Black water threatens fish kill
THOSE in the know reckon a fish kill is likely in the next couple of days as water low in dissolved oxygen drains from backswamps in the lower Richmond Valley.
Floodplain manager with the Richmond River County Council, Michael Woods, said last night that as the river dropped to allow discharge from Bungawalbyn and Rocky Mouth creeks, Tuckean Swamp and drains around Empire Vale, a dark murk known as "black water" was expected to enter the Richmond.
"It's a matter of wait and see," he said.
Based on research gleaned from a 2006 study, it takes just 2.5 to 3.5 days at 25 degrees Celsius to warm floodwater enough to kill vegetation, where those waters sit over paddocks and cropland.
Temperatures have been above that threshold since the rain stopped last Tuesday.
While floods in the Richmond were not nearly as severe as the record flow in the Clarence, Mr Woods pointed out that the Richmond floodplain was far greater in area, and therefore more prone to black water events and subsequent fish kills.
Mr Woods readily admits he is the "monkey in the middle" when it comes to debate over draining the backswamps and letting them return to a viable fish habitat. Fishermen want the drains filled in, farmers want them cut deeper.
"It is about striking a balance between landholders and river users," Mr Woods said.
He noted that of the 600 or so floodgates on the river, five were stuck open with sticks and debris, and the flooding of one drain at Swan Bay alone created more than a few disgruntled messages on his mobile.
But he said these regular black water events needed to stimulate further debate about the viability and the future of farming drained swampland.
"People living on very low-lying land need to assess the productivity of that country," he said.
Often drained swampland, situated on estuarine gel tended to dry and shrink, slumping lower to the point that some backswamps, especially those around Rocky Mouth Creek ,were at or below sea level.
What can be done with backswamps that grow poorly and create black water? Sadly the Federal Government has not included coastal backswamps in criteria that would allow them to be used as carbon sequestration sites - meaning landowners could get paid to let them revert to nature, and store carbon in their boggy soils.
Companies eager to offset carbon credits could then lease those low-lying swamps and pay the farmer a stipend.
That sticking point is being addressed by the county council, SCU, Monash University and the NSW Department of Agriculture in a partnership that has made an application to the government to look at carbon sequestration in these critical backswamps. Not all black water is bad because the black - carbon - when released into the river helps create building blocks that feed the ecosystem.
It is the amount of black water that causes the fish kill. Considering how society has changed its views since the backswamps were first drained early last century, and particularly since they were radically deepened in the 1960s, river health has improved. But there is still a long way to go before the Richmond Valley floodplain can be called healthy.
"In the past these backswamps were covered with water for months, even years in wet periods," Mr Woods said.