Nagur Cherukuru

Impact of an extreme flood event on optical and biogeochemical properties in a subtropical coastal periurban embayment (Eastern Australia)

Major floods impacted the city of Brisbane, eastern Australia, in January 2011, delivering large amounts of dissolved and particulate materials and nutrients into the adjacent coastal embayment, Moreton Bay. The resulting spatially resolved changes in biogeochemical and optical properties in Moreton Bay were examined 1, 2, 6, 19, and 49 weeks after the main freshwater discharge. One week postflood, total suspended matter (TSM) and chlorophyll a (TChla) concentrations varied over 1 order of magnitude throughout Moreton Bay, the particle scattering coefficient at 555 nm varied by a factor of 20, and the total absorption coefficient and colored dissolved organic matter (CDOM) absorption coefficient at 440 nm varied by a factor of 5. The largest changes in biogeochemical and optical properties observed during our study were from 1 to 2 weeks after the floods: near the Brisbane River mouth, TSM decreased by a factor of 3, CDOM by a factor of 2, while TChla increased by a factor of 3. Within a year, optical and biogeochemical properties recovered to levels similar to nonflood conditions. The strong changes in the characteristics of the particulate and dissolved material following the flood event and subsequent biological and photochemical processes led to a large spatial and temporal variability in the relative contribution of different constituents to the total absorption coefficient at 440 nm, the particle single scattering albedo, and the specific inherent optical properties. This work has significant implications for the accuracy of standard ocean color remote sensing algorithms in coastal waters during flood events.

Toward assimilation of ocean colour satellite observation into coastal ocean biogeochemical models: the tropical Fitzroy River Estuary case study

We present the first results of the assimilation of ocean colour datasets into coastal ocean biogeochemical models for the tropical Fitzroy Estuary and Keppel Bay system (FEKB) contingent to the Great Barrier Reef lagoon. As part of the Great Barrier Reef Monitoring Program, a regional algorithm for operational delivery of valid coastal ocean colour products was recently developed for FEKB. A new generation of regional specific algorithm for the FEKB system had to be developed for large satellite datasets of the MODIS sensors as the global algorithms failed. Concurrently, a biogeochemical model was developed for the system, built upon a three-dimensional hydrodynamic and sediment dynamic model, and simulating nitrogen and phosphorus dynamics including the dynamics of dissolved organic material as well as pelagic and benthic primary production. One of the aims was to provide estimates of material fluxes from Keppel Bay to the Great Barrier Reef Lagoon. The biogeochemical model was run first with fixed boundary conditions based on the limited in situ measurements, then with boundary conditions derived from satellite datasets using the region-specific algorithm. Several methodologies for linking of remote sensing observations to model variables were evaluated over a period of one year (2004). When remote sensing information was used to inform the boundaries, estimates of material fluxes in the model changed substantially in magnitude and direction.

Inland water quality monitoring in Australia

Consistent and accurate information on inland water quality over wider areas of the Australian continent are required to assess current condition and trends in response to key environmental and climatic impacts. Optical remote sensing offers a method to objectively assess this over multiple spatial scales provided retrieval algorithms are accurate. Here, we present the results of initial research aimed at exploring the optical variability in Australian inland waters and of linear matrix inversion algorithms applied to both in situ reflectance spectra and high resolution satellite data to retrieve water inland water quality parameters. In situ sampling reveals a high degree of optical variability both within and between lakes across the regions sampled with regional patterns evident; sub-tropical and tropical lakes exhibited greater optical complexity than deep lakes in mid-latitude regions. Clustering analysis indicated the presence of 8 different optical water types in the water bodies measured. The ability of the linear matrix inversion algorithm to map water quality, tested on in situ reflectance and WorldView2 image datasets, showed relative accuracy when parameter sets were sufficient to achieve algorithm closure. Improved algorithm parameterization will be required to account for the high degree in spatial and temporal optical variability observed in Australian inland waters.