield from gullies for the later period has decreased by 77 per cent, sediment scouring in channels has increased by 124 per cent, and sediment delivered from catchments has decreased by 78 per cent. However, average SDR for the tributaries was found to be not significantly different between these periods. This may reflect the small number of catchments examined. It is also due to the fact that the volume of sediment scoured from channels was very small relative to that produced by gullies. According to the equation for SDR determined for the Waipaoa headwaters, SDR increases with increasing catchment area in the case where A g and channel slope are fixed. This is because the amount of sediment produced from a channel by scouring increases with increasing catchment area. However, this relationship does not hold for the main stem of the study catchments, because sediment delivered from its tributaries still continues to accumulate in the channel. Higher order channels are, in effect, at a different stage in the aggradation/degradation cycle and it will take some time until a main channel reflects the effects of reforestation and its bed adjusts to net degradation. Results demonstrate significant differences among even low order catchments, and such differences will need to be taken into consideration when using SDR to estimate sediment yields. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

10.
An important gap in the management of land erosion in mining-affected areas is the understanding of the entire sediment routing system and the links between sources and storage at the catchment scale. In this study, we examine sediment delivery and its seasonality in the nickel mining-affected Santa Cruz and Pamalabawan catchments in the Philippines. We monitored discharge, suspended sediment concentrations and suspended sediment loads across 13 sub-catchments with contrasting degrees of mining influence from June 2018 to July 2019. First, we show the importance of the size of the area that has been physically disturbed within our sub-catchments, with as little as 10–22% of relative disturbance area being enough to generate four-fold to eight-fold increase in the sediment yield relative to less disturbed and pristine areas. We found that sub-catchments with > 10% disturbance exhibit the highest sediment yields (15.5 ± 44.7 t km−2 d−1) compared with sub-catchments with < 10% disturbance (3.6 ± 17.7 t km−2 d−1) and undisturbed catchments (2.0 ± 5.7 t km−2 d−1). We also show that sediment flushing predominantly occurs in the most disturbed sub-catchments at the onset of the wet season. A small number of flood events transports the bulk of the sediment, with hysteresis effects being most pronounced in disturbed areas. Lastly, we show that floodplain sediment recycling exerts a key control on sediment delivery at both reach and catchment scales, with the relative contribution of floodplain sources to the sediment budget becoming dominant in the latter stages of the wet season- up to 89% of the total sediment export per storm event. This study highlights the importance of both degree of disturbance and sediment pathways in controlling sediment transport in mining-disturbed areas, and that considering the entire sediment routing system including intermediate stores is crucial to optimizing existing and future measures against siltation and potential contamination of trace metals and metalloids downstream of mining areas.  相似文献   

11.
The variability of rainfall-dependent streamflow at catchment scale modulates many ecosystem processes in wet temperate forests. Runoff in small mountain catchments is characterized by a quick response to rainfall pulses which affects biogeochemical fluxes to all downstream systems. In wet-temperate climates, water erosion is the most important natural factor driving downstream soil and nutrient losses from upland ecosystems. Most hydrochemical studies have focused on water flux measurements at hourly scales, along with weekly or monthly samples for water chemistry. Here, we assessed how water and element flows from broad-leaved, evergreen forested catchments in southwestern South America, are influenced by different successional stages, quantifying runoff, sediment transport and nutrient fluxes during hourly rainfall events of different intensities. Hydrograph comparisons among different successional stages indicated that forested catchments differed in their responses to high intensity rainfall, with greater runoff in areas covered by secondary forests (SF), compared to old-growth forest cover (OG) and dense scrub vegetation (CH). Further, throughfall water was greatly nutrient enriched for all forest types. Suspended sediment loads varied between successional stages. SF catchments exported 455 kg of sediments per ha, followed by OG with 91 kg/ha and CH with 14 kg/ha, corresponding to 11 rainfall events measured from December 2013 to April 2014. Total nitrogen (TN) and phosphorus (TP) concentrations in stream water also varied with rainfall intensity. In seven rainfall events sampled during the study period, CH catchments exported less nutrients (46 kg/ha TN and 7 kg/ha TP) than SF catchments (718 kg/ha TN and 107 kg/ha TP), while OG catchments exported intermediate sediment loads (201 kg/ha TN and 23 kg/ha TP). Further, we found significant effects of successional stage attributes (vegetation structure and soil physical properties) and catchment morphometry on runoff and sediment concentrations, and greater nutrients retention in OG and CH catchments. We conclude that in these southern hemisphere, broad-leaved evergreen temperate forests, hydrological processes are driven by multiple interacting phenomena, including climate, vegetation, soils, topography, and disturbance history.  相似文献   

