title: The effects of river run-off on water clarity across the central Great Barrier Reef.
abstract: Changes in water clarity across the shallow continental shelf of the central Great Barrier Reef were investigated from ten years of daily river load, oceanographic and MODIS-Aqua data. Mean photic depth (i.e., the depth of 10% of surface irradiance) was related to river loads after statistical removal of wave and tidal effects. Across the ∼25,000 km(2) area, photic depth was strongly related to river freshwater and phosphorus loads (R(2)=0.65 and 0.51, respectively). In the six wetter years, photic depth was reduced by 19.8% and below water quality guidelines for 156 days, compared to 9 days in the drier years. After onset of the seasonal river floods, photic depth was reduced for on average 6-8 months, gradually returning to clearer baseline values. Relationships were strongest inshore and midshelf (∼12-80 km from the coast), and weaker near the chronically turbid coast. The data show that reductions in river loads would measurably improve shelf water clarity, with significant ecosystem health benefits.
authors.affiliation: Australian Institute of Marine Science, PMB No. 3, Townsville, Queensland 4810, Australia. Electronic address: k.fabricius@aims.gov.au.
authors.forename: K E
authors.initials: KE
authors.lastname: Fabricius
authors.affiliation: Australian Institute of Marine Science, PMB No. 3, Townsville, Queensland 4810, Australia.
authors.forename: M
authors.initials: M
authors.lastname: Logan
authors.affiliation: Biophysical Oceanography Group, School of Geography, Planning and Environmental Management, University of Queensland, Brisbane 4072, Australia.
authors.forename: S
authors.initials: S
authors.lastname: Weeks
authors.affiliation: Centre for Tropical Water & Aquatic Ecosystem Research, James Cook University, Townsville, Queensland 4811, Australia.
authors.forename: J
authors.initials: J
authors.lastname: Brodie
mesh_terms: D057894:Coral Reefs; D055868:Floods; D005618:Fresh Water; D010758:Phosphorus / Q000737:chemistry*; D045483:Rivers / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D060753:Water Quality
chemical_list: D014874:Water Pollutants, Chemical; D010758:Phosphorus
keywords: Generalized additive mixed models; Great Barrier Reef; Nutrient runoff; Photic depth; River floods; Turbidity