Elevated dissolved heavy metal discharge following rainfall downstream of intensive horticulture

• Heavy metals may be released from soils during rain events. Observations during the first flush (rain event preceded by dry period) are difficult, but may account for a large fraction of annual loads. Here, we report detailed time series measurements of dissolved heavy metals and the groundwater tracer radon (Rn-222) over multiple rain events from a creek draining a catchment dominated by intensive horticulture on the subtropical east coast of Australia. The creek drains to an intermittently closed and open lake or lagoon (ICOLL), a typical estuary type along the east coast of Australia. A sandbank prevents the estuary mouth from connecting with the ocean during dry conditions. Following a 109 mm rain event, the ICOLL began to drain to the coastal ocean. Mean export of Hg, Cu, and Zn was 0.23 +/- 0.05, 1.06 +/- 0.25, and 15.70 +/- 2.69 g m(-2) day(-1) for the entire time series and 0.72 +/- 0.17, 1.27 +/- 0.12, 24.14 +/- 3.82 g m(-2) day(-1) averaged from high resolution sampling over 72 h of the first flush event. Trends of Hg export differed from the other heavy metals. Over 79% of the estimated Hg export occurred within 72 h of the ICOLL opening, compared to 30 and 38% of Cu and Zn. The first flush and subsequent major rain events (> 50 mm day(-1)) drove concentrations of Hg, Cu and Zn to exceed the Australia and New Zealand Environment and Conservation Council (ANZECC) water quality guidelines (WQG) for both fresh and marine water. Comparisons of heavy metal export to downstream estuary sediment burial rates revealed that the estuary is likely a source of dissolved Hg and Cd to the coastal ocean when the ICOLL is open.

Ämnesord

NATURVETENSKAP  -- Biologi -- Ekologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Ecology (hsv//eng)

Nyckelord

Mercury

Catchment export

Radon

First flush

ICOLL

Marine protected

area

organic-carbon

agricultural runoff

water-quality

total mercury

trace-metals

land-use

estuaries

exports

groundwater

chemistry

Geochemistry & Geophysics

Publikations- och innehållstyp

ref (ämneskategori)

art (ämneskategori)