12.
Riparian vegetation can trap sediment and nutrients sourced from hillslopes and reduce stream bank erosion. This study presents results from a 10-year stream monitoring program (1991–2000), in a 6 km2 agricultural catchment near Albany, Western Australia. After 6 years, a 1.7 km stream reach was fenced, planted with eucalyptus species and managed independently from the adjacent paddocks. Streamflow, nutrient and sediment concentration data were collected at the downstream end of the fenced riparian area, so there are data for before and after improved riparian management. Suspended sediment (SS) concentrations fell dramatically following improved riparian management; the median event mean concentration (EMC) dropped from 147 to 9.9 mg l−1. Maximum SS concentrations dropped by an order of magnitude. As a result, sediment exports from the catchment decreased following improved riparian management, from over 100 to less than 10 kg ha−1 yr−1. Observations suggest that this was the result of reduced bank erosion and increased channel stability. Riparian management had limited impact on total phosphorus (TP) concentrations or loads, but contributed to a change in phosphorus (P) form. Before improved riparian management, around half of the P was transported attached to sediment, but after, the median filterable reactive P (FRP) to TP ratio increased to 0.75. In addition, the median FRP EMC increased by 60% and the raw median FRP concentration increased from 0.18 to 0.35 mg l−1. These results suggest that there was a change in the dominant P form, from TP to FRP. Changes in total nitrogen (TN) following improved riparian management were less clear. There were reductions in TN concentrations at high flows, but little change in the loads or EMC. This study demonstrates the benefits of riparian management in reducing stream bank erosion, but suggests that in catchments with sandy, low P sorption soils, there may be limitations on the effectiveness of riparian buffers for reducing P and N exports.  相似文献   

13.
This paper presents a multi-criteria based tool for assessing the relative impact of diffuse-source pollution to the Great Barrier Reef (GBR) from the river basins draining into the GBR lagoon. The assessment integrates biophysical and ecological data of water quality and pollutant concentrations with socio-economic information pertaining to non-point source pollution and (potential) pollutant impact. The tool generates scores for each river basin against four criteria, thus profiling the basins and enabling prioritization of management alternatives between and within basins. The results support policy development for pollution control through community participation, scientific data integration and expert knowledge contributed by people from across the catchment. The results specifically provided support for the Reef Water Quality Protection Plan, released in October 2003. The aim of the plan is to provide a framework for reducing discharge of sediment, nutrient and other diffuse-source loads and (potential) impact of that discharge and for prioritising management actions both between and within river basins.  相似文献   

14.
Hysteresis in the relationship between suspended sediment concentration and flow during run-off events is commonly used to inform on sediment sources and hydrological pathways. Less attention, however, has been paid to comparing the water and sediment hydrographs, which provide a more direct appreciation of in-event sediment dynamics and their relationship with the upstream catchment characteristics. The aim of this study is to better understand the catchment and hydrological controls on the phasing of water and sediment discharges during events and, in particular, to explore what controls sediment concentrations late on event recessions. Continuous records of flow and turbidity data (calibrated to suspended sediment concentration) were collected from 17 catchments across New Zealand for this purpose. Relationships between event sediment yield and peak flow showed, as anticipated, higher event sediment loads were generated in pasture compared with forested catchments and were also higher from catchments in more erodible terrain. One novel result was that these differences were greater during smaller, more frequent events, whereas the loads from larger flood events tended to converge between pasture and forest catchments. Another novel result was that event sediment load tends to be evenly split between rising and falling stages of the hydrograph in pasture catchments, but forested catchments yield more of their event loads on flood recessions, probably because of delayed erosion or more sediment sources remote from the channel network. Land cover, distance of the sediment sources from the monitoring site, and size of the catchments control sediment concentrations late on event recession. Pasture-dominated and more erodible catchments show longer sediment recessions and therefore stay dirtier for longer time periods. In addition, the size of previous flood events appeared to control the extent of sediment exhaustion after the flood peaks in some catchments.  相似文献   

