Nitrogen levels in the Tully River--a long-term view.

Area of Science:

• Environmental Science
• Marine Biology
• Agricultural Science

Background:

• Agricultural development in river catchments poses a threat to the Great Barrier Reef (GBR) due to nutrient runoff.
• The Australian Institute of Marine Science (AIMS) monitors nutrient levels in rivers flowing into the GBR shelf.
• The Tully River, in the wet tropics, has a 13-year data set collected in collaboration with the Bureau of Sugar Experiment Stations (BSES).

Purpose of the Study:

• To determine if river nutrient levels have changed over a thirteen-year period.
• To investigate the relationship between agricultural activity and nutrient concentrations in river water.
• To assess the potential impact of river runoff on the Great Barrier Reef's inshore reefs.

Main Methods:

• Monthly water samples were collected from the Tully River.
• Additional samples were taken during the wet season.
• Nutrient concentrations, specifically nitrate and particulate nitrogen, were measured.

Main Results:

• A trend of increasing nitrate (at low flow) and particulate nitrogen concentrations was observed in recent years.
• Agricultural activity in the Tully basin significantly increased, with sugarcane and banana cultivation doubling.
• Fertilizer nitrogen use within the basin rose by 130% during the study period.

Conclusions:

• Increased agricultural activity, including expanded cultivation and higher fertilizer use, is a likely cause of elevated nitrogen concentrations in the Tully River.
• Rising nutrient levels in river systems represent a potential risk to the health of the Great Barrier Reef's inshore reefs.