Tuesday 4 July 2017

What's going on at our New Zealand dune lake?


Welcome to the Midnight Collective Broadsheet 141
Actively supporting NZ’s endangered wetland birds
Early morning view of wetlands from townside - expressway cutting off view of Kapiti Island in distance. - 
It is very early days in the life of these new wetlands and we still haven’t a clear idea about their seasonal life, indeed, they have still to develop one. But the annual cycle is starting to look very different to the original dune lake as they enter a sixth month of their new existence
late June 2017 featuring plantings weeds, but where is the dune lake? 
We had a wet summer and autumn, but the past six weeks have made up for it, with very little rain (around 4mm in our rain gauge for June). The original lake would enlarge from April and reach its full 5-7 hectares early in July, then hold this through to mid November.
Raumati Beach dune lake - July 2012
This year the opposite is happening. The transformed wetlands have been carrying water through late summer and autumn and this attracted a lot of waterbirds, who didn’t seem at all put out by the new traffic hazards. But over the past 6 weeks these areas have been reducing and taken the birds with them. We’ve had a couple of big storms through both Islands, but they passed us by. And while it has been chilly, we haven’t had the severe frosts of other years. (We’re all still mowing our lawns!).

All that changed overnight when we got our first steady rain a couple of days ago. This supplied only 10mm over two to three hours, but it immediately swamped the wetlands and back came the birds.
Drying up
A day later with Canadian geese in residence 
Dried up - Drain 7 in foreground
A day later - 
The Wharemauku had risen about a third of metre on this rainfall, which isn’t  a lot, but in collusion with Drain 7, which boxes in the other end of the wetland, it had backfilled this western side of the expressway; topping it up to its highest level. It looks as though we now have an area which is acting more like a flood plain, than the  original dune lake.       

New things are also going on, on the other side of the expressway. It has become apparent that there is a difference of around two thirds of a metre in height between this townside and the former dune lake. The Wharemauku hadn’t risen high enough on this rainfall, to backfill this area but the drain coming into it was carrying around 3 times as much water than before the rain. So where is it coming from? This area is a closed system. It can drain out, but there is no through flow from local waterways. The area isn’t large enough to sustain such an increase from 10mm of rain? 

The NZTA’s theory is that this whole area has been lowered below the water table which would account for it holding its water over summer; but while this may keep  the wetland wet, it can’t explain the volume of water we are seeing. Is there some other entry point that breaches, when we see rain  at this level? It is difficult to get into this back area, but we will be keeping an eye on it to see if we can find out.
      
Neither of these areas are regularly flushed by natural water flow, so have remained discoloured since they were formed. This is of some concern, not only for nearby residents as the water turns fetid, but also for the health of the bird and marine life it will likely now sustain. The dunelake wasn’t flushed either, but it always ran reasonably clear and while there is usually a blackened tinge to water in pakihi (lowland swamp) country, this discolouration is light brown.

Another issue is the rapid increase in predators – we’ve seen rabbits, rats, and then native locals, including an increase in populations of pukeko and spur-winged plover, both of which will take the eggs and young of other birds, including pied stilt. The introduced Canadian geese are also a mixed blessing. They used to overnight in winter at the original dunelake, but never stayed through the day. The area was too close to human traffic. Now we are spotting them through the day which will have a detrimental effect on rarer native birds through competition for food and the mess they make in the water.
Scaup pair, Queen Elizbeth II park - In June?
We will be keeping an eye on developments here over time but in the meantime here is a scaup pair, spotted at the QE2 park wetland (10km south). They take off in early April and don’t usually come back until August/September, so we are not sure what’s going on with these two hanging around like this.
Fed up female dabchick -Where's that male?
Male after her...
Just around the bay at the same wetland, these two dabchicks suddenly surfaced. One dabchick appeared at our dunelake just before construction of the expressway got underway. We haven’t seen them here since, but they are very territorial which causes the young to move around; and we’ll be keeping an eye out for their return.

And now here is a wistful dose of nostalgia for all our Russian friends.

Калинка, калинка, калинка моя!
В саду ягода малинка, малинка моя!

Ах, под сосною, под зеленою,
Спать положите вы меня!
Ай-люли, люли, ай-люли, люли,
Спать положите вы меня.

Yes, they toured here too, and this LP was picked up in a local charity shop.