15.
A decline in the ecosystem health of Australia's Moreton Bay, a Ramsar wetland of international significance, has been attributed to sediments and nutrients derived from catchment sources. To address this decline the regional management plan has set the target of reducing the loads by 50%. Reforestation of the channel network has been proposed as the means to achieve this reduction, but the extent of revegetation required is uncertain. Here we test the hypothesis that sediment and nutrient loads from catchments decrease proportionally with the increasing proportion of the stream length draining remnant vegetation. As part of a routine regional water quality monitoring program sediment and nutrient loads were measured in 186 flow events across 22 sub‐catchments with different proportions of remnant woodland. Using multiple linear regression analysis we develop a predictive model for pollutant loads. Of the attributes examined a combination of runoff and the proportion of the stream length draining remnant vegetation was the best predictor. The sediment yield per unit area from a catchment containing no remnant vegetation is predicted to be between 50 and 200 times that of a fully vegetated channel network; total phosphorus between 25 and 60 times; total nitrogen between 1.6 and 4.1 times. There are ~48 000 km of streams in the region of which 32% drain areas of remnant vegetation. Of these 17 095 km are above the region's water storage dams. We estimate that decreasing the sediment and phosphorus loads to Moreton Bay by 50% would involve rehabilitating ~6350 km of the channel network below the dams; halving the total nitrogen load would require almost complete restoration of the channel network. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

16.
This study examined the temporal variability in herbicide delivery to the Great Barrier Reef (GBR) lagoon (Australia) from one of the GBR catchment's major sugarcane growing regions. Annual loads of measured herbicides were consistently in the order of 200+kg. Atrazine, it's degradate desethylatrazine, and diuron contributed approximately 90% of annual herbicide load, with early 'first-flush' events accounting for the majority of herbicide loads leaving the catchment. Assessment of herbicide water-sediment partitioning in flood runoff highlighted the majority of herbicides were transported in predominantly dissolved form, although a considerable fraction of diuron was transported in particulate-bound form (ca. 33%). Diuron was also the herbicide demonstrating the highest concentrations and frequency of detection in sediments collected from catchment waterways and adjacent estuarine-marine environments, an outcome aligning with previous research. Herbicide physico-chemical properties appear to play a crucial role in partitioning between water column and sediment habitat types in GBR receiving ecosystems.  相似文献   

17.
Agricultural land management requires strategies to reduce impacts on soil and water resources while maintaining food production. Models that capture the effects of agricultural and conservation practices on soil erosion and sediment delivery can help to address this challenge. Historic records of climatic variability and agricultural change over the last century also offer valuable information for establishing extended baselines against which to evaluate management scenarios. Here, we present an approach that combines centennial‐scale reconstructions of climate and agricultural land cover with modelling across four lake catchments in the UK where radiometric dating provides a record of lake sedimentation. We compare simulations using MMF‐TWI, a catchment‐scale model developed for humid agricultural landscapes that incorporates representation of seasonal variability in vegetation cover, soil water balance, runoff and sediment contributing areas. MMF‐TWI produced mean annual sediment exports within 9–20% of sediment core‐based records without calibration and using guide parameter values to represent vegetation cover. Simulations of land management scenarios compare upland afforestation and lowland field‐scale conservation measures to reconstructed historic baselines. Oak woodland versus conifer afforestation showed similar reductions in mean annual surface runoff (8–16%) compared to current moorland vegetation but a larger reduction in sediment exports (26–46 versus 4–30%). Riparian woodland buffers reduced upland sediment yields by 15–41%, depending on understorey cover levels, but had only minor effect on surface runoff. Planting of winter cover crops in the lowland arable catchment halved historic sediment exports. Permanent grass margins applied to sets of arable fields across 15% or more of the catchment led to further significant reduction in exports. Our findings show the potential for reducing sediment delivery at the catchment scale with land management interventions. We also demonstrate how MMF‐TWI can support hydrologically‐informed decision making to better target conservation measures in humid agricultural environments. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

