The NUFG Kamarooka Project 2014  

 

As the 2014 year draws to a close it seems timely to make some comments on the NUFG Kamarooka Project.

Perhaps the first thing to say is that NUFG celebrated an anniversary this year. It has been ten years since we came together to plan the site and turn the first sod. In September we celebrated this milestone with a dinner at the Raywood Hotel. It was an opportunity for a meal and to share  tales of our adventures as the Kamarooka Saltland project unfolded. The project remains central to the NUFG community and our fellow travellers and it is testament to community commitment, farm forestry, the pursuit of good natural resource management, and the quest to rehabilitate and regenerate degraded lands.

We have learnt such a lot about establishing plantation forestry in the saline lands and the groundwater flow systems that occur within the foot-slopes and plains of northern Victoria. Perhaps the most significant piece of the jigsaw puzzle was in understanding that it is not salt that kills our trees. Instead, it is a combination of salt and waterlogging. The 1996-2010 drought eliminated waterlogging and our plantations flourished despite growing in soil subject to shallow saline groundwater two thirds the salinity of sea water. In spite of the challenging environment our plantations continue to flourish. Over the last few months our magnificent Kamarooka trees, now some 8-10 metres tall, have been adorned with fresh new growth bursting out of the uppermost limbs. Our Kamarooka 'forest' is now very conspicuous in the Kamarooka landscape. 

What can we  tell you about Kamarooka given the numbers we have collected this year.  The first thing to say is that monitoring the project site is now largely voluntary. We visit Kamarooka and collect watertable data when we can. It is quite important to continue with this as the project now has an extensive longitudinal record that is, arguably, unrivalled in SE Australia.

In 2014 we experienced a very dry year (figure 1).  Heavy rainfall occurred in April (more than twice the long term average) and then again in June, however, monthly totals were well below average in May, July, August (lowest on record) and October.  Unless the heavens open in the next week Bendigo (some 30 km south of Kamarooka) will finish the year  with an annual total of about 460 mm, some 90 mm below the long term average, or about 30 mm above the average for the period 1997-2009 (figure 2).  Interestingly, once again, the November rainfall was slightly above the long term average. We understand from our research that elevated November rainfall is a phenomenon common to most droughts.     

Figure1:  Rainfall distribution (Bendigo) during 2014 compared with the long term average

 

Figure 2: Cumulative rainfall (Bendigo) during 2014 

The heavy falls in April and June were enough to make the watertable bounce around a little, but for the most part any rise was less than a metre (figure 3), and it soon dissipated with the dry conditions that followed. In November the watertable under the most saline land (amongst the ailing saltbush) was  about 2.2 - 2.5 metres below the land surface. In strong contrast our 2004 plantation pulled the watertable down to at least 7 metres. Our watertable monitoring bores, however, are only seven metres deep and at the centre of the plantation the groundwater is now deeper than we are able to measure. We need to deepen the plantation bores, particularly at bore 8 so that we can see just how deep our plantation can pull the watertable down.   

Figure 3: Watertable fluctuations across the project site sine 2004  

The dry conditions have meant the watertable has not been raised to any great extent by winter rainfall and as we enter hot dry  seasonal  conditions we can expect the groundwater recession to continue. In a few months we may witness the lowest watertable since we commenced readings in 2004. The current is now much more erratic climate than it was. Growing seasons are commonly much shorter, rainfall has declined, and seasons are much less predictable.      

Whilst wandering around the Kamarooka gathering numbers we get to see and experience a lot of things.  The thing that had the most profound influence in our thinking in November was the groundwater gradient (watertable) in moving from the saline saltbush land along a northerly transect into the plantation (figure 4). In the saline land 50 metres south of the plantation (bore 5) the watertable was where we expected it to be.  It was a little over 2 metres deep, and sitting close to the point where capillary connection with the surface is extinguished.  Thirty metres to the north, however, at bore 6 in the Fort Kamarooka weather recording enclosure and just 20 metres from the plantation boundary, it was more than three metres below the surface.  In normal climatic circumstances these two bores share a very similar depth to watertable, however, in these dry circumstances bore 6 is influenced by a deepening groundwater depression beneath the adjacent 2004 plantation.   

Figure 4: Watertable depth along north-south transect extending from saline land into the 2004 plantation

The plantation is transpiring small amounts of very saline groundwater. It uses this water when there are few other choices, when fresher water close to the soil surface is not available.  Amazingly, during these times these trees are able overcome enormous osmotic pressure and extract fresh water from the saline groundwater surrounding their roots.  As transpiration proceeds the watertable is lowered and a depression in the groundwater develops (figure 5). The process is most efficient where the water stored is low relative to volume, and the permeability is low.  These are conditions typical of clay rich landscapes. As the depression develops groundwater from adjacent areas begins to flow into it from surrounding land and it too will eventually be used by the plantation.  

 

Figure 5: Concept model along north-south transect illustrating groundwater flow toward the 
depression resulting from the 2014 plantation  

At this point in time we do not have a strong understand of how the salt dynamics will play out over the longer term. If the trees continue to use saline groundwater and concentrate salt they may eventually contribute to their own demise. Maybe this will happen, or perhaps in this erratic climate the big wet and big dry periods groundwater will continue to rise and fall dramatically. This might be sufficient to prevent excessive salt accumulation in the root zone?

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