Fine‐suspended sediment and water budgets for a large, seasonally dry tropical catchment: Burdekin River catchment, Queensland, Australia

Abstract

The Burdekin River catchment ( 130,400 km 2 ) is a seasonally dry tropical catchment located in north-east Queensland, Australia. It is the single largest source of suspended sediment to the Great Barrier Reef (GBR). Fine sediments are a threat to ecosystems on the GBR where they contribute to elevated turbidity (reduced light), sedimentation stress, and potential impacts from the associated nutrients. Suspended sediment data collected over a 5 year period were used to construct a catchment-wide sediment source and transport budget. The Bowen River tributary was identified as the major source of end-of-river suspended sediment export, yielding an average of 530 t km 22 yr 21 during the study period. Sediment trapping within a large reservoir (1.86 million ML) and the preferential transport of clays and fine silts downstream of the structure were also examined. The data reveal that the highest clay and fine silt loadswhich are of most interest to environmental managers of the GBR-are not always sourced from areas that yield the largest total suspended sediment load (i.e., all size fractions). Our results demonstrate the importance of incorporating particle size into catchment sediment budget studies undertaken to inform management decisions to reduce downstream turbidity and sedimentation. Our data on sediment source, reservoir influence, and subcatchment and catchment yields will improve understandings of sediment dynamics in other tropical catchments, particularly those located in seasonally wet-dry tropical savannah/semiarid climates. The influence of climatic variability (e.g., drought/wetter periods) on annual sediment loads within large seasonally dry tropical catchments is also demonstrated by our data.

Combining contemporary and long-term erosion rates to target erosion hot-spots in the Great Barrier Reef, Australia

“…For example, the high error estimate for the Bowen reflects the lower confidence in the contemporary loads data. The lower confidence is due to lower sample numbers in the last two years of monitoring, owing to issues such as access to sites (Bainbridge et al, 2014). Conversely, the higher error estimates for Hillslope 3 reflect the very large inter-annual variability of sediment concentrations for this site (Bartley et al, 2014b).…”

“…This study utilised the end of major sub-catchment fine sediment loads previously presented, and converted the data to represent contemporary erosion rates for the five major sub-catchments and at the end of the Burdekin catchment ( Figure 1). Bainbridge et al, (2014) presented site details, locations, and data history for each site. In brief, river water samples were collected from existing Government run streamflow gauging locations (https://www.dnrm.qld.gov.au/water/water-monitoring-and-data/portal) at each of the five major sub-catchments, and at the end of basin.…”

“…TSS (in mg L -1 ) was measured gravimetrically by weighing the fraction remaining on a pre-weighed Whatman GF/C filter (nominally 1.2 µm pore size), dried at 103-105 o C for 24 h, after vacuum filtration of a measured volume of sample (Method 2540D) (American Public Health Association, 2005). As acknowledged in Bainbridge et al (2014), this method tends to underestimate the ''true'' suspended sediment concentration (SSC) particularly where abundant (i.e. >25%) sand particles are present (Gray et al, 2000).…”

“…>25%) sand particles are present (Gray et al, 2000). A ''Loads Regression Estimator'' (LRE) model used the streamflow and corresponding TSS data from each of the gauged locations to calculate suspended sediment loads (in tonnes) with estimates of error for each sub-catchment site and each water year (Bainbridge et al, 2014). The lateral and vertical variability in TSS concentration measured in the stream profiles, and the potential mis-representation of the coarser (sand fraction) of suspended loads was taken into account in the error term of the LRE model (Bainbridge et al, 2014;Kuhnert et al, 2012).…”

“…coarse + suspended + dissolved sediment fractions). The measured contemporary sediment flux estimates from the major and minor sub-catchments represent fine (0.020-2000 µm) sediment (Bainbridge et al, 2014). Dissolved load fractions are considered to represent sediment less than ~0.5 µm (Gordon et al, 1992).…”