18.
Growing awareness of the wider environmental significance of fine sediment transport by rivers and associated sediment problems linked to sediment–water quality interactions, nutrient and contaminant transfer, and the degradation of aquatic habitats has resulted in the need for an improved understanding of the mobilization and transfer of sediment in catchments to support the development of effective sediment management strategies. The sediment budget provides a key integrating concept for assembling information on the internal functioning of a catchment in terms of its sediment dynamics by providing information on the mobilization, transfer, storage and output of sediment. One key feature of a catchment sediment budget is the relationship between the sediment yield at the catchment outlet and rates of sediment mobilization and transfer within the catchment, which is commonly represented by the sediment delivery ratio. To date, most attempts to derive estimates of this ratio have been based on a comparison of the measured sediment yield from a catchment with an estimate of the erosion occurring within the catchment, derived from an erosion prediction procedure, such as the Universal Soil Loss Equation (USLE) or its revised version, RUSLE. There is a need to obtain more direct and spatially distributed evidence of the erosion rates occurring within a catchment and to characterize the links between sediment mobilization, transfer, storage and output more explicitly. In this context, fallout radionuclides have proved particularly useful as sediment tracers. This paper reports the results of a study aimed at exploring the use of caesium‐137 (137Cs) measurements to establish sediment budgets for three catchments of different sizes and contrasting land use located in Calabria, southern Italy. Long‐term measurements of sediment output were available for the catchments, and, by using the estimates of gross and net rates of soil loss within the catchments provided by 137Cs measurements, it was possible to establish the key components of the sediment budget for each catchment. By documenting the sediment budgets of three catchments of different sizes, the study provides a basis for exploring the effects of scale on catchment sediment budgets and, in particular, the increasing importance of catchment storage as the size of the catchment increases. The results of this study demonstrate a reduction in the sediment delivery ratio from 98 to 2% as catchment area increases from 1·47 ha to 31·2 km2. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

19.
The intensity of soil loss and sediment delivery, representing hydrologic and geomorphic processes within a catchment, accelerates with rapid changes in land cover and rainfall events. An underlying component of sustainable management of water resources is an understanding of spatial and temporal variability and the adverse influences of regional parameters involved in generating sediment following widespread changes in land cover. A calibrated algorithm of soil loss coupled with a sediment delivery ratio (SDR) was applied in raster data layers to improve the capability of a combined model to estimate annual variability in sediment yields related to changes in vegetation cover identified by analyses of SPOT imagery. Four catchments in Kangaroo River State forest were assessed for annual changes in sediment yields. Two catchments were selectively logged in 2007, while the two other sites remained undisturbed. Results of SDR estimates indicated that only a small proportion of total eroded sediment from hillslopes is transported to catchment outlets. Larger SDR values were estimated in regions close to catchment outlets, and the SDR reduced sharply on hillslopes further than 200–300 m from these areas. Estimated sediment yield increased by up to 30% two years after land cover change (logging) in 2009 when more storm events were recorded, despite the moderate density of vegetation cover in 2009 having almost recovered to its initial pre‐logging (2005) condition. Rainfall had the most significant influence on streamflow and sediment delivery in all catchments, with steeply sloping areas contributing large amounts of sediment during moderate and high rainfall years in 2007 and 2009. It is concluded that the current scenario of single‐tree selection logging utilized in the study area is an acceptable and environmentally sound land management strategy for preservation of soil and water resources. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

20.
Delivery of fine sediment to fluvial systems is of considerable concern given the physical and ecological impacts of elevated levels in drainage networks. Although it is possible to measure the transfer of fine sediment at high frequency by using a range of surrogate and automated technologies, the demands for assessing sediment flux and sediment properties at multiple spatially distributed locations across catchments can often not be met using established sampling techniques. The time‐integrated mass‐flux sampler (TIMS) has the potential to bridge this gap and further our understanding of fine sediment delivery in fluvial systems. However, these devices have undergone limited testing in the field. The aim of this paper was to provide a critical validation of TIMS as a technique for assessing fluvial fine sediment transfer. Fine sediment flux and sediment properties were assessed over 2 years with individual sampling periods of approximately 30 days. Underestimation of sediment flux ranged between 66% and 99% demonstrating that TIMS is unsuitable for assessing absolute sediment loads. However, assessment of relative efficiency showed that six of seven samplers produced statistically strong relationships with the reference sediment load (P < 0.05). Aggregated data from all sites produced a highly significant relationship between reference and TIMS loads (R2 = 0.80; P < 0.001) demonstrating TIMS may be suitable for characterizing patterns of suspended sediment transfer. Testing also illustrated a consistency in sediment properties between multiple samplers in the same channel cross section. TIMS offers a useful means of assessing spatial and temporal patterns of fine sediment transfer across catchments where expensive monitoring frameworks cannot be commissioned. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

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